JPH11226781A - Manufacture of flux cored wire for welding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of a flux cored wire for welding without developing the crack on the outer shell of a welding tube by obtaining a sound edge joining part. SOLUTION: In the manufacturing method of the flux cored wire for welding, in which a metallic strip is formed as a U-shaped body and after supplying powdery and granular material in the U-shaped body, this U-shaped body is formed as a tubular body and both edge surfaces of the tubular body are welded and the diameter of the welded tube is shrunk, both edge surfaces of the tubular body are joined with a plasma-welding and the welded tube is water-cooled between the plasma-welding process and the rolling diameter-shrinking process to prevent the back flow of the air in the tube bulged with the welding heat. The sound edge joining part without biting flux is obtd., and the development of the crack at the time of shrinking the welding tube can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a flux cored wire for welding in which a metal pipe made of carbon steel, stainless steel or the like is filled with a welding flux as a powder.

[0002]

2. Description of the Related Art In a method of manufacturing a flux-cored seamless wire for welding, a strip is slit to a required width, and the strip after slitting is gradually formed from a U-shape to an O-shape by a forming roll. During this forming, the flux is supplied to the strip valley portion from the opening along the longitudinal direction of the U-shaped strip by a feeder. Next, at the same time as the O-shape is formed, the opposite edge surfaces of the opening are joined by welding, and subsequently the diameter is reduced. Further, if necessary, after annealing, the welded tube filled with the flux is drawn to a desired diameter, and wound to obtain a product.

[0003] As a welding method for producing the above-mentioned seamless pipe filled with the granular material, high-frequency welding such as high-frequency induction welding and high-frequency resistance welding and arc welding such as TIG welding are widely used. In the welding method using high-frequency current, the strip steel after slitting is changed from U-shape to O by a forming roll.
After forming into a letter shape, the edge surface of the opening is heated to the melting temperature by the generated Joule heat, and the opposing edge surfaces are pressed and joined by a pair of squeeze rolls. In any case, a strong magnetic field is generated in the vicinity of welding. There are a TIG welding method and a plasma welding method as an arc welding method with a small magnetic field, and are generally used.

[0004] When the diameter of a welded pipe filled with flux is reduced by rolling, drawing, or the like, a crack may be generated in the outer jacket of the pipe. The cause of this crack is considered as follows. At the time of welding, a part of a flux such as an oxide, a silicate, and iron powder 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 adsorbed on the opening edge surface by the magnetic force. At this time, the non-magnetic component and the ferromagnetic component in the granulated flux are adsorbed on the opening edge surface. The flux adsorbed on these opening edge surfaces intervenes in the welded portion and causes welding defects. Cracks are generated in the welded pipe at the time of diameter reduction due to this welding defect.

[0005] In arc welding such as TIG welding and plasma welding, the magnetic flux does not stick to the opening edge surface due to magnetic force and does not intervene in the welded portion.
It hits the weld directly, causing the flux to bite and create weld defects. The rising of the flux is due to the fact that the welded tubular body heats the whole tubular body by heat conduction, and the air that has expanded rapidly during welding is contained in the tube. As the diameter of the welded pipe is reduced, the expanded air is discharged to the outside through the welding process, and the filling rate of the flux increases. If the amount of air discharged at this time is large, the flux soars up, and a part of the flux sowed up when passing through the welding process is caught between the welding edges, resulting in welding defects. When the diameter of the welded pipe is reduced while the welding defects are present, cracks occur.
Further, the cracks cause disconnection in the process of elongation, which causes a reduction in productivity. Further, even if the diameter is reduced to the product size, when it is brought into the flux cored wire for welding, it is one factor that reduces welding workability.

As one of the techniques for solving such a problem, there is a "composite wire for welding" disclosed in Japanese Patent Application Laid-Open No. Sho 60-234794, in which a powder raw material having a relative magnetic permeability of 1.10 or less is substantially used. Is filled with non-magnetic powder to prevent the powder from adsorbing to the opening edge surface due to magnetic force. JP-A-63-589
The "method of manufacturing a composite pipe" disclosed in Japanese Patent Publication No. 7-214, removes fine powder finer than 48 mesh when powder is supplied, and prevents the fine powder from adhering to the opening edge surface. Japanese Patent Application Laid-Open No. 54-109040 discloses a method of manufacturing a tube filled with powder. The method includes supplying a powder so that the tubular body is not filled with the powder and forming a joint between the joint and the surface of the supplied powder layer. A gap or distance is provided between them to prevent the powder from rising and reaching the opening edge surface.

Various techniques have been disclosed for high frequency welding of a tubular body as described above, but this is a welding defect based on the fact that flux particles are magnetically attached to the opening edge surface of the tubular body by magnetic force. I reconfirmed that. To prevent this, it is necessary to supply only a substantially non-magnetic flux material, but there is a limit to eliminating magnetic adhesion and adhesion of powder particles to the opening edge surface of the tubular body. I also checked.

Japanese Patent Application Laid-Open No. 1-40719 discloses a method of manufacturing a flux-cored wire, in which the distance between the welding point and the cooling start position is 10 mm or more, the time until the start of cooling after welding is 0.8 seconds or less, and cooling is performed. A manufacturing method in which cooling is performed under the condition that the time is 0.5 second or less is disclosed. However, in this technique, cooling is started within 0.8 seconds immediately after welding, and the cooling time is set to 0.5 seconds or less, in order to prevent the gas in the tubular body from expanding due to welding heat to prevent the movement of the flux and the blowing up. This does not solve the problem of the flux adhering to the opening edge surface.

[0009]

Even if the above-mentioned prior art is used to improve the welded portion, the adhesion of the flux to the opening edge surface does not disappear, and cracks are still generated when the diameter of the welded pipe is reduced, thereby reducing the product yield. I was invited. Once cracks occur, even if the cracks are small at first, the pipe extends in the longitudinal direction as the diameter of the reduced diameter of the welded pipe becomes smaller, and becomes a length that can no longer be ignored in the product size.

Accordingly, an object of the present invention is to provide a method of manufacturing a flux-cored wire for welding without cracks in the outer periphery of a welded pipe by obtaining a sound edge joint.

[0011]

SUMMARY OF THE INVENTION A method of manufacturing a flux-cored wire for welding according to the present invention comprises forming a metal band into a U-shaped body, supplying powdery particles to the U-shaped body, and then forming the metal band into a tubular body. ,
In a method for manufacturing a flux cored wire for welding by welding both edge surfaces of a tubular body and reducing the diameter of a welded pipe, both edge surfaces of the tubular body are joined by plasma welding, and a plasma welding step and a rolling reduction step are performed. The welded pipe is water-cooled between the pipes to prevent backflow of the pipe expanded by the welding heat.

In the present invention, since the edge surface of the tubular body is plasma-welded, the magnetization of the edge surface is weak, and the magnetic particles in the flux do not adhere to the edge surface by magnetic force. In addition, since the air inside the pipe does not flow backward and blows out from the edge opening, soaring of the flux is prevented,
The flux does not adhere to the edge surface. Than this,
A sound edge joint without flux penetration is obtained,
It is possible to prevent the occurrence of cracks when the diameter of the welded pipe is reduced.

In the above method for producing a flux-cored wire for welding, it is preferable that water cooling be started within 8 seconds after the plasma welding and that the welded pipe be water-cooled for at least 3 seconds. Since water cooling is started within 8 seconds after welding, the amount of air in the tube that expands thermally due to welding heat is small, and since water cooling is performed for 3 seconds or more, air that has been thermally expanded sufficiently to prevent backflow can be cooled.

Further, water may be discharged from the water discharge hole toward the weld pipe while passing the weld pipe through a cooling pipe having a large number of water discharge holes. This allows the welded pipe to be rapidly
And it can be cooled uniformly.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Various kinds of raw material powders are selected and used according to the purpose of a welding wire as a flux of a granular material supplied to an opening of a U-shaped body. For example, rutile sand, magnesia clinker, etc. as a slag forming agent, sodium silicate, potassium titanate, etc. as an arc stabilizer, C-Fe-Si, Fe-
Si-Mn, Al-Mg, etc. are used, and ferromagnetic powders such as iron powder, nickel, iron oxide, etc. are used for improving welding speed, improving quality performance, adjusting flux filling rate, and improving welding workability. It is blended. The blended and mixed powder includes a non-granulated flux used as it is and a granulated flux granulated with sodium silicate and potassium silicate. Each of the fluxes contains fine powder that easily flies. When the diameter is reduced, the fine powder contained in the flux is discharged together with the air. Therefore, emphasis was placed on how to reduce the amount of air discharged.

The ratio of the flux layer and the air layer of the powder-filled tube after the plasma welding differs depending on the filling rate. As an example, the flux layer and the air layer are each about 50%. When this air is exhausted, it soars up the fine powder flux. The flux goes through the welding process in a soaring state. At this time, a part of the soared flux is caught in the welded portion and becomes a welding defect.

This is because the plasma gas, which is rapidly heated by the plasma welding and is composed of argon and air, is contained in the tube in an expanded state. Further, the temperature of the welded portion rapidly heats the entire welded pipe by heat conduction, and the expanded gas is carried as it is. As the pipe is reduced in diameter in the next diameter reduction step, the expanded gas flows back through the preceding welding step and is discharged to the outside.

Within 8 seconds after welding the welded pipe, at least 3
By cooling for 2 seconds, the amount of gas discharged to the outside due to the reduction of the diameter of the welded pipe is offset by the volume reduction of the gas contracted by cooling for 3 seconds or more. Therefore, since the gas flow centering on the welding process position, that is, the gas actually discharged to the outside is insignificant, the movement of air in the contained welding pipe is minimized to prevent the flux from rising. In addition, it is possible to eliminate the adhesion of the flux to the opening edge surface at the time of welding, thereby preventing the occurrence of welding defects.

The plasma welding can reduce the arc to a small size, and is suitable for forming a thin-walled small-diameter pipe by high-speed welding. Although it is plasma welding that can reduce the welding heat source, heating of the pipe and expansion of the gas inside the pipe are small but inevitable in welding small pipes having a small heat capacity as compared with other welding methods. Therefore, in order to prevent the flux from rising due to the gas flow in response to the gas due to the welding heat and the volume change in the pipe, the above-described appropriate cooling step is indispensable.

[0020]

An embodiment in which the present invention is applied to the production of a flux-cored wire for arc welding will be described. Used hoop JIS Z-3141 SPCC (1.2t × 23.0W) Used flux Rutile flux (granulated flux) Filling rate 14% Welding machine Plasma welding machine Welding current 240A Shielding gas (CO ₂ ) 10 ml / min Pilot gas {CO ₂ or CO ₂ + Ar (3 to 10%)} 0.8 ml / min Cooling start time 4 sec Welding speed 1.5 and 3 m / min

FIG. 1A is a schematic diagram showing the structure of an apparatus for carrying out the present invention, and FIG. 1B shows the formation of a hoop in each step. The hoop A has a width of 23 mm and a hoop thickness of 1.2 mm. As shown in FIG.
An uncoiler 1, a hoop cleaning device 2, a forming roll group 3, a side roll 4, and a flux supply device 5 are sequentially arranged along the hoop feed direction. A preforming roll (not shown) is provided upstream of the forming roll 3. A flux chute 6 is provided between the side rolls 4. The flux cut out from the flux supply device 5 is a U-shaped body C in the middle of molding.
Is filled. The U-shaped body D supplied with the flux,
After passing through the fin pass roll 7 and the seam guide roll 8,
Enter the plasma welding apparatus 9. The filler tube F is welded by the plasma welding apparatus 9 into a 8.0 mmφ filling tube F. The filling rate of the flux in the filling tube F (volume ratio of air and flux) is about 50
%. The filling tube F is cooled by the cooling device 11.

FIG. 2 is a detailed view of the cooling device 11. The cooling device 11 includes a tubular jacket 15 and a cooling pipe 18 provided coaxially with the jacket 15 in the jacket 15.
It has. A large number of water discharge holes 19 are provided in the upper half circumferential surface of the cooling pipe 18. The jacket 15 and the cooling pipe 18 are partitioned by a partition 22 to form a cooling channel 23. In the cooling device 11 configured as described above,
Pressurized cooling water is supplied into the jacket 15 from the water supply port 16. The cooling water is discharged from the water discharge hole 19 toward the filling pipe F, and the filling pipe F is cooled. The discharged cooling water 16 is discharged from an outlet 20 of the cooling pipe 18.

The cooled welding pipe F is rolled to 6.0 mmφ (filling rate: 130%) by a group of rolling rolls 12 (see FIG. 1), further drawn, and a flux-cored wire 3.2 mmφ.
It is wound up. Next, it is annealed, and in the wire drawing step, the outer shape 1.
The diameter is reduced to the product size of 0 to 1.2 mm φ.

Table 1 shows the results of investigating the occurrence of cracks by changing the welding conditions and cooling conditions.

[Table 1] Experiment No. Nos. 1 to 10 were obtained by plasma welding at a welding speed of 1.5 m / min. Further, the distance between the welding point and the cooling start position was changed to adjust the cooling start time from the welding point. According to the experimental results, the flux blowing phenomenon occurs unless the cooling holding time is 3 seconds or more. That is, the contained air is not shrunk in an instantaneous short time (less than 3 seconds). The temperature of the filled tube immediately before cooling was 280 ° C, and the temperature of the filled tube after cooling was 30 ° C or less. Even if the cooling time is further lengthened, there is no significant effect as the temperature drops to the temperature of the cooling water. When the time from welding to the start of cooling was 9 seconds or more, flux was blown out and welding defects occurred.
Experiment No. Nos. 11 to 20 are plasma-welded at a welding speed of 3 m / min. Filled tube temperature after cooling is 35
° C, which is higher than at a speed of 1.5 m / min. Approximately the same results as the conditions 1 to 10 were obtained.

[0025]

As described above, according to the present invention, by performing water cooling after plasma welding, a part of the flux does not get caught in the welded portion and no welding defect occurs. Further, it is possible to provide a manufacturing method capable of preventing the occurrence of skin cracks generated during the step of drawing and drawing, eliminating disconnection, improving the manufacturing yield, and improving the quality performance as a flux-cored welding wire.

[Brief description of the drawings]

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

FIG. 2 is a detailed view of a cooling device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Uncoiler 2 Hoop cleaning device 3 Forming roller 4 Side roller 5 Flux supply device 6 Flux chute 7 Fin path roll 8 Seam guide roll 9 Plasma welding device 11 Cooling device 12 Rolling roll group 15 Jacket 18 Cooling pipe 19 Water discharge hole 22 Partition A: Hoop material B: Preformed hoop material C: U-shaped body D: U-shaped body after filling with flux E: Tubular body before welding F: Welded tube G: Welded tube in diameter reduction process W: After diameter reduction Filling tube

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yasugi Kusunoki 3-5-4 Tsukiji, Chuo-ku, Tokyo Inside Nippon Steel Welding Industry Co., Ltd. (72) Inventor Ichiro Masuda 3-5-2 Tsukiji, Chuo-ku, Tokyo No. within Nittetsu Welding Industry Co., Ltd.

Claims (3)

[Claims] 1. A metal strip is formed into a U-shaped body, and after supplying powder and granules to the U-shaped body, the metal band is formed into a tubular body, both edges of the tubular body are welded, and the diameter of the welded pipe is reduced. In the method of manufacturing a flux-cored wire for welding, both edge surfaces of the tubular body are joined by plasma welding, and between the plasma welding step and the rolling reduction step, the welded pipe is water-cooled and the air inside the pipe expanded by welding heat is formed. A method for producing a flux cored wire for welding, characterized by preventing backflow. 2. The method for producing a flux-cored wire for welding according to claim 1, wherein water cooling is started within 8 seconds after the plasma welding, and the welded pipe is water-cooled for at least 3 seconds. 3. The flux cored wire for welding according to claim 1, wherein water is discharged from the water discharge hole toward the weld pipe while passing the weld pipe through a cooling pipe having a large number of water discharge holes. Method.