JPH0128672B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a welding method for overlaying the inner surface of a tube, for example, in which overlay is applied to the inner surface of the tube in order to improve the corrosion resistance of the inner surface of the tube.

[Prior art]

Conventional overlay welding, which applies overlay to the inner surface of a tube, has an outer diameter of 200 mm.
Spiral or step-over methods using MIG or TIG welding are used for the above pipes.

In the spiral method, as shown in Fig. 1, the welding torch 2 is continuously moved in the direction of the arrow B while swinging the welding torch 2 within the tube 1 rotating in the inner circumferential direction of the arrow A. This is a method in which a bead 3 is wound spirally around the inner surface of a tube 1 as shown in FIG.

In the step-over method, the welding torch 2 is oscillated within the rotating tube 1 shown in FIG.
This is a method in which one rotation of the tube 1 is detected and the welding torch 2 is intermittently moved by the width of the bead 3 as shown in FIG.

In the spiral method and step-over method, it is necessary to mechanically synchronize the rotation of the tube 1 and the movement of the welding torch 2, which requires a large gearbox, and the rotation mechanism that rotates the tube 1 and the welding device must be the same. Must be installed on the bed. Therefore, the entire device becomes large-scale and expensive.

In addition, the swing pitch of the welding torch 2 is determined by the gear ratio of the gearbox and is fixed in stages, such as 6 mm, 9 mm, 12 mm, etc., so the bead connection is not flat and it is necessary to match the welding conditions to the mechanical conditions. Because of this, it was not possible to adapt to changes in welding conditions when the material of the tube 1 was changed, which caused problems in the quality of the overlay on the inner surface of the tube 1.

Furthermore, for pipes with an outer diameter of 200 mm or less, the spiral method or step-over method described above cannot be applied because the pipe diameter is small, and a linear welding method using covered arc welding, which is performed by hand, is used.

The linear stacking method is a method in which a bead 3 is placed in the longitudinal direction of the inner surface of the tube 1 as shown in FIG. 4, and then the next bead 3 is placed shifted by the bead width.

According to this linear build-up method, since the welding torch is shifted by the bead width and the internal build-up is carried out, there is a problem that the bead width cannot be completely controlled and unevenness is likely to occur on the bead surface. In addition, in this linear build-up method, slag is generated because coated arc welding is performed, and it takes time to peel it off. Depending on the material, it may be difficult to peel it off, and slag is likely to become entangled. Furthermore, since this method is performed by hand welding, the length of the tube that can be overlaid is limited to the range that can be reached.If a long tube is required, multiple tubes with overlays on the inner surface are joined by circumferential welding. This results in an increase in man-hours, worsens the straightness of the tube, and causes problems such as depression at the welded portion and increased deformation.

[Purpose of the invention]

In order to solve the above-mentioned problems, this invention is an automatic overlay welding method based on the bead end face that was previously overlaid using the height displacement of the welding torch under a constant arc length. The object of the present invention is to provide a method for overlaying the inner surface of a tube that can be applied to the spiral method described above.

[Summary of the invention]

The pipe inner surface welding method of the present invention involves swinging the welding torch while keeping the arc length of the welding torch fixed at the tip of the elongated arm by arc voltage control, and making the height of the welding torch variable. The height displacement of the welding torch is detected during movement, and when the welding torch moves in the direction toward the end face of the bead that was previously overlaid welded, the height displacement of the welding torch is determined to be equal to the reference value set in advance according to the bead height. When a match is detected, the welding torch is reversed after a certain period of time from that time, and when the welding torch is moving in the opposite direction to the end face of the bead, the welding torch is reversed when a predetermined swing width is reached. This method involves copying the end face to obtain a smooth bead.

The reason why the swing motion of the welding torch is controlled by detecting the height displacement of the welding torch in this invention is as follows.

When the welding torch 2 and filler wire 6 are oscillated by a predetermined width as shown by the arrows as shown in FIG. 5 while performing arc voltage control to keep the welding arc length constant, the height of the bead 5 on the base metal 4 will be adjusted. Correspondingly, the height of the welding torch 2 rises, and when the height displacement of the welding torch 2 and the swinging of the welding torch 2 are measured with a potentiometer, a waveform shown in FIG. 6 is obtained. FIG. 6 shows time T on the horizontal axis and potential e on the vertical axis. In the figure, the waveform e _p indicates the oscillation waveform of the welding torch 2, and the waveform
e _A shows the waveform of the height displacement of the welding torch 2. As shown in the figure, there is a very good correspondence between the oscillation waveform e _p of the welding torch 2 and the height displacement waveform e _A. Therefore, by detecting the height displacement of the welding torch 2 during the oscillating motion while performing arc voltage control to keep the arc length constant, the welding torch 2 is oscillated by detecting the end face of the bead that has been overlaid earlier. can do.

[Embodiments of the invention]

7, 8 and 9 show one welding device used for carrying out the present invention, FIG. 7 is a front view, FIG. 8 is a plan view, and FIG. 9 is A-A in FIG. 7. FIG. In the figure, 7 is an arm made of a long and thin tube with a welding torch 2 attached to its tip. Reference numeral 8 denotes a holder to which an arm 7 is attached, and the welding torch 2 is moved vertically by rotation of a shaft 9 made of a trapezoidal screw. Reference numeral 11 denotes a lifting motor, which controls arc voltage by rotating a shaft 9 via a gear group 10. Reference numeral 12 denotes a swinging slider to which the lifting motor 11 and the like are fixed, and the welding torch 2 is swung by the rotation of a swinging shaft 14 made of a trapezoidal screw connected to a swinging motor 13. 15 is a main slider to which a swing motor 13 is attached, and has a guide 16 and a nut 17. The nut 17 is screwed onto a main shaft 18 made of a trapezoidal screw, and rotation of the main shaft 18 moves the main slider 15 along a guide rail 19. A main motor 20 rotates the main shaft 18 via a gear 21, a clutch 22, and a gear group 23. Reference numeral 24 denotes a rapid feed motor which rotates the main shaft 18 via a clutch 22A and a gear group 23. Note that 25 is a nut for attaching the main shaft 18 to the bed 26.

TIG using the welding equipment configured as above
When overlaying the inner surface of the small-diameter pipe 1 shown in FIG. While rotating with a rotating device (not shown), the main motor 20 is driven to automatically move the welding torch 2 in the direction of arrow B in the figure, and the swing motor 13 is driven to build up a certain width on the pipe 1. . Thereafter, the welding torch 2 is oscillated to follow the end surface of the bead 5 that has been built up previously, and the welding is continued on the inner surface of the tube 1.

FIG. 11 shows a flowchart when the welding torch 2 is oscillated.

In step 101, the direction of swinging of the welding torch 2 is confirmed, and if the direction of swinging of the welding torch 2 is toward the end face of the bead that was built up first, the height displacement of the welding torch 2 shown in FIG. e _A is detected by a potentiometer (not shown) (step 102), and this height displacement e _A
When the welding torch 2 rises from the lowest potential to the reference potential e _r set in advance according to the bead height, a reversal signal of the welding torch 2 is detected (step 103), and after a certain period of time T _A seconds from that time (step 105) A swing stop command is issued (step 106), and after a predetermined stop time T _B has elapsed (step 107), the welding torch 2 is reversed (step 100). If the welding torch 2 swings in the direction opposite to the end face side of the bead 5 that has been overlaid first, the swing width W is set in advance.
is detected (step 104), and the welding torch 2 is immediately reversed when the swing width W is reached. In addition,
In the above example, the case where overlay welding is performed using the above-mentioned spiral method using the TIG welding method is explained.
This invention can also be carried out using a spiral welding method using MIG welding.

〔Effect of the invention〕

As explained above, this invention performs build-up welding on the inner surface of the tube by following the previously built-up bead end face, so the bead surface becomes extremely smooth and there are no undercuts or valleys in the overlapped portions of the bead, which were problems with manual welding. This eliminates the need for non-destructive inspection after welding. Furthermore, since the weld bead width and build-up thickness required for build-up welding can be selected more freely than in other welding methods, the optimum build-up conditions that match the specifications can be adopted. Furthermore, since the bead can be joined at any position, even if the arc breaks for some reason during welding, welding can be continued again.

Further, in this invention, since the swinging and feeding of the welding torch and the rotation of the tube can be adjusted independently, it is possible to freely deal with changes in bead shape, width, and welding conditions due to differences in the material of the tube.

Furthermore, since this invention swings the welding torch to follow the bead end surface, the inner surface of the tube can be built up automatically by TIG welding using inert gas.
It can be applied to any material, and since slag is not generated, slag entrainment and associated welding defects are eliminated, and welding with stable quality is possible.

In addition, according to this invention, since the welding torch can be oscillated by the welding device main body, the arm to which the welding torch is attached can be made elongated, and as a result, it is possible to weld up to small diameter pipes with an inner diameter of about 50 mm after overlaying. By inverting the pipe and welding from each end individually, overlay welding of pipe lengths up to 1.2 m is possible, which is highly effective in improving quality.

[Brief explanation of drawings]

Figure 1 is a diagram of the arrangement of a pipe and welding torch when overlaying a pipe, Figure 2 is a schematic diagram of a bead produced by the conventional spiral method, Figure 3 is a schematic diagram of a bead produced by the conventional step-over method, Figure 4 is a schematic diagram of a bead formed by the conventional linear build-up method, Figure 5 is a schematic diagram of a bead formed by overlay welding, Figure 6 is a waveform diagram of the height displacement and oscillation of the welding torch, and Figure 7 ~9th
The figures are structural diagrams of a welding device used to carry out the present invention, in which Fig. 7 is a front view, Fig. 8 is a plan view, Fig. 9 is a sectional view taken along line A-A in Fig. 7, and Fig. 10 is a bead and FIG. 11, which is a layout diagram of a welding torch, is a flowchart when the welding torch is oscillated in an embodiment of the present invention. 1...Pipe, 2...Welding torch, 3, 5...Bead, 4...Base metal, 7...Arm, 8...Holder,
9... Axis, 10, 23... Gear group, 11... Lifting motor, 12... Rocking slider, 13... Rocking motor, 14... Rocking axis, 15... Main slider, 1
6... Guide, 17... Nut, 18... Main shaft,
19...Guide rail, 20...Main motor, 21
...Gear, 22, 22A...Clutch, 24...
Rapid feed motor, 26...bed.

Claims (1)

[Claims] 1. While keeping the arc length of the welding torch fixed at the tip of the elongated arm by arc voltage control, the welding torch is oscillated and the height of the welding torch is variable, and during this oscillation, the height of the welding torch is The height displacement of the welding torch is detected, and when the welding torch moves in the direction toward the end face of the bead previously overlaid, it is determined that the height displacement of the welding torch matches a reference value set in advance according to the bead height. The welding torch is reversed after a certain period of time from that time, and when the welding torch is moving in the opposite direction to the end face side of the bead, the welding torch is reversed when a predetermined swing width is reached. A welding method for overlaying the inner surface of a tube, which is characterized by performing edge copying.