Electric heating – Metal heating – Of cylinders
Patent
1986-08-06
1988-04-26
Shaw, Clifford C.
Electric heating
Metal heating
Of cylinders
219110, B23K 1108
Patent
active
047406658
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
1. Technical Field
The present invention relates to an apparatus for automatically controlling the heat input by a high frequency power source of welding. The apparatus according to the present invention is used, for example, for an automatic control of heat input during a high quality, high frequency welding of a tube to be electrically welded.
2. Background Art
In general, in the process for manufacturing an electric welded steel tube wherein a steel plate is bent into the form of a pipe and the butt joints of the edges of the bent steel plate are welded by high frequency welding, it is necessary to control the heat input to the optimal state and, therefore, variations of the frequency of the power source for the welding are monitored and a control of the heat input is carried out to obtain an optimal frequency of the power source for the welding.
A so-called V shape groove is formed in the electrically welded portion during welding, and the ridge of this V shape groove constitutes the welding point. However, the position of this welding point is not settled, and is varied to a small or large extent in accordance with the condition of the welding. For example, no variation of the welding point takes place when the level of the heat input is low, but the position of the welding point is varied with a certain amplitude and a certain frequency when the level of the heat input is high. For example, it is possible to classify the phenomena of welding into first, second, and third types, as follows. That is, the phenomenon in which the variation of the position of the welding point is small is the first type of welding phenomenon, the phenomenon in which the variation of the position of the welding point is medium is the second type of welding phenomenon, and the phenomenon in which the variation of the position of the welding is large and unlimited is the third type of welding phenomenon. By detecting to which type of welding phenomenon the present state belongs, and regulating the condition of welding to attain the desirable welding phenomenon, it is possible to attain a good quality welding. When the welding point is varied, the load of the high frequency oscillation circuit constituting the welding power source is varied, and the output oscillation frequency, the phase difference between the output voltage and current, and the output power are varied. Hence, by detecting one of the above-described variables, it is possible to detect the variation in the position of the welding point and to determine to which of the first to third types of the welding phenomena the present welding phenomenon belongs. In the case of the usual electrical seam welding, if the variations of the frequency or cycle period of the power source are detected and the control of heat input is carried out to attain the second type of welding phenomenon, it is possible to perform a suitable welding.
In the prior arts, for carrying out a control such as described above, the inverse of the width .DELTA.f of variation of frequency, and accordingly, the width .DELTA.(1/f) of the variation of a cycle period, are detected, and the output of the high frequency power source for welding is controlled to make the detected width .DELTA.(1/f) of variation of cycle period equal to the target optimal value of .DELTA.(1/f)(T). The steel pipe to be welded is the load of the power source, that is the high frequency oscillation circuit. The welding state has an influence on the oscillation frequency f(i) of the high frequency oscillation circuit. When the welding state is changed, the position of the welding point is changed, and accordingly, the oscillation frequency is changed. The frequency f(i) is supplied to the 1/f counter, the output of which is frequency-divided, for example, divided by 100, by a frequency divider. A pulse corresponding to the rising or falling edge of the frequency divided output f/100 is generated by a monostable multivibrator. The generated pulse is supplied to a latch circuit through a counter circuit. A first out
REFERENCES:
patent: 4254323 (1981-03-01), Takamatsu et al.
Miyata Shigehisa
Sanmiya Seietsu
Nippon Steel Corporation
Shaw Clifford C.
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