JPH11277117A - Method for preventing roll mark in multi-stage rolling mill - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent generation of roll marks by providing a gap between a lower work roll and a lower intermediate roll before upper and lower work rolls are tightened after a thin steel strip is passed, and spraying a rolling oil from the gap to clean the lower work roll and the lower intermediate roll. SOLUTION: A thin steel strip S is rolled by a multiple rolling mill provided with at least two first-stage lower intermediate rolls 2a, 2b to support lower work rolls 1a, 1b. After the thin steel strip S is passed, a gap is provided between the lower work roll 1b and the lower intermediate roll 2b before the upper and lower work rolls 1a and 1b are tightened. A rolling oil is sprayed from a header 4b toward the gap to clean the lower work roll 1b and the lower intermediate roll 2b. Foreign matters which are dropped while the thin steel strip S is passed and held between the lower work roll 1b and the lower intermediate roll 2b are washed away with the rolling oil.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for preventing the occurrence of roll defects in a multi-stage rolling mill having one or more work rolls and an intermediate roll supporting the work rolls.

[0002]

2. Description of the Related Art Thin steel strips such as cold rolled steel sheets are required to have high strength and thin gauges from the viewpoint of reducing the weight and cost of products. In order to respond to such a demand, a thin steel strip is rolled using a multi-high rolling mill having one or more intermediate rolls supporting a work roll.

When a thin steel strip is rolled by a multi-stage rolling mill, foreign matter is caught between a work roll and an intermediate roll, so that the work roll is dented. As a result, as shown in FIG. A very convex roll flaw occurs. Once the work roll is recessed, this recess will not be restored,
Roll flaws occur at the work roll circumference pitch over the entire length of the thin steel strip. When a roll flaw occurs, it becomes a scrap instead of a product, resulting in a large decrease in yield. Therefore, measures for preventing roll flaws have been conventionally required.

[0004] In recent years, the demand for higher quality of the surface of a thin steel strip has become stronger, so that even a small roll defect may not be a product. Therefore, the necessity of a countermeasure that can prevent the occurrence of roll flaws has been further increased.

Japanese Patent Application Laid-Open No. 61-108411 discloses that the hardness of an intermediate roll is made softer than the hardness of a work roll by a certain degree or more, thereby preventing the surface of the work roll from being scratched and preventing the occurrence of roll scratches. A method has been proposed.

[0006]

Problems to be Solved by the Invention JP-A-61-1084
In the method proposed in JP-A-11, the intermediate roll is soft, so that the intermediate roll is likely to be rough. Therefore, it is considered that the number of times of grinding of the intermediate roll increases and the intermediate roll basic unit increases, which may increase the cost of the roll and also complicate the roll operation.

An object of the present invention is to provide a method capable of easily preventing roll flaws without the above-mentioned problems of an increase in roll cost and complexity of roll operation.

[0008]

Means for Solving the Problems The present inventors have conducted an investigation on the tendency of roll defects to occur on a thin steel strip in a multi-high rolling mill, and have found the following.

[0009] Since the roll flaw is generated after the foreign matter is caught, the thin steel strip is inspected in the longitudinal direction of the rolling to find the starting point of the roll flaw, and the foreign matter is caught at any position in the longitudinal direction of the rolling. You can investigate FIG. 1 shows the result of investigation on the starting point of the roll flaw in the rolling longitudinal direction of the thin steel strip. From the results of this investigation, it was found that the occurrence of roll flaws due to foreign matter being caught in the course of steady rolling was extremely small, and that almost all roll flaws were generated due to foreign matter being caught at the same time as the start of rolling. Further, as shown in FIG. 2, it was also found that the occurrence of roll flaws was predominantly on the lower surface of the thin steel strip.

[0010] From these results, the roll flaws generated in the multi-stage rolling mill are due to the foreign matter caught between the lower work roll and the lower intermediate roll at the same time as the start of the rolling. It was thought that there was a problem with the work method. Therefore, as a result of reexamination of the working method before the start of rolling, a cheap and simple method that can prevent foreign matter from being caught between the lower work roll and the lower intermediate roll at the start of rolling was found.

The present invention is based on this finding, and the gist of the present invention for solving the above problems is as follows.

In the first invention, when a thin steel strip is rolled in a multi-stage rolling mill having one or more work rolls and an intermediate roll for supporting the work rolls, the upper and lower work rolls are released by tightening. After passing through the thin steel strip, before tightening the upper and lower work rolls, a gap is once created between the lower work roll and the lower intermediate roll, and rolling oil is sprayed on the gap to separate the lower work roll and the lower intermediate roll. This is a method for preventing roll flaws in a multi-high rolling mill, which comprises removing foreign substances by washing.

According to a second invention, in the first invention, the multi-stage rolling mill is a multi-stage rolling mill provided with at least two lower intermediate rolls of a first stage supporting a lower work roll. This is a method for preventing roll flaws.

Hereinafter, the roll flaw prevention effect of the present invention will be described in comparison with the roll flaw generation mechanism of the prior art.

First, a conventional working method before starting rolling in a multi-stage rolling mill will be described with reference to FIG.
The thin steel strip S is passed through with the gap between the upper and lower work rolls 1a and 1b opened, and wound around a tension reel (not shown).
Tighten the gap between b and start rolling.

During the sheet passing, the thin steel strip S comes into contact with each part in the rolling mill, so that the foreign matter 5 falls from the rolling mill stand and is caught between the lower work roll 1b and the lower intermediate roll 2b. In order to perform rolling, the gap between the upper and lower work rolls 1a and 1b is tightened, and when the rolls are rotated, the foreign matter 5 is caught between the lower work roll 1b and the lower intermediate roll 2b simultaneously with the rotation of the rolls. Is dented and becomes a roll flaw. For this reason, roll flaws occur at the work roll circumferential pitch at the entire length of the rolled thin steel strip.

That is, the work roll is rotated at the same time as the start of rolling. At this time, unless foreign matter is caught between the lower work roll 1b and the lower intermediate roll 2b, no roll flaw is generated. However, the size of the foreign matter is several hundred microns to several millimeters, and it is difficult to completely prevent the foreign matter from being brought in or dropped. Therefore, in the conventional working method, there are many roll flaws generated from the start of rolling.

Next, the working method of the present invention in a multi-high rolling mill will be described with reference to FIG. In the present invention, after passing the thin steel strip S, the upper and lower work rolls 1a and 1b
Before tightening, as shown in FIG. 4, a gap is once formed between the lower work roll 1b and the lower intermediate roll 2b, and rolling oil is sprayed from the header 4b toward this gap, so that the lower work roll 1b is The roll 2b is washed. Even if foreign matter falls during passing of the thin steel strip S and is caught between the lower work roll 1b and the lower intermediate roll 2b, the foreign matter is washed away with the rolling oil. When foreign matter is caught in the acute angle gap formed by the peripheral surfaces of the lower work roll 1b and the lower intermediate roll 2b, simply spraying the rolling oil without providing a gap between the lower work roll 1b and the lower intermediate roll 2b ,
Although foreign matter cannot be completely removed, in the present invention, since a gap is provided between the lower work roll 1b and the lower intermediate roll 2b and the rolling oil is sprayed for cleaning, such foreign matter can be reliably removed.

[0019]

Embodiments of the present invention will be described with reference to FIG. FIG. 5 is a view showing an example of a general multi-stage rolling mill used for rolling a thin steel strip, in which an intermediate roll has one stage.

In FIG. 5, (a) shows the arrangement of rolls during rolling, and (b) shows the arrangement of rolls during cleaning.
1b is a work roll, 2a and 2b are intermediate rolls, 3a,
Reference numeral 3b denotes a backup roll, and two intermediate rolls 2a and 2b are arranged vertically. The upper intermediate roll 2a, the upper backup roll 3a, the lower intermediate roll 2b, and the lower backup roll 3b are each mounted on a housing of a rolling mill. Lower work roll 1b
Is mounted on the two lower intermediate rolls 2b without being attached to the housing. Also, headers 4a and 4b for supplying a coolant (rolling oil) before and after the upper and lower work rolls 1a and 1b are provided. The headers 4a and 4b are provided with a swing mechanism (not shown) so that coolant can be sprayed on the work roll tool during rolling and can be rotated and retracted so as not to hinder the passing of the thin steel strip. .

The work rolls 1a and 1b are replaced by using a roll changing carriage. In order to replace the work rolls 1a and 1b, work roll supports 7a and 7b are set in a rolling mill.
And a work roll lift 8. The work roll supports 7a and 7b are capable of moving forward in the rolling mill exit side and retracting in the rolling mill entrance side, respectively.
b.

The work roll support 7a can move up and down by placing the upper work roll 1a at the forward position, and can move to the rolling mill side at the retreat position and stand by for a roll changing cart (not shown). Are arranged so that the work rolls 1a placed on each other can be transferred.

The work roll lift 8 is a lower intermediate roll 2b.
The lower work roll 1b placed on the upper lower work roll 1b is lifted or lowered, and the lower work roll 1b is placed on the lower intermediate roll 2b.
It is arranged so that it can be placed on top. Further, the work roll support 7b is arranged so that the lower work roll 1b placed on the work roll lift 8 can be transferred between the work roll lift 8 at the forward position and moved to the rolling mill side at the retreat position to stand by. The work rolls 1b placed on each other can be delivered to and from the existing roll changing cart.

The operation before the start of the rolling of the thin steel strip S in the above-mentioned rolling mill is as follows. First, the tightening of the upper and lower work rolls 1a and 1b is released. That is, the upper backup roll 3a and the upper intermediate roll 2a rise integrally with the housing, and the upper work roll 1a is supported by the work roll support 7a and rises above the lifting pass line. The lower work roll 1b descends integrally with the lower intermediate roll 2b and the lower backup roll 3b. Further, using a swing mechanism, the header 4a,
4b is retracted to a position where it does not hinder the passage of the thin steel strip. At this time, the blowing position of the header 4b is adjusted so that the coolant is blown between the lower work roll 1b and the lower intermediate roll 2b. Next, the thin steel strip S is passed through a gap formed between the upper work roll 1a and the lower work roll 1b, and wound around a tension reel (not shown).

Next, the neck portion of the lower work roll 1b placed on the lower intermediate roll 2b is supported by a work roll lift 8, and the lower work roll 1b is lifted. Then, coolant is sprayed from the header 4b toward the gap between the lower work roll 1b and the lower intermediate roll 2b to wash and remove foreign matter.

Next, the work roll lift 8 is lowered, and the lower work roll 1b is placed again on the lower intermediate roll 2b (at the position indicated by the two-dot chain line in FIG. 5B). Intermediate roll 2a, upper work roll 1
a, lower backup roll 3b, lower intermediate roll 2
b, raise the lower work roll 1b, tighten the upper and lower work rolls 1a and 1b, and start a predetermined rolling operation.

Even if foreign matter falls between the lower work roll 1b and the lower intermediate roll 2b during passing of the thin steel strip S, the foreign matter can be reliably removed by washing with a coolant.
Roll flaws generated from the start of rolling can be prevented.

The work roll lift 8 for providing a gap between the lower work roll 1b and the lower intermediate roll 2b and the header 4b for spraying a coolant used for cleaning are both existing ones, so that no special equipment modification is required. ,
Further, unlike the prior art, there is no problem of an increase in roll cost and complexity of roll operation, and roll flaws can be prevented by an inexpensive and simple method.

[0029]

EXAMPLE In the rolling mill shown in FIG. 5, the work roll lift is used to release the upper and lower work rolls, and after passing the thin steel strip through the rolling mill, the upper and lower work rolls are tightened and rolled. When rolling after passing through without opening the gap between the lower work roll and the lower intermediate roll (conventional example), cleaning by spraying coolant (rolling oil) without opening the gap between the lower work roll and the lower intermediate roll Rolling after the rolling (Comparative Example), and rolling after cleaning by spraying a coolant with a 10 mm gap opened by opening the lower work roll and the lower intermediate roll (Example of the present invention) The condition of roll flaws generated from the start was investigated. FIG. 6 shows the results of the investigation.

In the case of the comparative example in which the gap between the lower work roll and the lower intermediate roll is not opened before the start of rolling, the comparative example is slightly improved as compared with the conventional example, but the roll flaw is completely eliminated. Has not been reached.
In the case of the present invention in which a gap was provided between the lower work roll and the lower intermediate roll, washed with a coolant, and then rolled, there were no roll flaws due to foreign matter biting before rolling.

[0031]

As described above, according to the present invention,
No equipment remodeling is required, roll flaws can be significantly reduced using the current work roll and intermediate roll, and the yield can be improved by an inexpensive and simple method.

[Brief description of the drawings]

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a diagram showing the occurrence time of roll flaws in a thin steel strip in a conventional technique.

FIG. 2 is a view showing the tendency of roll flaws on a front and back surface of a thin steel strip to occur in a conventional technique.

FIG. 3 is a view for explaining a roll flaw generation mechanism according to the related art.

FIG. 4 is a view for explaining a mechanism for preventing occurrence of roll flaws in the present invention.

FIG. 5 is a diagram showing a multi-stage rolling mill used for describing the embodiment of the present invention.

FIG. 6 is a view showing a roll flaw reducing effect of the present invention.

FIG. 7 is a view showing roll flaws generated in a thin steel strip.

[Explanation of symbols]

 1a, 1b Work roll 2a, 2b Intermediate roll 3a, 3b Backup roll 4a, 4b Header 5 Foreign matter 7a, 7b Work roll support 8 Work roll lift S Thin steel strip

Claims (2)

[Claims] In rolling a thin steel strip in a multi-stage rolling mill having at least one work roll and an intermediate roll supporting the work roll, tightening of upper and lower work rolls is released to allow the multi-stage rolling mill to After passing the band, before tightening the upper and lower work rolls, once a gap between the lower work roll and the lower intermediate roll, wash the lower work roll and the lower intermediate roll by spraying rolling oil on the gap A method for preventing roll flaws in a multi-stage rolling mill, comprising removing foreign matter. 2. The multi-stage rolling mill according to claim 1, wherein the multi-stage rolling mill is a multi-stage rolling mill including at least two lower intermediate rolls of a first stage supporting a lower work roll. Prevention method.