JP2004098152A - Method for welding metallic pipe - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for welding a metallic pipe, which can solve problems of a method for welding metallic pipes using a squeeze roll, and can set a so-called V-shape angle in the vicinity of a welding point large, and can accurately constrain and press the cross section of the pipe, and can efficiently manufacture a straight seam welded pipe having high welding quality. <P>SOLUTION: Because the cross section of the pipe is continuously constrained and pressed during welding or just after welding along the longitudinal direction using dies instead of a squeeze roll, effects of variation of welding points, etc., upon welding results are reduced, and the spring-back behavior of the pipe after the welding point can be effectively suppressed, and the percentage of occurrences of welding defects can be remarkably reduced, and the productivity can be improved. Further, the friction between the dies and the pipe can be remarkably reduced by forming surface traveling waves by transferring the vibration to the surface of the dies by applying the ultrasonic vibration to the dies. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an improvement in the welding method of the butt end edges performed at the final stage in the production of a pipe by roll forming, using a die instead of the conventional squeeze roll, and further applying ultrasonic vibration to the die, The present invention relates to a metal pipe welding method capable of setting a so-called V-shape angle in the vicinity of a welding point, restraining and pressurizing the pipe section smoothly, and efficiently producing a straight seam welded pipe with high welding quality.
[0002]
[Prior art]
In the production of a straight-seam welded metal tube combining roll forming and welding, after forming a metal or alloy strip into a cylindrical shape with openings facing both ends by roll forming, the ends are butt-welded. . Various welding methods such as high-frequency welding, TIG welding, and laser welding are used for this welding.
[0003]
Although the mechanisms of these welding methods are different from each other, each employs a configuration in which a rotating roll called a squeeze roll is used to restrain and pressurize the pipe section during welding. That is, the welding method using the high-frequency induction welding apparatus shown in FIG. 1 will be described. The band 1 to be formed advances from the right-hand direction in the drawing, but both ends 2 and 2 of the band 1 are already roll-formed and face each other. It has a cylindrical shape with an opening and enters between the pair of squeeze rolls 3.
[0004]
A V-shaped angle 5 is formed between both end edges 2 and 2 of the strip 1 with a welding point 4 immediately before a straight line connecting the rotation center axes of the pair of squeeze rolls 3 and 3. The heating coil 6 disposed on the upstream side heats and melts both ends 2, and the squeeze rolls 3, 3 constrain and pressurize the pipe section before and after the welding point 4 to perform welding.
[0005]
[Problems to be solved by the invention]
The inventors have found that there is the following problem when using the squeeze roll described above. In other words, when a rotating body such as a squeeze roll is used as the means for restraining the cross section of the pipe, there is a common weakness that the form of restriction on the cross section of the pipe cannot be continuously maintained along the longitudinal direction. Hereinafter, considerations and findings of the inventors will be described in detail.
[0006]
The constraints and pressures caused by the rolls with the axis of rotation arranged in the same cross section of the tube occur geometrically only at the position of the cross section (immediately below the roll). Due to the pre-deformation and elastic recovery behavior of the tube, the actual constrained area is slightly wider, but strong confinement and pressure can be obtained in a very narrow area, including around the cross section. Such features have a detrimental effect on the welding.
[0007]
First, when viewed in the longitudinal direction, a region where necessary welding conditions are formed is in a state close to one point immediately below the roll. It can be said that the state of progress of welding at this part called the above-mentioned welding point has a decisive effect on welding quality. If a sound welding condition cannot be obtained for some reason when a section of the pipe passes through this point, there is a high possibility that a welding defect will occur as it is. For example, in high frequency welding, variations in welding points often lead to poor welding.
[0008]
Further, immediately after the cross section of the pipe has passed the welding point, the restraining force from the roll is lost, so that tensile stress is generated in the circumferential direction of the welded portion due to elastic recovery behavior. On the other hand, a certain period of time is required until the molten or semi-molten metal in the weld is completely solidified. As is well known, the state of tensile stress during the solidification process has a detrimental effect on the morphology of the metallographic structure of the weld formed and thus on its mechanical properties, possibly causing weld cracking.
[0009]
For example, in the case of TIG welding, which is a typical fusion welding, hot cracking immediately after welding is a major factor limiting welding speed and productivity. Even in high frequency welding similar to diffusion welding, maintaining pressure on the joint surface for a certain period of time immediately after welding seems to be advantageous for preventing defects such as cold welding.
[0010]
There are other disadvantages to using rolls. For example, in the case of high-frequency welding, the shorter the distance from the heating coil 6 or the contact to the welding point 4 is, the smaller the current loss is and the higher the welding efficiency is. However, due to the interference with the squeeze roll 3, it is physically possible. The shortest approach distance depends on the squeeze roll diameter.
[0011]
On the other hand, in order to obtain required strength and rigidity, the squeeze roll diameter must be equal to or larger than a certain size, and at present, problems of welding efficiency often occur. Further, to stabilize the welding point 4, it is necessary to increase the V-shooting angle 5 near the welding point, but the size of the V-shaping angle 5 is also limited by the squeeze roll diameter. At the manufacturing site, in order to increase the V-shape angle, a method of forcibly widening the interval between the opposing edges 2 of the strip 1 in front of the squeeze roll is often used. In the vicinity of immediately below the squeeze roll 3, the moving trajectory of the edge 2 is defined on the surface of the squeeze roll 3, so that the size of the V shape angle 5 that can be taken depends on the diameter of the squeeze roll.
[0012]
The present invention solves the problem of the above-described method of welding a metal pipe using a squeeze roll, can set a large so-called V-shape angle near a welding point, can restrain and press the pipe section accurately, and can improve welding quality. It is an object of the present invention to provide a method for welding a metal pipe that can produce a high straight seam welded pipe with high efficiency.
[0013]
[Means for Solving the Problems]
The present inventors have paid attention to the fact that many of the current problems in the above-mentioned straight seam welding are caused by using a rotating roll as a restraining tool, and as a result of various studies on means for replacing the squeeze roll, a It is found that the purpose can be achieved by using the dies, and the ultrasonic vibration is applied to the dies, and the vibrations are transmitted to the surface of the dies to form surface traveling waves, thereby significantly reducing friction with the pipe. We have found that we can do this and completed this invention.
[0014]
That is, the present invention relates to a method for welding a metal pipe in which both end edges of a metal material strip formed by roll forming and butting are welded to form a pipe. A method for welding a metal pipe, characterized in that the metal pipe is continuously restrained and pressed in a longitudinal direction using at least a pair of dies having a curved surface including a cross-sectional shape.
[0015]
Further, the present invention provides the welding method having the above configuration,
A method of applying ultrasonic vibration to a die to restrain and pressurize the pipe section,
A method in which ultrasonic vibration forms a surface traveling wave in the traveling direction of the tube on the die surface is also proposed.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
In the present invention, an advantage of using a die instead of a squeeze roll is that the pipe section during or immediately after welding can be continuously restrained and pressed along the longitudinal direction. Since the pipe section is continuously restrained and pressurized, it is less susceptible to changes in the welding point with respect to the welding result, and the elastic recovery behavior of the pipe after the welding point can be effectively suppressed. As a result, it is possible to significantly reduce the incidence of welding defects and improve productivity.
[0017]
In the case of high frequency welding as in the configuration of FIG. 1, the approach distance between the heating coil 6 or the contact and the welding point 4 is greatly increased by changing the squeeze roll and using the dies 10, 10 as shown in FIG. And the welding efficiency can be remarkably improved. Further, since the geometrical restriction of the tool means on the magnitude of the V-shape angle is relaxed, a V-shape angle larger than the conventional one can be easily formed.
[0018]
In the present invention, when a die is used, the relative sliding speed between a metal tube moving at a constant speed and a stationary die is higher than that of a rotating roll, so that a strong resistance force is generated due to friction, and the surface quality of the tube is increased. However, the friction can be reduced by using a known material having an appropriate lubricating function.
[0019]
On the other hand, if the production speed of the pipe mill is high and the object to be processed is a thick, high-strength metal tube, a sufficient effect may not be obtained even if a lubricant is used for the die. In some cases, even a lubricant cannot be used during welding, depending on the material and method of the pipe. Therefore, in the present invention, the above problem is solved by applying ultrasonic vibration to the die, and the friction with the pipe can be remarkably reduced regardless of whether a normal material or a lubricating material is used for the die.
[0020]
In other words, the friction between the die and the metal tube is greatly reduced by using the phenomenon that the frictional force is reduced when ultrasonic vibration is applied between the two surfaces that are in friction. By appropriately selecting the position where the ultrasonic vibrator is attached, the frequency, and the like, the relative slip between the tube and the die can be suppressed as much as possible. Further, as the ultrasonic vibrator, a vibrator having any structure such as a known piezoelectric structure can be employed.
[0021]
In the present invention, any known welding means and apparatus such as high-frequency welding, TIG welding, and laser welding can be adopted as the welding means. In addition, if the configuration of the dies is a configuration having a curved surface including the cross-sectional shape of the tube during welding or immediately after welding, or both of the portions, a pair of dies as shown in FIG. 2 may be used. In addition to the configuration in which the dies are arranged opposite to each other, various configurations such as a configuration in which the dies are divided in the traveling direction of the pipe, and two pairs or more dies are arranged in the same direction to face each other can be adopted.
[0022]
【Example】
A high-frequency induction welding apparatus using a die according to the present invention shown in FIG. 2 has a pair of dies 10, 10 abuttingly arranged so as to cover a tubular material strip 1 having a tubular shape. The surface has a concave surface similar to the outer peripheral surface of the semicircle, and is set so that the welding point 4 comes on a straight line connecting the vicinity of the upstream end of the pair of dies 10, 10. A required V-shape angle 5 is formed between the two rolls 3, and both ends 2, 2 are heated and melted by a heating coil 6 arranged on the upstream side of the rolls 3, 3. In addition, the pipe section is constrained and pressurized thereafter to complete the welding.
[0023]
The pair of dies 10, 10 are divided in the traveling direction of the pipe and attached to a holding device capable of adjusting the position, so that the degree of restraint on the metal pipe and the strength of the pressure can be adjusted. An ultrasonic vibrator 11 made of a piezoelectric material is provided on an outer peripheral portion of each die 10 not in contact with the band material 1.
[0024]
Here, when an AC voltage is applied to the ultrasonic vibrator 11 made of a piezoelectric body, ultrasonic vibration is generated, and this vibration is transmitted to the surface of the dice to form a surface traveling wave. As shown in FIG. 3, when ultrasonic waves that travel in the same direction as the moving speed of the pipe are generated on the surface of the die to be formed 1 that is being welded, that is, the surface of the die 10 that comes into contact with the metal pipe, the ultrasonic vibration is generated. The straight line on the surface (A) of the die 10 when not applied changes to the curve on the surface (B) of the die 10 when ultrasonic vibration is applied, that is, each material point on the surface of the die 10 draws an elliptical orbit, and the highest point Only the material point reaching and the vicinity thereof come into contact with the metal tube.
[0025]
Furthermore, when the vibration speed of these material points in the moving direction of the tube becomes the same as the moving speed of the tube, the relative sliding between the tube and the die has disappeared, and the strong resistance due to friction has disappeared, and therefore, during or immediately after welding. Since it is possible to continuously restrain and pressurize the pipe cross section, a metal pipe excellent in welding quality can be obtained. In a state where the relative slip between the pipe and the die has disappeared, it is also possible to apply a constant propulsive force to the metal pipe from the frictional force at the contact interface between the die and the pipe.
[0026]
【The invention's effect】
The present invention uses a die in place of a squeeze roll in welding a metal pipe to continuously restrain and pressurize the pipe section during or immediately after welding along a longitudinal direction, so that welding to a welding result is performed. This makes it less susceptible to the effects of point fluctuations and the like, and can effectively suppress the elastic recovery behavior of the pipe after the welding point, making it possible to significantly reduce the incidence of welding defects and improve productivity.
[0027]
Further, according to the present invention, by generating ultrasonic waves traveling in the same direction as the moving speed of the tube on the surface of the die in contact with the metal tube, there is no strong resistance due to relative sliding or friction between the tube and the die. By continuously restraining and pressing the pipe section during or immediately after welding, a metal pipe having excellent welding quality can be obtained.
[Brief description of the drawings]
FIG. 1 is an explanatory view from above a pipe showing a configuration of a conventional high frequency induction welding apparatus using a squeeze roll.
FIG. 2 is an explanatory view from above a pipe showing a configuration of a high-frequency induction welding apparatus using a die to which ultrasonic vibration is applied according to the present invention.
FIG. 3 is an explanatory diagram showing a contact state between a metal tube and a die when a surface traveling wave is applied.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Strip 2 Edge 3 Squeeze roll 4 Weld point 5 V shape angle 6 Heating coil 10 Dice 11 Ultrasonic vibrator A Dice surface when ultrasonic vibration is not applied B Dice surface when ultrasonic vibration is applied

Claims (3)

In a method for welding a metal pipe in which both ends of a metal material band formed by roll forming and butted are welded to form a pipe, the pipe section during welding or immediately after completion of welding, or both of the sections, a curved surface including the pipe section shape is formed. A method for welding a metal pipe that is continuously restrained and pressed in a longitudinal direction using at least a pair of dies. The method for welding a metal pipe according to claim 1, wherein ultrasonic pressure is applied to the die to restrain and pressurize the cross section of the pipe. 3. The method for welding a metal pipe according to claim 2, wherein the ultrasonic vibration forms a surface traveling wave in a traveling direction of the pipe on a die surface.

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