JPS6123586A - Detection of deffective welding of electric welded tube - Google Patents

Abstract

PURPOSE:To securely detect defective weldings and arc traces by using means of optical detection of arcs caused at both edges between a position of electric supply and a position where both edges are welded. CONSTITUTION:The beam from a V-shaped portion V is caught by an objective lens 3, illuminated into a photoelectric converting element 5 and converted to an electric signal corresponding to the luminous intensity. A tracking device 9 reckons the distance between a marker 12 facing toward the outer circumference of a tube P and a position of arc caused when an arc detecting signal is input from an arc comparing device 7, and counts a pulse signal transmitted from a measuring roll 11. When the count reaches a pulse number corresponding to a distance between the arc generated position and the marker 12, a signal is outputted at the marker 12 and prints a mark on the outer surface of the tube P. An alarm 9 starts ringing simultaneously when an arc detecting signal is outputted.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for detecting welding defects occurring in the seam portion of an electric resistance welded pipe, particularly cold welding defects caused by arcs generated in the V-shaped portion.

[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. The tube P is manufactured by applying side pressure to the squeeze roll 2 while heating its both side edges, and welding the molten side edges together (point 02). .

By the way, welding defects are formed in the seam portion of the electric resistance welded tube manufactured in this way due to various factors. One of these is that the strip S, which is curved to have a C-shaped cross section, In the process of heating the edges and moving toward the squeeze roll 2, the edges on both sides asymptotically form a V-shape (referred to as a V-shape section) in plan view, and just before reaching the squeeze roll 2, they become molten and come into contact with each other ( The seam convergence point 01) has a cold welding defect caused by an arc generated between both side edges during this process. Arcs occur at any time after passing through the work coil 1 and reaching the welding point 02, but the arc is particularly likely to lead to welding defects at the seam convergence point 0. This is an arc that occurs in the first part of the V-shoe in front of the V-shoe. If 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 and Or a cold welding defect occurs in the vicinity thereof, and the arc trace causes a welding failure at the arc occurrence point.

For this reason, in the past, the variation in the oscillation cycle of the high frequency wave for ERW pipe welding was processed as a signal, and this was extracted as a welding characteristic value.
A method of quantitatively detecting welding abnormalities by comparing the size, size, and shape with control values (Japanese Patent Application Laid-Open No. 14482/1982), and a method for detecting changes in magnetic flux density by installing a magnetic flux density change detection coil opposite to the vicinity of the welding point. A method for detecting welding abnormalities by processing
-84282) etc. have been proposed. However, in the former method, the oscillation cycle fluctuations caused by arc generation are minute;
In addition, it is difficult to distinguish between the arc generated at the weld and the arc generated at the V-shoe, which is directly connected to the defect, and the detection accuracy is low.In addition, the magnetic flux density of the latter is due to variations in the shape of the strip.
Alternatively, since it is affected by relative position fluctuations between the detection coil and the strip, it is difficult to quantitatively detect only the magnetic flux density caused by arcing, and there is also the problem of low detection accuracy.

〔the purpose〕

The present invention has been made in view of the above circumstances, and its purpose 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. To provide a method for detecting welding defects in electric resistance welded pipes, which enables accurate and easy detection of welding defects by optically capturing the occurrence of arcs that are highly likely to lead to.

〔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 welding abnormality is detected based on this.

, □(?IJ) ) 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, and in the figure S
indicates a strip, 1 indicates a work coil, 2 indicates a squeeze roll, and P indicates a tube. After the strip S is curved into a C-shaped cross section by a forming roller (not shown) so that both side edges face each other, the strip S passes through a work coil 1 and heads for a squeeze roll 2. In this process, the strip S is The welding current generated at both side edges flows along the edges, and the strip S is asymptotic toward the squeeze roll 2 side while the edges are heated by the welding current (■ shoe 1 Part V) moves, and both side edges are joined at a seam convergence point 01, and further welded to each other at a welding point 02.

■1 part of the shoe■ At the upper part, there is an objective lens 3 whose field of view is the 1 part of the V shoe (the rectangular part surrounded by a broken line) from the position passing the work coil 1 to the point in front of the seam convergence point 01. One end of a light guide 4 made of an optical fiber is disposed, and the light from the shoe 1 part V is captured by the objective lens 3, propagated through the light guide 4, and made incident on the photoelectric conversion element 5. It is converted into an electrical signal according to the light intensity and output to the bypass filter 6. The electrical signal converted by the photoelectric conversion element 5 is as shown in FIG. The corresponding signals appear as a, and the signals corresponding to the arcs generated within the field of view appear as c.

The bypass filter 6 is set at a predetermined control level so as to pass only the electrical signal caused by the arc and not pass the electrical signal caused by the heat on both edges of the strip S, and its output is sent to one terminal of the comparator 7. Enter. 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 whose level is slightly higher than the electrical signal is input, and the output from the bypass filter 6 is compared with the reference signal, and if it is higher than the reference signal, a pulsed arc is detected as shown in Figure 2 (c). A signal is output from the tracking device 9 and the alarm device 10.

When the arc detection signal is input from the comparator 7, the tracking device 9 calculates the distance from the marker 12 facing the outer circumferential surface of the tube P to the arc generation position, and also makes the marker 12 contact the outer circumferential surface of the tube P. When the pulse signals from the measuring roll II are counted and the number of pulses corresponds to the distance between the arc generation position and the marker 12, in other words, when the arc generation position reaches the marker 12, the marker 12 A signal is output to the tube P, and a mark is attached to 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, since the arc generated on both side edges of the strip is optically detected between the power supply position to the both side edges of the strip and the position where both side edges join, the arc can be detected. It is possible to reliably detect not only welding defects at the seam caused by the welding process, but also the arc group that occurs at the arc occurrence position.The detection accuracy is high, and since it can be detected online, the work efficiency is high and it contributes to improving the pipe quality. It's a huge amount.

[Brief explanation of drawings]

Figure 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, and FIG. 3 is a schematic diagram showing the 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...Bypass filter 7...Comparator 8...Reference value setter 9...Tracking device 10...Alarm device 11
...Measuring roll 12...Marker

Claims (1)

[Claims] 1. In the process of manufacturing an electric resistance welding tube by heating and melting and welding the both side edges of a strip which is curved so that the both side edges of the strip are curved so that the both side edges thereof face each other in the width direction, the both side edges are 1. A method for detecting welding defects in electric resistance welded pipes, comprising optically detecting arcs generated on both side edges up to the joining position, and detecting welding abnormalities based on this.