JP2000117448A - Plasma welding of small diameter pipes - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a small-diameter plasma welded tube capable of easily obtaining an appropriate penetration depth and a bead shape by adjusting a plasma arc direction while preventing a variation in a plasma arc direction. Provide a way. SOLUTION: In a welding pipe forming method in which a metal band is formed into a U-shaped body and then both edge surfaces of a tubular body C formed into an open seam pipe are plasma-welded, a plasma welding power source 1 is provided.
The rear earth 12 for directly using the plasma torch 6 as a cathode and the pipe D to be used as an anode is directly connected to the pipe D to be welded downstream of the plasma torch 6.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a small-diameter tube using a plasma welding method, and more particularly to a plasma welding method for producing a small-diameter tube using a high current at a high welding speed.

[0002]

2. Description of the Related Art Plasma welding has been used for welding small-diameter pipes. However, in order to improve the productivity of small-diameter pipes, the current of plasma welding has been increased to increase the pipe-making speed. However, the direction of a plasma arc (hereinafter, referred to as an arc) cannot be controlled, and the arc is unstable, and a good weld bead cannot be obtained.

For example, in a method of manufacturing a flux cored wire for welding by plasma welding, a hoop is formed from a U-shape to an O-shape as needed by a forming roll. During this molding, the flux is supplied to the hoop U-shaped valley by a feeder from an opening along the longitudinal direction of the U-shaped hoop. Then, the U-shaped hoop is formed into an O-shaped open seam tube, and at the same time, the opposite edge surfaces of the opening are joined by plasma welding and subsequently reduced in diameter. Further, if necessary, after annealing, the welded tube filled with the flux is drawn to a desired diameter and wound to obtain a product.

In the production of a flux-cored wire by the above-mentioned plasma welding, a method of using a plasma torch (hereinafter referred to as a torch) as a cathode and an open seam tube as an anode is used for plasma welding. Specifically, as shown in FIG. 6, a ground of a cathode is connected to a torch 6 from a plasma welding power source 1 (hereinafter referred to as a power source) as shown in FIG. Connect to In this method, there is no problem in low-current pipe forming at low current, but in high-speed pipe forming at high current, bead defects such as variation in penetration depth, undercut, and humping occurred. As a result of intensive investigations, the present inventors considered the following causes.

[0005] When the anode is grounded to the squeeze roll stand 2, the current Ia mainly flowing from the welding pipe D to the torch 6 via the squeeze roll shaft 4, the squeeze roll bearing 3, and the squeeze roll 5. However, on the gantry 15 there is a forming stand 8 on the upstream side of the torch 6 for forming an open seam tube C having a small edge-to-edge distance suitable for welding.
5, a current Ib flowing from the open seam tube C to the torch 6 via the forming stand 8, the forming roll shaft 10, the bearing 9, and the forming roll 11 also exists.

The current Ia and the current Ib are liable to fluctuate because the bearing contains grease having a high electric resistance and the electric resistance varies due to the variation in the contact state. FIG. 7 shows an electric equivalent circuit in this state. Here, R1 is a squeeze roll stand, R2 is a squeeze roll shaft, R3 is a squeeze roll bearing, R4 is a squeeze roll, R5 is a welded pipe, R6 is a stand, R7 is a forming roll stand, R8 is a forming roll shaft, and R9 is a forming roll. Bearings, R10 are forming rolls, and R11 is each resistance of the open seam pipe. Since the squeeze roll stand 2 is located at the shortest distance from the torch 6, and the resistance R5 of the welded pipe is much smaller than the resistance R11 of the open seam pipe, the current Ia is larger than the current Ib. Also,
The bearing resistances R3 and R9 are the same as the constantly varying variable resistance. Therefore, current Ia and current Ib are likely to fluctuate.

On the other hand, the direction of the arc is greatly affected by the current flowing through the pipes to be welded (showing the open seam pipe C and the welded pipe D). In other words, according to Fleming's left-hand rule,
When current Ia is greater than current Ib, the arc is deflected upstream, and when current Ia is less than current Ib, the arc is deflected downstream. When the current Ia is equal to the current Ib, the current is directed to the torch 6 without being deflected.

The penetration depth of the welded portion differs depending on the direction of the arc. The penetration depth is the largest when it is inserted into the pipe to be welded at a right angle, and the penetration depth decreases as the angle of deviation from the right angle increases. If the arc is deflected to the upstream side, the bead appearance becomes smooth, and if the arc is deflected to the downstream side, a bead defect such as undercut or humping tends to occur. When the current becomes large,
The effect becomes remarkable because the arc becomes strong. For the above-mentioned reasons, in high-speed pipe making with a large current, bead defects such as variation in penetration depth, undercut, and humping occur.

[0009]

SUMMARY OF THE INVENTION Accordingly, the present invention provides a plasma welding pipe forming method using a large current in high speed welding.
An object of the present invention is to provide a plasma welding pipe forming method for a small-diameter pipe capable of preventing variation in a plasma arc direction and adjusting a plasma arc direction to easily obtain an appropriate penetration depth and a bead shape.

[0010]

According to the method of the present invention for forming a small-diameter tube by plasma welding, a metal band is formed into a U-shaped body, and then both edges of the tubular body formed into an open seam tube are plasma-welded. In the welding pipe forming method, a plasma torch is used as a cathode using a plasma welding power source, and a rear ground for using the pipe to be welded as an anode is directly connected to the pipe to be welded downstream of the plasma torch.

In the present invention, most of the current downstream of the plasma torch does not pass through the bearing, the squeeze roll shaft, and the squeeze roll, but from the rear ground to the plasma torch through the pipe to be welded. Since the resistance of the downstream circuit is smaller than the resistance of the upstream circuit via the molding stand,
The downstream current also becomes larger than the upstream current. For this reason, the plasma arc is directed more upstream. Also, since the downstream current hardly passes through the bearing,
The plasma arc is stable without variation in direction.

In the above-described plasma welding tube forming method, the anode of the plasma welding power source is provided with two points, a front ground on the upstream side of the pipe to be welded and a rear ground on the downstream side, with the plasma torch interposed therebetween. It may be possible to insulate between the roll stand and the gantry in between and further insert a variable resistor in the circuit between the front ground and the plasma welding power supply to adjust the variable resistor so as to obtain the required plasma arc. .

According to the present invention, the direction of the plasma arc can be finely adjusted by the variable resistor, whereby the penetration depth and the bead shape can be adjusted.

In the above-mentioned plasma welding pipe forming method, the metal strip is
After forming into a U-shaped body and supplying the U-shaped body with the granular material, the U-shaped body can be formed into a tubular body and used for the production of a granular material filling tube in which both edge surfaces of the tubular body are plasma-welded. As the powder, a welding flux, a steelmaking additive, or the like is used.

[0015]

FIG. 1 is a schematic view showing a plasma welding method according to the present invention. The open seam pipe C formed by the forming roll 11 so that the distance between the edges is sufficiently small for plasma welding is welded to the seam portion 33 (see FIG. 5) by the arc 7 from the torch 6 to form a welded pipe D. Immediately thereafter, the squeeze roll 5 holds the welded portion until it is solidified by cooling and cannot be opened.

The ground of the cathode from the power source 1 is taken to the torch 6, and the ground of the anode is made of a copper plate pressing shoe directly contacting the welding pipe D on the downstream side of the squeeze roll 5, and an open ground before the forming roll. It is taken to the front ground 13 which is a pressing shoe made of a copper plate which directly contacts the seam pipe C. As described above, the molding stand 8 and the squeeze stand 2 are unstable because of the bearings 3 and 9, so they are insulated from the gantry 15 by the insulating plate 16. A variable resistor 14 is provided between the power supply 1 and the front ground 13 so that the direction of the arc 7 is on the downstream side and a bead failure does not occur, and the current Ib from the front ground 13 side is made larger than the current Ia flowing through the welding pipe D. Make it smaller. As shown in FIG. 3, the variable resistor 14 has a fixed end 17 connected from a power source (not shown) and a movable end connected to a front ground (not shown) using a round bar 19 of substantially the same cross-sectional area and the same material as the welding pipe D, as shown in FIG. It can be obtained simply by changing the distance L between the 18.

FIG. 2 shows an electric equivalent circuit. The current Ia from the downstream side of the torch 6 in FIG. 1 is inversely proportional to the contact resistance R20 between the rear ground 12 and the welding pipe D, and the resistance R21 of the welding pipe D between the rear ground 12 and the torch 6, and the upstream opening of the torch 6 is open. The current Ib flowing through the seam tube C is inversely proportional to the contact resistance R22 between the front ground 13 and the open seam tube C, the resistance R23 of the open seam tube C between the front ground 13 and the torch 6, and the variable resistance R24.

The contact resistances R22 and R20 between the front ground 13 and the rear ground 12 are structured so that the shoe is pressed with a sufficient pressure by a spring (not shown) so as to be stable. Therefore, by adjusting the variable resistor R24, the direction of the plasma arc 7 can be stabilized in an arbitrary direction without being directed to the downstream side where bead failure occurs, so that the penetration depth and the bead shape can be adjusted. Become.

FIG. 4 is a schematic view showing the structure of an apparatus for carrying out the present invention, and FIG. 5 is a cross-sectional view showing a state of forming a hoop in each step. The hoop A is unwound from the coil shape by the uncoiler 21, the dirt is removed by the cleaning device 22, and is formed into the U-shaped tube B by the forming roll group 23.
The flux 32 is introduced between the side rolls 24 by the flux feeder 25. Further, plasma welding is performed by a plasma welding device 28 via a fin pass roll 26 and a seam guide roll 27. The plasma welding device 28 forms an open seam pipe C having a seam distance of about 0.1 mm with the forming roll 11, plasma-welds the seam portion 33 with the torch 6, forms a weld pipe D, and welds with the squeeze roll 3. Hold until the strength of the part is sufficient. Thereafter, the welded pipe is cooled by the cooling device 29, and the outer diameter is reduced by the squeezing roll group 30 to a sufficient density so that the flux 32 does not move in the pipe axis direction in the pipe E. To Thereafter, the outer diameter is reduced to about 1 mm by a wire drawing machine (not shown).
At that time, annealing, pickling, plating, and the like are performed as necessary.

The present invention is suitable for producing steel pipes having an outer diameter of about 8 to 50 mm, such as ordinary steel and stainless steel. The welding current is a large current of, for example, 100 to 500 A, and the welding speed is a high speed of 1.5 to 10 m / min.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to a plasma welding pipe forming method for a small diameter pipe will be described. The welding method of the example was performed by the method shown in FIG. 1, and the variable resistor was performed by the method of FIG. The welding method of the comparative example was performed by the method shown in FIG. Detailed conditions are shown below and in Table 1. Experimental conditions (1) Hoop used JIS Z-3141 SPCC
(2) Welding outer diameter 8mm (3) Drawing outer diameter 6mm (4) Flux composition metal type Filling rate 19% (5) Pilot gas component Ar + 7% H2 flow See Table 1 (6) ) Shielding gas component Ar flow rate 10 l / min (7) Torch advance angle 10 ° (8) Variable resistor Round bar Material SS41 Dimension φ
6mm (9) Wire drawing after pipe making Die wire drawing at φ10mm with approx. 10% / pass reduction

[0022]

[Table 1]

Experiment No. Nos. 1 to 4 show examples of the present invention. 5 to 7 show comparative examples. Experiment No. 1
Is a case where only the rear ground is used at a welding speed of 1.5 m / min and there is no insulation of the forming stand and the squeeze stand. Experiment No. No. 2 is a case where the position of the front ground and the position of the rear ground are set to 20 cm from the torch, the forming stand and the squeeze stand are insulated from the stand, and the variable resistance value L is set to 30 cm. Experiment No. 3
In the case of 3.0 m / min, the position of the front ground was 30 cm, the position of the rear ground was 20 cm, the molding stand and the squeeze stand were insulated, and the variable resistance value was 70 cm.
Experiment No. Experiment No. 4 is an experiment No. 4. 3 is a case where the front ground, the rear ground, and the variable resistance value are changed. All of these have no bead defects such as humping and undercut,
It did not break even when it was drawn. From this result, even if the distance between the torch and the ground changes, the arc direction according to the welding conditions can be easily obtained by changing the distance L of the variable resistor.

Experiment No. of Comparative Example 5 is a case where the anode was taken on a squeeze stand, and the welding speed was 1.0 m / mi.
Because of the low current and low current, the bearing was not much affected by the low current, and the bead shape and the wire drawing were good.

However, in this method, experiment No. As shown in FIG. 6, at 1.5 m / min, a bead failure occurs and the wire breaks during wire drawing. Experiment No. In No. 7, the front ground and the rear ground were provided on the anode at 20 cm from the torch, however, because the molding stand and the squeeze stand were not insulated from the gantry, bead failure and disconnection during wire drawing occurred.

[0026]

As described above, according to the present invention, since the direction of the plasma arc is stabilized, insufficient penetration and bead failure are reduced. In addition, since the plasma arc direction can be selected easily and arbitrarily, appropriate conditions can be easily obtained according to the necessary penetration depth and bead shape, so that the quality is stable, the defect rate is reduced, and the welding speed is also reduced. It is possible to provide a method for manufacturing a small-diameter pipe that can be increased.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a plasma welding method of the present invention.

FIG. 2 is an electric equivalent circuit diagram of the present invention.

FIG. 3 is a schematic diagram of a variable resistor.

FIG. 4 is a schematic diagram showing a configuration of an apparatus for implementing the present invention.

FIG. 5 is a cross-sectional view showing a hoop molding state in each step.

FIG. 6 is an enlarged schematic view of a conventional plasma weld.

FIG. 7 is a conventional electric equivalent circuit.

[Explanation of symbols]

 1. Plasma power supply 2. 2. Squeeze roll stand 3. Squeeze roll bearing 4. Squeeze roll shaft Squeeze roll 6. Torch 7. 7. Plasma arc Forming stand 9. Formed roll bearing 10. Forming roll shaft 11. Forming roll 12. Rear ground 13. Front ground 14. Variable resistor 15. Mount 16. Insulating plate 17. Fixed end 18. Movable end 19. Round bar 21. Uncoiler 22. Hoop cleaning device 23. Forming roll group 24. Side roll 25. Flux feeder 26. Fin pass roll 27. Seam guide roll 28. Plasma welding device 29. Cooling device 30. Squeezing roll group 31. Winding machine 32. Flux 33. Seam A. Hoop B. U-shaped pipe C. Open seam tube D. Welded pipe E. Reduced diameter of welded pipe R1. Squeeze roll stand R2. Squeeze roll axis R3. Squeeze roll bearing R4. Squeeze roll R5. Welded pipe R6. Stand R7. Forming roll stand R8. Forming roll axis R9. Formed roll bearing R10. Forming roll R11. Open seam tube R20. Contact resistance between rear ground and welded pipe R21. Resistance of welded pipe between rear ground and torch R22. Contact resistance between front ground and open seam tube R23. Open seam tube resistance between front ground and torch R24. Variable resistance

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01R 4/64 H01R 4/64 F (72) Inventor Yuki Kayamori 3-5-4 Tsukiji, Chuo-ku, Tokyo Nippon Steel Welding Industry Co., Ltd. (72) Inventor Yasuki Kusunoki 3-5-4 Tsukiji, Chuo-ku, Tokyo Nippon Steel Welding Industry Co., Ltd. F-term (reference) 4E001 AA02 BB11 CC03 CC04 DC05 DE05 DF09 4E028 CA02 CA13 CA16

Claims (4)

[Claims] 1. A welding method for forming a metal strip into a U-shaped body and then plasma welding both edge surfaces of the tubular body formed into an open seam pipe, wherein a plasma torch is used as a cathode by using a plasma welding power source. A method for producing a small-diameter tube by plasma welding, wherein a rear earth for making the tube to be welded an anode is directly connected to the tube to be welded downstream of the plasma torch. 2. An anode of a plasma welding power source having two points, a front ground on an upstream side of a pipe to be welded and a rear ground on a downstream side with a plasma torch interposed therebetween, and a roll stand between the front ground and the rear ground. 2. The small diameter as claimed in claim 1, wherein a variable resistance is inserted into a circuit between the front ground and the plasma welding power source so as to obtain a required plasma arc. Plasma welding of pipes. 3. The method according to claim 3, wherein the metal band is formed into a U-shaped body, and after the powdery material is supplied to the U-shaped body, the metal band is formed into a tubular body and both edge surfaces of the tubular body are plasma-welded. Item 3. The method for producing a small-diameter tube by plasma welding according to item 1 or 2. 4. The plasma of a small-diameter tube according to claim 1, wherein the metal band is formed into a U-shaped body, and the powder to be filled in the U-shaped body is a welding flux. Welding pipe making method.