JPS62176686A - Production of clad steel pipe - Google Patents

Abstract

PURPOSE:To prevent the generation of undercut by performing a re-welding of the seam part by a laser beam by performing a seam welding in the specified upsetting quantity after forming a clad steel plate in a cylindrical shape. CONSTITUTION:Both end faces of a clad steel plate are joined by impressing a high frequency voltage by a contact chip 6, etc. by passing the clad steel plate 1 formed in cylindrical shape by a roll forming, etc. through the squeezing stand 5 consisting of the lower roll 2, the squeezing roll 3 giving an upsetting and squeezing top roll 4. The generation of the defect of an undercut, etc. can be prevented because the butt without any gap is obtd. in the laser beam welding to be performed later on when the welding is performed at <=1mm upset by high frequency resistance welding.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an improvement in a seam welding method for manufacturing laser-welded clad steel pipes.

(Prior art) One method for manufacturing clad steel pipes in which the inner and outer layers of the pipe are made of different materials is to form a clad steel plate into a cylindrical shape using a roll or the like, and then seam weld both end faces using a rede. There is also a method of manufacturing steel pipes with different materials for the inner and outer layers of the welded part.

However, in laser welding, even if a minute gap is created at the abutting portion, undercuts may occur, resulting in defective welding. On the other hand, when forming steel pipes using rolls, etc., it is difficult to ensure that the abutting portion is I-shaped with no gaps as shown in Figure 4(a), and it is difficult to form the butt part into an I-shape as shown in Figure 4(b) or a V-shape as shown in Figure 4(b). Figure 4(e)
This often results in an inverted V-shaped gap like this. For this reason, when manufacturing clad steel pipes by Rede welding, Fig. 5 (
There is a problem in that defects of undercuts 12 are likely to occur in the welded portion as shown in b) and (e).

(Problems to be Solved by the Invention) The present invention attempts to reliably prevent the occurrence of undercuts in the production of clad steel pipes that are seam welded by Rede.

(Means for Solving the Problems) The inventors of the present invention conducted research to solve the above problems, and as a result, they obtained the following knowledge. That is, by re-welding the sea wide portion welded by high-frequency resistance welding by Rede welding, it is possible to eliminate welding defects occurring in the high-frequency resistance welded portion and reliably prevent the occurrence of undercuts. On the other hand, when welding clad steel plates using high-frequency resistance welding, it is possible to reliably join even in V-shaped or inverted V-shaped butts, but if an appropriate amount of upset is not applied, defects may occur in the weld. If an upset is added in an amount that can prevent welding defects from occurring frequently, a large excess 9 will be generated in the welded portion, and bead cutting will remove the cladding portion, so the welded portion will not become a cladding. For this reason, it is difficult to seam-weld clad steel plates using only high-frequency resistance welding to produce clad steel plates.

The present invention has been made based on the above findings, and involves seam welding a steel plate formed into a cylindrical shape by roll forming or the like using high frequency resistance welding with a small amount of upset that does not cause a large excess buildup. Afterwards, the seam portion is re-welded using a rede, thereby reliably preventing undercuts.

(Example) The present invention will be described below with reference to embodiments shown in the drawings. FIG. 1 is an explanatory diagram of a high frequency resistance welding apparatus for implementing the present invention. A clad steel plate 1 formed into a cylindrical shape by roll forming or the like is placed on a squeeze stand 5 which is next to a lower roll 2, a squeeze roll 3 that gives an upset, and a squeeze roll 4 which is an adjustment roll to prevent the formation of a step. A high frequency voltage is applied through the contact tip 6 or the like to join both end surfaces of the clad steel plate.

In this case, the left and right squeeze rolls are movable in the left and right directions using hydraulic cylinders or the like, thereby adjusting the roll interval and giving an upset to the abutting portion. In order to prevent welding defects from occurring in high-frequency resistance welds, an upset of about 2+m to 4mg is required, and if this amount of upset is applied, Figure 2 (
&] A large extra layer 10 is formed, and when this extra layer is cut and removed, the cladding portion is removed as shown in FIG. 3(b), and the welded portion no longer becomes a cladding. On the other hand, if the upset amount is set to 1■ or less, the special excess amount in Fig. 3 becomes 0.
．． The length is 5 m or less, and the steepness of the backing is very gentle, so there is no need to cut or remove the backing. With this amount of upset, contaminated molten metal cannot be sufficiently discharged, so coarse oxides remain and weld defects occur frequently. Since there is no butt, defects such as undercuts will not occur. After performing high-frequency resistance welding, the steel pipe is cut to a predetermined length, and then passed between the left and right pinch rolls 7 as shown in Fig. 1(e).
Immediately after this pinch roll, approximately 150 mm above the steel pipe seam.
The high-frequency resistance welding seam portion is re-welded by the Rede welder 8 installed at the +m position to form a sound and clad welded portion.

When rede welding clad steel plates, it is desirable to weld as fast as possible in order to fully form the welded area into cladding.
A radar generator capable of high output, such as a CO□ laser, is used, and the radar beam is focused to, for example, about 0.5 m.

In the above description, after high-frequency resistance welding, the steel pipe is cut and then lede welded, but the steel pipe may be welded without cutting.

(Effects of the Invention) As explained above, in the present invention, after forming a clad steel plate into a cylindrical shape, seam welding is performed using high-frequency resistance welding using a small aggregation (fl) that does not produce a large excess. Undercuts can be reliably prevented by rewelding the seam portion using a rede.

[Brief explanation of drawings]

Figure 1 (a) s (b) + (c) is a diagram showing an embodiment of the present invention, Figure 2 (-) is a cross section of a welded part when an upset of 2 m or more is applied by high frequency resistance welding. Figure 2 (b) is a diagram of the cross-sectional shape of the welded part after cutting and removing the excess buildup, and Figure 3 (a) is a diagram of the shape of the welded part after welding with an upset of 1 mm or less by high-frequency resistance welding. Figure 3(b) is a diagram showing the cross-sectional shape of the welded part after the extra buildup has been removed, and Figure 4(a) is the welded part in the case where there is no gap. Diagram showing the butt part of the materials, 4th
Figure 4 (b) is a V-shaped case with a gap on the outer side, Figure 4 (e) is a V-shaped one with a gap on the inner side, and Figure 5 Figure (1) is a diagram showing the new surface shape of the weld without undercut, and Figure 5 (b) and Figure 5 (C) are diagrams showing the cross-sectional shape of the weld with undercut. It is.

Claims (1)

[Claims] A clad steel pipe characterized in that a clad steel plate is formed into a cylindrical shape using a roll or the like, then seam welded by high frequency resistance welding with an upset of 1 mm or less, and then the seam is rewelded using a laser. Production method.