JPS6046890A - Production of metallic pipe - Google Patents

Abstract

PURPOSE:To obtain a pipe usable for applications where conditions are severe with high productivity at a low cost by subjecting both side ends held to face each other in a non-pressed state by forming a plate-shaped metallic member to a cylindrical shape to laser welding and subjecting the metallic member to induction heating prior to welding. CONSTITUTION:High-frequency current is passed to an induction heating coil 10 to preheat an upper stream pipe material 1 at the V focusing point P with which both ends of the pipe 1 under formation to a circular shape of the material 1 passing through the inside of the coil 10 contacts first. The heating penetration depth in this case is set at about the same degree as the depth of the thermal influence of laser light 12a (i.e., degree of the wall thickness). The quantity of heat for preheating is set at the extent at which melting of metal arises hardly. The material 1 after preheating is conveyed in a direction A while the contact state of a joint part 1a is maintained by squeeze rolls 11a, 11b until the joint part 1a arrives right under the laser light 12a, where the joint part is melted. Since the joint part 1a is preheated, the laser power of small capacity is required and a considerable reduction in cost is attained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing metal pipes, and more particularly, to a method for manufacturing metal pipes that can produce high-quality pipes at high speed.

In areas where seamless pipes have been used,
The number of cases in which welded pipes are used is increasing,
The reasons for this are (1) improved quality of welding itself and higher precision of the inspection system, which allows us to provide quality products, (2) less uneven thickness (pipe hole deviation) than seamless pipes, and (3) ) The reason is that the cost is low. However, among welded pipes, pipes produced by the ERW pipe welding method cannot generally be used as stainless steel water pipes or pipes for chemical plants, although the quality of these pipes has significantly improved due to technological advances. Here, electric resistance welded pipe welding will be briefly explained.

In electric resistance welding, a plate-shaped hoop is passed through a forming line to form a pipe, and the joint is then heated by induction heating or by passing a high-frequency current through a contactor. Then, the pipe is tightened using tightening rolls to apply pressure to the heated joint, thereby causing impurities and oxides in the joint to squeeze out and welding is performed. In this case, since metal mixed with impurities protrudes from the front and inner surfaces, it is removed with a cutting knife or the like after welding. In this welding method, when welding is performed at low speed, heat is transferred in the lateral direction and melting of the weld zone progresses, resulting in pulsations in the tightening force and extremely poor welding stability. For this reason, the welding speed is set to a certain degree of speed, but the high speed causes drawbacks such as difficulty in gas shielding and difficulty in preventing air from entering from upstream. In addition, other drawbacks include (1) oxides are likely to be mixed in, and (2) there are few fused parts of metal, which is similar to pressure welding.

On the other hand, pipes manufactured by TTG (tungsten inert gas) welding can be used in applications with severe conditions such as pipes for chemical plants, but it is extremely difficult to increase the welding speed, so we use electric resistance welding pipe welding. It has a low productivity of 730 to 171008 degrees compared to the above. Here, the reason why the welding speed cannot be increased in T-work G welding will be explained. When the welding speed is increased, the arc current must necessarily be increased, but as the arc current increases, the arc pressure increases and the molten area on the surface side increases, and the surface tension of the molten area increases. Holes occur due to its own weight and arc pressure.

Furthermore, since the molten part is rapidly cooled, undercuts are likely to occur on both sides of the bead. The above-mentioned problem is extremely difficult to solve, and this has been a cause of hindering the speeding up of TTG welding.

Therefore, a method has been developed in which the speed of T-G welding is increased by increasing the number of electrodes. FIG. 1 is a diagram showing a schematic configuration of a welding device to which this method is applied. In the figure, 1 is a pipe material, and 2, 3 and 4 are electrodes provided opposite the joints of the pipe material 1. . 55L, 51) and 6a, 6b are rolls that press the pipe material 1 from both sides, and the pipe material 1 is conveyed in the direction of arrow A. Second
Figures (A) to (H) are diagrams showing the molten state near the electrodes 2 to 4, respectively, and the shaded area in the diagram indicates the molten part.

In this welding method, the arc pressure on each side of the electrodes is set relatively low, and welding is performed multiple times with a small current arc, which has a high preheating effect on the electrodes 2 and 3 and reduces the amount of melting. It is an effective welding method to obtain.

However, this welding method has the drawback that it is extremely difficult to balance the arc current values at each electrode, and requires considerable skill to perform stable welding. , there was a drawback that only a speed improvement of about 2f11 could be expected.

On the other hand, if welding is performed using a laser, it is possible to perform high-speed welding and to produce high-quality pipes that can be used in demanding applications. however,
Laser welding costs about 20 million yen per kW, which is extremely expensive and impractical. For example, 3t
Welding at a speed of 3 m/min or more requires more than 3 kW, which would cost nearly 100 million yen.

In view of the above-mentioned circumstances, the present invention provides a method for producing metal pipes that can be fully applied to applications with severe usage conditions, and that can achieve high productivity and low production costs. While transporting a metal member in the longitudinal direction, the metal member is sequentially formed into a cylindrical shape so that both end portions face each other, and further, the opposing both end portions are laser welded while maintaining a non-pressure contact state, and The metal member is preheated by induction heating prior to the laser welding.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 3 is a perspective view showing a schematic configuration of a metal pipe manufacturing apparatus which is an embodiment of the present invention.

In the figure, IO is an induction heating coil, and a pipe material 1 passes through the inside of this induction heating coil 10. P is a V convergence point, which is the point where both ends of the pipe 1, which is being formed into a cylindrical shape by a forming means (not shown), first come into contact. The induction heating coil 10 is provided on the upstream side of the convergence point P at a distance of a predetermined pressure. lla and llb are squeeze rolls whose sides are curved so as to fit into the cylindrical pipe material 1, and press the cylindrical pipe material 1 from both sides to close the joint la of the pipe material 1. This is to prevent them from becoming separated. However, the amount of tightening of the squeeze rolls lla and llb in this case is such that the amount of pressure applied at the joint 1a is approximately 0, that is, the amount of tightening of the squeeze rolls lla and llb is such that the both ends of the pipe material 1 simply touch each other (in a non-pressure contact state). ) is set to the tightening amount. A laser nozzle 12 is provided on the downstream side of the squeeze rolls lla and llb, and irradiates the joint portion 1a with a laser beam 12a to melt the metal in the irradiated portion. 13a and 13b are the above-mentioned squeeze rolls lla
, llb, and is provided on the downstream side of the laser nozzle 12.

Next, the operation of this embodiment having the above-described configuration will be explained with reference to FIG.

First, a high frequency current of 10 to 100 KIIz is passed through the induction heating coil 10, and the pipe material 1 on the upstream side of the convergence point P is
Preheat by induction heating. The heating penetration depth in this case is set to be approximately the same as the thermal influence depth of the laser beam 12a (that is, approximately the wall thickness). For example, in the case of a stainless steel material with a wall thickness of 3 mm, the high frequency current is set to about 40 KITz. Further, the preheating temperature is set to such an extent that almost no melting of the metal occurs. The pipe material 1 after preheating is then squeezed into the joint 1 by squeeze rolls lla and llb.
It is transported in the direction of arrow A while maintaining the contact state of a,
The joint 1a reaches directly under the laser beam 12a, and as a result,
The joint portion 1a directly under the laser beam 12a is melted. In this case, since the joint portion 1aid has already been preheated, a small laser power is sufficient for melting, resulting in significant cost savings.

In addition, the preheating effect improves the molten metal's lifting and sludge, and defects such as undercuts are less likely to occur. and,
The molten metal part is cooled and solidified while being transported, but the contact state (non-pressure contact state) of the joint part 1a is maintained by the squeeze rolls 13a and 13b until solidification. , the joint will not open before solidification, and welding will be completed successfully.

In addition, in this example, the laser welding is performed behind the squeeze rolls lla and llb. If the electrical contact of the joint ta is not firmly secured in this way, the laser welding may be caused by the bath water. This is because the point changes and heating becomes unstable.

Further, in this embodiment, squeeze rolls 11a, l
Since the amount of pressure applied to lb, 13a, and 13b is small (approximately 0 at joint 1&), the bead does not pop out, so there is no need to cut the pop-out bead, and only polishing work using an endless sand vapor etc. is required. Finishing is completed and efficient production can be carried out.

Next, in the embodiment described above, if it is necessary to perform gas shielding, for example, using the jig shown in FIGS. 4 to 6, from the induction heating coil 10 to the downstream side of the laser nozzle 12, , both the inner and outer surfaces of the pipe material 1 are shielded.

The jigs 20, 20 shown in FIG. 4 have a shape as shown in FIG. 5 when viewed from below, and have a conduit 20a.

The shielding gas sent into 2Oa enters the hollow cylindrical gas chamber ZobK, and then into the hole 20c.

Emitted from 20c... 20d is a part of a semi-cylindrical cover, and 't'+1 is located near the outer periphery of the pipe material 1, which is the shielding gas released from the holes 20c, 20c...
It is something to dedicate. As shown in FIG.
2 and on the downstream side of the laser nozzle 12.

Note that the downstream jig 20 has a function of preventing discoloration after welding.

The jig 25 shown in FIG. 6 is a hollow cylindrical jig made of resin, and has holes 25a, 25a, . In other words, it is provided over a position facing the jig 20, 20 shown in FIG. Inside this jig 25,
When inserting the shield gas in the direction shown by the dashed arrow, hole 2
Shielding gas is emitted upward from 5a, 25a, . . . , thereby shielding the inner surface of the pipe material 1.

As explained above, according to the present invention, a plate-shaped metal member is conveyed in the longitudinal direction and sequentially formed into a circular shape so that both side ends thereof face each other, and further, the opposite side ends are left unprocessed. Laser welding is performed while maintaining a pressure contact state, and the metal parts are preheated by thermal insulation heating before the laser welding, which is sufficient for applications with severe usage conditions such as pipes for chemical plants. It is possible to manufacture applicable high-quality products, improve productivity, and reduce production costs.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram showing an example of a conventional welded pipe manufacturing apparatus, and FIG.
3.3 is a schematic diagram showing the welding state in the vicinity of 4. FIG. 3 is a perspective view showing the configuration of a metal pipe manufacturing apparatus that is an embodiment of the present invention, and FIGS. It is a perspective view showing an example of the jig in the case of carrying out. 10---・ii1 conductive heating heating coil la, llb,
13a, 13'b...Squeeze roll, 12...
...Laser nozzle. Figure 1 C) 1 mouth) (I\n11 smoke 2) (A

Claims (1)

[Scope of Claims] 1. While conveying a plate-shaped metal member in the longitudinal direction, it is sequentially formed into a cylindrical shape so that both end portions face each other, and further, the opposing both end portions are maintained in a non-pressure contact state. A method for manufacturing a metal pipe, characterized in that the metal member is welded by laser, and the metal member is preheated by induction heating prior to the laser welding. 2. Claims characterized in that the induction heating part of the metal member and the part downstream of the melting part in the laser welding and where discoloration of the metal member is expected are gas-shielded on both the front and back of the metal member. The method for manufacturing a metal pipe according to item 1.