JPH059163B2 - - Google Patents

Description

[Detailed description of the invention]

(Field of Industrial Application) The present invention belongs to the field of steel cold rolling technology, and the content of the technology disclosed in this specification is to reduce edge drop, which is a concern during cold rolling, and to The purpose of the present invention is to propose a rolling method suitable for producing a cold rolled steel sheet with less stretch and edge cracking at the edges. (Conventional technology) “Edge drop” occurs in the rolled material after cold rolling.
A rapid decrease in thickness can be seen at both ends in the width direction. This edge drop is caused by the metal flow in the width direction of the edge portion of the rolled material and the surface flattening deformation of the work roll, and is caused by being dominated by the cold rolling conditions. Conventionally, as a technique for reducing this edge drop, for example, Japanese Patent Application Laid-Open No. 1983-1999 proposed by the present inventors has been proposed.
There is a method disclosed in No. 113904. The technology of this disclosure is
A four-high rolling mill is constructed in which each of a pair of work rolls has a tapered part that is ground at least on one side end, the tapered part is located on both sides of the material to be rolled, and the reinforcing roll is incorporated into the mill housing. This is intended to reduce edge drop by employing a row of cold tandem rolling mills in a stand arrangement in which work rolls are installed at least in the first stand and conventional work rolls are incorporated in the final stand. (Problems to be Solved by the Invention) FIG. 2a shows a known rolling method using a trapezoidal work roll, which is also used in the present invention, in which both ends of the work roll 1 are tapered. FIG. 2b shows a rolling method in which only one end of the work roll 1 is tapered and the work roll 1 is moved in the axial direction so that it can follow changes in the sheet width. However, when rolling a normal rolled material using such work rolls, the elongation rate at the width edges is smaller than that at the width center, so as shown in Figure 3, The tension on the exit side of the part becomes extremely high. Therefore, especially with brittle materials, occurrence of edge cracks as shown in FIG. 4 becomes a problem. Furthermore, even in the case of materials that do not cause edge cracking, shape defects such as belly stretching may occur, leading to operational inconveniences and a decrease in commercial value. The aim of the present invention is to propose a cold rolling method that is effective in reducing edge drops during cold rolling, obtaining a better shape, and preventing the occurrence of edge cracks in cold rolled sheets. be. (Means for Solving the Problems) In order to solve the above-mentioned problems that need to be solved, the present invention uses a cold rolling mill equipped with a pair of work rolls each having a tapered portion formed at least on one end. In a cold rolling method excellent in suppressing edge drops, in which the edge end of the material to be rolled is positioned at the tapered portion of the roll and the material to be rolled is rolled, the material to be rolled is subjected to a width reduction treatment on the entry side of the cold rolling mill. As a solution, we will adopt a cold rolling method that is characterized by thickening the steel sheet, has excellent edge drop suppression, and does not cause edge cracking. In this method, the width reduction process of the material to be rolled is performed in the first stand of the cold tandem rolling mill, and the tapered part of the work roll is ground into a tapered or curved shape. Use a crown-shaped one. (Effect) Next, the basis for using the above method as a means to solve the problem will be discussed below. FIG. 5a shows the thickness deviation of a typical mother plate before cold rolling, and a sharp edge drop occurs at the edge of the plate. The plate thickness deviation after rolling this in a cold tandem mill is shown in Fig. 5b. Normal work roll (flat roll)
When rolled with a tapered work roll (tapered roll) shown in FIG. 2, a large edge drop occurs, but when rolled with a tapered work roll (tapered roll) shown in FIG. 2, an effect of reducing edge drops is obtained. However, if this method uses only tapered rolls, the elongation rate at the edge of the plate is smaller than the elongation rate at the center of the width, which not only causes shape defects such as belly elongation, but also the edge of the plate. A large tension was generated at the edges (edges), and in the brittle material, edge cracking as shown in Figure 4 occurred. Therefore, the inventors conducted further research taking into consideration the shape defects and edge cracks mentioned above, and as a result, in order to increase the elongation rate of the edge portion in the width direction, the inventors performed width reduction using, for example, an edger roll before cold rolling. found that it is effective to increase the thickness of the edge portion and then roll it using a tapered work roll, a so-called tapered roll. That is, FIG. 6a shows the sheet thickness deviation after width reduction and before cold rolling, and the sheet thickness increases at the edge portion due to width reduction. When this plate with thickened edge portions is rolled with a tapered work roll, the edge portion becomes shaped as shown in FIG. 6b, and the thickness deviation of the plate is reduced. That is, the effect of the tapered work roll and the effect of increasing the thickness of the edge portion combine to almost eliminate edge drops.
Furthermore, the elongation rate of the edge portion and the elongation rate of the center portion became equal, and as shown in FIG. 7, the tension at the edge portion became approximately equal to the tension at the center portion, and the occurrence of shape defects and edge cracks could be prevented. On the other hand, when rolled with ordinary work rolls, the edge drop was slightly larger than in the case of implementing the method of the present invention, and defective shapes and edge cracks occurred.
As described above, according to the present invention, it is possible to reduce edge drop and further prevent the occurrence of poor shape and edge elongation. When applying the method of the present invention to a cold tandem rolling mill, it is necessary to consider the influence of plate thickness and tension on the formation of edge drops. 8th
As can be seen from Figures a and b, the thicker the entrance plate thickness, the more the edge drop is formed from the inside, and the smaller the tension, the greater the edge drop amount. By the way, Fig. 9 is an example showing the area where edge drop is improved by the tapered work roll, and each curve in this figure shows the plate thickness distribution (curve α) caused by the application of the tapered work roll and this. It shows the difference between the thickness distribution and the thickness distribution when using a normal work roll, that is, the amount of improvement in edge drop (curve β). The chain line γ in the figure is the profile of the tapered work roll, EH is the radius difference between the tapered part and the flat part, and EL is the distance from the boundary point between the tapered part and the flat part to the plate end. As can be seen from Fig. 9, the amount of improvement in edge drop by the tapered work roll method does not follow the profile of the work roll, and moreover, the improved area remains within about 50 mm from the edge of the board toward the center.
In other words, the edge drop improvement area by the tapered work roll method is not equal to the length of EL in this example, and is in the area closer to the center than the edge of the plate. An edge drop (in the range of 90 mm to 50 mm) suggests that improvement may not be possible. Considering that edge drops occur outward from around 50 mm from the sheet edge with normal work rolls, if the rolling conditions are constant in terms of the area where metal flow in the width direction is possible, the area where edge drops occur will coincide with the improvement area. It suggests that there is. In other words, this means that the application of tapered work rolls to a cold tandem mill is effective only for stands where rolling conditions are such that edge drop formation is significant. By the way, Table 1 shows typical examples of tension and plate thickness in a cold tandem rolling mill (5 stands).

[Table] As is clear from the comparison of Table 1 above with Figure 8 a and b, in terms of plate thickness, the upstream stand
On the other hand, from the point of view of tension, it can be seen that if tapered work rolls are applied to the first stand and the final stand, the edge drop can be greatly improved. In addition, when performing width reduction, it is better to perform width reduction in an upstream stand where the plate thickness is thicker, as the effect will be more effective (closer to the center) and the workability of the rolled material will be better. It is suitable as there is no occurrence of cracking or ear cracking. Therefore, in a cold tandem rolling mill, width reduction is performed at least at the position of the first stand (inlet side), and then the tapered part of the tapered part of the next work roll is positioned inside the material to be rolled, and rolling is performed. It is effective to do so, and the present invention can be applied appropriately to the second stand and beyond. In short, the present invention involves arranging an edger roll on the entrance side of a cold rolling mill to perform width reduction, and then forming a tapered part of a pair of work rolls having a tapered part or a tapered curve on at least one end.
By rolling the material at the inner side of the material to be rolled, it is possible to reduce edge drop, further prevent shape defects, and prevent the occurrence of edge cracks. (Example) An example of the present invention will be shown below, in which a mother plate having a width of 1100 mm and a thickness of 2.6 mm was cold rolled in a 5-stand cold tandem rolling mill as shown in FIG. Note that the reference numeral 3 in the drawing represents a material to be rolled, and the reference numeral 4 represents an edger roll. The width reduction amount is 3 mm on one side. Other stands do not perform width reduction. The profile of the tapered work roll is as shown in FIG. 2a, with both the upper and lower work rolls tapered and ground at their ends, with a roll diameter of 500 mm, El = 50 mm, and EH = 25 μm. This tapered work roll is used as the first stand, and the other stands are normal rolls. For comparison, a case was conducted in which normal rolls were used for all stands and a case in which a tapered work roll of the above shape was used in the first stand, without any width reduction. Figure 10 shows the amount of edge drop on the exit side of each stand. According to the present invention, edge drops are rapidly improved in the first stand, and although edge drops are formed in subsequent stands, the suppressing effect of the first stand continues until the final stand, and edge drops of about 20 μm are improved. Ta. In addition, no shape defects such as ear cracking or belly stretching occurred. (Effects of the Invention) As explained above, according to the present invention, not only edge drops can be reduced, but also shape defects and edge cracks can be prevented, resulting in high yield without impeding surface quality or shape defects. It becomes possible to manufacture cold-rolled steel sheets.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an example of equipment for implementing the present invention;
FIG. 2 shows a tapered work roll used in the present invention [a is a work roll with tapers at both ends;
b is a diagram explaining the relationship between a work roll with a taper on only one side] and a material to be rolled, and Figure 3 is a diagram illustrating the relationship between a material to be rolled in the width direction when a material to be rolled is generally rolled with a tapered work roll. Figure 4 is a graph showing the relationship between position and exit tension. Figure 4 is a diagram showing the state of edge cracks in the rolled material. Figure 5a is a graph showing the thickness deviation of the mother plate before general cold rolling. Figure 5b is a graph showing the sheet thickness deviation after cold rolling a, Figure 6a is a graph showing the sheet thickness deviation after width reduction and before cold rolling, Figure 6b 7 is a graph showing the plate thickness deviation according to the present invention after cold rolling a, FIG. 7 is a graph showing the relationship between the position in the width direction of the plate and the exit tension in the case of the present invention, and FIGS. 8 a and b 9 is a graph showing the influence of plate thickness and tension on edge drop during cold rolling. FIG. 9 is a graph showing areas where edge drop is improved. FIG. 10 is a graph showing edge drop during tandem rolling showing the effect of implementing the present invention. This is a transition diagram. 1... Work roll with tapers on both sides, 1'... Work roll with taper on one side, 2... Material to be rolled, 3... Edger roll.

Claims (1)

[Claims] 1. Using a cold rolling mill equipped with a pair of work rolls each having a tapered portion formed at least on one end, the edge end of the material to be rolled is positioned on the tapered portion of the work roll, and the rolled material is rolled. A cold rolling method for rolling a material that is excellent in suppressing edge drops, characterized in that the material to be rolled is subjected to a width reduction treatment on the entry side of the cold rolling mill to thicken it, which is excellent in suppressing edge drops and causing edge cracks. Cold rolling method without. 2. The cold rolling method according to claim 1, characterized in that the above rolling is performed in at least the first stand of a cold tandem rolling mill.