JP3328378B2 - High frequency heating equipment - Google Patents

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 a metal pipe.

[0002]

2. Description of the Related Art Pipe welding includes a submerged arc welding method, a plasma welding method, a TIG welding method, a high-frequency electric resistance welding method, and the like. Because it is a highly efficient process, it is generally widely used. In the high-frequency electric resistance welding, as shown in FIG. 4, an open pipe 50 is formed by continuously bending and forming an annular shape with a roll so that both welded end surfaces 51 and 52 of a metal strip form a V-shape. From the high-frequency heating device C via the contact tips 56, 56, both welding end surfaces 51, 52
Is heated and melted through a high-frequency current, and then a lateral pressure is applied by a squeeze roll 55, and the two welded end faces 51 and 52 are butted and welded to produce a metal pipe 54.

FIG. 5 is a block diagram showing the configuration of a high-frequency heating device C generally used in such a high-frequency electric resistance welding method. This high-frequency heating device C
Includes a step-down transformer 32, a thyristor circuit 33, a step-up transformer 34, a rectifier circuit 35, a filter circuit 36, an oscillation circuit 37, and a current transformer 38. The high-voltage transformer 32 is connected to the AC power supply 31, and the current transformer 38 is a load. The circuit 39 is connected to an open pipe 50. The three-phase commercial frequency voltage supplied from the AC power supply 31 is stepped down to a predetermined voltage by the step-down transformer 32, and further adjusted in the thyristor circuit 33 to a predetermined output by switching operation of circuit elements. Next, the voltage is converted into a DC voltage by a rectifier circuit 35 via a step-up transformer 34, smoothed by a filter circuit 36 including a capacitor or the like, and then applied to an oscillation circuit 37. Oscillation circuit 3
Reference numeral 7 denotes a circuit including a vacuum tube, a coil, a resistor, a capacitor, and the like.
It generates a high-frequency power W _RF of about 0KHz～450kHz. The high frequency power W _RF is supplied to the car rent after being output converted by the transformer 38, and finally open the pipe 50 is a load circuit 39 via a work coil or contact tips 56, 56.

In order to keep the quality of the metal tube 54 at the best, the thickness of the metal tube 54, the welding speed, the welding end face 5
Depending on butt state of 1, 52 need to be adjusted to the optimum value high frequency power W _RF with. That is, the high frequency power W
_{When the RF} is low, the welding end faces 51 and 52 are not sufficiently melted to generate a cold welding defect with insufficient weld strength. Conversely, when the high frequency power W _RF is high, a minute oxide defect called a penetrator is generated. It stays between both welding end faces 51 and 52.

[0005] In the practical production Therefore, the welding operator bead appearance after welding, the excess and deficiency of the high frequency power W _RF empirically determined by observing the like occurrence of red-hot state and sputtering (scattering of molten steel), the high-frequency The power W _RF was being adjusted. However, such a method based on the empirical judgment of the worker has a large individual difference, and it is difficult to perform an accurate power setting. In addition, there is a problem that a high skill is required for the worker. there were.

[0006] Therefore, recently, automatic control of the high frequency power W _RF has been various attempts, they Sho 54-33
No. 784 and Japanese Patent Publication No. 54-40454. As disclosed therein, generally, the welding point 53 in the electric resistance welding changes periodically in the welding line direction. This is because the molten metal is formed by the electromagnetic force induced by the welding current flowing through the two 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 surfaces 51 and 52 is reduced. Since such a periodic fluctuation of the welding point 53 changes the high-frequency current path, the impedance periodically increases and decreases, and the high-frequency voltage and the high-frequency current also change. These find the relationship between the above-mentioned periodic fluctuation phenomenon of the welding point 53 and welding quality, detect the fluctuation of the welding point 53 as a welding phenomenon characteristic value, and perform feedback control based on this characteristic value. It is. Specifically, the excess or deficiency of the high-frequency power is detected from the characteristic value indicating the periodic variation of the welding point 53, and the firing phase angle of the thyristor circuit 33 is adjusted based on this. Thereby, the plate voltage of the vacuum tube of the oscillation circuit 37 is adjusted, and the high-frequency power is adjusted to an optimum value.

[0007]

However, in these methods, since the control target by feedback is the thyristor circuit 33, there is a limit due to the commercial frequency in terms of transient response, and control response is poor. Therefore, with the conventional method, it is possible to control a welding phenomenon that fluctuates at a relatively long pitch of about several hundred msec.
It has been difficult to control in real time the welding phenomenon itself that fluctuates at short time intervals of about sec to several tens of msec or less.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned 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.

[0009]

A high-frequency heating apparatus according to the present invention comprises: a direct-current voltage generating means for generating a direct-current voltage according to a set high-frequency power; and a pulse signal generating means for generating a pulse signal according to the direct-current voltage. Means, a DC power supply voltage generating means for generating a predetermined DC power supply voltage, a power transistor for switching the DC power supply voltage in accordance with the pulse signal, and a high frequency power for generating a high frequency power in accordance with the switching of the power transistor Generating means;
Detecting means for detecting a periodic variation of the high-frequency power,
DC voltage increasing / decreasing means for increasing / decreasing the DC voltage according to the detection result of the detecting means.

[0010] The DC power supply voltage generating means may include a thyristor and a rectifier circuit for converting an AC voltage into a DC power supply voltage.

[0011]

The high-frequency heating apparatus according to the present invention includes high-frequency power generating means for generating high-frequency power in accordance with switching of the power transistor, and detecting means for detecting a periodic variation of the high-frequency power. The switching of the power transformer is controlled in accordance with the periodic fluctuation of the high frequency power. Therefore, the high-frequency power can be controlled at a higher speed and the welding phenomena can be controlled at a higher speed than in the related art in which the high-frequency power is controlled by adjusting the firing phase angle of the thyristor.

[0012]

FIG. 1 is a block diagram showing a configuration of a high-frequency heating apparatus A according to one embodiment of the present invention. This high-frequency heating apparatus A includes a step-down transformer 2, a rectifier circuit 3, a filter circuit 4, a power transistor circuit 5, a step-up transformer 6, a rectifier circuit 7, a filter circuit 8, an oscillator circuit 9, a current transformer 10, a rectifier circuit 12, a differential circuit. Circuit 13, adder / subtractor 1
4, including a pulse generation circuit 15 and a DC voltage generation circuit 16, the step-down transformer 2 is connected to the AC power supply 1, and the current transformer 10 is connected to the open pipe 50 which is the load circuit 11 described in FIG.

The three-phase commercial frequency voltage supplied from the AC power supply 1 is stepped down to a predetermined voltage by the step-down transformer 2 and further converted to a DC voltage by the rectifier circuit 3. Since this DC voltage contains a slight pulsating flow, it is smoothed by the filter circuit 4 composed of the following capacitors and the like.
The smoothed DC voltage is applied to power transistor circuit 5 as DC power supply voltage V _CC .

[0014] On the other hand, when the welding operator sets the high frequency power W _RF e.g. dial corresponding to the open pipe 50 to be welded, a direct current voltage generating circuit 16, via a subtracter 14 a DC voltage V _S corresponding thereto And outputs it to the pulse generation circuit 15. As shown in FIG. 2, the pulse circuit 15 includes a positive pulse P having a time width T _ON according to the DC voltage V _S.
⁺ (T _ON) and a negative pulse ^P - (T _ON) a predetermined period T
(However, 0 ≦ T _ON ≦ T).
This AC pulse signal P is supplied to the power transistor circuit 5 as a switching signal.

Therefore, the power transistor circuit 5
Are an AC pulse voltage v having a waveform similar to the AC pulse signal P.
_OIs output and the AC pulse voltage v_OThe effective value of
ON time ratio (T_ON/ T)
More tuned. Here, the switching frequency f (= 1)
/ T) is suitable for high frequency control as high as possible
However, in practice, it is sufficient that the frequency is several kHz to several tens kHz or more. This
After that, the AC pulse voltage v _OIs the conventional circuit shown in FIG.
In the same manner as described above, the voltage is stepped up by the step-up
7 again converts the voltage into a DC voltage, and the filter circuit 8 smoothes it.
And applied to the oscillation circuit 9. In the oscillation circuit 9
Generated high frequency power W_RFIs through the current transformer 10
And supplied to the open pipe 50 which is the load circuit 11.
You.

The rectifier circuit 12 detects a high-frequency current _IRF in the oscillation circuit 8 in order to detect a fluctuating welding phenomenon in the load circuit 11. As described above, the welding point 53 in the electric resistance welding changes periodically in the welding line direction, and this phenomenon changes the welding current path, and the high frequency current _IRF similarly changes because the impedance increases and decreases. . Originally, it is desirable to detect the high-frequency current _IRF or the high-frequency voltage in the load circuit 11. However, in the present embodiment, the high-frequency current _IRF in the oscillation circuit 9 is measured due to the difficulty of measurement.

The differentiating circuit 13 detects a variation ΔI _RF of the high-frequency current I _RF detected by the rectifier circuit 12, and based on the variation ΔI _RF , determines whether the high-frequency power W _{RF applied} to the open pipe 50 is sufficient. detects and outputs a DC voltage [Delta] V _S necessary to correct the excess and deficiency of the high frequency power W _RF in adder-subtracter 14. The adder / subtractor 14 adds and subtracts the DC voltage V _S input from the DC voltage generation circuit 16 and the DC voltage ΔV _S input from the differentiation circuit 13 and outputs the result to the pulse generation circuit 15. The pulse generation circuit 15 outputs a pulse signal P corresponding to the corrected DC voltage V _S + ΔV _S to the power transistor circuit 5. The power transistor circuit 15 outputs the AC pulse voltage v _O according to the pulse signal P, the AC pulse voltage v _O is converted to a DC voltage V _PP oscillation circuit 9
Is applied to Therefore, the high frequency power W _RF is corrected to an appropriate value.

Table 1 shows the occurrence rate of welding defects, the occurrence rate of surface defects due to spatter, and the number of times of mill stoppage due to the same cause when pipe production was performed under various conditions (outer diameter, wall thickness, pipe production speed). This is a comparison between the case where the high-frequency heating device A of this embodiment is used and the case where the conventional high-frequency heating device B is used. In Table 1, the welding defect occurrence rate and the like when the conventional high-frequency heating device C is used are set to 1, and the ratio when the high-frequency heating device A of the present embodiment is used is shown as a ratio to 1.

[0019]

[Table 1]

As shown in Table 1, when the high-frequency heating apparatus A of this embodiment is used, the welding defect occurrence rate and the like are reduced by a factor of 1 /
It was found that it could be reduced from 3 to about 1/10.

As described above, the use of the high-frequency heating apparatus A of the present embodiment not only stabilizes the welding phenomenon and reduces welding defects, but also suppresses the generation of spatters, deteriorating the surface quality due to the indentation of spatters and the inner surface beads. Deterioration in productivity such as a stoppage of the mill due to accumulation on the cutting jig is prevented.

In this embodiment, the high-frequency power W _RF is controlled by controlling the _ON time T _ON while keeping the switching period T of the AC pulse signal P constant. Conversely, the ON time T _ON is kept constant. it may control the high-frequency power W _RF by controlling the switching period T.

Further, in this embodiment, it detects a high-frequency current I _RF oscillation circuit 9 in order to detect the welding phenomenon that varies in the load circuit 11 is not limited to this,
High frequency voltage, frequency, phase difference, etc. may be detected. In addition, not only one, but a plurality may be detected.

Further, as shown in FIG.
If the thyristor circuit 17 and the step-up transformer 18 are provided between the rectifier circuit 3 and the rectifier circuit 3, the DC power supply voltage V _CC applied to the power transistor circuit 5 can also be adjusted, and the high-frequency power W _RF can be more appropriately controlled. it can.

[0025]

As described above, according to the present invention, the high frequency power is controlled by controlling the switching of the power transistor. Therefore, the high frequency power is controlled by controlling the firing phase angle of the thyristor. Compared with the conventional art, high-frequency power can be controlled at high speed, and welding phenomena can be controlled at high speed. In addition, it is possible to control the welding phenomenon at high speed and stabilize the welding phenomenon, and it is obvious that the incidence of welding defects is drastically reduced. Heat input management is also easy and the load on the welding operator is reduced. In addition, since the generation of spatter can be suppressed, excellent effects such as deterioration of surface quality due to indentation of spatter and no stoppage due to deposition on the inner bead cutting jig are eliminated.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a high-frequency heating device according to one embodiment of the present invention.

FIG. 2 is a waveform diagram illustrating an AC pulse signal P output from a pulse generation circuit of the high-frequency heating device shown in FIG.

FIG. 3 is a block diagram showing a configuration of a high-frequency heating device according to another embodiment of the present invention.

FIG. 4 is a partially broken front view showing a high-frequency electric resistance welding method using a high-frequency heating device.

FIG. 5 is a block diagram illustrating a configuration of a conventional high-frequency heating device.

[Explanation of symbols]

 Reference Signs List 5 power transistor circuit 9 oscillation circuit (high-frequency power generation means) 13 differentiating circuit (detection means) 14 adder / subtractor (DC voltage increasing / decreasing means) 15 pulse generation circuit 16 DC voltage generation circuit 50 open pipe 51, 52 welding end face 53 welding point 54 Metal tube A, B High frequency heating device

Continuation of the front page (51) Int.Cl. ⁷ identification code FI H05B 6/10 341 H05B 6/10 341 (58) Investigated field (Int.Cl. ⁷ , DB name) B23K 13/00 B23K 13/08 G05F 1/02 H02K 9/00 H05B 6/08 H05B 6/10

Claims (2)

(57) [Claims] 1. A DC voltage generating means for generating a DC voltage according to a set high frequency power, a pulse signal generating means for generating a pulse signal according to the DC voltage, and a DC for generating a predetermined DC power supply voltage Power supply voltage generation means, a power transistor that switches the DC power supply voltage in accordance with the pulse signal, high-frequency power generation means that generates high-frequency power in accordance with switching of the power transistor, and a periodic variation of the high-frequency power And a DC voltage increasing / decreasing means for increasing / decreasing the DC voltage according to a detection result of the detecting means. 2. The high-frequency heating apparatus according to claim 1, wherein said DC power supply voltage generating means includes a thyristor and a rectifier circuit for converting an AC voltage into a DC power supply voltage.