JP2005205490A - Method for evaluating surface roughening of work roll in hot rolling, grinding method of work roll using the same and hot-rolling method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress the generation of the defective surface quality of surface roughening and scale defects on products manufactured by hot rolling. <P>SOLUTION: The degree of the rough surface of a work roll is estimated by a surface roughening index ϕ which is defined by the following when hot-rolling a metallic material to be rolled. The above surface roughening index ϕ is defined by ϕ = ϕ0×(K2/D)×Σ(K1×L×P/W). In formula, ϕ0 is the proportional constant (m/kN), K1 is the constant decided by the kind, K2 is the constant decided by the kind, L is the rolling length (m) of a certain material to be rolled in the rolling mill, P is the rolling load (kN) of the certain material to be rolled, W is the width (m) of the certain material to be rolled, D is the diameter (m) of the work roll of the rolling mill and Σ is the sum of every material to be rolled. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a work roll surface roughness evaluation method in hot rolling, a work roll grinding method using the method, and a hot rolling method.

  Metal strips, especially thin steel plates typified by strips, are cast, cast into slabs, then manufactured through hot rolling, cold rolling, or further plated. To do.

  FIG. 9 shows an example of an equipment row of a hot rolling line 100 that is conventionally large. A metal material 8 having a thickness of 150 to 300 mm (hereinafter referred to as a material to be rolled) heated to 1000 to 1300 ° C. by the heating furnace 10 is rolled to a thickness of 1 to 25 mm by the rough rolling mill group 12 and the finish rolling mill group 18 to be thin. It is extended. In order to remove the fish scale-like film (hereinafter referred to as scale) of the oxide generated on the front and back surfaces of the material to be rolled at a high temperature, each of the rough rolling mills in the rough rolling mill group 12 (in the case of FIG. 9, R1, R2, R3 3 units, but the number is not necessarily limited to this) and the finish rolling mill (in the case of FIG. 9, seven units F1 to F7, but the number is not necessarily limited to this). On the side, a descaling device 16 is installed to remove scale by spraying high pressure water of 10 to 30 MPa on the surface of the material 8 to be supplied from the pump. In the figure, 14 is a crop shear for cutting and shaping the front and rear end crops (planar irregular portions) of the material 8 before finish rolling, and 22 is water for the material 8 after finish rolling. Or a cooling zone for cooling with air, 24 is a coiler for winding the material to be rolled 8 after cooling, 28 is an online roll grinder for grinding a roll online, 50 is a control device, and 70 is a process. A computer 90 is a business computer.

  The quality of the front and back surfaces (hereinafter simply referred to as the front surface for the sake of simplicity) of products manufactured by hot rolling, which rolls high-temperature rolled materials of several hundred to several hundreds of degrees Celsius, Generally, after hot rolling, it is further covered by the scale generated on the surface and the deterioration of the roll surface state due to the thermal load when the work roll of the rolling mill (hereinafter referred to as the roll) comes into contact with the hot material to be rolled. It is inferior to the surface quality of the product manufactured by cold rolling after removing the scale by pickling.

  Products that are not cold-rolled after hot rolling, are hot-rolled, or are manufactured and shipped after being hot-rolled, or after being subjected to small processing such as removal of the scale or further partial cutting of the width end. In this case, when hot rolling is performed with a roll whose surface condition has deteriorated, a surface quality defect called surface roughness scale wrinkles occurs locally or sporadically in the total length of the product metal band, and the yield due to truncation of the same part Causes a drop.

  Therefore, in hot rolling, it has been a big challenge to stably maintain the surface quality of the manufactured metal strip in a good state, and supply lubricant between the roll and the material to be rolled. Lubricating rolling technology to lubricate and development of rolls made of a material resistant to heat load such as high-speed rolls has been promoted.

  On the other hand, the wear of the roll surface is caused by the fact that the roll material has various widths, and the roll drum length center region where the contact frequency with the roll material is high and the drum length end regions where the contact frequency is low. The development is such that there is a level difference at the boundary part, but the level difference between the roll length and the center length of the roll length is ground by grinding both ends of the roll length so that the level difference on the roll surface is not transferred to the material to be rolled. For the purpose of eliminating the problem and flattening, as in Patent Document 1, Patent Document 2, Patent Document 3, etc., an online roll grinder is used to grind the roll in the rolling mill while continuing the rolling operation. Has been put to practical use with respect to the rear stage stand of the finishing mill (refers to the rear 3 stands among all 6 to 7 stands).

Japanese Patent Laid-Open No. 08-039115 Japanese Patent Laid-Open No. 07-314018 Japanese Patent Laid-Open No. 06-335716

  However, the above-described conventional techniques such as lubrication rolling and high-speed rolling have not solved the problem of surface quality defects such as surface roughness scale wrinkles generated in the product metal strip after hot rolling. In addition, due to the reduction in overall product thickness in recent years, the higher temperature of the material to be rolled due to the higher strength of the material, and the increase in rolling load, the above-mentioned surface roughness scale wrinkles will occur more frequently than before. It became a problem. In addition, in order to suppress the occurrence of surface roughness scale wrinkles, the types of surface roughness scale wrinkles that are likely to occur, the number of continuous rolls of the material to be rolled, the number of rolls that should be rolled within the roll immediately after polishing, Inconveniences that must be dealt with by such a roll chance regulation, and there are cases where it is necessary to frequently replace the roll, which has been a major obstacle to operations.

  That is, an object of the present invention is to suppress the occurrence of surface quality defects of surface roughness scale wrinkles in products manufactured by hot rolling.

  The gist of the present invention is as follows.

(1) When hot rolling a metal material to be rolled with a work roll, the work roll in hot rolling is characterized by estimating the degree of surface roughness of the work roll from the surface roughness index φ defined below. Surface roughness evaluation method.
φ = φ0 ・ (K2 / D) ・ Σ (K1 ・ L ・ P / W)
φ: Surface roughness index φ0: Proportional constant (m / kN)
K1: Constant determined by product type K2: Constant determined by rolling mill L: Rolling length of a material to be rolled in the rolling mill (m)
P: Rolling load (kN) of the material to be rolled in the rolling mill
W: Width of the material to be rolled in the rolling mill (m)
D: Work roll diameter in the rolling mill (m)
Σ: Sum for each rolled material

  (2) The present invention also provides a work roll grinding method, characterized in that the work roll is ground so that the surface roughness index is less than a predetermined value (for example, 1).

  (3) The present invention also provides a hot rolling method using the work roll ground by the above grinding method.

  ADVANTAGE OF THE INVENTION According to this invention, it can suppress that the surface quality defect of the surface roughness scale wrinkle generate | occur | produces in the product manufactured by hot rolling.

  FIG. 9 described above shows an example of the equipment row of the hot rolling line 100 that has been conventionally used. The hot rolling line to which the present invention is to be applied is not necessarily limited to this, but for the sake of convenience, the background to the present invention will be described below as an example.

  FIG. 1A shows the surface quality defect of the rough surface scale ridge generated on the surface of the material 8 to be rolled when rolled in such a hot rolling line 100. A black streak pattern is present in a part of the surface of the material to be rolled 8 in the width direction, and is scattered in the length direction of the material to be rolled 8. This black streak pattern is a trace of the scale biting into the material to be rolled. This scale bite occurs by the mechanism described later.

  FIG. 1B shows a state of the roll 19 extracted from a certain rolling mill in the finishing rolling mill group 18 immediately after the surface roughness scale flaw is generated. The surface of the roll 19 is densely attached with a scale in a range that coincides with the width of the material to be rolled immediately before, but the roll 19 corresponding to the width direction portion on the surface of the material to be rolled where surface roughness scale wrinkles are generated. It can be seen that the scale peels off on the surface of the surface.

  Surface roughness scale 疵 is a material that increases the rolling load due to hot rolling of steel strips, when the target material to be rolled is a thin product with a thickness of less than 2 mm, called a thin material, or because it is hard, such as medium carbon steel or high-tensile steel. In this case, it often occurs when the temperature of the material to be rolled is higher than a certain level, and the peeling of the scale from the surface layer of the roll 19 which is the cause is the rolling mill in front of the finishing mill group 18. Although it has been empirically known that it frequently occurs in (especially F2, 3), the conditions that cause scale peeling from the surface layer of the roll 19 and the mechanism that causes surface roughness scale wrinkles are not necessarily required. It was not clear.

  In order to clarify the generation mechanism of the surface roughness scale flaw, the inventors investigated the scale thickness and surface roughness of the surface layer of the roll 19 every time several rolls of the material to be rolled were rolled. The target materials were low carbon steel having a product thickness of 2 to 5 mm and a product width of 800 to 1500 mm for the first to fifteenth items, and low carbon steel having a product thickness of 1.2 mm and a product width of 1200 mm for the sixteenth and subsequent items. Table 1 shows the rolling conditions of low carbon steel having a product thickness of 1.2 mm and a product width of 1200 mm, and Table 2 and FIG.

  Incidentally, FIG. 2 shows the results of investigating the number of rolls, the thickness of the scale, and the surface roughness of the F2 roll, which is the second rolling mill counted from the front of the finish rolling mill group 18. The data is based on JISB0601-2001 and JISB0651-2001, a stylus type surface roughness tester is applied to the roll surface, moved in the axial direction of the roll, and the reference length lr (λc) for the roughness curve is obtained. It is a value measured with 0.8 mm, the reference length lw (λf) for the waviness curve being 8 mm, and the reference length lp for the sectional curve, that is, the evaluation length ln being 40 mm. By the way, it was measured at the axial center of the roll. As shown in FIG. 2, it was found that the scale thickness increases as the number of rollings increases. It was also found that the surface roughness once increased and then increased. In this investigation, peeling of the scale similar to that shown in FIG. 1B was observed on the surface of the roll 19 at the 50th roll.

  The inventors conducted the same investigation on the rolls 19 of each rolling mill in the rough rolling mill group 12 and the finishing rolling mill group 18 as described later, and other types of rolled materials such as stainless steel. It was carried out about. As a result, the conditions for the peeling of the scale from the roll 19 and the mechanism for the rough surface scale wrinkle were elucidated. The outline is shown in FIG.

  As shown in FIG. 3A, on the surface of the material to be rolled 8 once the scale is removed by the descaling device 16 on the rolling mill entrance side, as shown in FIG. The scale grows during the transport. As shown in FIG. 3 (c), the scale 8 is attached and grows on the surface of the roll 19 by rolling the material 8 to be rolled. As described above, as shown in FIG. 3D, the thickness of the scale of the surface layer of the roll 19 and the surface roughness are increased as many materials to be rolled are rolled. Since a shearing force is acting between the roll 19 being rolled and the material 8 to be rolled, as shown in FIG. 3E, it is considered that the scale of the surface layer of the roll 19 peels off. Here, if rolling of the material 8 to be rolled is continued at the concave portion of the roll from which the scale has been peeled off, every time the roll rotates and the material to be rolled is rolled at the same portion, the surface of the material to be rolled is uniformly generated. The scale is broken only at the portion of the rolled material 8 rolled at the recessed portion of the roll 19 and adheres in the form of periodically agglomerating in the length direction on the surface of the rolled material 8, and the next rolling It is pushed into the material 8 to be rolled by rolling in a machine, and becomes a rough surface scale. Each time the rolled material 8 is rolled at the concave portion of the roll, the scale that has been uniformly generated on the surface of the rolled material 8 is broken and periodically aggregates in the length direction on the surface of the rolled material 8. As shown in the enlarged view of FIG. 3 (e), it is presumed that the portion of the roll from which the scale peels off gives a stronger shearing force to the material to be rolled than the portion where the scale does not. .

  Based on this mechanism, the inventors devised the surface roughness index shown below.

φ = φ0 ・ (K2 / D) ・ Σ (K1 ・ L ・ P / W)
φ: Surface roughness index where
φ0: Proportional constant (m / kN)
K1: Constant determined by product type K2: Constant determined by rolling mill L: Rolling length of a material to be rolled in the rolling mill (m)
P: Rolling load (kN) of the material to be rolled in the rolling mill
W: Width of the material to be rolled in the rolling mill (m)
D: Work roll diameter in the rolling mill (m)
Σ: Represents the sum of each material to be rolled.

  That is, when taking a certain rolling mill, the longer the cumulative rolling length obtained by summing the rolling length of the material 8 to be rolled in the rolling mill, the smaller the work roll diameter, Since the number of times of contact between the roll (roll) and the material to be rolled becomes large and the scale of the roll becomes thick, surface roughness scale wrinkles are likely to occur along with this partial peeling. P / W indicates the rolling load per unit width, and the larger this, the greater the shearing force applied to the scale, and the more likely the surface roughness scale wrinkles occur.

  K2 is a constant determined by the rolling mill, and is determined as shown in Table 3 for each rolling mill in the rough rolling mill group 12 and each rolling mill in the finish rolling mill group 18 in the equipment row shown in FIG. It was.

  In the rough rolling mill (R1, 2, 3), K2 = 0. In the rough rolling mill, the distance from the descaling device 16 to the place where the roll 19 and the material to be rolled 8 are in contact (roll bite). Is about 1 to 3 m, shorter than 5 m in the case of the first stand F <b> 1 of the finishing mill group 18, and the conveying speed is 100 mpm or more, compared with a maximum of 60 mpm in the case of the finishing mill. In addition to the fact that the scale thickness on the surface of the material to be rolled is relatively thin, the scale is once peeled off from the roll, and rolled by the dent of the roll part from which the scale has been peeled off. Even if the scale is destroyed, the scale is removed again by another descaling device 16 on the entry side of the next rolling pass. Le flaws is because does not occur.

  The value of K2 in each rolling mill (F1 to F7) in the finish rolling mill group 18 was determined from the experimental results for the low-carbon steel thin objects shown in Table 1 and FIG. FIG. 4 shows the results of scale thickness of each rolling mill (F1 to F7) in the finish rolling mill group 18, and a straight line representing the surface roughness index calculated based on the rolling conditions of each rolled material. It is shown together. It can be seen that F1 has a smaller scale thickness of about 1/10 at the same number of rollings than F2. This is because the distance from the descaling device 16 is shorter than the inside and outside of 5 m and the inside and outside of 10 m of F2, and the scale thickness on the surface of the material to be rolled is relatively thin. In addition, regarding the finish rolling mills F5, F6, and F7, almost no scale adhered. This is because, as is conventionally known, since the peripheral speed of the roll is high, the roll is worn and the scale does not grow. For F3, the scale thickness was 80% of F2. F4 was 5% of F2. It is considered that there is an influence that the wear of the roll is larger than that of F2. K2 of each rolling mill is a coefficient representing the ease of surface roughness of each rolling mill when indices other than K2 in the surface roughness index formula are the same, and was determined as K2 = 1 in F2. For example, K2 in F1 was found to be 0.2 by multiplying the ratio of the scale thickness 1/10 to the rolling load ratio 26186/28635 and the ratio 243/131 of the length of the material to be rolled on the exit side of the rolling mill. K2 in F3 was determined to be 0.5 by multiplying the ratio of the scale thickness 0.8 to the rolling load ratio 26186/23972 and the ratio 243/441 of the length of the material to be rolled on the exit side of the rolling mill. K2 in F4 was found to be 0.02 by multiplying the ratio 1/20 of the scale thickness by the rolling load ratio 26186/18245 and the ratio 243/722 of the length of the material to be rolled on the rolling mill exit side. K2 in F5, F6, and F7 was set to 0 because almost no scale adhered to the roll.

  K1 is a constant determined by the type of material to be rolled. From the experimental results shown in FIG. 5, the slope of the regression line was 0.1 times in the case of stainless steel compared to the types other than stainless steel. , Determined as shown in Table 4.

Here, the distinction between low carbon steel, medium carbon steel and high carbon steel is based on C% (mass%), but the other components are JIS G 3131 in the case of low carbon steel and medium carbon steel. JIS for steel
According to G 3311. In the case of stainless steel, JIS G 4304 was followed.

  FIG. 5 is a material to be rolled having a product thickness of 3.0 mm under the same rolling conditions, in which different types of materials to be rolled are rolled and the thicknesses of the F2 roll scales are compared. Compared to low carbon steel, medium carbon steel, and high carbon steel, stainless steel had a scale thickness of 1/10. Stainless steel contains a large amount of Cr, and it is difficult for scales to be generated on the surface of the material to be rolled, and rough surface scale wrinkles are unlikely to occur.

  On the other hand, although it is φ0, this may be an appropriate proportionality constant.

  However, for ease of understanding, this φ0 is preferably handled as a normalization constant such that φ = 1 at the reference condition. For example, although 50 slabs having a thickness of 260 mm and a length of 8.12 m are continuously provided as shown in Table 5, the exit side plate thickness in each rolling mill in the finishing mill group 18 is as follows. If the standard condition is F2 (rolling load is not shown but 26186 kN) when rolling to the delivery length (F7 delivery thickness is 1.2 mm, the width is not shown but 1200 mm) = 3.0215E-09.

    (3.0215E-09 × 1 / 0.8 × 50 × 1 × 242.7 × 26186 / 1.2 = 1)

  Then, when φ = 1 or more, it is determined that there is a risk of surface roughness scale soot. If φ <1, it is determined that there is no risk of surface roughness scale soot. Therefore, it is convenient to easily determine whether or not there is a risk of surface roughness scale flaws above and below the surface roughness index φ = 1. However, since the surface roughness index φ increases with each rolling of each material to be rolled, not only the presence or absence of the risk of surface roughness scale flaws, but also the surface of the work roll. The degree of roughness can be estimated for each rolled material.

  The method of determining whether or not there is a risk of surface roughness scale wrinkles in the present invention and the method of estimating the degree of surface roughness of the work roll are above and below the surface roughness index φ = 1 as described above. Anyway, no matter what value is applied as the proportional constant φ0, there is a risk of surface roughness scale wrinkles above and below the surface roughness index φ. What is necessary is just to be able to judge the degree of surface roughness of the work roll.

  FIG. 6 shows an embodiment of an equipment row of a hot rolling line that is an object of the present invention. In addition to the conventional equipment row shown in FIG. 9, an on-line roll grinder 28 is also installed in the rolling mills F2 and F3 in the finishing rolling mill group 18.

  FIG. 7 is a diagram showing an example of the structure of the online roll grinder 28. One grinding unit 29 is installed for each of the upper and lower rolls 19. Each grinding unit 29 includes a grindstone A, a rotation motor 32, a pressing cylinder 31, an oscillation motor 33, a pinion 38, wheels 34, and the like. In a state where the grindstone A is rotated by the rotation motor 32, the grindstone A is pressed against the roll 19 by the pressing cylinder 31, and the roll 19 is ground. The grinding unit 29 rotates in the width direction of the material to be rolled 8 along with the rails 34 along the rail 40 by rotating the pinion 38 with the oscillating motor 33 and meshing with the rack 39 installed on the tilting frame 35. Further, the tilting frame 35 is configured to freely rotate around a tilting fulcrum pin 37 installed on the base frame 36. The base frame 36 is provided with a tilting jack 41 and a stabilizer cylinder 42, and determines a rotational position of the tilting frame 35 with respect to the base frame 36. Thereby, the center of the grindstone A can be directed to the center of the roll 19 in accordance with the change in the diameter of the roll 19. The roll 19 rotates in the conveying direction of the material 8 to be rolled, and the grindstone A rotates in the direction opposite to the roll on the contact surface with the roll 19.

  The entire range of the surface of the roll 19 is ground by tilting, rotating, pressing, and oscillating the online roll grinder 28 having such a structure in accordance with a command from the process computer 70.

  FIG. 8 shows the result of applying grinding of the roll 19 by the on-line roll grinder 28 to the rolling of 250 continuous materials to be rolled, including the thin low-carbon steel whose conditions are shown in Table 1. The horizontal axis represents the number of rolled sheets, and the vertical axis represents the scale thickness and surface roughness index of the F2 roll. Both F2 and F3 were ground once by 40 with the on-line roll grinder 28. As the number of rolls increases, both the thickness of the scale and the surface roughness index increase, but it can be seen that grinding with the online roll grinder 28 decreases both the thickness of the scale and the surface roughness index. By repeating this, a good result was obtained that 250 or more scales were not peeled off from the roll 19 and neither surface roughness scale wrinkles occurred. The work roll of the finish rolling mill is extracted from the rolling mill every time it is judged that the thickness of the thermal fatigue layer (cracked layer), which is not scale peeling, has progressed beyond a certain level, Although the rolls were exchanged, the grinding by the on-line roll grinder 28 was performed at F2 and F3. As a result, even when 250 rolled materials were rolled, the rolls were not exchanged for polished ones. The number of rolls of 250 corresponds to about 5000 tons as the weight of the material to be rolled, which is sufficiently large compared to the conventional limit of about 100 and about 2000 tons where grinding by the on-line roll grinder 28 was not performed. For the rough rolling mills (R1, R2, R3) and finish rolling mills (F1, F4), the on-line roll grinder 28 is not installed, but the surface roughness index is less than 1, and the scale peeling of the work roll does not occur. It was. For the finish rolling mills (F5, F6, F7), an online roll grinder 28 was installed and used for the purpose of eliminating and flattening the wear level difference on the roll surface.

  Here, the case of grinding once per 40 is shown, but for this grinding pattern, the surface roughness index may be less than 1, and the grinding timing (every other or constant grinding during rolling) Needless to say, the grinding amount (whether the roll surface scale is completely removed or left) can be appropriately adjusted depending on various conditions.

  Moreover, in the on-line roll grinder 28 which is currently practically used mainly in the rear three stands of the finishing rolling mill group 18, not only the scale of the roll surface layer but also the roll material and the wear of the center length of the body length. It is necessary to grind the generated convex part, that is, the lengthwise end region, and it is necessary to set the grinding volume (grinding ability) per unit time of the roll to 10 to 20 cc / min, and per unit time per grindstone A Since the grinding volume was 6 to 8 cc / min, it was necessary to use two or more grinding units for the upper and lower rolls. On the other hand, according to the evaluation method of the present invention, the on-line roll grinder 28 installed in F2 and F3 does not have to be ground and removed together with the roll dough. The grinding volume per unit time may be about 1 to 3 cc / min, and the grindstone and grinding unit can be one grindstone and grinding unit for each of the upper and lower rolls. is there.

  Here, an example in which the grinding unit is provided with one on-line roll grinder 28 for each of the upper and lower rolls in the finishing mills F2 and F3 is shown. However, for the purpose of preventing the occurrence of surface roughness scale wrinkles, the roughing mill The on-line roll grinder 28 is installed in all the rolling mills in the group 12 and finish rolling mill group 18 and how many grinding units are installed in each of the upper and lower rolls is appropriately determined depending on the grinding ability required from the rolling conditions. Needless to say, you can do it. However, even in this case, if the evaluation method as in the present invention is used, the number of installed online roll grinders 28 can be minimized, and the equipment cost can be suppressed. By the method, unnecessary wear of the grinding wheel A can be prevented and the running cost can be minimized.

The figure which shows the state of the surface of the work roll extracted immediately after the surface quality defect of the surface roughness scale ridge generated on the surface of the material to be rolled The figure which shows the experimental result which measures the thickness of the scale of F2 roll, and surface roughness Diagram showing roughening scale wrinkle generation mechanism Figure showing scale thickness and surface roughness index of finishing mill roll The figure which shows the thickness of the scale of the F2 roll at the time of rolling the to-be-rolled material of each kind The figure which shows one Example of the equipment row | line of the hot rolling line which has an on-line roll grinder The figure which shows one Example of an online roll grinder The figure which shows the F2 roll grinding result with the online roll grinder The figure which shows an example of the equipment row | line of a hot rolling line which is conventionally many

Explanation of symbols

DESCRIPTION OF SYMBOLS 8 ... Rolled material 10 ... Heating furnace 12 ... Rough rolling mill group 14 ... Crop shear 16 ... Descaling device 18 ... Finishing rolling mill group 22 ... Cooling zone 24 ... Coiler 28 ... Online roll grinder 29 ... Grinding unit A ... Grinding stone 31 ... Pushing cylinder 32 ... Rotary motor 33 ... Oscillating motor 34 ... Wheel 35 ... Tilt frame 36 ... Base frame 37 ... Tilt fulcrum pin 38 ... Pinion 39 ... Rack 40 ... Rail 41 ... Tilt jack 42 ... Stabilizer cylinder 50 ... Control device 70 ... Process computer 90 ... Business computer 100 ... Hot rolling line

Claims (3)

Work roll surface roughness evaluation in hot rolling, characterized by estimating the degree of surface roughness of the work roll by the surface roughness index φ defined below when hot rolling the metal material to be rolled. Method.
φ = φ0 ・ (K2 / D) ・ Σ (K1 ・ L ・ P / W)
φ: Surface roughness index φ0: Proportional constant (m / kN)
K1: Constant determined by product type K2: Constant determined by rolling mill L: Rolling length of a material to be rolled in the rolling mill (m)
P: Rolling load (kN) of the material to be rolled in the rolling mill
W: Width of the material to be rolled in the rolling mill (m)
D: Work roll diameter in the rolling mill (m)
Σ: Sum for each rolled material   A method for grinding a work roll, wherein the work roll is ground so that the surface roughness index defined in claim 1 is less than a predetermined value.   A hot rolling method using a work roll ground by the grinding method according to claim 2.

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