JP2003236696A - Method for producing flux cored wire for welding - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a flux cored wire for welding with which even in the case of developing the wear of a plasma arc welding torch or the stuck material onto a tip or an electrode, suitable joined part can be obtained and even after shrinking the diameter, crack on the outer shell of a welding pipe is not developed. <P>SOLUTION: In the method for producing the flux cored wire for welding, with which a steel strip is formed into U-shaped body, and after supplying the flux in the U-shaped body, this body is formed into a pipy body, and after plasma-arc welding both edge surfaces of this pipy body, this diameter is shrunk, a relation between the temperature of weld bead and the depth of penetration formed with the plasma-arc welding, is beforehand obtained, and the depth of penetration is kept to the constant by adjusting welding condition based on the measured result of the temperature in the weld bead. Further, the adjustment of the welding condition is performed with welding current or flow rate of pilot gas. <P>COPYRIGHT: (C)2003,JPO

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 flux-cored wire for welding in which a metal tube such as carbon steel or stainless steel is filled with flux.

[0002]

2. Description of the Related Art In a method for manufacturing a flux-cored seamless wire for welding, a metal strip steel is slit by a required width, and the strip steel strip after slitting is gradually formed into a tubular body from a U-shaped body by a forming roll. During this forming, flux is supplied from the opening along the longitudinal direction of the U-shaped strip steel to the valley portion of the strip steel by the feeder. Then, at the same time as forming the tubular body, the opposite edge surfaces of the opening are joined by welding, and subsequently the diameter is reduced. Further, after being annealed as necessary, the flux-filled welded pipe is drawn into a desired diameter and wound on a spool or the like to obtain a product.

As a welding method in the production of the seamless tube filled with the above-mentioned flux, high frequency welding such as high frequency induction welding method and high frequency resistance welding method and arc welding such as TIG welding are widely used. In high-frequency welding, when the metal strip steel after slitting is formed into a tubular body from a U-shaped body by a forming roll, the edge surface of the opening is heated to the melting temperature by the generated Joule heat, and the opposing edge surfaces are squeezed. Bonded by pressing with a roll. In either case, a strong magnetic field is generated in the vicinity of welding.

By the way, when a pipe filled with flux and welded is reduced in diameter by rolling, wire drawing or the like, cracks may occur in the outer skin of the pipe. The cause of this crack is considered as follows. During welding, a part of the flux of oxides, silicates, iron powder, etc. is adsorbed on the opening edge surface of the tubular body.
That is, at the welding position, the opening edge surface of the tubular body becomes a magnetic pole due to the magnetic field generated by the welding current. Therefore, the ferromagnetic component of the prepared flux is attracted to the opening edge surface by the magnetic force. At this time, the granulated flux is adsorbed on the edge surface of the opening along with the non-magnetic component and the ferromagnetic component. The flux adsorbed on the edge surfaces of the openings is present in the welded portion and becomes a welding defect. This welding defect causes cracks in the welded pipe when the diameter is reduced.

One of the techniques for solving such a problem is JP-A-60-234794, which has a relative magnetic permeability of 1.
Filling with substantially non-magnetic powder of 10 or less powder raw material,
Prevents the powder from being attracted to the opening edge surface by the magnetic force.
In Japanese Patent Laid-Open No. 63-5897, there is 48
Fine powder finer than the mesh is removed to prevent the fine powder from adhering to the opening edge surface. Also, JP-A-54-10
No. 9040 discloses that a powder is supplied so that the tubular body is not filled with the powder, and a gap, that is, a distance is provided between the joint portion and the surface of the supplied powder layer, so that the powder rises to the opening edge surface. I try not to reach it.

On the other hand, in arc welding such as TIG welding or plasma arc welding described in JP-A-58-209500 and JP-A-59-113996, it is necessary to intervene in the welded portion by attraction due to magnetic force on the opening edge surface. However, due to the soaring flux, it hits the weld directly,
The flux becomes trapped and creates welding defects. The flux rises because the welded tubular body heats the entire tubular body by heat conduction, and the air that is rapidly expanded during welding is contained in the tube. As the diameter of the welded pipe is reduced,
The expanded air passes through the welding process and is discharged to the outside, increasing the flux filling rate. If the amount of air discharged at this time is large, the flux rises up, and a part of the flux that rises up when passing through the welding process is caught between the welding edges, resulting in a welding defect. If the diameter of the welded pipe is reduced while the welding defect is inherently present, cracking occurs. Furthermore, this crack causes disconnection in the shrinking process, which causes a decrease in productivity.

As a method for preventing the cracks caused by the rising of the flux, Japanese Patent Laid-Open Nos. 1-40719 and 11 have been proposed.
JP-A-226781 discloses a technique of cooling a welded pipe after welding to prevent backflow of air in the pipe expanded by welding heat.

However, the cracks at the time of diameter reduction are not only caused by the above-mentioned defects due to the flux adsorbed on the edge surface or the flux caught in the edge surface, but in the case of continuous production for a long time, the adhered matter on the welding torch or tip The penetration depth changes due to a change in shape due to wear of the electrode and the electrode, and a defect occurs due to burn-through that a hole is formed in the melted portion or insufficient penetration depth. The melt-through portion causes a disconnection in the subsequent process, and the melt-insufficient portion has a penetration rate of 100 relative to the thickness of the metal strip steel sheet.
If it is less than%, the welded part cannot withstand the post-process diameter reduction processing and cracks occur in the welded part.

In particular, although burn-through can be visually confirmed, insufficient melt-through cannot be visually confirmed. Therefore, if insufficient melt-through occurs, cracks frequently occur in the welded portion in the subsequent process, which causes a large decrease in yield. .

[0010]

DISCLOSURE OF THE INVENTION The present invention can obtain a proper joint even when deposits on the plasma arc welding torch or tip or wear of the electrode occur, and the welded pipe can be obtained even after the diameter is reduced. An object of the present invention is to provide a method for manufacturing a flux-cored wire for welding, which has no cracks on the outer skin.

[0011]

SUMMARY OF THE INVENTION The gist of the present invention is to form a metal strip steel into a U-shaped body, supply a flux to the U-shaped body and then form a tubular body, and to form both edges of the tubular body. In the manufacturing method of the flux-cored wire for welding after the surface is plasma arc welded and then reduced in diameter, the relationship between the temperature and the penetration depth of the weld bead previously formed by plasma arc welding is obtained, and based on the result of the temperature measurement of the weld bead. It is characterized by adjusting welding conditions to adjust the penetration depth.

Further, there is a method of manufacturing a flux-cored wire for welding in which the welding condition is adjusted by the welding current or the pilot gas flow rate.

[0013]

DETAILED DESCRIPTION OF THE INVENTION The present invention will be described in detail with reference to the drawings. FIG. 1 (a) is a schematic view of an apparatus for manufacturing a flux-cored wire for welding using plasma arc welding, and FIG. 1 (b) is a cross-sectional view showing a forming state of a metal strip steel in each step. Metal strip steel 1, A is uncoiler 2
It is supplied by the molding roll group 4 through the looper 3 and is molded into a U-shaped body B. Then, the flux 14 is supplied between the side rolls 5 by the flux supply device 6 to fill the U-shaped body tube C.

The U-shaped body C filled with the flux passes through the fin pass roll 7 and the first squeeze roll 8 to become a tubular body D immediately before welding, which is welded by a plasma arc welding machine 9 to form a welded pipe E. . After that, the second squeeze roll 1
After 0, it is reduced to a predetermined outer diameter by the reduced diameter roll group 12,
The coiler 13 winds it into a coil. After that, the wire diameter is reduced to a product diameter (about 0.8 to 2.0 mm) by a wire drawing machine (not shown). At that time, if necessary, annealing, pickling, plating, etc. are performed.

In the present invention, after the plasma arc welding, the bead temperature surface temperature is measured by the radiation thermometer 11, the relationship between the bead temperature and the penetration depth is obtained in advance, the suitable bead temperature range is determined, and the result is obtained. Adjust the welding conditions.

The relationship between the bead temperature and the penetration depth is shown in FIG. The used metal strip steel has a SPCC plate thickness of 1.2 mm and a plate width of 23.0 mm specified in JIS G3141, and other conditions are shown in Table 1. As a result of changing the bead temperature and inspecting the penetration depth, assuming that the penetration to the bottom of the edge surface (total plate thickness) is 100%, the penetration depth is 60% at a bead temperature of 680 ° C and the bead temperature is 74
80% at 0 ° C. and 100% at a bead temperature of 780 ° C. It can be seen that there is a relationship that the penetration depth increases as the bead temperature increases. Therefore, the penetration depth can be controlled by measuring the bead temperature after welding and adjusting the welding conditions based on the measurement result.

[0017]

[Table 1]

FIG. 3 shows the relationship between the welding current and the bead temperature (penetration depth). The test conditions are shown in Table 1. The bead temperature was investigated when the welding current was changed to 240 A, 260 A, and 280 A while the pilot gas flow rate was kept constant at 1.2 liter / min. When the welding current is increased, the bead temperature rises and the penetration deepens. Therefore, the penetration depth can be controlled by measuring the bead temperature and adjusting the welding current based on the measurement result.

FIG. 4 shows the relationship between the pilot gas flow rate and the bead temperature (penetration depth). The test conditions are shown in Table 1. The welding current is kept constant at 280A, and the pilot gas flow rate is 0.8 liter / min, 1.0 liter / min, 1.2.
The relationship between the bead temperature and the penetration depth when changing to liter / minute was investigated. It is observed that increasing the pilot gas flow rate raises the bead temperature and deepens the penetration. Therefore, the penetration depth can be controlled by measuring the bead temperature and adjusting the pilot gas flow rate based on the measurement result.

In the manufacturing by plasma arc welding, if the manufacturing is carried out for a long time, the penetration depth changes due to subtle changes such as deposits on the tip and wear of the electrode. However, measuring the bead temperature near the welding point By adjusting the welding conditions such as the welding current or the pilot gas flow rate from the measurement result, it is possible to maintain the appropriate penetration depth continuously for a long time.

Since the absolute value of the bead temperature changes depending on the thickness of the metal strip steel plate, the welding speed, and the temperature measurement position, it is necessary to investigate the appropriate bead temperature allowable range in advance.
The measurement position of the bead temperature is preferably 20 to 200 mm downstream from the welding point where the relationship with the special depth is most clear.

[0022]

Example 1 First, a flux-cored wire was manufactured using the welding flux-cored wire manufacturing apparatus shown in FIG.

The radiation thermometer used has a measurement temperature range of 6
00 to 1600 ° C, resolution: 1 ° C, response speed: 0.02
sec, focal length; 1000 mm to infinity, measurement field of view; minimum diameter of 4 mm was used, and measurement was made at a position of 40 mm downstream from the welding point.

The metal strip steel used is SPCC plate thickness 1.2 mm, plate width 23.0 mm defined by JIS G3141, welding current at the start of plasma arc welding production; 290 A,
The pilot gas flow rate is 1.2 liters / minute, and the other conditions are as shown in Table 1. From the relationship between the bead temperature and the penetration depth obtained in advance, the penetration depth is 100
% Lower limit of bead temperature obtained is 900 ° C., upper limit is 1000 ° C.
The bead temperature was measured over the entire length in the longitudinal direction of the pipe, and the bead temperature was adjusted by increasing or decreasing the welding current from the measurement result of the bead temperature to continuously manufacture for 12 hours. As a result, it was possible to manufacture without causing burn-through, and as a result of examination with a full length eddy current flaw detector after reducing the diameter to 1.6 mm, there was no crack in the weld.

As a comparative example, as a result of manufacturing under constant welding conditions without performing the above-mentioned bead temperature measurement, burn-through occurred 30 minutes after the start of manufacturing, and the welding heat input amount was lowered to manufacture for 3 hours as a preventive measure. As a result of examination with a full length eddy current flaw detector after reducing the diameter to 1.6 mm, there were many weld cracks due to insufficient penetration.

[0026]

Example 2 Similar to Example 1, a flux-cored wire for welding stainless steel was produced using the apparatus for producing a flux-cored wire for welding shown in FIG. 1 and the radiation thermometer described above.

The metal strip steel used is a SUS304 steel sheet having a thickness of 0.8 mm and a sheet width of 23.7 specified in JIS G4305.
mm, welding current of plasma arc welding: 170 A, pilot gas flow rate at the start of production 1.1 liter / min, and other conditions are as shown in Table 1. From the relationship between the bead temperature and the penetration depth obtained in advance. The lower limit of the bead temperature at which the penetration depth is 100% is 780 ° C. and the upper limit is 88.
Measure the bead # temperature at 0 ° C over the entire length in the longitudinal direction of the pipe,
It was continuously manufactured for 12 hours while adjusting the bead temperature by adjusting the flow rate of the pilot gas based on the measurement result of the bead temperature. As a result, 1.2mm can be manufactured without burn-through.
As a result of examination with a full length eddy current flaw detector after reducing the diameter to the diameter, there was no crack in the weld.

As a comparative example, as a result of manufacturing under constant welding conditions without performing the above-mentioned bead temperature measurement, one hour after the start of manufacturing, burn through occurred, and as a preventive measure, the welding heat input amount was lowered and the manufacturing was carried out for 5 hours. However, as a result of examination with a full length eddy current flaw detector after reducing the diameter to 1.2 mm, there were many weld cracks due to insufficient penetration.

[0029]

As described above, according to the method for manufacturing a flux-cored wire for welding of the present invention, even if it is manufactured continuously for a long time, the welded pipe outer shell does not crack due to insufficient penetration into the welded portion after the diameter reduction. Flux-cored wire for welding can be manufactured.

[Brief description of drawings]

FIG. 1A is a schematic view of a welding flux-cored wire manufacturing apparatus, and FIG. 1B is a schematic cross-sectional view from a metal strip steel to a welding flux-cored wire in each step of the present invention.

FIG. 2 is a diagram showing a relationship between a bead temperature and a penetration depth.

FIG. 3 is a diagram showing a relationship between a welding current, a bead temperature, and a penetration depth.

FIG. 4 is a diagram showing a relationship among a pilot gas flow rate, a bead temperature, and a penetration depth.

[Explanation of symbols]

1 Metal strip steel 2 Uncoiler 3 looper 4 forming rolls 5 side rolls 6 Flux supply device 7 fin pass roll 8 first squeeze roll 9 Plasma arc welder 10 Second Squeeze Roll 11 Radiation thermometer 12 Reduced roll group 13 coilers 14 Flux A metal strip steel B U shape C U-shaped body after flux filling D Tubular body before welding E welded pipe F Filling tube after diameter reduction

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Yuki Kajimori             7-6-1, Higashi Narashino, Narashino, Chiba Prefecture             Nittetsu Welding Co., Ltd. Narashino Factory F-term (reference) 4E001 AA03 BB11 CA01 CA03 CC03                       EA01 EA08

Claims (3)

[Claims] 1. A metal strip steel is formed into a U-shaped body, a flux is supplied to the U-shaped body, then formed into a tubular body, and both edge surfaces of the tubular body are plasma arc welded and then reduced in diameter. In the method for manufacturing the flux-cored wire for welding, the relationship between the temperature and the penetration depth of the welding bead formed by plasma arc welding is obtained in advance, and the penetration depth is adjusted by adjusting the welding conditions based on the temperature measurement result of the welding bead. A method for manufacturing a flux-cored wire for welding, which is characterized by making it constant. 2. The method for producing a flux-cored wire for welding according to claim 1, wherein the adjustment of the welding condition is a welding current. 3. The method for producing a flux-cored wire for welding according to claim 1, wherein the adjustment of the welding condition is a pilot gas flow rate.