JPH10277614A - Edge drop reduction method for metal strip - Google Patents

Abstract

An object of the present invention is to obtain a uniform thickness profile in the width direction by reducing edge drops when rolling a metal strip that requires uniform thickness in the width direction. A cemented carbide containing 50% by weight or more and 88% by weight or less of tungsten carbide is rolled using a roll of a cemented carbide sleeve having a thickness of 3% or more of the roll radius and externally fitted to the shaft core. .

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for reducing an edge drop of a metal strip, and more particularly, to reducing a thickness deviation in a sheet width direction in hot rolling or cold rolling of a metal strip, particularly an amount of edge drop. The present invention relates to a rolling method for obtaining a uniform thickness profile in the width direction.

[0002]

2. Description of the Related Art In press forming, shearing, and the like of a metal strip, if the sheet thickness is not uniform, the deformation becomes uneven, and the product shape after molding may be defective or may not be broken into a product. Therefore, there is a strong demand for reducing not only the thickness deviation in the longitudinal direction of the metal strip but also the thickness deviation in the sheet width direction as much as possible.

Conventionally, metal strips have been manufactured by rolling. During rolling, thickness deviation in the sheet width direction is apt to occur, and particularly, edge drop, which is a remarkable decrease in sheet thickness, occurs at the end of the sheet. Therefore, it is necessary to cut the end of the metal strip after rolling and ship it as a cross section that is almost rectangular. However, since the cut portion extends over the entire length of the metal strip, the yield of the strip is reduced, which is a problem. Had become.

Therefore, various methods have been studied to reduce the edge drop. In Japanese Patent Publication No. 2-34364, Japanese Patent Publication No. 2-34241, and Japanese Patent Publication No. 5-56202, a work roll having a tapered end is disposed symmetrically with respect to a point and shifted in the plate width direction to drop an edge. Are disclosed. Also, Japanese Patent Application Laid-Open No. 7-39902 discloses a method for reducing edge drop by rolling a roll of cloth.

[0005]

However, when these methods are adopted, a large investment is required because it is necessary to modify a rolling mill and install desired equipment. Further, in the former method of shifting the work roll imparting the taper in the sheet width direction, the edge drop existing in the metal strip on the rolling mill entrance side, because the edge drop of the metal strip after rolling greatly fluctuates, It was necessary to change the shift amount of the taper roll for each rolling chance depending on the material and thickness of the metal strip, but the shift speed was remarkably slow, several thousandths of the rolling speed. As a result, in continuous tandem rolling between cold and hot, there is a problem that the edge drop cannot be sufficiently reduced when the width of the preceding material and the width of the succeeding material are different in the vicinity of the welded portion of the metal strip. Therefore, even in batch rolling such as hot rolling and cold reverse mill, there is a problem that the shift amount needs to be changed for each coil each time, and the work efficiency cannot be improved. In addition, only by shifting the taper, even if the plate thickness at a predetermined position from the plate end can be made substantially the same as the plate thickness at the center of the plate width, the plate thickness at a slightly distant position may be significantly different, It was difficult to obtain a cross section of a metal strip close to a rectangle, which was a problem.

Further, in the method of rolling by crossing rolls, the thickness is changed over the entire width of the sheet, and it is difficult to positively reduce only the edge drop, and it is desired to sufficiently reduce the edge drop. Then
The shape of the metal strip changed greatly, causing a problem that rolling of the sheet occurred during rolling and rolling became impossible. Therefore, the present invention advantageously solves the above-mentioned problems, and can significantly reduce edge drop without requiring modification even with a conventional rolling mill, and provide a metal strip having a good thickness accuracy in the sheet width direction. The purpose is to provide.

[0007]

DISCLOSURE OF THE INVENTION The present invention has been made to achieve the above-mentioned object, and its technical means is to reduce carbonization when rolling a metal strip which is required to have a uniform thickness in the width direction. This is a method for reducing edge drop of a metal strip, wherein rolling is performed using a work roll made of a cemented carbide containing 50% by weight or more and 88% by weight or less of tungsten.

In this case, it is preferable to use a roll provided with a cemented carbide sleeve having a thickness of 3% or more of the roll radius as the work roll, and a steel roll shaft is used as the work roll. It is preferable to use a roll fitted with a sleeve.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the rolling of a metal strip, an edge drop in which the thickness of the strip significantly decreases at the end of the roll is likely to occur inside the roll bite where the rolling roll and the strip contact. The present inventors have made various studies on the occurrence of edge drop, and as a result, unlike the central portion of the plate width, one end of the plate width direction is not restricted at the end portion of the plate, so that the plate is easily deformed in the width direction. It was found that unevenness of the sheet thickness occurred. During rolling, the roll flattens due to the load, but at the end of the plate, the load is greatly different from the center of the plate due to deformation in the width direction of the plate, making it difficult to flatten. Became thinner and caused edge drop.

Conventionally, it is known that when a work roll having a small diameter is used, edge drop is smaller than when a work roll having a large diameter is used. This is because the flatness of the roll is almost the same at the plate center portion and the plate end portion, so that the thickness of the plate at the plate end portion is not likely to be uneven. However, in the rolling using a small-diameter work roll, the shape is extremely unstable because the work roll is easily bent. Therefore, various measures such as a multi-stage cluster type and horizontal support rolls have been devised. However, the structure of the rolling mill is complicated and is not suitable for high-speed high-pressure rolling. As a result, a method of efficiently rolling a metal strip by increasing the roll diameter has been widely adopted.

Therefore, the present inventors have studied a method of manufacturing a good metal strip by reducing the edge drop. From the above findings, it is understood that the edge drop can be reduced when the flatness of the roll is made substantially the same at the plate center and the plate end. That is, if the roll is hardly flattened, the edge drop can be reduced. For this purpose, the present inventors paid attention to the roll material. That is, the flatness of the roll changes greatly depending on the Young's modulus, and the flattening can be made difficult by increasing the Young's modulus. Examining the Young's modulus of various materials, the Young's modulus of a conventional steel-based alloy roll is as small as 20,000 kg / mm ² and roll flattening is likely to occur. It turned out that it has the above-mentioned large Young's modulus. In addition, when a low-carbon steel sheet was cold-rolled as an example of an edge drop of a metal strip by rolling with a roll using these tungsten carbide-based cemented carbides, as shown in FIG. W
It has been found that a cemented carbide containing 50% by weight or more of C) can sufficiently reduce the edge top. On the other hand, if the content of tungsten carbide is too large, as shown in FIG. 2, the transverse rupture strength, which is an index of the roll strength, is reduced, and the roll is damaged during rolling and cannot be rolled. There is a need.

The type of the metal strip rolled by the roll of the present invention is not particularly limited. The present invention can be advantageously applied to any metal strip that requires a reduction in edge drop. In the roll of the present invention, the tungsten carbide cemented carbide is added to at least one of cobalt, nickel, chromium, titanium, a nickel-based alloy, and a cobalt-based alloy to tungsten carbide powder as a main component,
If necessary, titanium carbide, tantalum carbide, niobium carbide, boron, silicon, etc. are added and sintered. By adjusting the amount of cobalt, nickel, and the like, and the particle size of the carbide, the characteristics can be significantly changed. It is necessary to increase the pressure resistance of the rolling roll, and it is preferable to add a metal or alloy having high toughness such as nickel and cobalt.

Tungsten carbide cemented carbide is produced by mixing various raw material powders, molding and sintering. It is preferable to perform hot isostatic pressing after sintering in order to eliminate coarse voids. In addition, in order to increase the accuracy after the production of the roll, it is preferable to perform sintering by performing cold isostatic pressing after mixing the raw material powders. The roll made of the tungsten carbide cemented carbide according to the present invention is extremely expensive in terms of cost if an integrated roll is used. Therefore, a composite of a tungsten carbide cemented carbide was examined only for the roll barrel portion directly involved in the edge drop reduction of the metal strip. When rolls were manufactured and rolled by changing the thickness of the tungsten carbide cemented carbide in various ways, if the thickness was 3% or more of the roll radius, the strength of the tungsten carbide cemented carbide could be maintained and stable. Can be rolled. If the thickness is less than 3%, it is found that the tungsten carbide-based cemented carbide breaks and cannot be rolled. That is, conventionally, a tungsten carbide cemented carbide is sprayed on a process roll that is used only for threading and does not receive excessive stress such as rolling, but has a thickness of less than 1 mm and a roll radius of less than 1 mm. Is very thin, less than 3% of the thickness, so that it can withstand the thickness of its own weight of the sheet to be passed, but when a force is applied to change the sheet thickness by deforming the metal material like the rolling roll of the present invention. It was found that the film could not withstand the peeling and easily peeled off.

[0014]

【Example】

(Example 1) As an example of a metal strip, a hot-rolled steel sheet (sheet thickness: 4.0 mm) was used for pickling the steel sheet, and then the fifth sheet was picked up.
In the stand of the cold tandem mill, as a first example of the present invention, a tungsten carbide cemented carbide in which the outer periphery of the roll contains 13% by weight of cobalt and the remaining 87% is tungsten carbide is used as the example of the present invention. As a work roll, a composite roll formed by fitting a high-speed steel (high-speed steel) to a work roll is applied at 50 ° C., a concentration of 5%, and an average particle size of 8 μm as a rolling oil. While supplying the oil emulsion in a circulating lubrication system,
mm.

Further, as Example 2 of the present invention, after pickling the steel sheet using the same type of hot-rolled steel sheet (sheet thickness 4.0 mm),
Stands All the stands of the cold tandem mill are made of a tungsten carbide cemented carbide whose outer periphery contains 45% by weight of cobalt and the remaining 55% is tungsten carbide, and its thickness is set to 41 mm, which is 20% of the roll radius. Then, a composite roll formed by fitting a high-speed steel to a shaft core was applied as a work roll, and rolled under the same conditions as above.

As a comparative example, after the same type of hot-rolled steel sheet (sheet thickness: 4.0 mm) was pickled, the outer periphery of the steel sheet was coated with 55% by weight of cobalt on all stands of a five-stand cold tandem mill. A tungsten carbide cemented carbide alloy containing 45% tungsten carbide and having a thickness of 41 mm, which is 20% of the roll radius, is used as a work roll. And rolled under the same conditions as above.

Further, as a conventional example, a hot-rolled steel sheet (4.0 mm thick) from Dofu was pickled, and then the conventional 5% chromium forged steel was put on all the stands of the cold tandem mill. A work roll was applied and rolled to 1.2 mm as described above. After cold rolling, a sample was taken from the steel sheet and the edge drop was measured. Table 1 shows the results.

[0018]

[Table 1]

Table 1 shows the difference between the plate thickness (h ₁₀₀ ) at a position inside 100 mm from the plate end and the plate thickness (h ₁₀ ) at a position inside 10 mm from the plate end as an edge drop. is there. If by applying the work roll of the present invention example was cold rolled, the comparison examples and the conventional than in the case of rolling a steel alloy rolls (h ₁₀₀ -h ₁₀₎ of the value is smaller thickness is more uniform It turns out that edge lop is reduced.

Example 2 In hot rolling of ordinary steel,
As Example 1 of the present invention, from the fourth stand to the seventh stand of the 7-stand finishing mill, a tungsten carbide cemented carbide in which the outer periphery which is the roll of the present invention contains 25% by weight of cobalt and the remaining 75% is tungsten carbide The thickness of the roll is set to 200 mm, which is 59% of the roll radius, and a composite roll formed by fitting a hot rolled steel to the shaft is used as a work roll. And high-speed rolling from a sheet bar of 30 mm to a finished thickness of 2.6 mm.

Further, as Example 2 of the present invention, the outer periphery, which is the roll of the present invention, contains 25% by weight of cobalt from the fourth stand to the seventh stand of the seven-stand finishing mill, and the remaining 75%.
% Of tungsten carbide cemented carbide, the thickness of which is 3.2% of the roll radius of 11 mm.
As a work roll, a composite roll formed by fitting using a hot-rolling high-speed steel to the shaft core is used as a work roll, and the rest of the stand uses a conventional hot-rolling high-speed steel work roll, and a finish thickness of 2.6 mm from a sheet bar of 30 mm. Rolled at high speed.

Further, as a comparative example, the outer periphery, which is the roll of the present invention, contains 25% by weight of cobalt in the fourth to seventh stands of the seven-stand finishing mill and the remaining 75%.
Is a tungsten carbide cemented carbide, which is tungsten carbide, the thickness of which is 2.6% of the roll radius, 9 mm, and a composite roll formed by fitting using a hot-rolling high-speed steel to the shaft core is applied as a work roll, The rest of the stand uses the work roll of the conventional hot-rolling high-speed steel,
mm to a finish thickness of 2.6 mm.

As a conventional example, a work roll of high-speed hot-rolled high-speed steel was applied and hot-rolled to 2.6 mm in the same manner as described above. While observing the state of breakage of the roll during hot rolling, a sample was sampled from the steel sheet after hot rolling, and the edge drop was measured. Table 2 shows the results.

[0024]

[Table 2]

Table 2 shows the difference between the plate thickness (h ₁₀₀ ) at a position within 100 mm from the plate end and the plate thickness (h ₁₅ ) at a position within 15 mm from the plate end as an edge drop. Things. When hot rolling is performed using the work roll of the present invention, the value of (h ₁₀₀ -h ₁₅ ) is smaller and the plate thickness becomes uniform than when rolling is performed using a comparative example or a conventional steel-based alloy roll. It can be seen that the edge lop is reduced. Also,
When the roll of the present invention is applied, the roll does not break during hot rolling, but as in the comparative example, the roll is broken during rolling when the wall thickness is small and the amount of tungsten carbide is large, and the roll is broken during the rolling. I had to stop.

[0026]

As described above, according to the present invention, when a metal strip is rolled, the edge drop at the end of the strip is reduced, and a strip having a uniform thickness in the strip width direction can be obtained. This is a remarkably effective technique because it is possible to reduce the amount of trimming of the strip and improve the production yield, and it is possible to manufacture a uniform product without cracking by press molding or the like.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the amount of tungsten carbide and edge drop.

FIG. 2 is a graph showing the relationship between the amount of tungsten carbide and the transverse rupture force.

──────────────────────────────────────────────────続 き Continuation of the front page (51) Int.Cl. ⁶ Identification symbol FI // C22C 29/08 B21B 37/00 118 (72) Inventor Hirotaka Kano 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Kawasaki Steel Corporation (72) Inventor Junichi Tateno 1 Kawasaki-cho, Chuo-ku, Chiba City, Chiba Prefecture Kawasaki Steel Corporation Chiba Works (72) Inventor Hajime Nagai 1-Kawasaki-cho, Chuo-ku, Chiba City, Chiba Prefecture Company Chiba Works

Claims (3)

[Claims] When rolling a metal strip which is required to have a uniform thickness in the width direction, a work roll made of a cemented carbide having a roll surface containing 50% by weight to 88% by weight of tungsten carbide is used. A method for reducing edge drop of a metal strip, wherein the method is used to perform rolling. 2. The work roll having a roll radius of 3
2. The method according to claim 1, wherein a roll provided with a sleeve made of a cemented carbide having a thickness of at least% is used. 3. The method for reducing edge drop of a metal strip according to claim 1, wherein a roll having a sleeve externally fitted to a steel roll shaft is used as the work roll.