JPH01237005A - Method for cold rolling - Google Patents

Abstract

PURPOSE:To control edge drops without sacrifice of a shape by adjusting a displacement amount of a set position of a work roll taper starting point on the basis of a sheet edge in respective rolling stands. CONSTITUTION:As for >=2 rolling stands of a tandem mill provided with work rolls 2, a roll end part of which is formed into a taper down shape toward a roll body end and movable in the direction of a roll axis, cold rolling is performed by setting a taper starting point of the rolls 2 to an inside point from an edge of a rolled stock 1. In that time, edge drops are controlled by adjusting a displacement amount of a set point a work roll taper starting point on the basis of an edge of the stock 1 in respective rolling stands. Therefore, edge drops are effectively reduced and the stand performing tapered work roll shift rolling is specified, so that a cold rolled sheet having very small deviations in sheet thickness distribution and a good shape is obtained without interference with shape control.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a method for cold rolling a plate material, and aims to advantageously produce a plate material with excellent plate thickness accuracy, particularly at the edge portion of the plate, and a good shape. It is something to do.

(Prior art) When cold-rolling a plate material, in addition to having a good shape (flatness), the thickness distribution in the width direction of the plate material is uniform,
In other words, the plate crown and edge drop are required to be small. In general, the plate thickness distribution after cold rolling is rolled so that the shape is similar to that of the hot rolled plate that is the original plate for rolling, that is, the crown ratio is constant.
If it is not constant, the shape will deteriorate. Therefore, control of plate crown and shape is the same problem, and conventionally control has been carried out by roll bending or the like. However, the crown ratio is not constant at the ends of the plate width, that is, at the edges, and so-called edge drops occur due to the flow of the material in the width direction.

Regarding this problem, conventionally, for example, Japanese Patent Publication No. 60-5192
As shown in Publication No. 1, a tapered part is provided at one end of the upper and lower work rolls, and these work rolls are made movable in the roll width direction, and the tapered part of each work roll is provided near the edge part. A rolling method has been proposed that makes it possible to control the profile and shape of the plate material by setting the following conditions. This technology is called a single taper power crawl shift, and can be incorporated into a 4-high rolling mill or a 6-high rolling mill.

As an edge drop control method using such a rolling mill, for example, the document "Application of Ni-WRS Mill to Cold Rolling (1st Report - 2nd Report): 1985 Plastic Working Spring Conference Proceedings P41- 48, a method of forming an edge-up shape using a Taber roll in the first pass of cold rolling, and then performing normal rolling from the second pass onward to reduce edge drop (hereinafter referred to as method 1). ), or as shown in Japanese Unexamined Patent Publication No. 61-20601, a method (hereinafter referred to as method 2) of reducing edge drop by rolling using tapered rolls in all passes of cold rolling has been proposed. There is.

(Problem to be Solved by the Invention) All of the above conventional methods greatly contribute to reducing edge drops, but in Method I, when the thickness reduction ratio is large, edge drops increase after the second bath. In order to reduce the edge drop, it is necessary to create a large edge-up shape in the first pass. To achieve this, it is necessary to increase the distance between the plate edge and the taper start point (hereinafter referred to as the shift position) from the plate edge to the inside, but in this case, excessive tension will be generated at the plate edge. In some cases, cracks occurred, leading to plate breakage.

On the other hand, method 2 is a method that does not provide edge drop control capability only to the first path, but distributes the control capability to all paths within the range where cranks do not occur.
The problems in are solved. However, in method 2, setting the shift position in each pass poses a problem. In other words, in method 2, only the occurrence of a crank is considered as a condition for limiting the shift position of each pass, but
There are countless combinations of shift positions for each pass that satisfy these conditions, and it has not been clarified how much the shift position should be set for which pass when controlling edge drop after the final pass. do not have.

Furthermore, when tapered roll rolling is performed for all passes, the roll position is limited, which limits the ability to control the shape, which is the primary objective of cold rolling, and this becomes a serious problem, especially in the final pass. Furthermore, in actual rolling, the occurrence of disturbance in shape (flatness) due to changes in edge drop also poses a problem.

(Means for Solving the Problem) As a result of extensive research into edge drop control using taper power crawl shift in cold tandem rolling, the inventors have found that changes in edge drop and shape in each pass are They discovered that there is a close relationship between the relative movement distance of the shift position of the pass to the shift position of the pass, and were able to complete this invention.

That is, the present invention provides a tandem mill in which at least two rolling stands are provided with work rolls each having one end of the roll cylinder tapered toward the end thereof and movable in the axial direction of the rolls. When performing cold rolling by setting the taper start point of the work roll inside the edge of the plate to be rolled, the amount of displacement of the set position of the work roll taper start point with respect to the plate end in each of the rolling stands is calculated. It is a cold rolling method characterized by controlling the edge drop by adjustment, and in particular, the edge drop 1 of the original plate for rolling is a known amount, and the work roll taper starting point is set based on the edge of the plate in each rolling stand. It is preferable to set the position of the taper start point of the work roll in each rolling stand using the edge drop change coefficient of each rolling stand determined by the amount of positional displacement.

(for production) This invention will be specifically explained below.

First, the edge drop change rate δEd in l bus,
is defined by the following equation (1).

Here, hx is the plate thickness at the edge drop point,
hc is the plate thickness at the center in the width direction.

From equation (1), the edge drop rate Ed after n passes is expressed by the following equation, where Ed is the edge drop rate of the original plate for rolling.

In addition, the subscript O means the value of the original plate for rolling.

Also, if the i-th edge drop amount is HD, then HD4-EdHhct
(3).

According to the inventors' study, the edge drop change rate δEd+ in the l bus can be expressed by the following equation.

δ[Ed, -α, (Wδ, -Wδt,)+β1 (4) Here, W6. is the shift position in the L bus, and is the distance from the edge of the plate to the start point of the taper as shown in Figure 1. If the start point of the taper is inside the edge of the plate, it is a negative number; If it is, it is expressed as a positive number. Hereinafter, the relative displacement amount (Wδ, -Wδ, -1) of the relative shift position will be referred to as the relative shift position.

Note that when calculating the relative shift position, if the taper starting point is outside the edge of the plate, Wδ, -0 is used in all cases. Also, α4 and β are rolling material, rolling pass, and
It is a constant (edge drop change coefficient) determined by the taper shape, and takes a unique value for each stand once the material and pass schedule are determined, and is usually α, ≧O1β, ≧0.
It is.

By substituting equation (4) into equation (2), Ed can be expressed by a relative shift position as shown in the following equation.

Ed, −Ed, + Σ (α, (w δ,
−w δ 5-1)+βゑ)(5)i*1 Note that Wδ. =0. When formula (5) is transformed, it becomes. In other words, if the shift position of the l pass is changed by ΔWδ, the edge drop of the product will be (α, -α, .1)
It is possible to change only ΔWδ.

Next, it is generally known that the steepness of a sheet material is almost uniquely determined by a change in the crown ratio, but based on this fact, when cold rolling is performed with a constant crown ratio, The change in steepness is almost uniquely determined by the change in the edge drop ratio, that is, the encitrotube change rate. Combining this with the novel findings described above, the steepness in each path is also related to the relative shift position.

The inventors have found that this relationship is approximately linear in a range where a steepness of several percent is a problem, such as in cold rolling.

That is, the steepness λ8 in the l bus is expressed by the following equation.

λ, = ζ, (Wδ, -Wδ, -1) + ηN (7)
η is a constant (shape change coefficient) determined by the rolling material, rolling pass, and taper shape, similar to α1 and βm,
Once the material and pass schedule are determined, each stand takes a unique value, and usually ζi≧0 and η≧0. Therefore, if the maximum allowable steepness in each path is ±λmi, the following equation can be obtained.

Furthermore, the inventors have found that when the rate of change in edge drop reaches a certain value, the occurrence of cranking increases significantly. Therefore, the occurrence of cracks is also related to the relative shift position, and the minimum value T of the relative shift position is limited.

T, ≦Wδ, −Wδi −, (9) Here, if ζl is set, the conditions regarding the shape and crack occurrence are (8
), (9) are collectively expressed as the following equation.

ξ1≦Wδi−Wδ11≦ψ, 02) Furthermore,
00) In the formula, 1llin(a, b) means taking the smaller value of a and b.

Fig. 2 schematically shows the above relationship for a tandem mill consisting of three stands, and shows that the relative shift position of each stand is controlled within the range that satisfies equation 02) indicated by diagonal lines in the figure. Accordingly, (5) or (6
) can be obtained, and in this range, the edge drop rate Ed of the original plate for rolling and the target edge drop rate EdR satisfy the formula (5) or (6). By determining the relative shift position, the target edge drop rate can be obtained.

(Example) First, a method of determining the shift position for each pass will be explained.

Assuming that the m-stand and subsequent stands of the n-stand tandem mill are rolled with flat rolls for shape control, the pattern of the shift position δS that minimizes the edge drop in this tandem mill is given by the following equation.

(1-1, 2,..., m-1) Q■ Wδ Si =o (ix-, 11+1
+ ++, n) θ In formula (13), IIIax (a, b) means taking the larger value of a and b. At this time, the edge drop change rate δHds after all-stand rolling is expressed by the following equation.

Therefore, for the target edge drop rate Ed, Ed, -
If Ed, ≧δEds (16), edge drop can be controlled by taper power crawl shift rolling up to m stands.

When the condition of formula 00 is satisfied, the pattern of shift position W6i that matches the target edge drop rate is determined by, for example, the following formula, considering that the change in shape in each pass is uniformly relaxed. can.

Wδ,! --2------------W6Si surface Next, the method according to the present invention was applied to a tandem mill consisting of a 3-stand, 6-high rolling mill as shown in FIGS. 3 and 4. Let me explain the case.

The work rolls of each stand were formed into a tapered shape starting at one point in the roll body (taper start point) and tapering toward the end of the roll body with a taper of 1/150 (gradient device/300). First, the edge drop change coefficients αl, βL and the shape change coefficients ζ1, η, and then T
In order to determine i, ξ5, and ψi, the shift position Wδ as shown in FIG. 3 is varied in each stand,
Rolling was carried out according to the set pass schedule, and changes in edge drop, steepness, and occurrence of cranks were investigated at each stand. the result,
Relative shift position as shown in Fig. 5 (Wδ1-Wδt,
) and the edge drop change rate δEd, and the relative shift position (Wδi−Wδt, ) as shown in FIG.
and the steepness λ1, and the relative shift position (Wδ) as shown in FIG.

-Wδi-1) and the crack incidence rate Crl was obtained for each stand. Therefore, from Figure 5 (4)
α1 in the equation was determined from the slope of the straight line, and βe was determined for each stand from the value of the cutting edge. Also, from Figure 6 (7)
In the equation, ζ was determined from the slope of the straight line, and η was determined for each stand from the value of the cut edge. Furthermore, from Figure 7 (9
) was determined for each stand from the crack non-occurrence limit value.

Next, the maximum allowable steepness λm for each stand.

−±1% (i=1.2.3), 0ω was determined from the above-obtained G4, η, and Ti, and ξ and ψi were determined from the 00 formula. The results are shown in Table 1. Shown below.

Table 1 Also, in order to calculate the number of stands that perform roll shifting necessary to obtain the target edge drop, using the coefficients obtained as above, if the m-th stand and subsequent stands are flat roll rolling, The pattern of the shift position WδS that minimizes the edge drop after rolling of all stands is 03.
), from 0102, the maximum edge drop change rate δEds
was calculated from formula 09.

The results are shown in Table 2.

Table 2 Note) Wδ-0stdk means m in formula 03) (b).

Using this tandem mill, a rolling original plate having a thickness of 2.5 mm was rolled to a thickness of 0.5 m. The edge drop amount of the original sheet for rolling was 25 μm. Therefore, the edge drop rate Ed before rolling is, and the edge drop change rate δEds after all stand rolling required to make the edge drop rate Ed3 O after 3 bus rolling is δEds≦Eds −Ed, −−0, 01, it can be seen from Table 2 that roll shift rolling of taper power crawl is necessary at least up to the second pass. Therefore, using equation 07), the shift position where Ed, -0 can be determined was determined as shown below.

Wδ1=-33n+IIWδz--1111us W
δ3-+0mm FIG. 8 shows changes in each pass of the edge drop IED when rolled in this manner.

As is clear from the figure, edge drop is well controlled in the rolling according to the present invention.

Furthermore, for rolled Kawahara plate with an edge drop amount of 30 μm, Wδ, =, 35mm Wδz = -12n + a + W
Similarly, by changing the shift position such as δ, -+0 mm, it is not possible to obtain a good product without any cracks or cracks.

(Effect of the invention) or<1. According to this lever invention, it is possible to effectively reduce edge drop without damaging the shape, and it is also possible to specify the stand where taper power crawl shift rolling is to be performed, so there is no interference with shape control and thickness distribution deviation can be reduced. A cold-rolled plate with a very small size and good shape can be obtained.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram showing the shift position and relative shift position in taper power crawl shift rolling, Fig. 2 is a diagram showing the preferred relative shift position of each stand in a 3-stand tandem mill, and Fig. 3 is an explanatory diagram showing the shift position and relative shift position in taper power crawl shift rolling. Figure 4 is a front view of the rolling mill used in carrying out the invention; Figure 4 is a side view of the tandem mill used in carrying out the invention; Figures 5 (a), ■) and (C) are the first pass,
Graphs showing the relationship between the relative shift position (Wδ. -Wδ, -I) and the edge drop change rate δEdi in the second and third passes, Figures 6 (a), (b), and (C) are respectively , the relative shift position (Wδ
. Figures 7 (a), (b), and (C) are graphs showing the relationship between -Wδ, -I) and 2, and steepness λ, respectively.
Relative shift position (W
FIG. 8 is a graph showing the relationship between δE-WδM-3) and crack occurrence rate Cri, and FIG. 8 shows the edge drop amount ED of each pass when taper power crawl shift rolling according to the present invention is performed
It is a graph showing changes in i. 1... Rolled material 2... Taper power crawl 3... Intermediate roll 4... Backup roll Patent applicant Kawasaki Steel Corporation Fig. 1 Fig. 2 tYλNO1 Fig. 3 Fig. 4 Fig. 5 (a ) (b) Wδt (mm)
WS2-Wδl (mm) (
C) WSs-Wδz (mm) (rI('l)

Claims (1)

[Scope of Claims] 1. In a tandem mill in which at least two rolling stands are provided with a work roll whose one end of the roll cylinder is tapered toward the end of the cylinder and which is movable in the axial direction of the rolls. , when performing cold rolling with the taper start point of the work roll set inside the edge of the plate to be rolled, the displacement of the set position of the work roll taper start point with respect to the plate end in each of the rolling stands. A cold rolling method characterized by controlling edge drop by adjusting the amount. 2. Using the edge drop amount of the original plate for rolling as a known amount, and using the edge drop change coefficient of each rolling stand determined by the displacement amount of the set position of the work roll taper starting point with the plate end in each rolling stand as a reference, 2. The cold rolling method according to claim 1, further comprising setting the taper starting point of the work roll in each rolling stand.