JPH0431796B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is directed to the welding defects that occur at the seam portion of electric resistance welded pipes.
In particular, the present invention relates to a method for detecting cold welding defects caused by arcs generated in V-shape sections.

[Prior art]

FIG. 3 is a schematic plan view showing the general manufacturing process of electric resistance welded pipes. A strip S is formed into a C-shaped cross section by a forming roller so that both side edges thereof face each other. Then, while the both edges are heated, it faces the squeeze roll 2 and side pressure is applied by the squeeze roll 2, and the molten both edges are welded together (O ₂ points) to manufacture the pipe P. ing.

By the way, welding defects are formed at the seam of the electric resistance welded tube manufactured in this way due to various reasons.One of these is that the strip S, which is curved to have a C-shaped cross section, passes through the work coil 1 and is attached to both sides of the welding defect. In the process of moving toward the squeeze roll 2 while the edges are heated, both edges become V-shaped in plan view (referred to as the V-shape section).
Just before reaching the squeeze roll 2, they become molten and come into contact with each other (referred to as the seam convergence point O ₁ ), but during this process, there is a cold welding defect due to an arc that occurs between both edges. . An arc can occur anywhere between passing through the work coil 1 and reaching the welding point _O2 , but the arc that is most likely to lead to welding defects is the arc that occurs at the V-shape section before the seam convergence point _O1 . When an arc occurs in this part, the welding current is shunted to the arc short circuit part, so the current flowing to the weld part decreases, resulting in insufficient heat input, causing cold welding defects at or near the arc occurrence position, and the arc Because of the marks, welding defects occur at the point where the arc occurs.

For this reason, in the past, fluctuations in the oscillation cycle of high-frequency waves for ERW pipe welding were signal-processed, extracted as welding characteristic values, and compared with control values in size, size, and shape, to quantitatively identify welding abnormalities. Detection method (Unexamined Japanese Patent Publication 1983
14482) and a method in which a coil for detecting changes in magnetic flux density is provided facing the vicinity of the welding point and the signals are processed to detect welding abnormalities (Japanese Patent Application Laid-open No. 84282/1982), etc. have been proposed. However, in the former method, the fluctuation in the oscillation frequency due to arc generation is minute, and it is difficult to distinguish between the arc generated in the weld and the arc generated in the V-shaped part directly connected to the defect, and the detection accuracy is low. Since the magnetic flux density is affected by variations in the shape of the strip or by changes in the relative position between the detection coil and the strip, it is difficult to quantitatively detect only the magnetic flux density caused by arcing, and the detection accuracy is similarly low. There was a problem.

〔the purpose〕

The present invention has been made in view of the above circumstances, and its object is to provide a welding defect that occurs between the power feeding part for both side edges of a curved strip and the convergence point where both side edges touch each other. Welding of electric resistance welded pipes that enables accurate and easy detection of welding defects caused by arcs, that is, cold welding defects and arc marks, by optically capturing the occurrence of arcs that are likely to lead to The present invention provides a defect detection method.

〔composition〕

In the process of manufacturing an electric resistance welding tube by heating and melting and welding both side edges of a strip which is curved so that both side edges in the width direction face each other, both side edges are joined from a power supply position to the both side edges. The arc generated on both side edges is optically detected up to the position where the arc occurs, and this detected value is compared with a predetermined reference value. If the value exceeds the reference value, it is determined that a welding defect caused by the arc has occurred. Characterized by judgment.

〔Example〕

The present invention will be specifically described below based on drawings showing its implementation state.

FIG. 1 is a schematic diagram showing the implementation state of the present invention, in which S represents a strip, 1 represents a work coil, and 2 represents a strip.
indicates a squeeze roll and P indicates a tube. After the strip S is curved into a C-shaped cross section using a forming roller (not shown) so that both side edges face each other,
The welding current passes through the work coil 1 and then goes to the squeeze roll 2. In this process, the welding current generated by the work coil 1 on both side edges of the strip S flows along the edges of the strip S.
The edge part is heated by the welding current and moves toward the squeeze roll 2 side while being asymptotically approached on both sides (V-shape part V), and the seam convergence point O ₁
Both side edges are joined at the welding point O2, and then welded to each other at the welding point _O2 .

Above the V-shaped part V, there is an optical fiber equipped with an objective lens 3 whose field of view is the V-shaped part V from the position passing the work coil 1 to just before the seam convergence point _O1 (the rectangular part surrounded by a broken line). One end of the light guide 4 made of
The light is captured by the objective lens 3, propagated through the light guide 4, incident on the photoelectric conversion element 5, converted into an electrical signal according to the light intensity, and output to the high-pass filter 6. The electrical signal converted by the photoelectric conversion element 5 is as shown in FIG. A signal appears as a, and signals corresponding to arcs generated within the field of view appear as b and c.

The high-pass filter 6 passes only the electrical signals caused by the arc (signals b and c shown in Figure 2 A), and the electrical signal caused by the heat on both edges of the strip S (signal a shown in Figure 2 A). A predetermined pass characteristic is set to prevent this from occurring, and its output is input to one terminal of the comparator 7. The other input terminal of the comparator 7 receives an electric signal from the reference value setting device 8 which is a level slightly lower than that corresponding to the light intensity of an arc that has a high probability of leading to a welding defect, and corresponds to an arc that has a low probability of leading to a welding defect. A reference value (management level) whose level is slightly higher than that of the electrical signal is input, and the output from the high-pass filter 6 is compared with the reference signal, and if it is higher than the reference signal, the second
As shown in FIG. 3C, a pulsed arc detection signal is output to the tracking device 9 and the alarm 10.

When the tracking device 9 receives the arc detection signal from the comparator 7, it calculates the distance from the marker 12 facing the outer circumferential surface of the pipe P to the arc generation position, and also calculates the distance from the marker 12 facing the outer circumferential surface of the pipe P to the arc occurrence position. When the pulse signals from the yarn roll 11 are counted and the number of pulses corresponding to the distance between the arc generation position and the marker 12 is reached, in other words, when the arc generation position reaches the marker 12, the marker 1
A signal is output to 2 to mark the surface of the tube P. Note that the alarm 9 sounds at the same time as the arc detection signal is issued.

〔effect〕

As described above, in the method of the present invention, arcs generated on both side edges of the strip are optically detected between the power feeding position to the position where both side edges join. It is possible to reliably detect not only cold welding defects in the seam caused by cold welding, but also arc traces that occur at the arc occurrence position.The detection accuracy is high, and since it can be detected online, the work efficiency is high and contributes to improving pipe quality. However, it is quite large.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing the implementation state of the method of the present invention,
Figure 2 A, B, and C are graphs showing the signal processing process.
FIG. 3 is a schematic diagram showing a general manufacturing process of an electric resistance welded pipe. S... Strip, P... Tube, 1... Work coil, 2... Squeeze roll, 3... Objective lens, 4... Light guide, 5... Photoelectric conversion element,
6...High pass filter, 7...Comparator, 8...
Reference value setter, 9... Tracking device, 10...
...Alarm, 11...Measuring roll, 12...
…marker.

Claims (1)

[Claims] 1. In the process of manufacturing an electric resistance welded tube by heating and melting and welding both side edges of a strip which is curved so that both side edges in the width direction face each other, both side edges are The arc that occurs on both side edges up to the joining position is optically detected, and when this detected value exceeds a predetermined reference value, it is determined that a welding defect caused by the arc has occurred. Welding defect detection direction of ERW pipe.