METAL-CASTING METHOD AND APPARATUS, CASTING SYSTEM AND CAST-FORGING SYSTEM

Abstract: An automatic continuous casting system for producing a cast body, comprising: a casting apparatus that makes use of unidirectional solidification of molten metal and includes a molten metal reservoir (4) and a mold (5), in which molten metal in a molten metal source (2) is supplied through transfer means (3) to the molten reservoir, and the molten metal (45) supplied into the molten metal reservoir is suplied through an opening/closing plug (43) into the mold; target weight calculation/storing means (8) for calculating, on the basis of compositional proportions of metal elements contained in the molten metal (45), a specific gravity of an alloy obtained through solidification of the molten metal, calculating a target weight of a cast body on the basis of the specific gravity of the alloy and a capacity of the mold, and memorizing and storing the target weight; and first molten metal supply amount regulation means (9) for regulating an amount of the molten metal supplied from the molten metal reservoir into the mold by obtaining a measurement weight of the cast body and comparing a measurement weight of the cast body and comparing the measurement weight with the target weight.

Description: METAL-CASTING METHOD AND APPARATUS, CASTING SYSTEM AND CAST- FORGING SYSTEM This application claims the benefit of earlier applications based on U.S. Patent Application Nos. 60/251,379, 60/251,381 and 60/251,382, all filed December 6, 2000. Technical Field: The present invention relates to casting of materials to be subjected to plastic working, such as cold forging, hot forging, enclosed forging, rolling, extrusion and roll- forming, of metals including nonferrous metals, such as aluminum and magnesium (inclusive of respective alloys), and ferrous metals (i.e., iron and steel); to direct casting of products (i.e., castings); and to forging of the castings thus obtained. More particularly, the present invention relates to a casting system for automatically producing cast bodies continuously, including a casting method and apparatus that makes use of unidirectional solidification of molten metal and comprises a molten metal reservoir and a mold, in which molten metal in a melting furnace is supplied through a transfer trough to the molten metal reservoir, and the molten metal in the molten metal reservoir is supplied through an opening/closing plug to the mold, to thereby produce cast bodies. The present invention also relates to a cast-forging system for automatically forging the thus-produced cast bodies continuously, to thereby form products. Background Art : Conventionally, there has been known a casting system including a casting apparatus that makes use of unidirectional solidification of molten metal and comprises a molten metal reservoir and a mold, in which molten metal in a molten metal source is supplied through transfer means to the molten metal reservoir, and the molten metal in the molten metal reservoir is supplied through an opening/closing plug to the mold, to thereby produce a cast body. However, the conventional casting system is not necessarily of a continuous or automatic type, and may include a step requiring manpower. Therefore, there has been a demand for a high-performance system for producing a cast body. Furthermore, there has been a keen demand for a system for forging an as-produced cast body and subjecting the forged body to machining to thereby reduce production costs. In conventional metal mold casting, die casting and low-pressure or high-pressure casting, molten metal is teemed into a casting apparatus to form a cast body, after which the sprue portion and feeder portion are cut off to thereby provide a stock material. These conventional methods require simple steps and thus have an advantage of low production cost. However, they are not free from producing casting defects inside the cast bodies, including cavities, pinholes, shrinkage cavities and engulfment of oxides . As contrasted to such conventional methods , casting by way of unidirectional solidification provides excellent cast bodies in terms of quality regarding interior metallographic structure. However, if the molten metal has a free surface which is open to air, the meniscus portion that contacts side walls of the mold forms a curved surface having a large area, thus making it impossible to form a cast body having a top surface orthogonal to the circumferential side walls. Moreover, since controlling to a constant level the volume of molten metal to be teemed is difficult , various disadvantages result, including significant variation in weight of the as- produced stock materials, halting of the forging machine due to overload imposed during forging, and significant dimensional variation in the resultant forged products . In view of the foregoing, the present inventors previously proposed, as disclosed in JP-A Hei 8-155627, a casting method and apparatus capable of solving the aforementioned problems inherent to the technique of unidirectional solidification. Briefly, as shown in FIG. 42, molten metal 45 in a molten metal reservoir 4 is introduced into a mold 5 disposed on a cooling member 52 so as not to leave any space therein, via a sprue 42, from the molten metal reservoir 4 provided at the upper section of the mold 5 and subsequently the cooling member 52 is cooled, with the inside of the mold 5 being isolated by closing the sprue 42 with an opening/closing plug 43, to thereby cause molten metal 46 in the mold 5 to solidify unidirectionally. In FIG. 42, reference numeral 54 denotes a spray nozzle, numeral 61 an electric furnace for maintaining the molten metal at a predetermined temperature and preventing the molten metal poured into the mold from being cooled from the side walls of the mold, numeral 47 an upper lid, numeral 54b a case, and numeral 54c a discharge port for a cooling medium. By the employment of the above-described method and apparatus, teeming of a precise, predetermined amount of molten metal 46 into the mold 5 can be performed quite easily without need for measurement of the molten metal. Moreover, serial operations including teeming, cooling for solidification and removing the cast product can be performed continuously. In addition, since the molten metal is charged in the closed mold 5 without leaving any space therein, the resultant cast product has an outer surface conforming to the inner surface of the mold, thereby achieving high dimensional accuracy in thickness and shape. Also, the cast product has excellent quality in terms of internal metallographic structure, exhibiting no cavity, shrinkage cavity, pinhole, oxide engulfment or other similar defects. However, the aforementioned method and/or apparatus involve the following problem. That is, particularly when the cast body to be produced is a thin product having an axisymmetriσ disk shape of large outer diameter, time required for solidification of the molten metal at the sprue portion which is located virtually at the central portion of the disk, is different from that at a peripheral portion of the disk which is the remotest from the sprue portion. Therefore, an ideal unidirectional solidification state cannot be maintained, causing a local depression of the solidification interface at a location directly below the sprue and in some cases producing cracks at the central portion of a cast ingot . The conventional casting apparatus shown in FIG. 42 is provided, as shown in FIG. 43, with temperature detection means 43 using a thermocouple to detect the temperature of the cooling plate 52. The spray nozzle 54 for spraying cooling water for forcedly cooling the cooling member 52 is fixed in the hollow cylindrical case 54b that supports the cooling member 52. The nozzle 54 and the cooling member 52 are moved vertically by means of a cooling plate lifting mechanism 101. An opening/closing valve 113 is provided at an appropriate position of a water feed-pipe 102 for feeding cooling water to the nozzle 54. An electromagnetic valve 104 for opening and closing the valve 113 is controlled with casting control means 106. The casting control means 106 also controls a plug lifting mechanism 44 for vertically moving the plug 43 to open and close the sprue. However, the present inventors have found that, when a cast ingot is produced by the below-described procedure using the aforementioned casting apparatus that makes use of unidirectional solidification, the cast ingot involves some problems . The casting process using the aforementioned casting apparatus will be roughly described with reference to FIG. 44. The process is carried out under the following conditions. An aluminum alloy (JIS22218 alloy) melted in a molten furnace is employed as molten metal. A cooling plate formed from copper is employed. A mold, a molten metal reservoir and an opening/closing plug, which are formed from a commercially available heat insulating refractory material (named "Lumiboard" produced by Isoraito Kogyo Kabushiki Kaisha) , are employed. The other conditions are: the temperature in the molten metal reservoir = 720°C, the liquid level height of the molten metal in the reservoir = 50 mm, the amount of cooling water = 5 liter/min. , the shape of a product = 62.5 mm in outer diameter and 9 mm in thickness, the diameter of the sprue = 8 mm, the thickness of the cooling plate = 12 mm, the diameter of the thermocouple (alumel-σhromel sheath thermocouple) = 1 mm, the position of the thermocouple head = 6 mm from the surface of the cooling plate facing the sprue, and the casting cycle time approximately 16 seconds. For initiation of a casting cycle, a plug opening command is sent from the casting control means 106 to the plug lifting mechanism 44, the opening/closing plug 43 is moved upward by means of the mechanism 44, and the sprue 42 is opened, to thereby initiate feeding of the molten metal into the mold. When the casting cycle is initiated, the temperature (T 0 ) of the cooling plate 52 is maintained at approximately 150°C sufficiently higher than the allowable lower limit temperature (T c ) of 100°C. The term "the allowable lower limit temperature" used herein refers to the lowest temperature of a mold at which there is prevented formation of a blow defect, a type of casting defect, when molten metal is solidified in the mold. When the temperature of the mold is lower than the allowable lower limit temperature, a blow defect is formed. If the temperature of the cooling plate 52 is verified to be higher than the allowable lower limit temperature, formation of a blow defect can be prevented. Approximately five seconds after initiation of feeding of the molten metal 45 into the mold 5 including its main body and the cooling plate 52, feeding of the molten metal into the mold 5 is completed. When five seconds, as measured by a timer, elapse after sending of the plug opening command, a plug closing command is sent from the casting control means 106 to the plug lifting mechanism 44, the plug 43 is moved downward by means of the mechanism 44, and the sprue 42 is closed. Thereafter, when the temperature detection means 43 detects that the temperature of the cooling plate 52 reaches T- L = 500°C, the electromagnetic valve 104 is opened by means of the casting control means 106, and spraying of cooling water through the nozzle 54 is initiated. When the temperature detection means 43 detects that the temperature of the cooling plate 54 reaches T 2 = 30°C, the electromagnetic valve 104 is opened by means of the casting control means 106, and spraying of cooling water through the nozzle 54 is stopped. After completion of forced cooling of the cooling plate 52 by use of cooling water, heating of the cooling plate 52 by the molten metal 46 and further cooling of the molten metal 46 proceed. When the temperature detection means 43 detects that the temperature of the cooling plate 52 reaches an appropriate temperature T 3 that is 160°C, the casting control means 106 sends a command to the cooling plate lifting mechanism 101 for moving the cooling plate 52 downward, and the cooling plate 52 and the hollow cylindrical case 54b are moved downward. The cast ingot placed on the cooling plate 52 moved downward is removed by use of a cast ingot removal apparatus (not illustrated) . Thereafter, the cooling plate 52 is again moved upward and attached to the bottom portion of the mold main body, and then the next casting cycle can be initiated. No particular limitation is imposed on the timing at which the casting control means 106 sends a command to the cooling plate lifting mechanism 101 for moving the cooling plate 52 upward. The mechanism 101 may be associated with the cast ingot removal apparatus for moving the cooling plate 52 upward immediately after completion of removal of a cast ingot. Alternatively, the cooling plate 52 may be moved upward after a predetermined time elapses , which time is determined in accordance with a casting cycle time and is measured by a timer. After the cast ingot is removed, the cooling plate 52 is exposed to air and cooled gradually, and thus the temperature of the cooling plate 52 must be regulated such that the temperature does not become lower than the allowable lower limit temperature (T c ) when the next casting cycle is initiated. When the temperature of the cooling plate 52 is lowered to T 0 = 150°C, the cooling plate 52 is attached to the bottom portion of the mold main body, to thereby elevate the temperature of the cooling plate 52. Therefore, the next casting cycle can be initiated immediately after the temperature of the cooling plate 52 is elevated. However, when casting is carried out by use of the aforementioned casting apparatus in the aforementioned casting cycle, the molten metal fed into the mold is deprived of its heat merely by the cooling plate 52 per se before cooling of the cooling plate 52 with cooling water is initiated. Therefore, the speed of cooling the molten metal is slow to produce a cast ingot having a rough structure. This makes it difficult to produce a cast ingot having a dense structure. In addition, since cooling of the cooling plate is initiated after completion of feeding of molten metal, a cycle time required for casting cannot be shortened, resulting in poor casting efficiency. FIG. 45 schematically shows the cross section of a short cylindrical cast ingot piece (diameter: 63 mm, thickness: 10 mm) produced by use of the aforementioned casting apparatus . The ingot piece was cut vertically so as to include the axis, and the cross section was subjected to etching. As shown in FIG. 45, segregation of metal components occurs due to gradual cooling, and etching patterns attributed to the segregation are ubiquitously observed in the thickness direction. Etching was carried out using as the chemical treatment solution a 20% aqueous sodium hydroxide solution heated to 50°C for three-minute immersion. Observation of the metallographic microstructure of the aforementioned cast ingot shows that defects (i.e., micropores) are present at a portion of the cast ingot in the vicinity of the sprue. There are one or fewer micropore having a size of at least 200 μm (see FIG. 46) and 10 or fewer micropores having a size of 50-200 μm per 100 mm 2 of the cast ingot. As described above, cast ingots of good quality cannot necessarily be produced efficiently through the conventional casting process making use of the conventional casting apparatus . In view of the foregoing, an object of the present invention is to provide a casting system for enhancing the performance of a casting system including a casting apparatus which makes use of unidirectional solidification of molten metal and a cast-forging system for forging an as-produced cast body to thereby form a product. Another object of the present invention is to provide a metal casting process and apparatus that attains a flat solidification interface and yields cast ingots that have no cut surface and have healthy interior metallographic structure. Still another object of the present invention is to provide a metal casting process and apparatus for producing cast ingots of good quality at high productivity. Disclosure of the Invention: In order to attain the aforementioned objects, the invention provides an automatic continuous casting system for producing a cast body, comprising: a casting apparatus that makes use of unidirectional solidification of molten metal and includes a molten metal reservoir and a mold, in which molten metal in a molten metal source is supplied through transfer means into the molten metal reservoir, and the molten metal supplied into the molten metal reservoir is supplied through an opening/closing plug into the mold; target weight calculation/storing means for calculating, on the basis of compositional proportions of metal elements contained in the molten metal, a specific gravity of an alloy obtained through solidification of the molten metal, calculating a target weight of a cast body on the basis of the specific gravity of the alloy and a capacity of the mold, and memorizing and storing the target weight; and first molten metal supply amount regulation means for regulating an amount of the molten metal supplied from the molten metal reservoir into the mold by obtaining a measurement weight of the cast body and comparing the measurement weight with the target weight . In the target weight calculation/storing means, weight proportions of the metal elements contained in the molten metal are calculated on the basis of the compositional proportions of the metal elements, volume proportipns of the metal elements are calculated on the basis of the calculated weight proportions and specific gravities of the metal elements known beforehand, a specific gravity of an alloy of the metal elements is calculated on the basis of the calculated weight proportions and volume proportions , and the calculated specific gravity of the alloy is corrected so as to approximate the specific gravity to a real specific gravity. In the first molten metal supply amount regulation means, when the measurement weight is greater than the target weight, an opening time of the plug is shortened, and when the measurement weight is less than the target weight, the opening time of the plug is prolonged. The molten metal in the molten metal source is supplied to a plurality of casting apparatus to thereby produce cast bodies, and a sampling weight judgment apparatus is provided for sampling a cast body produced in each casting apparatus, and measuring a weight of the cast body to use the measured weight of the cast body as the measurement weight . The molten metal in the molten metal source is supplied to a plurality of casting apparatus to thereby produce cast bodies, and an all-product-weight judgment apparatus is provided for measuring the total weight of the cast bodies produced in the casting apparatus to use the measured total weight of the cast bodies as the measurement weight. The molten metal in the molten metal source is supplied to a plurality of casting apparatus to thereby produce cast bodies, and an all-product-weight judgment apparatus and a sampling weight judgment apparatus are provided and employed individually depending on a case involved, for measuring the weight of a cast body or bodies produced in the casting apparatuses to use the measured weight as the measurement weight . The all-product-weight judgment apparatus and/or the sampling weight judgment apparatus is employed for measuring the weight of a cast body that has been cooled in advance such that a temperature of the cast body falls within a predetermined temperature range. The automatic continuous casting system may further comprise liquid level measurement means provided on the transfer means for measuring a liquid level; and second molten metal supply amount regulation means for regulating an amount of the molten metal supplied from the molten metal source to the transfer means in accordance with the measured liquid level. The invention further provides an automatic continuous casting system for producing a cast body, comprising: a casting apparatus that makes use of unidirectional solidification of molten metal and includes a molten metal reservoir and a mold, in which molten metal in a molten metal source is supplied through transfer means into the molten metal reservoir, and the molten metal supplied into the molten metal reservoir is supplied through an opening/closing plug into the mold; molten-metal-in-trough temperature measurement means for measuring a temperature of the molten metal in the transfer means; heating region temperature measurement means for measuring a temperature of a heating region having a built-in heating body for heating the molten metal in the transfer means; temperature regulation means for regulating, by means of on-off control of power supply to the heating body, a temperature of the molten metal so as to fall within a predetermined temperature range and a temperature of the heating region so as to be not more than the predetermined temperature range. The invention further provides an automatic continuous casting system for producing a cast body, comprising: a casting apparatus that makes use of unidirectional solidification of molten metal and includes a molten metal reservoir and a mold, in which molten metal in a molten metal source is supplied through transfer means into the molten metal reservoir, and the molten metal supplied into the molten metal reservoir is supplied through an opening/closing plug into the mold; and cast body transfer means for transferring the cast body to transporting means for taking a subsequent step; wherein a bottom wall of the mold serves as a vertically movable cooling plate with which the molten metal supplied to the mold is forcedly cooled, and a cast body formed in the mold and placed on the cooling plate moved downward is transferred to the transporting means by the cast body transfer means . The cooling plate is provided on an upper surface with a gas discharge passage. The gas discharge passage is in a form of a rough surface formed on the upper surface of the cooling plate or slits formed radially on the upper surface. The automatic continuous casting system may further comprise another gas discharge passage formed on a lower surface of a sidewall of the mold that abuts on the cooling plate. The invention further provides an automatic continuous casting system for producing a cast body, comprising: a casting apparatus that makes use of unidirectional solidification of molten metal and includes a molten metal reservoir and a mold, in which molten metal in a molten metal source is supplied through transfer means into the molten metal reservoir, and the molten metal supplied into the molten metal reservoir is supplied through an opening/closing plug into the mold; gas introduction means for introducing pressurized gas between an upper surface of the mold and an upper surface of the cast body formed in the mold, in which a pressure equal to or higher than the atmospheric pressure ,is generated in a junction region between the upper surface of the mold and the upper surface of the cast body by introducing gas through the gas introduction means, to thereby allow the cast body to fall by means of the pressure. The gas introduction means can blow pressurized gas horizontally or vertically. The invention further provides an automatic continuous cast-forging system for forging a cast body into a forged body, comprising: a casting apparatus that makes use of unidirectional solidification of molten metal and includes a molten metal reservoir and a mold, in which molten metal in a molten metal source is supplied through transfer means into the molten metal reservoir, and the molten metal supplied into the molten metal reservoir is supplied through an opening/closing plug into the mold to produce a cast body; a forging apparatus for forging the cast body; transporting means for transporting the cast body to the forging apparatus; and a machining apparatus for machining the cast body; wherein a series of steps of supplying the molten metal into the molten metal reservoir and into the mold, transporting the cast body, forging the cast body and machining the forged body are taken continuously. The automatic continuous cast-forging system may further comprise a heat treatment furnace provided on an upstream side of the machining apparatus for subjecting the cast body to predetermined heat treatment before machining. When the forging apparatus is a hot forging apparatus, a preliminary heating furnace is provided for heating the cast body to a predetermined temperature range before the cast body is transported to the forging apparatus through the transporting means . The present invention further provides a metal casting process for producing a cast ingot, that comprises charging molten metal into a closed-space-definable mold which comprises mold members including a cooling member and in which an end face of an opening/closing plug serves as a portion of an inner wall of the mold, locally controlling removal of heat from the mold members in accordance with a shape of a cast ingot and a position and number of a sprue, thereby solidifying the molten metal so that a solidification interface advances to arrive at an end of the inner wall of the mold. The present invention further provides a metal casting apparatus for producing a cast ingot, that comprises a closed-space-definable mold which comprises mold members including a cooling member and into which molten metal is charged through a sprue, an opening/closing plug having an end face serving as a portion of an inner wall of the mold, a cooling capacity control mechanism which imparts , to the mold members , a heat removal profile appropriate for a shape of a cast ingot to be produced and for a number and position of the sprue . The present invention further provides a metal casting process for producing a cast ingot, that comprises using a mold which includes a mold main body having at an upper portion a sprue that can be opened and closed by means of an opening/closing plug, and a cooling member serving as a bottom portion of the mold, and into which molten metal is fed through the sprue and cooled by means of the cooling member; initiating feeding of the molten metal into the mold by opening the sprue with the opening/closing plug when a temperature of the cooling member of the mold is equal to or higher than a predetermined allowable lower limit temperature; initiating cooling of the cooling member so as to satisfy initial cooling conditions that the temperature of the cooling member does not become lower than the allowable lower limit temperature when the molten metal is brought into contact with a surface of the cooling member that faces an inside of the mold; feeding the molten metal into the mold continuously without closing the sprue with the opening/closing plug even after the mold is filled with the molten metal; closing the sprue by means of the opening/closing plug before the molten metal in the mold is solidified in the vicinity of the sprue to make closing of the sprue by means of the plug impossible; stopping cooling of the cooling member when predetermined cooling completion conditions are attained after the sprue is closed; and detaching the cooling member from the mold main body to thereby remove a cast ingot when predetermined cast ingot removal conditions are attained after cooling of the cooling member is stopped. The present invention further provides a metal casting apparatus comprising a mold including a mold main body having at an upper portion a sprue which can be opened and closed by means of an opening/closing plug, and a cooling member serving as a bottom portion of the mold; cooling means for cooling the cooling member of the mold; and casting control means for wholly carrying out opening/closing control of the sprue by means of the opening/closing plug, cooling control through the cooling means, and attachment/detachment control of the cooling member and the mold main body; wherein the casting control means comprises plug opening control means for opening the sprue with the opening/closing plug to thereby initiate feeding of molten metal into the mold on condition that a temperature of the cooling member is equal to or higher than a predetermined allowable lower limit temperature, initial cooling control means for controlling the cooling means so as to satisfy initial cooling conditions such that the temperature of the cooling member does not become lower than the allowable lower limit temperature when the molten metal is brought into contact with a surface of the cooling member that faces an inside of the mold after feeding of the molten metal is initiated through the plug opening control means, usual cooling control means for controlling the cooling means to thereby subject the cooling member to usual cooling after an entire surface of the cooling member that faces the inside of the mold is covered with the molten metal fed into the mold, plug closing control means for closing the sprue by means of the opening/closing plug to thereby stop feeding of the molten metal into the mold before the molten metal in the mold is solidified in the vicinity of the sprue to make closing of the sprue by means of the plug impossible, termination-of-cooling control means for stopping control of the cooling means by the usual cooling control means to thereby stop cooling of the cooling member when predetermined cooling completion conditions are attained after the sprue is closed through the plug closing control means; and attachment/detachment control means for detaching the cooling member from the mold main body so as to remove a cast ingot from the mold and then attaching the cooling member to the mold main body after the cast ingot is removed when predetermined cast ingot removal conditions are attained after cooling of the cooling member is stopped. The above and other objects, features and advantages of the present invention will become apparent from the description made with reference to the accompanying drawings . Brief Description of the Drawings : FIG. 1 is a schematic representation showing the structure of the automatic continuous casting system of the present invention. FIG. 2 shows the structure of a molten metal temperature regulation mechanism in a transfer trough. FIG. 3 shows a gas passage formed of a porous material. FIG. 4 shows a gas passage formed of grooves. FIG. 5 shows a gas passage formed of liners. FIG. 6 shows a gas passage formed of pores. FIG. 7 shows a gas passage formed of fire-resistant fibrous cloth. FIG. 8 shows a gas passage formed of another porous material . FIG. 9 shows a gas passage formed of another porous material included in an opening/closing plug. FIG. 10 shows a gas passage for causing even a large cast ingot to fall forcedly. FIG. 11(A) illustrates a gas discharge passage provided between the lower surface of the sidewall of a mold and a cooling plate, and FIG. 11(B) another gas discharge passage. FIG. 12(A) shows a mechanism for pushing a cast ingot up from a cooling plate, FIG. 12(B) another pushing mechanism, and FIG. 12(C) still another pushing mechanism. FIG. 13 shows the structure of a line including a sampling weight judgment apparatus. FIG. 14 is a plan view showing the structure of a line including an all-product-weight judgment apparatus and a sampling weight judgment apparatus. FIG. 15 is a schematic representation showing the structure of an automatic continuous cast-forging system. FIG. 16 is a schematic representation showing one example of a stock alignment apparatus according to the invention. FIG. 17 is a plan view showing a structure in which a plurality of casting apparatus are provided around a circular melting furnace. FIG. 18 is a plan view showing a structure in which a plurality of casting apparatus are provided along a longer side of a rectangular melting furnace. FIG. 19 is a plan view showing a structure in which a retention furnace is provided between a melting furnace and a casting apparatus. FIG. 20 shows a structure in which a robot is provided between a melting furnace and a nearby bath. FIG. 21 shows a mechanism in which molten metal in a melting furnace is fed to a transfer trough by means of a cone. FIG. 22 is a schematic cross-sectional view showing an exemplary metal casting apparatus of the invention. FIG. 23 is a schematic cross-sectional view showing another exemplary metal casting apparatus of the invention. FIG. 24 is a cross-sectional view showing holes that are adapted to maximize the cooling capacity. FIG. 25 is a schematic cross-sectional view showing another exemplary metal casting apparatus of the present invention. FIG. 26(A) is a plan view of a connecting rod member, FIG. 26(B) a side view thereof, and FIG. 26(C) a schematic cross-sectional view showing an exemplary metal casting apparatus for casting the connecting rod member. FIG. 27(A) is a schematic cross-sectional view showing another exemplary metal casting apparatus for producing a connection rod member having a shape identical with the connecting rod member shown in FIG. 26, and FIG. 27(B) a plan view showing the resultant connecting rod member. FIG. 28(A) is a schematic cross-sectional view showing another exemplary metal casting apparatus for producing a connection rod member having a shape identical with the connectxng rod member shown in FIG. 26, and FIG. 28(B) a plan view showing the resultant connecting rod member. FIG. 29 is a schematic cross-sectional view showing another exemplary metal casting apparatus of the invention. FIG. 30(A) is a schematic cross-sectional view showing another exemplary metal casting apparatus of the invention, and FIG. 30(B) a schematic cross-sectional view showing a modification of the metal casting apparatus of FIG. 30(A). FIG. 31 is a schematic cross-sectional view showing another exemplary metal casting apparatus of the invention. FIG. 32 is a schematic cross-sectional view showing another exemplary metal casting apparatus of the invention. FIG. 33(A) is a schematic cross-sectional view showing the situation under which a closed loop of solidification interface is formed within the cast ingot, and FIG. 33(B) a schematic cross-sectional view showing the situation under which solidification interface advances so as to reach the end portion of the mold. FIG. 34 is a schematic cross-sectional view showing another exemplary metal casting apparatus of the invention. FIG. 35 is a schematic cross-sectional view showing another exemplary metal casting apparatus of the invention. FIG. 36 is a schematic representation showing another exemplary metal casting apparatus of the invention. FIG. 37 is a time chart showing the casting process of the invention in relation to the temperature of a cooling plate. FIG. 38 is a photograph showing a vertical cross section of the cast ingot produced by the invention, with the cross section subjected to etching. FIG. 39 is a micrograph showing the microstructure of a vertical cross section of the cast ingot produced by the invention. FIG. 40 is a functional block diagram showing an embodiment of the casting control apparatus of the invention. FIG. 41 is a functional block diagram showing another embodiment of the casting control apparatus of the invention. FIG. 42 is a schematic cross-sectional view showing a conventional casting apparatus making use of unidirectional solidification. FIG. 43 is a schematic representation showing another conventional casting apparatus . FIG. 44 is a time chart showing a conventional casting process in relation to the temperature of a cooling plate. FIG. 45 is a photograph showing a vertical cross section of the cast ingot produced through the conventional casting process, with the cross section subjected to etching. FIG. 46 is a micrograph showing the microstructure of a vertical cross section of the cast ingot produced through the conventional casting process. Best Mode for Carrying Out the Invention: FIG. 1 schematically shows a casting system 1 of the present invention. As shown in FIG. 1, the casting system 1 comprises a casting apparatus 6 making use of unidirectional solidification of molten metal and including a molten metal reservoir 4 and a mold 5, in which molten metal in a melting furnace 2 (a source of molten metal) is supplied through a transfer trough 3 (transfer means) to the molten metal reservoir 4 , and the molten metal in the molten metal reservoir 4 is supplied through an opening/closing plug 43 to the mold 5 to thereby produce a cast body 7 (hereinafter referred to as "cast ingot"). As shown in FIG. 1, the mold 5 is disposed at the bottom of the molten metal reservoir 4 and includes a circumferential sidewall 51 and a bottom wall that serves as a cooling plate 52. A bottom wall 41 of the molten metal reservoir 4 forms an upper wall 53 of the mold 5. Thus, the mold 5 is formed of the upper wall 53, the sidewall 51, and the cooling plate 52. The cooling plate 52 is cooled with cooling water sprayed from a spray nozzle 52a disposed below the cooling plate 52 and can be moved vertically (upward and downward) by means of a cooling plate elevator 52b. The bottom wall 41 of the molten metal reservoir 4 has a sprue 42 that opens and closes by means of the opening/closing plug 43. When the sprue 42 is held open, molten metal contained in the molten metal reservoir 4 is poured into the mold chamber of the mold 5. The casting apparatus 6 including the molten metal reservoir 4 and the mold 5 also acts as an electric furnace by means of a heater 61 disposed around the periphery thereof. The molten metal poured into the mold 5 is cooled unidirectionally upward from the upper surface of the cooling plate 52 mainly with cooling water sprayed from the spray nozzle 52a toward the cooling plate 52, forming a cast ingot 7 having a metallographic structure in which the crystal growth direction almost coincides with the molten-metal elevation direction inside the mold 5. The thus obtained unidirectionally solidified cast ingot 7 does not include any cut surface and, as compared with castings or die-castings, is endowed with excellent internal quality and forgeability. Thus , the cast ingot 7 can be used as a material to be subjected to plastic processing such as impacting or rolling. In order to produce cast ingots continuously and automatically by use of the casting apparatus 6 that makes use of unidirectional solidification, various means, which will be described hereunder, are provided, and the overall system including such means constitutes the automatic continuous casting system 1. The automatic continuous casting system 1 includes a structure for controlling the volume of the cast ingot 7 to a predetermined value. The reason for controlling the cast ingot volume to a predetermined value is to prevent a possible short service life of a mold, which may otherwise be caused in the case in which a cast ingot is subjected to forging, in particular die-forging, during which a very small variation imposes a heavy load on the mold. Measurement of the volume of each cast ingot for the purpose of checking whether the volumes of the produced cast ingots are uniform across the products is cumbersome and time-consuming, and incorporation of product-by-product measuring means into the production line may be difficult . Needless to say, such volume measurement means would be useless when the cast ingots are in complicated form. In order to cope with this problem, the present invention checks the weight instead of the volume and controls the weight of a cast ingot so as to fall on a target value. However, the target weight of the cast ingot, which is introduced in an attempt to attain a constant volume among ingot products, varies depending on the specific gravity (density) of the molten metal and also on the capacity of the mold. In other words, even if the mold capacity is fixed, variation of alloy components in different runs (lots) of melting leads to variation in specific gravity of the solidified alloy. Therefore, the target weight of the cast ingot cannot be fixed to a constant value. Moreover, even when the specific gravity of molten metal obtained from a single lot is constant, when molten metal from such a single lot is used in a plurality of production lines, each line having its own mold, the target weight of the cast ingot still cannot be fixed to a constant value, because there may be a variation in capacity of the molds. In order to cope with this problem, the present invention employs a target weight calculation/storing means 8 and a first molten metal supply amount regulation means 9 which are adapted to determine a target weight for each lot and for each mold and to adjust the weight of a cast ingot to its target weight. The target weight calculation/storing means 8 is operated in accordance with software installed on a personal computer, for example. Briefly, as will be described hereunder, from the compositional proportions of molten metal, the specific gravity of an alloy which is to be formed is calculated, the thus-calculated specific gravity and the capacity of the mold 5 are used to calculate the target weight of the cast ingot 7, and the calculated target weight is to be memorized and saved. The compositional proportions can be determined from sampling a molten metal sample from the current lot and subjecting it to compositional analysis. Example means for compositional analysis include an emission spectral analyzer 81 (FIG. 1), a fluorometric analyzer and a chemical analysis apparatus. The emission spectral analyzer 81 is available in two types that are the solid photometric analyzer and the ICP atomic emission spectrometer. The solid photometric analyzer is manufactured by, among others, Shimadzu Corporation, Spectro (Germany) and Thermo Jarrell Ash (U.S.A.). The ICP atomic emission spectrometer is manufactured by, among others, Shimadzu Corporation, Seiko Instruments Inc. and Hitachi Ltd. The first molten metal supply amount regulation means 9 is constructed, for example, as a casting machine control unit which operates in accordance with software. The first molten metal supply amount regulation means 9 compares the as-weighed weight value of the cast ingot 7 and the target weight calculated through the target weight calculation/storing means 8 and regulates, on the basis of the result of comparison, the amount of molten metal to be supplied from the molten metal reservoir 4 to the mold 5. The specific gravity of an alloy, the capacity of a mold, the calculations performed by the target weight calculation/storing means 8, etc. will next be described in detail. Metallic materials used in practice have properties that greatly differ from those of pure metal (aluminum in this description) , because of addition of specific metal elements in specific amounts and because of processing and thermal treatment of a cast ingot of the material, to thereby make the ingot suitable for forging. For example, elements such as Cu, Mg, Ni, Si, Cr, Mn, Fe, Sn, Pb, Bi, Zn, Zr and Li are added to aluminum melted in a melting furnace 2 to thereby yield an Al alloy. The Al alloy further includes trace amounts of additive metal elements such as Ti, Sr and P, and also trace amounts of impurities that have migrated during a production process of Al. The species and the amounts of the additive metal elements are determined in accordance with the identity of the target alloy. Since the additive metal elements have different specific gravities, different alloys have different specific gravities . Meanwhile, the volume of the cast ingot obtained through casting depends on the mold capacity. When judgment as to whether or not the volume of the cast ingot is acceptable is to be performed on the basis of weight, different alloys should naturally have different target weights. Moreover, when considered in detail, according to JIS standards, compositional proportions of elements that constitute alloys have ranges, and therefore, the specific gravity of an alloy that is formulated in accordance with the upper limits as specified in JIS naturally differs from that of an alloy that is formulated in accordance with the lower limits. In practice, when the melt-production lots differ, compositional proportions of the resultant products also differ. Thus, as described above, the specific gravity varies depending on the lot. Accordingly, when a large number of ingots of narrow volume variation, i.e. narrow weight variation, are to be molded, the difference in specific gravity must be taken into consideration. The specific gravity is calculated as follows . A metal element contained in an alloy is expressed as "An", the percent by weight of the metal element An as determined by emission spectral analysis is expressed as "wAn", the specific gravity of the metal element An is expressed as "pAn", and the volume of the metal element An is expressed as "vAn." When elements Si and Fe are expressed as Al and A2 , respectively, for example, the percents by weight of Si and Fe are expressed as wAl and wA2, respectively, the specific gravities of Si and Fe are expressed as pAl and pA2, respectively, and the volumes of Si and Fe are expressed as vAl and vA2 , respectively. The volume "vAn" is calculated by equation ( 1 ) . vAn = wAn/pAn (1) If the total weight percent of alloy components is expressed as "W" and the total volume of the alloy components is expressed as "V, " the specific gravity "P" is calculated by equation (2) . P = W/V (2) Provided that W = ∑(wAn), v = ∑(vAn) (n = 1-N, N is the total number of the species of the alloy elements to be considered) . Notably, not all components contained in molten metal are necessarily considered in calculation of the specific gravity P. For example, even if a component contained in an amount not more than 0.005 wt.% is omitted from calculation, the calculated specific gravity of the alloy will not be affected. When a more precise specific gravity is required, the specific gravity P of the alloy is compensated for in accordance with equation (3) to thereby obtain a specific gravity closer to the actual specific gravity value PI. PI = αP - β (3) The above compensation formula (3) compensates for the difference between the specific gravity P calculated on the basis of the results of analysis, such as emission spectrometric analysis, and the actual specific gravity of the cast ingot as measured on the basis of the Archmedes ' principle. For example, α = 1.250 and β = -0.689. The difference between a calculated specific gravity P and an actual specific gravity PI is considered to result from crystal distortion due to segregation of components that occurs during solidification and from generation of an intermetallic compound. The capacity of the mold 5 calculated in advance is expressed as Vo. The capacity Vo may be calculated on the basis of the mold dimensions determined by use of a three- dimensional measurement apparatus 82. Alternatively, the measurements obtained from the three-dimensional measurement apparatus 82 may be sent to the target weight calculation/storing means 8, where the capacity Vo is calculated automatically. The capacity Vo of the mold 5 may be calculated through another method without use of the three-dimensional measurement apparatus 82. For example, there may be employed a method in which clay or resin is charged in the mold to thereby calculate the mold capacity from the amount of the clay or resin, or a method in which water is charged in the mold. When multiple casting is performed by use of a plurality of casting apparatus 6, variation in dimensions of molds 5 must be minimized. Preferably, after production of a mold 5, its dimensions are checked by use of the three- dimensional measurement apparatus 82 to thereby select molds having dimensions within acceptable ranges in terms of design. The target weight Wo of cast ingots can be calculated by use of the above equation (3), the mold capacity Vo and equation (4) or (5). When either lot or mold is changed, the target weight Wo is recalculated according to the new lot or mold. Wo = P x Vo (4) Wo = PI x Vo (5) The casting machine control unit (the first molten metal supply amount regulation means 9) acquires the target weight Wo from the personal computer (target weight calculation/storing means 8) and a weight W of the cast ingot 7 as weighed from a weight judgment apparatus 88 or 91, and compares W and Wo. When the difference between Wo and W falls within a predetermined acceptable range, the cast ingot 7 is judged as a good item and is sent to the next step. When the weight W as weighed falls outside the predetermined range and is greater than the target weight Wo, the casting machine control unit 9 commands an opening/closing plug operating device 44 to shorten the open time during which the opening/closing plug 43 is held open, whereas when the weight W as weighed is less than the target weight Wo, the casting machine control unit 9 commands the opening/closing plug operating device 44 to lengthen the open time during which the opening/closing plug 43 is held open. In this manner, the weight of the cast ingot 7 can be adjusted to the target weight, and thus cast ingots 7 of virtually uniform volumes are transferred to a forging step. The weight W is adjusted to, for example, within ±1.5%, preferably within ±0.5%, of the target weight Wo. When the weight W is greater than the upper limit of +1.5%, the open time during which the opening/closing plug is held open for pouring the molten metal is excessive, and molten metal in the vicinity of the sprue 42 solidifies, resulting in difficulty in operation of the opening/closing plug, whereas when the weight W falls below the lower limit of -1.5%, the shape of the produced cast ingot does not conform to the shape of the mold, or the cast ingot has a large number of microporosities (minute voids) due to reduced effect of self- pressurizatio . The target weight Wo is determined by use of the personal computer 8, preferably for every lot and for every mold. In the course of long-term operation, the compositional proportions of chemical components contained in the molten metal in the melting furnace 2 may change. Therefore, preferably, a sample is collected when the casting apparatus is in operation, the chemical components are verified through analysis by means of the emission spectrometric analyzer 81, and the new data of chemical components are stored in memory of the personal computer 8 , to thereby re-determine a new target weight of the cast ingot 7. Thus , an optimal volume of the cast ingot can be maintained in a timely manner. Regulation of the liquid level in the transfer trough 3 will next be described. In order to perform continuous casting, molten metal must be supplied continuously to the molten metal reservoir 4. To this end, the transfer trough 3 is installed between the melting furnace 2 and the molten metal reservoir 4. When the supply amount of molten metal from the melting furnace 2 is disturbed, the liquid level in the transfer trough 3 fluctuates, resulting in fluctuation of the liquid level in the molten metal reservoir 4. When the liquid level in. the molten metal reservoir 4 fluctuates, the static pressure applied onto the molten metal contained in the mold 5 fluctuates during casting, and the self- pressurizing effect fluctuates accordingly. Thus, the amount of the molten metal poured into the mold 5 varies, leading to variation in the weight of a cast ingot or generation of defects, such as micropores, inside the cast ingot. Therefore, the melting furnace 2 is required to supply molten metal in a precise amount that is required for casting so as to maintain a constant liquid level in the transfer trough 3. The range for regulation of the liquid level is, for example, within ±10%, preferably within ±3%, of the depth of the molten metal in the transfer trough 3. When the upper limit of +10% is surpassed, the self-pressurizing effect becomes significant to thereby increase alloy density, and as a result, the weight of cast ingot falls beyond the upper acceptable limit of the target weight , whereas when the liquid-level fluctuation falls below the lower limit of -10%, the shape of the produced cast ingot does not conform to the shape of the mold, or the cast ingot has a large number of micropores due to reduced effect of self-pressurization. In order to cope with this problem, liquid-level measurement means 31 and a furnace tilt motion regulation device 20 which serves as second molten metal supply amount regulation means are provided in the automatic continuous casting system 1. The liquid-level measurement means 31 is a sensor for measuring the liquid level in the transfer trough 3, and various types of such means may be employed. For example, a laser sensor for continuous monitoring of the displacement of the liquid level may be used in the following manner. The sensor emits a laser beam toward the surface of molten metal and detects the reflected beam, whereby the distance between the sensor and the surface of the molten metal is determined. In another sensor for measuring the displacement of the liquid level, a float having a specific gravity lower than that of molten metal is placed on the liquid surface and connected to a displacement sensor. In still another sensor for monitoring the liquid level, an electromagnetic coil is inserted in a ceramic sheath inert to molten metal and exhibiting no magnetism, and the resultant sheath is immersed in the molten metal in the trough so as to monitor the liquid level by means of the electromagnetic coil. In accordance with the liquid level measured by the liquid-level measurement means 31, the furnace tilt motion regulation device 20 regulates the amount of the molten metal supplied from the melting furnace 2 to the transfer trough 3. Briefly, when the liquid level is higher than a predetermined level, a hydraulic pump 21 is actuated so as to move the furnace tilting device 22 so that the melting furnace 2 is regulated to incline at a smaller angle, whereas when the liquid level is below the predetermined level, the melting furnace 2 is regulated to incline at a larger angle. Through this regulation of tilting, the amount of molten metal supplied from the melting furnace 2 can be regulated precisely, thereby attaining a virtually stabilized liquid level in the molten metal reservoir 4, except for unavoidable effects exerted by opening/closing motion of opening/closing plug 43. As a result, the amount of the molten metal charged in the mold 5 becomes constant, thereby yielding cast ingots of virtually uniform weight . Regulation of the temperature of molten metal in the transfer trough 3 will next be described. When the flow rate of the molten metal in the transfer trough 3 is high, a temperature drop of the molten metal is not a problem. However, when the cast ingot to be molded is small in size, a smaller amount of molten metal is consumed per unit period of time, and therefore, due to high heat radiation from the molten metal surface and the trough body, a temperature drop of the molten metal inevitably occurs. In such a case, since molten metal of low temperature is poured into the molten metal reservoir 4 , the temperature drop cannot be compensated for by heat generated in the electric furnace 61, and the molten metal in the vicinity of the sprue 42 may solidify, resulting in disabled casting. Even though such solidification does not occur, when casting is performed with the low internal temperature of the molten metal reservoir 4, the molten metal becomes viscous and the fluidity thereof in the mold 5 decreases. As a result, a cast ingot 7 of predetermined weight cannot be obtained, and there tend to occur problems in terms of quality, such as presence of casting defects, such as microshrinkage and cavities inside the cast ingot and non-uniformity of metallographic structure. Thus, the temperature of the molten metal in the transfer trough 3 must be maintained constant, irrespective of the molten metal flow rate or ambient temperature. To this end, as shown in FIG. 2, the automatic continuous casting system 1 of the present invention has a thermocouple TCI (molten-metal-in-trough temperature measurement means) for measuring the temperature of molten metal in the transfer trough 3, and a thermocouple TC2 (heater-section temperature measurement means) for measuring the temperature of a heater section (heating plate) 34, which includes a resistance heating body 33 for heating the molten metal in the transfer trough 3. The measurement results of the thermocouples TCI and TC2 are sent to an molten-metal-in- trough temperature regulation device (temperature regulation means) 30 which turns on or off, according to the measurement results, the electric supply to the heating body 33 so as to adjust the molten metal temperature to fall within a predetermined range and adjust the temperature of the heating plate 34 to be equal to or lower than the predetermined temperature . Regulation of the molten metal temperature will next be described in detail. As shown in FIG. 2, the transfer trough 3 includes an iron casing 36 and a trough body 37 that is disposed inside the iron casing 36 and is formed of a heat- insulating refractory material having a gutter shape. The heating plate 34 containing the heating body 33 is attached to the trough body 37 in close contact with the bottom surface thereof, and the heating body 33 is connected to an external power source 38. The thermocouple TCI contained in a thermocouple protection tube 32 is inserted in the molten metal 45 for monitoring the molten metal temperature. Below the heating plate 34, the thermocouple TC2 is disposed in close contact with the bottom surface thereof. The heating plate 34 must have a heat capacity which can sufficiently compensate for the heat released from the surface of the molten metal 45, heat released through the refractory heat insulating material of the trough body 37 and temperature fluctuation of the molten metal supplied from the melting furnace 2. The molten-metal-in-trough temperature regulation device 30 regulates power supply from the power source 38 on the basis of the molten metal temperature as measured by the thermocouple TCI, so that the molten metal temperature is adjusted to a predetermined temperature. Meanwhile, when molten metal is present in the transfer trough 3, heat generated by the heating plate 34 is not easily dispersed. As a result, heat accumulates in the vicinity of the heating plate 34. When heating is continued with the power source 38 of the heating plate 34 kept "on" in an attempt to reduce some difference between the intra-trough molten metal temperature and a preset temperature, heat accumulates in the vicinity of the heating plate 34 as time passes, resulting in overheat of the heating plate 34, which reaches a high temperature. As a result, the temperature not only elevates beyond the fireproof limit of the material of the heating plate 34, but also the heating body 33 itself deteriorates to shorten its service life. In order to avoid this problem, the present invention employs the thermocouple TC2 disposed directly below the heating plate 34 to thereby measure the temperature of the heating plate 34, and the temperature is monitored by the molten-metal-in-trough temperature regulation device 30. Power supply to the heating plate 34 is controlled automatically. When the temperature has reached a predetermxned temperature, for example, the power source 38 is turned off. In this manner, the molten metal in the transfer trough 3 can be controlled to maintain a specified temperature without imposing overload on the heating plate 34. As a result , flaws of the cast ingot 7 , such as casting defects and variation in metallographic structure, can be reduced, thereby improving quality of the cast ingot 7. In the aforementioned structure, the thermocouple TC2 is disposed beneath the heating plate 34. However, the location of the thermocouple TC2 is not particularly limited and may be determined in accordance with the trough structure. It may be disposed, for example, above or beside the heating plate 34. Next, regulation of the molten metal temperature in the molten metal reservoir 4 will be described. The molten metal poured into the molten metal reservoir 4 is heated by means of a heater 61. In order not to produce any defective product among all cast products, the temperature of the molten metal in the molten metal reservoir 4 must have reached a predetermined temperature at the beginning of the casting process. Meanwhile, when malfunction of the casting apparatus occurs, the molten metal in the molten metal reservoir 4 is retained therein. In such a situation, if the molten metal in the molten metal reservoir 4 is heated beyond the predetermined temperature by means of the heater 61, the quality of molten metal deteriorates, and energy is wasted. Therefore, the temperature of the molten metal in the molten metal reservoir 4 must be always maintained at a constant value . To this end, the automatic continuous casting system 1 of the present invention employs a thermocouple TC3 sheathed in a thermocouple protection tube 62 and inserted in the molten metal 45 in the molten metal reservoir 4 for measuring the molten metal temperature. The casting machine control unit 9 monitors the temperature as measured by the thermocouple TC3. When the molten metal temperature falls outside a predetermined range, the casting machine control unit 9 controls power supply from a power source 63 so as to regulate the amount of heat generated by the heater 61, thereby maintaining the molten metal at a constant temperature. In this manner, the temperature is controlled automatically, thereby ensuring cast ingots of reliable quality. Other than the resistance heating furnace employing the resistance heating body, the electric furnace (casting apparatus 6) can be in any form so long as the heat source is connected to the casting machine control unit 9 and automatic monitoring of the molten metal temperature can be effected. Examples of the electric furnace include a high-frequency- induction heating furnace, a low frequency heating furnace, a heavy oil burning furnace or other such furnaces utilizing liquid fuel and a gas burning furnace or other such furnaces utilizing gas fuel. Next, employment of pressurized gas for forced falling of a cast ingot 7 formed in the mold 5 will be described. Most cast ingots can be removed from the mold by means of gravitational force, and casting can be repeated in a constant cycle. However, when the time required for falling varies or the cast ingot fails to fall, the temperature of the mold changes, thereby hampering attainment of the state of unidirectional solidification. Therefore, forced falling has been found to be necessary for maintaining the unidirectionally solidified state. Meanwhile, there has conventionally been known a method for forcibly causing a cast ingot formed in a mold to fall, in which a vacuum pad is brought into contact with the bottom surface of the ingot to thereby withdraw the ingot mechanically. This method ensures reliable withdrawal of cast ingots from the mold, and production of cast ingots can be performed continuously. However, production of cast ingots in a constant cycle, without being interrupted, is not guaranteed. It has now been found that, in order to produce cast ingots in a constant cycle, effective and quick application of a compulsive external force is required upon completion of solidification shrinkage. However, the mold is high in temperature due to molten metal present thereabove. Thus, application of an external force to the cast ingot through mechanical means is extremely difficult . In order to cope with this problem, according to the automatic continuous casting system 1 of the present invention, a pressurized gas is introduced through a gas introduction passage onto the top surface of the cast ingot 7 formed in the mold 5 to thereby force the cast ingot 7 to fall by means of the pressure of the pressurized gas. When molten metal poured into the mold chamber traps air, the configuration of the cast ingot does not conform to that of the mold. Thus, the air in the mold chamber must be expelled, and a conventional approach therefor is the provision of an air-removal passage. Air may cause disturbance of molten metal upon teeming of the molten metal into the mold chamber, resulting in generation of oxides, which is detrimental to the quality of cast ingots. In order to avoid deterioration in quality, in one conventionally known casting apparatus, a passage for an inert gas is provided for purging air in the mold chamber before molten metal is poured into the chamber. The automatic continuous casting system 1 of the present invention employs , as a gas introduction passage for introducing the aforementioned pressurized gas, a portion of the air-removal passage or the passage for purging inert gas. Alternatively, in addition to these passages, a gas introduction passage used exclusively for gas pressurization may be formed in the automatic continuous casting system 1. The inner diameter, dimensions and the material of the end of the air-removal passage or the gas passage for purging of inert gas are designed such that the molten metal does not enter the passage. FIGs. 3-11 show some embodiments of gas introduction passages, wherein FIGs. 3-7 are drawn to the cases where air- removal passages are employed, FIGs. 8-10 are drawn to the cases where gas passages for purging inert gas are employed, and FIG. 11(A) or FIG. 11(B) is drawn to the case where a gas introduction passage used exclusively for gas pressurization is formed. As shown in FIG. 3, the end of a gas introduction passage 64 is formed of a porous material 64a that is interposed between the bottom surface (inner upper surface) of the upper wall 53 of the mold 5 and the top surface of the sidewall 51. An electromagnetic valve 65 and a pressure gauge 66 are disposed at the gas passage 64. The casting machine control unit 9 connected to the electromagnetic valve 65 opens the electromagnetic valve 65 at a predetermined timing during the casting process to thereby introduce a pressurized gas (e.g., air or argon) in a horizontal direction from a compressed gas supplying section (not shown) . The pressurized gas is jetted through the porous material 64a at the end of the gas passage 64, during which the pressure gauge 66 measures the pressure of the pressurized gas. The pressurized gas pushes the top surface of the cast ingot 7 to thereby detach the cast ingot 7 from the mold 5 and force the cast ingot 7 to fall. In this case, timing for introducing the pressurized gas may be simultaneous with, or subsequent to, descending of the cooling plate 52. The highest efficiency is attained when the top of the mold is pushed by means of a gas supplied through the gas passage 64. However, the side of the mold may be pushed. The pressurized gas is preferably air or an inert gas at a pressure of 0.5 kg/cm 2 or higher. Pushing a cast ingot once or a few times at an interval of a few seconds is effective. As shown in FIG. 4, grooves 64b connected to the gas introduction passage 64 are formed in either or both of the upper inner surface of the mold 5 and the top surface of the sidewall 51. The grooves 64b form an end of the gas passage 64. Thus, a pressurized gas flows directly into the gas introduction passage 64 and enters the grooves 64b and is then jetted through the grooves 64b toward the top surface of the cast ingot 7. As shown in FIG. 5, liners 64c in communication with external space are formed in either or both of the upper inner surface of the mold 5 and the top surface of the sidewall 51. The liners 64c form an end of the gas introduction passage 64. Thus, a pressurized gas flows directly into the gas introduction passage 64, enters passages 640c formed of the liners 64c and is jetted toward the top surface of the cast ingot 7. The liner 64c is preferably made of a metal, such as stainless steel, iron, etc., or refractory material, such as ceramic or ceramic fibers. As shown in FIG. 6, pores 64d are formed in the upper inner surface of the mold 5. The pores 64d form an end of the gas introduction passage 64. Thus, a pressurized gas flows through the gas introduction passage 64, enters the pores 64d and is jetted toward the top surface of the cast ingot 7. As shown in FIG. 7, a refractory fibrous cloth 64e is inserted between the upper inner surface of the mold 5 and the top surface of the sidewall 51. The refractory fibrous cloth 64e forms an end of the gas introduction passage 64. Thus, a pressurized gas flows through the gas passage 64, directly enters the refractory fibrous cloth 64e and is jetted through pores of the refractory fibrous cloth 64e toward the top surface of the cast ingot 7. When the refractory fibrous cloth 64e is thick, molten metal pulls out the fiber of the refractory fibrous cloth 64e, raising problems such as reduced fireproof properties of the cloth and non-uniformity of dimensions of the resultant castings. Therefore, a thin refractory fibrous cloth having a thickness of 1 mm or less is preferred. The refractory fibrous cloth may be any refractory cloth, such as a commercially available alumina fiber cloth, cloth made of a mixture of A1 2 0 3 fibers and Si0 2 fibers, glass fiber cloth or carbon fiber cloth. Alternatively, a porous ring may be provided instead of the refractory fibrous cloth 64e. In this case, the porous ring forms an end of the gas introduction passage. Thus, a pressurized gas flowing through the gas introduction passage 64 directly enters the porous ring and is jetted through pores of the porous ring toward the top surface of the cast ingot 7. The porous ring is preferably made of a material, such as A1 2 0 3 or Si 3 N 4 . As shown in FIG. 8, a porous material 64f is incorporated in the upper wall 53 of the mold 5. The porous material 64f forms an end of the gas introduction passage 64. Thus, a pressurized gas flowing through the gas introduction passage 64 directly enters the porous material 64f and is jetted through the porous material 64f toward the top surface of the cast ingot 7. As shown in FIG. 9, a porous material 64g is incorporated in the opening/closing plug 43 so that the bottom surface of the porous material 64g faces the mold chamber. The porous material 64g forms an end of the gas introduction passage 64 formed through the opening/closing plug 43. Thus, a pressurized gas is introduced in the vertically disposed gas introduction passage 64 and directly enters the porous material 64g, through pores of which the pressurized gas is jetted toward the top surface of the cast ingot 7. When the cast ingot 7 is large in size, greater force is required to detach the cast ingot 7 from the mold 5 and to force the cast ingot 7 to fall. In this case, use of the aforementioned air-removal passage or passage for purging inert gas is not sufficient, because the gas passage has such a structure that prevents molten metal from entering the gas passage and because a large amount of pressurized gas must be jetted from the end of the gas introduction passage. However, when the end of the gas introduction passage is formed with pores or slits having diameters or widths of 100 μm or more. molten metal enters the gas introduction passage, resulting in inability to use the passage for gas pressurization. In order to cope with this problem, when a gas introduction passage provided exclusively for pressurizing a gas has at an end thereof pores or slits having diameters or widths of 100 μm or more, an opening/closing valve is provided somewhere at the gas introduction passage dedicated for pressurizing a gas. The valve is closed during pouring of molten metal into the mold 5 to thereby prevent the molten metal from entering the passage, and the valve is held open immediately before or after completion of pouring ,of the molten metal so as to introduce the pressurized gas to thereby force the cast ingot to fall. Alternatively, if the valve is not used, a gas that is slightly pressurized to the extent that the molten metal does not enter the gas introduction passage may be passed through the gas introduction passage. For example, an inert gas at a pressure of 0.05 kg/cm 2 or higher may be used. In this manner, molten metal does not enter the gas introduction passage. Also in this case, the timing for introducing the pressurized gas for forced falling may be simultaneous with, or subsequent to, descending of the cooling plate 52. The pressurized gas is preferably air or an inert gas at a pressure of 0.5 kg/cm 2 or higher. Applying a pressure once or several times intermittently, for a few seconds each time. is effective. FIG. 10 shows an exemplary structure of a gas introduction passage that is provided exclusively for gas pressurization. Gas introduction passages 640 are formed in the upper wall 53 of the mold 5. The terminal portions of the gas introduction passages 640 are bent so that the ends of the gas introduction passages 640 face the mold chamber. The inner diameter of the end of each gas introduction passage 640 is 100 μm or more, and, as described hereinabove, preferably molten metal is prevented from entering the gas introduction passages 640. For example, intrusion of molten metal into the passages is prevented by closing valves during charging of molten metal, or through applying a pressure of 0.05 kg/cm 2 or more to the inside of the passage. The pressurized gas for forcing the cast ingot to fall is preferably air or an inert gas having a pressure of 0.5 kg/cm 2 or more. The pressurized gas is applied once or a few times at intervals of a few seconds. Each of the gas introduction passages provided exclusively for passing a pressurized gas therethrough has a large inner diameter, and thus enables a large quantity of pressurized gas to be blown into the mold chamber. Therefore, even a large cast ingot can be subjected to sufficient force to fall. As working examples of the present invention, the structures shown in FIGs. 4, 6, 8, 9 and 10 were employed, and cast ingots were forced to fall. The falling time and variation thereof were examined, and the results were compared with those obtained by use of a conventional structure in which the cast ingot was allowed to fall freely without use of gas pressurization. Examples 1, 2, 3, 4 and 5 correspond to the exemplary structures shown in FIGs. 4, 6, 8, 9 and 10, respectively. In Examples 1-5, materials (cast ingots) to be used for forging a VTR cylinder drum were subjected to casting. An aluminum alloy was melted in the melting furnace 2, and the molten metal was introduced in the molten metal reservoir 4. The cooling plate 52 was made of copper. The mold 5, molten metal reservoir 4 and opening/closing plug 43 were made of a commercially available heat-insulating refractory material named Lumiboard produced by Isoraito Kogyo Kabushiki Kaisha. The casting conditions and procedure are as follows. 1) Species of alloy: JIS2218 alloy 2) Internal temperature of molten metal reservoir: 720°C 3) Cooling plate temperature before charging of molten metal: 100°C 4) Flow rate of cooling water: 5 liters/minute 5) Diameter of sprue: 12 mm 6) Outer dimensions of material: 62.5 mm in diameter and 9 mm in thickness 7) Casting procedure: The sprue is closed with the opening/closing plug 1.5 seconds after teeming. Cooling by water starts when the cooling plate temperature has reached 500°C. Cooling by water stops when the cooling plate temperature has reached 300°C. Descending of the cooling plate starts when the cooling plate temperature has reached 200°C. 8) Pressurized gas is applied to cast products simultaneous with descending of the cooling plate to thereby cause the products to fall for collection. 9) Application of gas pressure of 0.6 kg/cm 2 : three times at intervals of 0.5 seconds In Examples 1 and 2, air was used as the pressurized gas, and in Examples 3, 4 and 5, argon was used as the pressurized gas. In Example 5, two gas introduction passages each having a diameter of 1 mm and designed exclusively for passing a gas for gas pressurization were formed. In order to prevent intrusion of molten metal into the gas introduction passages, valves provided in the vicinity of the ends of the gas introduction passages provided exclusively for gas pressurization were closed during teeming. In Comparative Example 1, which is drawn to a conventional technique, casting was performed by use of the structure employed in Example 5 but gas pressurization was not performed. Table 1 shows the results of Examples 1-5 and, for comparison, those of Comparative Example 1. [Table 1] Falling time: time from start of descending of the cooling plate to falling of the cast ingot. Variation range of falling time: (maximum falling time) - (minimum falling time) . As shown in Table 1, in Examples 1-5 that forced the cast ingot to fall through gas pressurization, the falling time was remarkably shortened and variation of the falling time was also significantly reduced. Thus, forcing the cast ingot to fall through gas pressurization reliably detaches the cast ingot from the mold and causes the cast ingot to fall. Moreover, it was found that forcing the cast ingot to fall through gas pressurization enables cast ingot production in a constant, continuous cycle. Next , exemplary structures of the aforementioned air- removal passages will be described. As shown in FIGs. 3-7, an air-removal passage is employed also as a gas introduction passage for gas pressurization. In the aforementioned structures, porous material, grooves, liners, pores and refractory fibrous cloth were used for the air-removal passage. In order to produce cast ingots 7 of constant weight, it is necessary to initiate, simultaneously with teeming of molten metal, expulsion of air contained in the mold 5 to the outside so as to replace the air with the molten metal as quickly as possible. However, it was found that, depending on the size of the cast ingot 7, air-removal passages (e.g., slits or small pores), which are in communication with the outside and are formed at the boundary surface between the upper wall 53 of the mold 5 and the top surface of the sidewall 51, cannot sufficiently discharge the air, resulting in variation in weight. In order to cope with this problem, air in the mold 5 must be discharged in a more effective manner. Accordingly, in the automatic continuous casting system 1 of the present invention, as shown in FIG. 11(A), the top surface of the cooling plate 52 and the bottom surface of the sidewall 51 of the mold 5 in contact with the cooling plate 52 are roughened to a surface roughness of 200 μm or less through shot-blasting to thereby form gas discharge passages. It was confirmed that the gas pressurized against the cooling plate 52 under the weight of molten metal poured from above could be smoothly expelled via the roughened top surface of the cooling plate 52 or the roughened bottom surface of the bottom surface of the sidewall 51 of the mold 5 (see arrows Yl in FIG. 11(A)), proving that this structure is effective for discharging gas. Moreover, as shown in FIG. 11(B), formation of groove- shaped slits S having a width of 100 μm or less and provided radially at the top surface of the cooling plate 52 or the bottom surface of the sidewall 51 of the mold 5 in contact with the cooling plate 52 was also found to be effective for discharging gas which has been compressed against the cooling plate 52 under the weight of the molten metal (see arrows Y2 in FIG. 11(B)) . The reason for provision of the slits S is as follows . Since the cooling plate 52 is made of Cu or Cu alloy, which have high thermal conductivity, during repeated collision between the cooling plate 52 and the bottom surface of the sidewall 51 of the mold 5, caused by the ascending and descending motions of the cooling plate 52 during the casting procedure, surface roughness of a shot-blast-roughened surface deteriorates, and therefore, shot-blasting must be performed periodically. The slits S do not require such maintenance. Either of the above approaches may be followed, depending on the size of the ingot to be cast . The aforementioned gas discharge passages are preferably provided at both the top surface of the cooling plate 52 and the bottom surface of the sidewall 51. However, the gas discharge passages may be provided at either one of these surfaces . Turning back to FIG. 1, the structure for removing a cast ingot will be described. When the cast ingot 7 is formed in the mold 5, the casting machine control unit 9 opens the electromagnetic valve 65 so as to apply gas pressure for forcing the cast ingot 7 to fall and commands the cooling plate elevator 52b to lower the cooling plate 52, followed by starting an operation for collecting the cast ingot 7 present on the cooling plate 52. The automatic continuous casting system 1 of the present invention includes cast ingot transfer means 68 for transferring a cast ingot 7 formed in the mold 5 and placed on the cooling plate 52 to a transporting conveyer 85 which conveys the ingot 7 to the subsequent step, thereby enabling automatic transportation to the subsequent step without need for manpower. As shown in FIG. 1, the cast ingot transfer means 68 includes a cylinder mechanism. The casting machine control unit 9 commands the cast ingot transfer means 68 to extend a movable piston to thereby push out the cast ingot 7 from the rear of the ingot toward the transporting conveyer 85. This operation is effective when the cooling plate 52 is flat. In another exemplary structure for the cast ingot transfer means 68, the cast ingot 7 is blown off by means of air blast from the rear of the cast ingot. In this case, the cast ingot 7 can be effectively blown off when the air blast is applied toward the boundary surface between the cast ingot 7 and the cooling plate 52. In still another exemplary structure, the cast ingot 7 is shoveled and scraped off by use of a movable rod having a claw. This approach is effective when the cast ingot 7 has a complicated configuration and the cooling plate 52 is partially recessed or projected. In yet another structure, a movable rod having a rotatable body is used. The rotatable body is brought into contact with the cast ingot 7 to thereby shovel the cast ingot 7 through friction drag arising between the rotatable body and the cast ingot 7. Alternatively, a sucker disk may be used to apply a suction force to the cast ingot 7 for transportation. Further alternatively, a nipper may be used to hold the cast ingot 7 for transportation. When the cooling plate 52 has a concave portion, as shown in FIG. 12(A), there may be employed two knockout pins 55 which penetrate the cooling plate 52. The knockout pins 55 push up the cast ingot 7 to thereby detach the cast ingot 7. Alternatively, as shown in FIG. 12(B), knockout pins 55 are loosely inserted in guide holes 521 formed through the cooling plate 52 and are moved upward or downward by means of flexible springs 56 inserted in generally L-shaped guides 57. The flexible springs 56 move upward or downward in accordance with the reciprocating motion of reciprocating means 58, thereby moving the knockout pins 55 upward or downward. Alternatively, two knockout pins 55 that extend from the cooling plate 52, as shown in FIG. 12(C), may be disposed below the cast ingot 7. Oil 59 filled in the generally L- shaped guides 57 is pressurized or depressurized by means of cylinder pistons 591 to thereby move the knockout pins 55 upward or downward. In the structure shown in FIG. 12(a), the knockout pins 55 penetrate the cooling plate 52. In contrast, in the structures shown in FIGs. 12(B) and 12(C), the knockout pins 55 do not penetrate the cooling plate 52, thereby surely preventing a cooling liquid sprayed from the spray nozzle 52a disposed below the cooling plate 52 from entering the mold chamber. The aforementioned structures can be effectively employed solely or in combination in one apparatus . The structure to be used is selected in accordance with the configuration of the cast ingot to be molded or the shape of the cooling plate. Next, measurement of the weight of the cast ingot 7 will be described with reference to FIG. 1. The automatic continuous casting system 1 of the present invention is constructed such that the cast ingot 7 formed in the mold chamber and conveyed by means of the transporting conveyer 85 is further conveyed to a transporting conveyer 86. To this transporting conveyer 86, cast ingots produced by other casting apparatus that are branched from a single melting furnace 2 are also transported in a sequential manner. The cast ingots 7 are cooled with water in a cooling bath 90. This cooling is performed in order to protect the below-mentioned all-product-weight judgment apparatus 88 from heat. The time for cooling by water in the cooling bath 90 is set in advance so that the temperature of the cast ingot 7 removed from the cooling bath 90 falls within a predetermined temperature range. Thus, the cast ingot 7 removed from the cooling bath 90 maintains proper high temperature, and the moisture remained on the cast ingot is evaporated due to the heat possessed by the cast ingot. As a result, the cast ingot is dried before it reaches the all-product-weight judgment apparatus 88. Therefore, undesirable situations, such as weighing of cast ingots together with accompanying water or possible corrosion of cast ingots due to the accompanying water, are avoided without fail. A cast ingot cooled in the cooling bath 90 is transported by means of a transporting conveyer 87 to the weight judgment apparatus 88, functioning also as a transporting conveyer, disposed downstream of the transporting conveyer 87. Thus, the weight judgment apparatus 88 can sequentially measure the weight of each of the transported cast ingots 7 precisely and promptly while conveying the same. The weight W as measured by the all-product-weight judgment apparatus 88 is output to the casting machine control unit 9 and compared with the target weight Wo as described above in order to judge whether or not the cast ingots 7 are good items. When a cast ingot 7 is judged by the casting machine control unit 9 to be a good item, i.e. as falling within an acceptable weight range around the target weight Wo, the cast ingot 7 is automatically transferred to a transporting conveyer 89 disposed downstream of the all- product-weight judgment apparatus 88, whereas when a cast ingot 7 is judged to be a non-good item, i.e. as falling outside the acceptable weight range around the target weight Wo, the casting machine control unit 9 commands a robot arm (not shown) to hold and remove the cast ingot 7 from the all- product-weight judgment apparatus 88. The removed cast ingot 7 is subjected to a procedure for removal of non-good items from the line. When a cast ingot is judged to be a non-good item, the casting apparatus that produced the cast ingot is identified by an identification numeral allotted to that ingot, and control of the opening/closing plug 43 for the casting apparatus 6 corresponding to the identification numeral is modified so as to yield an appropriate weight . FIG. 13 is a sketch of a line employing a sampling weight judgment apparatus. As shown in FIG. 13, cast ingots 7 produced by the casting apparatus 6 and transferred onto the transporting conveyer 85 are conveyed to a transporting conveyer 92. Similarly to the case in which the aforementioned all-product-weight judgment apparatus 88 is used, cast ingots produced by other casting apparatus that are branched from a single melting furnace 2 are also transported to this transporting conveyer 92 in a sequential manner. For example, when six casting apparatus are used, six cast ingots 71-76 are aligned in a sequential manner, and identification numerals 1-6 are allotted to the cast ingots 71-76, respectively. When a robot arm (not shown) holds a cast ingot 71 having an identification numeral 1 and transfers the cast ingot 71 to the sampling weight judgment apparatus 91, the sampling weight judgment apparatus 91 weighs the cast ingot 71 and outputs the as-measured weight W to the casting machine control unit 9. In this connection, since a heat insulation sheet is spread on a weighing table of the sampling weight judgment apparatus 91, the cooling process can be omitted, because cooling of the cast ingot to be weighed is not necessary. The casting machine control unit 9 judges, on the basis of the as-measured weight W, whether or not the cast ingot 71 is a good item. When the cast ingot 71 is judged to be a good item, the casting machine control unit 9 commands the robot arm to return the cast ingot 71 to the transporting conveyer 92, whereas when the cast ingot 71 is judged to be a non-good item, the casting machine control unit 9 commands start of the operation for removing the cast ingot 71 from the line. Subsequently, among the cast ingots transported on the transporting conveyer 92, the cast ingot 72 having identification numeral 2 is extracted and weighed. In this manner, the cast ingots are extracted and weighed in a sequential manner in accordance with the sequence of the line. When a cast ingot 7 is judged to be a non-good item, the casting machine control unit 9 identifies , by means of the identification numeral of the cast ingot 7, the casting apparatus that produced the cast ingot having a defect found to be attributed to the casting apparatus corresponding to identification numeral 1, for example, and control of the opening/closing plug 43 for that casting apparatus concerned is modified so as to yield an appropriate weight. When a produced cast ingot is weighed by use of the sampling weight judgment apparatus 91 in the aforementioned manner, the weight of the cast ingot can be regulated properly, and an identification numeral can be allotted to the cast ingot without fail, because the sampling weight judgment apparatus 91 weighs cast ingots on a measurement schedule of sufficiently long cycle. Therefore, the casting apparatus that produces a cast ingot having an unacceptable weight can be identified reliably and promptly. In the casting machine control unit 9, weight data from the all-product-weight judgment apparatus 88 and weight data from the sampling weight judgment apparatus 91 are stored in such a manner that respective weight data are related to the corresponding casting apparatus. On the basis of the stored data, when a statistically significant difference indicating that all data are shifted from the target weight is discovered, it is decided that a problem lies in the overall system, not in an individual casting apparatus. Thus, the casting machine control unit 9 notifies the operator that there is a problem in the overall system. Examples of such system-related problems may include wrong molds installed by an operator in all the casting apparatus, incorrect performance of emission spectrometric analysis of molten metal and considerable variation in components of molten metal. FIG. 14 is a schematic plan view of an exemplary structure in which both an all-product-weight judgment apparatus 88 and a sampling weight judgment apparatus 91 are used. When the all-product-weight judgment apparatus 88 is used, in some cases, the identification numeral cannot be allotted to all cast ingots 7. For example, because cast ingots from a plurality of casting apparatus are aligned on the transporting conveyer 86 so that the sequence of the cast ingot on the transporting conveyer 86 corresponds to that of the casting apparatus , and the sequence on the transporting conveyer 86 is recognized as representing the identification numerals, the production cycle (time from sending out of the cast ingot to sending out of the next cast ingot) varies from one casting apparatus to another casting apparatus . Therefore, the sequence on the transporting conveyer 86 may not correctly reflect the sequence of the casting apparatus. Moreover, the sequence of cast ingots may be disturbed when the cast ingots are in the cooling bath 90. In this case, even when a non-good item is found through the measurement by the all-product-weight judgment apparatus 88, identifying the casting apparatus that produced the non-good item is impossible. In order to cope with this problem, in the case shown in FIG. 14, both the all-product-weight judgment apparatus and the sampling weight judgment apparatus are employed. As shown in FIG. 14, six casting apparatus 6 are provided on each side of the transfer trough 3. There are twelve casting apparatus 6 in total. To either side of the transfer trough 3, a transporting conveyer 86 to be used for all-product weight measurement and a transporting conveyer 92 to be used for sampling weight measurement are disposed along the rows of casting apparatus 6. The aforementioned cooling bath 90 and the aforementioned all-product-weight judgment apparatus 88 are disposed downstream of the transporting conveyer 86, and the aforementioned sampling weight judgment apparatus 91 is disposed downstream of the transporting conveyer 92. Through the transfer trough 3, molten metal is supplied from the melting furnace 2 to the twelve respective casting apparatus 6. Cast ingots 7 produced in the respective casting apparatuses 6 are delivered therefrom onto the transporting conveyers 86, and are aligned in a sequential manner. On either of the adjacent transporting conveyers 92, cast ingots are aligned so as to correctly reflect the order of the casting apparatus, while taking into consideration the variation of the production cycle. In normal operation, the cast ingots aligned on the transporting conveyer 92 are conveyed to a location in front of the sampling weight judgment apparatus 91 and then transferred to the transporting conveyer 86 by means of a robot arm (not shown) , followed by measurement of the weight by means of the all- product-weight judgment apparatus. All the produced cast ingots are aligned on the transporting conveyer 86 irrespective of their sequence and then weighed one by one by means of the all-product-weight judgment apparatus 88. When a non-good item is found, the casting machine control unit 9 commands the sampling weight judgment apparatus 91 to start operation while maintaining the all-product-weight judgment apparatus 88 in operation. In response to the commands, the robot arm transfers the cast ingot on the transporting conveyer 92 to the sampling weight judgment apparatus 91, where the cast ingot is weighed. On the basis of the measurement result acquired by the sampling weight judgment apparatus 91, the casting machine control unit 9 identifies any casting apparatus in abnormal operation, and regulates the operation conditions (e.g. the time over which the sprue is held open) of the identified casting apparatus . Thus, all the cast ingots can be weighed without fail, and moreover, even when the identification number of a non- good item cannot be identifxed by the all-product-weight judgment apparatus, any casting apparatus that produces the non-good item can be promptly identifiable, making good use of the characteristics of the respective weight judgment apparatus. Moreover, operation cost can be reduced as compared with the case in which both the weight judgment apparatus are always in operation. The above description is drawn to the case in which cooled cast ingots are provided to the all-product-weight judgment apparatus 88 and cast ingots that have not been subjected to any cooling process are provided to the sampling weight judgment apparatus 91. However, whether or not cooled ingots are to be provided is determined in accordance with the nature of the two weight judgment apparatus. For example, ingots that have not been subjected to any cooling process may be provided to the all-product-weight judgment apparatus 88, and cooled ingots may be provided onto the sampling weight judgment apparatus 91. Next , how the automatic continuous casting system 1 of the present invention is connected to a forging line and a machining line will be described. As described above, the automatic continuous casting system 1 allows only good items selected by the weight judgment apparatus 88 and 91 to proceed to a forging apparatus disposed downstream of the automatic continuous casting system 1. If the forging apparatus is provided separately from the automatic continuous casting system 1, there arises the problem of intermediate stock of cast ingots. Moreover, in the case in which cast ingots are to be hot-forged, as described hereunder, they must be heated to a predetermined temperature before being subjected to forging. In such a case, if the forging apparatus is provided separately from the automatic continuous casting system 1, the temperature of the cast ingot drops . As a result , longer time is required for heating the cast ingot to a predetermined temperature, and energy is wasted. According to the present invention, as shown in FIG. 15, the final transporting conveyer 89 (shown in FIG. 1) of the automatic continuous casting system 1 is linked via connection means, such as transporting conveyers 94 and 96 and a robot (not shown), to a forging apparatus 93, a heat treatment furnace 95 disposed upstream of a machining process, and a machining apparatus 97 to thereby constitute an automatic continuous cast-forging system 100. A final-stage transporting conveyer 98 of the system 100 sends out machined products 99 as final products. The heat treatment furnace 95 is provided according to the needs from the machining process. When stocks to be worked with the forging apparatus 93 have a shape having upper and lower surfaces different in diameter, such as a truncated cone shape, and are transported to a mold of the forging apparatus 93 using a chuck, with their orientations made non-uniform, the positions of the stocks to be fixed are not uniform. This makes the positions of the stocks to be supplied to the mold instable, resulting in a reduction in precision of the worked products . Furthermore, when stocks having upper and lower surfaces different in physical properties that affect their workability are supplied to the mold, with their orientations made non-uniform, working of the stocks gives rise to deformed and damaged products due to different working conditions of their upper and lower surfaces. In order to transport stocks 71 to the forging apparatus 93, with their orientations made uniform, an alignment apparatus as shown in FIG. 16 is disposed between the transporting conveyer 89 and the forging apparatus 93. The alignment apparatus comprises a runway section 11, a discrimination section 12 and an alignment section 13. In the illustrated embodiment, the runway section 11 and discrimination section 12 are integral and aslant downstream. The runway section 11 is provided for accelerating advance of the stocks 71 to reduce or eliminate vibration in any direction other than the advancing direction. The discrimination section 12 is provided for discriminating the upper and lower surfaces 71a and 71b of the stocks 71 and supplying the stocks 71 with their upper surfaces 71a directed leftward to the left side of the alignment section 13 and the stocks 71 with their upper surfaces 71a directed rightward to the right side of the alignment section 13. The alignment section 13 is provided for directing upward the upper surfaces 71a of the stocks 71 put in two and aligning, at the right and left sides, the stocks 71 symmetrical with each other with respect to the center line of the alignment apparatus, with their upper surfaces 71a directed upward. When a stock 71 of truncated cone shape is supplied to the runway section 11 with a belt conveyer, chute, parts feeder or other such supplying apparatus, the stock 71 rolls on the bottom wall of the runway section 11, with its small- diameter upper surface 71a in contact with one of the sidewalls 11a and lib of the runway section 11, because the runway section 11 is aslant downstream and the side surface of the stock 71 is inclined, and is directed to the discrimination section 12. The discrimination section 12 comprises a bottom wall 12σ on which the stock 71 rolls and a pair of opposed sidewalls 12a and 12b with the space therebetween spread continuously. The sidewalls have a radius of curvature set larger than the rolling radius of a virtual cone of the shape of the stock 71 and are spread outward toward downstream. Therefore, the stock 71 is rolling on the discrimination section 12, with its one surface leaning on one of the sidewalls 12a and 12b, toward the alignment section 13. The alignment section 13 comprises a bottom wall having a bulged portion 14 at the center, and a pair of sidewalls 13a and 13b having overhanging portions on their downstream sides. In the alignment section 13, the stock 71 gradually changes its posture from the state leaning on one of the sidewalls to the upright state as it advances downstream. The overhanging portion of the sidewall 13a pushes the stock 71 onto the bulged portion 14, with the small-diameter upper surface 71a directed upward. The stocks 71 in this state while sliding are successively discharged from the alignment apparatus . Thus, the alignment apparatus can align the orientations of the stocks of truncated cone shape infallibly when the upper surfaces of the stocks are to be directed upward in discharging the stocks using a belt conveyer, parts feeder, etc. When the upper surfaces of the stocks of truncated cone shape are to be directed downward, the discrimination section 12 is extended, with the alignment section 13 omitted. This infallibly enables the stocks to be slid on the bottom wall of the extended discrimination section in the state of their respective upper surfaces leaning on one of the sidewalls thereof and discharged from the section. Furthermore, when the stocks are to be introduced into the forging apparatus 93 not horizontally but vertically, all the stocks are once aligned unidirectionally and introduced continuously into an apparatus for vertically aligning the stocks . This infallibly enables the stocks to be aligned unidirectionally. When a hot-forging apparatus is used as the forging apparatus 93 in the automatic continuous cast-forging system 100, a preliminary heating furnace is disposed upstream of the forging apparatus 93 so as to heat cast ingots to a temperature falling within a predetermined range before the cast ingots are transported to the forging apparatus 93. In this manner, temperature variation of cooled cast ingots can be overcome, and temperature drop resulting from system shutdown due to a problem of the casting apparatus or a forging apparatus can be compensated for, leading to reliable hot forging. Moreover, since the casting apparatus 6, the preliminary heating furnace and the hot forging apparatus are disposed successively, cast ingots can be transported to the preliminary heating furnace before they are unnecessarily cooled, leading to a shortened heating time in the preliminary heating furnace and avoiding waste of energy. Since an integrated continuous line from casting to machining is constructed as described above, final products can be obtained from the line without the raw material being taken out from the line before completion of the production process. Thus, the production facility realizes extremely high productivity, maintenance of product quality and significant cost reduction. Exemplary embodiments from the melting furnace (molten metal supply source) 2 through the transfer trough (transfer means) 3 to the casting apparatus 6 in the automatic continuous casting system 1 have been described with reference to FIGs. 1 and 14. The following layouts may also be employed. In the exemplary embodiment shown in FIG. 17, a plurality of casting apparatus 6 are disposed radially around the melting furnace 2, which is connected to each casting apparatus 6 through transfer troughs 3. In this case, each transfer trough 3 includes an opening/closing valve through which molten metal from the melting furnace 2 is poured. Alternatively, a fibrous cone that will be described hereunder may be employed. In the exemplary embodiment shown in FIG. 18, a plurality of casting apparatus 6 are disposed along a longer side of a melting furnace 2 having a rectangular cross section, wherein each casting apparatus 6 is connected to the melting furnace through the corresponding transfer trough 3. In a manner similar to that described above with reference to FIG. 1, molten metal in the melting furnace 2 is supplied through tilting of the melting furnace 2. Alternatively, an opening/closing valve through which molten metal is poured may be provided. Otherwise, a fibrous cone that will be described hereunder may be employed. In the exemplary embodiment shown in FIG. 19, molten metal in the melting furnace 2 is stored in a retention furnace 2a that serves as a temporary buffer, and molten metal is supplied from the retention furnace 2a, which serves as a source of molten metal, to the casting apparatus 6 via the transfer trough 3. Immediately after the entire molten metal contained in the melting furnace 2 is poured into the retention furnace 2a, the next lot of molten metal can be prepared, leading to enhanced operation efficiency of the facility. In the exemplary embodiment shown in FIG. 20, the melting furnace 2 is disposed separately from a nearby bath 3a which serves as a transfer means, between which is provided a robot R adapted to scoop the molten metal in the melting furnace 2 and to pour the molten metal into the nearby bath 3a. Therefore, means for tilting the melting furnace 2 is not required, realizing a relatively simple structure. In this exemplary embodiment, the liquid level in the nearby bath 3a is regulated through regulation of the cycle of the molten metal supply operations of the robot R. In the exemplary structure shown in FIG. 21, the transfer trough 3 is connected to an upper section of the melting furnace 2 in which a cone 29 made of ceramic fibers moves upward or downward. When the cone 29 is moved downward in the melting furnace 2, the molten metal overflows to thereby flow into the casting apparatus 6 via the transfer trough 3. In this case, the liquid level in the transfer trough 3 can be regulated through regulation of the depth of the immersed portion of the cone 29. In th Ω present invention, the automatic continuous casting system may be combined, not only with a forging system, but also with a plastic working system such as a rolling process, or with a machining process such as drilling, lathing or milling, to thereby form an automatic continuous production system. Conventionally, the difference in system structure has involved generation of intermediate stock and required manpower for handling, such as transporting of intermediate products . A continuous automatic production system in which a plurality of systems are combined eliminates intermediate stock and manpower for handling such as transporting, leading to reduction of production cost and remarkably shortened lead time up to shipping. An exemplary embodiment of the metal-casting process and apparatus usable in the automatic continuous casting system will be described with reference to FIG. 22. JP-A Hex 8-155627 cited herein above as prior art discloses the following methods for the forced cooling of a cooling member. (1) Jetting, in the form of spray or shower, a cooling medium onto the lower surface of the cooling member (to effect collision) . (2) Passing cooling water through cooling water piping provided in the cooling member. (3) Installing a cooling water tank at a lower section of the cooling member for passing water therethrough. Any of these methods attains virtually uniform cooling of a cooling member. Also, cast ingots to be produced are of simple disk shape, and this prior art does not contain any specific disclosure for the case of cast ingots of three- dimensionally complicated shape. As a result of continued energetic research, the present inventors have found that in accordance with the shape of a cast ingot, the location and number of sprue(s), etc., local control of heat removal can be attained by augmenting or reducing the cooling capacity of the mold members including a cooling member or through intentional heating, whereby the molten metal is solidified in such a manner that the solidification interface advances to arrive at an end surface of the mold, eliminates the risk of forming a closed loop of solidification front surface inside the mold and enables provision of a cast ingot having a healthy interior metallographic structure. Methods for forced cooling of mold members including a cooling member are basically divided into two types , one of which is a combination of the aforementioned methods (1) and (3) in which a cooling medium is brought into contact with the outer surface of the mold members including a cooling member to thereby cool the cooling member and the other of which is the aforementioned method (2) in which a cooling medium is passed through the piping provided in mold members including a cooling member. Either method, when combined with one of the following modes, establishes a cooling capacity control mechanism. Although the following description mainly focuses on a cooling member, heat removal from not only the cooling member, but also from mold members including the cooling member, is locally controlled by the present invention. Mode (I) in which cooling is performed by contacting a cooling medium with the outer surface of a cooling member. Specifically, there are two types of methods, one of which is a method wherein a cooling medium jetted in spray or shower form hits against the outer surface of a cooling member and the other of which is a method wherein a cooling bath into which a cooling medium is supplied is provided outside a cooling member. However, since local control of heat removal is difficult to attain when these methods (i.e., forced cooling methods) are used alone, one or more of the following modes "a" to "f" are combined with one of these two methods to thereby establish a cooling capacity control mechanism that locally controls heat removal. In the accompanying drawings, only apparatus applicable for top teeming (i.e. , molten metal is poured from above the apparatus) are shown. However, the pouring direction of molten metal is not limited thereto, and bottom teeming may also be employed. Mode (a) that employs a cooling member in which the wall thickness of a certain portion is different from that of other portions . The molten metal present at the location directly below the sprue is a lastly teemed portion, and accordingly, this portion of molten metal will be cooled and solidified last. Therefore, the corresponding portion of a cast ingot directly below the sprue is prone to microshrinkage, or cracks caused by solidification stress due to temperature difference in the cast ingot. In order to cope with this problem, the cooling member is partially thickened or thinned, and a cooling medium is brought into contact with the outer surface of the cooling member to thereby provide an appropriate profile of heat removal in accordance with the shape of a cast ingot and the location and number of the sprue(s). Thus, formation of a local depression at the solidification interface can be prevented. Specifically, when the cast ingot to be produced has a simple disk shape, for example, a portion of the cooling member which corresponds to the central portion of the ingot that is the region where solidification of molten metal delays, is thinned to thereby enhance the cooling capacity, and a portion of the cooling member which corresponds to a peripheral portion of the cast ingot that is the region where solidification of molten metal proceeds quickly, is thickened to thereby lower the cooling capacity. Moreover, in connection with the mechanism for supplying the cooling medium, the amount of the cooling medxum to be jetted and the timings to initiate and terminate the cooling process may be determined in accordance with the shape of the cast ingot. For example, cooling may be started either after ultimate completion (the filled-up state) of teeming of molten metal, or before completion. FIG. 22 is a cross-sectional view showing an exemplary apparatus of the present invention and depicting a cooling capacity control mechanism of mode (a). In the embodiment shown in FIG. 22, a mold 5 (an upper mold 5a and a side mold 5b) is disposed on a cooling member 52. A reservoir 4 for receiving molten metal 45 from a melting furnace (not shown) or a similar apparatus is provided in the upper section of the mold 5 and heated by means of an electric furnace (not shown) so as to maintain the molten metal at a predetermined temperature. The reservoir 4 is in communication with the interior space of the mold 5 via a sprue 42. Reference numerals 46a, 46b and 46c in FIG. 22 respectively represent solidified molten metal, solidification interface and unsolidified molten metal. The sprue 42 is equipped with an opening/closing plug 43. The molten metal 45 is teemed into the mold 5 by operating a plug elevating means (not shown) to elevate the opening/closing plug 43. When the mold 5 is completely filled up with molten metal 46 without leaving any space therein, the plug 43 is lowered to thereby block the molten metal 45 to be teemed. The thickness of the cooling member 52 is smaller at the center portion, in which solidification of molten metal 46 delays, and the thickness gradually increases toward the periphery, where solidification rate of molten metal 46 is high. A spray nozzle 54 disposed below the center of the cooling member 52 jets a cooling medium, such as water, supercooled water of 0°C or lower (e.g., that containing 0.5% or more sodium chloride or that containing a substance, such as ethylene glycol), a volatile liquid, such as ethyl alcohol, or an oil so that the cooling medium hits (or contacts) the lower surface of the cooling member 52 to thereby cool the cooling member 52. Structures other than the above-described one may be appropriately selected and determined in accordance with needs as described, for example, in the aforementioned JP-A Hei 8-155627. For example, when molten metal 45 (cast ingot) is Al, Mg, Zn or an alloy thereof, the cooling member 52 is preferably made of Cu, Al or any other metallic material endowed with excellent refractory property and mechanical strength. However, when molten metal 45 (cast ingot) is Fe, Cu or an alloy thereof, the cooling member 52 is preferably made of a ceramic material endowed with excellent refractory property, such as graphite, SiC, Si 3 N or BN-containing Si 3 N 4 . Examples of the material that constitutes the mold 5 include a heat-insulating refractory material composed predominantly of an ordinary refractory material, CaO, Si0 2 , A1 2 0 3 or MgO; a single substance or a refractory mixture of SiC, Si 3 N , black lead, BN, Ti0 2 , Zr0 2 or A1N; and metals, such as Fe and Cu. Of these materials, the material to be employed may be selected in general consideration of the metal or alloy to be subjected to casting, temperature in use, wettability with molten metal, corrosion resistance, etc. In order to supply the molten metal throughout the interior space of the mold without leaving any space, the molten metal 46 in the mold is preferably pressurized. In the apparatus shown in FIG. 22, pressurization is effected by the riser effect of the molten metal 45 in the reservoir 4. In this connection, the top surface of the molten metal 45 in the reservoir 4 is preferably 30 mm or more above the top surface of the molten metal 46 that fills the mold 5. When such a height difference is provided, oxides floating on the molten metal 45 in the reservoir 3 are prevented from entering the mold 5. Cooling of the molten metal 46 must be attained mainly by means of the cooling member 52, and cooling effected through sidewalls, etc. should be prevented. This allows the molten metal 46 to be solidified unidirectionally from the bottom toward above. Upon pouring the molten metal into the mold 5, the cooling member 52 preferably assumes a temperature of at least 100°C. When teeming is performed at a lower temperature, disadvantageously, the phenomenon called "blow," a type of defect typically found in metal mold casting, is caused. From the viewpoints of cooling efficiency and product quality, the upper limit would be approximately the temperature of molten metal. In order to prevent generation of blow, a mold release agent , which is widely used for the application to the cooling member 52, is also effective. Mode (b) in which an interior space is provided in a portion of a cooling member. In the above-described mode (a), the cooling member is partially thickened or thinned. Alternatively, when an interior space is provided in a part of the cooling member, thermal conductivity in the thickness direction can be varied even in the case in which the outer thickness of the cooling member is uniform, whereby a cooling capacity control similar to that mentioned above can be attained. Moreover, since the interior space prevents heat from flowing from molten metal to the outer surface of the cooling member, well-balanced cooling capacity can be attained throughout the cooling member, contributing to formation of a solidification interface of desired shape. Although the interior space is essentially a closed space, it may be an open space unless it allows a cooling medium to enter therein deeply. Since the thermal conductivity of the interior space region is lower than that of the cooling member, which is generally formed of a material of high thermal conductivity, there can be attained a cooling capacity control similar to that through mode (a), in which the cooling member is partially thickened or thinned. Moreover, the interior space prevents heat from flowing from the molten metal to the outer surface of the cooling member. An example of mode (b) is shown in FIG. 29, and a detailed description thereof will be given herein later. Mode (c) in which the cooling member is made of a composite materxal of different thermal conductivities . In the above-described mode (a), the cooling member is partially thickened or thinned. Alternatively, when a material segment having a thermal conductivity different from that of the remaining portion of the cooling member is integrally formed within the cooling member (FIG. 30(A)), or when a material segment having a thermal conductivity different from that of the remaining portion of the cooling member is integrally inserted into a portion of the outer surface of the cooling member (FIG. 30(B)), even when the outer thickness of the cooling member is uniform, the heat capacity in the thickness direction can be varied, attaining a function similar to the aforementioned one. Moreover, since the material segment having a different thermal conductivity prevents heat from flowing from the molten metal to the outer surface of the cooling member, well-balanced cooling capacity can be attained throughout the cooling member, contributing to formation of a solidification interface of desired shape. In this case, the cooling member preferably comprises a metallic material and a refractory heat-insulating material, which serves as the material segment having a different thermal conductivity and is integrally formed inside or outside of the part made of metallic material. Examples of suitable metallic materials include aluminum, copper, iron and an alloy thereof having a high thermal conductivity. Examples of suitable refractory heat-insulating materials incorporated into the inside of the part include a material in the form of plate, blanket or sheet made of alumina fiber or fused silica fiber, or a single substance of Si 3 N 4 , SiC, BN or graphite, or a mixture thereof. Examples of suitable refractory heat-insulating materials inserted from the outside of the part made of metallic material include a single substance of Si 3 N , SiC, BN or graphite, or a mixture thereof . An example of mode (c) is shown in FIG. 30(A) or FIG. 30(B), and a detailed description thereof will be given herein later. Mode (d) in which the outer surface of the cooling member is partially provided with an uneven surface so that the area that can contact a cooling medium locally varies . When a cast ingot to be produced does not have a simple disk shape but rather has, as viewed three-dimensionally, a non-uniform profile along the X-Y axis or, in addition thereto, also a non-uniform shape along the Z axis, cooling capacities of a cooling member and a mold member must be controlled in order to prevent formation of cracks in the resultant cast ingot , which are caused by the solidification interface being depressed locally and to prevent formation of internal defects including blowhole defect and microshrinkage, which are generated when the solidification interface forms a closed surface within a cast ingot . When a cooling member is excessively thin, rigidity of the cooling member lowers . Thus , heat cycle imposed upon each casting process distorts the cooling member, resulting in deformation thereof and production of cast ingots having an undesired shape. Furthermore, thermal shock or deterioration of the material of the cooling member produces cracks in the cooling member through which cooling water leaks , leading to disturbed operation of the apparatus . Thus , in order to continue the casting process for a long period in a stable manner, the cooling capacity and the rigidity of the cooling member must be enhanced. To this end, the cooling member is thickened so as to enhance the rigidity, and in addition, unevenness is provided on the outer surface of the cooling member, and a cooling medium is supplied to the outer surface of the cooling member, whereby the contact area between the unevenness-imparted portion and the cooling medium (hereinafter referred to as "cooling-medium-contact-area") is enhanced, leading to attainment of enhanced cooling capacity. The configuration of the unevenness is not particularly limited, and for example, a hole that does not reach the interior surface (blind hole) or a fin-like shape may be employed. Usually, the cooling medium is jetted radially from a spraying means such as a cooling spray. Thus, even when such unevenness is uniformly provided, the cooling-medium-contact- area of the uneven portion directly above the nozzle of the cooling spray is different from that of other uneven portions . The shape of the uneven portion (or dents) is determined so as to maintain the rigidity of the cooling member and to attain the desired cooling capacity. Preferably, a distance of at least 1 mm is left below the internal surface of the cooling member. If engraving is performed farther, rigidity of portions in the vicinity of dents cannot be secured, inviting the risk of generating cracks in the cooling member. Generally speaking, the cooling capacity of deeply engraved dents is higher than that of shallow dents due to a larger cooling-medium-contact-area. Therefore, deep dents may be formed in a portion where high cooling capacity is desired, and shallow dents may be formed in a portion where low cooling capacity is desired. The pitch of the dented portion (density of the formed dents) is determined in accordance with the shape of the cast ingot, and the pitch is not necessarily invariable. Depending on the case, the pitch may be long or short, and some portion may have no dents. On the other hand, when dents are formed at a certain unvaried pitch (uniform density of dents), cooling capacity can be controlled through regulating the diameter and/or depth of the dents . Thus , for example, portions for which high cooling capacity is desired may be provided with dents of narrow pitch (high density of dents), whereas other portions for which low cooling capacity is desired may be provided with dents of wide pitch (low density of dents). In particular, when holes are provided as the dents, the diameter of the holes is preferably 3 mm or more for the following reasons . When cooling water in the form of spray or shower is jetted toward the holes each having a diameter of less than 3 mm, cooling water entering the holes is vaporized under heat, and the steam prevents jetted cooling water from entering the holes, lowering the cooling effect as compared to the case in which no hole is provided. The maximum diameter is determined in accordance with the size of the cast ingot and the cooling capacity profile to be attained. However, holes of any size may be formed so long as the rigidity of the cooling member is secured. Generally, large holes, realizing a large cooling-medium-contact-area. provide higher cooling capacity as compared with small holes . Thus, large holes may be provided at a site where high cooling capacity is desired, and small holes may be provided at a site where low cooling capacity is desired. When the angle of the hole axis ("α"; hereinafter referred to as "inclination angle") coincides with the collision angle (β) at which the cooling water jetted in the form of spray or shower hits the cooling member, the maximum cooling capacity is attained. In other words, when high cooling capacity is desired, the relation of α = β ± 10° is preferably satisfied. When α and β do not satisfy this relation, the cooling capacity may decrease. FIG. 23 is a cross-sectional view showing an exemplary apparatus of the present invention and depicting a cooling capacity control mechanism of mode (d) . Elements identical to those shown in FIG. 22 are denoted by the same reference numerals . In this embodiment, molten metal is teemed through a single sprue 42 disposed at an approximately central portion to thereby produce a cast ingot having an almost uniform thickness. In this embodiment, a plurality of blind holes 55a which serve as the uneven portion are formed at almost the same intervals in the outer surface of a cooling member 52 having an almost uniform thickness, and a spray nozzle 54 for jetting a cooling medium is disposed beneath the approximately central portion of the cooling member 52. As described above, the holes 55a disposed directly above the spray nozzle 54, which are disposed at an approximately central position, have a larger cooling-medium- contact-area than the holes 55a in peripheral portion. Thus, the holes 55a disposed directly above the spray nozzle 54 provide higher cooling capacity. Therefore, in the cooling member 52, cooling capacity is high in the central portion and low in the peripheral portion. In this connection, as shown in FIG. 24 for example, when the holes 55a are formed in such a manner that the inclination angle of each of the holes is identical with its corresponding collision angle β of the cooling medium, the maximum cooling capacity can be obtained. The aforementioned controlling methods can be performed independently one another and may be appropriately combined in accordance with needs. For example, the aforementioned modes (a) and (d) are combined to thereby use a cooling member in which the thickness varies from portion to portion, and the outer surface thereof is partially provided with unevenness by means of holes, fins, etc. FIG. 25 shows an embodiment in which molten metal is teemed through a sprue 42 disposed at an approximately central position and the cast ingot has a thick wall in the central to right portion (as viewed in the drawing) and a thin wall in the left portion (in the drawing). The cooling member 52 of the present embodiment is designed such that the central to right portions which correspond to the thicker portion of the cast ingot and in which the solidification rate of molten metal 46 is slow, are formed to have a thin wall so as to lessen the heat capacity, and the thus-formed thin wall is provided with unevenness through formation of a plurality of holes 55a so as to increase the area that can contact a coolxng medium jetted from a cooling spray 54 disposed below an approximately central portion of the cooling member 52 to thereby enhance the cooling capacity of the central to right portions. In particular, the holes 55a are formed in such a manner that the inclination angles of the holes 55a coincide with corresponding collision angles of the cooling medium. In addition, the left portion of the cooling member 52 which corresponds to the thinner portion of the cast ingot and in which molten metal solidifies faster, is thickened, and no hole 55a is formed in the left portion to thereby lower the cooling capacity of the left portion. Mode (e) in which a cooling medium jetted in the form of spray or shower from a plurality of nozzles hits the outer surface of a cooling member. FIG. 26(C) shows an exemplary apparatus according to mode (e) in which molten metal is teemed through two sprues 42 provided on the right and left sides to thereby produce a connecting rod member having a more complicated three- dimensional shape as shown in FIGs. 26(A) and 26(B). In casting of such a product, a significant amount of molten metal 46 is accumulated in hemispheres directly below the two sprues 42, and the molten metal in the hemispheres has high heat capacity. Thus, the portion of the cast ingot directly below the two sprues 42 tends to generate cracks because local depressions corresponding to the positions of the two sprues 42 are produced in the solidification interface directly below the sprues 42. On the other hand, the space within the arm portion connecting the hemispheres is narrow and can contain less molten metal. In order to cope with this problem, the cooling member 52 of the present embodiment has been designed such that specific portions of the cast ingot directly below the two hemispheres, in which the molten metal 46 solidifies slower, is thinned, and the thinned portion is provided with unevenness through formation of a plurality of holes 55a, toward which a cooling medium is jetted from two spray nozzles 54 disposed at locations corresponding to the locations of the hemispheres to thereby enhance the cooling capacity of the portions directly below the two hemispheres. Moreover, the portion of the cooling member directly below the arm portion of the cast ingot, in which the molten metal 46 solidifies faster, is thickened, and the thickened portion is provided with no unevenness (no hole 55a) to thereby lower the cooling capacity of the portion directly below the arm portion. Notably, the connecting rod member produced by use of the present apparatus is drilled at points corresponding to the locations of the sprues 42 on the right and left sides as shown in FIG. 26(A). The present embodiment has been described as an example of mode (e) . However, the present embodiment also satisfies mode (a) since the thickness of the cooling member 52 is locally varied and also satisfies mode (d) since unevenness (holes 55a) is provided. The same applies throughout the following embodiments, and even when any combination of the aforementioned modes is used, no particular mention may be given . FIGs. 27(A) and 28(A) are views showing other exemplary apparatus for casting connecting rod members having a shape identical to that shown in FIG. 26(A). In both embodiments, molten metal is teemed through one sprue 42. In the apparatus shown in FIG. 27(A), molten metal is teemed through one sprue 42 disposed at an approximately central position. A cooling member 52 is formed in such a manner that the portion directly below the arm portion, in which solidification of the molten metal 46 delays, is thinned and that the thinned portion is provided with unevenness through formation of a plurality of holes 55a, toward which a cooling medium is jetted from a single spray nozzle 54 disposed at an approximately central position, to thereby enhance the cooling capacity of the portion directly below the arm portion. Moreover, the portions of the cooling member 52 directly below the right and left hemispheres are thickened outwardly, and the thickened portion is provided with no unevenness (no hole 55a) to thereby lower the cooling capacity of the portions directly below the hemispheres . In this connection, the connecting rod member cast by use of the present apparatus is drilled at an approximately central portion corresponding to the location of the sprue 42 as shown in FIG. 27(B). In the apparatus shown in FIG. 28(A), molten metal is teemed through one sprue 42 disposed on the left side. A cooling member 52 is formed in such a manner that the portion directly below the left hemisphere, in which solidification of molten metal 46 delays, is thinned and that the thinned portion is provided with a plurality of holes 55a serving as the uneven portion. A cooling medium is jetted from a single spray nozzle 54 disposed on the left side to thereby enhance the cooling capacity of the portion directly below the left hemisphere. Moreover, the portion directly below the central arm portion and the right hemisphere is thickened outwardly, and the thickened portion is provided with no uneven portion (no hole 55a) to thereby lower the cooling capacity of the portion directly below the central arm portion and the right- side hemisphere. The portion directly below the arm portion, through which molten metal is introduced into the right-side hemisphere, is particularly thickened. In this connection, the connecting rod member cast by use of the present apparatus is drilled at a single point on the left side corresponding to the location of the sprue 42 as shown in FIG. 28(B) . As described above, when the number and the location of sprue(s) are varied for cast ingots of the same shape, the cooling capacity control mechanism is modified accordingly, and cooling capacity can be appropriately controlled and adjusted. Thus, the critical point is to carry out solidification so that the solidification interface advances to reach an inner end of the mold to thereby produce a cast ingot having no cut surface or riser portion. Mode (f) in which unevenness is provided through formation of blind holes in such a manner that inclination angles differ from corresponding collision angles of a cooling medium jetted in the form of spray or shower and supplied to the outer surface of the cooling member. Holes are formed in a portion of the outer surface of a cooling member in such a manner that inclination angles of the holes differ from corresponding collision angles of a cooling medium in the form of spray or shower so as to prevent direct entering of the cooling medium into the holes . In this manner, the cooling capacity of the aforementioned portion is lowered, and well-balanced cooling capacity can be attained throughout the cooling member, contributing to formation of a solidification interface of desired shape. The relationship between the inclination angle of the hole and the collision angle β of the cooling medium is preferably α > β ± slO°. When the cooling medium does not enter the holes , the holes are cooled mainly through air-cooling, resulting in lower cooling capacity as compared with the case in which no hole is formed. For example, in the aforementioned embodiment shown in FIG. 23, holes in both the central and peripheral portions of the cooling member 52 are vertically formed and have almost the same depth. However, the cooling medium can enter deeply in the holes in the central portion because the inclination angle α virtually coincides with the collision angle β of the cooling medium, leading to large cooling-medium-contact-area, which enhances the cooling capacity of the central portion, whereas the cooling medium is prevented from penetrating deeply in the holes in the peripheral portion because the inclination angle significantly differs from the collision angle β of the cooling medium, resulting in lowered cooling capacity at the peripheral portion. Mode (g) in which a portion of the outer surface of a cooling member is provided with means for preventing the cooling member from contacting a cooling medium. As described above, forced cooling of a cooling member is performed through a method in which a cooling medium is supplied to the outer surface of the cooling member. In combination with this method, a portion of the outer surface of the cooling member provided with a step or a restriction plate for restricting the spray direction of the cooling medium is installed to thereby prevent the cooling medium from contacting the portion of the cooling member. Thus, since the cooling capacity resulting from the heat of vaporization of the cooling medium decreases (masking effect), well-balanced cooling capacity can be attained throughout the cooling member, contributing to formation of a solidification interface of desired shape. FIGs. 29, 30(A) and 30(B) are cross-sectional views showing exemplary apparatus of the present invention and depicting the cooling capacity control mechanisms of modes (f) and (g). Elements identical to those shown in FIG. 22 are denoted by the same reference numerals. Although the cast ingots schematically shown in FIGs . 29, 30(A) and 30(B) may look similar to the cast ingot shown in FIG. 22, in the present embodiments, molten metal is teemed through a sprue 42 disposed at an approximately central position, and the cast ingots are of a disk shape and have an almost uniform thickness which is extremely smaller than the outer diameter. In such a casting process, in which the thickness of the cast ingot is extremely smaller than the outer diameter. an ideal unidirectional solidification state cannot be maintained because the time requires for solidification of the center portion is different from that required for solidification of the peripheral portion that is the remotest portion from the sprue 42. Thus, the center portion of the cast ingot easily generates cracks . In order to cope with this problem, in the present embodiment, blind holes 55a serving as unevenness are formed in a central outer surface of a cooling member 52 in such a manner that the inclination angles coincide with corresponding collision angles of a cooling medium to thereby considerably enhance the cooling capacity. On the other hand, interior spaces 55b (in FIG. 30(A) or FIG. 30(B), material sections 55d having a different thermal conductivity) are provided in the peripheral portion in such a manner that the interior space 55b expands toward the periphery. Moreover, a spray nozzle 54 is provided with a restriction plate 54a for restricting the spray direction of a cooling medium so as to prevent the cooling medium from contacting the outer surface of the interior spaces 55b (the material sections 55d) . Moreover, a step 55c is provided in an intermediate portion of the slope surrounding the central portion so as to prevent the cooling medium from running down along the slope to thereby considerably lower the cooling capacity. Mode (h) in which a portion of the outer surface of a cooling member is covered with a heat-insulating material. As described above, forced cooling of a cooling member is performed through a method in which a cooling medium is supplied to the outer surface of the cooling member. In combination with this method, a portion of the outer surface of the cooling member is covered with a heat-insulating material so as to prevent the portion from contacting the cooling medium to thereby lower the cooling capacity attained through evaporation heat of the cooling medium (masking effect), and to prevent heat from radiating from the outer surface of the cooling member (insulation effect). Thus, well-balanced cooling can be attained throughout the cooling member, contributing to formation of a solidification interface of desired shape. Examples of the heat-insulating material include rubber, ceramic material and heat-insulating material made of fire retardant fibers or non-combustible fibers. FIG. 31 is a cross-sectional view showing an exemplary apparatus of the present invention and depicting a cooling capacity control mechanism of mode (h) . Elements identical to those shown in FIG. 22 are denoted by the same reference numerals . In the present embodiment, molten metal is teemed through a sprue 42 disposed on the left side to thereby produce a cast ingot in which the left and center portions (as viewed in the drawing) are thicker and the right portion (as viewed in the drawing) is thinner. In such a casting process, the left and center portions of the cast ingot tend to generate cracks for the following reasons. The thick, left and center portions of the cast ingot have large heat capacity, and solidification of molten metal 46 in the left and center portions delays because the sprue 42 is provided on the left side. In order to cope with this problem, a cooling member 52 of the present embodiment is designed in the following manner. A plurality of holes 55a, which serve as unevenness, are formed in the left and center portions, toward which a cooling medium is jetted from a cooling spray 54 disposed below the holes 55a to thereby enhance the cooling capacity of the left and center portions. A heater 56 is incorporated into the right portion, and the outer surface of the right portion is covered with a heat-insulating material 55e so as to prevent the cooling medium from contacting the outer surface to thereby lower the cooling capacity of the right portion. Mode (II) in which a circulation passage for a cooling medium is incorporated into a portion of a cooling member. In mode ( I ) , wherein the outer surface of the cooling member is cooled through contact with a cooling medium, at least one of modes (a) to (h) must be employed in combination therewith. In contrast, the present method can attain local cooling of the cooling member without employing such a mode in combination. Needless to say, the aforementioned mode may be used in combination in accordance with the shape of the cast ingot . The diameter, location, shape and depth from the upper surface of a circulation passage for the cooling medium are determined in accordance with the required cooling capacity. The flow rate and timings to initiate or terminate cooling are determined in accordance with the shape of the cast ingot . Examples of the cooling medium include, similarly to the cooling medium supplied to the outer surface of a cooling member as in the aforementioned mode, water, supercooled water of 0°C or lower (e.g., that containing 0.5% or more sodium chloride or that containing a substance, such as ethylene glycol) and an oil. FIG. 32 is a cross-sectional view showing an exemplary apparatus of the present invention and depicting a cooling capacity control mechanism of mode (II). Elements identical to those shown in FIG. 22 are denoted by the same reference numerals . In the present embodiment, molten metal is teemed through a sprue 42 disposed on the left side to thereby produce a cast ingot in which the right and center portions (in the drawing) are thicker, and the left portion (in the drawing) is thinner. In such a casting process, the thick right portion of the cast ingot is high in heat capacity, whereas the thin left portion is disposed directly below the sprue 42. Thus, each portion involves a factor that can cause crack formation. In order to cope with this problem, the cooling member 52 of the present embodiment is designed such that a plurality of holes 55a, which serve as unevenness, are formed in the right-side portion, toward which a cooling medium is jetted from a single spray nozzle 54 disposed below the holes 55a, and a circulation passage 57 through which a cooling medium flows is incorporated into the left portion to thereby regulate the cooling capacity of the respective portions through controlling their corresponding forced cooling mechanisms appropriately. Mode (III) in which a temperature-controlled cooling medium is brought into contact with a cooling member. As described above, the cooling medium is selected from water, supercooled water of 0°C or lower, a volatile liquid and an oil, each of which can be used singly or in combination. Needless to say, the cooling capacity of water at room temperature is different from supercooled water of 0°C or lower. In other words, the cooling capacity can be controlled through controlling the temperature of the cooling medium. An exemplary method for attaining this purpose will be described with reference to the embodiment shown in FIG. 26, wherein the cooling medium jetted through the spray nozzles 54 on the right side and that jetted through the spray nozzles 54 on the left side are controlled to have different temperatures from each other. In this case, for example, room-temperature water is jetted from the right side, and supercooled water of 0°C or lower is jetted from the left side to thereby control the cooling capacity of the cooling member 52 such that the cooling capacity of the portion directly below the left hemisphere is higher than that of the right portion. In this manner, balancing in cooling capacity can be more precisely controlled between the left and right portions . Mode (IV) in which the history of contact of a cooling medium with a cooling member is controlled. Needless to say, cooling capacity differs between the two cases that are continuous contact and intermittent contact each between the cooling medium and the cooling member. What is meant by the term "intermittent contact" is that contacting state and non-contacting state occur alternately. Thus, cooling capacity can also be controlled through controlling the ratio of contact time to non-contact time. In other word, cooling capacity can be regulated if the history of contact between the cooling medium and the cooling member is modified. For example, in the aforementioned embodiments shown in FIGs. 29, 30(A) and 30(B), the restriction plate 54a, which regulates the spray direction, is made movable and a control mechanism (not shown) for controlling the motion of the restriction plate 54a is connected thereto. In this manner, cooling capacity can be enhanced as compared with the case in which the cooling medium does not at all contact the outer surface of the interior space 55b (material section 55d) . As a result, balance of cooling capacities between the center and peripheral portions of the cooling member 52 is controlled more precisely. Mode (V) in which a heater is incorporated into a portion of a cooling member. Forced cooling of a cooling member is effected through a method in which either or both of modes (I) and (II) are implemented, and controlled through implementing either or both of modes (III) and (IV) in accordance with needs. In combination with the forced cooling, a heater for lowering cooling capacity is buried in a portion of a cooling member to thereby block heat flow from molten metal to the outer surface of the cooling member. As a result, well-balanced cooling can be attained throughout the cooling member, contributing to formation of a solidification interface of desired shape. The heater may be a resistance heater, superheated steam heater or high-temperature gas heater. As describe above with reference to, for example, FIG. 31, the left and center portions of the molten metal 46 solidify slowly, since in these portions the cast ingot is thick and the sprue 42 is disposed. Therefore, an attempt is made to enhance the cooling capacity of these portions . In contrast, the molten metal 46 in the right portion solidifies faster because the right portion of the cast ingot is thinner and is remote from the sprue 42. In order to attain a well-balanced cooling, the heater 56 is incorporated into the right portion, and the outer surface of the right portion is covered with the heat-insulating material 55e so as to prevent the cooling medium from contacting the outer surface of the right portion to thereby lower the cooling capacity of the right portion. Mode (VI) in which a heater is incorporated into a portion of a mold member. Forced cooling of a cooling member is effected through a method in which either or both of modes (I) and (II) are implemented, and controlled through implementing either or both of modes (III) and (IV) in accordance with needs. In combination with the forced cooling, a heater for lowering the cooling capacity is buried in a portion of a mold member to thereby block heat flow from molten metal to the mold member. As a result, well-balanced cooling capacity can be attained throughout the cooling member, contributing to formation of a solidification interface of desired shape. Mode (V) is effective when a portion of cast ingot that lowers cooling capacity is relatively thin. When such a portion is relatively thick, solidification performance is affected by the cooling member as well as the mold member. Therefore, a heater is incorporated into the mold member. The location of the incorporated heater is either or both of the side and upper sections of the mold member. The mold may be divided into a side member and an upper member. The heater may be a resistance heater, superheated steam heater or a high-temperature gas heater. FIG. 33(B) is a cross-sectional view showing an exemplary apparatus of the present invention and depicting a cooling capacity control mechanism of mode (VI). Elements identical to those shown in FIG. 22 are denoted by the same reference numerals . The shape of the cast ingot in this embodiment is such that thick portions A and B are formed on the right and left sides (as viewed in the drawing), respectively, with a thin portion being interposed therebetween, and molten metal is teemed through a sprue 42 disposed at the upper end of left- hand space B providing a thicker ingot portion. In such casting, molten metal filled in the smaller space A, which is remote from the sprue 42, solidifies faster than molten metal filled in the space B. While waiting for the completion of solidification of molten metal in space B, the mold member that defines space A is deprived of heat through the solidified cast ingot in space A. Therefore, the temperature of the side and upper walls of the mold member constituting space A becomes lower than the molten metal temperature. Since the molten metal in direct contact with the mold begins to solidify from the wall surfaces of the mold, the final solidification portion is generated within the cast ingot in space A as shown in FIG. 33(A), leading to a defective cast ingot including a blowhole or microshrinkage in the portion corresponding to the final solidification portion. In order to cope with this problem, as shown in FIG. 33(B), a heater 56 is buried in the mold member at the location directly above the space A so as to add heat commensurate with the amount of heat removed through the cast ingot , thereby heating the mold to a temperature higher than the molten metal temperature. As a result, solidification of the molten metal proceeds without producing a closed solidification interface within the space A, and solidification is completed with the solidification interface coinciding with the interior upper surface of the mold. Thus, a wholly non-defective cast ingot can be obtained. The heating conditions are preferably monitored through temperature measurement by means of a thermocouple buried in a representative position of the mold to thereby maintain the solidification interface in a predetermined shape. The heater is preferably connected to a power source and a control box in order to control the heater automatically. Unlike the case of application of heat by a heater, cooling does not provide any negative energy. However, in either of modes (I)(b) and (I)(c) in which a space or a material section of different thermal conductivity is provided within the cooling member and in the mode (I)(f) in which the inclination angle of holes formed in the outer surface of a cooling member is controlled in accordance with the collision angle of a cooling medium, similarly to the case in which a heater is provided (modes (V) and (VI)), prevention of heat from flowing from the molten metal to the outer surface of the cooling member can be realized. Mode (VII) in which a plurality of heating sections and cooling sections are provided within a cooling member, and the functions of the respective sections are controlled. When a mechanism that can be arbitrarily used for heating and cooling in accordance with needs is installed within a cooling member in advance, the temperature of an arbitrary portion of the cooling member can be arbitrarily controlled. Preferably, the heating section is similar to the aforementioned heater that performs heating in an arbitrary manner. The cooling section is a section or a chamber to which the aforementioned cooling medium is to be supplied and which preferably performs cooling in an arbitrary manner. These sections control temperatures (cooling capacity) of the respective portions of the cooling member in accordance with the shape of the cast ingot and the number and the location of the sprue(s). FIG. 34 is a cross-sectional view showing an exemplary apparatus of the present invention and depicting a cooling capacity control mechanism of mode (VII). Elements identical to those shown in FIG. 22 are denoted by the same reference numerals . In the present embodiment, molten metal is teemed through a sprue 42 disposed at an approximately central position to thereby produce a disk-shaped cast ingot having a shape similar to those shown in FIGs. 29, 30(A) and 30(B) that are cast ingots having a virtually uniform thickness wherein the thickness is extremely smaller than the outer diameter. In such casting, as described above, the thickness of the cast ingot extremely smaller than the outer diameter causes a solidification time difference between the center portion of the disk and the peripheral portion thereof that is the remotest portion from the sprue 42. Thus, the center portion of the cast ingot easily produces cracks because an ideal unidirectional solidification state cannot be maintained. In order to cope with this problem, cooling sections (chambers) 58, which are provided independently from one another and connected to a cooling control unit 58a, are disposed in the upper inner portion of a cooling member 52 of the present embodiment. Further, heating sections (chambers) 59, which are provided independently from one another and connected to a heating control unit 59a, are disposed in the lower inner portion of the cooling member 52. The cooling control unit 58a can supply a cooling medium to an arbitrary cooling section 58, and the heating control unit 59a can make an arbitrary heating section 59 generate heat. In this case, the cooling control unit 58a supplies the cooling medium to the cooling sections 58 that cool the center portion below the sprue 42, and supplies no cooling medium to the other cooling sections 58. Further, the heating control unit 59a make only the heating sections 59 that heat the peripheral portion of the disk generate heat. In this manner, the cooling member 52 of the present embodiment shown in FIG. 34 can be appropriately applied to a cast ingot of any shape as long as the lower surface of the cast ingot is flat. In the present invention, through use of a cooling capacity control mechanism that locally enhances or lowers cooling capacity of a cooling member or controls local heat removal through intentional heating in accordance with the shape of the cast ingot and the location and the number of the sprue(s), specifically through modes (I)(a) to (I)(h) and (II) to (VI), or appropriate combination thereof, control and regulation of solidification of a cast ingot is attained without producing a closed loop of solidification interface within the mold. The cast ingot obtained in the aforementioned manner does not include any riser portion or cut surface. Preferably, the upper corners of the cast ingot have a radius of curvature of 1 mm or less . Therefore, the cast ingot obtained through the aforementioned methods and apparatus is a non-defective product having no crack, blowhole defect or internal defect, and can, of course, directly serve as a product (casting) or can be used as a stock for plastic working for use in various processing such as forging. Furthermore, according to the present invention, a mechanism may be provided for opening at least a portion (a portion or the entirety) of a cooling member in the course of solidification of molten metal within a mold, and a mechanism may also be provided for supplying a cooling medium directly to the exposed outer surface of a cast ingot . The cast mechanism in the vicinity of a cooling member is finer because molten metal solidifies faster. As the solidification interface proceeds to a location remote from the cooling member, the solidification rate decreases. In other words, when a cooling member is used for cooling, the thicker the cast ingot, the larger the solidification rate difference between at a lower section and at an upper section of a cast ingot, resulting in wide cast mechanism difference, which leads to difference in terms of cast quality or forging property. Furthermore, the upper section of the cast ingot is apt to generate internal microshrinkage and forging cracks. The cooling capacity attained through indirect cooling by use of a cooling member is inferior to that of direct cooling in which a cooling medium is directly applied to the lower surface of a cast ingot. However, without using a cooling member, the aforementioned local control of heat removal from a mold member containing a cooling member cannot be performed. Thus, it is preferable to combine indirect cooling using a cooling member with direct cooling in order to enhance the cooling capacity. At the beginning of casting, a cooling member serving as part of the mold receives molten metal. For example, in the course of solidification, all or a portion of the cooling member contacting the lower surface of a cast ingot is opened to thereby apply a cooling medium, which has cooled the outer surface of the cooling member, directly to the lower surface of the cast ingot by means of cooling spray. As a result, the amount of heat removed from the cast ingot significantly increases, and the cooling rate and the solidification rate increase. In this manner, a cast ingot having small metallographic difference between an upper portion and a lower portion can be obtained. Alternatively, the cooling member may be lowered, after which a rotatable apparatus that comprises a spray device and a pan for collecting the cooling medium may be used. In this case, the cast ingot is held so as not to fall, in a manner appropriate for the ingot and the mold in terms of shape. The present method is particularly effective when the ingot to be cast is thick, and enables casting of any species of alloy without involving difficulties associated with a conventional casting of an alloy. FIG. 35 is a cross-sectional view showing an exemplary apparatus of the present invention in which a cooling member 52 is composed of plural members 55f and 55g. The member 55g is connected to a driving means 60 via a piston rod 60a so that the member 55g can slide while contacting the lower surface of the member 55f . The casting operation performed by use of the present apparatus is as follows . During teeming of molten metal 46, the member 55g is placed in order to close a hole in the member 55f. Subsequently, the molten metal 46 in a mold 5 is solidified from the upper surface of the cooling member 52 by means of a cooling spray (spray nozzle 54) and the cooling member 52. When the solidification interface 46b in the mold 5 has reached the position denoted by @, the driving means 60 is started to operate in order to slide the member 55g to thereby expose the lower surface of the cast ingot, to which a cooling medium is directly sprayed onto the exposed lower surface . After completion of solidification, the member 55f is lowered, and the cast ingot is removed. As described above, the cooling member may comprise a plurality of members . Each member constituting the cooling member is made of any of the aforementioned materials, and the member may be made up of homogeneous or heterogeneous material(s). Preferably, respective members are processed to have optimal shapes from the viewpoints of rigidity and cooling capacity. A hole or holes may be formed in each member, or no hole may be formed, and the thickness may be controlled in an appropriate manner. The driving means may be any apparatus such as an air cylinder, a. hydraulic cylinder or an electric cylinder. Although the driving means shown in FIG. 35 moves up and down along with the cooling member, the mechanism of the driving means is not limited thereto. A series of operations of casting-related apparatus may be performed through a timer control in accordance with a predetermined timetable. Alternatively, a measuring means such as a thermocouple may be inserted into a cooling member and/or a sidewall and/or an upper wall of the mold so as to measure and monitor the temperature of the respective portions, and the operation of each apparatus is started when the temperature has reached a predetermined point. In particular, when a movable portion (member 55g in the illustrated embodiment) is opened excessively early. unsolidified molten metal flows out into a cooling case equipped with a cooling spray, whereas when the movable portion is opened excessively late, microshrinkage is produced within the mold and the crystal grains become coarse. When the movable portion (the member 55g in the illustrated embodiment) is opened, the cast ingot being solidified should not fall from the mold. Therefore, the cast ingot is designed to have a shape for allowing the ingot of as-cast shape to be retained by the mold, as shown in FIG. 35. Alternatively, it is also effective to provide a fixed portion (member 55f in the illustrated embodiment) with a projection that does not impede the removal operation for the cast ingot. The projection, which forms a depression in a product, should have a shape that does not cause any problem during use of the cast ingot . This method can be used in combination with the. aforementioned various cooling control methods. Needless to say, the methods are preferably combined in accordance with the species of the alloy and the shape of the cast ingot to thereby provide optimal operational conditions. Working Examples 6 to 10 and Comparative Examples 2 to 6 will now be described. Example 6 : An aluminum alloy was melted in a separately provided melting furnace, and the molten metal was cast using the apparatus of FIG. 22. The thus obtained cast ingot was examined for metallographic microstructure. The cooling member 52 is made of copper. The mold 5, molten metal reservoir 4 and opening/closing plug 43 are made of a commercially available refractory heat-insulating material (Lumiboard produced by Isoraito Kogyo Kabushiki Kaisha) . A liner was inserted between the side mold 5b and the upper mold 5a to thereby secure a gas ventilation of the mold 5. The upper surface of the cooling member 52 has a step-down center, and the slope angle of the step-down portion is 45°. The cast ingot produced had a disk shape having a convex portion in its lower surface, with an outer diameter of 62.5 mm, an outer thickness of 7 mm at the periphery, a diameter of 30 mm at the central thick portion and a thickness of 12 mm at the central thick portion. The cooling member 52 has an outer shape depressed to form, a hollow cone toward the center. The central portion of the cooling member has an inner diameter of 30 mm and a thickness of 5 mm. The thickness of the cooling member increases at 45° from the edge of the central portion toward the periphery. The casting conditions and the procedure were as follows. 1) Alloy species: JIS 2218 alloy 2) Temperature of molten metal in the reservoir: 720°C 3) Cooling member temperature before teeming: 150°C 4) Flow rate of cooling water: 5 liters/minute 5) Diameter of sprue: 12 mm 6) Casting procedure: The sprue was closed with the plug two seconds after initiation of teeming. Cooling by water started when the cooling member temperature reached 500°C. Cooling by water stopped when the cooling member temperature reached 30°C. Descending of the cooling member started when the cooling member temperature reached 200°C. 7) The cast body was allowed to fall spontaneously together with the cooling member, and then collected. Example 7 : The apparatus of FIG. 23 was used, and cracks in the cooling member 52 were investigated. The cooling member 52 has a thickness of 12 mm, hole diameter of 4mm and hole depth of 10 mm. The holes were provided at nodes of 7 mm x 7 mm grid. The casting conditions and the procedure were the same as in Example 6. The cast ingot produced had an outer diameter of 62.5 mm and a thickness of 9 mm. Example 8: The apparatus as shown in FIG. 32 including a passage for circulating a cooling medium within the cooling member, was used in order to produce a cast ingot having a three- dimensionally complicated shape with no plane of symmetry. The cast ingot produced had a thickness of 9 mm at the thinner portion, a thickness of 15 mm at the thicker portion, a longest edge of 50 mm and a shortest edge of 35 mm. The casting conditions and the procedure were as follows . 1) Alloy species: JIS 6061 alloy 2) Temperature of molten metal in the reservoir: 720°C 3) Cooling member temperature before teeming: 100°C 4) Flow rate of cooling water: 8 liters/minute 5) Diameter of sprue: 10 mm 6) Casting procedure: The sprue was closed with the plug three seconds after initiation of teeming. Cooling by water started when the cooling member temperature reached 500°C. Cooling by water stopped when the cooling member temperature reached 30°C. Descending of the cooling member started when the cooling member temperature reached 200°C. 7) The cast body was allowed to fall spontaneously together with the cooling member, and then collected. 8) The metallographic microstructure of the cast ingot was investigate . Example 9 : The apparatus of FIG. 31 in which a heater was buried in a portion of the cooling member was used in order to produce a cast ingot having a three-dimensionally complicated shape with no plane of symmetry. The cast ingot produced had a thickness of 9 mm at the thinner portion, a thickness of 15 mm at the thicker portion, a longest side of 50 mm and a shortest side of 35 mm. The casting conditions and the procedure were as follows. 1) Alloy species: JIS AC2B alloy 2) Temperature of molten metal in the reservoir: 720°C 3) Cooling member temperature before teeming: 150°C 4) Flow rate of cooling water: 8 liters/minute 5) Diameter of sprue: 10 mm 6) Casting procedure: The sprue was closed with the plug three seconds after initiation of teeming. Cooling by water started when the cooling member temperature reached 500°C. Cooling by water stopped when the cooling member temperature reached 30°C. Descending of the cooling member started when the cooling member temperature reached 200°C. 7) The cast body was allowed to fall spontaneously together with the cooling member, and then collected. 8) Heater capacity: 5 kW 9) The metallographic microstructure of the cast ingot was investigated. Example 10: A material used for forging a VTR cylinder drum was produced using the apparatus of FIG. 29. The casting conditions and the procedure were as follows . 1) Alloy species: JIS 2218 alloy 2) Temperature of molten metal in the reservoir: 720°C 3) Cooling member temperature before teeming: 150°C 4) Flow rate of cooling water: 5 liters/minute 5) Diameter of sprue: 12 mm 6) Dimensions of the cast ingot: 62.5 mm in outer diameter and 7 mm in thickness 7) Casting procedure: The sprue was closed with the plug 1.5 seconds after initiation of the teeming. Cooling by water started when the cooling member temperature reached 500°C. Cooling by water stopped when the cooling member temperature reached 30°C. Descending of the cooling member started when the cooling member temperature reached 200°C. 8) . The cast body was allowed to fall spontaneously together with the cooling member, and then collected. 9) Height of the step provided on the outer surface of the cooling member: 5 mm 10) Slope angle of the outer surface of the cooling member: 45° 11) Thickness between the inner surface of the space 55b and the outer surface of the cooling member: 4 mm 12) Difference between the spray collision angle β and the hole-axis inclination angle: within 10° 13) The incidence of cracks of the cast ingot was investigated. Comparative Example 2 : Casting was performed using the apparatus of FIG. 42 and a cooling member having a flat outer surface, a thickness of 10 mm, a diameter of 30 mm at the central depressed portion and a depth of 5 mm at the central depressed portion. The casting conditions and the procedure were the same as in Example 6. The results of comparison of the thus obtained cast ingot with the cast ingot obtained from Example 6 were as follows . Example 6 : No defect was observed directly below the sprue . Comparative Example 2: A defect was observed directly below the sprue. Comparative Example 3 : Casting was performed using the apparatus of FIG. 42 and a cooling member having a thickness of 5 mm. The casting conditions and the procedure were the same as in Example 7. The results of comparison of the thus obtained cast ingot with the cast ingot obtained from Example 7 were as follows . Example 7: No crack was observed in the cooling member. Comparative Example 3: Cracks were observed in the central portion of the cooling member. Comparative Example 4 : Casting was performed using the apparatus of FIG. 42 including a cooling member having no mechanism for enhancing cooling capacity. The casting conditions and the procedure were the same as in Example 8. The results of comparison of the thus obtained cast ingot with the cast ingot obtained from Example 8 were as follows . Example 8 : No defect was observed in the portion of the cast ingot directly below the sprue. Comparative Example 4: Defects were observed in the portion of the cast ingot directly below the sprue. Comparative Example 5 : Casting was performed using the apparatus of FIG. 42 including a cooling member having no mechanism for enhancing cooling capacity. The casting conditions and the procedure were the same as in Example 8. The results of comparison of the thus obtained cast ingot with the cast ingot obtained from Example 8 are as follows . Example 8 : No defect was observed in the portion of the cast ingot directly below the sprue. Comparative Example 5 : Defects were observed in the portion of the cast ingot directly below the sprue. Comparative Example 6 : Casting was performed using the apparatus of FIG. 42 including a cooling member having a thickness of 5 mm. The casting conditions and the procedure were the same as in Example 8. The results of comparison of the thus obtained cast ingot with the cast ingot obtained from Example 8 were as follows . Example 8 : No crack was observed in the cast ingot . Comparative Example 6 : Cracks were observed in the center portion of the cast ingot . As described above, the metal casting method and apparatus of the present invention enable a cast ingot to solidify without forming a closed loop of solidification interface within a mold by means of a cooling capacity control mechanism which is adapted to locally enhance or lower the cooling capacity of a cooling member or to control local heat removal through intentional heating in accordance with the shape of the cast ingot and the location and the number of the sprue(s). Thus, there can be produced non- defective cast ingots having no crack or blowhole therein. In other words, the metal casting method and apparatus of the present invention control the number and the location of the sprue(s) in accordance with the shape of the cast ingot to be produced to thereby produce healthy cast ingots of desired shape having no internal defects, such as cracks, blowholes and microshrinσage . The cast ingots obtained through the aforementioned method and apparatus do not include any riser portion or cut surface, and can, of course, be directly used for casting of products (castings) or can be used for casting of a material for plastic working which is used in various processing such as forging. Embodiments of the casting method and apparatus usable in the automatic continuous casting system will be described below. FIG. 36 is a schematic representation showing a casting apparatus. A mold 5 is disposed on a cooling plate 52. A molten metal reservoir 4 for storing molten metal 45 fed from, for example, a molten furnace is provided on the mold 5. Feeding of the molten metal 45 in the molten metal reservoir 4 into the mold 5 is initiated or stopped by way of opening or closing a sprue 42 through which the reservoir 4 and the mold 5 are in communication by means of an opening/closing plug 43. When the plug 43 is moved vertically by means of a plug lifting mechanism 44, the sprue 42 is opened or closed. An upper lid 47 is provided above the reservoir 4 in order to prevent the upper surface of the molten metal 45 from being cooled. An electric furnace 61 is provided for heating the sides of the reservoir 4 to thereby maintain the temperature of the molten metal at a predetermined temperature. A cooling case 54b in which a spray nozzle 54 is fixed is provided below the cooling plate 52. When the cooling case 54b and the cooling plate 52 are moved upward by means of a cooling plate lifting mechanism 101, the lower opening of the mold 5 is closed with the cooling plate 52. In contrast, when the cooling case 54b is moved downward, the cooling plate 52 on which a cast product (cast ingot) is placed is detached from the mold 5, and the cast ingot can be removed. A cooling medium, such as water, supercooled water of 0°C or lower containing 0.5% or more of sodium chloride, a supercooled aqueous solution of 0°C or lower containing ethylene glycol or oil, is sprayed through a spray nozzle 54 to the lower surface of the cooling plate 52, and the cooling plate 52 is forcedly cooled. Hereinafter, a cooling medium sprayed through the spray nozzle 54 will be referred to as simply "cooling water." An opening/closing valve 103 is provided at an intermediate position on a water feed-pipe 102 for feeding cooling water to the spray nozzle 54. Feeding of cooling water to the spray nozzle 54 is initiated or stopped by means of on-off control of an electromagnetic valve 104 of the opening/closing valve 103. A thermocouple serving as temperature detection means 105 is provided on the cooling plate 52 for detecting the temperature of the cooling plate. Temperature data of the cooling plate are obtained by means of the thermocouple and employed in order to determine conditions for the casting process. The position of the cooling plate 52 into which the head of the thermocouple is inserted or the number of thermocouples inserted in the cooling plate may be appropriately determined in accordance with determination conditions required for controlling the casting process. In the present embodiment, the temperature of one position of the cooling plate 52 that is finally covered with the molten metal 46 fed into the mold 5 is detected as a representative temperature of the cooling plate 52. As in the present embodiment, when the sprue 42 is provided above the center of the mold 5 to thereby produce a cylindrical cast ingot, if the upper surface of the cooling plate 52 is virtually horizontal, the molten metal 46 fed through the sprue 42 and falling onto the cooling plate 52 is spread uniformly thereon toward the circumference. Therefore, the position of the cooling plate into which the head of the thermocouple is inserted may be appropriately determined, so long as the position is on the circle defined by the inner periphery of the mold 5 (see FIG. 36). In the casting apparatus of the present embodiment, casting control means 106 is used to automatically control the entire process including feeding of molten metal, cooling and removal of cast ingot . This control of casting process is carried out on the basis of the temperature data of the cooling plate 52 obtained by the temperature detection means 105 and timing measured using a timer. Specifically, one cycle of casting is carried out on the basis of the timing as shown in FIG. 37. The casting process is not limited only to an automatic-control-based process using the casting control means 106, and casting may be carried out through manual operation of apparatuses in accordance with appropriate timing of control. The casting process of the present embodiment is carried out under the following conditions . An aluminum alloy (JIS 22218 alloy) melted in a molten furnace is employed as molten metal. The cooling plate formed from copper is employed. The mold, molten metal reservoir and opening/closing plug are formed from a commercially available heat insulating refractory material named Lumiboard produced by Isoraito Kogyo Kabushiki Kaisha) . The temperature in the molten metal reservoir is 720°C. The liquid level height of molten metal in the molten metal reservoir is 50 mm. The amount of cooling water is 5 liter/min. The diameter of the sprue is 8 mm. The thickness of the cooling plate is 12 mm. An alumel-chromel sheath thermocouple having a diameter of 1 mm is employed, and the thermocouple is inserted such that the head thereof is positioned 2 mm below a position on the surface of the cooling plate. The position is on the circle defined by the inner periphery of the mold. A cast product has an outer diameter of 63 mm and a thickness of 10 mm. A casting cycle time is about 12 seconds. For initiation of the casting cycle, a command for moving the cooling plate upward is sent from the casting control means 106 to the cooling plate lifting mechanism 101 when a cast ingot is removed with a cast ingot removal apparatus, and the cooling plate 52 is attached to the lower portion of the cast to thereby form the mold. Upon satisfaction of the first condition that the cooling plate 52 is moved upward to form the mold and the second condition that the temperature of the cooling plate 52 is equal to or higher than an allowable lower limit temperature (T c ) , a plug opening command is sent from the casting control means 106 to the plug lifting mechanism 44, and the opening/closing plug 43 is moved upward by means of the plug lifting mechanism 44 which has received the command, thereby opening the sprue 42 to initiate feeding of the molten metal 45 into the mold 5. When the plug opening command is sent from the casting control means 106, a plug closing condition judgment timer (TM1) for measuring a certain period of time (e.g., 5 seconds) is set by the casting control means 106. The conditions required for initiating feeding of molten metal are determined such that the temperature of the cooling plate 52 is equal to or higher than the allowable lower limit temperature (T c that is 100°C, for example, but may vary in accordance with environmental conditions during casting or components of molten metal) . The reasons for this is that if the molten metal is fed into the mold including the cooling plate 52 having a temperature lower than the allowable lower limit temperature T c , a blow defect is formed when the molten metal 45 is brought into contact with the cooling plate 52 and solidified. As described in the present embodiment, when a certain time (approximately 1 to 2 seconds) elapses before the opening/closing plug 43 is opened and the molten metal 45 is fed into the mold 5 after the casting cycle is initiated by a command sent to the cooling plate lifting mechanism 101 for moving the cooling plate upward, the temperature of the cooling plate 52 may further be lowered within the time. Therefore, preferably, the temperature of the cooling plate 52 is sufficiently higher than the allowable lower limit temperature T c (for example, at least 10-20°C higher than T c ). In this embodiment, T 0 is determined at 150°C. After feeding of the molten metal into the mold 5 is initiated as described above, when the casting control means 106 detects that the temperature of the cooling plate 52 becomes Ti that is 155°C, for example, on the basis of the temperature data from the temperature detection means 105, the electromagnetic valve 104 is turned on to open the opening/closing valve 103 and feed cooling water to the spray nozzle 54 through the water feed-pipe 102. The timing for initiation of cooling of the cooling plate is not particularly limited, so long as the initial cooling conditions that the temperature of the cooling plate 52 is not lower than the allowable lower limit temperature T c when the molten metal 46 fed into the mold 5 is brought into contact with the mold-wall-enclosed surface of the cooling plate 52, are satisfied. If cooling of the cooling plate (i.e., opening control of the opening/closing valve 103) is initiated very early, the temperature of a portion of the mold-wall-enclosed surface of the cooling plate 52, when the molten metal 46 fed into the mold 5 does not reach the portion, may become lower than the allowable lower limit temperature T c . When the molten metal 46 is brought into contact with the portion of the cooling plate 52 having a temperature lower than the allowable lower limit temperature T c , a blow defect is formed. Since the molten metal 46 is rapidly spread over the mold-wall-enclosed surface of the cooling plate 52, when the temperature of the portion of the cooling plate 52, which is detected by the temperature detection means 105, is elevated to Ti, the molten metal 46 can be regarded to have reached the portion. Therefore, in the case in which a cast ingot having a size described in the present embodiment is produced, when the temperature of the portion of the cooling plate 52 is elevated to T if cooling of the cooling plate is initiated. In this case, the initial cooling conditions are satisfied, and formation of a blow defect can be prevented. Alternatively, a suitable cooling initiation timing, which is obtained empirically through use of an actual apparatus and structure, may be determined. For example, cooling of the cooling plate may be initiated a predetermined period of time after plug opening control of the opening/closing plug 43 to thereby satisfy the initial cooling conditions . The timing for initiation of cooling of the cooling plate so as to satisfy the initial cooling conditions is not limited to the aforementioned timing. For example, cooling of the cooling plate may be initiated when the following three conditions are all satisfied. The first condition is that the opening/closing plug 43 is in the open state. The second condition is that the temperature of the cooling plate 52 is equal to or higher than T c . The third condition is that an increase in the temperature of the cooling plate 52 is zero or positive. The third condition is provided for judging that the gradient of the tangent of the temperature variation curve of the cooling plate 52, which curve is obtained by detecting the temperature of the cooling plate 52 within a short cycle, is zero or positive. For example, the gradient of the tangent of the temperature variation curve may be determined by calculating the differential value of the temperature data of the cooling plate 52. When the differential value is zero or positive, the temperature of the cooling plate 52 can be thought of as being elevated by way of receiving heat from the molten metal 46 fed into the mold 5. Under the third condition, it can be inferred that the molten metal is brought into contact with the portion of the cooling plate at which the temperature is detected or that the molten metal is brought into contact with the cooling plate within a very short period of time. When the temperature variation of the cooling plate is inconsistent (for example, when a slight temperature variation of the cooling plate continues and it cannot be judged that the temperature of the cooling plate is reliably elevated) , in order to reliably control the temperature of the cooling plate, a threshold may be provided with respect to an increase in the temperature. When an increase in the temperature exceeds the threshold, the third condition may be judged as having been satisfied. The reason why the timing for initiation of cooling of the cooling plate is judged by the first condition (the opening/closing plug 43 is opened) and the second condition (the temperature of the cooling plate 52 is equal to or higher than T c ) is to enhance reliability of control of the temperature of the cooling plate. Usually, these conditions may be omitted because it does not cause any problem. When the size of the mold is large, a relatively long period of time may elapse before the molten metal spreads over the entire surface of the cooling plate. When cooling of the molten metal fed into the mold is not initiated until completion of spreading of the molten metal over the surface of the cooling plate, to thereby satisfy the initial cooling conditions, the molten metal may be cooled slowly. In such a case, when a plurality of spray nozzles are provided in accordance with the size of the mold, only a portion of the surface of cooling plate with which the molten metal fed through the sprue is brought into contact is cooled first, and portions of the cooling plate covered with the molten metal are sequentially cooled while the temperature of a portion of the surface of the cooling plate which is not covered with the molten metal is maintained at the allowable lower limit temperature or higher, the cooling plate can be cooled while the aforementioned initial cooling conditions are satisfied. As described above, when the cooling plate is cooled while the initial cooling conditions are satisfied, cooling of the portions of the cooling plate may be initiated when the temperatures of the portions reach a predetermined temperature or when the gradient of the temperature variation of the cooling plate becomes zero or positive. Alternatively, the proper timing for initiation of cooling of the cooling plate, which is obtained on the basis of tests making use of a practical apparatus, may be determined, and cooling of the cooling plate may be controlled by use of a timer. When the cooling plate 52 has a complicated shape to vary its thickness, portions of the cooling plate covered with the molten metal may be cooled such that the initial cooling conditions are satisfied. That is, the temperature of a portion of the surface of the cooling plate which is not covered with the molten metal should be maintained at the allowable lower limit temperature or higher, since the flow of the molten metal varies in accordance with the position of the sprue or the shape of the cooling member, and the time when a surface of the cooling plate that faces the inside of the mold is covered with the molten metal differs from portion to portion. When the entirety of the mold-wall- enclosed surface of the cooling plate (or cooling member) is covered with the molten metal, usual cooling can be carried out, since the cooling plate is not cooled under the initial cooling conditions. A predetermined period of time (e.g., five seconds) after cooling of the cooling plate 52 is initiated as described above, as measured using the plug closing condition judgment timer (TM1), a plug closing command is sent from the casting control means 106 to the plug lifting mechanism 44, and the sprue 42 is closed with the opening/closing plug 43. Closing of the sprue with the plug is not necessarily determined using the timer. Closing of the sprue may be determined by any method, so long as the sprue 42 is closed before the molten metal 46 in the mold 5 is solidified in the vicinity of the sprue 42 and closing of the sprue with the plug 43 becomes impossible. However, when the sprue is closed immediately after the mold 5 is filled with the molten metal 46, the feeding effect (the effect of compensating for a shortage portion formed through solidification and shrinkage of the molten metal 46 in the mold 5 through pressing of the molten metal 45 in the reservoir 4 into the mold 5) is not obtained. Therefore, the sprue 42 is preferably left open as long as possible until immediately before closing of the sprue becomes impossible. Closing of the sprue is not necessarily controlled using the timer as described in the present embodiment, and closing of the sprue with the plug 43 may be controlled by detecting, before closing of the sprue becomes impossible, by means of temperature detection means provided in the vicinity of the sprue of the mold 5, that the temperature of the molten metal reaches a predetermined temperature which is close to the solidification temperature of molten metal. When the temperature of the cooling plate 52 attains a predetermined temperature T 2 that is 70°C, for example, a cooling completion condition judgment timer (TM2) is set by the casting control means 106. When a predetermined period of time (e.g., four seconds), as measured by the cooling completion condition judgment timer, elapses, the electromagnetic valve 104 is turned off by the casting control means 106 to close the opening/closing valve 103 and stop feeding of cooling water through the water feed-pipe 102 to the spray nozzle 54. The temperature of the coolxng plate 52 does not necessarily become T 2 before the predetermined period of time elapses, which period is measured by the cooling completion condition judgment timer used for control of the plug 43. When the detection temperature T 2 for determining the conditions for setting the timer is determined at a relatively low temperature, the temperature of the cooling plate 52 may become T 2 after the plug 43 is closed. In consideration of possibilities that the temperature T 2 for determining the conditions for setting the timer is detected early for reasons of unexpected errors and that the predetermined period of time measured by the cooling completion condition judgment timer elapses during opening of the plug 43, verification of closing of the plug 43 is preferably carried out in order to judge completion of cooling of the cooling plate. As described above, temperature data of the cooling plate 52 and measurement by the timer are employed to determine whether the conditions for stopping cooling are satisfied, and this is for the reasons described below. When the temperature of the cooling plate 52 is lowered to a certain extent, the temperature of the cooling plate 52 to which cooling water is directly sprayed becomes to vary slowly (see FIG. 37), and an error of judgment for completion of cooling of the plate becomes large because of difficulty in detection of slight temperature variation. Consequently, cooling of the plate may be completed before the plate is satisfactorily cooled, or a casting cycle time may be lengthened wastefully because of overcool of the cooling plate. Therefore, the temperature of the cooling plate 52 is detected before the temperature lowering gradient is small and an error in detection of the temperature becomes large, and then supply of cooling water is stopped after elapse of a certain period of time, which is determined in accordance with the structure of a practical casting apparatus. If the temperature detection means for judging completion of cooling detects the temperature variation of the cooling plate 52 at significantly high accuracy, cooling of the cooling plate may be completed when the temperature of the cooling plate 52 reaches a predetermined temperature. Alternatively, a cooling time suitable for an actual casting apparatus is determined in advance, and cooling of the cooling plate may be completed after elapse of the cooling time measured using a timer. After completion of forced cooling of the cooling plate 52 with cooling water, the temperature of the cooling plate 52 is again elevated by heat of the cast ingot. When the casting control means 106 detects that the temperature of the cooling plate 52 becomes T 3 that is 160°C, for example, on the basis of temperature data from the temperature detection means 105, a command for moving the cooling plate downward is sent from the casting control means 106 to the cooling plate lifting mechanism 101, since cast ingot removal conditions are attained. Subsequently, the cooling plate 52 on which the cast ingot is placed is detached from the mold 5 and moved downward, and the cast ingot is removed through operation of a cast ingot removal apparatus (not illustrated) . The cast ingot removal conditions are not necessarily attained when the temperature of the cooling plate 52 reaches T 3 , and the cast ingot removal conditions may be attained a predetermined period of time after stopping of cooling water supply. When the cast ingot removal apparatus is stopped after the cast ingot is removed as described above, the casting control means 106 receives the signal of completion of removal of the cast ingot, and a command for moving the cooling plate upward is immediately sent from the means 106 to the cooling plate lifting mechanism 101 to thereby initiate the next casting cycle. As described above, according to the metal casting process of the present embodiment, the cooling plate 52 is cooled so as to satisfy the initial cooling conditions before the mold is filled with the molten metal. Therefore, the process has an advantage in that the casting cycle time can be shortened while formation of a blow defect in a cast product is prevented. For example, the casting cycle time can be shortened to 12 seconds in the process of the present embodiment, as contrasted with 16 seconds required for a casting cycle in a conventional casting process. In addition, after the cooling plate is cooled under the initial cooling conditions, usual cooling is carried out. Therefore, since solidification of the molten metal proceeds while the molten metal is fed into the mold, the cast ingot is rapidly cooled as compared with the case in which cast ingot is cooled in a conventional process . Thus , segregation of metallic components in the cast ingot is reduced. Furthermore, since the sprue is closed with the plug 43 immediately before closing of the sprue becomes impossible, the cast ingot has a dense structure because of the feeding effect, and formation of casting defects can be minimized. FIG. 38 is a photograph showing a cross section of a short cylindrical cast ingot piece 63 mm in diameter and 10 mm in thickness produced through the aforementioned casting process making use of the casting apparatus. The ingot piece was cut vertically so as to include the axis thereof, and the cross section was subjected to etching. As shown in FIG. 38, unlike the cast ingot produced through the aforementioned conventional process, segregation of metallic components does not occur, and etching patterns attributed to the segregation are not observed. Etching was carried out using as the chemical treatment solution a 20% aqueous sodium hydroxide solution of 50°C for three-minute immersion. Observation of the metallographic microstructure of the aforementioned cast ingot shows that defects (i.e., micropores) are present at a portion of the cast ingot in the vicinity of the sprue. There were 0.5 or fewer micropore of at least 200 μm (see FIG. 39) and 5 or fewer micropores of 50-200 μm, each per 100 mm 2 of the cast ingot. Thus, the quality of the cast ingot produced through the casting process of the present embodiment is greatly enhanced as compared with the case of the cast ingot produced through a conventional process . Control functions included in the casting control means 105 for carrying out whole control in order to realize the aforementioned casting process will next be described in detail with reference to a block diagram shown in FIG. 40. On the basis of temperature data from the temperature detection means 105, the casting control means 106 controls the plug lifting mechanism 44 for moving the opening/closing plug 43 vertically, the electromagnetic valve 104 for opening and closing the opening/closing valve 103 for opening and closing the water feed-pipe 102 for feeding to the spray nozzle 54 the cooling water used for cooling the cooling plate 52, and the cooling plate lifting mechanism 101 for moving the cooling case 54b and the cooling plate 52 vertically. In the casting apparatus, the cooling means functions by means of concerted operation of the spray nozzle 54, the water feed-pipe 102 and the opening/closing valve 103. In the casting control means 106 of the present embodiment, the cooling means functions by means of control of only the electromagnetic valve 104, since feeding of cooling water is initiated or stopped by control of the electromagnetic valve 104. When the casting control means 106 receives a cast ingot removal completion signal from the cast ingot removal apparatus 107, it controls the cooling plate lifting mechanism 101 for moving the cooling plate upward. Upon attainment of both of the first condition that the temperature T 0 of the cooling plate 52 is equal to or higher than the allowable lower limit temperature T c and the second condition that the cooling plate 52 is moved upward by means of the cooling plate lifting mechanism 101, feeding of the molten metal is initiated by means of plug opening control means 108, which receives temperature data from the temperature detection means 105. When these conditions are attained, a plug opening command is sent from the plug opening control means 108 to the plug lifting mechanism 44 to thereby move the opening/closing plug 43 upward, thereby feeding the molten metal 45 into the mold 5 through the opened sprue 42. As described in the present embodiment, when the casting apparatus is employed, in which there is a certain time between before the molten metal 45 is fed into the mold 5 and after the cooling plate is moved upward, the temperature T 0 of the cooling plate 52 must be equal to or higher than T c . In addition, preferably, the temperature T 0 of the cooling plate 52 is sufficiently higher than T c (e.g., T o ≥ 150°C) such that at no point on the mold-wall-enclosed surface of the cooling plate 52 the temperature drops below To before the temperature of the cooling plate 52 begins to rise after the molten metal 45 is fed into the mold 5. After feeding of the molten metal is initiated by means of the plug opening control means 108 as described above, in order to satisfy the initial cooling conditions that the temperature of the cooling plate 52 does not drop below the allowable lower limit temperature T c when the molten metal 45 fed into the mold 5 is brought into contact with the mold- wall-enclosed surface of the cooling plate 52, initial cooling control means 109 operates usual cooling means 110 to thereby control the electromagnetic valve 104 such that the valve is not opened. The initial cooling control means 109 included in the casting control means 106 does not directly control the cooling means such that the initial cooling conditions are satisfied, but controls the usual cooling control means 110 such that the means 110 does not initiate cooling control to thereby prevent formation of a blow defect, which is formed when the molten metal 46 is brought into contact with the cooling plate 52 having a temperature lower than the allowable lower limit temperature. When the temperature Ti of the cooling plate 52 reaches 500°C, as verified on the basis of temperature data from the temperature detection means 105, the initial cooling control means 109 judges that the entirety of the mold-wall-enσlosed surface of the cooling plate 52 is covered with the molten metal 46 fed into the mold 5. Subsequently, a command to initiate "usual cooling" is sent from the initial cooling control means 109 to the usual cooling means 110, and the electromagnetic valve 104 is turned on by means of the usual cooling control means 110 which has received the command to open the opening/closing valve 43 and spray cooling water through the spray nozzle 54, thereby initiating cooling of the cooling plate 52. In the case in which the initial cooling control means 109 controls initiation of cooling of the cooling plate, which is controlled by means of the usual cooling control means 110, in order to satisfy the initial cooling conditions, as described above, when the temperature of the cooling plate 52 reaches a predetermined temperature, or when an increase in the temperature of the cooling plate 52 becomes zero or positive, the cooling plate is judged not to have cooled under the initial cooling conditions . The cooling plate 52 may be subjected to usual cooling at a timing that is predetermined on the basis of the structure of an actual casting apparatus in operation. For example, the cooling plate 52 is subjected to usual cooling a predetermined period of time after the sprue is opened. The plug opening control means 108 sends a plug opening command to the plug lifting mechanism 44 and simultaneously sends to plug closing control means 111 a signal reporting that the sprue is opened. A plug closing control timer (TM1) for measuring a predetermined period of time (e.g., five seconds) is set by the plug closing control means 111. The plug closing control timer reports the time immediately before the molten metal in the mold 5 is solidified in the vicinity of the sprue 42 and closing of the sprue 42 with the plug 43 becomes impossible. Therefore, when the predetermined time, as measured by the timer, elapses, the plug closing means 111 sends a plug closing command to the plug lifting mechanism 44 to thereby close the sprue 42 with the plug 43, thereby stopping feeding of the molten metal into the mold 5. Shortly after the sprue is closed with the plug 43 as described above, solidification of the molten metal in the mold 5 is completed to thereby produce the cast ingot, and cooling of the cooling plate 52 by cooling water continues until the predetermined cooling completion conditions are attained. As described above, cooling of the cooling plate 52 is completed a predetermined period of time after the temperature of the cooling plate 52 reaches a predetermined temperature T 2 that is 70°C, for example. Therefore, a cooling completion condition judgment timer (TM2) is set by termination-of-cooling control means 112 that detects that the temperature of the cooling plate 2 reaches T 2 . When a predetermined period of time (e.g., four seconds), as measured by the timer, elapses, a cooling stop command is sent from the termination-of-cooling control means 112 to the usual cooling control means 110, and the electromagnetic valve 104 is closed by means of the usual cooling control means 110 to thereby stop forced cooling of the cooling plate. The termination-of-cooling control means 112, which has sent a cooling stop command to the usual cooling control means 110 as described above, sends to attachment/detachment control means 113 a signal that cooling of the cooling plate is stopped. When the attachment/detachment control means 113 which has received the signal detects, on the basis of temperature data from the temperature detection means 105, that the predetermined cast ingot removal conditions are attained (i.e., the temperature of the cooling plate 52 reaches T 3 that is 160°C, for example), the control means 113 sends to the cooling plate lifting mechanism 101 a command for moving the cooling plate downward. Subsequently, the cooling plate 52 is moved downward and detached from the mold 5 by means of the cooling plate lifting means 101 that has received the command, such that the cast ingot is removed from the mold 5, and the cast ingot is removed by means of the cast ingot removal apparatus 107. When removal of the cast ingot is completed, the cast ingot removal apparatus 107 sends to the attachment/detachment control means 113 a signal that the removal of the cast ingot is completed. Upon receiving the signal, the attachment/detachment control means 113 sends to the cooling plate lifting mechanism 101 a command for moving the cooling plate upward, and the cooling plate 52 is attached to the lower portion of the mold 5 by means of the mechanism 101 to thereby initiate the next casting cycle. In the present embodiment, in order to initiate the next casting cycle, the attachment/detachment control means 113 sends to the plug opening control means 108 a signal that the cooling plate is moved upward, after the control means 113 receives from the cooling plate lifting mechanism 101 a signal that the cooling plate has been moved upward. However, the attachment/detachment control means 113 may send to the plug opening control means 108 a signal that the cooling plate is moved upward, without having received from the cooling plate lifting mechanism 101 a signal that the cooling plate has been moved upward, a period of time, sufficient for the cooling plate 52 to be attached to the lower portion of the mold 5, after the attachment/detachment control means 113 sends a command for moving the cooling plate 52 upward to the cooling plate lifting mechanism 101. In the aforementioned embodiment of the casting control means 106, the initial cooling control means 109 does not directly control the cooling means for cooling the cooling plate 52 such that the initial cooling conditions are satisfied. However, control by the initial cooling control means is not limited to the aforementioned control. FIG. 41 shows casting control means 106' (another embodiment) including three temperature detection means and three cooling means, which are provided on the cooling plate 52. First temperature detection means 105a is provided on such a position of the cooling plate 52 that the molten metal 45 fed through the sprue 42 into the mold is most difficult to reach. Second temperature detection means 105b is provided on another position of the cooling plate 52, at which the molten metal can easily arrive as compared with the position on which the first temperature detection means 105a. Third temperature detection means 105c is provided on yet another position of the cooling plate 52, such as a position directly below the sprue 42. It is easiest for the molten metal 45 to reach this position. A region of the cooling plate 52 whose representative temperature is detected by the first temperature detection means 105a, is cooled by first cooling means 104a. A region of the cooling plate 52 whose representative temperature is detected by the second temperature detection means 105b, is cooled by second cooling means 104b. A region of the cooling plate 52 whose representative temperature is detected by the third temperature detection means 105c, is cooled by third cooling means 104c. The casting control means 106' controls a casting process by use of the aforementioned casting apparatus including a plurality of temperature detection means and cooling means . Means , mechanisms and apparatus included in the casting control means 106' shown in FIG. 41, which are identical with those included in the casting control means 106 shown in FIG. 40, are assigned the same reference numerals, and repeated description thereof is omitted. Hereinafter, the function of only initial cooling control means 109" will be described. On the basis of temperature data of the cooling plate 52 obtained by the first temperature detection means 105a showing that the temperature To of cooling plate is equal to or higher than a predetermined temperature (e.g., 150°C, which is sufficiently higher than the allowable lower limit temperature T) , the plug opening control means 111 sends a plug opening command to the plug lifting mechanism 44 to thereby move the plug 43 upward. When the plug 43 is moved upward, the sprue 42 is opened, and the molten metal 45 is fed into the mold 5, the temperature of the cooling plate 52 is elevated, which is detected by the third temperature detection means 105c. When temperature data obtained by the third temperature detection means 105c show that cooling initiation conditions are attained (e.g., the temperature of the cooling plate reaches a predetermined temperature Tι c , or an increase in the temperature of the cooling plate becomes zero or positive), the initial cooling means 109' operates only the third cooling means 104c to thereby initiate local cooling of the cooling plate. Initiation of cooling of the cooling plate may be judged on the basis of, instead of the temperature data obtained by the third temperature detection means 18c, the elapse of a certain period of time that is predetermined on the basis of the structure of an actual casting apparatus. By means of the third cooling means 104c, a region to be cooled may be limited or cooling power may be suppressed, such that the temperature of a portion of the surface of the cooling plate which is not covered with the molten metal does not drop below the allowable lower limit temperature . Subsequently, when temperature data obtained by the second temperature detection means 105b show that the cooling initiation conditions are attained (e.g., the temperature of the cooling plate reaches a predetermined temperature T ib , or an increase in the temperature of the cooling plate becomes zero or positive), the initial cooling means 109' operates the second cooling means 104b in addition to the third cooling means 104c. In this case, initiation of cooling of the cooling plate may be judged on the basis of, instead of the temperature data obtained by the second temperature detection means 105b, the elapse of a certain period of time that is predetermined on the basis of the structure of an actual casting apparatus . By means of the second and third cooling means 104b and 104c, a region to be cooled may be limited or cooling power may be suppressed, such that the temperature of a portion of the surface of the cooling plate which is not covered with the molten metal does not drop below the allowable lower limit temperature. Subsequently, when temperature data obtained by the first temperature detection means 105a show that the cooling initiation conditions are attained (e.g., the temperature of the cooling plate reaches a predetermined temperature T ia , or an increase in the temperature of the cooling plate becomes zero or positive), the initial cooling means 109' operates the first cooling means 104a in addition to the second and third cooling means 104b and 104c. In this case, initiation of cooling of the cooling plate may be judged on the basis of, instead of the temperature data obtained by the first temperature detection means 105a, the elapse of a certain period of time that is predetermined on the basis of the structure of an actual casting apparatus. By means of the first through third cooling means 104a through 104c, a region to be cooled may be limited or cooling power may be suppressed, such that the temperature of a portion of the surface of the cooling plate which is not covered with the molten metal does not drop below the allowable lower limit temperature . The first and second temperature detection means 105a and 105b detect the temperature of the cooling plate when heating by the molten metal 46 fed into the mold and cooling by the third cooling means 104c, the second cooling means 104b or the third cooling means 104c proceed simultaneously., The first through third temperature detection means 105a through 105c detect only the representative temperature of a specific portion of the cooling plate 52. Therefore, in the case in which a cooling member having a complicated shape is employed instead of the aforementioned cooling plate 52 having a simple plate-like shape, in order to control cooling of the cooling member on the basis of temperature profiles of portions of the cooling member, the temperatures of a large number of portions of the member must be detected, resulting in an increase in production cost. Meanwhile, it is effective to control by a timer the proper timing for initiating cooling of the cooling plate, which timing is determined on the basis of the size and shape of the mold corresponding to those of a cast product. When local cooling of the cooling plate is initiated by means of control making use of a timer, cooling of a region of the cooling plate that is not covered with the molten metal may be initiated. However, if the molten metal reaches the region before the temperature of the region drops below the allowable lower limit temperature T c , formation of a blow defect can be prevented. Therefore, error in the timing for initiating cooling of the cooling plate can be neglected to some extent. After initial cooling control is carried out by means of the initial cooling control means 109' as described above, the initial cooling control means 109' sends a usual cooling initiation command to usual cooling control means 110, and the means 109' stops direct control of the first through third cooling means 104a through 104c, when it is judged that the entirety of the mold-wall-enclosed surface of the cooling plate 52 is covered with the molten metal 46, i.e. that the cooling plate can be subjected to usual cooling instead of cooling under the initial cooling conditions. The judgment time is, for example, when a predetermined period of time elapses after attainment of the cooling initiation condition that the temperature of the cooling plate detected by the first temperature detection means 105a reaches ι a , that the an increase in the temperature of the cooling plate becomes zero or positive, or that a certain period of time, which is predetermined on the basis of the structure of an actual casting apparatus, elapses. The cooling plate is cooled by the cooling power of the first through third cooling means 104a through 104c, which are controlled by the usual cooling control means 110 which has received the usual cooling initiation command. When a region to be cooled or cooling power is not controlled by the first through third cooling means 104a through 104c, cooling of the cooling plate by means of all the first through third cooling means 104a through 104σ substantially refers to the case in which the cooling plate is subjected to usual cooling. In such a case, the initial cooling control means 109' employs only the second and third cooling means 104b and 104c for initial cooling control and is allowed to judge that the cooling plate can be subjected to usual cooling when temperature data obtained by the first temperature detection means 105a show that the cooling initiation conditions are attained (e.g., the temperature of the cooling plate reaches a predetermined temperature Tι a , or an increase in the temperature becomes zero or positive). When the initial cooling control means 109 ' judges that the cooling plate can be subjected to usual cooling, it may send a usual cooling initiation command directly to the usual cooling control means 110 to thereby allow the usual cooling control means 110 to control the first through third cooling means 104a through 104c. Alternatively, instead of direct control of the first through third cooling means 104a through 104c by means of the initial cooling control means 109 ' , the means 109 ' may sequentially send a command to the usual cooling control means 110 to thereby allow the usual cooling control means to control the first through third cooling means 104a through 104c. No particular limitation is imposed on the method for sending a command from the initial cooling control means 109' to the usual cooling condition means 110, so long as cooling of the cooling plate 52 is controlled so as to satisfy the initial cooling conditions until the entirety of the mold-wall-enclosed surface of the cooling plate is covered with the molten metal. As described above, according to the metal casting process of the invention, a cooling member is cooled so as to satisfy initial cooling conditions before a mold is filled with molten metal. Therefore, a casting cycle time can be shortened while formation of a blow defect in a cast product is prevented. In addition, after the cooling member is cooled under the initial cooling conditions, usual cooling is carried out. Therefore, since solidification of the molten metal in the mold proceeds while the molten metal is fed into the mold, the resultant cast ingot is cooled rapidly as compared with the case in which a cast ingot is cooled in a conventional process. Thus, segregation of metallic components in the cast ingot is reduced. Furthermore, since a sprue is closed with an opening/closing plug immediately before closing of the sprue becomes impossible, the cast ingot has a dense metallographical structure because of the feeding effect, and formation of casting defects can be minimized. According to the metal casting apparatus of the invention, initial cooling control means controls cooling of a cooling member so as to satisfy initial cooling conditions before a mold is filled with molten metal. After the cooling member is cooled under the initial cooling conditions, usual cooling is carried out by means of usual cooling control means while the molten metal is fed into the mold. Therefore, a casting cycle time can be shortened while formation of a blow defect in a cast product is prevented. In addition, since usual cooling is carried out by means of the usual cooling control means after the cooling member is cooled under the initial cooling conditions , solidification of the molten metal in the mold proceeds orderly while the molten metal is fed into the mold. Therefore, the resultant cast ingot is cooled rapidly as compared with the case in which a cast ingot is cooled by use of a conventional casting apparatus. Thus, segregation of metallic components in the cast ingot is reduced. Furthermore, since a sprue is closed with an opening/closing plug controlled by plug opening control means immediately before most of the molten metal in the mold is solidified and closing of the sprue becomes impossible, the cast ingot has a dense structure because of the feeding effect, and formation of casting defects can be minimized. Industrial Applicability: According to the present invention, the specific gravity of an alloy is obtained on the basis of the compositional proportions of metals contained in molten metal, and the target weight of a cast body is determined on the basis of the specific gravity and the capacity of a mold. Thus, the target weight can be determined for different lots or molds. Therefore, even when lots or molds vary, cast bodies of a substantially constant volume can be produced consistently. Even when the cast body produced is subjected to forging, the mold used is not adversely affected, and the service life of the mold can be prolonged. Thus, production costs can be reduced. Furthermore, forging can be carried out reliably. In addition, the weight of a cast body to be produced can be easily regulated within a short period of time, because the weight is easier to measure than the volume. According to the invention, the specific gravity of an alloy is corrected so as to approximate the specific gravity to the real specific gravity. Thus, the target weight of a cast body can be determined accurately, and the volume of the cast body can be regulated more consistently. According to the invention, the amount of molten metal to be supplied is regulated through control of an opening/closing plug when the weight of a cast body is regulated so as to attain the target weight. Thus, the weight of the cast body can be regulated correctly and accurately. According to the invention, the weight of a cast body to be produced is measured using a sampling weight judgment apparatus. Thus, the weight of the cast body can be controlled appropriately. Furthermore, a cast ingot can be reliably provided with an identification numeral, since the measurement cycle allows sufficient time. Therefore, a casting apparatus that may possibly produce a cast body of insufficient weight can be specified reliably and promptly. According to the invention, the weight of a cast body to be produced is measured using an all-product-weight judgment apparatus that can measure the weight at high accuracy and high speed. Thus, the weight of the cast body can be controlled reliably, and invasion of a poor product can be prevented reliably. According to the invention, the weight of a cast body to be produced is measured using the all-product-weight judgment apparatus or sampling weight judgment apparatus. Thus, the weight of all cast ingots can be measured reliably, and a casting apparatus that may possibly produce a poor product can be specified promptly even when the identification numerals are not specified through all-product measurement. In this case, each apparatus exhibits its characteristics satisfactorily. Furthermore, running costs can be reduced as compared with the case in which these apparatus are employed simultaneously. According to the invention, the all-product-weight judgment apparatus is employed for measuring the weight of a cast body that has been cooled in advance such that the temperature of the cast body falls within a predetermined temperature range. Thus, the apparatus can be protected from heat. Furthermore, when the weight of the cast body is measured, water adhering to the cast body is evaporated. Thus, the dry cast body is obtained. Therefore, problems, such as measurement of the weight of the water not to be measured and corrosion of the surface of the cast ingot caused by the water, can be prevented reliably. According to the invention, the amount of molten metal supplied from a melting furnace is regulated so as to maintain the liquid level of the molten metal in a transfer trough consistent. Thus, the amount of the molten metal supplied from the melting furnace is regulated accurately, and the liquid level of the molten metal in a molten metal reservoir is barely varied. Therefore, the amount of the molten metal supplied to a mold becomes consistent, and consequently, the weight of cast ingots becomes consistent. According to the invention, the temperature of molten metal in the transfer trough and the temperature of a heating region below the transfer trough are regulated. Thus, overheating of the heating region and impairment of a heating body can be prevented. Furthermore, since the temperature of the molten metal in the transfer trough is regulated consistently, defects of cast ingots and variation in the structure of the cast ingots can be reduced, and thus the quality of the cast ingots can be enhanced. According to the invention, cast body transfer means is provided to enable a cast body placed on a cooling plate to be automatically fed to the subsequent step. Therefore, no manpower is required, and automatic operation can be realized. According to the invention, a gas discharge passage is provided on the upper surface of the cooling plate by giving roughness or slits to the surface of the cooling plate. Thus, compressed gas present between the cooling plate and molten metal supplied from above the cooling plate is discharged smoothly through the rough surface or slits to reliably prevent deformation or oxidation of a cast body, which would otherwise be caused by the existing gas . According to the invention, a gas discharge passage is provided on the cooling plate and the lower surface of the sidewall of a mold that abuts on the cooling plate. Thus, compressed gas present between the cooling plate and molten metal supplied from above the plate is discharged more smoothly through the gas discharge passages of the cooling plate and the lower surface of the sidewall of the mold to further reliably prevent deformation or oxidation of a cast body, which would otherwise be caused by the existing gas. According to the invention, a pressure equal to or higher than atmospheric pressure is generated in a junction region between the upper surface of the mold and the upper surface of a cast body through gas introduction means . Thus , an external force can be applied to the cast body rapidly and effectively. Consequently, the cast body is forcedly exfoliated from the mold to thereby allow the cast body to fall reliably. Therefore, cast bodies can be produced continuously at a rapid cycle. According to the invention, a forging apparatus and a machining apparatus are connected to an automatic continuous casting system to thereby form an automatic continuous cast- forging system including a series of casting and machining steps. A stock can be formed into a product in the system, and high productivity is realized. Therefore, the quality of the product can be maintained, and production costs can be greatly reduced. According to the invention, an automatic continuous cast-forging system includes a preliminary heating furnace provided upstream of a hot forging apparatus. Therefore, a cast body can be continuously and automatically subjected to hot forging. Through use of the preliminary heating furnace, variation in cooling of the cast body can be eliminated. Furthermore, even when the system is stopped because of breakdown of a casting apparatus or a forging apparatus. lowering of the temperature of the cast body can be prevented, and the cast body can be reliably subjected to hot forging.

Claims: CLAIMS 1. An automatic continuous casting system for producing a cast body, comprising: a casting apparatus that makes use of unidirectional solidification of molten metal and includes a molten metal reservoir (4) and a mold (5), in which molten metal in a molten metal source (2) is supplied through transfer means (3) to the molten metal reservoir, and the molten metal (45) supplied into the molten metal reservoir is supplied through an opening/closing plug (43) into the mold; target weight calculation/storing means (8) for calculating, on the basis of compositional proportions of metal elements contained in the molten metal (45), a specific gravity of an alloy obtained through solidification of the molten metal, calculating a target weight of a cast body on the basis of the specific gravity of the alloy and a capacity of the mold, and memorizing and storing the target weight; and first molten metal supply amount regulation means (9) for regulating an amount of the molten metal supplied from the molten metal reservoir into the mold by obtaining a measurement weight of the cast body and comparing the measurement weight with the target weight. 2. An automatic continuous casting system according to claim 1, wherein in the target weight calculation/storing means ( 8) , weight proportions of the metal elements contained in the molten metal are calculated on the basis of the compositional proportions of the metal elements, volume proportions of the metal elements are calculated on the basis of the calculated weight proportions and specific gravities of the metal elements known beforehand, and a specific gravity of an alloy of the metal elements is calculated on the basis of the calculated weight proportions and volume proportions of the metallic elements. 3. An automatic continuous casting system according to claim 1 , wherein the calculated specific gravity of the alloy is corrected so as to approximate the specific gravity to a real specific gravity. 4. An automatic continuous casting system according to claim 1, wherein in the first molten metal supply amount regulation means ( 9 ) , when the measurement weight is greater than the target weight, an opening time of the plug is shortened, and when the measurement weight is less than the target weight, the opening time of the plug is prolonged. 5. An automatic continuous casting system according to claim 1, wherein the molten metal in the molten metal source is supplied to a plurality of casting apparatus to thereby produce cast bodies, and a sampling weight judgment apparatus (91) is provided for sampling a cast body produced in each casting apparatus, and measuring a weight of the cast body to use the measured weight as the measurement weight. 6. An automatic continuous casting system according to claim 1, wherein the molten metal in the molten metal source is supplied to a plurality of casting apparatus to thereby produce cast bodies, and an all-produσt-weight judgment apparatus (88) is provided for measuring a total weight of the cast bodies produced in the casting apparatus to use the total weight as the measurement weight. 7. An automatic continuous casting system according to claim 1, wherein the molten metal in the molten metal source is supplied to a plurality of casting apparatus to thereby produce cast bodies, an all-product-weight judgment apparatus (88) and a sampling weight judgment apparatus (91) are provided and employed individually depending on a case involved, for measuring a weight of a cast body produced in each casting apparatus to used the measured weight as the measurement weight . 8. An automatic continuous casting system according to claim 6 or claim 77, wherein the all-product-weight judgment apparatus (88) and/or the sampling weight judgment apparatus (91) is employed for measuring a weight of a cast body which has been cooled in advance such that a temperature of the cast body falls within a predetermined temperature range. 9. An automatic continuous casting system for producing a cast body, comprising: a casting apparatus that makes use of unidirectional solidification of molten metal and includes a molten metal reservoir (4) and a mold (5), in which molten metal in a molten metal source (2) is supplied through transfer means (3) to the molten metal reservoir, and the molten metal (45) supplied into the molten metal reservoir is supplied through an opening/closing plug (43) into the mold; liquid level measurement means (31) provided on the transfer means; and second molten metal supply amount regulation means (20) for regulating an amount of the molten metal supplied from the molten metal source to the transfer means in accordance with the measured liquid level. 10. An automatic continuous casting system for producing a cast body, comprising: a casting apparatus that makes use of unidirectional solidification of molten metal and includes a molten metal reservoir (4) and a mold (5), in which molten metal in a molten metal source (2) is supplied through transfer means (3) to the molten metal reservoir, and the molten metal (45) supplied into the molten metal reservoir is supplied through an opening/closing plug (43) into the mold; molten-metal-in-trough temperature measurement means (30) for measuring a temperature of the molten metal in the transfer means; heating region temperature measurement means (TC2) for measuring a temperature of a heating region having a built-in heating body for heating the molten metal in the transfer means ; and temperature regulation means (30) for regulating, by means of on-off control of power supply to the heating body, a temperature of the molten metal so as to fall within a predetermined temperature range and a temperature of the heating region so as to be not more than the predetermined temperature . 11. An automatic continuous casting system for producing a cast body, comprising: a casting apparatus that makes use of unidirectional solidification of molten metal and includes a molten metal reservoir (4) and a mold (5), in which molten metal in a molten metal source (2) is supplied through transfer means (3) to the molten metal reservoir, and the molten metal (45) supplied into the molten metal reservoir is supplied through an opening/closing plug (43) into the mold; cast body transfer means (85) for transferring the cast body to transporting means (86, 87, 88, 89) of a subsequent step, wherein a bottom wall of the mold serves as a vertically movable cooling plate (52) with which the molten metal supplied to the mold is forcedly cooled, and a cast body formed in the mold and placed on the cooling plate moved downward is transferred to the transporting means by the cast body transfer means . 12. An automatic continuous casting system for producing a cast body, comprising: a casting apparatus that makes use of unidirectional solidification of molten metal and includes a molten metal reservoir ( 4 ) and a mold ( 5 ) , in which molten metal in a molten metal source (2) is supplied through transfer means (3) to the molten metal reservoir, and the molten metal (45) supplied into the molten metal reservoir is supplied through an opening/closing plug (43) into the mold; a bottom wall of the mold serves as a vertically movable cooling plate (52) with which the molten metal supplied to the mold is forcedly cooled, and a gas discharge passage (64) is formed on an upper surface of the cooling plate. 13. An automatic continuous casting system according to claim 12, wherein the gas discharge passage (64) is in a form of a rough surface formed on the upper surface of the cooling plate or in a form of slits formed radially on the upper surface . 14. An automatic continuous casting system according to claim 12, further comprising another gas discharge passage (S) formed on a lower surface of a sidewall (51) of the mold that abuts on the cooling plate. 15. An automatic continuous casting system for producing a cast body, comprising: a casting apparatus that makes use of unidirectional solidification of molten metal and includes a molten metal reservoir (4) and a mold (5), in which molten metal in a molten metal source (2) is supplied through transfer means (3) to the molten metal reservoir, and the molten metal (45) supplied into the molten metal reservoir is supplied through an opening/closing plug (43) into the mold; gas introduction means (64) for introducing pressurized gas between an upper surface of the mold and an upper surface of the cast body formed in the mold, in which a pressure equal to or higher than an atmospheric pressure is generated in a junction region between the upper surface of the mold and the upper surface of the cast body by introducing gas through the gas introduction means, to thereby allow the cast body to fall by means of the pressure. 16. An automatic continuous casting system according to claim 15, wherein the gas introduction means (64) can blow pressurized gas horizontally. 17. An automatic continuous casting system according to claim 15, wherein, the gas introduction means (64) can blow pressurized gas vertically. 18. An automatic continuous cast-forging system for forging a cast body into a forged body, comprising: a casting apparatus that makes use of unidirectional solidification of molten metal and includes a molten metal reservoir (4) and a mold ( 5 ) , in which molten metal in a molten metal source ( 2 ) is supplied through transfer means (3) into the molten metal reservoir, and the molten metal (45) supplied into the molten metal reservoir is supplied through an opening/closing plug (43) into the mold to produce a cast body; a forging apparatus for forging the cast body; transporting means for transporting the cast body to the forging apparatus ; and a machining apparatus for machining the cast body; wherein a series of continuous steps of supplying the molten metal into the molten metal reservoir and into the mold, transporting the cast body, forging the cast body and machining the cast body are taken continuously. 19. An automatic continuous cast-forging system according to claim 18, further comprising an alignment apparatus that aligns orientations of cast bodies before the cast bodies are transported to the forging apparatus. 20. An automatic continuous cast-forging system according to claim 19, wherein the alignment apparatus comprises a runway section on which the cast bodies rolls , a discrimination section for discriminating upper and lower surfaces of the cast bodies and supplying the cast bodies with their upper surfaces directed leftward to a left side and the cast bodies with their upper surfaces directed rightward to a right side, and an alignment section for directing upward the upper surfaces of the cast bodies put in the left and right sides and aligning the cast bodies symmetrical with each other with respect to a center line of the alignment apparatus, with their upper surfaces directed upwar . 21. An automatic continuous cast-forging system according to claim 18, further comprising a heat treatment furnace (95) provided upstream of the machining apparatus (97), and the cast body is subjected to predetermined heat treatment before machining. 22. An automatic continuous casting and forging system according to claim 18, wherein when the forging apparatus (93) is a hot forging apparatus, and further comprising a preliminary heating furnace in which the cast body is heated such that a temperature of the cast body falls within a predetermined temperature range, before the cast body is transported to the forging apparatus through the transporting means . 23. A metal casting method for producing a cast ingot, comprising charging molten metal (46) into a closed-space- definable mold (5) which comprises mold members including a cooling member (52) and in which an end surface of an opening/closing plug (43) serves as a portion of an inner wall of the mold, locally controlling removal of heat from the mold members in accordance with a shape of a cast ingot and a location and number of a sprue (42), thereby solidifying the molten metal so that a solidification interface advances to arrive at an end of an inner surface of the mold. 24. A metal casting method according to claim 23, wherein an outer surface of at least one portion of the cooling member (52) is opened during solidification of the molten metal in the mold to expose an outer surface of a cast ingot, and the exposed outer surface of the cast ingot is cooled directly with a cooling medium. 25. A metal casting apparatus for producing a cast ingot, comprising a closed-space-definable mold (5) which includes mold members including a cooling member (52) and into which molten metal is charged through a sprue (42), an opening/closing plug (43) having an end face serving as a portion of an inner wall of the mold, a cooling capacity control mechanism which imparts, to the mold members a heat removal profile appropriate for a shape of a cast ingot to be produced and for a position and number of the sprue. 26. A metal casting apparatus according to claim 25, wherein the cooling member (52) is cooled by bringing an outer surface of the cooling member into contact with a cooling medium. 27. A metal casting apparatus according to claim 25, wherein the cooling member (52) has partially different thicknesses. 28. A metal casting apparatus according to claim 25, wherein the cooling member (5) is formed with spaces (55b) therein. 29. A metal casting apparatus according to claim 25, wherein the cooling member is made of a composite material (55d) of partially different thermal conductivites . 30. A metal casting apparatus according to claim 25, further comprising at least one nozzle for jetting a cooling medium toward an outer surface of the cooling member (52) in a form of spray or shower to hit the outer surface of the cooling member. 31. A metal casting apparatus according to claim 25, wherein the cooling member (52) has an outer surface partially provided with unevenness so that an area that can contact a cooling medium locally varies. 32. A metal casting apparatus according to claim 31, wherein the unevenness comprises holes which do not communicate with an interior surface, and inclination angles of the holes are regulated in accordance with collision angles of the cooling medium jetted in the form of spray or shower and supplied to the outer surface of the cooling member. 33. A metal casting apparatus according to claim 25, further comprising means, provided on an outer surface of the cooling member (52), for enabling local prevention of a cooling medium from contacting the cooling member. 34. A metal casting apparatus according to claim 33, wherein the means is a step (55c) provided at a portion of the outer surface of the cooling member. 35. A metal casting apparatus according to claim 33, wherein the means is a heat-insulating material (55e) that partially covers the outer surface of the cooling member. 36. A metal casting apparatus according to claim 35, wherein the heat-insulating material is a species or a combination of species selected from the group consisting of rubber, ceramic material, and fibrous heat-insulating material . 37. A metal casting apparatus according to claim 25, further comprising a cooling medium circulation passage (57) provided within a portion of the cooling member (52). 38. A metal casting apparatus according to claim 26, wherein the cooling medium is a species or a combination of species selected from the group consisting of water, supercooled water of 0°C or lower, a volatile liquid and an oil. 39. A metal casting apparatus according to claim 26, wherein the cooling medium is temperature-controlled and then brought into contact with the cooling member. 40. A metal casting apparatus according to claim 26, wherein the cooling medium is controlled in terms of a history of contact with the cooling member. 41. A metal casting apparatus according to claim 25, further comprising a heater provided within a portion of the cooling member. 42. A metal casting apparatus according to claim 25, further comprising a heater provided within a portion of the mold member. 43. A metal casting apparatus according to claim 41 or claim 42, wherein the heater is a heating device making use of resistance heating, a superheated steam heater or a high- temperature gas heater. 44. A metal casting apparatus according to claim 25, further comprising a plurality of heating sections and a plurality of cooling sections provided within the cooling member and controlled in respective functions of the sections. 45. A metal casting apparatus according to claim 25, further comprising a mechanism for opening at least a portion of the cooling member during solidification of molten metal within a mold to expose an outer surface of and a cast ingot and a mechanism for supplying a cooling medium directly to the exposed outer surface. 46 A metal casting process for producing cast ingot, comprising: using a mold which includes a mold main body having at an upper portion a sprue that can be opened and closed by means of an opening/closing plug, and a cooling member serving as a bottom portion of the mold, and into which molten metal is fed through the sprue and cooled by means of the cooling member; initiating feeding of the molten metal into the mold by opening the sprue with the opening/closing plug when a temperature of the cooling member of the mold is equal to or higher than a predetermined allowable lower limit temperature; initiating cooling of the cooling member so as to satisfy initial cooling conditions that the temperature of the cooling member fed into the mold does not become lower than the allowable lower limit temperature when the molten metal is brought into contact with a surface of the cooling member that faces an inside of the mold; feeding the molten metal into the mold continuously without closing the sprue with the opening/closing plug even after the mold is filled with the molten metal; closing the sprue with the opening/closing plug before the molten metal in the mold is solidified in the vicinity of the sprue to making closing of the sprue with the plug impossible; stopping cooling of the cooling member when predetermined cooling completion conditions are attained after the sprue is closed; and detaching the cooling member from the mold main body to thereby remove a cast ingot when predetermined cast ingot removal conditions are attained after cooling of the cooling member is stopped. 47. A metal casting apparatus comprising: a mold including a mold main body having at an upper portion a sprue which can be opened and closed by means of an opening/closing plug, and a cooling member serving as a bottom portion of the mold; cooling means for cooling the cooling member of the mold; and casting control means for wholly carrying out opening/closing control of the sprue by means of the opening/closing plug, cooling control through the cooling means, and attachment/detachment control of the cooling member and the mold main body; wherein the casting control means comprises plug opening control means for opening the sprue with the opening/closing plug to thereby initiate feeding of molten metal into the mold on condition that a temperature of the cooling member is equal to or higher than a predetermined allowable lower limit temperature, initial cooling control means for controlling the cooling means so as to satisfy initial cooling conditions such that the temperature of the cooling member does not become lower than the allowable lower limit temperature when the molten metal fed into the mold is brought into contact with a surface of the cooling member that faces an inside of the mold after feeding of the molten metal is initiated through the plug opening control means , usual cooling control means for controlling the cooling means to thereby subject the cooling member to usual cooling after an entire surface of the cooling member that faces the inside of the mold is covered with the molten metal fed into the mold, plug closing control means for closing the sprue by means of the opening/closing plug to thereby stop feeding of the molten metal into the mold before the molten metal in the mold is solidified in the vicinity of the sprue to make closing of the sprue by means of the plug impossible, termination-of-cooling control means for stopping control of the cooling means by the usual cooling control means to thereby stop cooling of the cooling member when predetermined cooling completion conditions are attained after the sprue is closed through the plug closing control means, and attachment/detachment control means for detaching the cooling member from the mold main body so as to remove a cast ingot from the mold and then attaching the cooling member to the mold main body after the cast ingot is removed when predetermined cast ingot removal conditions are attained after cooling of the cooling member is stopped.

Inventors: FUKUDA MASASHI, HIRANO KUNIO, KUZUHARA TOORU, NAKAHARA TAKAFUMI, UCHIDA TOMOO, YANAGIMOTO SHIGERU, FUKUDA, MASASHI, HIRANO, KUNIO, KUZUHARA, TOORU, NAKAHORA, TAKAFUMI, UCHIDA, TOMOO, YANAGIMOTO, SHIGERU
Applicants: FUKUDA MASASHI, HIRANO KUNIO, KUZUHARA TOORU, NAKAHARA TAKAFUMI, SHOWA DENKO KK, UCHIDA TOMOO, YANAGIMOTO SHIGERU, FUKUDA, MASASHI, HIRANO, KUNIO, KUZUHARA, TOORU, NAKAHORA, TAKAFUMI, SHOWA DENKO K.K., UCHIDA, TOMOO, YANAGIMOTO, SHIGERU
Application year: 2001
Main classification: B21D39
IPC codes: B22D7, B22D9, B22D15, B22D27, B22D29, B22D39, B22D47