JP2008194744A - Method of straightening electric resistance welded steel pipe - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of straightening an electric resistance welded steel pipe by which the twist angle of a weld bead part is fallen in a prescribed range when performing rotating straightening by advancing the pipe while rotating it with a pair of upper and lower rotating straightening rolls which are cross arranged to increase the straightness of the electric resistance welded pipe having approximately round cross section obtained by cutting into prescribed length after drawing and rolling in the temperature range of 400°C to a transformation point A<SB>c3</SB>. <P>SOLUTION: In this method of straightening the electric resistance welded pipe, a cross angle formed by the axial centers of the pair of the upper and lower rotating straightening rolls is set to 90-105°. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

In order to increase the straightness of the ERW steel pipe having a substantially round cross section obtained by drawing in a temperature range of 400 ° C. or more and below the _{AC 3} transformation point and then cutting to a predetermined length, The present invention relates to a method for correcting an electric resistance welded steel pipe that allows the twist angle of a weld bead portion to be within a predetermined range when rotating forward and rotating with a pair of upper and lower rotation correction rolls arranged.

  In the production of ERW steel pipes, an electric resistance welding method is mainly employed in which the circumferential end of the open pipe is heated and welded by Joule heat due to electric resistance. Such an electric resistance welded steel pipe includes a forming process in which a steel strip is roll-formed to form an open pipe, an electric resistance welding process in which the open pipe is electroformed to be welded, and an outer diameter is drawn and rolled. Is produced through a drawing and rolling process to produce a substantially round cross-section ERW steel pipe close to the product size, and a cutting process to cut a substantially circular cross-section ERW steel pipe obtained by drawing to a predetermined length. ing.

2. Description of the Related Art In recent years, a method for manufacturing an electric resistance welded steel pipe having high elongation and excellent workability and its equipment line have been proposed and realized (Patent Document 1). The method for producing an ERW steel pipe described in Patent Document 1 is a method in which the whole pipe is heated and then drawn and rolled in a temperature range of 400 ° C. to AC ₃ transformation point, preferably 700 ° C. to _{AC 3} transformation point ( In the following, the HIS method is applied, and in addition to this, before the whole tube is heated, the swell of the weld bead formed in the ERW welding process is cut and removed, and then partially bead rolled or partially beaded. This is a method of performing heat treatment of the part. Furthermore, it is also preferable to perform heat treatment of the entire steel pipe in a subsequent process of the drawing rolling process.

  FIG. 1 shows an example of a production facility for an ERW steel pipe adopting the preferred HIS method to which the present invention is applied. In FIG. 1A, reference numeral 9 denotes a heating device for heating the whole raw tube, and for example, an induction coil 9A is suitable. The induction coil 9A is disposed in the vicinity of the reducer (drawing mill) 7 and has the ability to bring the whole raw tube running in the direction of the arrow into the temperature range when induction heating is performed and the drawing mill 7 performs the drawing rolling. . In addition, 8 shown to the right side in Fig.1 (a) is a cutting machine which cut | disconnects the ERW steel pipe W to predetermined length according to the length of a product. The process upstream of the cutting machine 8 is a pipe making process for continuously making an electric-welded steel pipe W having a substantially round cross section from the steel strip S and having an outer diameter close to the product size.

According to this HIS method, the rolling load can be reduced as compared with the method of cold-drawing the raw tube, and the diameter reduction ratio in the reducer (drawing mill) 7 can be increased. Production of various types of ERW steel pipe products can be advantageously performed. The diameter reduction rate is defined by equation (1).
Reduction ratio = {(outer diameter of element tube before drawing-roller-outer diameter of ERW steel pipe after drawing-rolling) / outer diameter of element tube before drawing} × 100 (%) (1)
By the way, when manufacturing the ERW steel pipe W by the HIS method, the diameter reduction ratio by the drawing mill 7 may be 20% or more, preferably 60% or more according to the product size. Thus, the electric resistance welded steel pipe W manufactured by the HIS method has a severe demand for its straightness. For this reason, an electric resistance welded steel pipe W having a substantially round cross section obtained by cutting to a predetermined length using the rotational correction type correction device 10 as shown in FIG. It is essential to correct the rotation. The straightening device 10 of the rotation correction type that takes the bending of the electric resistance welded steel pipe is formed by arranging a plurality of tandem roll stands in which a pair of upper and lower rotation correction rolls 11 are arranged in a cross manner.
JP 2001-239315 A

However, when this rotary roll type straightening device 10 is used to rotate and straighten the ERW steel pipe W having a substantially round cross section produced by the HIS method, the twist angle of the weld bead portion exceeds 90 degrees. Problems occurred.
In order to exert the function of increasing the straightness of the ERW steel pipe W using the rotating roll type straightening device 10, the cross angle θ formed by the shaft cores 11A and 11B of the pair of upper and lower rotating straightening rolls 11 is larger than 0 degree. The angle is set, for example, as shown in FIGS. 2A and 2B, the pair of upper and lower rotation correcting rolls 11 are rotationally driven in the direction indicated by the rotation direction 12, so that the ERW steel pipe W having a predetermined length is formed. It is necessary to apply a force to rotate toward the rotation direction 13 and a force to advance toward the forward direction 14. At that time, in order to take the bend of the electric resistance welded steel pipe W, the cross angle θ is set to an angle larger than 105 degrees, and when the rotation is straightened between the pair of upper and lower rotation straightening rolls 11, the twist angle of the weld bead portion is increased. In some cases, the angle exceeds 90 degrees, and there is a problem that it is difficult to meet the demand for setting the twist angle of the weld bead within a predetermined range, for example, within 10 degrees.

  Here, FIGS. 3 and 4 show that the torsion angle α of the weld bead portion R is larger at the rear than before the rotation correction. In general, in the ERW steel pipe W manufactured by the HIS method, the value of the twist angle α of the weld bead R before rotation correction per predetermined length L = 6 m (however, depending on the product) is within 10 degrees, rotation After correction, it exceeds 90 degrees. P and Q are points on the weld bead.

Therefore, the present invention eliminates the above-mentioned problems of the prior art, and after being drawn and rolled in a temperature range of 400 ° C. or more and A _C3 transformation point or less, is cut into a predetermined length, and has a substantially round cross-sectional shape. In order to increase the straightness of the electric resistance welded steel pipe, the twist angle of the weld bead portion can be kept within a predetermined range when rotating and correcting by rotating with a pair of upper and lower rotation correction rolls arranged in a cross. The purpose is to provide a correction method.

The present inventor has intensively investigated the cause of the twist of the weld bead part of the electric resistance welded pipe product manufactured by the HIS method, and the cause is the cross angle of the pair of upper and lower rotational correction rolls arranged in the roll stands of the correction device. We have found out that there is a present invention.
That is, the present invention includes a forming step of roll-forming a steel strip into an open tube, an electro-welding welding step in which the open tube is electro-welded to form a base tube, and the base tube is heated to 400 ° C. The above-described drawing rolling process in which the ERW steel pipe having a substantially round cross-section is drawn in the temperature range below the _AC3 transformation point, and the cutting process for cutting the ERW steel pipe having a substantially round cross-section into a predetermined length; A rotation correction step of rotating the obtained electric resistance welded steel pipe between a pair of upper and lower rotation correction rolls arranged in a cross, and a rotation correction step. A crossing angle formed by an axis of a straightening roll is set to 90 degrees or more and 105 degrees or less.

  More preferably, the cross angle is 93 degrees or more and 99 degrees or less.

  According to the present invention, the twist angle of the weld bead portion after the rotation correction can be maintained at the level before the rotation correction. As a result, the twist angle of the weld bead portion of the ERW steel pipe product can be set within a predetermined range, for example, within 10 degrees, without imparting torsional deformation to the ERW steel pipe.

First, the manufacturing equipment for a suitable ERW steel pipe to which the present invention is applied will be described in detail.
In FIG. 1A, 1 at the left end indicates an uncoiler that rewinds the steel strip S that is a material of the electric resistance welded steel pipe, and 2 indicates a leveler that flattens the steel strip S by repeatedly bending. Reference numerals 3 and 4 denote a plurality of forming rolls which are obtained by cutting off both ears of the steel strip S and roll-forming the flat steel strip S into a substantially round open tube. The roll arrangement of the forming rolls 3 and 4 is shown in FIG. The cage roll 3 roll-forms the lower half of the open pipe from the steel strip S from which both edges are removed, and the fin pass roll 4 has a role of roll-forming the upper half of the open pipe.

  Reference numeral 5 denotes an electric resistance welding machine which uses an open pipe as an element pipe by electro-welding, and includes an induction coil 5A and a pair of squeeze rolls 5B. According to the electric seam welding machine 5 as described above, the circumferential end of the substantially round open pipe is heated by Joule heat due to electric resistance, and the pipe outer peripheral surface is pressed by the pair of squeeze rolls 5B to achieve good pressure welding.・ Can be joined. Reference numeral 6 denotes an inner / outer surface bead cutting machine that removes a raised portion formed by press-contacting and joining the circumferential ends of the open pipe, and 7 is the drawing rolling machine described above, and its roll arrangement is shown in FIG. It was shown to.

The drawing mill 7 is composed of a four-roll reducer having a plurality of stands. Although this roll stand is not shown in the figure, for example, there are 24 stands, and the base tube having the weld bead portion R is drawn and rolled with a 4-roll reducer of each stand, and the outer diameter is an electric electrode having a substantially round cross section close to the product size. A sewn steel pipe W is used. That is, the inner peripheral shape of the roll of the four-roll reducer has a shape closer to the raw tube on the upstream side, and has a substantially circular cross section whose outer diameter is closer to the product size on the downstream side. When manufacturing ERW steel pipe products by the HIS method, a heating device 9 arranged close to the drawing mill 7, for example, an induction coil 9 </ b> A is used to induction-heat the entire raw pipe running in the direction of the arrow, and the drawing mill 7 performs drawing rolling. The temperature range when the temperature is 400 degrees or more and the _AC3 transformation point or less.

The electric resistance welded steel pipe W whose outer diameter has a substantially round cross section close to the product size in the drawing mill 7 is cut into a predetermined length by the cutting machine 8, and the obtained electric resistance welded steel pipe W having the predetermined length is obtained. Is passed through the straightening device 10 and rotated and then cooled in the cooling bed.
The cause of the twist of the weld bead portion of the ERW steel pipe product manufactured by the HIS method using the ERW steel pipe manufacturing equipment described above is caused by the cross angle of the pair of upper and lower rotational correction rolls arranged in the roll stands of the correction device 10. The experimental results that have been found in the above will be described.

  In this experiment, by changing the cross angle θ formed by the shaft cores 11A and 11B of the pair of upper and lower rotation correcting rolls 11 shown in FIG. 2, an electric resistance steel pipe having a predetermined twist angle α of the weld bead R is obtained. It is investigated whether or not it changes before and after passing through the rotary roll type straightening device 10. In addition, the size of the ERW steel pipe used for the experiment was set to an outer diameter = 22.2 to 101.6 mm, a wall thickness 2.0 to 6.0 mm, and L = 6 m. Further, the twist level of the weld bead R before the rotation correction of the ERW steel pipe used in this experiment was within 10 degrees in terms of the twist angle α.

  As a result, when the ERW steel pipe W having a predetermined length L is passed through the rotary roll type straightening device 10 and rotated and corrected, if the cross angle θ is set to an angle larger than 105 degrees, the weld bead after rotational correction is set. The twist angle α of the part may exceed 90 degrees, and the weld bead part after rotation correction is made by setting the cross angle θ formed by the shaft cores 11A and 11B of the pair of upper and lower rotation correction rolls 11 to 105 degrees or less. The twist angle α of R was made within 10 degrees.

On the other hand, if the cross angle θ is excessively small (for example, θ = 0 degrees), the circumferential component of the force applied to the steel pipe side through the contact portion between the pair of upper and lower rotation correcting rolls 11 and the steel pipe is zero (zero). In the case: the steel pipe W cannot be rotated in the rotation direction 13), and the rotation correction becomes insufficient, so the cross angle θ is set to 90 degrees or more.
From the above results, the cross angle θ formed by the shaft cores 11A and 11B of the pair of upper and lower rotation correcting rolls 11 was set to 90 degrees or more and 105 degrees or less.

  More preferably, the cross angle α is set to 93 degrees or more and 99 degrees or less for stable rotation correction.

Using the ERW steel pipe manufacturing equipment shown in FIG. 1, a steel strip equivalent to JIS STKM13B is roll-formed to form an open pipe. After this open pipe is electro-welded, the inner and outer surfaces are bead cut and the outer diameter is 90 mm. A blank tube was used. Next, the base tube is drawn and rolled in a temperature range of 400 ° C. or more and the AC ₃ transformation point or less to obtain an ERW steel tube having an outer diameter of 42.7 mm and a wall thickness of 2.0 mm, and a predetermined length L. = 6 m. When the ERW steel pipe W whose outer diameter is close to the product size is supplied to the rotary roll type straightening device 10 for rotational correction in the subsequent process of the cutting process, the shaft cores 11A and 11B of the pair of upper and lower rotational correction rolls 11 are formed. The cross angle θ was set to 95 degrees. The speed in the forward direction 14 of the ERW steel pipe having a substantially round cross section was set to 100 mpm (see FIG. 2).

  As a result, the twist angle α of the weld bead portion R of the ERW steel pipe after rotation correction can be made within 10 degrees, and the twist angle of the weld bead portion does not exceed 90 degrees as in the conventional case. Further, when the present invention was applied and the cross angle θ was set to 95 degrees, the straightness of the ERW steel pipe after the rotation correction was about the same as the conventional one.

It is a perspective view (a), (b) and a side view (c) which show an example of the manufacturing equipment of the suitable ERW steel pipe to which the present invention is applied. It is the perspective view (a) which shows the correction | amendment apparatus of the ERW steel pipe to which this invention is applied, and the top view (b) which shows the principal part. It is the perspective view (a) which shows the twist state of the weld bead part before rotational correction, and the front view (b) which shows the principal part. It is the perspective view (a) which shows the twist state of the weld bead part after rotation correction, and the front view (b) which shows the principal part.

Explanation of symbols

θ Cross angle α Torsion angle P, Q Point on weld bead R Weld bead S Strip steel (material)
W ERW steel pipe L Length 1 Uncoiler 2 Leveler 3 Cage roll (Forming roll)
4 Fin pass roll (molding roll)
5 Electric Welding Machine 5A Induction Coil 5B Squeeze Roll 6 Inner / Outer Surface Bead Cutting Machine 7 Reducer (Drawing Roller)
8 Cutting machine 9 Heating device 9A Induction coil 10 Straightening device 11 Rotation straightening roll 11A, 11B Axle core 12, 13 Rotating direction 14 Forward direction

Claims (1)

A forming process of roll-forming steel strip to form an open pipe, an electric resistance welding process in which the open pipe is electro-welded to form a base pipe, and after heating the base pipe, the temperature is not less than 400 ° C. and not more than the _AC3 transformation point. A drawing process in which the ERW steel pipe having a substantially round cross-section is drawn in the temperature range, a cutting process for cutting the ERW steel pipe having a substantially round cross-section into a predetermined length, and a predetermined length obtained. A rotation correcting step of rotating the electric resistance welded steel pipe between a pair of upper and lower rotation correcting rolls arranged in a cross, and a rotation correcting step having the shaft core of the pair of upper and lower rotation correcting rolls. A method for correcting an electric resistance welded steel pipe, characterized in that a cross angle formed is 90 degrees or more and 105 degrees or less.

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