JPH0418954B2 - - Google Patents

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 allows high-quality pipes to be manufactured at high speed.

Welded pipes are increasingly being used in areas where seamless pipes have been used, and this is due to (1) improvements in the quality of welding itself and higher accuracy in inspection systems; (2) Compared to seamless pipes, there is less uneven wall thickness (pipe hole deviation); and (3) lower cost. However, among welded pipes, pipes produced using the ERW pipe welding method are
Although quality has improved significantly due to technological advances, it is generally not possible to use stainless steel water pipes or pipes for chemical plants. 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 tube is tightened with a tightening roll 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 level, but the high speed makes gas shielding difficult.
This resulted in the drawback that it became difficult to prevent air from entering from upstream. In addition, other disadvantages include that oxides are easily mixed in, and there are few metal fused parts, which is similar to pressure welding.

On the other hand, pipes manufactured by TIG (tungsten inert gas) welding can be used in demanding applications such as pipes for chemical plants, but it is extremely difficult to increase the welding speed.
The productivity is only about 1/30 to 1/100 compared to the ERW pipe welding method. Here, we will explain why welding speed cannot be increased in TIG welding. Increasing the welding speed inevitably requires increasing the arc current, but when 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 portion is rapidly cooled, undercuts are likely to occur on both sides of the bead. and,
The above-mentioned problem is extremely difficult to solve, and this has been the cause of hindering the speeding up of TIG welding.

Therefore, a method has been developed that aims to speed up TIG welding 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, 2, 3, 4
are electrodes provided facing the joints of the pipe material 1, respectively. 5a, 5b and 6a, 6b are tightening rolls that press the pipe material 1 from both sides;
The pipe material 1 is conveyed in the direction of arrow A. Figure 2 I~
C is a diagram showing the molten state in the vicinity of electrodes 2 to 4, and the shaded area in the diagram indicates the molten part.
In this welding method, the arc pressure of each electrode is set relatively low and welding is performed multiple times using a small current arc, which has a high preheating effect on electrodes 2 and 3 and reduces the amount of melting. It is an effective welding method to obtain.

However, this welding method has the disadvantage that it is extremely difficult to balance the arc current values of each electrode, and requires considerable skill to perform stable welding. The drawback was that the speed could only be improved by about twice as much.

On the other hand, laser welding allows for high speed welding and produces high quality pipes that can be used in demanding applications. However, laser welding requires 2000 per kW.
It costs about 10,000 yen, making it extremely expensive and impractical. For example, welding 3 tons at a speed of 3 m/min or more requires more than 3 kW, which costs nearly 100 million yen.

In view of the above-mentioned circumstances, this invention can be fully applied to applications with severe usage conditions, and moreover,
This method provides a method for manufacturing metal pipes that can achieve high productivity and low production costs, in which a plate-shaped metal member is conveyed in the longitudinal direction and sequentially formed into a cylindrical shape with both ends facing each other. As the metal member is being formed into a cylindrical shape, the metal member is heated by an induction heating coil that is wound around the metal member at a predetermined distance upstream from the V convergence point where both ends of the metal member first come into contact with each other. Preheating the metal member by supplying a high-frequency current at a frequency such that the penetration depth is approximately the same as the thickness of the metal member and at a level that hardly causes melting of the metal member, and further,
Manufacturing a metal pipe in which a joint portion of the metal member downstream of the V convergence point is welded by laser welding means whose output is set so that the depth of heat influence on the metal member is equal to the thickness of the metal member. In the method, the metal member is tightened from both sides with a tightening amount such that both ends of the metal member simply touch between the V convergence point and the molten part in laser welding; On the side, the metal member is tightened from both sides with a tightening amount such that both end portions of the metal member simply come into contact with each other.

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, 10 is an induction heating coil, and the 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 at a predetermined distance upstream from the V convergence point P. 11a and 11b are squeeze rolls whose side surfaces 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 1a of the pipe material 1. This is to prevent them from becoming separated. however,
In this case, the amount of tightening of the squeeze rolls 11a and 11b is such that the amount of pressure applied at the joint portion 1a is approximately 0, that is, the both ends of the pipe material 1 are simply in contact (non-pressure contact state). The tightening amount is set to . A laser nozzle 12 is provided on the downstream side of the squeeze rolls 11a and 11b, and irradiates the joint portion 1a with a laser beam 12a to melt the metal in the irradiated portion. 13a and 13b are squeeze rolls having exactly the same structure as the squeeze rolls 11a and 11b described above, and the laser nozzle 1
It is provided downstream from 2.

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

First, the induction heating coil 10 has a frequency of 10 to 100 KHz.
The pipe material 1 on the upstream side of the V convergence point P is preheated by induction heating. and,
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 thickness). For example, for a stainless steel material with a wall thickness of 3 mm, the high frequency current is set to about 40 KHz. Further, the amount of preheating is set to such an extent that almost no melting of the metal occurs. After preheating, the pipe material 1 is conveyed in the direction of arrow A with the joint 1a kept in contact with the squeeze rolls 11a and 11b, and the joint 1a reaches directly below the laser beam 12a. , the joint 1 directly under the laser beam 12a
a melts. In this case, since the joint portion 1a has already been preheated, a small laser power is sufficient for melting, resulting in significant cost savings. Moreover, the preheating effect improves the flow of the molten metal, and defects such as undercuts are less likely to occur. The molten metal part is cooled and solidified while being transported, but until solidification, the joint part 1a is kept in a contact state (non-pressure contact state) by squeeze rolls 13a and 13b.
is maintained, the joint will not open before solidification, and welding will be completed successfully.

In this embodiment, the laser welding is performed behind the squeeze rolls 11a and 11b, because if the electrical contact of the joint 1a is not firmly secured in this way, it may be damaged by the molten metal. This is because the convergence point changes and heating becomes unstable.

In addition, in this embodiment, squeeze roll 1
Since the amount of pressure applied to 1a, 11b and 13a, 13b is small (approximately 0 at the joint 1a), the bead does not pop out, so cutting the pop-out bead is not necessary, and only polishing work using endless sandpaper etc. Finishing is completed and production can be carried out with high efficiency.

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, , pipe material 1
Shield both the interior and exterior surfaces of the

The jigs 20, 20 shown in FIG. 4 have a shape as shown in FIG. 5 when viewed from below, and the pipe line 20
The shielding gas sent into the holes 20a and 20a enters the hollow cylindrical gas chamber 20b, and then enters the hole 20a.
c, 20c... Reference numeral 20d denotes a semi-cylindrical cover portion, which allows the shielding gas released from the holes 20c, 20c, . . . to stay near the outer periphery of the pipe material 1. And this jig 2
0,20 is the induction coil 10 as shown in FIG.
and the laser nozzle 12 and the laser nozzle 12
installed on the downstream side of Note that the jig 20 on the downstream side
has the 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 the upper part.
... are provided from the position of the induction heating coil 10 to the downstream side of the laser nozzle 12, that is, the position facing the jigs 20, 20 shown in FIG. When the shielding gas is inserted into this jig 25 in the direction shown by the broken line arrow, the holes 25a, 25
Shielding gas is released upward from a...
Thereby, the inner surface of the pipe material 1 is shielded.

As explained above, according to the present invention, between the V convergence point where both ends of a metal member being formed into a cylindrical shape first come into contact with each other and the fusion zone in laser welding, both ends of the metal member are simply Tighten the metal member from both sides to the extent that they touch each other, and further tighten the metal member from both sides to the extent that both ends of the metal member simply touch each other on the downstream side of the fusion zone. Since it is tightened, the bead does not pop out when tightening both ends of the metal member. Therefore, there is no need to cut the protruding bead, and finishing can be completed only by polishing using endless sandpaper, allowing for efficient production.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram showing an example of a conventional welded pipe manufacturing apparatus, and FIGS. 2A to 2C are schematic diagrams showing welding states near electrodes 2, 3, and 4 shown in FIG.
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. 4 to 6 are perspective views showing an example of a jig for performing gas shielding in the same embodiment. It is. 1... Pipe material (metal member), 1a... Joint part,
10...Induction heating coil, 11a, 11b...Squeeze roll, 12...Laser nozzle, 13a,
13b...Squeeze roll, P...V convergence point, 2
0,25...Jig. applicant

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 ends thereof face each other, and both ends of the metal member that is being formed into a cylindrical shape are an induction heating coil wound around the metal member at a predetermined distance upstream from the V convergence point where it first contacts the metal member, at a frequency such that the heating penetration depth into the metal member is approximately the thickness of the metal member, and The metal member is preheated by supplying a high frequency current to an extent that almost no melting of the metal member occurs, and the joint portion of the metal member downstream of the V convergence point is heated to a depth of heat influence on the metal member. In the manufacturing method of a metal pipe, the metal pipe is welded by a laser welding means whose output is set so that the thickness of the metal member becomes the wall thickness of the metal member, in which both ends of the metal member are Tighten the metal member from both sides with a tightening amount such that the metal members simply touch each other, and further tighten the metal member with a tightening amount such that both ends of the metal member simply touch on the downstream side of the molten part. A method of manufacturing metal pipes characterized by tightening from both sides. 2. A part of the metal member that is downstream of the induction heating part and the melted part in the laser welding and is expected to discolor is gas-shielded on both the front and back of the metal member. A method for manufacturing a metal pipe according to scope 1.