JPS6264406A - Rolling method for strip with tandem type rolling mill - Google Patents

Abstract

PURPOSE:To decrease edge drops at a low cost in the stage of rolling a strip for which the requirement for decreasing the edge drops is high by preliminarily bringing both side ends of a strip group to the specific position of a thermal profile of rolls generated in rolling. CONSTITUTION:>=1 pieces of the strips having the width slightly smaller than the width of a strip group are preliminarily rolled prior to rolling of said strip group. Work rolls are then thermally expanded and the thermal profile thereof is as shown in the figure. More specifically, the quantity of expansion is approximately uniform in the central part of a roll body and decreases at a steep grade in the neighborhood of both ends of the rolled strip. The quantity of expansion is small on the end sides of the roll body, thus the uniform distribution is exhibited. Both side ends of the above-mentioned strip group are brought to the position where the steepest grade at approximately the center of the width DELTAW in the steepest part of the grade is shown, then the strip group is rolled.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industry) 2-1'11 The present invention relates to a strip rolling method in a tandem rolling mill, and particularly to a method for reducing edge drop.

(Prior Art) (2) In lip rolling, (1) The thickness distribution in the width direction of the sheet after rolling tends to decrease rapidly toward the side edges, especially in the vicinity of both side edges. This is called an edge drop, and when expressed as the difference in plate thickness between a position 75 mm from the side edge and a position 25 mm111 from the side edge, for example, in a high-strength hot rolled steel strip, this edge drop can reach as much as 80 μm.

Since edge drops greatly affect the yield of strip material, various methods have been proposed to reduce edge drops. For example, depending on the width of the plate, rolling can be carried out using a taper roll that is ground into a trapezoid shape from a position slightly narrower than the width of the plate to the work roll @ i section, or one of the body ends may be ground into a tapered shape. There is a method in which upper and lower work rolls with tapered portions located on opposite sides are appropriately moved in opposite directions along the roll axis to position the tapered portions at both ends of the strip material for rolling.

(Problem to be Solved by the Invention) However, according to the former method, it is necessary to use different work rolls depending on the width of the strip, and when reducing the edge drop of a narrow strip, it is necessary to This has the drawback that the roll unit is extremely long and the taper depth at the end of the roll body is extremely deep, resulting in a high roll unit consumption. On the other hand, the latter method requires a device for moving the work roll in the axial direction, and has the disadvantage of requiring a high cost for equipment modification.

Furthermore, in such a strip rolling method, the shape of the tapered part of the work roll is either a straight line shape as shown in Figure 4 or at most a quadratic curve shape (from a circular arc) due to constraints on the grinding machine or the roll grinding time. ). However,
The filter plate thickness reduction curves at both ends of the strip where the mechanical/fuji drops have occurred are often μ-order curves ranging from the 8th to the 14th orders.

Therefore, due to the mismatch between the two curves, the cross-sectional profile of the strip located at the starting point of the work roll becomes concave, as shown in FIG. In addition, this plate cross-sectional profile is represented in FIG. 5 by a plate thickness deviation distribution in the plate width direction, where the plate thickness of the strip located at the center of the roll is taken as a standard. This concave shape becomes more obvious as the taper of the work roll is increased in order to reduce edge drop. Such a concave shape is not preferable because it causes poor flatness when the rolling section 1 is further performed in the next step rather than exhibiting the effect of reducing erran drop.

The present invention has been made in view of such problems, and it is possible to effectively reduce edge drops at low cost and without equipment modification when rolling strips with a particularly high demand for edge drop reduction using a tandem rolling mill. An object of the present invention is to provide a strip rolling method in a tandem rolling mill that enables the following steps.

(Means for Solving the Problems) In order to solve the above problems, the present invention provides that, before rolling a group of strips in which reduction of edge drop is strongly required,
After rolling at least one strip having a slightly narrower width than the strip group in advance, position both ends of the strip group at a position where the thermal profile of the roll produced by this rolling exhibits the steepest gradient. This is a type of plate that performs cutting and rolling.

That is, the present invention has 5. By rolling another strip in advance to thermally expand the work roll, and creating a thermal profile that has a steep slope from the vicinity of both ends of the rolled strip to the outside thereof, a tapered part due to thermal expansion is created in the work roll. The strip is rolled at step 17 so that both ends of the strip, where edge drop is strongly required, are located at the position with the steepest slope.

(Example) Next, one embodiment of the present invention will be described with reference to the drawings.

FIG. 2 shows the axial distribution (so-called thermal profile) of the amount of thermal expansion of the work roll diameter that occurs when the strip is rolled. This thermal profile is almost uniform in the center of the roll cylinder, and degrades with a steep gradient from near both ends of the rolled saw strip to the outside thereof.
On the other hand, on the roll body end side, the amount of expansion is small and shows a uniform distribution. The width ΔW of the steeply sloped portion near both ends of the strip in this surf full profile is:
Although it varies depending on the work roll diameter, I00mnr-:300 for roll diameters in the range of about 500mm to 800mm.
The difference is about mm. In addition, the ratio ΔWR/ΔWC of parts with steep gradients of this thermal profile existing in the rolled part and the non-rolled part outside it is approximately 2; 3, and the position showing the steepest gradient is approximately at the center of the ΔW part. It is.

Therefore, in the case of ΔW = 200 mm, for example, in order to roll both ends of the next strip to be rolled at the thermal profile portion with the steepest slope, it is necessary to Difference in plate width of I lip ΔB
ΔB≧2×(ΔW/2−2ΔW15)=40 mm. However, if ΔB becomes too large, ΔB will be located at both ends of the next strip to be rolled, in a part with a relatively gentle slope within the range of ΔW, or even in a part outside the range of ΔW. is preferably kept within the range of the following formula.

ΔL3≦2×((ΔW/2+Δ~■15)=2Δ'vV
/ 5) = 120mm ΔW/2 on the roll center side within the ΔW range shown in Figure 2
The thermal profile in the range of , that is, the decreasing curve of the amount of roll thermal expansion is represented by a 6th to 10th order curve. Therefore, when rolling by the method according to the present invention, the roll profile of the portions located at both ends of the strip is represented by a high-order curve, so that the tapered portion is represented by a straight line or quadratic curve as in the conventional method. It is possible to correct the plate thickness reduction curve with higher accuracy than when rolling with a tapered roll having a tapered roll, and it is possible to reduce edge drop.

Figure 1 shows the construction of seven stands using the method according to the present invention.
Figure 6 shows the relationship between the rolling order, strip width, and edge drop when rolling is performed using a pot strip rolling mill with a pot strip mill, and Figure 6 shows the relationship between the rolling order, strip width, and edge drop according to the conventional method. show. The edge drop was determined as the difference in plate thickness between a position 751 m from both ends and a position 25 mm from both ends.

In Figure 1, Δ is 50 Kg/mm! Strip material, which is required to reduce edge dents in grade steel, [3 is 3
This is a strip material made of 0 Kg/mm' grade steel that precedes the rolling of A, and the width of B is 50 mm narrower than that of A.

Note that the diameter of the work roll of the finishing mill of each stand is in the range of 700 mm to 800 mm in all cases.

When applying the method according to the present invention, after rolling the preceding uB,
Although there is a tendency for the edge drop to increase slightly as the rolling number of A increases, the edge drop decreases by 4011 m to 50 μm compared to the conventional method. In addition, in the conventional method shown in FIG.
M' grade steel edge drop or A, i.e. 50Kg/mm
The reason why it is smaller than that of second class steel is that the rolling load of 30 Kg/mm2 class steel is lower than that of 50 Kg/mm2 class steel due to the difference in deformation resistance of these rolled materials.

Figure 3 shows 50Kg/rm2 rolled by the method according to the present invention.
An example of a plate cross-sectional profile for handling is shown. The plate cross-sectional profile shown in this figure is expressed by the plate thickness deviation distribution as in FIG. 5 above. In the figure, the cross-sectional profile of the plate shows a smooth profile with no concave shapes near both ends, and it is clear that this method of the present invention is effective in reducing edge drops.

In addition, in the above embodiment, the case of a hot tandem rolling mill was explained, but as is well known, a similar thermal profile occurs in a cold tandem rolling mill.
The method according to the present invention is applicable to cold tandem rolling mills.

(Effects of the Invention) As is clear from the above description, according to the present invention, the increase in roll consumption rate 51 can effectively reduce edge drops without any special equipment modification. Exists.

[Brief explanation of drawings]

Figure 1 is a diagram showing the relationship between the rolling order, sheet width, and its edge drop by the method according to the present invention, Figure 2 is a diagram showing the thermal profile of the roll, and Figure 3 is a diagram showing the relationship between the rolling order and the sheet width and its edge drop by the method according to the present invention. Figure 4 is a diagram showing the roll profile of a conventional tapered roll.
The figure shows the cross-sectional profile of a plate when the conventional method using tapered rolls is applied, and FIG. 6 is a diagram showing the relationship between the conventional rolling order, the plate width, and its edge drop. Patent Applicant Kobe Steel Co., Ltd. Agent Patent Attorney Aoyama Aoyama and 2 others No. 11! Rolling*? '8's Qlifl 1mm1 Fig. 6/+3-LA-bed

Claims (1)

[Claims] (1) Before rolling a strip group that requires a strong reduction in edge drop, roll at least one strip with a slightly narrower width than the strip group, and then roll thermal damage caused by this rolling. A method for rolling a strip in a tandem rolling mill, characterized in that rolling is performed by positioning both ends of the strip group at a position showing the steepest slope among the profiles.