Method for manufacturing pass line rolls and steel plates

Abstract

To provide a pass line roll arranged between a plurality of rolling machines, the pass line roll being capable of preventing influence on a surface quality of a steel plate and suppressing generation of slip between the pass line roll and the steel plate.SOLUTION: Provided is a pass line roll arranged between a plurality of rolling machines in a rolling line including the plurality of rolling machines. A surface roughness Ra of a contact surface with a steel plate passed in the rolling line is 1.0 μm or more and 3.0 μm or less.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a pass line roll disposed between a plurality of rolling mills in a rolling line having the plurality of rolling mills and a method for manufacturing a steel sheet.

Background Art

[0002] In the rolling of steel sheets, tandem rolling is performed in which a plurality of rolling mills are arranged in tandem along a rolling line and the steel sheet to be rolled is passed through the plurality of rolling mills. In tandem rolling, in order to roll the steel sheet to be passed through to a predetermined thickness, measurement and control of the tension between the rolling mills are essential. For this reason, a pass line roll is disposed between the rolling mills, and the pass line roll measures and controls the tension in the rolling line. Specifically, measurement and control are performed on the tension on the outlet side of the rolling mill disposed upstream of the rolling line with respect to the pass line roll. The pass line roll includes a tension meter roll that measures the tension in the rolling line and a deflector roll that is used as an auxiliary roll for the tension meter roll.

[0003] In tandem rolling, slip occurs between the steel sheet and the rolls (work rolls and pass line rolls in the rolling mill) due to the speed difference between the steel sheet to be passed through and the rolls on the rolling line. In contrast, Patent Document 1 discloses a method of preventing slip between the work roll and the steel sheet by adjusting the surface roughness Ra of the work roll.

[0004] Slip also occurs between the steel sheet and the pass line roll. Since the pass line roll is configured to rotate in a non-driven manner, it stops rotating when slip occurs. Therefore, when slip occurs between the steel sheet and the pass line roll, scratch-like defects occur on the surface of the steel sheet. Scratch-like defects are likely to occur when the steel sheet is a thin material with a thickness of less than 0.6 mm.

[0005] Therefore, to prevent slippage between the steel sheet and the pass line rolls, a method is employed in which roughness is applied to the surface of the work rolls of a rolling mill located upstream of the pass line, and the roughness is transferred to the surface of the steel sheet by rolling with these work rolls. With this method, when the steel sheet with the transferred roughness passes through the pass line rolls, the frictional force (coefficient of friction) between the steel sheet and the pass line rolls increases, suppressing slippage. Furthermore, in the case of thin materials where higher surface quality is required, in order to avoid slippage between the thin material and the pass line rolls, the work rolls are replaced with those that have been given a rough surface prior to rolling on the rolling line. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 08-24903 [Overview of the project] [Problems that the invention aims to solve]

[0007] However, the method of increasing the coefficient of friction between the steel plate and the pass line roll by applying roughness to the surface of the work roll and transferring that roughness to the surface of the steel plate has a significant impact on the surface quality of the steel plate, making it difficult to actively apply. Furthermore, since the surface of the work roll wears down remarkably quickly due to repeated rolling, suppressing slip by transferring the roughness of the work roll surface to the surface of the steel plate is practically difficult in operation.

[0008] The present invention has been made in view of the above circumstances, and its object is to provide a pass line roll that can avoid affecting the surface quality of steel sheets and suppress the occurrence of slippage between the pass line roll and the steel sheets, when the pass line roll is arranged between a plurality of rolling mills. [Means for solving the problem]

[0009] [1] A pass line roll disposed between a plurality of rolling mills in a rolling line having a plurality of rolling mills, wherein the surface roughness Ra of the contact surface with the steel sheet passed through the rolling line is 1.0 μm or more and 3.0 μm or less. [2] The pass line roll according to [1], having a hard metal plating layer on the contact surface. [3] A method for manufacturing steel sheets, comprising passing a steel sheet through a rolling line having a plurality of rolling mills and rolling it, wherein the steel sheet is passed through a pass line roll disposed between the plurality of rolling mills and having a surface roughness Ra of the contact surface with the steel sheet of 1.0 μm or more and 3.0 μm or less. [Effects of the Invention]

[0010] According to the present invention, it is possible to avoid affecting the surface quality of steel sheets and suppress the occurrence of slippage between the steel sheets and pass line rolls arranged between multiple rolling mills. [Brief explanation of the drawing]

[0011] [Figure 1] This figure shows a schematic side view of an example of a rolling line. [Figure 2] This figure shows the relationship between the surface roughness transferred to the steel plate and the work roll pressure extension. [Figure 3] This figure shows the relationship between the surface roughness of a pass line roll and its service life. [Figure 4] This figure shows the relationship between the rotation speed of the work rolls and the rotation speed of the pass line rolls when pass line rolls with a surface roughness Ra of 0.2 μm or less are applied to a rolling line. [Figure 5] This figure shows the relationship between the rotation speed of the work roll and the rotation speed of the pass line roll when a pass line roll with a surface roughness Ra of 2.5 μm is applied to a rolling line. [Modes for carrying out the invention]

[0012] Embodiments of the present invention will be described in detail below. Figure 1 shows a schematic side view as an example of a rolling line 1. The rolling line 1 may be a rolling facility capable of tandem rolling having a plurality of rolling mills. The rolling line 1 has, in order from the upstream side along the sheet passage direction T of the steel sheet S, an upstream rolling mill 10, a pass line roll 20, and a downstream rolling mill 30.

[0013] The upstream rolling mill 10 has a pair of upper and lower backup rolls 11 and a work roll 12 that sandwich the steel plate S. The pass line roll 20 has a tension meter roll 21 and a deflorer 22. The tension meter roll 21 measures the tension of the steel plate S in the rolling line 1. The deflorer 22 is used as an auxiliary roll for the tension meter roll. The upstream rolling mill 10 and the downstream rolling mill 30 roll the steel plate S as it passes through the rolling line 1.

[0014] Here, we will explain the relationship between the surface roughness of the steel plate and the work roll pressure extension when roughness is applied to the surface of the work roll and this roughness is transferred to the surface of the steel plate, thereby increasing the frictional force between the steel plate and the pass line roll, using Figure 2. Figure 2 is a diagram showing the relationship between the transferred surface roughness on the steel plate and the work roll pressure extension. The work roll pressure extension refers to the total length of the steel plate rolled using the work roll.

[0015] As shown in Figure 2, when the work roll pressure extension is short, the surface roughness Ra of the steel plate is in the range of 0.4 to 0.6 μm. Therefore, it can be confirmed that when the work roll pressure extension is short, the occurrence of slip between the steel plate, which has had its roughness transferred, and the pass line roll is suppressed. In other words, it is thought that by maintaining a high surface roughness Ra of the steel plate, the frictional force (coefficient of friction) between the steel plate and the pass line roll increases, and slip is suppressed.

[0016] On the other hand, when the length of work roll rolling increases, the surface roughness Ra of the steel sheet becomes a value of 0.4 μm or less, and it can be confirmed that slip is likely to occur between the steel sheet with the transferred roughness and the pass line roll. As shown in FIG. 2, this can be confirmed from the fact that slip occurs at the timing when the surface roughness Ra of the steel sheet decreases.

[0017] Therefore, in order to suppress the occurrence of slip between the steel sheet and the pass line roll, the frictional force (friction coefficient) between the steel sheet and the pass line roll becomes an important factor, and it is necessary to increase the frictional force (friction coefficient).

[0018] Note that the relationship between the surface roughness of the steel sheet and the length of work roll rolling shown in FIG. 2 is the result based on the method of transferring the surface roughness of the work roll to the surface of the steel sheet, so it is difficult to apply it positively with a large influence on the surface quality of the steel sheet.

[0019] Therefore, in the present invention, by imparting roughness to the surface of the pass line roll, the occurrence of slip is suppressed between the steel sheet passing through the pass line roll. Specifically, by setting the surface roughness Ra of the pass line roll to 1.0 μm or more, it became possible to suppress the occurrence of slip. And in the rolling using the rolling line 1, regarding the value of the surface roughness Ra of the pass line roll, 1.0 μm is used as a threshold value, and when the surface roughness Ra is less than 1.0 μm, the pass line roll is replaced.

[0020] In a rolling facility (rolling line 1) capable of tandem rolling, a dull roll with a high surface roughness is used for the rolling mill on the most downstream side among a plurality of rolling mills. The dull roll has a surface roughness Ra exceeding 3.0 μm. Therefore, when manufacturing a steel sheet in the rolling facility, the surface roughness of the steel sheet is controlled (adjusted) by finally using a dull roll having a surface roughness Ra having a value exceeding 3.0 μm. Based on this, from the viewpoint of the influence on the surface quality of the steel sheet, in order to suppress the influence on the control of the surface roughness Ra of the steel sheet using the dull roll, the upper limit of the surface roughness Ra of the pass line roll is set to 3.0 μm or less.

[0021] Here, based on the range of the surface roughness Ra of the pass line roll 20 (1.0 μm or more and 3.0 μm or less), the change in the surface roughness Ra when the pass line roll 20 with a surface roughness Ra value of 2.5 ± 0.5 μm was applied to the rolling line 1 was investigated.

[0022] The change in the surface roughness Ra of the pass line roll 20 will be described using FIG. 3. FIG. 3 is a diagram showing the relationship between the surface roughness of the pass line roll 20 and the service period. As shown in FIG. 3, it can be confirmed that at the time when the pass line roll 20 with a surface roughness Ra value of 2.5 ± 0.5 μm was applied to the rolling line 1 (the left end of the graph), the surface roughness Ra value showed a value of 2.0 μm or more. And even after one year of use, it was confirmed that the surface roughness Ra value could be maintained at 1.0 μm or more.

[0023] The surface roughness of the pass line roll 20 may be imparted (surface processed) by a shot blasting method, a sand blasting method, a grid blasting method, or the like. Also, compared with the shot blasting method, the surface roughness may be imparted to the pass line roll 20 by dimple processing that can locally relieve the pressure concentration by spheroidizing the surface.

[0024] It is preferable to apply a hard metal plating layer to the contact surface having surface roughness after surface roughening (surface processing) of the pass line roll 20. By having a hard metal plating layer on the contact surface having surface roughness, the surface roughness achieved by the surface processing can be maintained for a long period of time. In this case, the hard metal plating layer may be formed, for example, starting from the side closest to the surface of the pass line roll 20, with the first layer being made of a Ni-based self-fluxing alloy containing Ni or Cr with a hardness of about HV650, and the second layer being formed by WC cermet processing with a hardness of about HV1000. Even when the hard metal plating layer is formed as a single layer by WC cermet processing, it is effective in maintaining surface roughness. However, due to the large difference between the hardness of the pass line roll 20 and the hard metal plating layer, delamination between the pass line roll 20 and the hard metal plating layer is likely to occur. For this reason, it is preferable to form a layer with a lower hardness than the hard metal plating layer between the hard metal plating layer and the pass line roll 20.

[0025] Furthermore, the steel sheet manufacturing method according to the present invention involves rolling a steel sheet S through a rolling line 1 having a plurality of rolling mills (upstream rolling mill 10 and downstream rolling mill 30). Specifically, the steel sheet S is passed through a pass line roll 20 which is positioned between the plurality of rolling mills (upstream rolling mill 10 and downstream rolling mill 30) and whose contact surface with the steel sheet S has a surface roughness Ra of 1.0 μm or more and 3.0 μm or less. [Examples]

[0026] Next, we will explain the results of applying the pass line roll according to the present invention to a rolling line and performing rolling processing by passing a steel sheet through the rolling line. The steel sheet passing through the rolling mill passes through the exit side of the rolling mill at a passing speed equivalent to the rotational speed of the work rolls in the rolling mill. The pass line roll, which is located downstream of the rolling mill, is a non-driven type, and therefore rotates at a rotational speed equivalent to the passing speed of the steel sheet due to contact with the passing steel sheet.

[0027] Based on these speed-related relationships, in this embodiment, the relationship between the rotational speed of the work rolls and the rotational speed of the pass line rolls in the rolling mill was evaluated. Specifically, when the rotational speed of the work rolls and the rotational speed of the pass line rolls in the rolling mill were the same, the pass line rolls were evaluated as "no slip," and when the rotational speed of the work rolls was faster than the rotational speed of the pass line rolls, the pass line rolls were evaluated as "slip present."

[0028] Figure 4 shows the results of investigating the relationship between the rotation speed of the work rolls and the rotation speed of the pass line rolls when a pass line roll with a surface roughness Ra of 0.2 μm was applied to the rolling line. Figure 5 shows the results of investigating the relationship between the rotation speed of the work rolls and the rotation speed of the pass line rolls when a pass line roll with a surface roughness Ra of 2.5 μm was applied to the rolling line. In both cases, surface roughness was imparted by the shot blasting method. The steel plates used to pass through the rolling line had a tensile strength of 270 MPa and a surface roughness Ra of approximately 0.3 μm (estimated). The rolling speed in the rolling line was set to a speed of around 1000 mpm. No work rolls were changed before rolling. The surface roughness Ra of the pass line rolls described above was measured based on "JIS B 0601:2013 Surface Roughness," with an evaluation length of 4 mm and a cutoff of 0.8 mm.

[0029] As shown in Figure 4, when a pass line roll with a surface roughness Ra of 0.2 μm was applied to the rolling line, a large speed difference was observed between the rotation speed of the work roll and the rotation speed of the pass line roll, and it was confirmed that slip occurred between the pass line roll and the steel sheet.

[0030] On the other hand, when a pass line roll with a surface roughness Ra of 2.5 μm was applied to the rolling line, as shown in Figure 5, the rotation speed of the work roll and the rotation speed of the pass line roll always matched, confirming that no slip occurred between the pass line roll and the steel sheet.

[0031] As described above, by applying surface roughness to the contact surface between the steel plate and the pass line roll, the frictional force (coefficient of friction) between the steel plate and the pass line roll was increased, thereby suppressing the occurrence of slip between the steel plate and the pass line roll regardless of the surface roughness of the steel plate. Furthermore, it became unnecessary to apply roughness to the surface of the work roll and transfer that roughness to the surface of the steel plate to increase the frictional force (coefficient of friction) between the steel plate and the pass line roll, thus avoiding any impact on the surface quality of the steel plate. Moreover, based on the suppression of slip, it is possible to improve the surface quality of the steel plate and improve the yield in the manufacturing of steel plates. [Explanation of Symbols]

[0032] 1. Rolling line 10 Upstream rolling mill 11 Backup Role 12 Work Roles 20 Pass Line Roll 21 Tension Meter Roll 22 Deflor 30 Downstream rolling mill S steel plate T Threading direction

Claims

1. A pass line roll disposed between a plurality of rolling mills in a rolling line having a plurality of rolling mills, wherein the surface roughness Ra of the contact surface with the steel sheet passed through the rolling line is 1.0 μm or more and 3.0 μm or less, and the contact surface has a hard metal plating layer consisting of a Ni-based self-fluxing alloy layer and a layer formed by WC cermet processing, in order from the side closest to the surface of the pass line roll.

2. A method for manufacturing steel sheets, comprising passing a steel sheet through a rolling line having multiple rolling mills, wherein the steel sheet is passed through a pass line roll having a hard metal plating layer on its contact surface, which is disposed between the multiple rolling mills and has a surface roughness Ra of 1.0 μm or more and 3.0 μm or less on the contact surface with the steel sheet, and which has a layer of Ni-based self-fluxing alloy and a layer formed by WC cermet processing in order from the side closest to the surface of the pass line roll, in which case the steel sheet is passed.

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