JPH01245971A - Method and device for oxygen plasma cutting - Google Patents

Abstract

PURPOSE:To reduce obstructions to other equipments by supplying a pilot power source from a main arc power source and regulating the power source output before starting the main arc and repeating its supply and stop for a specified period and stopping a pilot arc corresponding to the start of the main arc. CONSTITUTION:In oxygen plasma cutting, the pilot arc is generated between a main electrode 4 and a chip electrode 5. The main arc is generated between the main electrode 4 and a material 6 to be worked by the help of said arc to perform cutting. Here, a pilot arc current is supplied from the main arc power source. Before the main arc is stated, the stage to supply the output of the power source for the main arc for a period of 10ms-100ms and the stage to stop it for a period of 40ms-400ms are repeated. The pilot arc is stopped corresponding to the start of the main arc. A rectifier circuit 2, a switching circuit 3, an opening and closing means control circuit, etc., are used. By this method, the obstructions to other equipments can be reduced.

Description

[Detailed Description of the Invention] [Industrial Application Field 1] The present invention uses a tip electrode made mainly of carbon,
The present invention relates to an oxygen plasma cutting method using oxygen as a cutting gas and improvements to the apparatus.

[Prior Art] In oxygen plasma cutting, which uses oxygen as the cutting gas, it is known that the life of the tip will be longer if carbon is used as the tip material than copper, which is conventionally used in general plasma cutting. It is being In oxygen plasma cutting using this carbon tip, when the tip wears out and the diameter of the orifice at the tip increases, the cutting performance decreases, the cut surface becomes uneven, or in extreme cases, cutting becomes impossible. .

FIG. 5 is a partial cross-sectional view showing the state of wear and tear of a carbon tip electrode; in the same figure, 101 is the main electrode;
Reference numeral 02 denotes tip electrodes, both of which are concentrically incorporated into the cutting torch. The tip electrode 102 has an orifice portion 102a consisting of a small hole at its tip, and oxygen is supplied as a working gas between the tip electrode 102 and the main electrode 101 and is ejected from the orifice portion 102a at high speed. A pilot arc DC power source 103 is connected between this tip electrode and the main electrode via a switch 104 and a resistor 105 with the polarity shown. 105 is a pilot arc, which is a current flowing in a direction from the tip electrode 102 to the main electrode 101. This pilot arc current is stretched by the working gas emitted at high speed to the tip electrode 1.
It will be concentrated near the tip of 02.

106 is a portion of the working gas that is ionized by the pilot arc, and extends to the outside of the orifice portion 102a. In addition, the same figure (at shows the cross section of the tip electrode in a new state, the same figure (bl shows the state when it is worn out to the extent that it does not interfere with cutting, and the same figure fc) shows the state of the tip electrode when it is worn out to the extent that it does not interfere with cutting. This shows the condition when the cutting becomes difficult.

[Problem to be solved by the invention 1 As mentioned above, the pilot arc is a current that uses the tip bridge as the anode, so the arc generation point of the tip electrode is overheated, and the carbon molecules gradually sublimate and are consumed. It turns out. On the other hand, the main arc current does not completely flow through the tip electrode, so the tip electrode is not consumed by the main arc current.

Therefore, suppressing the wear caused by the pilot arc current will extend the life of the tip electrode.

[Means to solve the problem]

The present invention solves the above problems by repeating a period in which a pilot arc current is supplied for 10 to 100 ms and a period in which it is stopped for 40 to 400 ms. A DC power supply whose output is adjusted by switching is used in the circuit, and power for the pilot arc is supplied from this DC power supply through a current limiting means and an opening/closing means to close the circuit only when necessary. By turning the operation of the circuit 0N-OFF, the power source is used for the pilot arc, and when the establishment of the main arc is detected, the main power output is switched to the desired continuous output, and the pilot arc circuit is cut off by the opening/closing means. The equipment was provided.

[Effect]

In the present invention, by determining both the supply and stop periods of the pilot arc as described above, the wear of the tip is small and the transition to the main arc and workability are improved.

Further, by sharing the power source for supplying the main arc current as the power source for supplying such pilot arc current, it is not necessary to prepare a special power supply device.

[Embodiment 1] FIG. 1 is a connection diagram showing an example of an apparatus for carrying out the oxygen plasma cutting method of the present invention. In the same figure, 1
is a commercial AC power source and can be single-phase or three-phase. 2
3 is a rectifier circuit that rectifies the output of the commercial AC power supply 1 to obtain a DC output, and 3 is a switching circuit for adjusting the DC output of the rectifier circuit 2 to a predetermined output. A forward comparator that adjusts the output by changing the conduction time rate of the transistor by combining a switching transistor, a transformer, and a circuit that rectifies and smoothes the output of the transformer. A DC conversion circuit or the like can be used. 4 is a main electrode, 5 is a chip electrode, 6 is a workpiece, and the main electrode 4 is connected to the negative output terminal of the switching circuit 3.
The workpiece 6 is connected to the positive output terminal of the switching circuit 3 via a DC reactor 7. Also, the tip electrode 5
is the switching means 8 consisting of transistors, contact relays, etc.
It is connected to the positive output terminal of the switching circuit 3 via a current limiting means 9 consisting of a resistor and a resistor.

When a transistor is used as the opening/closing means 8, the transistor may be analog-controlled to limit the conducting current, thereby also serving as the current limiting means 9. Further, the connection point of the opening/closing means may be located outside the DC actuator other than as shown in the drawings.

Furthermore, a coupling coil 11 for superimposing the output of the high frequency generator 10 is connected in series in the middle of the current supply circuit to this chip electrode, and between the main electrode 4 and this coupling coil 11. A capacitor 12 is connected to bypass the high frequency voltage. 13 is a diode, which together with the DC reactor 7 constitutes a smoothing circuit that smoothes the output of the switching circuit 3. 1
4 is a pulse width control circuit, which generates a pulse with a duty according to the input voltage to the terminal S while the input to the terminal C is at a high level, and turns the switching circuit 3 ON-OFF.
supply the signal. 15 is a main earth current setting circuit for disconnection, which outputs a reference signal s2.

A main arc current detection circuit 16 outputs a voltage signal s4 corresponding to the main arc current supplied to the workpiece.

A comparator 17 is a circuit that compares the reference signal s2 and the output signal s4 of the main arc current detection circuit and supplies a difference signal to the pulse width control circuit 14. 18 detects when the main arc current reaches a predetermined value or more, and
54) This is a main arc establishment detection circuit that detects that the current has been established, and compares the output Is of the reference signal setting circuit 19 with the output signal s4 of the main arc current detection circuit 16, and outputs a high level signal when the output signal s4 reaches 54) Is. A comparator that outputs is used.

20 is a mono-multivibrator that generates pulses with a preset period and duty. 2
Reference numeral 1 denotes a startup command circuit, which outputs a signal s1 that becomes high level during startup of the device. 22.23 is an AND gate,
24 is an OR gate, and 25 and 26 are inverters for polarity reversal.

The operation of the embodiment of FIG. 1 will be explained with reference to the diagram of FIG. 42. FIG. 2(a) is the output of the starting command circuit sl, (bl is the output pulse S-1 of the mono-multivibrator 20, (c) is the output s6 of the main arc establishment detection circuit 18, (dl is the main arc current Io, e) is the output so of the AND gate 22, (
fl is the output S of the high frequency generation circuit 10? , (- indicates the output sso of the AND gate 23, and (h) indicates the pilot arc current 1p. Note that the supply state of the working gas is omitted in FIGS. 1 and 2.

In FIG. 11, before time 1=11, that is, until the operator presses the push button of the cutting torch, the output 8g of the start command circuit 21 is at a low level, and the main arc current Io is not flowing, so Io (rs, and therefore, the output s6 of the main arc establishment detection circuit 18 is also at a low level, so the output s6 of the inverter 25, 26 which inverts this is at a high level, and the opening/closing means 8 is closed. When the activation command is issued at t = ti, the signal s1 becomes high level, and the AND gate 22 outputs a high level because the surface input signals 81 * 86 become high level, and the high frequency wave generator 10 starts and generates high frequency. A voltage is applied between the tip electrode 5 and the main electrode 4 via the coupling coil 11. On the other hand, when the activation signal S1 is high,
The output s6 of the main arc establishment detection circuit 18 even if the
Since it is still at a low level, the AND gate 23 outputs a signal 81G which becomes high level every time the mono multivibrator 20 outputs a signal.

As a result, the pulse width control circuit 14 is also activated for each output pulse of the mono-multivibrator 20. At this time, the main arc current is not flowing, so the output S of the detector 16
4 is zero, and therefore the output of the comparator 17 is the output 1r of the main arc current setting device 15 as it is, and the pulse width control circuit 14 sends a drive signal to the switching circuit 3 so as to obtain the maximum output. s6 is supplied for each output pulse of the mono-multivibrator 20. As a result, a pulsed voltage is applied between the main electrode 47, the workpiece 6, and the tip electrode 5. Chip electrode 5
As described above, a high frequency voltage is applied between the main electrode 4 and the switching circuit 3 to generate a spark discharge.
Every time a pulse voltage is supplied from the spark discharge, it discharges and becomes a pilot arc. This pilot arc is limited by the current limiting means 9 to a relatively small current of about several amperes to several tens of amperes.

When the cutting torch (main electrode and tip electrode) is brought close to the workpiece in this state, the working gas ionized by the pilot arc breaks the insulation between the main electrode and the workpiece and shifts to main arc discharge. In Fig. 2, time t = t
If it shifts to the main arc at z, then the main arc current! 0 increases rapidly and becomes a high level at time t. This signal S6
changes to high level, AND gate 23
Since the plane input signal is at a high level regardless of the output state of the mono multivibrator 20, the pulse width control circuit 1
4 will operate continuously. At this time, the pulse width control circuit 14 operates to determine the pulse width of the drive signal to the switching circuit 3 in accordance with the output of the main arc current detection circuit 18 or the set value s2 of the thousand arc current setting circuit 15. . On the other hand, it becomes the main bell, and the opening/closing means 8 of the pilot arc circuit becomes open, and similarly A
Since one input signal of the ND gate 22 also becomes low level, the high frequency generator 10 also stops its operation, so the pilot arc stops. At time t=t4, when the output 81 of the start command circuit 21 is set to a low level in order to finish cutting, the outputs of the AND gates 22 and 23 are set to a low level, and the pulse width control circuit 14 stops its operation. In addition, the high frequency generator also remains in a stopped state, and time 1 = 1
．． Return to previous state.

In FIG. 1, the high frequency generator 10 continuously generates an output from the start command until the main arc is established, but this high frequency is for igniting the pilot arc. Therefore, it may be supplied intermittently in synchronization with the pilot arc power output. In order to do this, it is preferable to add the output of the mono-multivibrator 20 to the input of the AND gate 22, as indicated by the dotted line in FIG.

The operation in this case is shown in FIG. In Figure 3 (h>), (a) to Keyaki are (a) to (hl) in Figure 2.
correspond to each of them. Figure 3 tel and (
As shown in fl, the high frequency generator operates only during the period when the output signal of the mono multivibrator 20 is at a high level. As a result, the high frequency voltage is generated only during the necessary period. The reason why this high-frequency voltage is continuously supplied at least during the period when the pilot arc current is flowing is that the pilot arc may be blown out by the working gas flowing at the box speed, but even in such cases, it is immediately re-ignited. This is because the arc was taken into account.

Next, using the apparatus shown in FIG. 1, the amount of wear on the tip electrode was measured when the duration of the pilot arc was varied in various ways. The results are shown in Table 1.

Experimental conditions: Peak value of pilot arc current 20A generation time:
Starts for 5 seconds, stops for 10 seconds Tip electrode: Material: Carbon orifice Diameter: 1.3mm φ Working gas: Oxygen 201! /min After generating only the pilot arc 50 times under the above conditions, the tip diameter of the orifice part of the tip electrode is φ and the depth of the enlarged diameter part is l! The so-called thieves were measured. (See Figure 4 4) l1 Table 1 also takes into consideration the ease of transition from pilot arc to main arc as a phenomenon other than wear and tear of the tip electrode, and includes △...machi,
○...good, ◎...good, X...unsatisfactory. From this, the pilot arc supply time is 10~
100ms and a pause time of 40 to 400ms are usable ranges, and among these, a supply time of 20 to 60ms and a pause time of 60 to 200ms, as shown by the bold line in Table 1, are excellent, and even more, a supply time of 20 to 40ms. Downtime 80~
It was found that a range of 100 ms is a range in which the amount of consumption is small and the transition to the main arc is also good. In addition, Table 1
As shown in the above, if the supply time is less than 10ms, the amount of gas ionized by the pilot arc is small and it is difficult to transition to the main arc, and even if the supply time is 10ms or more than 12L, if the pause time exceeds 400ms, the main arc will not start. There is a strong feeling that there is a time delay, and work efficiency deteriorates. Furthermore, if the supply time exceeds 100 ms, the amount of wear of the tip electrode increases, and there is little difference from the conventional method of continuously supplying a pilot arc (as a result, a sufficient effect cannot be obtained).

Table 1 [Effects of the Invention 1] As mentioned above, in the present invention, when performing oxygen plasma cutting using a carbon tip electrode, the pilot arc current that causes the least amount of wear on the tip electrode is adopted, so compared to the conventional method. Under normal usage conditions, the life of the chip could be extended by more than 1 o@. Further, since the average value and effective value of the pilot arc current are significantly reduced, not only the current capacity can be reduced, but also the life of the components of one circuit can be extended. Furthermore, the supply of high-frequency voltage is turned on and off when the power for the pilot arc is turned on and off.
When turning ON-OFF in synchronization with F, interference δ to other equipment due to high frequency current is reduced.

[Brief explanation of the drawing]

FIG. 1 is a connection diagram showing an embodiment of the apparatus for carrying out the oxygen plasma cutting method of the present invention, FIG. 2 is a diagram for explaining the operation of the apparatus shown in FIG. 1, and FIG. 1 is a diagram for explaining the operation when the dotted line portion is provided; FIG. 4 is a diagram for explaining the measurement portion when the amount of consumption of the tip electrode is measured by the embodiment of FIG. FIG. 5 is a diagram for explaining how a tip electrode wears out in a conventional oxygen plasma cutting device. DESCRIPTION OF SYMBOLS 1... AC power supply, 2... Rectifier circuit, 3... Switching circuit, 4... Main electrode, 5... Chip electrode, 6
. . . Workpiece, 7. DC reactor, 8. Switching means, 9. Current limiting means, 10. High frequency generator, 11. Coupling coil, 12. Capacitor. , 13... Diode, 14... Pulse width control circuit, 15... Main arc current setting circuit, 16... Main arc current detection circuit, 17... Comparator, 18... Main arc establishment Detection circuit, 19... Reference signal setting circuit, 2
0...Mono multivibrator, 21...Start command circuit Agent: Hiroshi Nakai, patent attorney

Claims (1)

[Claims] 1. A pilot arc is generated between the main electrode and a tip electrode whose main material is carbon, and with the help of the pilot arc, a main arc is generated between the main electrode and the workpiece. In an oxygen plasma cutting method using oxygen as a main component in a cutting gas that generates a 10ms to 100ms by adjusting the output of the main arc power supply.
Oxygen plasma cutting method 2, characterized in that the step of supplying for a period of ms and the step of stopping for a period of 40 ms to 400 ms are repeated, and the pilot arc is stopped in response to the start of the main arc. Cutting in which a pilot arc is generated between a tip electrode used as a raw material, and with the help of the pilot arc, a main arc is generated between the main electrode and a workpiece to cut the workpiece. An oxygen plasma cutting device that uses oxygen as a main component of the gas includes (a) a rectifier circuit that rectifies a commercial AC power source to obtain DC power; and (b) a switching circuit that adjusts the output of the rectifier circuit to a predetermined output by switching. and (c) means for connecting between the negative output terminal of the switching circuit and the main electrode, means for connecting between the positive output terminal and the workpiece, and between the positive output terminal and the tip electrode. means for connecting the switching means and the current limiting means via the switching means; (d) a switching means control circuit for closing the switching means in response to an activation command and opening the circuit in response to establishment of a main arc; (e) the switching means; a pulse width control circuit for driving the circuit; (f) supplying an intermittent starting signal to the pulse width control circuit based on a predetermined cycle and duty until the main arc current reaches a predetermined value; An oxygen plasma cutting device comprising: an output current control circuit for supplying a difference signal between a reference signal and an output current detection signal so as to maintain the output current at the set value after the main arc current reaches a predetermined value. 3. The oxygen plasma according to claim 2, further comprising a high-frequency voltage supply circuit that superimposes a high-frequency voltage for igniting the pilot arc on the pilot arc current supply circuit in conjunction with the closing of the switching means. Cutting device. 4. Applying a high frequency voltage for igniting the pilot arc to the pilot arc current supply circuit intermittently in conjunction with an intermittent pulse width control circuit activation signal from the output current control circuit during the closing period of the switching means. The oxygen plasma cutting apparatus according to claim 2, further comprising a high frequency voltage supply circuit superimposed on the oxygen plasma cutting apparatus.