JPS5933083A - Welding method of electric welded steel pipe - Google Patents

Abstract

PURPOSE:To weld an electric welded steel plate having large thickness while preventing welding defects without decreasing the speed for making pipe in welding of the electric welded steel pipe, by preheating beforehand the central part in the thickness of the steel pipe on the upstream side than the joint point of the steel pipe then subjecting the same to electric resistance welding. CONSTITUTION:A TIG preheater 1 is inserted into the spacing before joining of a steel pipe 6, and the spacing between the forward end of the preheater 1 and the pipe 6 is maintained at a prescribed spacing. An arc is generated in the central part of the thickness of the pipe 6 to preheat said central part of the pipe 6. The pipe 6 is moved in the arrow direction and the central part of the thickness of the pipe 6 is heated continuously. Thereafter the end faces (joint parts) of the pipe 6 are uniformly heated by a high-frequency resistance welding device 4 whereby the end faces are welded at a joint point 5.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of welding an electric resistance welded copper pipe. ．．・
? Conventionally, electrical resistance welding is often used as a welding method for ERW steel pipes;
The main method is to use (・force・method).This method uses 450K
Directly supplies high frequency current around I{z,
1.1 The surface/skin effect of cows? Utilizing the proximity effect to effectively heat only the steel emperor? This is a method for joining.

Shikajinaga ``) in this way/method/i''. ll'
In addition to manufacturing thick-walled steel pipes for G, it cannot be handled in terms of welding edge property.It is not possible to cope with the problem.1: Is L'5 allowed for steel? The flesh of the obi is glaring at the steel belt, and there is an electric current in the upper and lower parts of the steel belt.
Is it just one piece? Melt? It is obvious that welding defects or welding defects in the center of the thickness of the end face of the copper strip tend to increase.

However, due to an increase in the bath welding input or a slowdown of the welding speed, a certain amount of damage may occur. But production? Avoid a drastic decline in sexuality? Can't kick 1,'? Doesn't this invention reduce productivity? Kototo <,? Moreover, the weldable interlayer is also yarn resistant.
Is it basic? This idea provides a two-step welding method (composite welding) with heating conditions. But JP-A No. 56 Ichikawa 68981? v1th love,?
A method for manufacturing electric resistance welded pipes is carried out using a high-frequency current on the first heating stage and the second heating handle. The technology described in this publication attempts to produce an ERW pipe without welding defects by reducing the number of finished products that occur during heating. Both the heating means and the second heating means heat the thickness of the copper strip from the upper and lower surfaces, and the first heating means heats the joining point to a temperature at or near the melting temperature. Then, by the second heating means, from the downstream side near the welding point until it reaches the welding point,
It is heated to a temperature above the melting temperature sufficient to perform butt welding.

However, even with this welding method for electric resistance welded pipes, heating is applied from above and below the thickness of the copper strip, so the welding speed is not sufficiently applied to the center of the thickness of the copper strip. If the thickness increases, there will be a drawback that poor welding will occur at the center of the plate thickness.

Even if the present invention performs composite welding, it is not possible to increase the welding speed by simply arranging conventional heating means from the upper and lower surfaces of the steel strip thickness in series; By using a heating means of This is a welding method for electric resistance welded steel pipes, which is characterized in that the central part of the plate thickness is preheated on the upstream side of the point, and then electric resistance welding is performed.

Next, the present invention will be described in detail.

In the high-frequency resistance heating method, the heating of the center of the plate tends to be delayed compared to the top and bottom surfaces of the plate, and the thicker the plate, the more difficult it is to uniformly heat the plate. ) and welding defects such as poor welding in the center of the plate.

Therefore, welding defects inevitably occur with only such electric resistance welding bath welding, so in the present invention, the central part of the wall thickness of the plain paulownia steel pipe is preheated in advance before electric resistance welding.

Figure 1 shows the relationship between the wall thickness of a steel pipe and the heating temperature. When the central part of the wall thickness of a steel pipe stack is preheated, the temperature of the central part of the wall increases as shown in Figure 1 a. The temperature decreases as you go to the top and bottom of the wall. That is, the central part of the plate thickness is locally preheated, and the local preheating is performed so that the temperature difference between the central decoration of the plate thickness and the upper and lower surfaces of the plate is approximately 100°C. If the temperature difference is widened, the problem of R netrator (oxide remaining in the weld) remains, which is not preferable. After performing such local preheating, high frequency electric resistance welding is performed as shown in FIG. 1b.

As mentioned above, high-frequency electric resistance welding uses the skin effect and proximity effect, which are the characteristics of high-frequency current, to perform welding.
Therefore, as shown in Figure 1b, the temperature at the center of the plate thickness becomes lower,
The temperature increases as you go up and down the plate thickness. Therefore, when welding is performed by applying heating that combines the steps a and b in FIG.
As shown in Figure C, the central part of the plate thickness and the upper and lower surfaces of the plate thickness are uniformly heated, so that good welding can be performed even if the tube manufacturing speed is increased.

That is, the present invention is characterized in that the welded joints of steel pipe materials are heated to a uniform temperature, and then joined and welded. Conversely, the aspect of heating to a uniform temperature after joining is a method that prevents welding defects such as cold welding. Due to this problem, it is not possible to increase the pipe production speed, which is not desirable.

Next is the preheating method.
3, local preheating is performed, and the preheating means is also, for example, preheating using a TiG arc shown in FIG. In other words, 1 in the figure is the TIG preheating device, 2 is the TIG preheating device, and 2 is the TIG preheating device.
Arc welding lance 1, 3 is a ground block for TIG arc, and 6 is a steel pipe. Insert the TIG preheating device 1 into the gap (about 15 mm) between the steel pipes 6 before joining, and connect the tip of the TIG preheating device 1 with the lance. The distance between the steel pipe 6 and the steel pipe 6 is maintained at about 3 mm, and an arc is generated at the center of the thickness of the steel pipe 6 to preheat the center of the thickness of the steel pipe 6. The steel pipe 6 moves in the direction of the arrow in the figure, and the central part of the thickness of the steel pipe 6 is continuously preheated.

Thereafter, the end face (joint part) of the steel pipe 6 is uniformly heated by a high frequency resistance welding device 4, and welding is performed at the joint point shown at 5. 7 indicates a cable. That is, on the upstream side of the joint 5 of the steel pipes 6, the TIG preheating device 1 and the high frequency resistance welding device 4 uniformly heat the joint.

Further, as a local preheating method, in addition to the above-mentioned 'I'IG arc method, methods such as laser, electron beam, plasma, contact energization, etc. may be used, and the method is not particularly limited to TIG arc. Regarding the thickness of steel pipes, 12 to 19
Although this range is particularly effective for the present invention, plate thicknesses outside that range may also be used. Furthermore, resistance welding may also be performed using low or medium frequencies, and is not particularly limited to high frequencies.

? As described above, according to the welding method for ERW steel pipes of the present invention, it is possible to weld thick ERW steel pipes without reducing the pipe manufacturing speed and without welding defects, which is extremely effective. It is advantageous.

Next, embodiments of the present invention will be described in detail.

In this example, welding quality evaluation after TIG preheater high-frequency resistance heating is shown, where ◎ indicates good, Δ indicates partial failure, and × indicates occurrence of welding defect in the center of wall thickness.

[Brief explanation of drawings]

Figure 1a shows the temperature distribution of local preheating in the center of the plate thickness, and b
C shows the temperature distribution of the steel plate edge by high-frequency resistance heating method, and C shows the temperature distribution of a. FIG. 2 is an explanatory diagram showing an example of an apparatus for carrying out the present invention.

Claims (1)

[Claims] When roll forming a steel strip and applying electric resistance welding to manufacture an electric resistance welding steel wire, the central part of the repulsion thickness is preheated on the upstream side of the joining point α of the r tube. 4) A method for welding one tube with a lock stitch. 5.1.