JPS6225470B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an alternating current arc stabilizing device, and more particularly to an arc stabilizing device for use in, for example, an alternating current welding machine, which has little high frequency noise.

In an AC arc welding machine, the output current drops to zero every half cycle, and the arc repeats extinction and ignition. Therefore, problems such as arc instability and arc breakage due to restriking failure are likely to occur. Therefore, in AC TIG welding machines, high-frequency voltage is superimposed on the output voltage of the welding machine using the spark electrode oscillation method shown in Figure 1 to facilitate restriking, improve the cleaning effect, and stabilize the arc. This has traditionally been the case.

In Figure 1, 1 is a torch, 2 is an arc, and 3 is a torch.
is the base material to be welded, 4 is the transformer of the welding machine, 5 is the high frequency transformer, 6 is the high frequency oscillation capacitor, 7 is the spark electrode, 8 is the coupling coil, 9 is 5, 6,
7 is a high frequency generator, and 10 is a high frequency bypass capacitor. 11 and 12 are power supply terminals. In the device shown in FIG. 1, the voltage across the capacitor 6 increases together with the secondary voltage of the high-frequency transformer, and when that voltage exceeds the dielectric breakdown voltage of the spark electrode 7, the electric charge stored in the capacitor 6 is discharged through the coupling coil 8. However, the induced voltage is superimposed on the output voltage of the welding machine. In this device, for example, the voltage of the high-frequency output waveform of the high-frequency generator 9 shown in FIG. 2b is superimposed on the welding current waveform shown in FIG. 2a.

However, when such a high frequency is generated, this high frequency voltage has a magnitude of approximately several thousand volts, and causes radio wave interference to other electrical and electronic devices such as radios and televisions as a large high frequency noise. Therefore, measures have been taken to reduce high-frequency noise by generating high-frequency waves only at the time of restriking, as shown in FIG. 2c. However, even if high frequency waves are generated intermittently in this way, it has not been possible to achieve a great effect in preventing radio wave interference.

In order to solve the above problems, the present invention connects the primary winding of a high-frequency transformer to the secondary winding of an input voltage switching transformer through a normally closed contact of a welding current detection relay that detects welding current and operates to excite it. and connecting a normally open contact of the welding current detection relay in parallel to a series circuit of a part of the secondary winding and the normally closed contact,
An oscillation capacitor is connected to both ends of the secondary winding of the high-frequency transformer, and a coupling coil is connected to a plurality of series-connected spark gaps and a coupling coil that superimposes the output voltage of the high-frequency transformer on the output voltage of the welding transformer. A series circuit is connected, and a normally open contact of a high voltage relay that detects welding current and operates to excite is connected in parallel to at least one of the plurality of spark gap connected in series. .

In the above configuration, at the time of arc start, the welding current detection relay is OFF and a high voltage is input to the primary side of the high frequency transformer, so a high voltage is also induced on the secondary side. When the secondary voltage exceeds the discharge starting voltage of the plurality of spark gaps connected in series, the high frequency current flows through the coupling coil, and the high frequency voltage is superimposed on the output of the welding transformer. This high frequency voltage is a voltage that can be sufficiently discharged even when the welding electrode is cold and has low thermionic emission capability.

Next, after the arc occurs, the welding current detection relay
Since it is ON and a low voltage is input to the primary side of the high frequency transformer, a low voltage is also induced on the secondary side. When this secondary voltage becomes higher than the energization start voltage, which was short-circuited by the high-voltage relay, the high-frequency current flows through the coupling coil, and a high-frequency voltage lower than that at arc start is superimposed on the output of the welding transformer. Ru. The high frequency voltage required for restriking after arc generation is such that the electrode is hot and the thermionic emission ability is higher than at the time of arc start, so a sufficiently stable arc start can be maintained even with the above-mentioned low high frequency voltage. Therefore, a welding device with low noise can be realized without impairing the stability of the arc.

FIG. 3 shows the main parts of an AC arc stabilizing device according to an embodiment of the present invention, and the same parts as in FIG. 1 are given the same numbers. Reference numeral 21 denotes an input voltage switching transformer for switching the input voltage of the high frequency transformer 5, and its primary input is applied from power supply terminals 11 and 12. A normally closed contact 22 of a welding current detection relay and a normally open contact 23 of the detection relay are connected to the secondary side of this transformer 21. That is, at the start of welding before the detection relay operates, the normally closed contact 22
A high input voltage is applied to the high frequency transformer through the transformer 5, and a high high frequency voltage is generated from the transformer 5. Spark gaps 24 and 25 are provided in the high-frequency generator 9, and are composed of spark electrodes 26, 27, and 28, forming a two-point planar spark gap. Reference numeral 29 represents a normally closed contact of a high voltage relay that operates when detecting a welding current, and in this embodiment is a vacuum switch having a high voltage resistance. This switch allows voltage switching of approximately several thousand volts to be performed without any problem. Figure 4 shows the configuration near this spark gap, in which a normal flat electrode 28' is used as the electrode 28, and a needle-shaped electrode 28'' that can increase the electric field strength is used in b. Spark discharge oscillation can be made possible even if the input voltage to the high frequency transformer 5 is lower than that of a.

Now, to explain the operation shown in Figures 3 and 4, at the time of arc start, both the welding electrode (tungsten electrode) and the base metal are in a cold state and have no ability to emit thermionic electrons, so the temperature is too high to start the discharge. A high frequency voltage (for example, on the order of several thousand volts) is required. However, once the transition to arc discharge occurs, the electrode is hot, so
The high frequency voltage required at the time of restriking is a fraction of the high frequency voltage required at the time of arc starting. Therefore, at the time of arc start, a high input voltage is applied to the high frequency transformer 5 by the normally closed contact 22 of the transformer 21 in FIGS. applied to torch 1. When a welding current is detected by the detection relay, contacts 22 open and contacts 23 close to reduce the voltage applied to the high frequency transformer 5, thereby significantly reducing the high frequency voltage of the transformer 5.

By the way, if the input voltage to the high frequency transformer 5 is lowered after detecting the welding current in this way, if the spark gap is for a large high frequency voltage at the time of starting as shown in FIG. This causes the inconvenience that the discharge starting voltage of 7 is not reached and no high frequency is generated.

Therefore, the present invention increases the input voltage of the high frequency generator at the time of arc start, and connects two spark gaps 24, 2 connected in series as shown in FIGS. 3 and 4.
After detecting the welding current, the input voltage of the high frequency generator is lowered, and at one point of the two spark gaps 24, 25 connected in series, that is, the electrodes 26, 2.
7 with the high voltage switch 29, 27, 28
The structure is such that a spark discharge is caused by a single electrode, and a high frequency voltage lower than that at arc start can be stably obtained. Furthermore, as shown in Figure 4b,
The reason why a needle-shaped electrode is used on one side is that the electric field strength can be increased as described above, and spark oscillation can be made even if the high-frequency input voltage is lower than that in FIG. 4a. In this way, short-circuiting some of the plurality of spark gaps is advantageous in terms of speeding up and reliable operation.

FIG. 5 shows the above-mentioned changes in the input voltage of the high-frequency generator before and after welding current detection, the voltage that allows spark discharge, and the relative changes in the high-frequency voltage that occur as a result. FIG. 5 shows the output voltage of the high frequency transformer 5, the input voltage to the high frequency transformer 5, and the voltage capable of spark discharge. Note that FIG. 5 does not show the absolute value of each voltage, but shows the relative change of each voltage. As described above, according to the present invention, the high frequency voltage is lowered and the spark gap is shortened during arc generation, so that the high frequency voltage can be significantly lowered and stable high frequency oscillation can be performed.

As described above, according to the present invention, spark discharge is caused through a relatively long gap at the time of arc start, and after the welding current is detected, the input voltage of the high frequency generator is lowered, and the spark gap is controlled by a high withstand voltage switch or the like. Since the welding speed is shortened, it is possible to construct a welding machine with stable low-frequency oscillation and low noise, which greatly contributes to the realization of a high-performance welding machine.

[Brief explanation of the drawing]

Figure 1 is a schematic circuit configuration diagram of the AC arc stabilizing section of a conventional AC arc welding machine, Figure 2 a, b, and c are waveform diagrams of the welding current, high-frequency current, and intermittent high-frequency current, respectively. A schematic circuit diagram of main parts of an AC arc stabilizing section in an AC arc welding machine according to an embodiment of the invention, FIGS. 4a and 4b are diagrams of a spark electrode section of the circuit, and FIG. It is a figure which shows the change state of each voltage. 5... High frequency transformer, 6... Oscillation capacitor, 9... High frequency generator, 21... Transformer for input voltage switching, 22, 23... Normally closed, normally open contact, 24, 25... Discharge gap, 26, 27,
28...Spark electrode, 29...Vacuum switch.

Claims (1)

[Claims] 1. A primary winding of a high-frequency transformer is connected to a secondary winding of an input voltage switching transformer via a normally closed contact of a welding current detection relay that detects a welding current and operates to excite the transformer. A normally open contact of the welding current detection relay is connected in parallel to a series circuit of a part of the secondary winding and the normally closed contact, and an oscillation capacitor is connected between both ends of the secondary winding of the high frequency transformer. With,
A series circuit is connected between a plurality of series-connected spark gaps and a coupling coil that superimposes the output voltage of the high-frequency transformer on the output voltage of the welding transformer, and at least one of the plurality of series-connected spark gaps is connected. An AC arc stabilizing device that connects the normally open contact of a high-voltage relay that detects welding current and excites it in parallel to a spark gap. 2. The AC arc stabilizing device according to claim 1, wherein the normally open contact of the high voltage relay is a vacuum switch.