JPS61216873A - Method for controlling welding of electric welded pipe - Google Patents

Abstract

PURPOSE:To prevent the cold junction defect of an electric welded pipe and to execute satisfactory welding by controlling the welding current value of the electric welded pipe in such a manner that said current value attains a reference current value and that the temp. at the welding point attains a reference temp. value. CONSTITUTION:The welding current is controlled 12 to the reference value by the detected welding current value 15 for welding of the electric welded pipe P and the temp. 5 detected at the welding point is subjected to current control 12 so as to attain the reference temp. The corresponding correction current value is subjected to addition control 12 to the reference current value by a detected arc 6 in the stage of arc generation. The generation of the cold junction defect in the electric welded pipe P is surely prevented by the above- mentioned welding current control and the weld zone is satisfactorily welded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an automatic welding control method for preventing welding defects caused by arcs generated in V-shaped portions during welding of electric resistance welded pipes.

[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 moving towards the squeeze roll 2 while the edges are heated, both side edges asymptotically approach a V-shape (referred to as a V-shape part g) in plan view, and just before reaching the squeeze roll 2, they become molten and melt into each other. There is a cold welding defect (referred to as seam convergence point 01) caused by an arc generated between both side edges during this process. Arcs occur at any time after passing through work coil 1 and before reaching welding point 02, but arcs that occur at the V-shaped portion before seam convergence point 0 are particularly likely to lead to welding defects. 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.
Insufficient heat input causes cold welding defects in the area from the arc generation location to the welding point, and arc scars cause welding defects at the arc generation location.

For this reason, the conventional method is to measure the temperature at the welding point, compare the measured temperature with a predetermined reference temperature, and control the high frequency power source to eliminate the deviation (Japanese Patent Laid-Open No. 57-79084).
(No. 55-109582), or a method of measuring the welding current, comparing the measured current with a predetermined reference current, and controlling a high-frequency power source to eliminate the deviation has been proposed. .

[Problem that the invention seeks to solve]

By the way, in the conventional welding control method as mentioned above, in the former case, the arc generation time is extremely short (10m5
ec) Temperature control with a slow response speed has the problem of a large time delay. In addition, in the latter case, it is necessary to change the setting of the reference current based on the strip thickness, feed rate, invider deterioration, etc., but this change adjustment is extremely difficult, and under this constant welding current control, V When a short circuit occurs in the shape part, the welding current increases instantaneously, and the welding current constant control system detects this and functions to suppress the increase in welding current, thereby increasing the welding point current. There was a problem in that the heat input was further reduced and the insufficient heat input was expanded.

Figures 4 (a) and (b) show the case where constant current control is not performed when a short circuit occurs in the shape section [Fig. 4 (a)] and the case where constant current control is performed [Fig. 4 figure(
FIG. 2 is a waveform diagram showing changes in welding current, welding point current, and arc current with (b)]; both are shown with time on the horizontal axis and current on the vertical axis. First of all, when no arc is generated in the V-shaped part, whether constant current control is not performed or constant current control is performed, the welding current (shown by the solid line) 1sy1 will all flow through the welding point. , the welding point current (indicated by a broken line) i-2 has a value approximately equal to the welding current i1J. However, when an arc occurs in the V-shape section, the welding current i as a result of the arc current ia, that is, the short circuit current. 1 increases, and the welding point current iw2 decreases, but as shown in FIG. 4(a), when the welding current is not controlled, the welding current iw1. Welding point current f11
Both of them show a change in waveform depending on the arc current ia, but
When constant current control is applied, the increase in welding current quotient 1 is suppressed as shown in Figure 4 (b), and as a result, arc current ia is reduced, but welding point current iw2 is also reduced at the same time, resulting in an even greater heat input deficiency. As a result, cold welding defects are promoted.

[Means for solving problems]

The present invention was made in view of the above circumstances, and its purpose is to simultaneously control the temperature at a welding point to a constant level and the welding current to a constant level, the former in a major loop, and the latter in a minor loop. In addition, the reference current value used in the minor loop is corrected in accordance with the arc detection signal to prevent the welding point current from decreasing when arcing occurs due to constant current control, and to reduce the cooling caused by arcing. An object of the present invention is to provide a method for controlling welding PiI of an electric resistance welded pipe, which eliminates contact defects and improves the quality of the pipe.

The welding control method for an ERW pipe according to the present invention detects the temperature of a welding point during the ERW welding process of an ERW pipe, and performs constant temperature control in a major loop to control the temperature to match a predetermined reference temperature. In addition, the welding current to the V-shaped part is detected, and constant welding current control is performed in a minor loop to make it match a predetermined reference current.
The present invention is characterized in that occurrence of an arc in the V-shape portion is detected, and a correction current corresponding to the current of the arc is added to the reference current in the minor loop.

〔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, and in the figure S
indicates a strip, 1 indicates a work coil, 2 indicates a squeeze roll, and P indicates a tube. The strip S is curved into a C-shaped cross section by a forming roller (not shown) so that both side edges thereof face each other, and then passes through a work coil 1 to a squeeze roll 2. In this process, the work coil 1 The welding current generated at both side edges flows along the edges, and the edges of the strip S are heated by the welding current, and the both side edges are asymptotic toward the squeeze roll 2 side (V-shaped). Part ■)
The two side edges are joined at the seam convergence point o1, and further welded to each other at the welding point 02.

Information on the welding point 02 includes one end of an optical fiber light guide 4a equipped with an objective lens that has a field of view of the entire strip S and the pipe P in the width direction (diameter direction) around the welding point 02, Further, above the V-shaped portion V, there is an optical fiber equipped with an objective lens whose visual field is the V-shaped portion V from the position passing through the work coil 1 to just before the seam convergence point o1 (the rectangular portion surrounded by a broken line). light guide 4 made by
One end of b is arranged.

The other end of the light guide 4a is connected to a welding point temperature detector 5 constituting a part of the measuring loop Mj, and the welding point temperature detector 5 receives the input image signal of the welding point 0° and its surroundings. Based on this, the temperature of the welding point 02 is calculated and outputted to the subtractor 8.

The other end of the partial light guide 4b is connected to an arc detector 6 constituting a part of the minor loop Mn. (not shown) converts it into an electrical signal according to the light intensity and outputs it to the bypass filter, selects only the signal based on the arc, amplifies the signal according to the light intensity of the arc with the amplifier 7, and outputs it to the bypass filter. It is designed to output to 10.

Figure 2 (a) shows the output of the phototube in the arc detector,
Also, Fig. 2 (B) is a graph showing the output of the same bypass filter, and in both cases, time is plotted on the horizontal axis.As is clear from the graph shown in Fig. 2 (A), V
Under normal conditions with no arc occurring in the shape portion, the output from the phototube is constant at about 5V, but when an arc occurs, a pulse-like output is emitted for about 10+wsec. When such a photocell output is passed through a bypass filter as shown in Figure 2 (b), an electrical signal corresponding to the light intensity of the arc is output corresponding to the time when the arc occurs, and this signal is used as described above. As described above, the signal is outputted to the adder 10 via the amplifier 7.

The set temperature of the welding point o2 is determined in advance based on the dimensions of the pipe, pipe manufacturing conditions, etc., and input into the subtractor 8. Temperature deviation Δ from the manually measured temperature at welding point 02
t is calculated and output to the temperature controller 9.

The temperature controller 9 calculates a control signal for the high frequency power supply 13 necessary to eliminate the input temperature deviation Δt, and outputs this to the adder 10. The adder 10 receives the input control signal and the input from the arc detector 6 as shown in FIG.
The current command signal shown in FIG. 2(c) is outputted to the subtracter 11 by adding the arc detection signal corresponding to the strength of the arc as shown in FIG. 2(c).

The subtracter 11 calculates the current deviation between the welding current (work coil current in the embodiment) input from the welding current detector 16 and the current command signal, and outputs it to the welding current controller 12.

Welding current controller 12 calculates a control signal necessary to eliminate current deviation and outputs it to high frequency power source 13.

In the high frequency power supply 13, a voltage is set according to the control signal, and a predetermined current is passed through the work coil 1 through the output transformer 14, and the welding point o of the strip S is
The required current is made to flow through 2.

FIG. 2(d) is a waveform diagram of the welding current calculated by the welding current detector 15 based on the voltage signal from the output transformer 14 to the work coil l, and as is clear from this waveform diagram,
Since the welding current 1111 is in a state in which a correction amount corresponding to the strength of the arc is added at the timing of arc generation, the current drop at welding point 02 is compensated for and a cold welding defect occurs at welding point 02. This means that this can be reliably prevented.

〔effect〕

As described above, in the method of the present invention, constant temperature control and constant welding current control for the welding point are performed simultaneously in the major loop and minor loop, respectively.
Not only does it have better responsiveness than when each is done individually, but it also eliminates the difficulty of changing the reference current setting, and since the reference current is corrected according to the strength of the arc, it is easier to place orders for arcs. The present invention has excellent effects such as being able to compensate for the decrease in the welding point current during the welding process and reliably preventing cold welding defects.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the implementation state of the method of the present invention together with its control system, and FIGS. 2(a) and (b). (C) and (D) are waveform diagrams showing the control contents, Figure 3 is an explanatory diagram showing the flow of current in the ERW welding part of the ERW pipe, and Figure 4
Figures (a) and (b) are explanatory diagrams of welding current, welding point current, and arc current. 1... Work coil 2... Squeeze roll 4a,
4b...Light guide 5...Welding point temperature detector 6
...Arc detector 7...Amplifier 8...Subtractor 9...Temperature controller lO...Adder 11...Subtractor 12...Welding current controller 13...High frequency power supply 14... Output Lance 15... Welding current detector S
...Strip P...Pipe Patent Applicant: Sumitomo Metal Industries Co., Ltd. Agent Patent Attorney: Noboru Kono 4-grain Heat Resistance Hibiki 1#Lz“ζ′
Iloki (in-temple moxibustion dawn fI7yLshiz-ichiruta 1 (b) 4 Figure

Claims (1)

[Claims] 1. During the ERW welding process of ERW pipes, the temperature at the welding point is detected and controlled to match the predetermined reference temperature using a measure loop, and the welding current to the V-shaped part is controlled. Welding current constant control is performed in a minor loop to match the welding current to a predetermined reference current, and the occurrence of an arc in the V-shaped portion is detected, and a correction current corresponding to the current of the arc is detected. A welding control method for an electric resistance welded pipe, characterized in that the current is added to the reference current in a minor loop.