JP2005046893A - Method for suppressing deviation in wall-thickness of seamless steel tube and guide for manufacturing seamless tube - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for suppressing deviation in the wall-thickness of a seamless steel tube which can produce a seamless steel tube having a more even, that is, less deviated wall-thickness in a tubular circumferential direction than a conventional one, and to provide a guide for manufacturing a seamless steel tube. <P>SOLUTION: A technique, wherein a heated round steel billet is passed through a tubular guide and led to a piercing mill, and rolled and pierced by pressing a shell-shaped plug against the front end of the billet, is improved. The outline of the improvement is as follows: the round steel billet is supplied to the piercing mill in a state that the outlet side position of the guide is set to be 250-300 mm apart from the position of the minimum roll-gap of the piercing mill while making the gap between the round steel billet and the guide to be 10-15 mm. Furthermore, a guide for manufacturing a seamless steel tube is also developed. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a seamless steel pipe unevenness suppressing method and a seamless steel pipe manufacturing guide, and more particularly, to a technique for reducing the uneven thickness of a seamless steel pipe as compared with the prior art and increasing the product yield during the manufacture.

  The seamless steel pipe is manufactured through a process as shown in FIG. 4, for example.

  First, a steel slab (also referred to as a round billet) 1 having a round cross section is used as a raw material, heated to a predetermined temperature (usually 1000 to 1200 ° C.) in a heating furnace 2, and then a tubular body called a guide (not shown) ) Is guided to a piercing and rolling machine called a piercer 3, and the plug 4 is rolled while being pressed with a bullet-shaped jig to make a base tube 5. Next, in the case of a product having a small diameter (for example, an outer diameter of 88.9 mmφ and a thickness of about 9.0 mm), the mandrel bar 7 is inserted into the base tube 5 by a rolling mill called a mandrel mill 6. After stretching, the tube is heated in the reheating furnace 8, and the tube diameter is reduced and the size is adjusted by a multi-stage rolling mill as a hot stretch reducer 9. On the other hand, when the product size is made a little larger (for example, an outer diameter of 323.8 mmφ and a wall thickness of about 12.7 mm), the element pipe 5 is an elongator via a separately provided tubular body (also not shown). After being led to a rolling mill of 10 and expanded there, it is stretched by a rolling mill of a plug mill 11, polished by a rolling mill of a reeler 12, heated in the reheating furnace 8 described above, and then in a multi-stage rolling mill of sizer 14. Reduce the tube diameter or adjust the size.

  By the way, seamless steel pipes manufactured through such processes are used for oil well pipes, line pipes, and the like. Recently, demands for improvement of quality characteristics and reduction of product costs have become more severe than before.

  One of the quality characteristics is the uniformity of the wall thickness in the pipe cross section. That is, the wall thickness is required to be uniform in the circumferential direction of the tube. Therefore, the cause was investigated so as to hinder the uniformity of the wall thickness. As one of the causes, the rear end of the material rolled by the piercer is separated from the roll, so that the position is restrained until it is pinched by the roll. It was thought that there was a big swing. And in order to suppress the touch of a rear-end part, the said cylindrical body came to be provided as a guide which guides a raw material to a roll. In addition, the closer the tip (exit side) of this cylindrical body is to the roll, the smaller the back end deflection of the material should be. However, the space in the vicinity of the roll is very narrow with a support member (referred to as a guide shoe) that suppresses the lateral (or vertical) swing of the material being rolled, and when the tip of the cylindrical body is brought closer to the roll, the cylindrical body It comes into contact with the roll itself, and the rolling operation cannot be performed. As a countermeasure, a guide has been proposed in which a notch is provided at the tip of a cylindrical body (see Patent Document 1).

However, since the guide described in Patent Document 1 is mainly intended to avoid contact between the guide and the roll, it does not pay much attention to suppressing the shake of the rear end portion of the material. In other words, no information is disclosed about how close the tip of the guide can be to the roll to ensure satisfactory thickness uniformity, and the technology is incomplete and further research is required. In addition, if the thickness distribution can be improved further than before, the product yield is improved as compared with the conventional product, and as a result, the manufacturing cost can be expected to be reduced.
Utility Model Registration Gazette No. 2580519

  In view of such circumstances, the present invention provides a seamless steel pipe uneven thickness suppressing method and a seamless steel pipe manufacturing guide that can manufacture a seamless steel pipe having a uniform wall thickness in the circumferential direction of the pipe, that is, less uneven thickness. The purpose is to provide.

  The inventor has intensively studied to achieve the above object, and the results have been embodied in the present invention.

That is, in the present invention, a heated round steel slab is passed through a guide which is a tubular body and guided to a piercer rolling mill, and rolled and punched while pressing a bullet-shaped plug on the tip of the round steel slab. When making a tube,
The slab exit side position of the guide is 250 to 300 mm from the minimum position of the roll gap of the piercer rolling mill, and the gap between the round steel slab and the guide is 10 to 15 mm. A method for suppressing the uneven thickness of a seamless steel pipe, characterized in that a slab is supplied to a piercer mill.

Further, the present invention is a guide composed of a tubular body that guides a heated round steel slab to a piercer mill, or guides a raw pipe punched by the piercer mill to an elongator,
A guide for producing a seamless steel pipe, characterized in that a sleeve having a claw-like tip is provided on the side from which the round steel slab or the raw pipe comes out. In this case, it is preferable that the sleeve having the claw-shaped tip is fixed to the guide with a bolt / nut or a pin. When the sleeve is worn, replace the sleeve with a new one.

  ADVANTAGE OF THE INVENTION According to this invention, the shake | fluctuation and impact at the time of a round steel slab or a base pipe slipping out from a seamless steel pipe manufacturing guide come to be relieved more conventionally. As a result, a seamless steel pipe having a uniform wall thickness in the pipe circumferential direction, that is, having less uneven thickness can be stably manufactured, and the product yield is improved, and the manufacturing cost is reduced.

  Embodiments of the present invention will be described below based on the circumstances leading to the invention.

  First, the inventor decided to suppress the tail end of the round steel slab, which had slipped out of the tubular guide, during the piercing with the piercer, and to stabilize the shaft.

  Then, in the manufacturing process shown in FIG. 4, in the line on the plug mill 11 side, drilling using an existing guide (not shown) is made of the round steel slab 1 having an outer diameter of 207 mmφ and a length of 1560 mm. While performing, the uneven thickness state of the obtained pipe | tube 5 was investigated. In addition, the slab exit side position of the existing guide (position where the round steel slab is pulled out) is set at a position 560 mm away from the position where the roll gap of the piercer becomes the minimum, and the guide and the inside thereof are set. There is a gap (clearance) of 30 mm between the round steel slab passing through. The blank obtained by this operation had an outer diameter of 225 mmφ, a thickness of 18.5 mm, and a length of 4150 mm. Then, the thickness is measured at 16 locations in the circumferential direction of the pipe every 100 mm over the rear end of 1000 mm in the length direction of the raw pipe, and the thickness deviation rate (%) at each position is calculated by the following equation (1). did.

Unevenness ratio = ((maximum value−minimum value) / 16 average value) × 100 (1)
As a result, the thickness deviation rate of the raw tube showed a tendency to increase as it approached the tail end, and it was not constant and varied in the longitudinal direction of the tube. That is, as the inventor expected, it was confirmed that uneven thickness had already occurred at the stage of drilling the round steel slab.

  Therefore, in order to prevent the occurrence of uneven thickness at this stage, the inventor made as much as possible that the tail end of the round steel slab slid out from the tubular guide called the inlet cannon sway during the piercing in the piercer 3. Judging that it was necessary to suppress, we examined specific means.

  And when the slab exit side position of the guide is made closer to the piercer side, the length of the swinging part becomes shorter than before, the shaft of the round steel slab becomes stable, and the inner diameter and passage of the guide If the gap between the round steel slab and the outer diameter of the round steel slab is reduced, the impact at the time of slipping will be reduced more than before, contributing to the stability of the shaft. This completes the present invention.

  Therefore, in the present invention, as shown in FIG. 1, the slab exit side position 16 of the guide 15 is made closer to the roll 17 of the piercer rolling mill 3 than ever before. That is, the distance (L) from the minimum position 18 of the roll gap is determined to be 250 to 300 mm. If it exceeds 300 mm, the effect of suppressing touching cannot be exhibited, and it cannot be made less than 250 mm due to the space problem described later. Moreover, in this invention, the clearance gap 13 between the said round steel slab and this guide 15 shall be 10-15 mm, and the round steel slab 1 is supplied to the piercer rolling mill 3. FIG. This is because if the gap 13 is less than 10 mm, the round steel slab 1 does not proceed smoothly, and if it exceeds 15 mm, the impact cannot be mitigated when the steel slab 1 is pulled out.

  Next, the structure of the guide 15 for implementing the above-described present invention was examined. However, between the rolls 17 arranged in a pair on the upper and lower sides of the piercer mill 3 (rolling region), in addition to the round steel slab 1 to be rolled, there are guide shoes (symbol 22 in FIG. 2 described later) that surround and support it. There is no space to extend the length of the guide 15 while maintaining the cylindrical shape. Therefore, the inventor extends the length of the guide 15 as compared with the conventional case, as shown by a longitudinal section in FIG. 1 and a cut surface in FIGS. 2 (a) to 2 (c). It was decided to plan. In other words, the cylindrical wall was broken, and a member (sleeve) that finally became four claws 21 was inserted into the guide to stop the system. This is because even with such a structure, the round steel slab can be guided to the piercer.

The sleeve 19 shown in FIG. 1 has a claw 21 with a cross-sectional area as thin as about m ² , but this is an example, and the shape and size of the claw 21 can be changed within the space allowed. Also good. As shown in FIG. 1, the sleeve 19 can be attached to and fixed to the existing guide 15 by using a pin 20 or a structure in which a pressing plate is fastened with bolts and nuts. The material of the sleeve is not particularly limited, but general carbon steel is sufficient.

  Using a round steel slab 1 (steel type standard SCM435) having an outer diameter of 207 mmφ and a length of 1560 mm as a raw material, a seamless steel pipe was manufactured using the plug mill 11 side in the manufacturing process shown in FIG. At that time, in the piercing process in the Piercer rolling mill 3, the guide 15 according to the present invention and the conventional one were separately used and operated. The differences between the guides 15 are collectively shown in Table 1. The main operating conditions are a heating temperature of the round steel slab 1 of 1280 ° C. and a round steel slab rolling speed of 250 m / min in the piercer 3.

  As a result of this implementation, the thickness deviation rate in the vicinity of the tail end of the obtained raw pipe 5 (outer diameter 225 mmφ, wall thickness of about 18.5 mm) is obtained by the above equation (1) and evaluated, and an example is shown in FIG. Shown in From FIG. 3, it is clear that according to the present invention, the thickness deviation rate is remarkably improved as compared with the conventional case. Subsequently, the raw tube 5 was drawn and rolled with a mandrel mill 6 and drawn and rolled with a reducer 9 to obtain a product steel tube. However, the product acceptance rate (number of products accepted / number of products produced × 100) and yield (product weight / material weight × 100). ) Also improved by 5.0% compared to the conventional method.

It is a longitudinal cross-sectional view explaining the thickness control method of the seamless steel pipe which concerns on this invention. It is a figure explaining the front-end | tip of the sleeve provided in the guide for seamless steel pipe manufacture which concerns on this invention, (a) is CC arrow cross section of FIG. 1, (b) is AA arrow cross section, and (c ) Is a cross section taken along the line B-B. It is the figure evaluated by the thickness deviation rate of the raw tube which obtained the implementation result of this invention, and compared with the conventional result. It is a flowchart which shows the manufacturing process of a general seamless steel pipe.

Explanation of symbols

1 Round steel slab (round billet)
2 Heating furnace 3 Piercer (rolling mill)
4 Plug 5 Base pipe 6 Mandrel mill 7 Mandrel bar 8 Reheating furnace 9 Hot stretch reducer 10 Elongator 11 Plug mill 12 Reeler 13 Clearance
14 Sizer 15 Seamless steel pipe manufacturing guide (simply guide)
16 slab or raw pipe exit side position 17 roll 18 minimum position of roll gap 19 claw-shaped sleeve 20 pin 21 claw 22 guide shoe

Claims (3)

When the heated round steel slab is passed through a tubular guide and guided to a piercer rolling machine, while pressing and pressing a shell-shaped plug on the tip of the round steel slab,
The slab exit side position of the guide is 250 to 300 mm from the minimum position of the roll gap of the piercer rolling mill, and the gap between the round steel slab and the guide is 10 to 15 mm. A method for suppressing the uneven thickness of a seamless steel pipe, characterized in that the slab is supplied to a piercer mill. A guide made of a tubular body that guides a heated round steel slab to a piercer mill, or guides a raw pipe punched by the piercer mill to an elongator,
A guide for producing a seamless steel pipe, characterized in that a sleeve having a claw-like tip is provided on the side from which the round steel slab or the raw pipe comes out. The seamless steel pipe manufacturing guide according to claim 2, wherein the sleeve having the claw-shaped tip is fixed to the guide with a bolt, a nut, or a pin.

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