JPH10137817A - Tube end bending preventing device in sizing mill for seamless steel tube - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the cutting allowance of a tube end and to product a seamless steel tube with an excellent yield by providing a wear resistant layer on the guide surface coming into contact with the steel tube and moreover arranging so that the gap between a rolling roll and the guide becomes a specified value or below. SOLUTION: A sizing mill is composed of plural roll stands, and the guide 4 for preventing the bending of the seamless steel tube under rolling is provided between the final stand 1 and the stand 2 just before the final stand. In this guide 4, the gap between the roll and the guide is meant by (g) and the difference of the roll caliber surface and the guide inner peripheral surface is meant by (d). In order to roll without the tube being caught (g) is necessitated to be <=3mm. Further, the guide is arranged so that (d) becomes e.g. <=1.5mm at the maximum. Also, wear resistant metal containing Cr3 C2 powder (compounding ratio 50%) is thermally sprayed on the guide surface coming into contact with the tube.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for correcting a bent end of a pipe in a fixed rolling mill for a seamless steel pipe in a rolling line.

[0002]

2. Description of the Related Art In a hot final step of a seamless steel pipe, a fixed rolling mill having a plurality of stands is used to produce a predetermined outer diameter. The end is easily bent. Further, the seamless steel pipe is supplied to a standard rolling mill through a process such as continuous rolling or elongation rolling after the material is pierced and rolled, so that the pipe end has a surface perpendicular to the axis at a stage prior to the standard rolling mill. It usually does not have.

[0003] In addition to bending due to the difference in deformation during rolling, when a fixed form rolling mill is passed in such a state of poor shape, bending of the pipe end is promoted, which causes a reduction in yield. Since it is difficult to correct the bending of the pipe end even by a straightening machine in a subsequent process, it is necessary to reduce the bending amount of the pipe end in the rolling process in order to avoid a decrease in yield.

In view of such a problem, as a method of suppressing the bending of the pipe end of the steel pipe, a facility for disposing a ring-shaped guide between the rolls of the final stand of the fixed rolling mill and the preceding stand (see Japanese Utility Model Application Laid-Open No. 50803/1987). Gazette).
However, in this means, there is a problem that the wear at the pipe contact portion of the guide is severe, the bending correction effect is reduced by rolling of several hundreds of rolls, and that the tip of the pipe is liable to be caught by the guide, etc. There is a limit to continuous use for a large number of rolled materials.

[0005]

Accordingly, in the present invention, a ring-shaped guide provided between the rolls of the final stand and the preceding stand of the fixed rolling mill is designed to reduce wear and prevent the pipe from being caught. By setting an appropriate clearance between the roll and the roll, it is intended to continuously and stably prevent the occurrence of bending at the pipe end even in a large amount of rolling.

[0006]

SUMMARY OF THE INVENTION According to the present invention, there is provided an apparatus for preventing tube end bending, in which a ring-shaped guide is arranged between the rolls of a final stand and a preceding stand of a standard rolling mill for steel pipes, and a conventional guide is provided. Is characterized in that a material made of alloy tool steel such as SKD is used as a guide made of a material having high abrasion resistance on the pipe contact surface, and the gap between the roll and the guide is set to 3 mm or less.

As a method of manufacturing a guide made of a material having high wear resistance, there is a technique of coating a target material on a surface of a base material such as an alloy tool steel. The coating of the guide is made of a material with excellent wear resistance consisting of carbide powder and alloy powder and is applied by thermal spraying technology such as plasma arc welding.However, carbide is applied from the viewpoint of wear resistance and seizure resistance , Cr ₃ C ₂ or NbC,
The compounding ratio is suitably from 20 to 70%.

In the present invention, as an appropriate guide arrangement,
The reason for setting the gap between the roll and the guide to be within 3 mm is that if the gap between the roll and the guide is too large, more than 3 mm, the pipe being rolled is caught by the guide and causes trouble. The inner diameter of the guide may be equal to or larger than the caliber diameter of the rolling roll. However, in order to improve the effect of correcting the tube end bending, it is desirable that the inner diameter of the guide be as close as possible to the caliber diameter of the rolling roll.

[0009]

FIG. 1 is a conceptual diagram for applying the present invention to a standard rolling mill. The standard rolling mill is composed of a plurality of roll stands, and a guide 4 for preventing bending of the pipe 3 during rolling is installed between the final stand 1 and the preceding stand 2. The guide 4 has a structure as shown in FIG. The gap between the roll and the guide is indicated by g, and the difference between the roll caliber surface and the inner peripheral surface of the guide is indicated by d. Reference numeral 5 denotes a coating material which is to be in contact with the pipe on the inner peripheral surface of the guide 4. Table 1 shows the relationship between the maximum value of the gap g between the roll and the guide and the catch of the pipe.

[0010]

[Table 1]

[0011] Thus, in order to roll the pipe without being caught, it is necessary to set g to 3 mm or less. In addition,
d was set to be within 1.5 mm at the maximum. Abrasion-resistant metal containing Cr ₃ C ₂ powder (mixing ratio: 50%) is thermally sprayed on the pipe contact surface 5 of the guide by powder plasma overlay welding.

When the seamless steel pipe was rolled with this guide attached, there was no trouble due to the pipe being caught, and the wear of the guide after 2,000 rolls was about 0.1 mm. Even for the above number of rolls, it was possible to stably suppress the bending of the pipe end without replacing the guide. On the other hand, in the conventional guide, 10
The rolling of the 00 rolls resulted in a wear of about 3.0 mm, and the effect of suppressing the bending of the pipe end was small. FIG. 3 shows the effect of straightening the pipe end when the guide of the present invention is installed. The maximum value of the amount of bending at the end of the pipe is 0.3 when the conventional guide is not installed and when the present invention is implemented.

[0013]

As described above, according to the present invention, pipe end bending of a seamless steel pipe can be effectively and continuously suppressed for a long period of time in a fixed rolling mill, and the cutting end of the pipe end can be reduced. Therefore, seamless steel pipes can be produced with good yield.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram showing a relationship between a standard rolling mill and a guide for applying the present invention.

FIG. 2 is an enlarged structural view of a guide embodying the present invention.

FIG. 3 is a diagram illustrating a comparison between the present invention and a conventional device in terms of a straightening effect.

[Explanation of symbols]

 1 Final Stand 2 Final Front Stand 3 Seamless Steel Pipe 4 Guide 5 Coating Material g Clearance between Roll and Guide d Difference between Roll Caliber Surface and Guide Inner Surface

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Shigeo Kusuhara 1-1-1, Hibata-cho, Tobata-ku, Kitakyushu-shi, Fukuoka New Nippon Steel Corporation Yawata Works

Claims (3)

[Claims] 1. A pipe end bending prevention device in a seamless rolling mill for a seamless steel pipe having a plurality of rolling stands and a ring-shaped guide disposed between adjacent stands, wherein a wear-resistant layer is provided on a steel pipe contact surface of the guide. A pipe end bending prevention device in a seamless rolling mill for seamless steel pipes, wherein a gap between the rolling roll and the guide is set to 3 mm or less. 2. The apparatus according to claim 1, wherein the ring-shaped guide is disposed between the final rolling stand and the immediately preceding rolling stand. 3. The apparatus according to claim 1, wherein the wear-resistant layer is a thermal sprayed layer comprising a carbide powder and an alloy powder.