Cold rolling method, steel plate manufacturing method, cold rolling equipment, and control method of cold rolling equipment

Abstract

To maintain the temperature of the steel plate within the range of ductile-brittle transition temperature to the temperature at which non-uniform deformation occurs, the steel plate is rolled. In a cold rolling method, rolling is performed by supplying rolling oil to a plurality of rolling mill stands (std) arranged along the transport direction of the steel plate (S). At least a portion of the rolling oil recovered from the rolling mill stand (std) located downstream of the steel plate (S) in the transport direction is supplied to a predetermined number of rolling mill stands (std), including the upstream rolling mill stand (std) located in the transport direction of the steel plate (S).

Description

[Technical Field]

[0001] This invention relates to a cold rolling method, a method for manufacturing steel plates, cold rolling equipment, and a method for controlling the cold rolling equipment. [Previous Technology]

[0002] For example, in steel sheets containing silicon (Si), such as electromagnetic steel sheets, the higher the silicon content, the lower the temperature at which the material loses its ductility and exhibits obvious brittleness (hereinafter referred to as the "ductility-brittleness transition temperature"). Therefore, when cold rolling such steel sheets, it is desirable to make the temperature of the steel sheet above the ductility-brittleness transition temperature.

[0003] As a method for raising the temperature of the steel plate to above the ductile-brittle transition temperature, examples include Patent Document 1 and Patent Document 2. Patent Document 1 discloses heating the steel plate by spraying steam at 100-160°C from the lower surface of the steel plate moving at a certain speed toward the steel plate. Patent Document 2 discloses heating the steel plate using a solenoid-type induction heating device. [Prior Art Documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2006-169546 [Patent Document 2] Japanese Patent Application Publication No. 2005-169458 [Summary of the Invention]

[0005] [Problem to be Solved by the Invention] However, in order to efficiently heat steel plates, it is desirable to use a fluid (or gas) with high values ​​for density, specific heat, temperature, thermal transfer coefficient, and flow rate to exchange heat with the steel plate. For example, since the specific heat and density of steam are lower than those of water and rolling oil (coolant), the method of heating steel plates using steam requires a larger amount of steam compared to heating steel plates using hot water or rolling oil. Furthermore, the higher the speed (hereinafter referred to as "conveyor speed") of the steel plate moving towards the pair of work rolls undergoing rolling, the less steam is sprayed towards the steel plate, thus making it difficult to heat the steel plate to the target temperature.

[0006] Also, the method of heating steel plates using a solenoid induction heating device has the advantage of heating steel plates to the target temperature, but due to the large size of the heating device, it is difficult to install it on the rolling mill.

[0007] However, in tandem cold rolling mills where multiple rolling stands are arranged along the conveying direction of the steel sheet, in addition to the steel sheet heating methods disclosed in Patent Documents 1 and 2, there are also methods that use coolant circulating in each of the multiple rolling stands to heat the steel sheet before rolling. However, it is known that during the rolling process, the steel sheet heats up due to its own plastic deformation. In tandem cold rolling mills, the temperature of the steel sheet rises as it is conveyed downstream in the conveying direction by repeated rolling processes across multiple rolling stands. This temperature rise not only causes deformation of the work rolls used for rolling the steel sheet but also becomes a cause of steel sheet deformation (non-uniform deformation). Therefore, it is desirable to maintain the temperature of the steel sheet during rolling below the temperature at which the work rolls and the steel sheet deform (the temperature at which non-uniform deformation occurs). In other words, in tandem cold rolling mills equipped with multiple mill stands, there are increasing demands for new cold rolling methods, steel plate manufacturing methods, and cold rolling equipment that can roll steel plates while maintaining their temperature within the range of ductile-brittle transition temperature to non-uniform deformation temperature.

[0008] This invention was developed in view of the above-mentioned problems, and its purpose is to provide a new cold rolling method, a method for manufacturing steel plates, cold rolling equipment, and a method for controlling the cold rolling equipment, which enables the rolling process of steel plates while maintaining the temperature of the steel plates within the range of the ductile-brittle transition temperature to the temperature at which uneven deformation occurs. [Technical Means for Solving the Problem]

[0009] A single-state cold rolling method involves supplying rolling oil to a plurality of rolling mill stands arranged along the conveying direction of the steel plate while performing rolling processing on the steel plate by the plurality of rolling mill stands. At least a portion of the rolling oil recovered from the rolling mill stand arranged downstream of the steel plate conveying direction is supplied to a predetermined number of rolling mill stands, including the rolling mill stand arranged upstream of the steel plate conveying direction.

[0010] Preferably, the device is equipped with a rolling oil spraying device, which is arranged at least on the upstream side of the rolling mill stand located at the farthest end in the steel plate conveying direction, and is used to spray rolling oil toward the steel plate. The rolling oil used by the rolling mill stand located on the downstream side in the steel plate conveying direction is supplied to the rolling oil spraying device as needed, in addition to supplying a predetermined number of rolling mill stands.

[0011] Preferably, the temperature of the rolling oil supplied to a predetermined number of rolling mill stands is above 80°C.

[0012] Preferably, the rolling oil recovered from a predetermined number of mill stands is supplied to mill stands other than the predetermined number of mill stands, so that the rolling oil circulates among the plurality of mill stands.

[0013] Another type of steel plate manufacturing method includes: a cold rolling process using the cold rolling method described above, and a final annealing process of performing a final annealing on the steel plate that has undergone the cold rolling process as needed.

[0014] Another type of cold rolling equipment supplies rolling oil to a plurality of mill stands arranged along the conveying direction of the steel plate while performing rolling processing on the steel plate by the plurality of mill stands. The cold rolling equipment includes: a supply system that can supply rolling oil to the plurality of mill stands respectively; a recovery system that can recover rolling oil from the plurality of mill stands; a plurality of control valves arranged in each of the supply system and the recovery system; and a control device that switches the opening and closing states of the plurality of control valves. The control device switches the opening and closing states of the plurality of control valves so that the recovery system forms a first recovery path for recovering rolling oil from the mill stands arranged downstream in the conveying direction of the steel plate, and the supply system forms a first supply path for supplying a portion of the rolling oil recovered by the first recovery path to a predetermined number of mill stands, including the mill stand arranged at the upstream end in the conveying direction of the steel plate.

[0015] Preferably, the device is equipped with a rolling oil spraying device, which is arranged at least on the upstream side of the rolling mill stand located at the upstream end in the conveying direction of the steel plate, and is used to spray a portion of the rolling oil recovered from at least one rolling mill stand located on the downstream side in the conveying direction of the steel plate toward the steel plate.

[0016] Preferably, when the recycling system forms the first recycling path, it also forms a second recycling path to recycle the rolling oil used in a predetermined number of mill stands, and when the supply system forms the first supply path, it also forms a second supply path to supply the rolling oil recovered through the second recycling path to mill stands other than the predetermined number of mill stands.

[0017] Another type of cold rolling equipment control method involves supplying rolling oil to a plurality of mill stands arranged along the conveying direction of the steel plate while performing steel plate rolling processing by the plurality of mill stands. The cold rolling equipment includes: a supply system that can supply rolling oil to the plurality of mill stands respectively; a recovery system that can recover the rolling oil used in the plurality of mill stands; a plurality of control valves arranged in each of the supply system and the recovery system; and a control device that switches the opening and closing states of the plurality of control valves respectively. The control device switches the opening and closing states of the plurality of control valves according to the temperature of the rolling oil supplied to the plurality of mill stands and the temperature of the steel plate, thereby forming a first recovery path in the recovery system for recovering rolling oil from the mill stand arranged downstream in the conveying direction of the steel plate, and forming a first supply path in the supply system for supplying a portion of the rolling oil recovered by the first recovery path to a predetermined number of mill stands including the mill stand arranged upstream in the conveying direction of the steel plate.

[0018] Preferably, when the recovery system forms the first recovery path, it also forms a second recovery path for recovering rolling oil from a predetermined number of mill stands; and when the supply system forms the first supply path, it also forms a second supply path for supplying a portion of the rolling oil recovered through the second recovery path to mill stands other than the predetermined number of mill stands. [Effects of the Invention]

[0019] According to this disclosure, brittle fracture of the steel plate during rolling, deformation of the work roll, and deformation of the steel plate caused by the deformation of the work roll can be prevented.

Implementation Method

[0021] Referring to Figures 1 to 3, the structure of a cold rolling mill according to an embodiment of the present invention will be described. Figure 1 is a schematic diagram showing the structure of a cold rolling mill according to an embodiment of the present invention. Figure 2 is a schematic diagram showing the structure near the first mill stand and the second mill stand of the rolling mill, and Figure 3 is a schematic diagram showing the structure near the third to fifth mill stands.

[0022] Hereinafter, as an example of the material to be rolled, steel sheet S such as electromagnetic steel sheet will be used for explanation. However, aluminum sheet or other metal sheets can also be used as the material to be rolled.

[0023] In the cold rolling mill 1 shown in Figure 1, the steel sheet S is conveyed from the right side to the left side in Figure 1. As shown in Figure 1, the cold rolling mill 1 includes a cold tandem rolling mill 2. Hereinafter, the cold tandem rolling mill 2 will be simply referred to as the mill 2. The mill 2 includes a plurality of mill stands std arranged along the conveying direction of the steel sheet S. Although not shown in the figure, the mill 2 includes tension rolls and deflector rolls, a plate thickness gauge, a shape gauge, etc., between adjacent mill stands std.

[0024] The following describes the case where the rolling mill 2 has 5 rolling mill stands (std). Among the 5 rolling mill stands (std), the rolling mill stand (std) located on the upstream side in the conveying direction of the steel plate S is referred to as the first rolling mill stand (std1), and the rolling mill stand (std) located on the downstream side in the conveying direction of the steel plate S is referred to as the fifth rolling mill stand (std5). In this embodiment, although the example shows a rolling mill 2 with 5 rolling mill stands (std), the number of rolling mill stands (std) provided on the rolling mill 2 is not limited to 5, and is preferably 2 or more.

[0025] The first mill stand std1, the second mill stand std2, the third mill stand std3, the fourth mill stand std4 and the fifth mill stand std5, as an example, include: a pair of work rolls 11 for rolling steel plates S, a pair of support rolls 12 supporting the pair of work rolls 11, and a pair of intermediate rolls 13 disposed between the work rolls 11 and the support rolls 12.

[0026] The cold rolling equipment 1, in addition to the aforementioned rolling mill 2, also includes a lubrication coolant manifold 21 and a cooling coolant manifold 22. The lubrication coolant manifold 21 and the cooling coolant manifold 22 are provided corresponding to each of the plurality of mill stands stds of the rolling mill 2. In the conveying direction of the steel plate S, the lubrication coolant manifold 21 is provided on the upstream side of each mill stand std, and the cooling coolant manifold 22 is provided on the downstream side of each mill stand std.

[0027] In this embodiment, although the lubricating coolant manifold 21 and the cooling coolant manifold 22 are constructed separately from the rolling mill 2, these manifolds 21 and 22 can also be included in the rolling mill 2.

[0028] Here, the structures of the lubrication coolant manifold 21 and cooling coolant manifold 22, which are correspondingly provided in each of the rolling mill stands std, are the same. Therefore, in FIG1, only the structures of the lubrication coolant manifold 21 and cooling coolant manifold 22 corresponding to the first rolling mill stand std1 are given symbols.

[0029] Rolling oil sprayed from the lubricating coolant manifold 21 reduces the friction between the work roll 11 and the steel plate S and cools the work roll 11, the support roll 12 and the intermediate roll 13. The lubricating coolant manifold 21 is equipped with nozzles 23a, 23b and 23c.

[0030] Nozzle 23a is positioned above the conveying surface L of the steel plate S (refer to Figure 2 or Figure 3). Nozzle 23a sprays rolling oil (coolant) towards the work roll 11, support roll 12 and intermediate roll 13 positioned above the conveying surface L.

[0031] Nozzle 23b is positioned above the conveying surface L of the steel plate S and below nozzle 23a. Nozzle 23b sprays rolling oil toward the upper surface of the work roll 11 positioned above the conveying surface L and the steel plate S.

[0032] Nozzle 23c is disposed below the conveying surface L. Nozzle 23c sprays rolling oil toward the lower surface of the work roll 11 and the steel plate S disposed below the conveying surface L.

[0033] Rolling oil sprayed from the cooling coolant manifold 22 cools the work roll 11, the support roll 12, and the intermediate roll 13. The cooling coolant manifold 22 is equipped with nozzles 24a and 24b.

[0034] Nozzle 24a is positioned above the conveying surface L of the steel plate S. Nozzle 24a sprays rolling oil toward the work roll 11, support roll 12 and intermediate roll 13 positioned above the conveying surface L.

[0035] Nozzle 24b is positioned below the conveying surface L of the steel plate S. Nozzle 24b sprays rolling oil toward the work roll 11 and intermediate roll 13 positioned below the conveying surface L.

[0036] Hereinafter, the lubrication coolant manifold corresponding to the first mill stand std1 will be referred to as lubrication coolant manifold 21a, the lubrication coolant manifold corresponding to the second mill stand std2 will be referred to as lubrication coolant manifold 21b, and the lubrication coolant manifold corresponding to the third mill stand std3 will be referred to as lubrication coolant manifold 21c. Sometimes the lubrication coolant manifold corresponding to the fourth mill stand std4 will be referred to as lubrication coolant manifold 21d, and the lubrication coolant manifold corresponding to the fifth mill stand std5 will be referred to as lubrication coolant manifold 21e.

[0037] Similarly, the coolant manifold corresponding to the first mill stand std1 is called coolant manifold 22a, the coolant manifold corresponding to the second mill stand std2 is called coolant manifold 22b, and the coolant manifold corresponding to the third mill stand std3 is called coolant manifold 22c. Sometimes the coolant manifold corresponding to the fourth mill stand std4 is called coolant manifold 22d, and the coolant manifold corresponding to the fifth mill stand std5 is called coolant manifold 22e.

[0038] In the conveying direction of the steel plate S, the heating device 25 is provided on the upstream side of the lubricating coolant manifold 21a and between the cooling coolant manifold 22a and the lubricating coolant manifold 21b. The heating device 25 is equivalent to the rolling oil spraying device described in the claim.

[0039] The heating device 25 includes a plurality of nozzles disposed below the conveying surface L of the steel plate S. Here, the heating device 25 has, for example, five nozzles. The plurality of nozzles in the heating device 25 spray rolling oil from below the steel plate S toward the steel plate S. Although the rolling oil is sprayed from below the steel plate S toward the steel plate S, it can also be sprayed from above and below the steel plate S, and can also be sprayed from above the steel plate S toward the steel plate S.

[0040] Hereinafter, the heating device 25 disposed on the upstream side of the first mill stand std1 will be referred to as heating device 25a. The heating device 25 disposed between the cooling coolant manifold 22a and the lubrication coolant manifold 21b will be referred to as heating device 25b.

[0041] In this embodiment, the case where heating devices 25a and 25b are provided is described. However, if the temperature of the steel plate S is made to fall within the range of ductile-brittle transition temperature to non-uniform deformation temperature by spraying rolling oil sprayed from the lubricating coolant manifold 21 onto the steel plate S, the heating devices 25a and 25b can be omitted.

[0042] An oil pan 26 is provided below each mill stand std of the above-mentioned mill 2. The oil pan 26 is used to collect the rolling oil sprayed from the lubrication coolant manifold 21 and the cooling coolant manifold 22 which are correspondingly arranged with the mill stand std.

[0043] The cold rolling equipment 1 includes a first storage tank 31, a second storage tank 32, and a third storage tank 33, which serve as storage tanks for rolling oil. The first storage tank 31 stores rolling oil supplied to the aforementioned lubricating coolant manifold 21 and cooling coolant manifold 22. Rolling oil from the third storage tank 33 flows into the first storage tank 31.

[0044] A heating device 34 is provided in the first storage tank 31. The heating device 34 heats the rolling oil by spraying steam into it, for example. The heating device 34 makes the temperature of the rolling oil stored in the first storage tank 31 a predetermined temperature measured by the liquid thermometer 111. Here, the temperature of the rolling oil stored in the first storage tank 31 is, for example, 50~60°C.

[0045] The second storage tank 32 stores the rolling oil supplied to the aforementioned lubricating coolant manifold 21 and cooling coolant manifold 22. A portion of the rolling oil recovered from the rolling mill 2 flows into the second storage tank 32.

[0046] A heating device 35 is provided in the second storage tank 32. Similar to the heating device 34, the heating device 35 heats the rolling oil by spraying steam into it, for example. The heating device 35 maintains the temperature of the rolling oil stored in the second storage tank 32 at a predetermined temperature measured by the liquid thermometer 112. Here, the temperature of the rolling oil stored in the second storage tank 32 is, for example, 90°C.

[0047] A portion of the rolling oil recovered from the rolling mill 2 flows into the third storage tank 33. The third storage tank 33 is connected to the first storage tank 31 via a delivery path 41. A pump 42 is provided in the delivery path 41. The pump 42 delivers the rolling oil stored in the third storage tank 33 toward the first storage tank 31.

[0048] In this embodiment, although it is described that there are three storage tanks, namely the first storage tank 31, the second storage tank 32 and the third storage tank 33, which serve as storage tanks for rolling oil, the third storage tank 33 shown in FIG1 can be omitted, and a portion of the rolling oil recovered from the rolling mill 2 can flow into the first storage tank 31.

[0049] The cold rolling mill 1, as a supply system for supplying rolling oil to each mill stand std, has a first supply system Sr1 (thick line in FIG. 1) and a second supply system Sr2 (dashed line in FIG. 1). The cold rolling mill 1 also has a recovery system C1 (dotted chain line in FIG. 1) for recovering the rolling oil contained in the oil receiving trays 26 provided for each mill stand std. By having two supply systems Sr1 and Sr2 and a recovery system C1, the rolling oil in the cold rolling mill 1 can circulate within the cold rolling mill 1.

[0050] The first supply system Sr1 includes: a supply path 45 connected to the first storage tank 31; a lubrication supply path 46 branching from the supply path 45 and connected to the lubrication coolant manifold 21; and a cooling supply path 47 branching from the supply path 45 and connected to the cooling coolant manifold 22. The lubrication supply path 46 and the cooling supply path 47 are respectively provided corresponding to the lubrication coolant manifold 21 and the cooling coolant manifold 22 installed on the rolling mill 2.

[0051] A pump 51 and a heat exchanger 52 are provided in the supply path 45. The pump 51 delivers the rolling oil stored in the first storage tank 31 toward the downstream side of the supply path 45. The heat exchanger 52 cools the rolling oil by exchanging heat between the rolling oil delivered by the pump 51 toward the downstream side of the supply path 45 and the heat transfer medium as needed.

[0052] A plurality of control valves 48 are provided in the supply path 45. Here, the control valves 48 in the supply path 45 are located between the connection portion of the cooling supply path 47 to the cooling coolant manifold 22 corresponding to the upstream mill stand std in the adjacent mill stand std, and the connection portion of the lubrication supply path 46 to the lubrication coolant manifold 21 corresponding to the downstream mill stand std in the adjacent mill stand std. Hereinafter, the control valves 48 provided in the first supply path 45 are referred to as control valves 48a, 48b, 48c, and 48d sequentially from the downstream side of the rolling oil delivery direction of the first supply path 45, that is, the upstream side of the steel plate S conveying direction.

[0053] When the cold rolling mill 1 is in operation, any one of the control valves 48a, 48b, 48c, and 48d remains in the closed state, while the remaining control valves remain in the open state. Thus, the mill stands std of the rolling mill 2 are grouped as follows: mill stands std supplied with rolling oil by the first supply system Sr1, and mill stands std supplied with rolling oil by the second supply system Sr2.

[0054] The lubrication supply path 46 is connected to the first branch path 56, the second branch path 57, and the third branch path 58 of the lubrication coolant manifold 21. A control valve 61 is provided in the lubrication supply path 46. A control valve 62 is also provided in the first branch path 56 of the lubrication coolant manifold 21. A control valve 63 is also provided in the second branch path 57 of the lubrication coolant manifold 21. A control valve 64 is also provided in the third branch path 58 of the lubrication coolant manifold 21. Here, the first branch path 56 of the lubrication coolant manifold 21 is connected to the nozzle 23a, the second branch path 57 is connected to the nozzle 23b, and the third branch path 58 is connected to the nozzle 23c.

[0055] The lubrication supply path 82, branching from the branch path 77a of the second supply system Sr2, is connected downstream of the control valve 61 to the lubrication supply path 46, which is provided corresponding to the first mill stand std1. Similarly, the lubrication supply path 82, branching from the branch path 77b of the second supply system Sr2, is connected downstream of the control valve 61 to the lubrication supply path 46, which is provided corresponding to the second mill stand std2.

[0056] The cooling supply path 47 is connected to the first branch path 65 and the second branch path 66 of the cooling coolant manifold 22. A control valve 68 is provided in the cooling supply path 47. A control valve 69 is provided in the first branch path 65 of the cooling coolant manifold 22. A control valve 70 is provided in the second branch path 66 of the cooling coolant manifold 22. Here, the first branch path 65 of the cooling coolant manifold 22 is connected to the nozzle 24a, and the second branch path 66 is connected to the nozzle 24b.

[0057] The second supply system Sr2 has: a supply path 76 connected to the second storage tank 32, and two branch paths 77a and 77b branching off at the downstream end of the supply path 76. A pump 79 is provided near the second storage tank 32 on the supply path 76. The pump 79 pumps the rolling oil stored in the second storage tank 32 towards the downstream side of the supply path 76. Since the downstream configuration of branch path 77a is the same as that of branch path 77b, the following description focuses on the downstream configuration of branch path 77a, omitting the description of the downstream configuration of branch path 77b.

[0058] Branch path 77a branches into a heating supply path 81 and a lubrication supply path 82 at its downstream end. A control valve 83 is provided in the heating supply path 81. A control valve 84 is provided in the lubrication supply path 82. Here, the heating supply path 81 is connected to the heating device 25, and the lubrication supply path 82 is connected to the lubrication supply path 46.

[0059] The recovery system C1 has: discharge paths 91a, 91b, 91c, 91d, 91e connected to the oil receiving pan 26 disposed below each mill stand std; recovery path 92 connected to the discharge paths 91a, 91b, 91c, 91d, 91e; and return flow paths 93, 94 branching from the recovery path 92.

[0060] Control valves 96, 97, 98, and 99 are respectively provided in the flow paths 92a, 92b, 92c, and 92d that constitute the recycling path 92. These control valves 96, 97, 98, and 99 are controlled to open and close by the control device 110.

[0061] In flow path 92a, one of the flow paths 92a, 92b, 92c, and 92d constituting the above-mentioned recovery path 92, a connection is made between the discharge path 91a and the control valve 96 and the upstream end of the return flow path 94. In flow path 92d, one of the flow paths 92a, 92b, 92c, and 92d, a connection is made between the discharge path 91e and the control valve 99 and the upstream end of the return flow path 93. A control valve 100 is provided upstream of the return flow path 93 (on the recovery path 92 side).

[0062] The control device 110 outputs necessary signals (control signals) to each part of the cold rolling equipment 1 based on the signals (measurement signals) from each measuring part (thickness gauge, shape gauge, thermometer, etc.) installed in each part of the cold rolling equipment 1.

[0063] The process of manufacturing cold-rolled steel coils from hot-rolled steel coils will be described next. As shown in Figure 4, the process of manufacturing cold-rolled steel coils from hot-rolled steel coils includes, for example, a pickling process, a cold rolling process, and a final annealing process. Although not shown in the figure, the heated slab is rolled (hot-rolled) by rolling mills such as roughing mills and finishing mills, and the steel sheet S generated by hot rolling is wound by a coiler to generate hot-rolled steel coils.

[0064] The pickling process is a process of removing the oxide film covering the surface of the steel plate S. Although not shown in the figure, the pickling process is carried out in pickling equipment, which includes: a pickling tank for storing strong acids such as sulfuric acid, a washing tank for storing washing water, and a dryer. That is, the pickling process includes: immersing the steel plate S in the pickling tank and conveying it, immersing the steel plate S in the washing tank and conveying it, and drying the surface of the steel plate S.

[0065] The cold rolling process is to roll the steel plate S after the oxide film has been removed by the pickling process using the above-mentioned cold rolling equipment 1, thereby generating a steel plate S of the target thickness.

[0066] The final annealing process is used to anneal the steel sheet S that has been rolled in the cold rolling process. By performing the final annealing process, the steel sheet S that has been hardened by the cold rolling process can be softened to the target hardness. The steel sheet S that has undergone the final annealing process is wound by a winding machine.

[0067] Also as the final annealing process, although annealing is carried out while the steel plate S is being transported, it can also be performed on the coiled steel coil formed by winding the steel plate that has undergone the cold rolling process.

[0068] In the process of manufacturing cold-rolled steel coils from hot-rolled steel coils shown in Figure 4, although the final annealing process is included, the final annealing process may be omitted depending on the type of material to be rolled.

[0069] The cold rolling process will now be described. In the process of manufacturing cold-rolled steel coils from hot-rolled steel coils, the steel sheet S is transported to a pickling facility and then to the cold rolling mill 1. During the manufacturing process, the control device 110 starts the cold rolling mill 1. That is, the control device 1 operates the mill 2 of the cold rolling mill 1, causing one pair of work rolls 11 on the mill stand std of the mill 2 to rotate. Simultaneously, the control device 110 switches the opening and closing states of the control valves provided in the cold rolling mill 1 as needed. Furthermore, the control device 110 drives pumps 42, 51, and 79.

[0070] First, an example of switching the opening and closing state of the control valve installed in the cold rolling equipment 1 will be explained.

[0071] (1) Regarding the control valve 48a, the control device 110 calculates the temperature of the steel plate S being rolled by the first mill stand std1 based on the temperature of the rolling oil supplied to the lubricating coolant manifold 21a, the amount of rolling oil sprayed to the lubricating coolant manifold 21a, the temperature of the conveyed steel plate S, and the conveying speed of the steel plate S. The temperature of the conveyed steel plate S is measured by thermometer 114. The temperature of the rolling oil is measured by liquid thermometer 112. The conveying speed refers to the speed of the steel plate S entering each mill stand.

[0072] When the calculated temperature of the steel plate S is above the ductile-brittle transition temperature, the control device 110 switches the control valve 48a installed in the supply path 45 from the closed state to the open state. If the control valve 48a installed in the supply path 45 is in the open state, the control device 110 does not switch the control valve 48a and maintains the state of the control valve 48a.

[0073] On the other hand, when the calculated temperature of the steel plate S is lower than the ductile-brittle transition temperature, the control device 110 switches the control valve 48a installed in the supply path 45 from the open state to the closed state. If the control valve 48a installed in the supply path 45 is in the closed state, the control device 110 does not switch the control valve 48a and maintains the state of the control valve 48a.

[0074] (2) Regarding the control valve 48b, the control device 110 calculates the temperature of the steel plate S being rolled by the second mill stand std2 based on the temperature of the rolling oil supplied to the lubricating coolant manifold 21b, the spray volume of the rolling oil supplied to the lubricating coolant manifold 21b, the temperature of the conveyed steel plate S, and the conveying speed of the steel plate S. The temperature of the conveyed steel plate S is measured by thermometer 115. The temperature of the rolling oil is measured by liquid thermometer 112.

[0075] When the calculated temperature of the steel plate S is above the ductile-brittle transition temperature, the control device 110 switches the control valve 48b installed in the supply path 45 from the closed state to the open state. If the control valve 48b installed in the supply path 45 is in the open state, the control device 110 does not switch the control valve 48b and maintains the state of the control valve 48b.

[0076] On the other hand, when the calculated temperature of the steel plate S is lower than the ductile-brittle transition temperature, the control device 110 switches the control valve 48b installed in the supply path 45 from the open state to the closed state. If the control valve 48a installed in the supply path 45 is in the closed state, the control device 110 does not switch the control valve 48a and maintains the state of the control valve 48a.

[0077] (3) Regarding control valves 48c and 48d: For example, if either control valve 48c or control valve 48d in the supply path 45 is in a closed state, the control device 110 will switch the closed control valve to an open state. On the other hand, if both control valves 48c and 48d in the supply path 45 are in an open state, the control device 110 will not switch control of control valves 48c and 48d and will maintain the state of control valves 48c and 48d.

[0078] (4) Regarding control valve 61: When control valve 48a is in the closed state, control device 110 switches control valve 61, which corresponds to the lubrication supply path 46 of the first mill stand std1, from the open state to the closed state. If control valve 61 is in the closed state, control device 110 does not switch control of control valve 61 and maintains the state of control valve 61.

[0079] On the other hand, when the control valve 48a is in the open state, the control device 110 switches the control valve 61, which is located in the lubrication supply path 46 corresponding to the second mill stand std2, from the closed state to the open state. If the control valve 61 is in the open state, the control device 110 does not switch the control valve 61 and maintains the state of the control valve 61.

[0080] When control valve 48b is in the closed state, control device 110 switches control valve 61 of the lubrication supply path 46 corresponding to the second mill stand std2 from the open state to the closed state. If control valve 61 is in the closed state, control device 110 does not switch control on control valve 61 and maintains the state of control valve 61. When control valve 48b is in the open state, control device 110 switches control valve 61 of the lubrication supply path 46 corresponding to the second mill stand std2 from the closed state to the open state. If control valve 61 is in the open state, control device 110 does not switch control on control valve 61 and maintains the state of control valve 61.

[0081] The control device 110 switches the control valves 61 located in the lubrication supply paths 46 corresponding to the third mill stand std3, the fourth mill stand std4, and the fifth mill stand std5 from the closed state to the open state. If the control valves 61 are in the open state, the control device 110 does not switch the control valves 61 and maintains the state of the control valves 61.

[0082] (5) Regarding control valves 62, 63, and 64: When control valves 62, 63, and 64 remain open, control device 110 does not switch control on control valves 62, 63, and 64, but maintains the state of control valves 62, 63, and 64. When at least one of control valves 62, 63, and 64 is closed, control device 110 switches that control valve from the closed state to the open state. Although this is an example of all control valves 62, 63, and 64 being open, any one or any two control valves 62, 63, and 64 can also be made open according to the temperature and lubrication status of the steel plate S. The temperature of the steel plate S can be obtained from thermometers 114, 115, 116, 117, and 118 located on the upstream side of each mill stand.

[0083] (6) Regarding control valve 68: When it is not necessary to cool the rolls of each mill stand std, the control device 110 switches the control valve 68 corresponding to the cooling supply path 47 of the 1st to 5th mill stands from the open state to the closed state. If the control valve 68 is in the closed state, the control device 110 does not switch the control valve 68 and maintains the state of the control valve 68.

[0084] On the other hand, when it is necessary to cool the rolls of each mill stand std, the control device 110 switches the control valve 68 of the cooling supply path 47 corresponding to the first to fifth mill stands std1 to 5 from the closed state to the open state. If the control valve 68 is in the open state, the control device 110 does not switch the control valve 68 and maintains the state of the control valve 68.

[0085] (7) Regarding control valves 69 and 70: When it is necessary to cool the rolls of each mill stand std, the control device 110 switches control valves 69 and 70 from the closed state to the open state. For example, when control valves 69 and 70 are in the open state, the control device 110 maintains the state of control valves 69 and 70.

[0086] (8) Regarding control valve 83 As described above, the control device 110 calculates the temperature of the steel plate S being rolled by the first mill stand std1 based on the temperature of the rolling oil supplied to the lubricating coolant manifold 21a, the amount of rolling oil sprayed to the lubricating coolant manifold 21a, the temperature of the steel plate S being transported, and the transport speed of the steel plate S.

[0087] When the calculated temperature of the steel plate S is lower than the ductility-brittle transition temperature, the control device 110 switches the control valve 83 of the heating supply path 81 connected to the heating device 25a from the closed state to the open state. If the control valve 83 is in the open state, the control device 110 does not switch the control valve 83 and maintains its state. On the other hand, when the calculated temperature of the steel plate S is higher than the ductility-brittle transition temperature, the control device 110 switches the control valve 83 of the heating supply path 81 connected to the heating device 25a from the open state to the closed state.

[0088] (9) Regarding control valve 84 As described above, the control device 110 calculates the temperature of the steel plate S being rolled by the second mill stand std2 based on the temperature of the rolling oil supplied to the lubricating coolant manifold 21b, the amount of rolling oil sprayed to the lubricating coolant manifold 21b, the temperature of the steel plate S being transported, and the transport speed of the steel plate S.

[0089] When the calculated temperature of the steel plate S is lower than the ductility-brittle transition temperature, the control device 110 switches the control valve 83 of the heating supply path 81 connected to the heating device 25b from the closed state to the open state. If the control valve 83 is in the open state, the control device 110 does not switch the control valve 83 and maintains its state. On the other hand, when the calculated temperature of the steel plate S is higher than the ductility-brittle transition temperature, the control device 110 switches the control valve 83 of the heating supply path 81 connected to the heating device 25b from the open state to the closed state.

[0090] (10) Regarding control valves 96, 97, 98, and 99: When control valve 48a is closed, control device 110 switches control valve 96 from open to closed. Simultaneously, control device 110 switches control valves 97, 98, and 99 from closed to open. If control valve 96 is closed, control device 110 does not switch control valve 96 and maintains its state. If control valves 97, 98, and 99 are open, control device 110 does not switch control valves 97, 98, and 99 and maintains their states.

[0091] When control valve 48b is in the closed state, control device 110 switches control valve 96 from the closed state to the open state and switches control valve 97 from the open state to the closed state. Simultaneously, control device 110 switches control valves 98 and 99 from the closed state to the open state. If control valve 96 is in the open state, control device 110 does not switch control valve 96 and maintains the state of control valve 96. If control valve 97 is in the closed state, control device 110 does not switch control control valve 97 and maintains the state of control valve 97. Furthermore, if control valves 98 and 99 are in the open state, control device 110 does not switch control control control valves 98 and 99 and maintains the state of control valves 98 and 99.

[0092] (11) Regarding the control valve 100, for example, when the second reservoir 32 is not used, the control device 110 switches the control valve 100 from the open state to the closed state. On the other hand, when the second reservoir 32 is used, the control device 110 keeps the control valve 100 in the open state.

[0093] As described above, when the cold rolling equipment 1 starts to operate, the control device 110 drives pumps 42, 51, and 79.

[0094] For example, when control valve 48a is closed and control valves 48b, 48c, and 48d are open, if pumps 42 and 51 are driven, the rolling oil stored in the first reservoir 31 will be supplied to the lubricating coolant manifolds 21b, 21c, 21d, and 21e through the first supply system Sr1. That is, after the rolling oil flows through supply path 45 and each lubrication supply path 46, it is supplied to the lubrication coolant manifolds 21b, 21c, 21d, and 21e respectively. Here, supply path 45 and each lubrication supply path 46 correspond to the second supply path described in the claim.

[0095] Furthermore, if the pump 79 is driven, the rolling oil stored in the second reservoir 32 will be supplied to the lubricating coolant manifold 21a through the second supply system Sr2. That is, after the rolling oil flows through the supply path 76, the branch path 77a, the lubricating supply path 82, and the lubricating supply path 46, it is supplied to the lubricating coolant manifold 21a. Here, the supply path 76, the branch path 77a, the lubricating supply path 82, and the lubricating supply path 46 correspond to the first supply path described in the claim.

[0096] At this time, when the control valve 83 located in the heating supply path 81 connected to the branch path 77a is in the open state, the rolling oil flows through the heating supply path 81 and is supplied to the heating device 25a.

[0097] As described above, the temperature of the rolling oil stored in the second storage tank 32 is maintained at 90°C. Therefore, the rolling oil sprayed from the lubricating coolant manifold 21a and the rolling oil sprayed from the heating device 25a are sprayed onto the steel plate S. As a result, the steel plate S is heated. Therefore, the temperature of the steel plate S becomes above the ductile-brittle transition temperature.

[0098] As described above, the rolling oil stored in the first storage tank 31 is supplied to the lubricating coolant manifolds 21b, 21c, 21d, and 21e through the first supply system Sr1. The temperature of the rolling oil stored in the first storage tank 31 is 50~60°C. Therefore, the steel plate S rolled in each of the second to fifth mill stands std2 is cooled by the rolling oil sprayed from the lubricating coolant manifolds 21b, 21c, 21d, and 21e. That is, the steel plate S is cooled by the rolling oil in the second to fifth mill stands std5, so the rolling process is carried out in a state where the temperature of the steel plate S is at the ductile-brittle transition temperature to the temperature at which non-uniform deformation occurs.

[0099] However, the rolling oil used in the rolling process of the steel plate S in the rolling mill 2 is collected in the oil receiving pan 26 corresponding to each rolling mill stand. For example, when the control valve 96 is closed, the rolling oil collected in the oil receiving pan 26 located below the first rolling mill stand std1 flows sequentially through the discharge path 91a, the recovery path 92, and the return flow path 94 and is recovered to the third storage tank 33. At this time, since the control valves 97, 98, 99 and the control valve 100 are open, the rolling oil collected in the oil receiving pans 26 located below the second rolling mill stand std2 to the fifth rolling mill stand std5 flows sequentially through the discharge paths 91b, 91c, 91d, 91e connected to each oil receiving pan 26 through the recovery path 92 and the return flow path 93 and is recovered to the second storage tank 32. Here, discharge path 91a, recycling path 92, and return flow path 94 correspond to the first recycling path described in the request. The path from discharge paths 91b, 91c, 91d, and 91e to recycling path 92 and return flow path 93 correspond to the second recycling path described in the request.

[0100] In this case, the rolling oil stored in the first storage tank 31 is supplied to the second to fifth mill stands std2, std3, std4, and std5. Furthermore, the rolling oil used in the second to fifth mill stands std2, std3, std4, and std5 is recycled back to the second storage tank 32 and then supplied to the first mill stand std1. Moreover, the rolling oil used in the first mill stand std1 is recycled back to the first storage tank 31. That is, the rolling oil is circulated among the mill stands of the rolling mill 2.

[0101] When control valve 48b is closed and control valve 48a is open, control valves 96, 98, 99 and control valve 100 are opened, and control valve 97 is closed. In this case, the rolling oil stored in the first storage tank 31 is supplied to the lubricating coolant manifolds 21c, 21d, 21e through the first supply system Sr1. On the other hand, the rolling oil stored in the second storage tank 32 is supplied to the lubricating coolant manifolds 21a, 21b through the second supply system Sr2. At this time, if the control valve 83 of the heating supply path 81 connected to the branch path 77a and the control valve 83 of the heating supply path 81 connected to the branch path 77b are open, the rolling oil will be supplied to the heating devices 25a, 25b.

[0102] That is, the rolling oil stored in the first storage tank 31 is supplied to the third to fifth mill stands std3, std4, and std5. Furthermore, the rolling oil used in the third to fifth mill stands std3, std4, and std5 is recycled to the second storage tank 32 and then supplied to the first and second mill stands std1 and std2. Moreover, the rolling oil used in the first and second mill stands std1 and std2 is recycled back to the first storage tank 31. In other words, in this case, the rolling oil is also circulated among the mill stands of the rolling mill 2.

[0103] Thus, in the cold rolling mill 1 of this embodiment, the control device 110 sets the mill stand std, which supplies used rolling oil, to the mill stand std located downstream of the mill stand std in the conveying direction of the steel plate S, based on the temperature of the rolling oil and the steel plate S. Furthermore, the control device controls the opening and closing of each control valve according to this setting. This allows for switching between heating and cooling of the steel plate S at appropriate times.

[0104] However, the temperature of the rolling oil recovered from the first rolling mill stand std1, the second rolling mill stand std2, the third rolling mill stand std3, the fourth rolling mill stand std4 and the fifth rolling mill stand std5 respectively is the highest temperature of the rolling oil recovered from the fifth rolling mill stand std5 which is located at the downstream end.

[0105] Therefore, control valves 96, 97, and 98 can also be opened, and control valve 99 can be closed. In this case, the rolling oil recovered from the first mill stand std1, the second mill stand std2, the third mill stand std3, and the fourth mill stand std4 is recovered to the third storage tank 33. On the other hand, the rolling oil recovered from the fifth mill stand std5 is recovered to the second storage tank 32.

[0106] If the temperature of the rolling oil recovered from the 5th mill stand std5 is low, the control valve 99 can be opened and the control valve 98 can be closed to recover the rolling oil recovered from the 4th mill stand std4 and the 5th mill stand std5 to the 2nd storage tank 32.

[0107] For example, as shown in FIG5(a), in conventional cold rolling equipment 1', the rolling oil stored in the first storage tank 31 is supplied to the lubrication coolant manifold 21 corresponding to each mill stand std. At this time, as shown in FIG5(b), the temperature of the steel plate S being rolled in the first mill stand std1 is lower than the brittle transition temperature. Therefore, during the rolling process in the first mill stand std1, the steel plate S is prone to brittle fracture.

[0108] Furthermore, the temperature of the steel plate S after rolling at the first mill stand (std1) exceeds the temperature at which uneven deformation occurs. At this point, during rolling processes at the second mill stand (std2 and beyond), the steel plate S is cooled by rolling oil sprayed from the lubrication coolant manifold 21, causing the temperature to reach the ductile-brittle transition temperature—the temperature at which uneven deformation occurs. Therefore, brittle fracture does not occur during rolling processes at the second mill stand (std2 and beyond).

[0109] In the rolling process after the second mill stand std2, the temperature of the steel plate S is cooled by the rolling oil sprayed from the lubricating coolant manifold 21, so that the temperature is below the temperature at which uneven deformation occurs. Therefore, the deformation of the work roll 11 and the deformation of the steel plate S caused by the deformation of the work roll 11 will not occur.

[0110] However, if the temperature of the rolling oil sprayed from the lubricating coolant manifold 21 is insufficient or the amount of rolling oil sprayed is insufficient, the rolling process after the second mill stand std2 may result in uneven deformation and temperature.

[0111] On the other hand, in this embodiment, for example, during the rolling process at the first rolling mill stand std1, the temperature of the steel plate S being rolled at the first rolling mill stand std1 can be heated to the ductility transition temperature to the temperature at which uneven deformation occurs by supplying high-temperature rolling oil that has been used in the third to fifth rolling mill stands. As a result, brittle fracture can be prevented during the rolling process of the steel plate.

[0112] In this embodiment, the rolling oil used by the mill stand std on the downstream side in the conveying direction of the steel plate S is supplied to the mill stand std on the upstream side, and the rolling oil used by the mill stand std on the upstream side is supplied to the mill stand std on the downstream side. As a result, when supplying rolling oil from the first reservoir and the second reservoir to the mill 2, it is not necessary to cool the rolling oil with the heat exchanger 52.

[0113] In this way, the rolling oil used in the mill stand std located downstream of the steel plate S in the conveying direction of the mill 2 is supplied to the mill stand std located upstream of the conveying direction. At this time, the temperature of the rolling oil used in the mill stand std located downstream of the steel plate S in the conveying direction of the mill 2 becomes high due to the heating of the steel plate S, which has become high temperature through multiple rolling processes. Therefore, by using such rolling oil in the mill stand std located upstream of the steel plate S in the conveying direction of the mill 2, the steel plate S can be heated without the need to install a new heating device.

[0114] The rolling oil used in the mill stand std located upstream of the steel plate S in the conveying direction is supplied to the mill stand std located downstream of the conveying direction. The temperature of the rolling oil used in the mill stand std located upstream of the steel plate S in the conveying direction is relatively low. Therefore, by using such rolling oil in the mill stand std located downstream of the steel plate S in the conveying direction, the steel plate S can be cooled without the need for a new cooling device.

[0115] Thus, by spraying rolling oil onto the steel plate S before the rolling process at each mill stand std, the temperature of the steel plate S before being rolled by each mill stand std can be kept within the range of the ductility-brittle transition temperature to the temperature at which uneven deformation occurs. Here, the range of the ductility-brittle transition temperature to the temperature at which uneven deformation occurs is a temperature range in which the rolling process can be performed appropriately. Therefore, brittle fracture of the rolled steel plate S and thermal deformation of the work rolls during the rolling process can be prevented, and the occurrence of shape defects of the steel plate S caused by the work rolls after thermal deformation can be prevented.

[0116] Finally, when the conveying speed of the steel plate S was changed, the error temperature ΔT of the steel plate S at the bite section of the first mill stand std1 relative to the target temperature and the fracture rate of the steel plate were measured. The measurement results of the error temperature ΔT and the fracture rate of the steel plate are shown in Table 1.

[0117]

[0118] In Table 1, the test results No.1 to No.4 of the cold rolling equipment of this embodiment are used as examples of the invention, and the test results No.5 to No.8 of the cold rolling equipment using a steam-based heating device shown in Patent Document 1 are used as comparative examples.

[0119] The biting section of the first mill stand std1 refers to the part where the steel plate is rolled by a pair of work rolls 11. Hereinafter, the target temperature of the steel plate at the biting section of the first mill stand std1 is set to 80°C. Measurements were also performed with the steel plate conveying speed set to 15, 50, 100 and 150 mpm.

[0120] In the inventive example, when the conveying speed of the steel plate S is set to 15, 50, 100, and 150 mpm, the temperature error ΔT of the steel plate S relative to the target temperature is +18°C, +15°C, +10°C, and +5°C, respectively. In contrast, in the comparative example, the temperature error ΔT of the steel plate S relative to the target temperature is +15°C, +8°C, -5°C, and -10°C, respectively. It can be seen that in the inventive example, even when the conveying speed of the steel plate is increased, the steel plate can still be reliably heated.

[0121] In the inventive example, because the temperature is higher than the target temperature, the fracture rate during rolling is less than 0.15%, compared to less than 0.25% in the comparative example. That is, in the inventive example, the steel plate can be heated more efficiently than in the comparative example. As a result, it can be seen that, compared to the comparative example, the inventive example is less prone to brittle fracture during rolling.

[0122] In this embodiment, although it is described that the steel plate S is rolled without supplying rolling oil to the cooling coolant manifold 22, it is also possible that the steel plate S is rolled by supplying rolling oil not only to the lubrication coolant manifold 21 but also to the cooling coolant manifold 22.

[0123] In this embodiment, the rolling oil used in the first mill stand std1 or the second mill stand std2 is recycled to the first storage tank 31, and the rolling oil used in the third mill stand std3, the fourth mill stand std4 and the fifth mill stand std5 is recycled to the second storage tank 32.

[0124] However, in the rolling process using a plurality of mill stands arranged along the conveying direction of the steel plate S, the temperature of the steel plate S rises downstream in the conveying direction of the steel plate S. Therefore, the amount of rolling oil sprayed from the lubrication coolant manifold 21 corresponding to the mill stand std located downstream is greater than the amount of rolling oil sprayed from the lubrication coolant manifold 21 corresponding to the mill stand std located upstream. As a result, the amount of rolling oil stored (recovered) in the second storage tank 32 becomes greater than the amount of rolling oil stored (recovered) in the first storage tank 31. That is, it may be impossible to supply rolling oil from the first storage tank 31 to the third mill stand std3, the fourth mill stand std4, and the fifth mill stand std5. Therefore, a portion of the rolling oil used in the third rolling mill std3, the fourth rolling mill std4, and the fifth rolling mill std5 can flow to the second storage tank 32, while the remainder flows to the first storage tank 31.

[0125] In this embodiment, there is no particular limitation on the amount of rolling oil sprayed from the lubrication coolant manifold 21 corresponding to each mill stand std, and the amount of rolling oil sprayed can be changed according to the position of the lubrication coolant manifold 21.

[0126] In this embodiment, the rolling oil used in the downstream mill stand std is supplied to the upstream mill stand, and the rolling oil used in those mill stands is supplied to the downstream mill stand std, thereby circulating the rolling oil. However, it is not necessary to circulate the rolling oil within the cold rolling equipment 1; for example, it is not necessary to supply the rolling oil used in the upstream mill stand std in the conveying direction of the steel plate S to the downstream mill stand.

[0127] <Summary of Effects> The cold rolling method of the present invention supplies rolling oil to a plurality of rolling mill stands std arranged along the conveying direction of the steel plate S, and performs rolling processing on the steel plate S by means of the plurality of rolling mill stands std. At least a portion of the rolling oil recovered from the rolling mill stand std arranged downstream of the steel plate S in the conveying direction of the plurality of rolling mill stands std is supplied to a predetermined number of rolling mill stands std including the rolling mill stand std arranged upstream of the steel plate S in the conveying direction of the steel plate S.

[0128] For example, in a rolling process using multiple rolling mill stands (std), the temperature of the steel plate S increases with the number of rolling processes. That is, the temperature of the rolling oil used in the rolling process of the rolling mill stand (std) located downstream in the conveying direction of the steel plate S becomes higher as it is heated further downstream. Therefore, by supplying the rolling oil recovered from the rolling mill stand (std) located downstream to a predetermined number of rolling mill stands (std), including the rolling mill stand (std) located upstream, the steel plate S being rolled in a predetermined number of rolling mill stands (std) is heated. As a result, the occurrence of brittle fracture of the steel plate S can be suppressed during the rolling process of these rolling mill stands (std).

[0129] It also includes a heating device 25, which is arranged at least upstream of the upstream mill stand std in the conveying direction of the steel plate S, and is used to spray rolling oil toward the steel plate S. The rolling oil used by the mill stand std arranged downstream in the conveying direction of the steel plate S is supplied to the heating device 25 as needed, in addition to a predetermined number of mill stands std.

[0130] According to this configuration, the rolling oil used in the mill stand std located on the downstream side is not only supplied to a predetermined number of mill stands std, including the mill stand std located at the upstream end, but also supplied to the heating device 25, which can increase the amount of rolling oil sprayed onto the steel plate S, thereby effectively heating the steel plate S that has been rolled.

[0131] The temperature of the rolling oil supplied to the rolls of a predetermined number of rolling mill stands std is above 80°C.

[0132] Based on this configuration, the steel plate S before rolling can be effectively heated.

[0133] The rolling oil recovered from a predetermined number of rolling mill stands std is supplied to rolling mill stands std other than the predetermined number of rolling mill stands std, and the rolling oil is circulated among the plurality of rolling mill stands std.

[0134] Based on this configuration, by supplying the rolling oil heated in the downstream mill stand std to the mill stand std located on the upstream side in the conveying direction of the steel plate S, and supplying the rolling oil cooled in the upstream mill stand std to the mill stand std located on the downstream side in the conveying direction of the steel plate S, the temperature of the rolled steel plate can be adjusted to the ductility-brittle transition temperature to the temperature at which non-uniform deformation occurs, even without installing new heating or cooling devices.

[0135] Furthermore, the manufacturing method of the steel plate S of the present invention includes: a cold rolling process using the cold rolling method shown in the present invention, and a final annealing process for performing a final annealing on the steel plate S that has undergone the cold rolling process as needed.

[0136] Based on this configuration, even without installing new heating or cooling devices, it is still possible to prevent brittle fracture of the steel plate during rolling, deformation of the work roll, and deformation of the steel plate caused by the deformation of the work roll.

[0137] Furthermore, the cold rolling equipment of the present invention supplies rolling oil to a plurality of mill stands std arranged along the conveying direction of the steel plate S, and performs rolling processing on the steel plate S by means of the plurality of mill stands std. The cold rolling equipment includes: supply systems Sr1, Sr2 that can supply rolling oil to the plurality of mill stands std respectively; a recovery system C1 that can recover rolling oil from the plurality of mill stands std; a plurality of control valves arranged in each of the supply systems Sr1, Sr2 and the recovery system C1; and a switching system. The control device 110 controls the opening and closing states of several control valves. The control device 110 switches the opening and closing states of the multiple control valves, so that the recovery system C1 forms a first recovery path for recovering rolling oil from the mill stand std located downstream of the conveying direction of the steel plate S, and the supply systems Sr1 and Sr2 form a first supply path for supplying a portion of the rolling oil recovered through the first recovery path to a predetermined number of mill stands std located upstream of the conveying direction of the steel plate S.

[0138] For example, in a rolling process using multiple rolling mill stands (std), the temperature of the steel plate S increases with the number of rolling processes. That is, the temperature of the rolling oil used in the rolling process of the rolling mill stand (std) located downstream in the conveying direction of the steel plate S becomes higher as it is heated further downstream. Therefore, by supplying the rolling oil recovered from the rolling mill stand (std) located downstream to a predetermined number of rolling mill stands (std), including the rolling mill stand (std) located upstream, the steel plate S being rolled in a predetermined number of rolling mill stands (std) is heated. As a result, brittle fracture of the steel plate S can be prevented during the rolling process of these rolling mill stands (std).

[0139] It also includes a heating device 25, which is arranged at least on the upstream side of the upstream mill stand std in the conveying direction of the steel plate S, and can spray a portion of the rolling oil recovered from at least one mill stand std arranged on the downstream side in the conveying direction of the steel plate S toward the steel plate S.

[0140] According to this configuration, the rolling oil used in the downstream mill stand std is not only supplied to a predetermined number of mill stands std, including the upstream mill stand std, but can also be supplied from the heating device 25, so that the steel plate S before rolling can be effectively heated.

[0141] When the recycling system C1 forms the first recycling path, it also forms a second recycling path to recycle the rolling oil used by a predetermined number of rolling mill stands std. When the supply system forms the first supply path, it also forms a second supply path to supply the rolling oil recovered through the second recycling path to rolling mill stands std other than the predetermined number of rolling mill stands std.

[0142] For example, the temperature of the rolling oil used in a predetermined number of rolling mill stands std1, including the first rolling mill stand std1, is lower than the temperature of the rolling oil used in the rolling mill stands stds located downstream of the predetermined number of rolling mill stands stds. Therefore, by supplying such rolling oil to the rolling mill stands stds located downstream, the steel plate S can be effectively cooled.

[0143] Furthermore, the control method of the cold rolling equipment of the present invention involves supplying rolling oil to a plurality of mill stands std arranged along the conveying direction of the steel plate S, while performing rolling processing on the steel plate S by the plurality of mill stands std. The cold rolling equipment includes: supply systems Sr1, Sr2 capable of supplying rolling oil to the plurality of mill stands std respectively; a recovery system C1 capable of recovering rolling oil from the plurality of mill stands std; a plurality of control valves arranged in each of the supply systems Sr1, Sr2 and the recovery system C1; and the ability to switch the opening and closing of the plurality of control valves. The state control device 110 switches the opening and closing states of a plurality of control valves according to the temperature of the rolling oil supplied to a plurality of mill stands std and the temperature of the rolled steel plate S. This forms a first recovery path in the recovery system C1 for recovering the rolling oil from the mill stand std located downstream of the conveying direction of the steel plate S, and a first supply path in the supply systems Sr1 and Sr2 for supplying a portion of the rolling oil recovered through the first recovery path to a predetermined number of mill stands std, including the upstream mill stand std located in the conveying direction of the steel plate S.

[0144] Based on this configuration, the mill stand std that heats the steel plate S during the rolling process can be easily set by controlling the control valve.

[0145] When the recycling system C1 forms the first recycling path, it also forms a second recycling path to recycle the rolling oil used by a predetermined number of rolling mill stands std. When the supply systems Sr1 and Sr2 form the first supply path, they also form a second supply path to supply the rolling oil recovered by the second recycling path to rolling mill stands std other than the predetermined number of rolling mill stands std.

[0146] Based on this configuration, by circulating rolling oil between multiple mill stands, rolling processing can be performed at each mill stand to keep the temperature of the steel plate S within the range of ductile-brittle transition temperature to non-uniform deformation temperature. As a result, the occurrence of brittle fracture during rolling processing, deformation of the work rolls, and deformation of the steel plate S caused by deformation of the work rolls can be suppressed. [Simplified Explanation of the Diagram]

[0020] [Figure 1] is a schematic diagram showing the structure of a cold rolling mill according to one embodiment of the present invention. [Figure 2] is a schematic diagram showing the structure near the first and second mill stands of the rolling mill. [Figure 3] is a schematic diagram showing the structure near the third to fifth mill stands of the rolling mill. [Figure 4] is a schematic flowchart showing the process of manufacturing cold-rolled steel coils from hot-rolled steel coils. [Figure 5(a)] is a schematic diagram showing the flow of rolling oil during the operation of conventional cold rolling mills, and [Figure 5(b)] is a graph showing the temperature change of the steel plate of the cold rolling mill shown in Figure 5(a).

Claims

1. A cold rolling method comprising supplying rolling oil to a plurality of rolling mill stands arranged along the conveying direction of a steel plate while performing rolling processing on the plurality of rolling mill stands, recovering at least a portion of the aforementioned rolling oil from a rolling mill stand arranged downstream of the steel plate in the conveying direction of the plurality of rolling mill stands, and supplying it to a predetermined number of rolling mill stands including the rolling mill stand arranged upstream of the steel plate in the conveying direction of the steel plate, recovering the aforementioned rolling oil from the predetermined number of rolling mill stands and supplying it to rolling mill stands other than the predetermined number of rolling mill stands, and circulating the aforementioned rolling oil among the plurality of rolling mill stands.

2. The cold rolling method as described in claim 1, wherein, The device is equipped with a rolling oil spraying device, which is arranged at least upstream of the aforementioned upstream mill stand in the conveying direction of the aforementioned steel plate, and is used to spray the aforementioned rolling oil toward the aforementioned steel plate. The rolling oil used by the mill stand arranged downstream in the conveying direction of the aforementioned steel plate is supplied to the aforementioned rolling oil spraying device as needed, in addition to the predetermined number of mill stands.

3. The cold rolling method as described in request item 1, wherein, The temperature of the rolling oil supplied to the aforementioned predetermined number of rolling mill stands is above 80°C.

4. A method for manufacturing a steel plate, comprising: a cold rolling process using any one of claims 1 to 3, and a final annealing process for performing a final annealing on the steel plate having undergone the aforementioned cold rolling process as required.

5. A cold rolling apparatus that supplies rolling oil to a plurality of mill stands arranged along the conveying direction of a steel plate while performing rolling processing on the aforementioned plurality of mill stands, the cold rolling apparatus comprising: a supply system for supplying rolling oil to the aforementioned plurality of mill stands; a recovery system for recovering the aforementioned rolling oil from the aforementioned plurality of mill stands; a plurality of control valves disposed in each of the aforementioned supply system and the aforementioned recovery system; and a control device for switching the opening and closing states of the aforementioned plurality of control valves, wherein the control device switches the opening and closing states of the aforementioned plurality of control valves such that the aforementioned recovery system forms a first recovery path for recovering the aforementioned rolling oil from a mill stand arranged downstream in the conveying direction of the aforementioned steel plate, and the aforementioned supply system forms a first supply path for supplying a portion of the rolling oil recovered through the aforementioned first recovery path to a predetermined number of mill stands, including the mill stand arranged upstream in the conveying direction of the aforementioned steel plate. When the aforementioned recycling system forms the aforementioned first recycling path, it also forms a second recycling path to recover the rolling oil used in the aforementioned predetermined number of rolling mill stands. When the aforementioned supply system forms the aforementioned first supply path, it also forms a second supply path to supply the rolling oil recovered through the aforementioned second recycling path to rolling mill stands other than the aforementioned predetermined number of rolling mill stands.

6. The cold rolling equipment as requested in item 5, wherein, It is equipped with a rolling oil spraying device, which is arranged at least on the upstream side of the aforementioned mill stand located in the conveying direction of the aforementioned steel plate, and can spray a portion of the aforementioned rolling oil recovered from at least one of the aforementioned mill stands located on the downstream side in the conveying direction of the aforementioned steel plate toward the aforementioned steel plate.

7. A control method for a cold rolling mill, comprising supplying rolling oil to a plurality of rolling mill stands arranged along the conveying direction of a steel plate while performing rolling processing on the aforementioned plurality of rolling mill stands, wherein the cold rolling mill includes: a supply system capable of supplying rolling oil to the aforementioned plurality of rolling mill stands respectively; a recovery system capable of recovering rolling oil used in the aforementioned plurality of rolling mill stands; a plurality of control valves disposed in each of the aforementioned supply system and the aforementioned recovery system; and a control device for switching the opening and closing states of the aforementioned plurality of control valves. The aforementioned control device switches the opening and closing states of the aforementioned plurality of control valves according to the temperature of the rolling oil supplied to the aforementioned plurality of rolling mill stands and the temperature of the aforementioned steel plate. This forms a first recovery path in the aforementioned recovery system for recovering the aforementioned rolling oil from the rolling mill stand located downstream of the aforementioned steel plate in the conveying direction, and a first supply path in the aforementioned supply system for supplying a portion of the rolling oil recovered through the aforementioned first recovery path to a predetermined number of rolling mill stands, including the rolling mill stand located upstream of the aforementioned steel plate in the conveying direction. When forming the aforementioned first recovery path, the aforementioned recovery system also forms a second recovery path for recovering the aforementioned rolling oil from the aforementioned predetermined number of rolling mill stands. When forming the aforementioned first supply path, the aforementioned supply system also forms a second supply path for supplying a portion of the rolling oil recovered through the aforementioned second recovery path to rolling mill stands other than the aforementioned predetermined number of rolling mill stands.

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