JPH0328259B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an extremely effective welding method for producing high-quality, highly efficient steel pipes in the production of spiral steel pipes made by spirally winding and welding hot-rolled coils or strip-shaped thick plate materials. .

Traditionally, the mainstream method for welding spiral steel pipes is to weld the inner and outer surfaces using submerged arc welding, and in some cases submerged arc welding is performed in a separate process after tack welding using CO ₂ arc welding.
Alternatively, there is a method of performing electric resistance welding. Improving the productivity of spiral steel pipes means improving pipe manufacturing efficiency, or welding speed, and in conventional submerged arc welding, efforts have been made to use multiple welding electrodes and develop fluxes for high-speed welding. Currently, we cannot expect a dramatic improvement.

Although electric resistance welding allows for faster welding than submerged arc welding, it has rarely been applied to spiral steel pipes, and has only been applied to thin plates with a thickness of 6 mm or less and small diameters. On the other hand, as an electric resistance welding method for relatively thick plates of spiral steel pipes, there are
There is a number. In particular, the latter uses a crimping process that is different from straight seam steel pipes in order to continuously apply uniform pressure to the electric resistance welded part.The root gap is guided in a negative state (see Figure 1a), and semi-molten by high-frequency heating. Although the concept of automatically pressing the opposing surfaces of molten steel plates in the thickness direction and welding them together has been proposed, there is no example of this being implemented.

The main reason for this is that with a minus gap, it is difficult to obtain sufficient squeezing force when pressing, so the molten metal is not squeezed out sufficiently at the joint, especially on the thick side, and the complete weld cross-sectional area ( This is because it is difficult to obtain a throat thickness of 100% or more, making it difficult to use as a final product.

Therefore, electric resistance welding is only effective for temporary attachment, and conventional arc welding must be performed within the same process or in another process, so no improvement in pipe manufacturing efficiency could be expected.

The present invention solves the above-mentioned problems associated with manufacturing spiral steel pipes, and makes it possible to manufacture spiral steel pipes with ultra-high efficiency and high quality. In this method, the protrusions are pressed with a minus gap to automatically pressure-weld them, and then arc welding is performed on the inner and outer surfaces.The throat thickness of the electric resistance weld is made large, and only the inner and outer surfaces that are not fully fused are made into beads. By performing decorative welding by arc welding after shaping, the amount of welding and penetration of arc welding can be reduced. Also, since the internal arc welding point is not performed at the seam butt part, it is possible to reduce the amount of welding and penetration by arc welding. welding position in eccentric direction from )
By combining the high speed of electric resistance welding with decorative welding by arc welding, we can combine the high speed of electric resistance welding with the decorative welding of arc welding. This makes it possible to manufacture ultra-high-speed, high-quality composite welded steel pipes that are more than twice as fast as arc welding. Further, depending on the required qualities such as strength and toughness, the composite degree can be changed by changing the ratio of the electric resistance welded part and the arc welded part to the plate thickness. In addition, even if the throat thickness of the electric resistance welded part is 100% of the plate thickness, it is necessary to compensate for the disadvantages such as poor bendability of the electric resistance welded part by arc welding, and if this is not necessary, After electrical resistance welding, the final product can be made by simply shaping the welded parts on the inner and outer surfaces.

The method for shaping the inner and outer welds after electric resistance welding is as follows:
The soft excess under high temperature generated by electric resistance welding may be crushed and shaped using a pressure welding roll, or may be cut and removed using a cutting tool or the like. However, if the excess is formed in a constant shape without defects,
There is no need to force the shape, and the next arc welding can be performed as is. Further, when welding the inner and outer surfaces in another process after electric resistance welding, the excess buildup from electric resistance welding is hardened, and if the excess buildup is not a defect-free bead of constant shape, it is preferable to cut and remove it.

In other words, the present invention overcomes the drawbacks such as difficulty in obtaining a perfect throat thickness with thick walls by press-type electric resistance welding of spiral steel pipes, and can be used to weld ordinary spiral steel pipes from thin to thick sides and from small diameters to large diameters. This technology enables the final product to be electrical resistance welded steel pipes of all sizes.

This method is a completely new process that has never been put into practical use, and especially when electric resistance welding and arc welding are performed in the same process, it is unlikely that high-efficiency and high-quality spiral steel pipes can be manufactured in 1 mil. It became a high-productivity mill for a long time.

The present invention solves the problems associated with the conventional manufacturing of spiral steel pipes and provides an extremely innovative, high-quality, highly efficient welding method. , At the position where the root gap meets in a negative state, the butt parts on both sides are continuously electrically resistance welded using an electric resistance welding machine, and the outer and inner surfaces are welded continuously or continuously using the arc welding method, and the welded parts are melted and pressure welded. It is characterized by the formation of a composite arc welded part, and the throat thickness of the welded part melted and pressure-welded by electric resistance welding is increased to 50% to 100% of the plate thickness. This welding method is characterized in that arc welding of the outer and inner surfaces is performed by reducing the amount of welding and the amount of penetration, so that part or all of the throat thickness of the melt-welded weld remains.

Next, the method of the present invention will be explained in detail with reference to the drawings.

FIG. 1 illustrates a conventional arc welding method. At 3, latent arc welding is performed from the inside of the butted side edges, and after half a turn, latent arc welding is performed at 4 on the outer surface, resulting in a joint in which the inner and outer surfaces are fully metal-touched by latent arc welding beads.
As shown in Figure 1b, the welding positions in the submerged arc welding method are as follows: In the 3rd position, the inner welding torch is eccentric by l ₁ , and in the 4th position, the outer welding torch 6 is also eccentric by l ₂ .
It's only eccentric. The reason for this is to solidify the molten steel advantageously while maintaining a good bead shape and welding at a higher speed, but in the case of inclined welding, the amount of molten steel that does not flow down and the length of l ₁ at the 3 positions are required. Due to limitations, it is currently difficult to expect a significant increase in welding speed.

In contrast, FIG. 2a illustrates the welding process according to the invention.

As shown in Fig. 2c, a strip steel plate 1 on which protrusions have been formed in advance is wound spirally, and immediately before one side edge and the other side edge meet with a negative gap 7
Then, the side edges are made into a molten or semi-molten state by high-frequency heating, and pressure is applied from above and below with pressure rolls at 8. At the same time, the squeezed out molten metal is shaped using protruding pressure rolls, and after half a turn, the outer surface is heated at 9. In this method, arc welding is performed on the inner surface in step 10, and then arc welding is performed on the inner surface in step 10. The type shown in FIG. 2a is a case where an electric resistance weld is used as tack welding, and welding is performed by arc welding in a conventional manner so that the outer surface weld metal and the inner surface weld metal meet. In this case, the quality is significantly improved compared to conventional welding methods, but the line speed is hardly improved.
For types 7 and 8, the throat thickness Sc of the electric resistance welded part is made as large as possible, 50% to 100% of the plate thickness, and incomplete welded parts that occur on the inner and outer surfaces are squeezed out by electric resistance welding. The bead containing a large amount of oxide is remelted by arc welding from the outer surface at 9 and from the inner surface at 10,
The electrical resistance weld at the center of the plate thickness is used as the main bead.
This remains in the joint, and compared to other types, the amount of welding and penetration required by arc welding is extremely small, and by serving only as a decorative layer, high-speed arc welding can be performed at more than twice the speed of conventional methods. becomes possible. The type is electric resistance welding only and 100% of the plate thickness.
This is the case when the throat thickness is obtained, and after applying sufficient squeezing by setting a large negative gap, the final product is made by simply shaping the squeezed out beads on the inner and outer surfaces. This makes it possible to weld a wider area at high speed.

Next, examples of the method of the present invention will be shown.

The photograph in Fig. 2b shows a cross-sectional macro photograph of the welded joint when the pipe was actually manufactured using the type. The plate thickness is 12mm, welding speed is 6.0m/
This is the case when the pipe is manufactured at a speed of 100 min, which is approximately twice the conventional pipe manufacturing and welding speed. In addition, the electric resistance welding machine used to manufacture the above spiral steel pipe was installed at the third
Shown in Figure 4. The frequency can be used from 1KHz to 200KHz. FIG. 3 is a side view of the welding machine, in which power is supplied from a high frequency oscillator 19 installed on the lower surface of the pipe 2 and the steel plate 1 to the pipe side and the steel plate side via the bus bar 20, the welding head 21, and the contact chip 22.
Apply current at welding point 7. Electric resistance welding head 21
The position and angle of power supply and the pressing force of the contact chip are variable, and the steel plate side of the pipe side can be adjusted independently. FIG. 4 shows a plan view, in which electric resistance welding equipment is arranged along the side edge of the steel plate, and the pretreatment frame 2
Since the entire device is placed on the top of the 3rd floor, it can be applied to pipes of all sizes at any forming angle. Furthermore, the features of the present invention will be explained using an example in which a pipe was actually produced with a plate thickness of 12 mm.

As already explained, FIG. 2b shows a composite welded joint of electric resistance welding and arc welding that was actually made into a pipe. In order to control the ratio of the electric resistance welded part and the arc welded part in this composite welded joint, data such as those shown in FIGS. 5 and 6 are required.

First, in order to control the throat thickness Sc of an electric resistance weld, it is necessary to know the relationship between the negative gap amount λ (lap margin) and the throat thickness Sc. According to FIG. 6, the relationship is shown that the larger the amount of wrapping, the larger the throat thickness, and by selecting the amount of wrapping, the desired throat thickness can be determined. Furthermore, in FIG. 5, an appropriate amount of heat input can be determined in accordance with the welding speed. The highest speed can be achieved by making the throat thickness as large as possible to minimize the area to be remelted by arc welding. Figures 7 and 8 show throat thickness Sc and groove depth G relative to plate thickness.
FIG. 3 is a diagram showing the relationship between the above and the welding speed, and simply shows the reason why high-speed welding is possible based on the results of actual pipe manufacturing. In other words, by increasing the throat thickness Sc obtained by electric resistance welding relative to the plate thickness, the groove depth G to be remelted later can be increased.
It has been shown that the arc welding becomes extremely small, and that the speed of arc welding as a decorative bead is greatly increased accordingly. Whether electric resistance welding and arc welding are performed in the same process or in different processes, pipe manufacturing efficiency is determined by the speed of arc welding, so the speed-up effect of this decorative coating is significantly larger.

Next, we will discuss the quality effects of composite welded joints of electric resistance welds and arc welds. The first effect is that since electric resistance welding is performed prior to arc welding of the inner and outer surfaces, internal defects such as blowholes and slag entrainment are drastically reduced, similar to when CO ₂ tack welding is performed. As the next effect, the results of the joint performance investigation were
Shown in Figures 0 and 11. Generally, performance evaluation of welded joints is performed by tensile test, impact test, and hardness of the welded part. Figure 9 shows the relationship between the electrical resistance remaining in the composite joint, the length of the welded part, and the joint strength (removal of excess metal). The joint strength of a compound joint is equivalent to the joint strength of conventional double-sided single-layer arc welding, and the joint strength does not change even if the composite degree (ratio of the length of the arc weld to the length of the electric resistance weld) is changed. . FIG. 10 shows the impact values of electric resistance welds at different speeds. The impact value of electric resistance welds depends on the welding speed,
The higher the speed, the better the value. When electric resistance welding and arc welding are performed in the same process, the welding speed is
It is thought to be between 4.0m/min and 10m/min, but even when making pipes at low speeds, which are disadvantageous for electric resistance welding,
It can be seen that the impact value shows a sufficient value. 1st
Figure 1 shows the ratio of the hardness distribution after electric resistance welding alone to the hardness distribution of the electric resistance weld after arc welding (Bitzkers hardness, load 10 kg). The maximum hardness is approximately Hv=220, which is a good value, and after arc welding, the maximum hardness shows an even lower value due to the reheating effect.

That is, it can be seen that the quality of the composite welded joint of electric resistance welding and arc welding is not inferior in any way compared to the conventional arc welded joint, and has excellent joint performance.

As described above, the present invention is a welding method applied to the manufacture of spiral steel pipes, in which the electric resistance weld is made into a regular bead instead of tack welding, and decorative arc welding is performed on the inner and outer surfaces. The quality is higher than that of the conventional method, and the efficiency of pipe production can be more than doubled. In addition, it becomes possible to manufacture joints with different ratios of electric resistance welding and arc welding according to the purpose, and ultimately it becomes possible to manufacture products using only electric resistance welding, which can yield significant effects. . In particular, the method of performing electric resistance welding and arc welding in the same process has no industrial effect in that it has made it possible to manufacture spiral steel pipes with high efficiency and quality without increasing the number of process equipment personnel compared to conventional methods. It is extremely large and unique.

[Brief explanation of the drawing]

Figure 1a is a plan view showing the welding order of spiral steel pipes according to the conventional method and a cross-sectional view of the weld bead formed at each position; Figure 1b is a diagram showing the positions of internal and external arc welding in the conventional method; Figure 2a is a cross-sectional view of the welding sequence and weld beads formed at each position according to the present invention, Figure 2b is a cross-sectional photograph of a composite welded part obtained by actual pipe manufacturing, and Figure 2c is a spiral steel pipe. FIG. 3 is a side view of the electric resistance welding machine and welding position according to the present invention, FIG. 4 is a plan view of the electric resistance welding machine and welding position according to the present invention, and FIG. 5 is a diagram showing the electric resistance welding method according to the present invention. Diagram showing the relationship between throat thickness and heat input,
Figure 6 is a diagram showing the relationship between lap width and throat thickness, Figure 7
The figure shows the relationship between plate thickness, throat thickness, and groove depth, and Figure 8 shows an example of welding speed improvement with respect to plate thickness.
FIG. 9 is a diagram showing the relationship between the length of the ERW part and joint strength, FIG. 10 is a diagram showing the relationship between welding speed and impact value, and FIG. 11 is a diagram showing the hardness distribution before and after arc welding. 5... Electrode for internal arc welding, 6... Electrode for external arc welding, 11... Butt portion, 12... Squeezed out metal, 13... Shaped metal, 14... External arc welding bead, 15...
...Inner surface arc welding bead, 16...Outer surface decorative bead, 17...Inner surface decorative bead, 18...Resistance welding bead by electric resistance welding, 23...Pretreatment frame.

Claims (1)

[Claims] 1. In manufacturing spiral steel pipes, the butt portions on both sides are continuously welded by electric resistance welding at the position where one side edge and the other side edge of the steel strip meet with the root gap in a negative state λ. High quality in the manufacture of spiral steel pipes characterized by electric resistance welding and continuous or continuous arc welding on the outside and inside welds to form a composite of melt-welded welds and arc welds. , a highly efficient welding method. 2. By increasing the throat thickness of the welded part welded by electric resistance welding by 50% to 100% of the plate thickness, the amount of welding and penetration in the subsequent arc welding of the outer and inner surfaces is reduced, Claim 1, characterized in that welding is performed so that a part or all of the throat thickness of the welded part that has been molten and pressure-welded remains.
Welding method described in section.