JPH0740062A - High frequency heating device - Google Patents

Abstract

PURPOSE:To provide a high frequency heating device capable of controlling welding phenomenon in high speed. CONSTITUTION:A DC voltage generating circuit 11 outputs DC voltage Vs corresponding to a resonance frequency f0 of a resonance circuit 8. A switching control circuit 13 executes on/off for the power transistor of a switching circuit at the frequency f=f0 corresponding to the DC voltage given through an addition/subtraction unit 12. An arithemetic unit 10 detects excess/shortage of a high frequency power WRF by detecting a cyclic fluctuation DELTAIRF of high frequency current of the resonance circuit 8, and then the DC voltage DELTAVS required for correcting the excess/shortage is outputted to the addition/subtraction unit.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high frequency heating device, and more particularly to a high frequency heating device used for high frequency electric resistance welding of metal pipes.

[0002]

2. Description of the Related Art Pipe forming welding methods include a submerged arc welding method, a plasma welding method, a TIG welding method, and a high frequency electric resistance welding method. Of these, the high frequency electric resistance welding method is the most It is widely used because it is a highly efficient process. In the high frequency electric resistance welding method, as shown in FIG. 3, after continuously bending and forming a tubular shape with a roll so that both welding end surfaces 51 and 52 of the metal strip form a V shape, an open pipe 50 is formed. Both welding end faces 51, 52 from the high-frequency heating device C via the contact tips 56, 56.
Is a method of manufacturing a metal tube 54 by subjecting both welding end faces 51, 52 to abutting welding by applying a lateral pressure by a squeeze roll 55 by heating and melting by passing a high frequency current.

FIG. 4 shows the high-frequency electric resistance welding method.
Of the high frequency heating device C that has been generally used
It is a block diagram which shows a structure. This high frequency heating device C
Is an AC voltage adjusting circuit 32, a transformer 33, a rectifying circuit 3
4, including a filter circuit 35 and a high frequency circuit 36,
The flow voltage adjusting circuit 32 is connected to the AC power source 31,
The circuit 36 is connected to the open pipe 50 which is the load circuit 37.
Will be continued. In the figure, the AC voltage adjustment circuit 32 is not set.
High frequency power W_RFFiring position of the built-in thyristor according to
Commercial frequency supplied from AC power supply 31 by adjusting the phase angle
Adjust the rms value of the number voltage. AC voltage adjusting circuit 32
Therefore, the AC voltage whose RMS value is adjusted is
After being boosted,
Is converted to high DC voltage in the current circuit 34,
It is smoothed by the filter circuit 35 including a capacitor. smooth
The converted DC high voltage is supplied to the next high frequency circuit 36 as a DC power source.
Voltage V _PPGiven as.

FIG. 5 is an electric circuit diagram showing the configuration of the high frequency circuit 36. In the figure, the vacuum tube 38 performs a class C amplification operation, and the DC power supply voltage V _PP described above is applied to the vacuum tube 3.
8 between the plate P and the cathode K. Between the grid G of the vacuum tube 38 and the cathode K, a grid resistance 4
0 is connected, which provides a bias voltage. Between the plate P of the vacuum tube 38 and the cathode K,
A resonance circuit 45 in which a resonance coil 44 and a resonance capacitor 43 are connected in parallel is connected via a coupling capacitor 39. Further, the capacitor 4 is connected in parallel with the resonance circuit 45.
A voltage dividing circuit formed by connecting 1 and 42 in series is connected, and the connection point of the capacitors 41 and 42 is connected to the grid G of the vacuum tube 38. Therefore, the high frequency voltage generated in the resonance circuit 45 is divided by the voltage dividing capacitors 41 and 42 and fed back to the grid G of the vacuum tube 38. As a result, the vacuum tube 38 performs a switching operation in synchronization with the high frequency voltage generated in the resonance circuit 45, and the vacuum tube 38 oscillates. The high frequency current at this time is a kind of pulsating current with various frequency components,
Of these, components other than the resonance frequency component of the resonance circuit 45 are attenuated,
Only the resonance frequency component remains. A secondary coil 46 is linked to the resonance coil 44, and the two coils 44, 4
6 is a current transformer. The secondary coil 46 is connected to the contact chips 56, 56, and the high frequency current generated in the resonance circuit 45 is supplied to the open pipe 50 which is the load circuit 37.

Recently, instead of the high frequency heating device C using the vacuum tube 38 as described above, a high frequency heating device using a semiconductor element (for example, a power transistor) is being developed and put into practical use. This is because the recent progress in power electronics technology has led to the development of a semiconductor element that can withstand a high frequency and a high output of about 200 to 500 kHz, which is used for welding electric resistance welded pipes. This is because the high-frequency heating device using is advantageous in that it has less energy loss as compared with the conventional vacuum tube system and that the equipment is compact, so there are few restrictions on installation. The high frequency heating device using a semiconductor element has almost the same structure as the conventional one shown in FIG. 4, but the conventional high frequency heating device C generates high frequency power W _RF by utilizing the oscillation action of the vacuum tube 38. In contrast to this, the semiconductor system is different in that the high frequency power W _RF is generated by performing the switching operation of the element at high speed. The switching frequency at this time can be arbitrarily changed by changing the switching cycle of the semiconductor element, but in order to avoid attenuation in the resonance circuit 45, it matches the resonance frequency determined by the resonance capacitor 43, the resonance coil 44, and the like. It is normal to let them do it.

By the way, in order to keep the quality of the metal pipe 54 at the best level, the thickness of the metal pipe 54, the welding speed, the welding end surface 5
It is necessary to adjust the high frequency power W _RF to an optimum value according to the matching state of 1, 52 and the like. That is, the high frequency power W _RF
If the welding temperature is low, both welding end faces 51, 52 do not melt sufficiently, and a cold welding defect with insufficient weld strength occurs. On the contrary, if the high-frequency power W _RF is high, a small oxide defect called a penetrator occurs. Remains between the weld end faces 51 and 52.

Therefore, in actual production, the welding operator empirically determines whether the high frequency power W _RF is excessive or insufficient by observing the appearance of the bead after welding, the state of red heat and the state of spatter (scattered molten steel). The power W _RF was being adjusted. However, such a method based on the empirical judgment of the operator has a large individual difference, and it is difficult to perform accurate power setting. Moreover, there is a problem that the operator is required to have a high degree of skill. there were.

Therefore, recently, various attempts have been made to automatically control the high frequency power W _RF , which are disclosed in Japanese Patent Publication No. 54-33.
It is disclosed in Japanese Patent Publication No. 784 and Japanese Patent Publication No. 4040454. As disclosed in these documents, generally, the welding point 53 in electric resistance welding periodically fluctuates in the welding line direction. This is an electromagnetic force induced by a welding current flowing through both the welding end faces 51, 52 so that the molten metal is welded by the welding end faces 51, 52.
This is caused by the fact that it is extruded to the outside of 52 and the approach speed of both welding end faces 51, 52 slows down. As described above, the periodical change of the welding point 53 changes the high frequency current path, so that the impedance periodically changes and the high frequency voltage and the high frequency current also change. These are for finding the relationship between the periodic fluctuation phenomenon of the welding point 53 and the welding quality as described above, detecting the fluctuation of the welding point 53 as a welding phenomenon characteristic value, and performing feedback control based on this characteristic value. Is. Specifically, the excess or deficiency of the high frequency power W _RF is detected from the characteristic value indicating the periodic fluctuation of the welding point 53, and the ignition phase angle of the thyristor of the AC voltage adjusting circuit 32 is adjusted based on this. As a result, the plate voltage of the vacuum tube 38 of the high frequency circuit 36 is adjusted, and the high frequency power W _RF is adjusted to an optimum value.

[0009]

However, in these methods, since the object to be controlled by feedback is the thyristor of the AC voltage adjusting circuit 32, there is a limit in the transient response due to the commercial frequency, and the control response is low. It was bad. Therefore, in the conventional method, it is possible to control the welding phenomenon that fluctuates at a relatively long pitch of several hundred msec, but the welding phenomenon itself that fluctuates in a short time interval of several msec to several tens msec or less. Was difficult to control in real time.

The present invention has been made in view of the above conventional drawbacks, and an object of the present invention is to provide a high frequency heating apparatus capable of controlling a welding phenomenon at a high speed.

[0011]

A high-frequency heating apparatus according to the present invention comprises a resonance means having a predetermined resonance frequency, a DC voltage generation means for generating a predetermined DC voltage according to the resonance frequency, and a DC voltage A switching means for switching a DC power supply voltage at a frequency corresponding to the generated resonance frequency and applying a high frequency power to the resonance means, a detection means for detecting a periodic fluctuation of the high frequency power, and a detection result of the detection means. And a DC voltage increasing / decreasing means for increasing / decreasing the DC voltage.

[0012]

A high frequency heating apparatus according to the present invention comprises a switching means for switching a DC power supply voltage and applying it to a resonance means to generate a high frequency power, and a detection means for detecting a periodic variation of the high frequency power. The switching frequency of the switching means is controlled according to the detected periodic fluctuation of the high frequency power. The high frequency power becomes maximum when the switching frequency is equal to the resonance frequency of the resonance means, and the high frequency power becomes smaller as the switching frequency deviates from the resonance frequency. Therefore, the high frequency power can be controlled by controlling the switching frequency. Therefore, the high frequency power can be controlled at a higher speed and the welding phenomenon can be controlled at a higher speed than in the conventional case where the high frequency power is controlled by controlling the effective value of the AC voltage of the commercial frequency with the thyristor.

[0013]

1 is a block diagram showing the structure of a high frequency heating apparatus A according to an embodiment of the present invention, and FIG. 2 is a block diagram of a high frequency circuit 6 including electric circuit diagrams of a switching circuit 7 and a resonance circuit 8 thereof. . The high frequency heating device A includes an AC voltage adjusting circuit 2, a transformer 3, a rectifying circuit 4, a filter circuit 4 and a high frequency circuit 6, and further includes a high frequency circuit 6.
Includes a switching circuit 7, a resonance circuit 8, a high frequency current detection circuit 9, an arithmetic circuit 10, a DC voltage generation circuit 11, an adder / subtractor 12 and a switching control circuit 13. The AC voltage adjustment circuit 2 is connected to the AC power supply 1, and the resonance circuit 8 is connected to the load circuit 14 which is the open pipe 50 described in FIG.

When the welding operator sets the high frequency power W _RF corresponding to the open pipe 50 to be welded by, for example, a dial, the AC voltage adjusting circuit 2 adjusts the firing phase angle of the built-in thyristor accordingly. AC power supply 1
Adjust the effective value of the commercial frequency AC voltage supplied from. The AC voltage whose effective value is adjusted by the AC voltage adjusting circuit 32 is boosted by the transformer 3 and further converted into a DC high voltage by the rectifying circuit 4. Since this DC high voltage contains some pulsating current, it is smoothed by the filter circuit 5 composed of the following capacitor and the like and is given to the high frequency circuit 6 as the DC power supply voltage V _CC .

The high frequency circuit 6 generates a high frequency power W _RF having a magnitude corresponding to the DC power supply voltage V _CC and supplies it to the open pipe 50 which is the load circuit 14. More specifically, the DC power supply voltage V _CC is applied between the input terminals 7a and 7b of the switching circuit 7, as shown in FIG. In the switching circuit 7, the NPN power transistor 15,
The emitter of 17 is connected to the collectors of NPN power transistors 16 and 18 via nodes N1 and N2, respectively, and the collectors of NPN power transistors 15 and 17 are connected to one input terminal 7a, and NPN power transistors 16 and 18 are connected. The emitter of is connected to the other input terminal 7b. Also, the NPN power transistor 1
The bases of 5, 16, 17, and 18 are connected to the switching control circuit 13.

The resonance circuit 8 has a resonance capacitor 19 and a resonance coil 20 connected in parallel, and is connected between the nodes N1 and N2 of the switching circuit 7. A secondary coil 21 is linked to the resonance coil 20, and the two coils 20 and 21 form a current transformer. The secondary coil 21 has contact chips 56, 5
It is connected to the open pipe 50 via 6.

The DC voltage generating circuit 11 has the same function as the resonance circuit 8.
Swing frequency f₀DC voltage V according to_SAdder / subtractor 1
2 to the switching control circuit 13. Sui
Of the DC voltage V_SFrequency according to
f = f₀Power transistors 15, 18; 16, 17
Alternate on and off. Power transistors 15 and 18
Turns on and turns off the power transistors 17 and 18.
As shown by the arrow a in the figure, the input terminal 7a, the power
Transistor 15, node N1, resonance circuit 8, node N
2, power transistor 18 and input terminal 7b
The flow flows. In addition, the power transistors 17 and 16 are turned on.
When the power transistors 15 and 18 are turned off,
Input terminal 7a, power transistor
Star 17, node N2, resonant circuit 8, node N1, power
-Current flows through the path of transistor 16 and input terminal 7b
It By repeating the above operation at high speed,
High frequency current I_RFCan be generated. This high frequency
Current I_RFAre power transistors 15, 18; 16, 1
The frequency f for turning on / off 7 is the resonance frequency f of the resonance circuit 8.
₀Power transistor 1 becomes maximum when
5, 18; frequency f for turning on and off 16, 17 is the resonance frequency
Wave number f₀It gets smaller as it goes away from.

The high frequency current detection circuit 9 detects the high frequency current I _RF in the resonance circuit 8 in order to detect the fluctuating welding phenomenon in the load circuit 14. As described above, the welding point 53 in the electric resistance welding periodically fluctuates in the welding point direction, and the welding current path changes due to this phenomenon, and the impedance increases and decreases, so the high-frequency current I _RF also changes. . Originally, it is desirable to detect the high-frequency current I _RF in the load circuit 14, but due to the difficulty of measurement, the high-frequency current I _RF in the resonance circuit 8 is measured in this embodiment.

The arithmetic circuit 10 detects the variation [Delta] I _RF of the detected high-frequency current I _RF in the high-frequency current detecting circuit 9, the high frequency power W _RF have given open pipe 50 on the basis of the variation [Delta] I _RF Detects excess and deficiency and high frequency power W _RF
The DC voltage ΔV _S required to correct the excess or deficiency of the above is output to the adder / subtractor 12. The adder / subtractor 12 adds and subtracts the DC voltage V _S input from the DC voltage generation circuit 11 and the DC voltage ΔV _S input from the arithmetic circuit 10 and outputs the added voltage to the switching control circuit 13. Switching control circuit 13
Is the frequency f according to the corrected DC voltage V _S + ΔV _S
= F ₀ + Δf ₀ , power transistors 15, 18; 1
7 and 16 are turned on and off, and the high frequency current I is fed into the resonance circuit 8.
Generate _RF . Therefore, the high frequency power W _RF is corrected to an appropriate value.

Table 1 shows the welding defect occurrence rate, the surface flaw occurrence rate due to spatter generation, and the number of mill stoppages due to the same cause when pipes were produced under various conditions (outer diameter, wall thickness, pipe production speed). It is a comparison between the case where the high frequency heating apparatus A of the present embodiment is used and the case where the conventional high frequency heating apparatus C is used. In Table 1, the welding defect occurrence rate when the conventional high-frequency heating apparatus C is used is set to 1, and when the high-frequency heating apparatus A of this embodiment is used, it is shown as a ratio to 1.

[0021]

[Table 1]

As shown in Table 1, it has been found that the use of the high frequency heating apparatus A of this embodiment can reduce the welding defect occurrence rate to about 20 to 40% of the conventional rate.

As described above, when the high frequency heating apparatus A of the present embodiment is used, not only the welding phenomenon is stabilized and welding defects are reduced, but also spatter generation is suppressed, the surface quality is deteriorated due to the indentation of spatter, and the inner surface bead is suppressed. Productivity deterioration such as mill stoppage due to accumulation on the cutting jig is prevented.

In this embodiment, the NPN power transistor is used as the switching semiconductor element in the switching circuit 7. However, the present invention is not limited to this, and a PNP power transistor may be used.
An OS power transistor may be used.

Further, the high frequency current I _RF of the resonance circuit 8 is detected in order to detect the fluctuating welding phenomenon in the load circuit 14, but the present invention is not limited to this, and high frequency voltage, frequency, phase difference, etc. are detected. Good. Further, the number is not limited to one, and a plurality may be detected.

[0026]

As described above, according to the present invention, since the high frequency power is controlled by controlling the switching frequency of the switching means, the high frequency is controlled by controlling the effective value of the AC voltage of the commercial frequency with the thyristor. High-frequency power can be controlled at a high speed, and the welding phenomenon can be controlled at a high speed, as compared with the conventional case where the power is controlled. Also, of course, high-speed control of the welding phenomenon will be possible, the welding phenomenon will be stabilized, and the incidence of welding defects will drastically decrease.
Heat input management is also facilitated and the load on the welding operator is reduced. Further, since it is possible to suppress the generation of spatter, excellent effects such as deterioration of surface quality due to indentation of spatter and stoppage due to deposition on the inner bead cutting jig are eliminated.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a high frequency heating apparatus according to an embodiment of the present invention.

FIG. 2 is a block diagram of a high frequency circuit including electrical circuits of a switching circuit and a resonance circuit in the high frequency heating device shown in FIG.

FIG. 3 is a partially cutaway front view showing a high frequency electric resistance welding method in which a high frequency heating device is used.

FIG. 4 is a block diagram showing a configuration of a conventional high-frequency heating device.

5 is an electric circuit diagram of a high frequency circuit of the high frequency heating device shown in FIG.

[Explanation of symbols]

 A high-frequency heating device 7 switching circuit 8 resonance circuit 9 high-frequency current detection circuit 10 arithmetic circuit 11 DC voltage generation circuit 12 adder / subtractor 13 switching control circuit 50 open pipe 51, 52 welding end face 53 welding point 54 metal pipe

Claims (1)

[Claims] 1. A resonance means having a predetermined resonance frequency, a DC voltage generation means for generating a predetermined DC voltage according to the resonance frequency, and a DC power supply voltage that is switched at a frequency according to the DC voltage. Switching means for applying high-frequency power to the resonance means to generate high-frequency power, detection means for detecting a periodic fluctuation of the high-frequency power, and direct-current voltage increasing / decreasing means for increasing / decreasing the direct-current voltage according to the detection result of the detecting means. A high-frequency heating device comprising: