JP5380877B2 - ERW steel pipe manufacturing method with excellent seam quality - Google Patents

Description

  The present invention relates to a method for manufacturing an electric resistance welded steel pipe for efficiently manufacturing an electric resistance welded steel pipe excellent in seam part quality.

In order to efficiently manufacture an electric resistance welded steel pipe, the steel strip is continuously formed into an open pipe in the forming process, and in the next electric resistance welding process, as shown in FIG. A high-frequency current (200 to 450 kHz) is passed, and both ends heated by the induction current are butt-welded to form a seam tube W.
When the heated both end faces are butt-welded, the molten metal is squeezed out and a raised seam portion S is formed. Therefore, the swell is removed, and then the seam portion S is optionally heat treated, and then the seam tube W is finished to product dimensions in a sizing process (for example, Non-Patent Document 1).

The angle formed by both end faces opened in a V shape shown in FIG. 1B is referred to as a shape angle θ. The shape angle θ is determined by the distance between the pair of side rolls 1 and the seam guide roll 3 disposed on the upstream side thereof.
Here, the shape angle θ determined by the equipment and the time during which both end surfaces heated to a predetermined temperature are exposed to the atmosphere greatly affect the quality of the seam portion.

  In addition, a pair of side roll 1 has the surrounding surface shape according to the outer diameter dimension of a pipe | tube, and comprises the squeeze apparatus for pressing the outer periphery of an open pipe | tube from both sides. In general, the squeeze device has an upper roll 4 as shown in FIG. 2 in addition to the pair of side rolls 1. The upper roll 4 has a groove at the center in the axial direction, and is a roll for regulating the outer shape of the seam portion S while preventing contact with the raised seam portion S.

In order to improve the seam quality of an ERW welded steel pipe that is efficiently manufactured with such a configuration, it is necessary to reduce seam defects.
Edited by Japan Iron and Steel Association, 3rd edition, Steel Handbook III (2), published by Maruzen Publishing, May 15, 1980, p1076-1077

However, it has been difficult to reduce seam portion defects in which a relatively short unwelded portion remains in the seam portion due to the occurrence of sparks. For this reason, there has been a problem in that the quality of the seam portion varies greatly at the position in the longitudinal direction of the pipe.
An object of the present invention is to provide a method for manufacturing an electric-welded steel pipe that can eliminate the above-described problems of the prior art and reduce seam defects caused by the occurrence of sparks.

  The present inventors have intensively studied the seam defect caused by the occurrence of sparks. As a result, when a conventional squeeze device is used, the occurrence of sparks due to spattering of the squeeze device tends to occur and is prevented. To this end, it was found that the distance from the work coil to the welding point should be shortened to suppress the formation of oxides, and the shape angle θ should be increased to improve the discharge of molten steel. The present invention has been made based on the above.

That is, the present invention is as follows.
1. On the upstream side of the pair of side rolls sandwiching the open tube, a work coil that heats both end faces opened in a V shape of the open tube, and a seam guide roll that determines the shape angle formed by the both end faces opened in a V shape Are arranged in order, and the outer diameter of the ERW steel pipe is 100 to 165.2 mm and is heated to a predetermined temperature by the work coil. A method for producing an ERW steel pipe having excellent seam quality, characterized in that the time during which both end faces are exposed to the atmosphere is 0.07 seconds or less and the shape angle is 3.3 degrees or more.

  ADVANTAGE OF THE INVENTION According to this invention, the seam part defect produced by spark generation can be decreased, As a result, the ERW steel pipe excellent in seam part quality can be manufactured efficiently.

  When a conventional squeeze device is used, the distance L between the pair of side rolls 1 and the work coil 2 is restricted, for example, until both end surfaces heated by the work coil 2 to 1000 ° C. reach the welding point P, The time of exposure to the atmosphere was 0.10 seconds, and the shape angle θ was 3.0 degrees (see FIGS. 1A and 1B). The shape angle θ is determined by the distance between the pair of side rolls 1 and the seam guide roll 3.

On the other hand, the present invention reduces the seam defects caused by the occurrence of sparks, as will be described later, by reducing the diameter of the pair of side rolls 1 constituting the squeeze device and the upper roll 4 in addition thereto. did it.
That is, if the distance L between the pair of side rolls 1 and the work coil 2 can be shortened, the time during which the both end surfaces heated to a predetermined temperature that can be butt-welded by the work coil 2 are exposed to the atmosphere during pipe forming. And the generation of oxides can be suppressed.

Further, if the distance L between the pair of side rolls 1 and the work coil 2 is shortened, the seam guide roll 3 for determining the shape angle θ can be disposed close to the pair of side rolls 1 and the shape angle θ is increased. can do.
When the seam guide roll 3 is disposed close to the pair of side rolls 1 and the shape angle θ is increased, the heat affected width at the welding point P is reduced, the discharge of molten steel is promoted, and it effectively acts to suppress the generation of spatter. At the same time, the induced current is concentrated in the vicinity of the welding point P, and the current density is increased. Therefore, discharge of molten steel by electromagnetic force is promoted, and effectively acts to suppress the generation of spatter.

As a result, the generation of sparks due to spattering can be prevented by the synergistic effect of suppressing the generation of oxide and promoting the discharge of molten steel.
In order to do this, the pair of side rolls 1 constituting the squeeze device and the upper roll 4 in addition to that are reduced in diameter. To reduce the roll diameter of the squeeze device means to reduce the distance from the axial center to the outer periphery. Fig. 3 shows the roll shape before and after modification.

  Here, a squeeze device suitable for use in the present invention is shown in FIG. 1 a is a roll bearing that supports the pair of side rolls 1, and 4 a is a roll bearing that supports the upper roll 4. The upper roll 4 can be moved up and down by a lift antibacklash screw jack 4b via a roll bearing 4a and can be traversed by a transverse antibacklash screw jack 4c.

  In the following, an embodiment will be described in which the roll coil diameter of the squeeze device is set to 0.07 seconds or less and the shape angle is 3.3 degrees or more while both end surfaces heated to a predetermined temperature by the work coil 2 are exposed to the atmosphere.

The present invention was applied to a production line for a small diameter electric resistance welded steel pipe having a pipe outer diameter of 70 to 165.2 mm, and the quality of the seam portion in the longitudinal direction of the pipe before and after application of the present invention was examined as follows.
A sample tube W1 having a length of 300 mm is taken from a predetermined position in the longitudinal direction of a plurality of ERW steel pipes (outer diameter: 100 mm, wall thickness: 5.5 mm) that have been passed through a normal pipe making process, and two flat tests are performed. Then, the opening length generated in the sample tube W1 was measured to evaluate the seam quality. The quality of the seam portion was evaluated as follows: flat aperture ratio = opening length / sample tube length × 100, and the results are shown in FIGS.

Before application of the present invention: Time during which both end surfaces heated to a predetermined temperature by the work coil 2 are exposed to the atmosphere = 0.10 seconds, and a shape angle θ = 3.0 degrees.
After application of the present invention: time during which both end surfaces heated to a predetermined temperature by the work coil 2 are exposed to the atmosphere = 0.07 seconds, and a shape angle θ = 3.3 degrees.
However, the predetermined temperature at which both end faces having a wall thickness of 5.5 mm are heated by the work coil 2 = 1000 ° C.

  From the characteristic diagram showing the relationship between the tube longitudinal position and the flat aperture ratio shown in FIGS. 4 (a) and 4 (b), by applying the present invention, the seam in the tube longitudinal direction except immediately after the start of pipe making It can be seen that an electric resistance welded steel pipe with a small variation in part quality can be obtained. Further, from the result of the average flat aperture ratio in the longitudinal direction of the pipe shown in FIG. 5, it can be seen that by applying the present invention, an ERW steel pipe with good seam part quality can be obtained.

The two flat test methods are shown in FIGS. FIG. 6 shows a JIS flat type flat test method using the flat type 5, and FIG. 7 shows a reverse wedge type flat test method using the wedge type 6. In the JIS flat type flat test, the sample tube W1 is arranged so that the circumferential position of the seam portion S is 90 degrees with respect to the moving direction of the flat type 5. On the other hand, in the reverse wedge type flat test, at the tip of the wedge type 6 The sample tube W1 was disposed so that the seam portion S hits, and was flattened until the inner surfaces overlapped. Note that the radius of the tip of the wedge-shaped mold 6 was 3 mm.
(Normal process of ERW steel pipe)
In the forming process, the steel strip is continuously formed into an open pipe, and in the next electric welding process, both ends of the open pipe are butt-welded to form a seam pipe, and the rise of the seam pipe is removed, followed by heat treatment by gas firing. gave. Thereafter, the outer diameter was finished to 100 mm in a sizing process.
(Specification of squeeze device before and after modification)
Before remodeling: The maximum diameter of the pair of side rolls 1 = 320 mm, and the maximum diameter of the upper roll 4 = 370 mm.
After modification: The maximum diameter of the pair of side rolls 1 = 250 mm, and the maximum diameter of the upper roll 4 = 250 mm.

(a) is a perspective view which shows the welding and press-contacting process of an electric resistance welded steel pipe, (b) is a top view which shows the vicinity of a squeeze apparatus. It is a front view showing a squeeze device suitable for use in the present invention. It is a front view which shows the roll shape of the squeeze apparatus before and after remodeling. It is a characteristic view which shows the effect of this invention. It is another characteristic view which shows the effect of this invention. It is sectional drawing which shows the JIS flat type flatness test method of a pipe | tube. It is sectional drawing which shows the reverse wedge-shaped flatness test method of a pipe | tube.

Explanation of symbols

W seam pipe S seam part W1 sample pipe θ shape angle P welding point L distance between a pair of side rolls 1 and work coil 2 1 side roll 1a roll bearing 2 work coil 3 seam guide roll 4 upper roll 4a roll bearing 4b Anti-backlash type screw jack 4c Anti-backlash type screw jack for traversing 5 Flat type 6 Wedge type

Claims (1)

On the upstream side of the pair of side rolls sandwiching the open tube, a work coil that heats both end faces opened in a V shape of the open tube, and a seam guide roll that determines the shape angle formed by the both end faces opened in a V shape Are arranged in order, and the outer diameter of the ERW steel pipe is 100 to 165.2 mm and is heated to a predetermined temperature by the work coil. A method for producing an ERW steel pipe having excellent seam quality, characterized in that the time during which both end faces are exposed to the atmosphere is 0.07 seconds or less and the shape angle is 3.3 degrees or more.

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