JP3566862B2 - Plasma welding of small diameter pipes - Google Patents

Description

【００２３】
実験Ｎｏ．１〜４は、本発明の実施例を示し、実験Ｎｏ．５〜７は比較例を示す。実験Ｎｏ．１は、溶接速度１．５ｍ／ｍｉｎ で後アースのみ使用し、成形スタンドおよびスクイズスタンドの絶縁はない場合である。実験Ｎｏ．２は、溶接速度１．５ｍ／ｍｉｎ 前アースの位置と後アースの位置をトーチから各２０ｃｍにし、成形スタンドおよびスクイズスタンドを架台から絶縁し、可変抵抗値Ｌを３０ｃｍにした場合である。実験Ｎｏ．３は、３．０ｍ／ｍｉｎ で前アースの位置を３０ｃｍ、後アースの位置を２０ｃｍにし、成形スタンドおよびスクイズスタンドを絶縁し、可変抵抗値を７０ｃｍにした場合である。実験Ｎｏ．４は、実験Ｎｏ．３の前アース、後アースおよび可変抵抗値を変更した場合である。これらはいずれもハンピング、アンダーカット等のビード不良はなく、伸線しても断線しなかった。この結果からトーチとアース間の距離が変わっても可変抵抗器の距離Ｌを変更することにより溶接条件に合わせたアーク方向が容易に得られている。
【００２４】
比較例の実験Ｎｏ．５は、陽極をスクイズスタンドにとった場合であるが、溶接速度が１．０ｍ／ｍｉｎ と低速で、低電流のため軸受などの影響をあまり受けず、ビード形状、伸線結果も良好であった。
【００２５】
しかし、この方法では実験Ｎｏ．６に示すように１．５ｍ／ｍｉｎ になるとビード不良が発生し伸線中に断線する。また、実験Ｎｏ．７では陽極に前アースと後アースをトーチから各２０ｃｍに設けているが、成形スタンドとスクイズスタンドに架台からの絶縁が施されてないのでビード不良と伸線中の断線が発生した。
【００２６】
【発明の効果】
以上のように本発明によれば、プラズマアークの方向が安定するので、溶込み不足、ビード不良が減少する。また、プラズマアーク方向が容易にかつ任意に選べるので、必要な溶込み深さおよびビード形状に応じて適正条件が簡単に得られることから、品質が安定し、不良率が減少し、溶接速度もアップできる小径管の製造方法を提供することができる。
【図面の簡単な説明】
【図１】本発明のプラズマ溶接方法を示す模式図である。
【図２】本発明の電気等価回路図である。
【図３】可変抵抗器の模式図である。
【図４】本発明を実施する装置の構成を示す模式図である。
【図５】各工程におけるフープの成型状態を示す断面図である。
【図６】従来のプラズマ溶接部の拡大模式図である。
【図７】従来の電気等価回路である。
【符号の説明】
１．プラズマ電源
２．スクイズロールスタンド
３．スクイズロール軸受
４．スクイズロール軸
５．スクイズロール
６．トーチ
７．プラズマアーク
８．成形スタンド
９．成形ロール軸受
１０．成形ロール軸
１１．成形ロール
１２．後アース
１３．前アース
１４．可変抵抗器
１５．架台
１６．絶縁板
１７．固定端
１８．可動端
１９．丸棒
２１．アンコイラー
２２．フープ洗浄装置
２３．成形ロール群
２４．サイドロール
２５．フラックス供給機
２６．フィンパスロール
２７．シームガイドロール
２８．プラズマ溶接装置
２９．冷却装置
３０．絞りロール群
３１．巻き取り機
３２．フラックス
３３．シーム部
Ａ．フープ
Ｂ．Ｕ形管
Ｃ．オープンシーム管
Ｄ．溶接管
Ｅ．縮径後の溶接管
Ｒ１ ．スクイズロールスタンド
Ｒ２ ．スクイズロール軸
Ｒ３ ．スクイズロール軸受
Ｒ４ ．スクイズロール
Ｒ５ ．溶接管
Ｒ６ ．架台
Ｒ７ ．成形ロールスタンド
Ｒ８ ．成形ロール軸
Ｒ９ ．成形ロール軸受
Ｒ１０．成形ロール
Ｒ１１．オープンシーム管
Ｒ２０．後アースと溶接管の接触抵抗
Ｒ２１．後アースとトーチ間の溶接管の抵抗
Ｒ２２．前アースとオープンシーム管の接触抵抗
Ｒ２３．前アースとトーチ間のオープンシーム管の抵抗
Ｒ２４．可変抵抗[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for producing a small-diameter pipe using a plasma welding method, and particularly relates to a plasma welding method for producing a small-diameter pipe using a high current and a large current.
[0002]
[Prior art]
Plasma welding was used for welding small diameter pipes, but the plasma welding current was increased and the pipe forming speed was increased in order to improve the productivity of small diameter pipes. However, the direction of a plasma arc (hereinafter, referred to as an arc) cannot be controlled, and the arc is unstable, so that a good weld bead cannot be obtained, and there is a limit in improving the pipe forming speed.
[0003]
For example, in a method of manufacturing a flux-cored wire for welding by plasma welding, a hoop is formed as needed from a U-shape to an O-shape 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. Next, 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.
[0004]
In the production of the flux-cored wire by the 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 when performing plasma welding is adopted. 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), and a ground wire la of an anode is connected to a squeeze stand 2 on a gantry 15 as shown in FIG. Connect to. In this method, there is no problem in low-current pipe forming at a low current, but in high-speed pipe forming at a large current, irregularities in penetration depth, bead defects such as 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 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 becomes main. However, on the gantry 15, there is a forming stand 8 on the upstream side of the torch 6 for forming an open seam pipe C having a small edge-to-edge distance suitable for welding, and from the squeeze roll stand 2 to the gantry 15, the forming stand 8, There is also a current Ib flowing from the open seam tube C to the torch 6 via the forming roll shaft 10, the bearing 9, and the forming roll 11.
[0006]
Since the bearing contains grease having a large electric resistance, and the contact state varies, the electrical resistance varies, so that the current Ia and the current Ib are likely to fluctuate. 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 welding tube, R6 is a stand, R7 is a forming roll stand, R8 is a forming roll shaft, and R9 is a forming roll. A bearing, R10 indicates a forming roll, and R11 indicates 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 considerably smaller than the resistance R11 of the open seam pipe, the current Ia is larger than the current Ib. The resistances R3 and R9 of the bearing are the same as the variable resistance that constantly varies. Therefore, the current Ia and the current Ib tend to fluctuate.
[0007]
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). That is, according to Fleming's left-hand rule, when the current Ia is larger than the current Ib, the arc is deflected upstream, and when the current Ia is smaller than the current Ib, the arc is deflected downstream. When the current Ia is equal to the current Ib, the current Ia is directed toward the torch 6 without being deflected.
[0008]
The penetration depth of the welded portion differs depending on the direction of the arc, and is the largest when it is inserted into the pipe to be welded at a right angle. The penetration depth decreases as the angle of deviation from the right angle increases. When the arc is deflected to the upstream side, the bead appearance becomes smooth, and when 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 arc becomes strong and the effect becomes remarkable. For the above-described reasons, in high-speed pipe forming with a large current, bead defects such as variation in penetration depth, undercut, and humping occur.
[0009]
[Problems to be solved by the invention]
In view of the above, the present invention provides a plasma welding tube forming method using a large current in high-speed welding, while preventing variations in the plasma arc direction and adjusting the plasma arc direction to easily obtain an appropriate penetration depth and bead shape. It is intended to provide a plasma welding pipe forming method for a small-diameter pipe which can be performed.
[0010]
[Means for Solving the Problems]
The plasma welding method for forming a small-diameter pipe according to the present invention is a method for forming a metal band into a U-shaped body, and then performing plasma welding on both edge surfaces of the tubular body formed into an open seam pipe. Is used to connect the plasma torch to the cathode and the rear ground for the anode of the welded pipe directly to the welded pipe downstream of the plasma torch.
[0011]
In the present invention, most of the current downstream of the plasma torch passes from the rear ground to the plasma torch through the pipe to be welded without passing through the bearing, the squeeze roll shaft, and the squeeze roll. Since the resistance of the downstream circuit is smaller than the resistance of the upstream circuit passing through the molding stand, the downstream current is also larger than the upstream current. For this reason, the plasma arc is directed more upstream. In addition, since the downstream current hardly passes through the bearing, the plasma arc is stable with no direction variation.
[0012]
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 welded pipe and a rear ground on the downstream side with the plasma torch interposed therebetween, and is located between the front ground and the rear ground. It is also possible to insulate between the roll stand and the gantry, insert a variable resistor in the circuit between the front ground and the plasma welding power source, and adjust the variable resistor so as to obtain a required plasma arc.
[0013]
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.
[0014]
The above-mentioned plasma welding pipe forming method comprises forming a metal band into a U-shaped body, supplying the U-shaped body with the powdered body, forming the metal body into a tubular body, and plasma-welding both edge surfaces of the tubular body. It can be used for the production of filling tubes. As the powder, a welding flux, a steelmaking additive, or the like is used.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 is a schematic view showing the plasma welding method of the present invention. The open seam pipe C formed by the forming roll 11 so that the distance between 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.
[0016]
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 12 directly contacting the welding pipe D on the downstream side of the squeeze roll 5, and the open seam pipe C before the forming roll. To the front ground 13 which is a pressing shoe made of a copper plate that directly contacts the ground. As described above, the molding stand 8 and the squeeze stand 2 are unstable due to the bearings 3 and 9 interposed therebetween. 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 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 is easily obtained by changing the distance L between the 18.
[0017]
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 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.
[0018]
The contact resistances R22 and R20 of the front ground 13 and the rear ground 12 are configured to press the shoe with a sufficient pressure by a spring (not shown) so as to be stable. Therefore, by adjusting the variable resistor R24, it is possible to stabilize the plasma arc 7 in an arbitrary direction without directing the direction of the plasma arc to the downstream side where the bead failure occurs, so that the penetration depth and the bead shape can be adjusted. Become.
[0019]
FIG. 4 is a schematic view showing a configuration 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 washing device 22, the U-shaped tube B is formed by the forming roll group 23, and the flux 32 is put between the side rolls 24 by the flux supply device 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 apparatus 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, 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 axial direction in the pipe E, and finally the coiled shape is formed by the winding machine 31. 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.
[0020]
The present invention is suitable for manufacturing 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]
【Example】
An embodiment in which the present invention is applied to a small-diameter pipe plasma welding pipe forming method 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 1.2 mm thick and 23.0 mm wide
(2) Outer diameter of welding 8mm
(3) Diameter 6mm
(4) Flux composition metal type Filling rate 19%
(5) Pilot gas component Ar + 7% H2 flow rate See Table 1 (6) Shield gas component Ar flow rate 10 l / min
(7) Torch advance angle 10 °
(8) Variable resistor round bar Material SS41 on the market Dimension φ6mm
(9) Wire drawing after pipe forming Die wire drawing with φ10 mm at approximately 10% / pass reduction rate
[Table 1]

[0023]
Experiment No. 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 each set to 20 cm from the torch, the forming stand and the squeeze stand are insulated from the gantry, and the variable resistance value L is set to 30 cm. Experiment No. No. 3 is a case where the front ground position was set to 30 cm and the rear ground position was set to 20 cm at 3.0 m / min, the forming stand and the squeeze stand were insulated, and the variable resistance value was set to 70 cm. Experiment No. Experiment No. 4 is Experiment No. 4. 3 is a case where the front ground, the rear ground, and the variable resistance value are changed. All of these did not have bead defects such as humping and undercut, and did not break even when 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.
[0024]
Experiment No. of the comparative example. No. 5 shows a case where the anode was taken on a squeeze stand. The welding speed was as low as 1.0 m / min, and the current was low, so it was not much affected by bearings and the like, and the bead shape and wire drawing results were good. Was.
[0025]
However, in this method, experiment No. As shown in FIG. 6, when the speed becomes 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, respectively. However, since the molding stand and the squeeze stand were not insulated from the gantry, bead failure and disconnection during wire drawing occurred.
[0026]
【The invention's effect】
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 of 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. 1. Plasma power supply 2. Squeeze roll stand 3. Squeeze roll bearing 4. Squeeze roll shaft Squeeze roll6. Torch 7. Plasma arc8. Forming stand 9. Formed roll bearing 10. Forming roll shaft 11. Forming roll 12. Rear ground 13. Front ground 14. Variable resistor 15. Stand 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 path roll 27. Seam guide roll 28. Plasma welding device 29. Cooling device 30. Squeezing roll group 31. Winding machine 32. Flux 33. Seam part A. Hoop B. U-shaped tube C. Open seam tube D. Welded pipe E. Welded pipes R1. Squeeze roll stand R2. Squeeze roll axes 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 the rear ground and the welded pipe R21. Resistance of weld 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

Claims (4)

In a welding pipe forming method in which a metal band is formed into a U-shaped body, and then both edge surfaces of the tubular body formed into an open seam pipe are plasma-welded, a plasma torch is used as a cathode using a plasma welding power source, and a pipe to be welded is used. A method for producing a small-diameter pipe by plasma welding, wherein a rear earth for use as an anode is directly connected to a pipe to be welded downstream of a plasma torch. The anode of the plasma welding power source has two points, a front ground on the upstream side of the pipe to be welded and a rear ground on the downstream side with a plasma torch in between. 2. The plasma welding method according to claim 1, wherein a variable resistor is inserted into a circuit between the front ground and the plasma welding power source, and the variable resistor is adjusted so as to obtain a required plasma arc. Tube method. 3. The metal band is formed into a U-shaped body, and after supplying the granular material 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. Of small diameter pipe by plasma welding. 4. The method of claim 1, 2 or 3, wherein the metal strip is formed into a U-shaped body, and the powder to be filled in the U-shaped body is a welding flux.

Images