JPH02133173A - Arc starter - Google Patents

Abstract

PURPOSE:To decrease high-frequency leak currents by bisecting the secondary winding of a high frequency generator, connecting one winding in series to a main electrode, connecting the other winding in series to an auxiliary electrode and providing the same polarities to the two electrodes. CONSTITUTION:The secondary winding 3 of the high-frequency coupling coil 3 of a plasma are working device is bisected to 3b1, 3b2. The winding 3b1 is connected in series to the main electrode 26 and the winding 3b2 is connected in series to the auxiliary electrode (chip electrode) 27. The polarities are determined at the polarities at which the voltage of the sum of the output voltages of the windings 3b1 and 3b2 is impressed between the main electrode 26 and the chip electrode 27. z1, z2a, 2zb, z3a, z3b are respectively the leak impedances of high frequencies and i1, i2a, i2b, i3a, i3b are the leak currents of closed circuits. The currents flowing in cables 23, 32 are offset to approximately zero and the high-frequency leak currents are decreased to the value as low as about 1/2 to 1/3.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention applies a high frequency high voltage between a main electrode and an auxiliary electrode (for example, a tip electrode in a plasma arc processing device, a trigger electrode for arc starting in TIG welding). The present invention relates to an improvement of an arc starting device of a type in which a main arc is induced by applying a spark discharge and thereby inducing a main arc.

[Conventional technology]

In plasma arc processing equipment and TIG welding equipment equipped with an arc start trigger electrode, high voltage is applied between the main electrode and auxiliary electrodes such as tip electrodes and trigger electrodes surrounding the main electrode prior to processing. is applied to generate a spark discharge between both electrodes, and the spark discharge induces a main arc between the main electrode and the auxiliary electrode or between the main electrode and the workpiece. The high voltage applied at this time is several M to prevent electric shock accidents for workers.
A high voltage with a high frequency of Hz or more is used.

FIG. 5 shows an example of a conventional plasma arc processing device. In the figure, 1 is a DC power supply section, and 2 is a high frequency generating circuit, which generates a high frequency high voltage of usually several million % and several hundred volts. 3 is a coupling coil for superimposing the output of the high frequency generation circuit 2 on the output circuit of the DC power supply section 1; It consists of a secondary winding 3b connected in series.

4 to 8 are capacitors for bypassing high frequencies and protecting them from entering the DC power supply section 1, 9 is a current limiting resistor, and 10 and 11 are high frequency and other electromagnetic noises to the control circuit of the DC power supply section 1. A choke coil 12 is a relay contact that is closed when an activation command is issued. The DC power supply section or relay contact 12 constitutes a plasma processing power supply section 100. Further, 21 is a power cable connecting between the negative output terminal (a) of the power supply unit 100 and the main electrode 26 of the processing torch 200, and 22 is a power cable connecting the power supply unit 1
A cable 23 connecting between the auxiliary terminal (b) of 00 and the auxiliary electrode of the processing torch 200, that is, the tip electrode 27;
is a torch switch control cable that connects between the start command switch (hereinafter referred to as a torch switch) 25 provided on the processing torch 200 and the control signal input terminals (C) and (d) of the power supply unit 100; Each of these cables 2 to 23 is housed in a common sheath 24 together with a hose for supplying plasma operating gas (not shown) and a torch cooling water supply hose provided as necessary. Appearance - consists of one torch cable. The processing torch 200 mainly includes a main electrode 26, a tip electrode 27, and a gas passage for introducing a plasma operating gas formed by these picture electrodes.

Further, 31 is a workpiece, and 32 is a workpiece 31 and a power supply section 10.
This is an electric cable that connects between the positive output terminal ((3) of 0 and 0).

In the device shown in the figure, when the torch switch 25 is pressed, the DC power supply section 1 generates a DC output, and at the same time activates the high frequency generation circuit 2 and starts supplying high frequency power to the coupling coil 3.

On the other hand, when the torch switch 25 is closed, the relay contact 12 is closed, and thereby the output voltage of the DC power supply section 1 is applied between the main electrode 26, the tip electrode 27, and the workpiece 31. The high frequency, high voltage output of the high frequency generating circuit 2 is superimposed on the output of the DC power supply section 1 at the secondary winding 3b of the coupling coil 3.

This high frequency and high voltage passes through the capacitors 4 and 7, breaks the insulation between the tip electrode 27 and the main electrode 26, and generates a spark discharge. This spark discharge causes the main electrode 26 and the tip electrode 2 to
7, an arc is induced by the power from the DC power supply section 1. This arc is a small current arc limited by resistor 9 and is usually called a pilot arc.

Also, at this time, when a gas for plasma operation, such as argon, oxygen, air, etc., is flowed between the main electrode 26 and the tip electrode 27, these gases are ionized by the pilot arc, and this ionized gas flows into the tip electrode. 27
It is ejected from an orifice section 27a provided at the tip of the. When the torch is brought close to the workpiece in this state, this ionized gas reaches the workpiece 31, and an arc is generated between the main electrode 26 and the workpiece 31. Since there is nothing to limit the current between this arc and the DC power supply section 1, the current increases to a value determined by the output setting of the DC power supply section 1, and thereby the workpiece 31 is cut, welded, or melted. . At the same time, the pilot arc generated in the tip electrode 27 disappears because the resistor 9 is present in its current path. Note that the high frequency generating circuit 2 is normally configured to stop outputting when a pilot arc occurs.

[Problem to be solved by the invention]

In the apparatus shown in FIG. 5, consider the situation when applying a high frequency and high voltage to generate a spark discharge.

As mentioned above, the output frequency of the high frequency generation circuit 2 is several MHz.
As described above, these signals are bypassed by capacitors 4 to 8 in the plasma processing power supply section, so that they are not transmitted to the left side of these capacitors in FIG.

Therefore, the arrangement of FIG. 5 for high frequencies can be rewritten as shown in FIG. In the figure, Zl is the leakage impedance between the main electrode side machine cable 21 and the workpiece side type cable 32, Z2 is the leakage impedance between the power cable 21 and the chip side cable 22, and Z3 is the power cable 21 and control cable 23 for torch switch
The leakage impedance between Further, since the capacitors 4 to 8 have sufficiently low values with respect to the respective leakage impedances z1 to Z3, they can be regarded as substantially short-circuited for high frequencies, so they are shown as shown. These leakage impedances are stray capacitances and leakage resistances distributed between each cable, and the distributed leakage impedances related to the closed circuit currents tl, 12, and t3 in the directions shown in the figure are shown as lumped constants. Due to the existence of these leakage impedances, a leakage current of i=il+12+13su1+1+1)e ZI Z2 Z3 (where e is the output voltage of the secondary winding of the coupling coil) flows. This leakage current increases as the torch cable becomes longer, and since the internal impedance of the high frequency generation circuit 2 including the coupling coil 3 is relatively large, the leakage current flows between the main electrode 26 and the tip electrode 27. The high frequency voltage that reaches the cable is attenuated, making it difficult to generate spark discharge when the cable is long. In order to compensate for this attenuation, in the conventional device configured as shown in Fig. 5, there is no choice but to increase both the output voltage and power of the high frequency generation circuit 2, but in order to do so, the insulation voltage of the torch cable must be increased accordingly. This not only requires stricter measures to prevent high frequencies from entering the control circuit, but also increases the amount of high frequency radiation outside the device, causing an increase in radio interference.

[Means to solve the problem]

The present invention divides the secondary winding of the coupling coil for high frequency superimposition into two parts, one of which is connected in series to the main electrode as before, and the other to the auxiliary electrode, and the polarity of both windings is reversed. The drawbacks of the conventional device described above are improved by using the polarity in which the sum of the induced voltages of the windings is applied between the main electrode and the auxiliary electrode.

[For production]

In the device of the present invention, by doing as described above, leakage current is significantly reduced, and as a result, high frequency voltage,
It becomes possible to use long cables by eliminating attenuation of high frequency voltage without increasing power.

〔Example〕

FIG. 1 is a connection diagram showing an embodiment in which the present invention is applied to a plasma arc processing apparatus. The figure shows that in the conventional device shown in FIG. 5, the secondary winding 3b of the high-frequency coupling coil 3 is divided into two halves to form 3b1 and 3b2, the winding 3bl is in series with the main electrode 26, and the auxiliary winding 3b2 is The polarity is determined so that the voltage is the sum of the output voltages of both windings 3bl and 3b2 and is applied between the main electrode 26 and the tip electrode 27 so as to be in series with the electrode, that is, the tip electrode 27. . The rest of the configuration is the same as the conventional device shown in FIG. 5, so the same reference numerals are given to the same functions.

FIG. 2 is a connection diagram for high frequency of the device shown in FIG. 1,
In the figure, 21 is the leakage impedance between the cables 21 and 32, Z2a is the leakage impedance between the cables 21 and 22, Z2b is the leakage impedance between the cables 22 and 32, and Z3a is the leakage impedance between the cables 21 and 23. Leakage impedance between Z3b
indicates the leakage impedance between the cable 23 and the cable 22, and the closed circuit leakage current il in the direction shown in the figure, respectively.

The distributed leakage impedance related to 12a, 12b, 13a, and 13b is shown as a lumped constant. In the figure, if the induced voltage of the coupling coils 3b1 and 3b2 that superimposes the output voltage of the high frequency generation circuit 2 onto the cable is el, then 11-ea/ZL, 12a = (ea +
ea)/Z2a.

12b -e a/Z 2b, i3a -e a/
Z3a.

13b -e a/Z 3b . Here, the cables 21, 22 and 23 are housed in one sheath and manufactured as one torch cable as explained in the conventional device of FIG.
Leakage impedance between each Z 2 as Z 3
aSZ 3b are considered to be approximately equal.

Furthermore, it may be considered that Z2b and Zl, which are the leakage impedances between the torch cable thus created and the cable 32 connecting the workpiece 31 and the power supply section, are approximately equal. Therefore, the above closed circuit currents are respectively 12a1 + 13bl in 1Iaal and 111 + in their absolute values.
12b. And since the direction of each current is as shown in the figure,
The currents flowing through the cables 23 and 32 cancel each other out and become approximately zero, resulting in substantially loop currents 11° 12b, 13
The cable current due to a, i3b does not flow.

As a result, the high frequency leakage current that actually flows is approximately 12a
= 2 e a/Z 2a only.

Here, 2ea is equal to the output e of the coupling coil in the conventional device shown in FIG. 5, and Z2a is considered to be approximately equal to Z2 or z3 in FIG. The high frequency leakage current in the device will be as low as 1-2-173).

Next, consider the voltage applied between each cable and ground potential. Each of the induced voltages of the coupling coils 3b1 and 3b2 is applied to the cable 21 and the cable 22 with respect to the ground potential. This voltage generates a spark voltage between the two electrodes because the polarities of the coupling coils 3bl and 3b2 are such that the added voltage is applied between the main electrode 26 and the tip electrode 27 as shown in the figure. This means that half of the voltage required for each is sufficient. Therefore, the dielectric strength voltage of each cable may be as low as 1/2. Conversely, this shows that when using cables with the same withstand voltage, it is possible to apply twice as high a voltage.

Note that the present invention is not only applicable to plasma arc machining equipment that generates a pilot arc between the main electrode and the tip electrode and transfers it to the machining plasma arc, but also applies to It can also be applied to equipment that directly induces a machining plasma arc between the main electrode and the workpiece by applying a high-frequency, high-voltage between the main electrode and the tip electrode under the same condition, and using the spark discharge generated thereby. can. In this case, the resistor 9 and relay contact 12 may be removed from the connection diagram of FIG. 1, and the other components may be the same as in FIG. 1, so detailed explanations will be omitted.

In addition, as explained above, the apparatus shown in Fig. 1 is used not only for directly processing workpieces, but also for starting other arcs, such as non-contact welding for TIG arc welding and MIG arc welding. Of course, it can also be used as a means for injecting ionized gas into the main arc path for triggering arc starting, arc furnace starting, etc. In this case, in the apparatus shown in FIG. 1, instead of the workpiece 31, plasma is injected toward the arc path (for example, the gap between the welding electrode and the workpiece) where the arc is activated. All you have to do is connect the welding electrode or workpiece in this way. Figure 3 shows the situation around the torch at this time.

In FIG. 3, 41 is a TIG arc welding torch, which has a welding electrode 41a made of tungsten and a gas shield nozzle 41b. This welding torch 41 is connected to one output terminal of a welding power source 42, and the other output terminal of the welding power source 42 is connected to the workpiece 31. A plasma arc generating torch 200 is also attached to the welding torch 41, and this plasma arc generating torch 200 is connected to the plasma generating power source section 100. These power supply unit 100 and torch 200 correspond to the power supply unit 100 and torch 200 in FIG. 1, and those having the same functions are given the same reference numerals, and some internal structures are omitted. The other output of the power supply section 100 is connected to the workpiece 31.

In the device shown in the figure, when the torch switch 25 is pressed, a high frequency voltage is applied between the main electrode 26 and the tip electrode 27, causing a spark discharge, which is induced to cause a gap between the main electrode 26 and the tip electrode 27. A pilot arc is generated, and plasma working gas ionized by this pilot arc is injected into the gas shield nozzle 41b from the orifice portion 27a at the tip of the tip electrode 27. At this time, when the welding power source 42 also generates an output and a voltage is applied between the welding electrode 41a and the workpiece 31, the orifice portion 27
The welding electrode 41 is heated by the ionized gas injected from a.
The insulation between a and the workpiece 31 is broken and arc discharge is induced. As a result, the welding arc can be started without contact between the welding electrode 41B and the workpiece 31.

Furthermore, the present invention is not only applicable to the plasma arc generator shown in FIGS. The present invention can be applied to all types of arc machining equipment that apply a high frequency and high voltage to generate spark discharge, thereby inducing a main discharge.

FIG. 4 is a connection diagram showing an example when the present invention is applied to a TIG welding device. The apparatus shown in Fig. 4 is the apparatus shown in Fig. 1 in which the plasma arc processing torch 200 is replaced with a TIG arc welding torch 200'', and by replacing the torch, a metal gas shield nozzle is used as an auxiliary electrode. Similar to the example shown in Fig. 1, high frequency waves are superimposed between the tungsten welding electrode 26°, which is the main electrode, and the metal gas shield nozzle 27', which is the auxiliary electrode. Coupling coils 3bl and 3b2 are connected in series.

The rest is exactly the same as the device shown in FIG.

In the apparatus shown in FIG. 3, when the torch switch 25 is pressed,
The output of the DC power supply section 1 is connected to the welding electrode 26' and the workpiece 31.
At the same time, a high frequency voltage is applied between the welding electrode 26' and the gas shield nozzle 27' (and the workpiece 31). This high frequency voltage generates a spark discharge between the welding electrode 26' and the gas shield nozzle 27', and this spark discharge causes a limit between the welding electrode 26' and the gas shield nozzle 27' with the resistor 9. The welding arc is started when the ionized shielding gas reaches the workpiece 31 and a welding arc is started.

In the device shown in FIG. 4, the resistor 9 may be omitted as in the device shown in FIG. A spark discharge occurs between the welding electrode 26' and the gas shield nozzle 27', thereby inducing a main arc.

Since the device of the present invention is as described above, there is little attenuation of high frequencies, and the ground potential of each cable is 1/2 that of the conventional device.
becomes. For this reason, it is possible to use a cable with a low dielectric strength voltage, or to use a cable with the same dielectric strength as a conventional cable, but to supply a higher voltage than the high frequency voltage between the main electrode and the tip electrode, so the cable can be made longer. Even when this happens, a good arc start can be obtained.

[Brief explanation of drawings]

Fig. 1 is a connection diagram showing an example when the present invention is applied to a plasma arc processing device, Fig. 2 is an equivalent circuit at high frequency of the embodiment of Fig. 1, and Figs. 5 is a connection diagram showing an example of application to another application, FIG. 5 is a connection diagram showing an example of a conventional device, and FIG. 6 is a diagram showing an equivalent circuit of the device of FIG. 5 at high frequency. 1...DC power supply section, 2...High frequency generation circuit, 3...Coupling coil, 3a...
...-Next coil, 3b, 3b1. 3b2...
...Secondary coil, 21, 22゜23.32...
・Cable, 25...Torch switch, 26・
...Main electrode, 26°...Welding electrode, 2
7...Tip electrode (auxiliary electrode), 27゛...
...Metal gas shield nozzle (auxiliary electrode) 31...
...Workpiece, 41...TIG torch, 4
1a...Welding electrode, 41b...Gas shield nozzle, 42...Welding power source, 100
...Plasma processing power supply section, 200...
Processing torch, Zl, Z2. Z3. Z2a, Z2b
, Z3a, Z3b---Leakage impedance, il, 12a, 13a, 13b---High frequency leakage current

Claims (1)

[Claims] 1. In an arc starting device that applies a high frequency high voltage between a main electrode and an auxiliary electrode to generate a spark discharge and induce an arc discharge, a high frequency generator and the output of the high frequency generator are connected to a primary winding. As well as input, the secondary winding is divided into two, one winding of the divided secondary winding is connected in series with the main electrode, and the other winding of the secondary winding is connected in series with the auxiliary electrode. and a high frequency coupling coil connected to the main electrode and the auxiliary electrode such that the polarity of the two secondary windings is such that the sum of output voltages is applied between the main electrode and the auxiliary electrode.