JPH04251602A - Hot rolling method - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot rolling method for thin steel sheets, and more particularly to a hot rolling method suitable for preventing narrowing of the tail end of a rolled material in a finishing tandem rolling mill.

0002

[Prior Art] When rolling thin steel plates using a hot tandem rolling mill, the material to be rolled meanderes significantly when it passes through the end of each stand, collides with the side guide, folds double, and then bites into the next stand. , which often causes scratches on the work roll. When such so-called throttling occurs, it becomes necessary to inspect and maintain the work roll, or to replace the work roll, forcing the line to stop, resulting in a reduction in operating efficiency. Furthermore, if rolling continues without detecting work roll flaws or with insufficient care of work roll flaws, a large number of defective products with surface flaws will be produced.

Various proposals have been made in the past as methods for suppressing the meandering of a rolled material, which is a direct cause of reduction, but they can be roughly divided into two types.

The first proposal, typified by Japanese Patent Publication No. 59-37682, focuses on the fact that the greater the rolling reduction in the rolling mill, the more meandering occurs. This is intended to prevent meandering by widening the roll gap and reducing the rolling reduction ratio when the roll ends.

The second proposal is a method of suppressing meandering by detecting the amount of meandering of the material to be rolled in the rolling stand and adjusting the left and right roll gap etc. in the direction of suppressing meandering. There are 1980-191510, etc.

[0006]

[Problems to be Solved by the Invention] According to the first proposed method, the effect of preventing drawing can be reliably obtained, but since the roll gap is widened at the tail end of the material to be rolled, There is a problem that the product board thickness of the parts is out of tolerance. Conventionally, a large portion of the tail end was often cut off due to flaws or material defects, so even if the thickness of the plate fell outside the tolerance, it did not affect the yield, but in recent years, due to technological advances, countermeasures have been taken to prevent flaws and material defects. The amount of cut-offs tends to decrease year by year.
Even at the tail end, deviation from the tolerance of plate thickness is not appropriate as it causes a decrease in yield.

According to the second proposed method, it is theoretically possible to suppress meandering without causing the plate thickness at the tail end to deviate from the tolerance. However, this is so-called feedback control in which control is performed after detecting the amount of meandering, and there are limits to control responsiveness and stability, making it difficult to completely prevent throttling.

SUMMARY OF THE INVENTION An object of the present invention is to prevent meandering of a rolled material and reliably prevent the occurrence of drawing, without causing deviations in plate thickness tolerance.

[0009]

[Means for Solving the Problems] The present invention provides a hot rolling method in which finish rolling is carried out using a tandem rolling mill having a plurality of stands, in which the plate thickness of the tail end in the longitudinal direction of a rolled material is thinned in advance, and then finishing is carried out. Rolling is carried out, and the rolling reduction ratio for at least the tail end portion of the downstream stand during finish rolling is made smaller than the rolling reduction ratio for the steady portion.

0010

According to the present invention, the plate thickness of the tail end in the longitudinal direction of the material to be rolled is thinned before finishing rolling is performed, and then finishing rolling is performed. For this reason, it is possible to finish the thickness of the product plate within the tolerance up to the tail end while reducing the rolling reduction rate for the part where there is no rear tension at the tail end of the plate, which tends to meander, than that of the steady part. By preventing meandering when coming out, it is possible to reliably prevent the occurrence of throttling.

[0011] Note that the reduction rate of the rolling reduction rate at each stand with respect to the tail end of the material to be rolled is such that the thinner the sheet thickness, the more likely the tail end will meander, so the rolling reduction ratio will be smaller as the stand becomes later. It is preferable to set it to .

0012

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an example of the equipment configuration for carrying out the present invention.

A rough rolling mill row 11 that rolls the slab 1 into a sheet bar 2, an induction heating device 12 that heats the low temperature part of the sheet bar 2, and a finishing mill row 13 that rolls the sheet bar 2 into a product 3. It consists of

The last stand of the rough rolling mill row 11 and all the stands of the finishing rolling mill row 13 are equipped with a hydraulic rolling device 14 for controlling the roll gap between the upper and lower work rolls at high speed;
A load cell 15 for detecting the rolling load is also installed, making it possible to arbitrarily control the plate thickness at the exit side of each stand.

FIG. 2 is an example of the plate thickness schedule at the exit side of each stand when the present invention is implemented using the example of the equipment configuration shown in FIG.

The sheet bar 2 is rolled on the exit side of the final pass of the rough rolling mill so that the plate thickness at the tail end in the longitudinal direction becomes thinner, and then finish rolled.

[0017] Then, the final stand of the finishing rolling mill (F7)
The target exit plate thickness for the stand is given a constant value over the entire length, but the target exit plate thickness for other stands is determined from the point 2m before the end of the seat bar (seat bar length search). The plate thickness is set to gradually become thinner toward the tail end. By implementing gauge meter-type plate thickness control at each stand based on such plate thickness target values, the rolling reduction rate for the tail end of the downstream stand of the finishing rolling mill row can be compared to the rolling reduction rate for the steady part. Can be made smaller.

In the example shown in FIG. 2, in the F5 stand, the rolling reduction ratio in the steady section is 0.30, while at the tailmost end it is 0.29, and the reduction ratio in the F6 stand is 0.30.
0.26 on stand is 0.24, 0 on F7 stand
．． 14 has decreased to 0.08.

As described above, by keeping the rolling reduction ratio low at least in the downstream stand of the finishing rolling mill row, it is possible to prevent the material to be rolled from meandering and to prevent the occurrence of narrowing.

[0020] In the present invention, since the plate thickness at the tail end of the sheet bar is made thinner, there is a risk that a temperature drop may occur, resulting in poor material quality, or defective plate thickness due to increased deformation resistance during finish rolling. However, this problem can be solved by providing an induction heating device to heat the temperature drop section as in the example of the equipment configuration shown in FIG.

Furthermore, although the sheet bar is manufactured by a row of rough rolling mills in FIG. 1, the present invention does not limit the sheet bar manufacturing method; for example, the sheet bar can be manufactured by continuous casting equipment. You can also do it.

[0022] By using the hot rolling method of the present invention, the occurrence rate of squeezing can be significantly reduced, productivity is improved by improving the operating rate, and product surface defects caused by work roll flaws are significantly reduced. becomes possible.

In addition, in the case of a tandem rolling mill, when the material to be rolled passes through the upstream stand, the backward tension is lost, resulting in the problem that the thickness of the material to be rolled becomes excessively large on the exit side of the rolling mill. However, in the present invention, since the plate thickness at the tail end of the seat bar is thinned in advance, it is possible to prevent the plate thickness from becoming too thick as described above, and there is also the effect of improving the plate thickness accuracy at the tail end of the product.

[0024] In the present invention, the rolling reduction ratio of not only the downstream stand but also the tail end portion of all the stands in finish rolling may be made smaller than the rolling reduction ratio of the steady portion.

[0025]

As described above, according to the present invention, it is possible to prevent meandering of the rolled material and reliably prevent the occurrence of drawing, without causing deviations in plate thickness tolerance.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an example of the equipment configuration for implementing the present invention.

FIG. 2 is an explanatory diagram showing an example of a plate thickness schedule on the outlet side of each stand in the present invention.

[Explanation of symbols]

1 Slab 2 Seat bar 3. Product 11 Rough rolling mill row 12 Induction heating device 13 Finishing rolling mill row

Claims (1)

[Claims] Claim 1: In a hot rolling method in which finish rolling is performed using a tandem rolling mill having a plurality of stands, the finish rolling is performed after the plate thickness of the tail end in the longitudinal direction of the material to be rolled is thinned in advance, and A hot rolling method characterized in that the rolling reduction ratio for at least the tail end portion of the downstream stand is made smaller than the rolling reduction ratio for the steady portion.