Metal plate rolling apparatus

Abstract: A metal plate rolling apparatus equipped with a direct resistance heating means is disclosed, which comprises a first pair of pinch rolls (4-1,4-2) provided on the inlet side of the rolling apparatus and connected to an electric source (5), and a pair of electrically grounded work rolls (2-1,2-2) installed in the apparatus.

Description: The present invention relates to a metal plate rolling apparatus in which a metal plate, sheet, or strip to be rolled is heated to a predetermined temperature by directly applying an electric current to the metal plate, sheet, or strip during rolling. Metal plate, metal sheet, and metal strip are collectively referred to as metal plate hereunder. Metal plates such as steel plates are usually heated in a heating furnace and then are passed into a rolling mill when hot or warm rolling is carried out. Alternatively, in certain cases a metal plate may be heated before rolling by an induction heating device employed in the rolling line with or without using a conventional heating furnace. It is extremely important to heat metal plates to a specified temperature before rolling. When the heating temperature is much lower than the specified one, many difficulties may occur such that it is hard to carry out rolling, excess loads are imposed on the rolling mill, and desirable properties cannot be obtained for the rolled plates. A metal plate is cooled due to heat radiation while the metal plate is being transferred to a rolling mill after being discharged from a heating furnace. The metal plate is further cooled when it is contacted with a work roll just before rolling. Therefore, the metal plate is heated to a temperature which is determined by taking into account such a decrease in temperature. However, if an excessively high temperature is set as the heating temperature, not only an increase in scale loss but an increase in energy costs are inevitable. Furthermore, it is rather difficult to estimate the decrease in temperature after heating, so it is also difficult to adjust the temperature of metal plate to a predetermined one during rolling even if a higher, precisely-predetermined temperature is previously set. Under these circumstances, it is advisable to heat metal plates while in a location as close as possible to a rolling mill, i.e., to heat metal plates to a predetermined temperature during rolling. For such purposes it is conceivable to employ induction heating. However, such a heating method requires a complicated control system for electric current, for example, making the heating apparatus expensive. The heating efficiency, i.e., the ratio of generated thermal energy to the electric energy supplied, is as low as about 30%. In a very special case, such as in the production of steel wires, direct resistance heating is practiced. An electric current is directly supplied to a rolling material so as to heat the rolling material to a rolling temperature by Joule heat. However, application of direct resistance heating to a metal plate, such as steel sheet and steel strip, is quite difficult. Furthermore, when the hot rolling of steel sheet in which the temperature of the rolling material increases to higher than 1000°C is carried out, the steel easily reacts with oxygen in air to form scale, resulting in a decrease in product yield. Gases, such as nitrogen gas in air also penetrate into rolling materials, resulting in a degradation in the properties of rolled products. Although it is possible to remove scale by means of pickling, for example, after rolling, additional equipment and operations are required, making production costly. In order to avoid such disadvantages it is conceivable to employ a vacuum or an inert gas atmosphere to cover the whole line of rolling so as not to allow the rolling material to contact air. However, this idea is not practical, since an unjustified, vast investment is necessary. Publication DE-C-702 241 discloses a metal product rolling apparatus comprising a pair of pinch rolls provided on the inlet side of the rolling apparatus and connected to an electric source and a pair of work rolls installed in the apparatus. Figure 1a and Figure 1b illustrate a conventional direct resistance heating system employed for hot rolling of wire 15 using a grooved roll which serves as an electric current supply roll 14. As shown in section in Figure 1a, a wire 15 contacts the roll 14 in the groove 16. Since the wire contacts the roll 14 along the periphery at an angle of α, the contact area between the wire and the roll is enlarged, and an electric current supplied through the roll to the wire effectively heats the wire. It is desirable to supply as much electric current as possible in order to effect as rapid heating as possible. However, from a practical viewpoint, the current density of an electric current to be supplied to the roll is limited to 2 A/mm 2 so as to achieve a stable supply of electric current while suppressing occurrence of flashing or sparking between the wire and roll. In the arrangement shown in Figures 1a and 1b, the contact area between the wire and roll can be expressed by the following formula: S = (πd/2) x 2πR(α/360) = (π 2 dαR)/360 wherein, d: wire diameter R: roll radius α: winding angle Provided that d= 2 mm, R= 50 mm, α= 120°, the contact area S can be calculated to be S= 329 mm 2 . Thus, if the upper limit of the electric current to be supplied is restricted to 2 A/mm 2 , a supply of electric current of about 658 A can be achieved. In addition, since the volume of wire per unit length (1 mm) is about 3 mm 3 , the heat content of the wire is small and it is easy to heat it rapidly. In contrast, in the case of plate, it is rather difficult to wind it around a roll in the manner shown in Figure 1b due to irregularities in shape, such as edge waves and middle waviness. In this respect, it is to be noted that the roll should contact a flat surface of the plate. Even if a pair of pinch rolls is used, the contact length is too short to thoroughly heat the plate. Provided that the plate width is 100 mm and the thickness is 0.5 mm, then the contact area S is 10 mm 2 , and the volume per unit length is 50 mm 3 . According to these dimensions, when the current density is 2 A/mm 2 at maximum, the upper limit of electric current is 20 A per roll, so that it is impossible to effect rapid heating of a steel plate having a large heat content. Thus, in the case of plate it is impossible to increase the contact area between the roll and plate, and supply of a large electric current, which is necessary to achieve a rapid heating of plate, is also impossible. Furthermore, since a plate has irregularities in shape, when the roll contacts the plate, the presence of non-uniform contact and gaps between the roll and plate in the widthwise direction are inevitable. Disadvantages, such as formation of flaws caused by sparking, and non-uniform temperature distribution in the widthwise direction are fatal. Japanese Unexamined Published Patent Application Specification No.183706/1988 discloses a rolling mill equipped with a direct resistance heating system. A sketch of this apparatus is shown in Figure 2, in which a rolling material 1 is contacted with a pair of work rolls 2, 2 which serve as positive and negative electrodes, respectively, and through which an electric current is supplied from the positive electrode to the negative electrode via the rolling material 1. Thus, not only the rolling material, but also the work rolls themselves are heated. According to this apparatus, at least one of the electrodes, i.e., work rolls 2, 2 should be electrically isolated from the environment, such as the housing and drive systems. Such isolation of work rolls is costly, since large loads are applied to the work rolls, and high techniques are required with respect to the materials and mechanism to be employed for isolation. Furthermore, according to this arrangement, since the rolling material is heated only by an electric current which is passed in the direction of thickness of the plate through a very limited, narrow area between the upper and lower rolls, there is a need of a large capacity electric source, i.e., a large-scale electric current source in order to generate a large amount of Joule heat. SUMMARY OF THE INVENTION An object of the present invention is to provide a metal plate rolling apparatus with which it is possible to control a rolling temperature precisely by effecting rapid heating within a rolling line, resulting in a decrease in energy costs as well as material costs and in a uniforme temperature distribution in the widthwise direction. A more specific object of the present invention is to provide a metal plate rolling apparatus in which an electric current is directly supplied to a rolling material so as to directly heat the material. Another object of the present invention is to provide a rolling apparatus in which rolling and heat treatment can be conducted simultaneously in the same production line. Still another object of the present invention is to provide a metal plate rolling apparatus in which an inert atmosphere may be employed and rapid cooling can be achieved after rolling so that a rolling material at a high temperature does not contact ambient air. Thus, the present invention is a metal plate rolling apparatus which comprises a first pair of pinch rolls which are provided on the inlet side of the rolling apparatus and connected to an electric source, and a pair of work rolls, characterized in that said work rolls are electrically grounded and in that at least one of the pinch rolls is movable in the widthwise direction. In a preferred embodiment, the apparatus further comprises a pair of pinch rolls which are provided on the outlet side of the rolling apparatus and are connected to an electric source. The apparatus may comprise one or more additional pairs of pinch rolls which are provided upstream of the first ones on the inlet side of the rolling apparatus and which are grounded. The metal plate rolling apparatus may comprise a fluid injection means, i.e., a gas or liquid injection means either on the inlet or outlet side of the rolling apparatus. In this embodiment, the work rolls and the surroundings may be isolated from the ambient air, or metal plate may be cooled immediately after the rolling. The metal plate used includes, for example, plates, sheets, and strips of steel such as carbon steel, alloyed steel, and stainless steel, titanium, and cladded material thereof, or complex plate of the metal plate with an organic or inorganic layer. Namely, so long as the plates produce Joule heat when they are supplied with an electric current, they are not limited to specific ones. The temperature attained by the present invention can be controlled precisely depending on the purposes of the heating. The heating of the present invention may be carried out for hot rolling, heat treatment, or warm rolling. The temperature can be controlled to high temperatures for hot rolling and various heat treatment and to lower temperatures for warm rolling. Needless to say, in order to reduce heating costs heating by a conventional heating furnace may be employed for pre-heating. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1a and 1b are partial schematic views of a direct resistance heating mechanism for wire rolling in the prior art; Figure 2 is a partial schematic view illustrating direct resistance heating during rolling of metal sheet in the prior art; Figure 3 is a schematic side view of an embodiment of the rolling apparatus of the present invention; Figure 4 is a schematic illustration of another example of a pinch roll arrangement; Figure 5 is a detailed side view of an embodiment of the rolling apparatus of the present invention; Figure 6 is an enlarged partial view of a work roll which may be employed in the present invention; Figure 7 is a schematic side view of another example of the rolling apparatus of the present invention; Figure 8 is a detailed side view of still another embodiment of the rolling apparatus of the present invention; and Figure 9 is a schematic side view of a still further embodiment of the rolling apparatus of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Figure 3 illustrates a manner in which a rolling material 1 is rolled with a metal plate rolling apparatus embodying the present invention, in which the rolling material 1 is passed in the direction shown by an arrow and is rolled by means of a pair of rolls 2-1 and 2-2 which are supported by back-up rolls 3-1 and 3-2, respectively. According to the present invention, a pair of pinch rolls 4-1 and 4-2 are provided on the inlet side, i.e., upstream of the rolling apparatus in order to supply an electric current to the rolling material. At least one of the pinch rolls is connected to an electric power source 5. At least one additional pair of pinch rolls may be provided. For the purpose of avoiding plastic deformation of the rolling plate, the contact pressure of the pinch rolls may be on the order of 1 kgf/mm 2 , i.e., a rolling force of about several tons for the pinch rolls having a diameter of 200 mm onto a rolling plate 1000 mm wide. When a rolling plate has irregularities such as edge waves with respect to the flatness of the surface, formation of gaps between the roll and the rolling plate is inevitable, resulting in formation of sparks along the edges. In such a case, two or more pairs of pinch rolls may be provided on the inlet side of the rolling apparatus in such a manner that one of them may be shifted downwards or upwards to provide an intermesh between the neighboring pinch rolls. For this purpose, as shown in Figure 4, it is advisable to provide at least three pairs of pinch rolls 4-1, 4'-1, and 4''-1 on the inlet side of the rolling apparatus. According to this arrangement, it is possible to provide an intermesh "d" between the neighboring pinch rolls 4'-1, 4'-2, 4''-1, and 4''-2 by shifting the roll axes of the pinch rolls 4-1 and 4-2 upwards or downwards so as to make the plate wind around the rolls with the purpose of increasing the peripheral contact area. In such an arrangement it is possible to lower the current density between the roll and the plate and also ensure contact between the roll and the plate in the widthwise direction. Furthermore, if the rolling plate has edge drops in the edges in its transverse section, the pinch rolls do not contact the plate in the edges. In such a case, the pinch rolls which are movable in the widthwise direction ensure an intimate contact between the roll and the plate. For this purpose any types of deflection rolls can be used. A variable-crown roll in which a gas or liquid under pressure is fed into a gap provided between a sleeve and roll arbor may be employed so as to ensure contact of the pinch rolls with the rolling plate even in its edges areas. The work rolls 2-1 and 2-2 are grounded so as to be at zero potential. The electric power source 5 may be either of the direct current or alternating current type. When the rolling material is rolled with a rolling apparatus of the present invention, the rolling material is passed into the rolling apparatus in which the rolling material is contacted with the pair of pinch rolls and then with the pair of work rolls. Between the pinch rolls and the work rolls an electric current which is determined by the electric potential and current density passes through the rolling material to generate Joule heat due to the electric resistance of the rolling material. Since the distance between the pinch rolls and the work rolls is substantial, the effective electric resistance between them is enough to generate a sufficient amount of heat for rolling and heat treatment. Thus, the distance between the pinch rolls and the work rolls may be determined depending on the material to be rolled, a target heating temperature, rolling conditions, and the like. In Figure 3, an additional pair of pinch rolls 5-1 and 5-2 is provided downstream of the rolling apparatus. Though the additional pinch rolls 5-1 and 5-2 are not essential, the provision of such pinch rolls is desirable for the purpose of maintaining hot conditions of a rolled material and heating to a predetermined temperature for heat treatment. Such additional pinch rolls 5-1 and 5-2 may be connected to the electric source 6, like the pinch rolls 4-1 and 4-2. In this embodiment, when reverse rolling is carried out from the downstream to the upstream side in Figure 3, the pinch rolls 5-1 and 5-2 are positioned upstream of the rolling apparatus and the pinch rolls 5-1 and 5-2 serve as heating means prior to rolling. Furthermore, another pair of pinch rolls 7-1 and 7-2 may be provided on the upstream side. These additional pinch rolls 7-1 and 7-2 are grounded in the same manner as the work rolls 2-1 and 2-2. Thus, the pinch rolls 7-1 and 7-2 are effective not only to heat the rolling material prior to rolling, but also to keep the potential of the rolling material at zero upstream of the pinch rolls 4-1 and 4-2. The pinch rolls 4-1 and 4-2 are also effective to hold the rolling material, apply a tension to the rolling material in the area between the rolling apparatus and the pinch rolls, and maintain a stable manner of passing and a desirable degree of the contact force. According to the arrangement of the pinch rolls and work rolls of the present invention, it is possible to supply an extremely large electric current. Namely, it has been thought that the upper limit of the electric current which can be supplied for wire rolling is 2 A/mm 2 , but it is possible to supply an electric current at a density of 200 A/mm 2 without problems such as generation of sparks. Therefore, rapid heating is possible, even for a wide plate having a high heat content, merely by increasing the current density. This is because employment of pinch rolls enables the application of a suitable amount of tension to the sheet, which improves the state of contact between the rolls and rolling material. Figure 5 shows a side view of the rolling apparatus including work rolls 2-1 and 2-2 and pinch rolls 4-1 and 4-2 which can be used in the present invention. The rolling mill itself contains back up rolls 3-1 and 3-2 and work rolls 2-1 and 2-2. The basic structure of the rolling mill and the mechanism of rolling a rolling material using this mill are the same as for a conventional rolling mill. As shown in Figure 6 in an enlarged view, an electrically conductive brush 9 is placed against the axes of the work rolls 2-1 and 2-2 by means of a spring 10. The brush 9 is electrically connected to a housing 11 so that the potential of the work rolls is the same as that of the ground. On the other hand, the pinch rolls 4-1 and 4-2 are connected to an electric source 5 (see Figure 3) by way of a brush (not shown). Optional pinch rolls 5-1 and 5-2 and pinch rolls 7-1 and 7-2 are also electrically connected in the same manner as described above. Rolling of a metal plate using this apparatus is carried out as follows. A brush is made to contact pinch rolls 4-1 and 4-2, and an electric current (direct current or alternative current) is supplied. On the other hand, a brush is made to contact the work rolls 2-1 and 2-2 and is grounded. In this state, while the metal plate 1 is being passed through the apparatus, the electric current passes from the pinch rolls to a circuit comprising the rolling metal plate, the work rolls, the housing, and ground, so a sufficient amount of heat, i.e., Joule heat may be generated in the rolling plate. The amount of heat, i.e., the temperature of the rolling material can be easily controlled by adjusting the electric power supplied to the apparatus. It is desirable to provide a temperature sensor near the inlet of the work rolls so as to detect the temperature of the rolling material. A sufficient length of heating zone for the rolling material is ensured by suitably selecting the distance between the position of the pinch rolls and the rolling mill itself. This is because the amount of heat electrically generated, i.e., Joule heat, depends on the effective resistance, and the effective resistance is proportional to the distance between the pinch rolls and the rolling mill. So, it is possible to effect efficient heating by applying an electric current in an amount much smaller than that required in the case of Figure 2. This means that an electric power source and distribution line of smaller capacity may be employed to reduce equipment costs. Furthermore, since the work rolls are grounded, there is no need to worry about insulation. Figures 3 and 5 show a conventional 4Hi-roll mill, but the present invention is not limited to such a roll mill. The rolling apparatus of the present invention may be applied to a variety of rolling lines which comprise rolling mills, such as a 2Hi-roll mill without a back-up roll, a 6Hi-roll mill, and a roll mill of the so-called roll-shift type in which an intermediate roll is traversed in an axial direction. Figure 7 shows another embodiment of the present invention, in which work rolls 2-1 and 2-2 of a small diameter, intermediate rolls 12-1 and 12-2, and support rolls 13-1 and 13-2 are incorporated in an assembly to form a 6Hi-rolling mill. A rolling mill of this type can be used to roll a thin plate and a hard plate, since under the same rolling loads a larger contact pressure can be applied to the plate to be rolled compared to the 2Hi-roll mill. This is because the diameter of the work rolls is smaller than in the 2Hi-roll mill. If a direct resistance heating system such as shown in Figure 2 is employed, either the intermediate rolls 12-1 and 12-2 or back-up rolls 3-1 and 3-2 must be electrically insulated from the work rolls. However, the back-up rolls are mechanically connected with a drive system, so it is rather difficult to apply insulation between the work rolls and the drive system. Furthermore, since this type of a roll mill is characterized by a small diameter work roll to achieve a high pressure rolling, and since the contact pressure between the work rolls and intermediate rolls is extremely high, it is quite difficult to apply insulation between the work rolls and the intermediate rolls, too. In contrast, according to the present invention in which an electrical current is supplied through a pair of pinch rolls, there is no need apply such insulation. This is a great advantage of the present invention when applied to a complicated, multi-functional rolling mill. Figures 8 and 9 show another embodiment of a metal plate rolling apparatus of the present invention. This embodiment is substantially the same as that illustrated in Figures 3 and 5 except that the apparatus shown in Figures 8 and 9 is equipped with gas or liquid injection nozzles 8-1, 8-2, 8-3, and 8-4. The same member as in Figures 3 and 5 are indicated by the same reference numerals in Figures 7 and 8. As is apparent from Figures 8 and 9, on the inlet and outlet sides of the rolling mill are provided means for injecting gas or liquid, e.g., nozzles 8-1, 8-2, 8-3, and 8-4. These nozzles are placed in a row, or in rows on the upper and lower sides of the plate so as to thoroughly isolate the plate from its surroundings in the widthwise direction. Though Figures 8 and 9 illustrate the case in which the nozzles are provided on both the inlet and outlet sides of the rolling mill, the nozzles may be provided on one side only on either the upstream or downstream side. Another set of nozzles 8-1', 8-2', 8-3', and 8-4' may also be provided so as to further strengthen the isolation of the plate from its surroundings during rolling. The temperature of the metal plate to be rolled increases rapidly while approaching the work rolls where the temperature reaches a maximum. When a metal plate is rolled with this rolling mill, the length of time when the heated plate is exposed to the atmosphere, i.e., to air is minimized compared to the case wherein a conventional heating furnace or induction heating apparatus is used to heat the metal plate prior to rolling. Furthermore, according to the above-described embodiment of the present invention, a row or rows of nozzles are provided on the inlet and/or outlet sides of the rolling mill. When argon gas is injected through the nozzles 8-1 and 8-2 provided on the inlet side of the mill, an area where the temperature is maximized may be thoroughly isolated from the ambient atmosphere during rolling, resulting in less occurrence of undesirable oxidation. Within the roll gap the metal plate is sealed by the upper and lower work rolls from the ambient atmosphere, so rolling is carried out completely in non-oxidizing environments. Therefore, hot rolling at a temperature of 1000°C or higher may be carried out without a fear of oxidation. In addition, when cooling water is injected through the nozzles provided in the outlet side of the rolling mill to rapidly cool the metal plate after rolling, it is possible to prohibit oxidation of the metal plate after leaving the work rolls. Alternatively, the nozzles 8-3 and 8-4 in the outlet side may be used to inject an inert gas, such as argon gas. A rapid cooling with cooling water after rolling a metal plate is also effective for carrying out heat treatment to provide the metal plate with specific characteristics. The present invention will be further described in conjunction with working examples which are presented merely for illustrative purposes and are not intended to limit the present invention in any way. Example 1 A rolling apparatus like that shown in Figure 5 was used to roll a stainless steel (JIS SUS 304) plate. The dimensions of the rolling mill and hot rolling conditions employed are summarized as follows. Work roll diameter: 100 mm Back-up roll diameter: 330 mm Front tension: 5 kgf/mm 2 Back tension: 5 kgf/mm 2 Maximum rolling load: 100 tons Pinch roll diameter: 80 mm Axial distance between work roll and pinch roll: 700 mm Rolling material (plate): SUS 304 Initial thickness (before rolling): 0.25 mm Final thickness (after rolling): 0.20 mm Plate width: 300 mm Temperature before heating: 20°C Rolling rate: 1.5 m/min Rolling load: 85 tons Electric source: Alternating current (commercial frequency), 10 V, 1500 A Target heating temperature (target rolling temperature): 740°C Supplied power: 15 KVA During rolling under the conditions described above, the temperature of the rolling plate just before reaching the work rolls was determined to be 740°C ± 5°C. The hot rolling was carried out smoothly without any troubles, such as occurrence of sparks. It was also experimentally determined that there were no sparks even for a light duty reduction, i.e., a rolling force of about 1 ton. It was also confirmed that a rolling force for the pinch rolls of about 100 kg or more is enough for the total of the rolls in the driving and working sides. However, it is also advisable to maintain the flatness of the rolling material by controlling the rolling force balance as well as the tension of the rolling material between the pinch rolls and the work rolls. Example 2 In this example, Example 1 was repeated except that a rolling apparatus like that shown in Figure 8 was used, the rolling rate was 10 m/min, and the heating temperature was 1150°C on the inlet side of the rolling mill. At a point 50 mm away from the work rolls four pairs of nozzles placed in a row in the widthwise direction of the plate were installed on both the inlet and outlet side of the rolling apparatus. As shown in Table 1, the thickness of scale was determined for the cases in which argon gas or water was injected through the nozzles, and for the cases in which the nozzles were not used. The test results are also shown in Table 1. The water or gas injection conditions were as follows. Nozzles on the inlet side: Ar gas: Pressure: 5kgf/cm 2 Feed : 10 l/min Nozzles on the outlet side: Water: Pressure: 2.5kgf/cm 2 Feed : 5 l/min Test No. Ar gas Injection through Inlet side nozzles Water Injection through Outlet side nozzles Temperature at the Outlet (°C) Thickness of Scale after Rolling (µm) Remarks 1 None None 1050 5.2 Comparative 2 Yes None 1050 3.1 Invention 3 None Yes 120 0.7 Invention 4 Yes Yes 120 < 0.01 Invention In Table 1, Test No.1 was a comparative example in which no injection was carried out on both the inlet and outlet sides. The temperature of the plate after rolling was 1050°C and the scale thickness was 5.2 µm. Test No. 2 was a working example of the present invention in which Ar gas injection was carried out only on the inlet side. In this case the cooling on the outlet side was the same as in Test No.1, and the temperature of the plate after rolling was the same as in Test No. 1. However, since prior to rolling the plate was sealed from its surroundings, the scale thickness was reduced to 3.1 µm. Test No. 3 was also a working example of the present invention, in which only water injection was carried out on the outlet side. After cooling with water, the temperature of the plate was reduced to 120°C, and the scale thickness was also reduced to 0.7 µm. Test No. 4 was also an example of the present invention, in which both argon gas injection on the inlet side and water injection on the outlet side were carried out. There was substantially no scale, and the thickness of scale could not be measured. As is apparent from the foregoing, heating of a rolled plate can be carried out efficiently, and it is easy to control the temperature. Thus, the present invention is advantageous from the standpoint of energy savings, operating efficiency, and product quality. Namely, the rolling apparatus of the present invention does not require the provision of an insulation layer or member, and an electric source of a small capacity may be used with a marked reduction in equipment costs. Furthermore, when at least one fluid injection nozzle is installed on either the outlet or inlet side of the rolling mill, a metal plate can easily be isolated from the ambient atmosphere before, during, or after rolling merely by injecting an inert gas or water against the metal plate. According to this embodiment of the present invention, the formation of oxide scale is prevented markedly, and it is easy to effect descaling, or sometimes it is not necessary to effect descaling, making the process and apparatus for rolling a plate simple. Furthermore, it is also possible to prevent degradation in properties of the rolled metal plate, which is caused by the absorption of nitrogen gas in the metal plate under hot conditions. It is also possible to modify or further improve the properties of the metal plate by quenching it after rolling.

Claims: A metal plate rolling apparatus comprising a first pair of pinch rolls (4-1, 4-2) provided on the inlet side of the rolling apparatus and connected to an electric source (5), and a pair of work rolls (2-1, 2-2), characterized in that said work rolls are electrically grounded and in that at least one of the pinch rolls is movable in the widthwise direction. A metal plate rolling apparatus as set forth in claim 1, characterized in that the apparatus further comprises a second pair of pinch rolls (5-1, 5-2) provided on the outlet side of the rolling apparatus and connected to an electric source (6). A metal plate rolling apparatus as set forth in claims 1 or 2, characterized in that one or more additional pairs of electrically grounded pinch rolls (7-1, 7-2) are provided umstream of the first pair on the inlet side of the rolling apparatus. A metal plate rolling apparatus as set forth in any one of claims 1 through 3, characterized in that the apparatus further comprises a fluid injection means (8-1, 8-2, 8-3, 8-4) either on the inlet or outlet side of the rolling apparatus. A metal plate rolling apparatus as set forth in any one of claims 1 through 4, characterised in that two or more pairs of pinch rolls (4'-1, 4''- 1) are provided on the inlet side of the rolling apparatus so that at least one of them is shiftable upwards or downwards. A metal plate rolling apparatus as set forth in any one of claims 1 through 5, characterized in that at least one of the axes of the work rolls (2-1, 2-2) are made to contact a housing (11) of the rolling apparatus through an electrically conductive brush (9).

Inventors: ISAKA KAZUMI, ISAKA, KAZUMI
Applicants: SUMITOMO METAL IND, SUMITOMO METAL INDUSTRIES, LTD.
Application year: 1992
Main classification: B21B45
IPC codes: B21B45, B21B9, C21D9, H05B3, B21B39