Process and apparatus for the production of semi-solidified metal composition

Abstract: In a process and an apparatus for stably and continuously producing a solid-liquid metal mixture in which non-dendritic primary solid particles are dispersed into the remaining liquid matrix, molten metal is charged into a clearance between a wall member (12) and a rotating agitator (1) composed of a cylindrical drum having a horizontally rotational axis.

Description: This invention relates to a process for stably and continuously producing a semi-solidified metal composition and an apparatus used therefor. The term "semi-solidified metal composition" used herein means that molten metal (generally molten alloy) is vigorously agitated while cooling so as to convert dendrites produced in the liquid matrix into a spheroidal or granular shape (which are called non-dendritic primary solid particles) such that dendritic branches are substantially eliminated or reduced, and then to disperse these primary solid particles into the liquid matrix. As the non-dendritic primary solid particles dispersed in the liquid matrix become fine, the semi-solidified metal composition develops excellent working properties in subsequent steps, such as casting or the like, and cast articles have an excellent quality. Therefore, in the production of the semi-solidified metal composition, it is required to provide the following two conditions: (1) vigorous agitation capable of breaking and separating dendrites into fine non-dendritic primary solid particles in which dendritic branches are eliminated or reduced into a generally spheroidal or granular shape; (2) strong cooling capable of increasing the cooling rate as far as possible. However, in the production of the semi-solidified metal composition, the viscosity increases together with the increase in fraction solid. Thus, it is difficult continuously to discharge the semi-solidified metal composition from the production apparatus and, finally, discharge becomes impossible. Japanese Patent Application Publication No. 56-20944 discloses a process for continuously producing such a semi-solidified metal composition, in which molten metal is cooled and vigorously agitated in a cylindrical cooling agitation vessel by means of the high-speed rotation of an agitator. This converts dendrites produced in the remaining liquid matrix into non-dendritic primary solid particles in which dendritic branches are eliminated or reduced into a spheroidal or granular shape. These non-dendritic primary solid particles are then dispersed into the liquid matrix to form a slurry of semi-solidified metal composition, which is continuously discharged from a nozzle arranged at the bottom of the cooling agitation vessel. In this process, molten metal is charged into a clearance between a high-speed rotating agitator having a vertical axis of rotation and the cylindrical cooling agitation vessel which is coaxially arranged around the agitator. Molten metal is changed into a semi-solidified state through proper cooling and vigorous agitation in the vessel, and is then continuously discharged from the nozzle as a semi-solidified metal composition. According to this process, the cooling rate is undesirably restricted to not more than 2°C/s (in case of Aℓ-10% Cu alloy) so as to prevent clogging in the clearance due to the formation and growth of a solidification shell on the cooled wall face. Furthermore, it is difficult to control the degree of agitation cooling rate and discharging rate due to the growth of the solidification shell. The inventors have examined the above technique and confirmed the following problems: (i) In order to enhance the agitating effect, it is effective to increase the revolution number of the rotating agitator or to reduce the clearance between the cooling agitation vessel and the agitator. However, when the revolution number is increased, the liquid matrix strongly tends to separate away from the agitator through centrifugal force and thereby increase the risk of entrapping gas. Also, the increase of the revolution number is critical in view of the structural strength of the apparatus. On the other hand, when the clearance is made small, a solidification shell is easily formed and the viscosity resistance increases. Thus, the clearance cannot be made small in practical use. (ii) When a strong cooling means is adopted for increasing the cooling rate, the solidification shell is formed on the cooled wall face to cause adhesion to the agitator, whereby operation is made impossible. (iii) In non-steady heat transfer, such as when heat is applied at the initial operation stage or the like, it is difficult to control temperature, and hence adhesion of the solidification shell to the agitator may be caused due to excessive cooling. That is, it is difficult stably to start the operation. (iv) When the semi-solidified metal composition is discharged under gravity, the force for passing the semi-solidified metal composition through the clearance between the cooling agitation vessel and the agitator is only based on gravity. Accordingly, discharge is impossible when the fraction solid in the semi-solidified metal composition increases to raise the viscosity thereof. Embodiments of the invention aim to solve the aforementioned problems of the conventional technique. The inventors have made various studies considering the following important conditions: (1) the agitating effect is enhanced; (2) the cooling rate is increased; (3) a homogeneous semi-solidified metal composition is continuously and easily discharged without entrapping gas and the like. In general, the agitating effect is proportional to the revolution number of the rotating agitator. That is, as the diameter of the agitator becomes larger or as the clearance between the agitator and the cooled wall face becomes smaller, a sufficient agitating effect is obtained without requiring high-speed rotation. In addition, it has been noticed that according to the conventional technique, the clearance between the agitator and the cooled wall face cannot be controlled during operation and the discharging force of the semi-solidified metal composition is only by gravity. Moreover, the rotational axis of the agitator is vertical in the conventional technique. Also in the prior art, JP-A-60-15047 discloses a casting apparatus for continuously producing a cast slab of metal. In the apparatus, molten metal is poured into the gap between a rotating cylinder having a horizontal axis of rotation and a base portion adjacent the cylinder and extending around the periphery thereof. According to a first aspect of the invention, there is provided a process for producing a semi-solidified metal composition, comprising: continuously charging molten metal into a clearance defined between a rotating agitator, which comprises a cylindrical drum, and a wall member having a concave face extending around the outer periphery of the cylindrical drum, cooling the molten metal so as to produce dendrites in the liquid matrix of the molten metal, the rotation of the agitator creating a shearing force which breaks the dendrites thereby to form a semi-solidified metal composition with fine non-dendritic primary solid particles suspended in a liquid matrix, and continuously discharging the semi-solidified metal composition from a lower part of the clearance, characterised in that the cylindrical drum, which is movable relative to the wall member, is rotated around a horizontal axis of rotation. According to a second aspect of the invention, there is provided apparatus for producing a semi-solidified metal composition, comprising: a rotatable agitator comprising a cylindrical drum; and a wall member having a concave face extending around the outer periphery of the drum to define between it and the outer periphery of the drum a clearance into which molten metal is charged, characterised in that the cylindrical drum has a horizontal axis of rotation and is movable relative to the wall member thereby to adjust the size of the clearance. For a better understanding of the invention, and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which:- Fig. 1 is a graph showing the relationship between fraction solid of a semi-solidified metal composition and apparent viscosity; Fig. 2a is a schematic perspective view illustrating a first embodiment of the apparatus according to the invention; Fig. 2b is a front view of the apparatus shown in Fig. 2a; Fig. 3 is an enlarged schematic view of a cooling/agitation portion of the apparatus shown in Fig. 2a; Fig. 4 is a schematic view of a second embodiment of the apparatus according to the invention; Fig. 5 is a schematic longitudinal sectional view of a third embodiment of the apparatus according to the invention; Fig. 6 is a schematic lateral sectional side view of a seal portion of the apparatus shown in Fig. 5; Fig. 7 is a schematic enlarged sectional view of a discharge portion in the apparatus shown in Fig. 5; Fig. 8 is a schematic view of a fourth embodiment of the apparatus according to the invention; Fig. 9 is a schematic view of a fifth embodiment of the apparatus according to the invention; Fig. 10 is a graph showing the relationship between load torque, discharging rate and time when the clearance is and is not controlled in the operation of the apparatus of first embodiment; and Fig. 11 is a graph showing the relationship between solidification rate, shear rate, discharging rate and fraction solid with respect to time in the apparatus of the second embodiment. According to the invention, the axis of rotation of the rotating agitator comprising the cylindrical drum is horizontal, so that the diameter of the agitator can be large, whereby a vigorous agitating action can be provided without considerably increasing the revolution number of the agitator. Also, when the rotating agitator is provided with water cooling means, the area for cooling molten metal is increased, so that rapid cooling can be attained. Therefore, sufficient cooling and agitating effects can be obtained. In certain embodiments, the clearance can be adjusted to be maintained at an optimum clearance for the discharge of the semi-solidified metal composition. Furthermore, the force discharging the semi-solidified metal composition from the apparatus is the sum of gravity and the force based on the rotation of the agitator, so that a semi-solidified metal composition having a higher fraction solid and viscosity can be discharged. As a result, the start of the operation is easy and troubles, such as clogging of the clearance with semi-solidified metal composition and the like, can be avoided and hence a stable and steady operation can be attained. If it is intended subsequently to supply the semi-solidified metal composition to a twin roll casting machine or the like, according to the conventional technique, it is very difficult to supply the semi-solidified metal composition uniformly between the rolls. However, according to the present invention, the semi-solidified metal composition discharged is uniform in the longitudinal direction of the agitator, so that a casting can easily be made in a twin roll casting machine. In general, it is well-known that the quality of the semi-solidified metal composition, such as crystal particle size and the like, is largely influenced by the cooling rate in the production thereof or an increasing rate of fraction solid per unit time in the solid-liquid coexisting state (hereinafter referred to as the solidification rate), the average value of rate change per unit distance of fluid depending on the agitating rate (hereinafter referred to as the shear strain rate), fraction solid and the like. In order continuously and stably to discharge a semi-solidified metal composition having a poor fluidity from the production apparatus, it is preferred to ensure that the discharge port has a given sectional area. In an apparatus for the production of a semi-solidified metal composition, comprising a cylindrical drum having a horizontal axis of rotation and a fixed wall member, it is preferred to prevent the formation and growth of a solidification shell in the cooling agitation zone and to stabilize the cooling rate, the solidification rate, the shear rate, the fraction solid and the discharging rate in order that a semi-solidified metal composition having desired quality can be continuously and stably produced over a long time. The inventors have made further studies with respect to the various factors affecting crystal particle size, fraction solid and discharging rate of desirable semi-solidified metal composition. In general, an apparent viscosity as an indication of fluidity (η) in the semi-solidified metal composition is largely influenced by the degree of suspension or fraction solid (fs) in the liquid matrix, as well as the solidification rate and shear rate in the production of the semi-solidified metal composition, as shown in Fig. 1. That is, as the fraction solid becomes higher, the viscosity becomes higher, although there is an upper limit to the fraction solid at which the semi-solidified metal composition is no longer fluid. The upper limit of fraction solid is known to become smaller as the solidification rate becomes larger or the shear rate becomes smaller. Therefore, the fraction solid or viscosity at which the semi-solidified metal composition is capable of being discharged is naturally determined by the solidification rate, the shear rate, the discharging rate and the shape of the discharge port in the apparatus, so that a semi-solidified metal composition having a fraction solid greater than the upper limit fraction solid or viscosity cannot be discharged. In order to raise the fraction solid or viscosity at which the semi-solidified metal composition can be stably and continuously discharged at given solidification rate over a long period of time, the inventors have made many experiments relating to the production of a slurry of semi-solidified metal composition under various solidification rates, agitating conditions and discharging conditions. They have also examined the relationship between cooling conditions and fraction solid in the cooling agitation of the semi-solidified metal composition, and the relationship between the state of formation of a solidification shell on the cooled wall face and the solidification rate and discharging rate. As a result, it has been found that the above problems can advantageously be solved by carefully selecting the manner of cooling at the cooling agitation portion to enable a stable discharging operation, and using a scraping member for removing a solidification shell formed on the cooled wall face. That is, according to preferred embodiments of the invention, cooling is carried out by passing cooling water through the inside of the wall member and/or the agitator, and a solidification shell formed on the outer surface of the drum is scraped off with a scraping member arranged at a discharge port for continuously discharging the semi-solidified metal composition from the lower part of the clearance. In order further to ensure stable discharging, a mechanism capable of varying the sectional shape and sectional area of the discharge port, i.e. a slide valve, is preferably arranged beneath the clearance. In this way, the semi-solidified metal composition can be held above the slide valve and the discharging rate and shape of the discharge port can be adjusted. Furthermore, a water-cooled rotating roller may be located at the lower end of the wall member beneath the clearance and be driven together with the agitator. The semi-solidified metal composition formed and collected at the lower part of the clearance can continuously pass over the water-cooled rotating roller further to cool and solidify the metal into a sheet product. In this case, the water-cooled rotating roller strongly cools and solidifies the semi-solidified metal composition, so that it is preferably made from a metal having a high heat conductivity capable of strongly conducting cooling. Moreover, when the semi-solidified metal composition is continuously discharged from the lower part of the clearance, the discharging properties thereof may largely depend on the structure of the discharge portion. Particularly, the following problems are considered to occur: (1) When the flow of the semi-solidified metal composition is changed at the discharge portion from the direction of rotation of the agitator to a direction perpendicular thereto, if the fraction solid is high, the composition accumulates at the discharge portion and eventually causes the discharge port to clog. (2) Even if the semi-solidified metal composition is discharged successfully, the discharged composition leaves the discharge port in an aggregated or scattered state, which causes the entrapment of air or gas. This becomes a serious problem in the transfer to subsequent processing steps and in the quality of final product. In order to solve these problems, one embodiment of the invention provides that the semi-solidified metal composition is discharged from the discharge port in a direction tangential to the outer periphery of the cylindrical drum onto a belt or caterpillar for continuous introduction into subsequent processing steps. It is desired that the tangential direction is horizontal to reduce the construction costs and to lower the height of the apparatus. Furthermore, the discharging rate can be controlled by adjusting the velocity of the belt or caterpillar. A first embodiment of the method and apparatus of the present invention will now be described with reference to Figs. 2a and 2b. The illustrated apparatus comprises a rotating agitator 1 comprising a cylindrical drum having a horizontal axis of rotation, a water cooling jacket 2 having a cooling wall 2a, a refractory plate 3 and a refractory side plate 4 constituting a molten metal reservoir, refractory plates 5a and 5b constituting a discharge portion, a driving mechanism 6 for adjusting the clearance between the cooling wall 2a and the rotating agitator 1, and a driving mechanism 7 for rotating the agitator 1. The agitator 1 is rotated by means of the driving mechanism 7, whereby an agitating action is applied to molten metal under cooling conditions to break dendrites produced in the remaining liquid matrix into fine non-dendritic primary solid particles, which are uniformly dispersed into the resulting semi-solidified metal composition. The diameter of the agitator 1 is determined by the amount of the semi-solidified metal composition to be discharged into the apparatus and the cooling ability of the apparatus. The cooling rate is usually controlled by having the outer surface of the agitator coated with a refractory material, but if it is intended to increase the cooling rate of the semi-solidified metal composition, the agitator 1 may be of metal and be cooled by passing cooling water through the inside thereof. Forced cooling is carried out in the water cooling jacket 2 having a cooling wall 2a by passing cooling water 11 through the inside of the jacket 2, whereby molten metal is directly cooled to a semi-solidification temperature. Furthermore, the jacket 2 is connected to a hydraulic driving mechanism 6, whereby the cooling wall 2a can be moved towards the agitator 1 in the radial direction thereof to adjust the clearance between the rotating agitator 1 and the cooling wall 2a. The refractory plate 3 located above the water cooling jacket 2 constitutes a molten metal reservoir for covering the change of the amount of molten metal 8 to be poured. The side refractory plate 4 functions to prevent leakage of molten metal and closes the side face of the jacket 2. Plate 4 is spaced slightly from the side face of the rotating agitator 1 so as to be slidable thereover. The discharge portion of the apparatus is constituted by a front refractory plate 5a and a rear refractory plate 5b extending in the longitudinal direction of the agitator 1. The resulting semi-solidified metal composition 10 is uniformly discharged from the discharge portion in the longitudinal direction of the agitator 1. In operation, molten metal is transferred by a ladle to the clearance between the rotating agitator 1 and the cooling wall 2a through a pouring nozzle. The supplied molten metal is cooled by the cooling wall 2a, while a strong shearing force is applied thereto by the rotating agitator 1. In this case, the agitator 1 is rotated so as to promote the flow of the resulting semi-solidified metal composition (as shown by an arrow A in Fig. 2a), which, together with gravity, acts as a discharging force for the semi-solidified metal composition. Thus, a semi-solidified metal composition having a high viscosity can easily and uniformly be discharged from the discharge portion. The agitator is rotated at a certain rotating rate and therefore the torque loaded to the agitator 1 is detected by means of a torque detector. Based on the detected value, the hydraulic driving mechanism 6 is actuated to move the water cooling jacket towards the rotating agitator, whereby the clearance between the cooling wall 2a and the agitator 1 is adjusted to an optimum clearance for the passing semi-solidified metal composition. Thus, a semi-solidified metal composition having a constant viscosity can be discharged, so that clogging of the semi-solidified metal composition inside the apparatus due to a rapid change in the cooling conditions can be avoided. The behaviour created in the cooling agitation zone defined by the cooling wall 2a and the rotating agitator 1 will be described in detail with reference to Fig. 3. The cooling wall 2a of the water cooling jacket 2 is made from copper plate for increasing the cooling rate as much as possible, and cooling water is passed through the inside of the jacket 2 at a high speed, so that rapid cooling can be attained. Molten metal 8 charged into the clearance between the cooling wall 2a and the rotating agitator 1 is forcibly cooled by direct contact with the cooling wall 2a to form a solidification shell 9 on the cooling wall. The thickness d of the solidification shell 9 is determined by the balance between the cooling ability and the agitating effect and becomes very unstable in operation. Particularly, the thickness of the solidification shell tends to become thicker at the start of the operation. On the other hand, the agitating effect provided by the rotation of the agitator 1 is proportional to the peripheral speed of the rotating agitator and inversely proportional to the clearance. The agitating effect is generally represented as a factor of shear rate. The rotating speed of the agitator is critical in view of gas entrapment due to centrifugal force and the structural strength of the apparatus. Thus, a peripheral speed of not less than 10 m/s is generally difficult and a higher speed rotation is not preferable from the viewpoint of safety. Therefore, in order to provide a sufficient agitating effect, it is most practical to maintain a proper clearance for molten metal (corresponding to a value obtained by subtracting the thickness (d) of the solidification shell from the clearance (c) of the apparatus in Fig. 3). When the solidification shell 9 is formed to a thickness (d) by strong cooling, the actual effective clearance is narrow (c-d) with respect to-the clearance (c) of the apparatus. Since such an actual clearance is very unstable if it is too narrow, the viscosity of the semi-solidified metal composition increases and creates excessive torque in the agitator. Thus there is a danger of the semi-solidified metal composition adhering to the agitator. In this connection, the conventional technique could not provide a sufficient agitating effect because the clearance (c) was made large in view of the design safety. On the other hand, according to the invention, the water cooling jacket 2 can be moved towards the agitator 1 to adjust the clearance (c), so that a sufficient agitating effect can be obtained. Fig. 4 illustrates a second embodiment of the apparatus of the invention, in which numeral 1 is a rotating agitator comprising a cylindrical drum, numeral 12 is a movable wall member made from a refractory material, numeral 3 is a refractory plate constituting a molten metal reservoir, numeral 4 is a side refractory plate constituting a side wall of the reservoir, numeral 5 is a refractory plate constituting a discharge port 13 together with the lower part of the wall member 12, numeral 6 is a driving mechanism for adjusting the position of the wall member 12, numeral 8 is molten metal, numeral 9 is a solidification shell, numeral 10 is a semi-solidified metal composition, numeral 11 is a cooling water system, numeral 14 is a heater for heating the wall member 12, numeral 15 is a ladle, numeral 16 is a pouring nozzle, numeral 17 is shaping rolls, numeral 18 is a scraping member, numeral 19 is a driving mechanism for adjusting the position of the scraping member 18, and numeral 20 is a strip of semi-solidified metal composition 10. In the illustrated embodiment, the wall member 12 has a concave face running along the outer peripheral surface of the cylindrical drum as the agitator 1 and serves as an adiabatic wall. In order to enlarge the clearance between the wall member and the agitator according to the fluidity of the semi-solidified metal composition as previously mentioned in Fig. 1, the temperature of the semi-solidified metal composition is measured by means of a thermometer (not shown) arranged in the discharge port 13. From the temperature, the fraction solid of the discharged semi-solidified metal composition is calculated according to an equilibrium phase diagram. Also, the load torque of the agitator is simultaneously measured by means of a torque detector (not shown) and the revolution speed of the shaping roll 17 or the discharging rate of the semi-solidified metal composition is measured by means of a load cell (not shown) attached to a receiver for the semi-solidified metal composition. Based on these measured values of the fraction solid, load torque and discharging rate, the wall member is moved radially towards the agitator to adjust the clearance between the wall member and the agitator so that, at the discharging portion, there is a degree of an opening sufficient to provide given fraction solid and discharging rate. Thus, a semi-solidified metal composition having a given fraction solid can continuously and stably be discharged at a given discharging rate. In the illustrated embodiment, the agitator 1 comprises a cylindrical drum having a horizontal axis of rotation. The drum is provided with a cooling water system 11 therein, and is rotated by means of a driving mechanism (not shown) connected to the rotational axis thereof, whereby the agitating effect is applied to molten metal under cooling conditions to form a semi-solidified metal composition having fine non-dendritic primary solid particles uniformly dispersed therein. In the discharge port 13, solidification shells or semi-solidified shells 9 adhered to the outer periphery of the rotating agitator 1 are scraped by means of the scraping member 18 which is made from a heat-resistant tool steel or the like, thereby to promote the separation and discharge of the semi-solidified metal composition from the agitator 1. The molten metal 8 transferred through the pouring nozzle 16 of ladle 15 is discharged into a clearance between the agitator 1 and the wall member 12. Here it is cooled by the water cooling system 11 in the agitator 1 and simultaneously subjected to strong shearing forces by the agitator 1 to form a slurry of semi-solidified metal composition 10 with fine non-dendritic primary solid particles suspended therein. In the discharge of such a semi-solidified metal composition 10 from the apparatus, the clearance between the agitator 1 and the wall member 12 is adjusted to an optimum value by moving the wall member 12 radially towards the agitator 1 as mentioned above, so that the clogging inside the apparatus can be avoided. In order to increase the adiabatic effect, a heater 14 is preferably arranged in the wall member 12, whereby the fraction solid of the discharged semi-solidified metal composition can be adjusted to a given value. Moreover, it is desirable that the driving mechanism 19 for moving the scraping member 18 towards the agitator 1 is connected to the scraping member 18 so that a part of the solidification shell 9 is left adhered to the outer periphery of the agitator 1 so as to protect the surface of the agitator 1 which contacts the molten metal 8. In this case, the agitator 1 is rotated so as to promote the discharge of the semi-solidified metal composition 10, while the solidification shell adhered to the outer periphery of the agitator 1 and the semi-solidified metal composition are peeled off by the scraping member 18 to maintain at the same level the surface of the agitator 1 and therefore the sectional area of the discharge portion 13. Thus the cooling conditions and the discharging rate are uniform and hence a semi-solidified metal composition having a higher viscosity can continuously and stably be discharged. Particularly, the scraping member 18 is preferably arranged at a distance of not more than 2 mm from the outer surface of the drum to leave a part of the solidification shell on the outer surface of the agitator 1 as a coating. In this way, the service life of the agitator 1 can be prolonged by preventing damage to the agitator due to the reaction with molten metal or semi-solidified metal or the like. A third embodiment of the apparatus of the invention will now be described with reference to Figs. 5-7. The apparatus comprises a rotating agitator 1 comprising a cylindrical drum having a horizontal axis of rotation and provided with a water cooling system 11, a wall member 21 lined with a refractory material 21a and having a concave face around the outer periphery of the agitator 1, a water-cooled roller 22 having an axis of rotation parallel to the axis of rotation of the agitator 1, a scraper 23 and a refractory side plate 4 provided at its outer face with a sealing push member 4a. The rotating agitator 1 is formed by fitting a ceramic sleeve lb onto a roller body la or by coating the roller body la with a ceramic material lb. The agitator 1 can be cooled by passing cooling water 11 through the inside of the agitator and can be heated by means of a heating member 24 such as gas burner or the like. Furthermore, the surface temperature of the drum is measured by means of a temperature detecting device 25, whereby the heat supplied to the agitator is adjusted so as to maintain a given surface temperature and to control the cooling ability of the apparatus. A clearance is defined by the rotating agitator 1, the wall member 21 and the side refractory plate 4. The wall member 21 is lined with a refractory material or ceramic 21a so as not to apply excessive cooling to molten metal 8 and may be preliminarily heated by means of a heating member (not shown). The sealing push member 4a is closed onto the side face of the wall member 21 together with the side refractory plate 4 by means of a spring or the like and is slidably attached to the side face of the agitator 1 to seal molten metal 8 therein. Moreover, it is preferable that the wall member 21 can be moved by means of a screw, hydraulic cylinder or the like to adjust the clearance between the agitator and the wall member. At the lower end of the discharge portion of the wall member 21 is arranged a water-cooled rotating roller 22 integrally united with the wall member and spaced from the rotating agitator 1. The roller 22 is rotated in a direction to discharge the semi-solidified metal composition, i.e. the direction shown by arrow B (the rotating direction of the agitator 1 is shown by an arrow A). Roller 22 is driven by means of the same driving mechanism that drives the agitator l or by different driving mechanism (not shown) at a peripheral speed that is lower than that of the agitator l. The water-cooled rotating roller 22 acts strongly to cool the semi-solidified metal composition contacting with the surface thereof so as to solidify the composition into a sheet strip. Thus, the roller 22 may be made from a metal having a high heat conductivity such as Cu or the like and the strong cooling may be conducted by passing cooling water through the inside of the roller 22. A semi-solidified metal composition is produced by using the apparatus of Figs. 5-7 as follows. First, molten metal 8 is continuously charged from the upper part of the apparatus into the clearance between the agitator 1 and the wall member 21. The molten metal 8 is subjected to a strong agitating effect by the rotating agitator 1 under appropriate cooling conditions to form a semi-solidified metal composition 10 containing fine non-dendritic primary solid particles dispersed therein. The semi-solidified metal composition 10 is moved in a discharging direction with the fraction solid increasing through the rotation of the agitator 1 thereby to obtain a semi-solidified metal composition having a given fraction solid at the discharge portion of the apparatus. Such a semi-solidified metal composition 10 is strongly cooled by contact with the water-cooled roller 22 rotating in synchrony with the agitator 1 and is then continuously discharged in form of a strip. In order to prevent the strip 10 winding around the agitator 1, the scraper 23 is arranged so as to contact the outer peripheral surface of the agitator 1. Thus, the strip 10 is peeled off from the outer surface of the agitator 1 by the scraper 23 and is continuously discharged in a given direction. The most important action in the discharge portion in this apparatus will be described in detail with reference to Fig. 7. The semi-solidified metal composition 10 produced in the clearance between the agitator 1 and the wall member 21 is obtained by uniformly dispersing non-dendritic primary solid particles 10a into the remaining liquid matrix. This moves in the discharging direction and is further cooled to form a semi-solidified metal composition having a given fraction solid at the discharge portion. This semi-solidified metal composition 10 is strongly cooled by contacting the water-cooled roller 22 rotating in the direction of arrow B and is continuously discharged as a strip. The discharging amount of the strip of the semi-solidified metal composition 10 is represented by [drum width of the rotating agitator l] x [space between the agitator 1 and the water-cooled rotating roller 22] x [peripheral speed of the roller 22], so that when the peripheral speed of the roller 22 is held at a constant value, there is a constant discharge. Moreover, the portion of the water-cooled rotating roller 22 contributing to the cooling of the metal is a narrow surface region defined by a line drawn from the axis of the roller to the discharge end C of the wall member 21 and a line drawn from the axis of the roller to the kissing end of the roller 22. The respective lines intersect at an angle α. Before the semi-solidified metal composition arrives at this region, most of the latent heat thereof has previously been released, so that the cooling sufficient for solidification and shaping into strip can be conducted in this region. On the other hand, the respective peripheral speeds of the agitator l and the water-cooled rotating roller 22 may be same, but in order to provide an agitating force sufficient for the formation of the semi-solidified metal composition, the peripheral speed of the agitator 1 is preferably larger than that of the roller 22, whereby a strip of semi-solidified metal composition having a good quality is obtained. A fourth embodiment of the apparatus of the invention is shown in Fig. 8, wherein the reference numerals indicate like parts to those indicated by the same reference numerals in Fig. 4. In addition, numeral 27 is a thermometer, numeral 28 is a slide valve, and numeral 29 is an operating mechanism for the slide valve. The illustrated apparatus is operated in the same manner as the apparatus of Fig. 4. In this case, the shape of the discharge portion 13 can be adjusted by the slide valve 28 arranged beneath the clearance between the agitator 1 and the wall member 12 by means of the operating mechanism 29. Furthermore, the temperature of the semi-solidified metal composition is measured by means of the thermometer 27, from which the discharged fraction solid is calculated according to an equilibrium phase diagram, while the load torque of the agitator 1 is measured by a torque detecting device (not shown). Based on these measured values, the slide valve 28 is adjusted by means of the operating mechanism 29 so as to provide a given rate of discharge. Thus, a semi-solidified metal composition having a certain fraction solid can stably and continuously be discharged and also clogging of the apparatus can be prevented. The shape in the nozzle of the slide valve 28 can be selected from rectangle, circle and the like, if necessary. Fig. 9 shows a fifth embodiment of the apparatus of the invention. Numeral 1 represents a rotating agitator comprising a cylindrical drum having a horizontal axis of rotation and provided with a water cooling system, numeral 21 a wall member having a concave face around the outer periphery of the agitator 1, numeral 15 is a ladle for molten metal 8 and numeral 23 is a scraper. In the illustrated apparatus, molten metal 8 is poured from the ladle 15 into the clearance defined between the agitator 1 and the wall member 21, where it is agitated and cooled to form a semi-solidified metal composition 10. The semi-solidified metal composition 10 is discharged in a direction tangential to the direction of rotation of the agitator 1 and moved onto a belt 31 driven by drive rollers 30, which are arranged beneath the discharging port of the clearance, towards the outside of the apparatus. The discharged semi-solidified metal composition 10 is passed through shaping rolls 17 to obtain a strip of semi-solidified metal composition 10. Thus, the semi-solidified metal composition 10 can smoothly and continuously be discharged without causing clogging in the vicinity of the discharge port and the like. As a result, there is caused no entrapment of atmosphere in the semi-solidified metal composition and the like. Furthermore, the transferring rate of the belt 31 can be changed by changing the rotating speed of the drive rollers 30, whereby the discharge rate of the semi-solidified metal composition can be adjusted and hence the fraction solid thereof can easily be controlled. In the aforementioned apparatuses, a strip of semi-solidified metal composition having a larger width can easily be obtained by enlarging the longitudinal lengths of the agitator and wall member. The following examples are given as illustrations of the invention and are not intended as limitations thereof. Example 1 In this example, a strip of semi-solidified metal composition was continuously produced using an apparatus as shown in Fig. 2 and a twin roll casting machine. Molten metal 8 was charged from a ladle through a pouring nozzle into a clearance of about 10 mm defined between a rotating agitator 1 comprising of a cylindrical drum having a radius of 500 mm and a length of 1000 mm, and a water-cooled copper wall member 2. The size of the clearance was controlled by adjusting the position of the wall member 2 according to the load torque of the agitator. The agitator was rotated at 100 rpm under cooling conditions to form a semi-solidified metal composition having a fraction solid of 0.3. Then, the semi-solidified metal composition 10 was continuously discharged from the apparatus and fed into a twin roll casting machine having a roll radius of 300 mm and a length of 700 mm to form a cast strip having a thickness of 3 mm and a width of 500 mm. Fig. 10 shows the effect of controlling the clearance between the rotating agitator and the water cooled wall member, in which dotted lines show the change of load torque of the agitator and the discharging rate of the semi-solidified metal composition when the clearance is fixed at 10 mm. As seen from Fig. 10, in the case where there is no control over the clearance, the load torque changes in accordance with the temperature change of molten metal charged, cooling change of the wall member and the like, and finally the load torque considerably increases and further discharge becomes impossible resulting in clogging. On the other hand, as shown by a solid line in Fig. 10, when the clearance is controlled by detecting the load torque of the agitator, the load torque is maintained at an approximately constant value and hence the semi-solidified metal composition having a fraction solid of 0.3 is stably discharged. Example 2 A semi-solidified metal composition was produced from molten Al-4.5% Cu alloy by using the apparatus shown in Fig. 4. The molten metal was poured into a clearance of 5 mm defined between the refractory wall member 12 and the agitator 1 in the discharge portion 13. The agitator 1 had an outer diameter of 400 mm and was rotated at 250 rpm while cooling under conditions that the average solidification rate was 3.0%/s. In this way, a semi-solidified metal composition was formed. The temperature of the resulting semi-solidified metal composition discharged from the discharge portion 13 was measured by means of a thermometer (not shown), from which the fraction solid was calculated to be 25% according to an equilibrium phase diagram. Thus, the semi-solidified metal composition could continuously and stably be produced and discharged without causing clogging of the clearance. Fig. 11 shows a comparison between Example 2 (solid line) and a Comparative Example in which there was no clearance control (dotted lines), in changes of fraction solid and discharging rate with the lapse of time. As seen from Fig. 11, the fraction solid and the discharging rate become stable in the invention, while in the comparative example, the changes of the fraction solid and discharging rate cause clogging of the apparatus and stop the discharge of the semi-solidified metal composition. Example 3 A semi-solidified metal composition was produced from molten Al-10% Cu alloy in the same manner as in Example 2. The molten metal was poured into a clearance of 5 mm defined between the refractory wall member 12 and the agitator 1 in the discharge portion 13. The agitator 1 was rotated at 120 rpm while cooling under a conditions that the average solidification rate was 0.45%/s, whereby a semi-solidified metal composition was formed. Furthermore, the scraping member 18 was arranged at a distance of 1 mm from the agitator 1 so as to form a coating of solidification shell having a thickness of 1 mm on the outer surface of the agitator 1. As a result, a semi-solidified metal composition having a fraction solid of 32% as calculated from the temperature measured at the discharge portion 13 could continuously and stably be produced and discharged. Example 4 A semi-solidified metal composition was continuously produced from molten Al-10% Cu alloy by using the apparatus shown in Fig. 5. First, molten metal was poured at about 700°C into a clearance of 5 mm defined between the water cooled rotating agitator l comprising a cylindrical drum having a diameter of 400 mm and a drum width of 100 mm and the wall member 21. The wall member was preliminarily heated to 550°C by means of a gas burner and the outer surface of the drum was heated to 530°C, the agitator being rotated at 100 rpm (peripheral speed: 2093 mm/s) under a controlled cooling state of 600 kcal/min without the water-cooled rotating roller. As a result, a semi-solidified metal composition having a fraction solid of 0.2 and a good quality could be produced, but it was actually difficult continuously to discharge this semi-solidified metal composition because the composition was substantially at the state just before the loss of fluidity. A water-cooled rotating roller 22 having a diameter of 150 mm was arranged at the lower end portion of the wall member 21, spaced 2 mm from the agitator 1 and rotated at 100 rpm (peripheral speed: 785 mm/s) in synchronism with the agitator 1 under a cooling condition of 400 kcal/min. As a result, a strip of semi-solidified metal composition having a thickness of 2 mm and a width of 100 mm was continuously discharged from the apparatus of Fig. 5 at a discharging rate of about 785 mm/s. The thus obtained strip was in a substantially solidified state and had sufficient strength to be continuously wound into a coil. Example 5 A semi-solidified metal composition was continuously produced from molten Al-4.5% Cu alloy by using the apparatus shown in Fig. 8. First, molten metal was poured into a clearance of 5 mm defined between the water-cooled rotating agitator 1 comprising a cylindrical drum having an outer diameter of 400 mm and the wall member 21. The agitator 1 was rotated at 250 rpm while cooling under conditions that the average solidification rate was 3.1%/s. The slide valve 19 having a diameter of 20 mm was arranged beneath the discharge portion 13 so as to have a nozzle opening degree of 10 mm, while the temperature of the resulting semi-solidified metal composition was continuously measured by means of the thermometer 27, from which a fraction solid was calculated to be 0.27 according to an equilibrium phase diagram. Thus, the semi-solidified metal composition could continuously and stably be produced and discharged without causing clogging of the apparatus. Example 6 A semi-solidified metal composition was continuously produced from molten Al-10% Cu alloy in the same manner as in Example 5. In this case, molten metal was poured into a clearance of 5 mm defined between the water-cooled rotating agitator 1 and the wall member 21. The agitator 1 was rotated at 120 rpm while cooling under conditions that the average solidification rate was 0.46%/s. The resulting semi-solidified metal composition was discharged through the slide valve 28 with a diameter of 20 mm and a nozzle opening degree of 10 mm. A self-coating solidification shell of 1 mm onto the outer surface of the agitator 1 was formed on the agitator 1 by arranging the scraping member 18 at a distance of 1 mm therefrom. Thus, a semi-solidified metal composition having a fraction solid of 0.31 as calculated from a temperature measured at the discharge portion could stably be produced and discharged. Example 7 A semi-solidified metal composition was produced from molten Al-10% Cu alloy by using the apparatus shown in Fig. 9. In this case, the rotating agitator 1 comprised a cylindrical drum having a horizontal axis of rotation, a diameter of 400 mm and a width of 100 mm and was arranged adjacent the wall member 21 so as to form an outlet size of 5 mm in a clearance defined therebetween. The molten metal was continuously poured into the clearance at about 700°C, and the agitator 1 was rotated at 100 rpm to form a semi-solidified metal composition having a fraction solid of 0.3. In the conventional technique of discharging downwardly by gravity, a semi-solidified metal composition having such a high fraction solid could not be discharged because the viscosity thereof was too high. However, in the apparatus of Fig. 9, the semi-solidified metal composition could be continuously discharged by horizontally guiding the flow of the semi-solidified metal composition in a direction tangential to the outer periphery of the agitator l and simultaneously taking it away by means of the belt drive system 30, 31. As mentioned above, the invention has the following merits in the production of the semi-solidified metal composition: (1) It is possible to conduct a strong cooling operation at an optimum minimum clearance for the agitation effect and for safety. Thus the cooling rate can be not less than 3°C/s (in case of Aℓ-10% Cu alloy) and a semi-solidified metal composition containing fine non-dendritic primary solid particles therein and having improved properties can be produced. In particular, the productivity is high and practical because of the strong cooling. (2) Since agitation is carried out at an optimum minimum clearance, sufficient agitating effect is attained even when the speed of rotation of the cylindrical drum is slow compared with the conventional technique. This also reduces significantly the risk of entrapping gas during and many problems with respect to the structure, strength and safeness of the apparatus. (3) The quality of the semi-solidified metal composition is stabilized because the operation can be carried out at an optimum minimum clearance and cooling rate. (4) The operation can easily cope with the excessive formation of a solidification shell in a non-steady state in the initial operation stages. Furthermore, since the load torque is constantly controlled in the continuous operation, there is no trouble, such as adhesion or clogging of semi-solidified metal composition in the apparatus. (5) When the semi-solidified metal composition is discharged onto a twin roll casting machine, it can uniformly be supplied in the widthwise direction of the machine, so that it is possible to produce thin and homogeneous metal sheets having excellent properties. (6) When the water-cooled rotating roller is arranged at discharge end of the-apparatus, a strip of the semi-solidified metal composition can continuously and stably be produced, so that it largely contributes to the practicability of semi-solidified working process. (7) A self-coating of solidification shell can be formed on the surface of the rotating agitator used under severe conditions, so that the service life of the agitator can be prolonged and also the agitator can be made of a wider variety of materials. (8) The semi-solidified metal composition can be continuously and stably produced and discharged from the apparatus, even when it is poor in fluidity and high in solidification rate, so that a stable operation can be attained without causing clogging inside the apparatus.

Claims: A process for producing a semi-solidified metal composition, comprising: continuously charging molten metal (8) into a clearance defined between a rotating agitator (1), which comprises a cylindrical drum, and a wall member (2a) having a concave face extending around the outer periphery of the cylindrical drum, cooling the molten metal (8) so as to produce dendrites in the liquid matrix of the molten metal, the rotation of the agitator creating a shearing force which breaks the dendrites thereby to form a semi-solidified metal composition with fine non-dendritic primary solid particles suspended in a liquid matrix, and continuously discharging the semi-solidified metal composition (10) from a lower part of the clearance, characterised in that the cylindrical drum, which is movable relative to the wall member, is rotated around a horizontal axis of rotation. A process as claimed in claim 1, wherein cooling is carried out by passing cooling water (11) through the inside of the agitator (1) and/or the inside of the wall member (2a). A process as claimed in claim 1 or claim 2, wherein the viscosity of the semi-solidified metal composition (10) is maintained by detecting the load torque of the agitator (1) and adjusting the size of the clearance by moving the agitator (1) or the wall member (2a) according to the detected torque. A process as claimed in claim 1, 2 or 3, further comprising scraping off a solidification shell adhered to the outer peripheral surface of the drum by means of a scraping member (18; 23) arranged adjacent the drum at a discharge port (13) for continuously discharging the semi-solidified metal composition (10) from the lower part of the clearance. A process as claimed in claim 4, wherein the semi-solidified metal composition (10) is passed over a water-cooled rotating roller (22) located opposite the scraping member (18; 23) at the lower end of the wall member (2a) below the clearance, the water-cooled rotating roller (22) having an axis of rotation that is parallel to the axis of rotation of the cylindrical drum. A process as claimed in claim 5, wherein the peripheral speed of the cylindrical drum is higher than that of the water-cooled rotating roller (22). A process as claimed in claim 4, wherein the shape of the discharge port (13) is adjusted by a slide valve (28) arranged beneath the clearance to adjust the rate of discharge of the semi-solidified metal composition (10). A process as claimed in any one of claims 1 to 4, wherein the semi-solidified metal composition (10) is horizontally discharged in a direction tangential to the outer periphery of the cylindrical drum onto a belt (31) for continuous introduction into subsequent processing steps, the rate of discharge of the semi-solidified metal composition (10) being adjusted by controlling the take-up velocity of the belt (31). Apparatus for producing a semi-solidified metal composition, comprising: a rotatable agitator (1) comprising a cylindrical drum; and a wall member (2a) having a concave face extending around the outer periphery of the drum to define between it and the outer periphery of the drum a clearance into which molten metal is charged, characterised in that the cylindrical drum has a horizontal axis of rotation and is movable relative to the wall member thereby to adjust the size of the clearance. Apparatus as claimed in claim 9, further comprising a torque detector arranged on the axis of rotation of the cylindrical drum. Apparatus as claimed in claim 9 or claim 10, further comprising cooling means (11) arranged inside the wall member (2a) and/or the agitator (1). Apparatus as claimed in claim 9, 10 or 11, further comprising scraping means (18; 23), for scraping off a solidification shell adhered to the outer peripheral surface of the cylindrical drum, arranged adjacent the outer peripheral surface of the cylindrical drum below the clearance. Apparatus as claimed in claim 12, further comprising a water-cooled rotating roller (22) located opposite the scraping member (23) at the lower end of the wall member (2a) below the clearance, the axis of rotation of the water-cooled rotating roller (22) being parallel to the axis of rotation of the cylindrical drum. Apparatus as claimed in any one of claims 9 to 13, further comprising a slide valve (28) arranged beneath the clearance to adjust the rate of discharge of the semi-solidified metal composition (10).

Inventors: FUJIKAWA YASUO, HIRAI MASAZUMI, KIUCHI MANABU, NANBA AKIHIKO, NODA MASATO, YAMAGUCHI RYUJI, FUJIKAWA, YASUO, HIRAI, MASAZUMI, KIUCHI, MANABU, NANBA, AKIHIKO, NODA, MASATO, YAMAGUCHI, RYUJI, Fujikawa, Yasuo, c/o Rheo Technology, Ltd., Hirai, Masazumi, c/o Rheo Technology, Ltd., Nanba, Akihiko, c/o Rheo Technology, Ltd., Noda, Masato, c/o Rheo Technology, Ltd., Yamaguchi, Ryuji, c/o Rheo Technology, Ltd.
Applicants: RHEO TECHNOLOGY LTD, RHEO-TECHNOLOGY, LTD
Application year: 1991
Main classification: B22D11
IPC codes: B22D11