JPS5982167A - Production of spiral steel pipe - Google Patents

Abstract

PURPOSE:To obtain an intact weld zone having a uniform bead shape by providing a coil near the weld zone to generate a shifting magnetic field, and applying the thrust in the direction opposite from the outflow direction of a molten metal on said metal that flows downward as a pipe inclines in its position according to its rotation. CONSTITUTION:A welding position 15 where a steel hoop 7 and a spiral pipe 14' contact with each other is internally welded by a welding torch and a shifting magnetic field heading toward the rotating direction (b) of the pipe is generated from a magnetic field coil L attached near a molten metal 22. As a result, the thrust in a direction F is acted on the molten metal 22 moving diagonally upward according to the rotation of the pipe and the outflow of the metal 22 going to flow downward by its own weight is prevented by such thrust. An electromagnetic stirring effect by the shifting magnetic field is generated in the metal 22 in this stage. The formation of a recess in the weld bead of the spiral steel pipe is thus averted and the intact weld zone is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a spiral steel pipe, which is intended to improve the bead shape of a spiral welded portion.

Figures 1 and 2 show an outline of current spiral pipe manufacturing equipment. A brief description of the line process is as follows. The coiled steel strip 2 that has been cenotted by the unwinding machine 1 is rewound by the pinch rolls 3, the curling curls are corrected by the plane straightening device 4, and the tip 6 is already cut by the cutting and plate welding device 5. After the rear end 8 of the strip material 7 that had entered the line was welded, the end surfaces 9 and 10 on both sides of the plate were passed through an inner beveling device.

It is sent to a spiral tube forming device 12 by a main drive device 11 . Here, the strip steel material 7 is formed by forming rollers 13 on the inner and outer surfaces.
It is formed into a cylindrical spiral tube part 14' whose axis intersects the above-mentioned line at a predetermined angle, that is, a spiral tube part 14' having a pinotti angle α, and is first internally welded by an internal welding device 16 at a joint 15 on the side surface of the spiral shaped plate. Ru. The spiral tube portion 14' formed in this way is passed through the outer surface beveling device 17, and then welded by the outer surface welding device 18.
It is produced as a spiral steel pipe 14.

To explain this seven-step welding process in detail, as shown in FIG.
Joint location 15 between the end face of the portion 4′ and the steel strip 7
are internally welded by an internal welding torch 16. After this, about half of the plate thickness, that is, the inner side, is welded.

The pipe portion 14° is pushed out in the direction of arrow O while rotating in the direction of arrow S. For external welding, the external welding torch 18 is moved near the top of the pipe in the same downward position as for internal welding. A spiral steel pipe 14 is obtained.

However, in the spiral steel pipe 14 manufactured by this method, the shape of the inner weld bead h is deteriorated compared to the general downward welding of a flat plate, as shown in Fig. 6.The reason for this is thought to be as follows. It will be done.

As shown in FIG. 4, inner welding is performed at the tube bottom 21, which forms the joint 15 between the steel strip 7 fed in the direction of arrow a and the formed tube 141, and the bead formation situation at that time is shown in FIG. It becomes like this.

In other words, since the welding part 1.-chi]6 is stationary,
It is always in a downward position at the bottom.

Since the pipe portion 14' and the strip-shaped preparation 7 are moving in the directions of arrows a and b, the welded portion assumes an inclined position immediately after that. In other words, the part to be welded by the welding torch 16 is welded in a downward position at the tube bottom 21, but the molten metal 22 melted by the arc heat moves diagonally as the tube section 14' rotates in the direction of the arrow. As it moves upward, it completely solidifies, and the position where weld metal is formed is shifted to the left of the welding position 21, and solidification progresses in an inclined position. Therefore, the molten metal 22 before solidification
The force of the molten metal flowing forward (toward the lower right of the drawing) is exerted by its own weight.

Since the solidification rate of the molten metal 22 is faster on the sides of the bead h than on the center of the bead, solidification progresses relatively quickly, and therefore both the left and right ends of the bead solidify earlier than the center.
The remaining molten metal in the center of the bead that has not yet completely solidified will flow forward as described above, and when complete solidification is completed, the molten metal in the center will flow forward as shown in Figure 6. The bead becomes an abnormal bead with a deep depression in the center due to the volume reduction caused by this. As a result of this constant continuation of the throat forming mechanism, the spiral steel pipe has a concave center portion of the inner bead.

In order to prevent the formation of such a concave weld at the center of the dome, it is understood that the solidification process of the molten metal 22 should be carried out in a horizontal position for the reasons described above. Therefore, in the conventional beam, a welding torch 16 as shown in FIG.
There are cases where welding is performed by slightly shifting the band preparation 7 from the bottom 21 of the pipe joint 15 toward the front in the direction of movement of the band preparation 7, that is, toward the supply side, but the movement distance S is limited by the dimensions and shape of the narrow inner surface of the pipe. However, there are only 20 to 30 songs at most, and the above-mentioned drawbacks have not been completely eliminated. If the distance S is further increased, as shown in FIG. 8, the joining points 5 between the formed pipe portion 14'' and the strip steel plate 7 will not match, making internal welding difficult.

In order to eliminate the drawbacks of the conventional methods as described above, the present invention involves winding a steel strip material into a spiral tube shape and welding the side edges of the strip copper phase to the side edges of the tubular portion while rotating. A coil that generates a moving magnetic field in the direction of rotation of the tube is attached near the tube, and as the molten metal moves diagonally upward as the tube rotates, an electromagnetic field is generated in the opposite direction to the direction in which the molten metal flows down due to its own weight. Provided is a spiral steel pipe welding method characterized by welding while applying a holding force by induction.

In the method of the present invention, as described above, a moving magnetic field is generated by attaching a coil near the welding part, and the direction in which the molten metal flows out due to the tilted posture accompanying the rotation of the tube is
Applying thrust in the opposite direction to alleviate the outflow of molten metal and avoid the formation of dents in the weld bead of spiral steel pipes.

A sound weld can be created.

An embodiment of the method for improving the bead shape of a welded portion of a spiral steel pipe according to the present invention will be described with reference to FIGS. 9 and 10.

First, in FIG. 9, the steel strip 7 and the spiral pipe portion 14 are
"i) A moving magnetic field coil is attached in close proximity to the molten metal 22 produced by welding by the -chi 16. This coil L
Connect a three-phase AC power supply with low frequency current to generate a moving magnetic field. In this way, a linear motor is formed between the moving magnetic field coil and the molten metal welded by the arc, but in this case, the next side is the coil L,
The secondary side becomes molten metal 22.

In this way, when a three-phase AC power source is connected to the coil L to generate a moving magnetic field, a thrust shown in the direction of arrow F acts on the molten metal 22 generated by arc welding, so that
As described above, the molten metal 22 moves obliquely upward as the tube rotates, and the force of the molten metal 22 flowing forward can be blocked by its own weight.

What is the principle behind the thrust F generated in this molten metal?

An eddy current is generated in the molten metal 22 by the magnetic field lines of the magnetic field coil L, and a current component perpendicular to the longitudinal direction of the coil is
It contributes to the generation of thrust F.

The principle is the same as that of a conventional electromagnetic gutter or electromagnetic pump.

Furthermore, the thrust force F acting on the molten metal M is.

As mentioned above, it not only prevents the force that causes the molten metal M to flow forward (downward), but also exerts a stirring action on the molten metal M, preventing segregation of impurities in the molten metal and refining crystal grains. Re.

It also effectively works to improve the mechanical properties of weld metal.

Next, this state is shown in Figures 10A to 10, which show the cross section of Figure 9.
Diagram D will be explained.

The AA' cross section shown in Figure 10A is the welding point, that is, the surface of the molten metal M is deeply depressed by the arc force, but while the welded material is melted by the arc heat, solidification does not progress. do not have.

The BB' cross section shown in FIG. 10B shows the rear position of the welding point, where solidification is about to proceed. However, since the solidification has not yet progressed completely, the molten metal M is in a full state, and in order to maintain this state at a point where the molten metal is completely solidified, a moving magnetic field is already generated by the magnetic field coil. A thrust force F is applied to the molten metal M.

The O-0' cross section shown in FIG. 10C is the region where the molten metal M influences the bead surface shape the most from this vicinity until final solidification. In other words, over time, B-
Proceeding further backward from the state of cross section B', the molten metal M gradually begins to solidify from the interface where it is in contact with the unmolten base material around it.

Molten metal M [solidifies from the part in contact with the base metal.

A coagulated layer is formed. At this time, the molten metal near the 2nd surface also begins to solidify, so no matter how fluid the molten metal is in the center, the edges become fixed, so the molten metal that fills the cross section The surface shape of the bead h is determined by the amount of metal.

Therefore, if this area has a large inclination angle,
The weight of the molten metal M causes a flow in the downward direction of the weld line, which affects the bead surface shape. That is, in the conventional method.

As mentioned above, it flows to the lower side and the filling amount becomes insufficient. As a result, a large dent occurs on the bead surface.2 However, in the method of the present invention, a moving magnetic field is generated by a magnetic field coil, and a thrust force F is applied in the opposite direction to the direction in which the molten metal M flows out. Even if there is an inclination due to rotation, this phenomenon is alleviated and a so-called normal bead shape with a slight bulge is formed.

An appropriate method for controlling the thrust force F by the magnetic field coil acting on the molten metal M is to adjust the current value flowing through the coil, adjust the distance between the molten metal M and the coil L, or adjust the distance between the molten metal M and the coil L.
This is done by adjusting the frequency of the current flowing through the

The D-DI cross section shown in the first O diagram shows a completely solidified bead shape. In the traditional way.

The molten metal remains near the center of the bead, resulting in a bead shape that flows out from the inclined PC. However, in the method of the present invention, the direction in which the molten metal flows out is determined so that the molten metal is not forced to flow down due to the principle of a linear motor. Since the opposite thrust force F is applied, there is no flow of the molten metal M unlike in the conventional method, and the bead-shaped surface solidifies to the point where it remains in good condition.

Although the present invention is described only for internal welding, it is of course applicable to external welding in which welding is performed at the top of a pipe.

As described above, in the method of the present invention, a moving magnetic field is generated by attaching a coil near the welding part, and a thrust is applied in the opposite direction to the direction in which the molten metal flows out due to the tilted posture caused by the rotation of the pipe. hand.

It is possible to alleviate the outflow of bath molten metal and improve the weld bead of spiral steel pipes. With this method, there is no need to perform welding by shifting the entire inner welding position slightly forward in the direction of movement of the strip steel plate, as was the case in the past.

[Brief explanation of the drawing]

Figures 1 and 2 are a front view and a plan view of a device made of Sunokuiral steel pipes, Figures 3 and 4 are a perspective view and a side view showing the outline of a conventional welding process for spiral steel pipes,
FIG. 5 is a partially enlarged view of FIG. 4, and FIG. 6 is an explanatory diagram of the welding hole 1. 7 and 8 are explanatory diagrams of measures for improving bead shape, FIG. 9 is a schematic diagram of an embodiment of the bath welding process in the manufacturing method of the present invention, and FIGS. 10A, B, and O. D are A-A', LL-13', and LL-13' in FIG. 9, respectively.
7: Steel strip 4d', 14': Spiral steel pipe section. 22: Molten metal, L: Coil.

Claims (1)

[Claims] When winding a steel strip into a spiral tube shape and welding the side end of the steel strip to the side end of the tubular portion while rotating, a moving magnetic field directed in the direction of rotation of the tube is applied near the welded portion. Attach the resulting coil. Spiral steel pipe manufacturing characterized by welding while applying a holding force by electromagnetic induction in the opposite direction to the direction in which the molten metal moves diagonally in two directions as the pipe rotates and flows down due to its own weight. Method.