Pass line roll and steel plate manufacturing method

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 a plurality of rolling mills, and a method for manufacturing a steel plate. [Background technology]

[0002] In the rolling of steel sheets, a tandem rolling method is used 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 to perform rolling. In the tandem rolling method, in order to roll the steel sheet to be passed through the plurality of rolling mills to a predetermined thickness, it is essential to measure and control the tension between the rolling mills. For this reason, pass line rolls are arranged between the rolling mills, and the tension in the rolling line is measured and controlled by the pass line rolls. Specifically, the tension on the exit side of the rolling mill arranged upstream of the rolling line with respect to the pass line rolls is measured and controlled. The pass line rolls include a tension meter roll that measures the tension in the rolling line, and a diff roll that is used as an auxiliary roll for the tension meter roll.

[0003] In tandem rolling, slippage occurs between the steel sheet and the rolls due to the speed difference between the passing steel sheet and the rolls on the rolling line (the work rolls and pass line rolls in the rolling mill). In response to this, Patent Document 1 discloses a method for preventing slippage between the work rolls and the steel sheet by adjusting the surface roughness Ra of the work rolls.

[0004] Slippage also occurs between the steel sheet and the pass line roll. Since the pass line roll rotates in a non-driven manner, it stops rotating when slippage occurs. Therefore, when slippage occurs between the steel sheet and the pass line roll, a scratch-like defect occurs 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] For this reason, a method for preventing slippage between a steel sheet and a pass line roll is to impart roughness to the surface of the work roll of a rolling mill arranged upstream of the pass line, and transfer the roughness to the surface of the steel sheet by rolling with the work roll. With this method, when the steel sheet to which the roughness has been transferred passes through the pass line roll, the frictional force (friction coefficient) between the steel sheet and the pass line roll increases, suppressing slippage. For thin materials, which require higher surface quality, work is performed to replace the work rolls with those having roughness on the surface prior to rolling in the rolling line in order to prevent slippage between the thin material and the pass line roll. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 08-24903 Summary of the Invention [Problem to be solved by the invention]

[0007] However, the method of increasing the coefficient of friction between the steel sheet and the pass line roll by imparting roughness to the surface of the work roll and transferring the roughness to the surface of the steel sheet has a large effect on the surface quality of the steel sheet and is difficult to actively apply. Moreover, since the surface of the work roll wears rapidly due to repeated rolling, it is practically difficult to suppress slippage by transferring the roughness of the work roll surface to the surface of the steel sheet in practical terms.

[0008] The present invention has been made in consideration of the above circumstances, and an object of the present invention is to provide a pass line roll that is disposed between a plurality of rolling mills and that can avoid an effect on the surface quality of a steel sheet and suppress the occurrence of slippage between the steel sheet and the pass line roll. [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, the pass line roll having a surface roughness Ra of 1.0 μm or more and 3.0 μm or less on a contact surface with a steel sheet passing through the rolling line. [2] The pass line roll according to [1], having a hard metal plating layer on the contact surface. [3] A method for producing a steel sheet, comprising rolling the steel sheet by passing it through a rolling line having a plurality of rolling mills, wherein the steel sheet is passed through pass line rolls which are disposed between the plurality of rolling mills and have a surface roughness Ra of 1.0 μm or more and 3.0 μm or less on the contact surface with the steel sheet. Effect of the Invention

[0010] According to the present invention, it is possible to prevent the pass line rolls disposed between a plurality of rolling mills from affecting the surface quality of a steel sheet and to suppress the occurrence of slippage between the steel sheet and the pass line rolls. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 shows a schematic side view of an example of a rolling line. [Diagram 2] FIG. 1 is a diagram showing the relationship between the surface roughness transferred to a steel sheet and the rolling length of a work roll. [Diagram 3] FIG. 1 is a diagram showing the relationship between the surface roughness of a pass line roll and the period of use. [Figure 4] FIG. 1 is a diagram showing the relationship between the rotation speed of a work roll and the rotation speed of a pass line roll when a pass line roll having a surface roughness Ra of 0.2 μm or less is applied to a rolling line. [Diagram 5] FIG. 1 is a diagram showing the relationship between the rotation speed of a work roll and the rotation speed of a pass line roll when a pass line roll having a surface roughness Ra of 2.5 μm is applied to a rolling line. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, an embodiment of the present invention will be described in detail. Fig. 1 shows a schematic side view of 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 passing 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 that sandwich the steel sheet S, and a work roll 12. The pass line roll 20 has a tension meter roll 21 and a deflated roll 22. The tension meter roll 21 measures the tension of the steel sheet S in the rolling line 1. The deflated roll 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 sheet S passing through the rolling line 1.

[0014] Here, the relationship between the surface roughness of a steel sheet and the work roll rolling length in the case where roughness is imparted to the surface of a work roll and the roughness is transferred to the surface of a steel sheet to increase the frictional force between the steel sheet and the pass line roll will be explained with reference to Fig. 2. Fig. 2 is a diagram showing the relationship between the transferred surface roughness of a steel sheet and the work roll rolling length. The work roll rolling length means the total length of the steel sheet rolled using the work roll.

[0015] As shown in Figure 2, when the work roll rolling length is short, the surface roughness Ra of the steel sheet is in the range of 0.4 to 0.6 μm. This confirms that when the work roll rolling length is short, the occurrence of slippage between the steel sheet to which the roughness has been transferred and the pass line roll is suppressed. In other words, it is believed that by maintaining a high surface roughness Ra of the steel sheet, the frictional force (friction coefficient) between the steel sheet and the pass line roll is increased, suppressing slippage.

[0016] On the other hand, it has been confirmed that when the rolling length of the work rolls is increased, the surface roughness Ra of the steel sheet becomes 0.4 μm or less, and slippage is likely to occur between the steel sheet to which the roughness has been transferred and the pass line roll. This can be confirmed by the fact that slippage occurs at the timing when the surface roughness Ra of the steel sheet decreases, as shown in Figure 2.

[0017] For this reason, in order to suppress the occurrence of slippage 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 plate and the rolling length of the work roll shown in Fig. 2 is the result assuming a method in which the roughness of the work roll surface is transferred to the surface of the steel plate, and therefore has a large impact on the surface quality of the steel plate, making it difficult to actively apply this relationship.

[0019] For this reason, in the present invention, roughness is imparted to the surface of the pass line roll to suppress the occurrence of slippage between the pass line roll and the steel sheet passing through the pass line roll. Specifically, by making the surface roughness Ra of the pass line roll 1.0 μm or more, it is possible to suppress the occurrence of slippage. In rolling using the rolling line 1, the threshold value for the surface roughness Ra of the pass line roll is set to 1.0 μm, and when the surface roughness Ra falls below 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 high surface roughness is used in the most downstream rolling facility among multiple rolling facilities. The dull roll has a surface roughness Ra of more than 3.0 μm. For this reason, when manufacturing steel sheets in the rolling facility, the surface roughness of the steel sheets is controlled (adjusted) by using a dull roll having a surface roughness Ra of more than 3.0 μm in the end. In light of this, and in terms of the effect on the surface quality of the steel sheets, the upper limit of the surface roughness Ra of the pass line roll is set to 3.0 μm or less in order to suppress the effect on the control of the surface roughness Ra of the steel sheets using the dull roll.

[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 progress of the surface roughness Ra was investigated when a pass line roll 20 with a surface roughness Ra value of 2.5±0.5 μm was applied to a rolling line 1.

[0022] The progress of the surface roughness Ra of the pass line roll 20 will be described with reference to Fig. 3. Fig. 3 is a diagram showing the relationship between the surface roughness of the pass line roll 20 and the period of use. 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 is applied to the rolling line 1 (left end of the graph), the surface roughness Ra value is 2.0 µm or more. It was also confirmed that the surface roughness Ra value can be maintained at 1.0 µm or more even after one year of use.

[0023] The surface roughness of the pass line roll 20 may be imparted (surface processing) by a shot blasting method, a sand blasting method, a grid blasting method, etc. In addition, the surface roughness of the pass line roll 20 may be imparted by a dimple processing, which can reduce localized pressure concentration by roughening the surface into spherical shapes, in comparison with the shot blasting method.

[0024] After the pass line roll 20 is given a surface roughness (surface processing), it is preferable to form a hard metal plating layer on the contact surface having the surface roughness. By providing a hard metal plating layer on the contact surface having the surface roughness, the surface roughness obtained 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, from the side closer to the surface of the pass line roll 20, with a first layer being formed of a Ni-based self-fluxing alloy containing Ni, Cr, etc. having a hardness of about HV650, and a second layer being formed by WC cermet processing having a hardness of about HV1000. The hard metal plating layer is effective in maintaining the surface roughness even when formed as a single layer by WC cermet processing. However, due to the large difference between the hardness of the pass line roll 20 and the hard metal plating layer, peeling 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 having a hardness lower than that of the hard metal plating layer between the hard metal plating layer and the pass line roll 20.

[0025] In the steel sheet manufacturing method according to the present invention, the steel sheet S is passed through a rolling line 1 having a plurality of rolling mills (an upstream rolling mill 10 and a downstream rolling mill 30) to perform rolling. Specifically, the steel sheet S is passed through a pass line roll 20 which is disposed between the plurality of rolling mills (the upstream rolling mill 10 and the downstream rolling mill 30) 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 S. EXAMPLES

[0026] Next, the pass line roll according to the present invention is applied to a rolling line, and a rolling result is described in which a steel sheet is passed through the rolling line to perform rolling processing. The steel sheet passes through the rolling mill at a passing speed equivalent to the rotational speed of the work rolls in the rolling mill. The pass line rolls disposed downstream of the rolling mill are of a non-driven type, and therefore rotate at a rotational speed equivalent to the passing speed of the steel sheet due to contact with the passing steel sheet.

[0027] Considering the relationship between these speeds, in this example, an evaluation was made of the relationship between the rotational speed of the work rolls in the rolling mill and the rotational speed of the pass line rolls. Specifically, when the rotational speed of the work rolls in the rolling mill and the rotational speed of the pass line rolls were equivalent, 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."

[0028] A pass line roll with a surface roughness Ra of 0.2 μm was applied to the rolling line, and the relationship between the rotation speed of the work roll and the rotation speed of the pass line roll was investigated. The results are shown in FIG. 4. A pass line roll with a surface roughness Ra of 2.5 μm was applied to the rolling line, and the relationship between the rotation speed of the work roll and the rotation speed of the pass line roll was investigated. The results are shown in FIG. 5. In both pass line rolls, the surface roughness was imparted by the shot blasting method. The steel sheet passing through the rolling line had a tensile strength of 270 MPa and a surface roughness Ra of about 0.3 μm (estimated). The rolling speed in the rolling line was set to be about 1000 mpm. The work roll was not replaced before rolling. The surface roughness Ra of the pass line roll 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 Fig. 4, when a pass line roll with a surface roughness Ra of 0.2 μm was applied to a rolling line, it was confirmed that there was a large speed difference between the rotational speed of the work roll and the rotational speed of the pass line roll, and slippage 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, the rotational speed of the work roll and the rotational speed of the pass line roll always matched, as shown in Fig. 5, and it was confirmed that no slippage occurred between the pass line roll and the steel sheet.

[0031] As described above, by imparting surface roughness to the contact surface of the pass line roll with the steel sheet and increasing the frictional force (friction coefficient) between the steel sheet and the pass line roll, it was possible to suppress the occurrence of slippage between the steel sheet and the pass line roll, regardless of the surface roughness of the steel sheet. In addition, it became unnecessary to carry out a method of increasing the frictional force (friction coefficient) between the steel sheet and the pass line roll by imparting roughness to the surface of the work roll and transferring the roughness to the surface of the steel sheet, thereby avoiding an effect on the surface quality of the steel sheet. Furthermore, since the occurrence of slippage could be suppressed, it was possible to improve the surface quality of the steel sheet and the yield in the production of the steel sheet. [Explanation of symbols]

[0032] 1. Rolling Line 10 Upstream rolling mill 11 Backup Role 12 Work roll 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 the plurality of rolling mills, the pass line roll having a surface roughness Ra of 1.0 μm or more and 3.0 μm or less of a contact surface with a steel sheet passing through the rolling line.

2. 2. The pass line roll according to claim 1, wherein the contact surface has a hard metal plating layer.

3. A steel sheet manufacturing method in which a steel sheet is rolled by passing it through a rolling line having a plurality of rolling mills, the steel sheet being passed through pass line rolls that are disposed between the plurality of rolling mills and have a surface roughness Ra of 1.0 μm or more and 3.0 μm or less on a contact surface with the steel sheet.

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