Steel strip grooving method, cold rolling method and method for manufacturing cold-rolled steel strip

Abstract

Provided is a method for grooving a steel strip, wherein after a notch is formed at an end portion in the plate width direction of a joint portion, at least a portion of the notch is removed by grinding, the effect of suppressing chattering is excellent, and a reduction in tool life can be suppressed. A method for grooving a steel strip, wherein after a notch is formed at an end portion in the plate width direction of a joint portion where a rear end of a preceding steel strip and a front end of a succeeding steel strip are joined, at least a portion of the notch is removed by grinding, wherein a rotary grinding tool is used, the rotary grinding tool is fed in the plate width direction, the region is cut into, and the rotary grinding tool is fed in a direction perpendicular to the steel strip at a feed speed that is within a predetermined range relative to the feed speed of the rotary grinding tool in the plate width direction, and in parallel, a predetermined feed amount is provided in the length direction of the steel strip while a predetermined feed amount is fed in the plate width direction, and the region is removed by grinding while the rotary grinding tool is swung in the length direction of the steel strip.

Description

Technical Field

[0001] The invention relates to a steel strip grooving method, a cold rolling method and a method for manufacturing a cold rolled steel strip. Background Art

[0002] In the cold rolling process of steel strips, the rear end of the preceding material (preceding steel strip) and the front end of the succeeding material (following steel strip) are usually joined and continuously supplied to the cold rolling line. This enables continuous rolling of coils, which improves the productivity of the production line. In addition, since the steel strip can be rolled while tension is applied to the entire length, the thickness shape of the steel strip can be controlled with high precision at the front and rear ends, which also improves the yield rate.

[0003] The steel plate joining method uses welding techniques such as flash butt welding and laser welding. Regardless of the welding technique used, the width-direction end of the joint (weld portion) between the preceding and succeeding materials will inevitably form a width step due to the difference in the width of the steel strips between the preceding and succeeding materials or positional offset. This width step sometimes hangs on the rollers during the plate passing process due to the protruding corners of the steel strip, causing damage to the equipment. Furthermore, the welding at the ends of the joint in the width direction is incomplete, the welding strength is insufficient, and the risk of the joint breaking during rolling increases. In the case of joint breaking, the production line is stopped to handle the broken plate, resulting in a decrease in the operating rate. Furthermore, in the case of work roll damage during breaking, the work roll has to be replaced, resulting in a deterioration in unit cost. In particular, in recent years, the thinning of cold-rolled steel strips has been continuously developed for the purpose of lightweighting components and improving characteristics, and the high pressure reduction associated with this has led to an increase in the fracture rate of the joint.

[0004] Therefore, rolling is usually performed after grooving to form a notch (nick) at the end of the joint in the plate width direction. Grooving can remove the corners of the steel strip at the width step and the incomplete weld where welding is incomplete, and thus the joint can be prevented from breaking during rolling. As a grooving method, for example, a method of mechanically shearing a semicircular notch without a corner at the end of the joint in the plate width direction is generally used (for example, refer to Patent Documents 1, Figure 4 ). However, the curvature of the outer edge of the semicircular notch is the same, and the width of the steel strip becomes the smallest at the joint, so the maximum stress is generated at the joint after the notch is formed. In order to solve this problem, Patent Document 1 proposes a method of making the maximum stress generation point outside the joint by forming the shape of the notch into a roughly isosceles trapezoid.

[0005] However, in the notching method described in Patent Document 1, in the cold rolling of brittle materials and high-alloy materials such as silicon steel sheets and high-tensile steel sheets, the fracture of the joint portion during rolling cannot be sufficiently suppressed.

[0006] In this regard, Patent Document 2 describes a method for notching a steel strip, wherein a first-level notch is formed by shearing at both edges in the steel strip width direction of the junction between the rear end of the preceding steel strip and the front end of the succeeding steel strip, and then a second-level notch is formed by grinding the end faces of both edges in the steel strip width direction of the junction. According to the notching method described in Patent Document 2, even in the case of brittle materials and high-alloy materials such as cold-rolled silicon steel sheets and high-tensile steel sheets, the effect of suppressing fracture of the junction during rolling is excellent.

[0007] However, in the grooving method described in Patent Document 2, when grinding the end faces of both edge portions in the width direction of the steel strip at the joint, large chatter vibrations may occur. In addition, the grinding tool may be worn more and the tool life may be significantly reduced.

[0008] Prior art literature

[0009] Patent Literature

[0010] Patent Document 1: Japanese Patent Application Publication No. 2014-50853

[0011] Patent Document 2: Japanese Patent Application Publication No. 2017-144467 Summary of the invention

[0012] Problems to be solved by the invention

[0013] The object of the present invention is to provide a method for grooving a steel strip, which has an excellent effect of suppressing vibration after forming a notch at the end portion of the joint in the plate width direction, and can suppress the reduction of tool life by removing at least a portion of the notch, especially the end portion of the joint in the plate width direction, by grinding.

[0014] Another object of the present invention is to provide a cold rolling method using the above-mentioned steel strip grooving method and a method for producing a cold-rolled steel strip using the cold rolling method.

[0015] Means for solving problems

[0016] In order to solve the above problems, the present invention forms a notch at the end of the joint in the plate width direction, and then removes at least a part of the notch, especially the end of the joint in the plate width direction, by grinding using a rotary grinding tool such as a rotary burr.

[0017] The inventors of the present invention have found that when observing the ends of the joint in the width direction after forming a notch in the ends of the joint in the width direction and cold rolling, as shown in FIG. Figure 4As shown, a crack X with a length of about 2 mm is formed in the plate width direction at the end portion of the joint 3 of the preceding steel strip 1 and the succeeding steel strip 2. The rupture develops from the crack X, resulting in a fracture of the joint. The inventors of the present application found that the reason for the formation of the crack X is that the plate width direction end portion of the joint after the notch is work-hardened due to the formation of the notch. The mechanism is as follows. First, if a notch is formed at the plate width direction end portion of the joint, the plate width direction end portion of the joint after the notch is work-hardened. The work-hardened portion (work-hardened portion) becomes difficult to deform compared to other portions. If the work-hardened portion is rolled, it cannot be deformed during rolling and crack X is generated.

[0018] Therefore, it is thought that in order to suppress the fracture of the joint, it is sufficient to remove the work hardened portion generated at the end of the joint in the plate width direction after the notch is formed. Furthermore, in the present invention, the work hardened portion is removed by grinding. If grinding is used, no new work hardening will be generated at the end of the joint in the plate width direction after grinding, and only the work hardened portion generated by the notch can be removed.

[0019] Furthermore, in the present invention, a rotary grinding tool is used as a grinding method. In particular, if a rotary file is used as a rotary grinding tool and processing is performed under optimal conditions, the chatter during grinding can be more effectively suppressed, the deterioration of the grindability caused by the wear and clogging of the rotary file (tool edge) can be minimized, and the work hardening portion after the notch is formed can be removed.

[0020] The present invention has the following structure.

[0021] [1] A method for grooving a steel strip, comprising forming a notch at the end portion in the plate width direction of the joint where the rear end of the preceding steel strip and the front end of the succeeding steel strip are joined, and then removing at least a portion of the notch by grinding, wherein:

[0022] A rotary grinding tool is used, the rotary grinding tool is fed in the plate width direction, the area of ​​the notch to be removed by the grinding is cut, and the rotary grinding tool is fed in the vertical direction of the steel strip at a feed speed within a specified range relative to the feed speed of the rotary grinding tool in the plate width direction. In parallel, while feeding a specified feed amount in the plate width direction, a specified feed amount is provided in the length direction of the steel strip, and the area is removed by grinding the cut-in area while swinging the rotary grinding tool in the length direction of the steel strip.

[0023] [2] The method for grooving a steel strip according to [1], wherein the rotary grinding tool is a rotary file, and the rotary file is fed in a direction perpendicular to the steel strip at a feed speed of 0.3 to 10.0 times the feed speed of the rotary file in the plate width direction.

[0024] [3] A method for grooving a steel strip according to [1] or [2], wherein the rotary grinding tool is a rotary file, and while feeding a prescribed feed amount of less than 1.0% of the diameter of the rotary file in the plate width direction, a feed amount of more than 5.0% of the diameter of the rotary file is provided in the steel strip length direction.

[0025] [4] A cold rolling method comprising cold rolling a steel strip grooved by the steel strip groove forming method according to any one of [1] to [3] above.

[0026] [5] A method for producing a cold-rolled steel strip, comprising producing the cold-rolled steel strip using the cold rolling method described in [4] above.

[0027] Effects of the Invention

[0028] According to the method for grooving a steel strip of the present invention, a method for grooving a steel strip can be provided, which, after forming a notch at the end portion in the plate width direction of the joint portion, removes at least a portion of the notch by grinding, especially at the end portion in the plate width direction of the joint portion after the notch is formed, thereby achieving excellent effect of suppressing vibration and suppressing reduction in tool life.

[0029] According to the present invention, the work-hardened portion that causes the fracture of the joint is removed by grinding, so that even when brittle materials and high-alloy materials such as silicon steel plates and high-tensile steel plates with high Si and Mn contents are rolled, the fracture of the joint (fracture of the weld) can be suppressed. Furthermore, the method of the present invention is applied using a rotary grinding tool to perform the above-mentioned grinding, so that the chatter during grinding can be suppressed. In particular, by using a rotary file as a rotary grinding tool, the chatter during grinding can be more effectively suppressed, and by performing processing under optimal conditions, the reduction in tool life and deterioration in grindability caused by wear and clogging of the rotary file (tool edge) can be suppressed, and the work-hardened portion after the notch is formed can be removed. According to the present invention, by using a rotary grinding tool such as a rotary file to perform the above-mentioned grinding processing in an appropriate manner, it is possible to simultaneously achieve effective removal of the work-hardened portion of the steel strip joint caused by the formation of the notch and suppression of the reduction in tool life. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] [ Figure 1 ] is a diagram illustrating an embodiment of a method for grooving a steel strip according to the present invention.

[0031] [ Figure 2] is a graph showing the hardness distribution from the end 3b in the plate width direction of the joint after the notch is formed toward the center of the plate width.

[0032] [ Figure 3 ] is a graph showing the hardness distribution of the joint portion after grinding using a rotary file, from the end portion 3c in the plate width direction toward the center of the plate width.

[0033] [ Figure 4 ] Photograph of the state (crack) of the end portion in the plate width direction of the joint after notch formation and cold rolling.

[0034] [ Figure 5 ] is a photograph showing the state of the end portion in the plate width direction of the joint after a notch is formed, prescribed grinding is performed, and cold rolling is performed.

[0035] [ Figure 6 ] is an explanatory diagram showing the positional relationship between the rotary file and the steel belt when grinding is performed using the rotary file.

[0036] [ Figure 7 ] is viewed from the side Figure 6 Side view of.

[0037] [ Figure 8 ] is viewed from the top side Figure 6 Top view of the .

[0038] [ Fig. 9 ] is an explanatory diagram for explaining a grinding method using a rotary file in an embodiment.

[0039] [ Fig.10 ] is an explanatory diagram for explaining a grinding method using a rotary file in an embodiment.

[0040] [ Fig.11 ] is an explanatory diagram for explaining a grinding method using a rotary file in an embodiment. DETAILED DESCRIPTION

[0041] Hereinafter, one embodiment of the present invention will be described with reference to the drawings. However, the present invention is not limited to the embodiment described below.

[0042] Figure 1 It is a figure explaining one embodiment of the method for grooving a steel strip according to the present invention. Figure 1 The arrow A in the figure indicates the conveying direction of the steel strip.

[0043] like Figure 1 As shown in (a), first, the rear end of the leading steel strip 1 and the front end of the trailing steel strip 2 are joined by welding. Thus, a joint 3 is formed. The method of welding the rear end of the leading steel strip 1 and the front end of the trailing steel strip 2 is not particularly limited, and for example, flash butt welding, laser welding, etc. may be used. It should be noted that in Figure 1 In (a), the leading steel strip 1 and the trailing steel strip 2 have substantially the same width, but the present invention is not limited thereto and the widths of the two steel strips may be different. In addition, the joining method is not limited to welding and may be brazing, friction joining (solid phase joining), etc.

[0044] As described above, at the end 3a in the plate width direction of the joint 3 (hereinafter also referred to as "end 3a"), a width step is formed due to the difference in strip width or positional deviation between the preceding steel strip 1 and the succeeding steel strip 2, which causes the joint 3 to break during rolling. Therefore, after the preceding steel strip 1 and the succeeding steel strip 2 are joined by welding to form the joint 3, a notch 4 (notch 4) is formed at the end 3a ( Figure 1 (b)). Figure 1 In (b), the blank area within the dotted line indicates the area where the notch 4 is formed. Figure 1 As shown in (b), the notch 4 is formed in a predetermined area including the end portion in the plate width direction of the joint portion toward the center of the plate width. Figure 1 (b) shows a case where a substantially semi-elliptical notch is formed, but in the present invention, the shape of the notch is not particularly limited.

[0045] When such a notch is formed at the end 3a of the steel strip, work hardening occurs at the end 3b in the plate width direction of the joint 3 after the notch is formed (hereinafter also referred to as "end 3b"). In order to investigate the range of this work hardening, the results of measuring the hardness distribution from the end 3b of the joint 3 to the center of the plate width are shown in FIG. Figure 2 .like Figure 2 As shown in FIG. 1 , due to the work hardening, the Vickers hardness at the end 3b increases the most, and the increase in the Vickers hardness decreases as it moves from the end 3b toward the center of the plate width. Moreover, in the range of more than 1 mm from the end 3b to the center of the plate width, the Vickers hardness becomes the same as that of the end 3a before the notch is formed (Hv240). That is, Figure 2 It is known that work hardening occurs in the range of 1 mm from the end 3b to the center of the plate width. Therefore, it is considered that the occurrence of cracks can be prevented if the range of 1 mm from the end 3b to the center of the plate width is removed.

[0046] Therefore, in the present invention, if Figure 1 As shown in (c), the end portion 3b after work hardening is removed by grinding. Figure 1 In (c), the blank area within the dotted line represents the grinding area 5 removed by grinding. Figure 1As shown in (c), the above-mentioned grinding is grinding to remove the end portion 3b further toward the center of the plate width, and the range of grinding in the length direction of the steel strip is a part of the specified area where the notch is formed. As described above, since work hardening occurs in the range of 1 mm from the end portion 3b to the center of the plate width, it is preferred to remove the range of 1 mm from the end portion 3b to the center of the plate width by grinding. On the other hand, when the grinding width T in the plate width direction (the distance from the end portion 3b of the joint 3 to the center of the plate width) is made too large, stress is concentrated on the notch portion, which in turn causes the joint to break. Therefore, the grinding width T is preferably in the range of 2 mm or less. As an example, the grinding width T is preferably greater than 0.5 mm. In addition, as an example, the grinding width T is preferably less than 2.0 mm. In addition, in order to suppress the rapid change in the width of the steel strip, it is preferred that the grinding range in the length direction of the steel strip, i.e. Figure 1 The grinding length L in (c) is greater than 8 mm. From the viewpoint of further improving the effect of suppressing fracture of the joint, it is preferred that the increase in the Vickers hardness of the end 3c in the plate width direction of the joint 3 after grinding (hereinafter also referred to as "end 3c") is less than Hv50 relative to the Vickers hardness of the end 3a (or the Vickers hardness of the parent material). The above-mentioned grinding width T is appropriately adjusted according to the Vickers hardness of the end 3c and its work hardening range. It should be noted that, in this specification, the Vickers hardness is measured in accordance with JISZ 2244. It should be noted that in Figure 1 In the process, a portion of the notch removed by grinding is set as the area including the end 3b, but sometimes cracks may occur in the notch portion outside the joint due to some reasons such as work hardening. Therefore, the method of the present invention can also be used to grind and remove a portion of the notch other than the end portion in the plate width direction of the joint.

[0047] In addition, in the present invention, the end 3b after work hardening is removed by grinding using a rotary grinding tool. As the rotary grinding tool, there is no particular limitation, and a rotary file, a shaft grindstone, a rotary file, a grinder, a belt sander, etc. can be used. As the rotary grinding tool, a rotary file is particularly preferably used. As the rotary file, there is no particular limitation, for example, a commonly commercially available rotary file can be used. As the rotary file, for example, a cutting edge coated with superhard materials such as tungsten carbide or diamond abrasives, a cutting edge using high-speed steel (also including a cutting edge implemented with various coatings such as Ti) can be cited. In the present invention, from the viewpoint of small cutting resistance and better effect of suppressing chatter during grinding, a cross-shaped rotary file is preferably used. Examples of suitable rotary files include carbide rotary files, and more specifically, rotary files with a cylindrical head having a cross blade coated with a carbide material.

[0048] In addition, as a rotary file, when the hardness of the steel strip as the cut material is high, it is preferred to select a rotary file with a large number of teeth. In addition, the diameter and shape of the rotary file are not particularly limited, but it is preferred to easily achieve the above-mentioned grinding width T and grinding length L. In the present invention, it is preferred to use a rotary file with a diameter of 10 mm or more, which is a range that is generally commercially available. In addition, it is preferred to use a rotary file with a diameter of 26 mm or less. It should be noted that the diameter of the rotary file refers to the maximum diameter of the rotary file (cutting edge).

[0049] Next, a method for grinding at least a part of the notch using a rotary grinding tool will be described. Here, as an example, a method for grinding the work-hardened end portion 3 b using a rotary file as a rotary grinding tool will be described.

[0050] Figure 6 This is an explanatory diagram showing the positional relationship between the rotary file and the steel belt when the rotary file is used for grinding. Figure 7 Indicates viewing from the side Figure 6 Side view of Figure 8 Indicates viewing from above Figure 6 Top view of the .

[0051] In the present invention, along the plate width direction ( Figure 6 to Figure 8 The rotary file is fed in the x direction) to cut into the end of the plate width direction, and in the vertical direction of the steel strip ( Figure 6 , Figure 7 The rotary file is fed at a feed speed in a predetermined range relative to the feed speed of the rotary file in the plate width direction, and in parallel (simultaneously), the rotary file is fed by a predetermined feed amount in the plate width direction, and the rotary file is fed by a predetermined feed amount in the steel strip length direction ( Figure 6 , Figure 8 A predetermined feed amount is provided (in the y direction) and the rotary file is swung along the length direction of the steel strip while cutting into the end portion in the plate width direction of the joint.

[0052] The feed speed (cut-in speed) of the rotary file along the plate width direction is preferably above 0.3 mm / sec. In addition, the feed speed along the plate width direction is preferably below 5.0 mm / sec. When the feed speed along the plate width direction is above 0.3 mm / sec, the formation of built-up edge and the deterioration of chip discharge can be suppressed, and the deterioration of grindability caused by increased processing heat generation can be easily suppressed. In addition, if the feed speed along the plate width direction is below 5.0 mm / sec, it is easy to suppress the increase of cutting resistance and the progress of blade wear. The rotation speed of the rotary file can be set according to the recommended rotation speed determined by the diameter and shape of the rotary file.

[0053] In addition, the rotary file is fed in the plate width direction to cut into the plate width end of the above-mentioned joint, and is fed in the vertical direction of the steel strip at a feed speed that is within a predetermined range relative to the feed speed of the rotary file in the plate width direction. At this time, it is preferred to feed the rotary file in the vertical direction of the steel strip at a feed speed of 0.3 to 10.0 times the feed speed of the rotary file in the plate width direction. This makes it easier to promote the discharge of chips, and does not use the same position of the blade for cutting, so it is easy to increase the life of the blade.

[0054] Furthermore, the rotary file is fed in the vertical direction of the steel strip at a feed speed within a prescribed range relative to the feed speed of the rotary file in the plate width direction, and in parallel with this, while feeding the prescribed feed amount in the plate width direction, the prescribed feed amount is provided in the length direction of the steel strip, and the rotary file is swung (reciprocated) in the length direction of the steel strip while cutting into the plate width end of the joint. At this time, it is preferred that while feeding the prescribed feed amount of less than 1.0% of the diameter of the rotary file in the plate width direction, a feed amount of more than 5.0% of the diameter of the rotary file is provided in the length direction of the steel strip, and the rotary file is swung (reciprocated) in the length direction of the steel strip. That is, it is preferred that the movement of the rotary file in the length direction of the steel strip is reversed before the feed amount of the rotary file in the plate width direction exceeds 1.0% of the diameter of the rotary file. Furthermore, it is preferred that the feed amount (swing width) in the length direction of the steel strip from this return to the next return is more than 5.0% of the diameter of the rotary file. As a result, the contact area between the blade and the steel strip can be reduced, and the cutting resistance can be further reduced, that is, the effect of suppressing chattering can be improved. When chattering occurs or the cutting resistance is too large, new work hardening may occur due to excessive load applied to the ground part of the steel strip. In addition, the life of the tool is reduced, and the time required for tool replacement is increased, which may lead to a reduction in the efficiency of the production line. According to the present invention, by using a rotary file for the above-mentioned grinding, new work hardening will not occur, and the reduction in tool life and deterioration in grindability can be suppressed, while the work hardening portion after the notch is formed can be removed. In addition, although not specifically limited, the specified feed amount along the plate width direction is preferably not less than 0.2% of the diameter of the rotary file. In addition, although not specifically limited, the feed amount along the length direction of the steel strip is preferably not more than 300% of the diameter of the rotary file.

[0055] It should be noted that when grinding a steel strip with a rotary grinding tool such as a rotary file, clamping is required to prevent the cut material from moving during processing. This is the same as general processing, and the form of clamping is not particularly limited. From the viewpoint of making it easier to suppress vibration, it is preferred to clamp a position very close to the processing point. In addition, with regard to cutting oil, the use of cutting oil can reduce cutting resistance and can be expected to improve grindability. However, it is rare that there is an environment in which cutting oil can be used in the production line of a cold-rolled steel strip rolling equipment. In the present invention, there is no special provision for the use of cutting oil. It has been confirmed that the grinding conditions in the present invention can achieve the effect even without cutting oil.

[0056] The end portion 3c (see Figure 1 (c) The hardness distribution in the center of the plate width is shown in Figure 3 .like Figure 3 As shown, by appropriately performing grinding, new work hardening will not occur, and only the work hardened portion generated when the notch 4 is formed can be removed.

[0057] Example

[0058] A cold-rolled steel strip (silicon steel sheet) was manufactured to evaluate the effect of the present invention. The steel strip used for evaluation had a Si content of 3.0 mass % or more and less than 3.5 mass %, and a plate thickness of 1.8 mm or more and 2.4 mm or less. The Vickers hardness of the base material was about HV240. A plurality of such steel strips were prepared, and similarly to the above-mentioned embodiment, the rear end of the preceding steel strip 1 and the front end of the succeeding steel strip 2 were welded, and a notch was formed at the end 3a of the joint 3 formed at this time. Next, a rotary file was used to grind a portion of the notch after the notch was formed, i.e., the end 3b of the joint 3, under the grinding conditions shown in Table 1.

[0059] Figures 9-11 The rotary file used in this embodiment is a cylindrical head rotary file (superhard rotary file) with a diameter of 25 mm and cross blades coated with superhard material (tungsten carbide), and the grinding width T is fixed to 1 mm (refer to Fig. 9 ). It should be noted that Fig. 9 , an example is shown in which the feed amount (swing width) of the rotary file in the steel strip length direction is 2 mm (8% of the rotary file diameter) and the grinding length L is 11.6 mm. In this embodiment, grinding is performed at a rotation speed of 3600 rpm.

[0060] Fig.10 This is an explanatory diagram for explaining the movement of the rotary file on the xy plane (movement of the tip of the rotary file) under the grinding conditions of No. 1, 4, 8, and 9 in Table 1 described later. Fig.10As shown, in these examples, while a feed amount of 0.25 mm (1.0% of the diameter of the rotary file) is fed in the direction of the plate width, a feed amount of 2 mm (8% of the diameter of the rotary file) is provided in the length direction of the steel strip, and the cutting of the end portion in the plate width direction of the joint is performed while swinging with a swing width of 2 mm in the length direction of the steel strip. Fig.11 This is an explanatory diagram for explaining the movement of the rotary file on the xy plane (movement of the tip of the rotary file) under the grinding conditions of No. 5, 10, 11, and 12 in Table 1 described later. Fig.11 As shown, in these examples, while a feed amount of 0.125 mm (0.5% of the diameter of the rotary file) is fed in the direction of the plate width, a feed amount of 2 mm (8% of the diameter of the rotary file) is provided in the length direction of the steel strip, and the cutting of the end portion in the plate width direction of the joint is performed while swinging with a swing width of 2 mm in the length direction of the steel strip.

[0061] The properties of the ground surface when grinding with a rotary file as described above, the presence or absence of chatter, the Vickers hardness of the end face of the steel strip after grinding (the position of the end 3c), and whether it can be used continuously are evaluated, and the results are shown in Table 1. Regarding chatter, it is judged based on whether there is sound and the roughness of the ground surface. Then, the steel strip is cold rolled to a final thickness of 0.21 mm or more and less than 0.25 mm to make a cold-rolled steel strip. For each grinding condition, a comprehensive judgment is made according to the following judgment criteria. Comprehensive judgments of ◎, ○, and △ are qualified (the effect of suppressing chatter is excellent and the reduction of tool life can be suppressed), and comprehensive judgments of × are unqualified.

[0062] Comprehensive judgment: ◎: The increase in Vickers hardness of the end portion in the plate width direction of the joint portion after grinding relative to the base material portion is Hv30 or less, no chatter vibration or spark generation occurs, and 150 continuous grindings can be performed.

[0063] Comprehensive judgment: ○: The increase in Vickers hardness of the end portion in the plate width direction of the ground joint portion relative to the base material portion was Hv30 or less, and although slight chatter and sparks occurred, continuous grinding was possible for 150 times.

[0064] Comprehensive judgment △: The increase in Vickers hardness of the end portion in the plate width direction of the joint after grinding is less than Hv50 relative to the base material portion, and although slight sparks are generated and heat is increased, continuous grinding can be performed up to 50 times (continuous grinding cannot exceed 50 times).

[0065] Comprehensive judgment ×: There is vibration, sparks, blade chipping, and it cannot perform 50 continuous grinding times.

[0066] [Table 1]

[0067]

[0068] As shown in Table 1, when the rotary file is fed in the plate width direction and in the vertical direction of the steel strip during grinding, and is fed in the plate width direction and in the length direction of the steel strip to be swung, the deterioration of the grinding surface properties and the significant reduction in tool life can be suppressed compared to the case where this method is not performed. In particular, when the ratio of the feed speed in the vertical direction of the steel strip to the feed speed in the plate width direction and the feed amount in the length direction of the steel strip (swing width) to the feed amount in the plate width direction are within the preferred range of the present invention, by grinding under such conditions, continuous grinding can be performed without deterioration of the grinding surface properties and significant reduction in tool life. In addition, in the examples of the present invention, the generation of cracks at the ends of the joints of the cold-rolled steel strip after cold rolling can be suppressed (refer to Figure 5 ), which can inhibit the fracture of the joint during cold rolling.

[0069] As described above, by performing the grinding method of the present invention, it is possible to achieve both a prolonged tool life and effective removal of the work-hardened portion of the steel strip.

[0070] It should be noted that, in this embodiment, the case of a silicon steel sheet is described, but the present invention is not limited thereto, and can also be applied to other cold-rolled steel strips.

[0071] Description of Reference Numerals

[0072] 1. Leading steel strip

[0073] 2. Rear steel belt

[0074] 3. Joint (welding)

[0075] 3a to 3c, end portions of the joint in the plate width direction

[0076] 4. Notch

[0077] 5. Grinding area

Claims

1. A method for grooving a steel strip, comprising forming a notch at the end in the plate width direction of the joint where the rear end of the preceding steel strip and the front end of the succeeding steel strip are joined, and then removing at least a portion of the notch including the joint by grinding, wherein: A rotary grinding tool is used, the rotary grinding tool is fed in the plate width direction, the area including the joint portion in the notch to be removed by the grinding is cut into, and the rotary grinding tool is fed in the vertical direction of the steel strip at a feed speed within a prescribed range relative to the feed speed of the rotary grinding tool in the plate width direction, and in parallel, a prescribed feed amount is provided in the length direction of the steel strip while feeding a prescribed feed amount in the plate width direction, and the area is removed by grinding by cutting into the area while swinging the rotary grinding tool in the length direction of the steel strip, in, The rotary grinding tool is a rotary file, which is fed in the vertical direction of the steel strip at a feed speed of 0.3 to 10.0 times the feed speed of the rotary file in the plate width direction, and before the feed amount of the rotary file in the plate width direction exceeds 1.0% of the diameter of the rotary file, the movement of the rotary file in the length direction of the steel strip is turned back, and the feed amount in the length direction of the steel strip from the turn to the next turn, that is, the swing width, is more than 5.0% of the diameter of the rotary file.

2. A cold rolling method comprising cold rolling a steel strip grooved by the steel strip groove forming method according to claim 1.

3. A method for manufacturing a cold-rolled steel strip, comprising manufacturing the cold-rolled steel strip using the cold rolling method according to claim 2.

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