JP2000000678A - Power unit for flash butt welding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power unit for flash butt welding capable of generating a stable superior flash against fluctuation of a power unit voltage. SOLUTION: An AC of three-phase AC power unit 1 is converted to DC by the rectifier 3 of an inverter power unit circuit 2; the inverter input voltage is detected by a voltage detector 4; the frequency of square wave DC optimal for the voltage so detected is calculated by a computing element 7; on the basis of such frequency, the output current of an output part 6 is controlled by a controller 8, as is the rising speed of the output current; it is then converted to a low voltage high current; it is further rectified to a DC on the secondary side, with a constant welding current energized to an object 12 to be welded, regardless of the fluctuation of the power unit voltage.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a power supply device used for flash butt welding.

[0002]

2. Description of the Related Art In flash butt welding, a voltage is applied between two members to be welded to generate a flash to heat and melt the end surfaces of the members (flash process), sufficiently heat the end surfaces, and then rapidly press the members together. (Upset process). In such flash butt welding, when the power supply voltage fluctuates due to the installation location of the welding equipment or the power load of other equipment, it directly leads to fluctuations in the applied voltage of members and flash current, and ultimately reduces the flash generation rate. Cause damage to welding quality. For this reason, in the conventional flash butt welding equipment, many taps are provided on a down transformer or a welding transformer from the power transmission line, and the power tap is manually or automatically switched to a voltage tap that is optimal for flash generation in response to a fluctuation in power supply voltage. Fluctuations in the member applied voltage and flash current due to the voltage fluctuations are prevented as much as possible.

[0003]

However, in the conventional flash butt welding apparatus, an automatic transformer type that automatically switches taps is very expensive and can cope with voltage fluctuations during welding. Can not. If a thyristor-type tap changer is installed between the tap of the welding transformer and the power transformer, automatic switching can be performed for voltage fluctuations during welding. It is. Therefore,
It is difficult to finely switch the voltage tap in accordance with the time variation of the voltage, and a high voltage applied to the member is set by predicting the voltage drop in advance. In this case, it is possible to prevent a decrease in the flash generation rate due to a voltage drop, but if there is no voltage drop, the flash becomes rough because the applied voltage to the member is high, which adversely affects welding quality.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and has been made stable without introducing a voltage tap switching system for keeping a member applied voltage constant with respect to a power supply voltage fluctuation. It is an object of the present invention to provide a power supply device for flash butt welding capable of generating a good flash.

[0005]

A flash butt welding power supply according to the present invention comprises an inverter power supply circuit for converting three-phase alternating current from a three-phase alternating current power supply into a rectangular wave alternating current, and converting the rectangular wave alternating current to a low voltage high voltage. In a power supply device for flash butt welding, comprising a welding transformer for converting to a current, and a rectifying circuit for rectifying to a direct current on a secondary side thereof and supplying current to a material to be welded,
A voltage detector for detecting an input voltage of the inverter power supply circuit, and changing a frequency of the rectangular wave AC with respect to a change in the voltage detected by the voltage detector; And a control circuit for controlling the rising speed.

[0006] In flash butt welding, the conditions for the material to be welded and the optimum voltage applied to each welding machine exist depending on the cross-sectional area of the member and the impedance of the welding machine.
This is due to the fact that there is an optimum flash welding current for generating a stable and good flash and a rising speed of the current. Therefore, it is possible to generate a stable flash by controlling the flash current value and its rising speed with respect to voltage fluctuations, in addition to switching the voltage taps to make the applied voltage constant as in the related art. A flash including an inverter power supply circuit that outputs a rectangular wave AC, a welding transformer that converts the rectangular wave AC into a low voltage and a high current, and a rectifier circuit that rectifies the DC to a secondary side and supplies the current to the workpiece. In the butt welding power supply device, the rising speed and the maximum current value of the flash welding current may decrease as the frequency of the rectangular wave AC increases due to the inductance of the welding main circuit portion from the inverter output section to the diode side of the rectifier circuit. know. Therefore, in the inverter power supply circuit, since the three-phase alternating current of the commercial power supply is once converted to direct current, and then the rectangular wave alternating current is output by the switching elements such as thyristors and transistors, the rectangular wave alternating current can be easily changed by changing the switching timing. Can be changed. Therefore, by providing a detector of the input voltage of the inverter power supply circuit and a control circuit for changing the frequency of the output rectangular wave AC with respect to the change of the input voltage,
When the power supply voltage is reduced, the frequency is lowered to increase the rising speed of the welding secondary current and the current, and when the power supply voltage is increased, the frequency is raised to increase the welding secondary current and the rising of the current. The speed is decreased, and thus the welding current can be kept constant irrespective of the fluctuation of the power supply voltage, and a stable and good flash can be generated.

[0007]

FIG. 1 is a circuit diagram of a power supply device for flash butt welding according to an embodiment of the present invention.
In FIG. 1, reference numeral 1 denotes a three-phase AC power supply, and reference numeral 2 denotes an inverter power supply circuit, in which a three-phase AC full-wave rectifier 3, a voltage detector 4, a capacitor 5, and an inverter output unit 6 are connected in parallel. 7 is an inverter frequency calculator for calculating the frequency of the rectangular wave AC rectified by the rectifier 3, 8 is an inverter control device for controlling the output current of the inverter output section 6 and the rising speed of the output current based on the optimum frequency, 9 Is a welding transformer, and 10 is a rectifier circuit on the secondary side of the welding transformer, which in this example is configured as a midpoint tap type using a diode 11. Reference numeral 12 denotes a material to be welded.

In the inverter power supply circuit 2, the three-phase AC from the three-phase AC power source 1 is full-wave rectified by the rectifier 3, and then stored in the capacitor 5 and converted to DC. By monitoring this DC voltage with the voltage detector 4, the voltage fluctuation of the three-phase AC power supply 1 is detected. An optimum inverter output frequency is calculated by the inverter frequency calculator 7 according to the detected voltage value, and the inverter control device 8
To be transmitted. As a result, the inverter output section 6 outputs a rectangular wave having an optimum frequency, converts the rectangular wave into a low voltage and a high current by the welding transformer 9, further rectifies the current to a direct current by the rectifier circuit 10 on the secondary side, and flows to the work 12. The welding current can be kept constant.

FIG. 2 shows the relationship between the inverter frequency and the output current value. The higher the frequency is, the lower the output current becomes. When increasing the power supply voltage V ₀ to V ₂ the curve rises overall, it decreases when reduced to V _1. Assuming that the inverter frequency at which the optimum output current is obtained at the power supply voltage V ₀ is f ₀ , the power supply voltages are V ₁ and V
The inverter frequencies for keeping the output current constant when it changes to ₂ are f ₁ and f ₂ , respectively. When this is converted into the relationship between the power supply voltage and the inverter frequency, the function f = g (V) is obtained as shown in FIG. The inverter frequency calculator 7 of FIG. 1 obtains the inverter frequency from the power supply voltage based on this function. The function f = g (V) can be a step-like function when it is not necessary to change the frequency finely other than a continuous curve as shown in FIG.

FIG. 4 shows the relationship between the inverter frequency and the rising speed of the output current when the power supply voltage is constant. When the inverter frequency increases, the rising speed of the output current decreases, and when the inverter frequency decreases, the rising speed increases. At a predetermined power supply voltage, an inverter frequency at which the output current has an optimum rising speed is determined, and a function indicating a relationship between the inverter frequency and the power supply voltage at which the output current rising speed is optimized when the power supply voltage fluctuates is obtained.
The inverter output unit 6 is controlled based on this function. Further, the voltage detector 4 in FIG. 1 may be installed anywhere as long as the fluctuation of the power supply voltage can be detected, and may be provided between the three-phase AC power supply 1 or between the three-phase AC power supply 1 and the rectifier 3.

[0011]

As described above, according to the present invention, an optimum welding current can always be maintained even during welding with respect to fluctuations in the power supply voltage, so that a stable and good flash can be generated. . Further, in the case of performing feedback control using a parameter including a flash current value in the member feed control of the flash butt welding device, since the flash welding current changes due to a change in the power supply voltage,
Unless the control conditions are changed accordingly, the proper control state cannot be maintained. However, according to the present invention, the flash welding current can always be kept constant regardless of the fluctuation of the power supply voltage. There is no need to bring about an effect that an appropriate control state can be maintained.

[Brief description of the drawings]

FIG. 1 is a circuit configuration diagram of a power supply device for flash butt welding according to the present invention.

FIG. 2 is a diagram showing a relationship between an inverter frequency and an output current value.

FIG. 3 is a diagram illustrating a relationship between a power supply voltage and an inverter frequency when an output current is constant.

FIG. 4 is a diagram illustrating a relationship between an inverter frequency and a rising speed of an output current when a power supply voltage is constant.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 3 phase alternating current power supply 2 Inverter power supply circuit 3 3 phase alternating current full-wave rectifier 4 Voltage detector 5 Capacitor 6 Inverter output part 7 Inverter frequency calculator 8 Inverter control device 9 Welding transformer 10 Rectifier circuit 11 Diode 12 Workpiece

Claims (1)

[Claims] 1. An inverter power supply circuit for converting a three-phase AC from a three-phase AC power supply to a rectangular wave AC, a welding transformer for converting the rectangular wave AC to a low voltage and a high current, and a rectifier to a DC on a secondary side thereof. A flash butt welding power supply device comprising: a rectifier circuit for energizing the work to be welded; and a voltage detector for detecting an input voltage of the inverter power supply circuit; and a voltage detector for detecting a change in the voltage detected by the voltage detector. A control circuit for changing a frequency of the rectangular wave AC to control an output current of the inverter power supply circuit and a rising speed of the output current.