JPH049637B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a plasma cutting device that cuts a workpiece using a plasma arc, and is particularly applicable to cutting workpieces that require intermittent plasma arc generation, such as wire mesh, gratings, etc. The present invention relates to a plasma cutting device suitable for cutting a certain workpiece.

[Background of the invention]

Generally, in plasma cutting equipment, a pilot arc is generated between the main electrode and the nozzle electrode surrounding it before cutting starts, and with the help of this pilot arc, a plasma arc is started between the main electrode and the workpiece. A method is being taken.

FIG. 5 is an explanatory diagram of the operation of a conventional plasma cutting apparatus, and FIG. 6 is a block diagram showing its control system.

5 and 6, when the start switch 7 is turned on, an operating signal is sent from the control circuit 8 to the main power supply 9, pilot arc power supply 10, high frequency generation circuit 11, switch 13, and solenoid valve 16, thereby starting the gas cylinder 18. The first stage plasma gas (argon) is supplied to the torch 1 through the solenoid valve 16 and discharged from the nozzle electrode 6, and the pilot arc power supply 1 is connected between the main electrode 5 and the nozzle electrode 6.
When the DC output voltage is 0, the switch 13 and the current limiting resistor 14
A DC output voltage of the main power source 9 is applied between the main electrode 5 and the workpiece 4. Then, the high frequency generated by the high frequency generation circuit 11 is applied superimposed on the output voltage of the pilot arc power supply 10, so that the main electrode 5 and the nozzle electrode 6 are first
A pilot arc 2 occurs during this period. When a signal detecting the occurrence of a pilot arc from the pilot arc detector 12 is transmitted to the control circuit 8, the generation of high frequency waves is stopped after a predetermined time (t ₁ ) has elapsed. When the torch 1 is brought close to the workpiece 4 in this state, the first stage plasma gas ionized by the pilot arc 2 becomes a conductive path, and a plasma arc 3 is generated between the main electrode 5 and the workpiece 4. When a signal detecting plasma arc generation from the plasma arc detector 15 is transmitted to the control circuit 8, an operation signal is sent to the solenoid valve 17, and the solenoid valve 17 is activated from the gas cylinder 19.
through the second stage plasma gas (nitrogen or hydrogen)
Cutting is started by being supplied to the torch 1. On the other hand, the pilot arc 2 is stopped by opening the switch 13 after a predetermined time (t ₂ ) has elapsed since the plasma arc was generated. If the pilot arc 2 is maintained with the same force as at the time of starting even during plasma arc generation, it will be connected from the main electrode 5 to the nozzle electrode 6, and further from the nozzle electrode 6 to the workpiece 4. This is because a so-called double arc occurs, leading to poor cutting and damage to the nozzle electrode. By moving the torch 1 in a state of transition to plasma arc, cutting of the workpiece 4 progresses. Then, when the arc length of the plasma arc 3 increases at the terminal end of the workpiece 4 and the arc can no longer be maintained, the plasma arc 3 automatically disappears.

After the cutting of the workpiece 4 is completed and the plasma arc disappears, when the starting switch 7 is turned off, the holding of the control circuit 8 is released and all operations are stopped. Here, the emission of the second stage plasma gas is stopped at the same time as the plasma arc disappears, but only the first stage plasma gas is released after a predetermined time (t ₃ ) has elapsed after the start switch 7 is turned off to protect the main electrode. Continue emitting until When restarting cutting, the above operation is repeated by turning on the start switch 7 again.

In this way, conventional plasma cutting equipment has a configuration in which, after the plasma arc has disappeared, cutting cannot be resumed unless the starting switch is turned off, the control circuit is released, and the starting switch is turned on again. There are no operational problems when cutting long objects that have been cut, but for workpieces that require intermittent plasma arc generation in short cycles, such as wire mesh and gratings, it is difficult to start cutting. The startup switch has to be operated repeatedly every time, and the operation is complicated and time-consuming.
The drawback was that it was inefficient.

[Object of the Invention] The object of the present invention is that if the start switch is operated, even after the plasma arc has disappeared, the plasma arc can be generated and the cutting can be restarted by simply bringing the torch close to the workpiece, and cutting can be restarted every time. To provide a plasma cutting device that does not require the operation of a start switch and is free from the risk of double arc generation.

[Summary of the invention]

The present invention includes means for generating a pilot arc between the main electrode and the nozzle electrode surrounding it, and with the help of this pilot arc, a plasma arc is started between the main electrode and the workpiece, and the workpiece is means for detecting the disappearance of the plasma arc, and restarting the plasma arc after the plasma arc has disappeared, provided that the means detects the disappearance of the plasma arc and a start switch is in operation. output control of the pilot arc generating means so as to generate a pilot arc with a predetermined current value necessary for plasma arc generation, and to stop the pilot arc during plasma arc generation or to limit the current value to a low current value necessary to sustain the pilot arc; The present invention is characterized by comprising a control circuit that performs the following.

[Embodiments of the invention]

FIG. 1 is an explanatory diagram of the operation of one embodiment of the present invention, and FIG.
The figure is a block diagram showing the control system.

In FIGS. 1 and 2, 1 is a plasma cutting torch having a main electrode 5 and a nozzle electrode 6 surrounding it, 7 is a manual or foot-operated starting switch, 8 is a control circuit for overall control of the entire device, and 9 is a Main electrode 5
A main current 10 applies a DC voltage to generate a plasma arc 3 between the main electrode 5 and the workpiece 4, and a pilot current 10 applies a DC voltage to generate a pilot arc 2 between the main electrode 5 and the nozzle electrode 6. An arc power source, 11 a high frequency generation circuit for starting the pilot arc 2, 12 a pilot arc detector (for example, a current relay) for detecting the occurrence of the pilot arc 2, and 15 detecting the occurrence and disappearance of the plasma arc 3. a plasma arc detector (for example, a current relay), 16 and 17 are electromagnetic valves for plasma gas supply, 18 is a gas cylinder for supplying the first stage plasma gas (argon), 19
2 is a gas cylinder for supplying the second stage plasma gas (nitrogen or hydrogen); 20 is a switch for switching the current value of the pilot arc 2 between high and low;
1 and 22 are current limiting resistors with different resistance values, and in this example, the above-mentioned 10, 11, 12, 20, 2
Each of the parts 1 and 22 constitutes a pilot arc generating means 23.

The operations in this embodiment from the initial turning on of the starting switch 7 to the generation of the pilot arc 2 and plasma arc 3 are the same as those of the conventional example (FIGS. 5 and 6), and therefore their explanation will be omitted. At the time of starting, a pilot arc current flows through the "large" side contact of the changeover switch 20 and the low resistance 21, and the current value is equal to that of the plasma arc 3.
The predetermined current value i ₁ is required for starting the plasma arc detector 15. However, when a signal detecting the occurrence of a plasma arc from the plasma arc detector 15 is transmitted to the control circuit 8, after a predetermined time (t ₂ ) has elapsed, the control circuit 8 The changeover switch 20 is switched to the "small" side by the signal , and the high resistance 22 is inserted into the circuit.

Therefore, the pilot arc current is limited to a current value sufficiently lower than the predetermined current value i ₁ , that is, the minimum current value i ₂ necessary to sustain the pilot arc 2 during plasma arc generation. The current values of i ₁ and i ₂ differ depending on the rated current of the plasma cutting device, but for example, in a device with a rated current of 150A, i ₁ =
The resistors 21 and 22 are set so that the current is about 20A and i ₂ =5A. By thus limiting the pilot arc current during plasma arc generation, double arc generation can be avoided.

In this state, the torch 1 is moved to cut the workpiece 4. Then, the disappearance of the plasma arc at the end of cutting is detected by the plasma arc detector 15,
Under the condition that the start switch 7 is in the ON state, the changeover switch 20 is again switched to the "high" side by the signal output from the control circuit 8, and the pilot arc current is transferred from the pilot arc power source 10 through the low resistance 21. is applied to control the pilot arc 2 to return it to the predetermined current value _i1 . At this point, the cutting of the workpiece 4 is completed,
Since the plasma arc 3 has disappeared and only the pilot arc 2 has been generated, when the torch 1 is brought close to the workpiece 4 again from this state, the plasma arc 3 is generated and cutting is restarted. Therefore, when cutting is performed by intermittently generating a plasma arc, there is no need to operate the starting switch to generate the pilot arc 2 each time as in the conventional case, and the next cutting can be started immediately. In addition, if the pilot arc 2 is maintained at a small current such that there is no risk of double arc generation even during plasma arc generation as in this embodiment, there is no need to apply high frequency when restarting cutting, thereby reducing high frequency noise. The cleaning phenomenon of the main electrode 5 is accelerated due to generation and frequent application of high frequency, and damage such as difficulty in generating pilot arcs can also be avoided.

FIG. 3 shows an example of the configuration of the control circuit 8 for performing the above-described control.

In FIG. 3, R is a relay that operates when the start switch 7 is turned on, R _a is its normally open contact, and TM ₁ is a delayed return timer for releasing the first stage plasma gas for a predetermined period of time even after the start switch 7 is turned off.
MV ₁ is the electromagnetic coil of the first stage plasma gas supply solenoid valve 16 which is operated by closing the timer contact TM _1a , and MV ₂ is the second electromagnetic coil which is operated by closing the relay contact R _a and the contact X _a of the plasma arc detector 15. an electromagnetic coil of a stage plasma gas supply electromagnetic valve 17;
MC ₁ is an electromagnetic coil for starting the main power supply 9 and pilot arc power supply 10 which are operated by closing relay contact R _a , and TM ₂ is a pilot arc detector 12
MC 2 is a delay-action timer that is activated by the closing of contact Y _a and stops high-frequency generation after a predetermined period of time has elapsed from the point at which the pilot arc occurs. MC ₂ is a relay contact.
The starting electromagnetic coil of the high frequency generation circuit 11 is activated by the closing of R _a and the timer contact TM _2b , and TM ₃ is activated by the closing of the contact X _a of the plasma arc detector 15, and is switched after a predetermined time has elapsed from the time of plasma arc generation. MC ₃ is a delay-action timer that switches the switch 20 to the "small" side, and is an electromagnetic coil for driving the changeover switch 20 that is operated by closing the relay contact R _a and timer contact TM _3b . During the ON operation, even if cutting is completed and the plasma arc disappears, the pilot arc continues to be generated, and all operations are stopped when the start switch 7 is turned OFF.

The output of the pilot arc generating means 23 can be changed by switching the resistor 2 using the changeover switch 20 as described above.
In addition to the method of switching 1 and 22, it can be realized using any means such as continuously variable non-contact control using transistors or thyristors.

FIG. 4 is an explanatory diagram of the operation of another embodiment of the present invention,
In the previous embodiment, a method was adopted in which the pilot arc was switched to a small current and maintained even during the plasma arc generation, but as shown in this figure, the pilot arc circuit is switched off after a predetermined time (t ₂ ) has elapsed from the time when the plasma arc generation is detected. Turn off the switch (Fig. 6, 13) to stop the pilot arc 2, and when cutting is completed and the disappearance of the plasma arc 3 is detected, turn on the pilot arc circuit again to generate a high-frequency wave between the main electrode and the nozzle electrode. Similarly to the previous embodiment, the next cutting can be started without the need to operate the start switch by applying the same amount of pressure to generate the pilot arc 2. The configuration of the control circuit in this case can be easily inferred from Figure 3, so
Illustrations are omitted.

〔Effect of the invention〕

According to the present invention, a pilot arc with a predetermined current value necessary for restarting the plasma arc is generated after the plasma arc has disappeared, on the condition that the disappearance of the plasma arc is detected and the start switch is in operation. Because of this configuration, when cutting workpieces that require intermittent plasma arc generation in short cycles, such as wire mesh or gratings, it is possible to move the torch directly to the workpiece without having to repeatedly operate the start switch each time. You can start the next cut just by bringing it close to , improving work efficiency.

Furthermore, when plasma cutting a thin plate with a small current of 70A or less using a manual torch, the plasma arc often disappears due to a decrease in the cutting speed or an increase in the arc length. For example, it becomes possible to immediately generate a plasma arc from the cutting position without requiring the operation of a starting switch, improving workability and operability.

Moreover, since the current value is limited to a low value necessary to stop the pilot arc or maintain the pilot arc while the plasma arc is occurring, it is possible to avoid the occurrence of double arcs.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of the operation of one embodiment of the present invention, and FIG.
The figure is a block diagram showing the control system, FIG. 3 is a detailed diagram showing an example of the configuration of the control circuit, FIG. 4 is an explanatory diagram of the operation of another embodiment of the present invention, and FIG. 5 is an explanatory diagram of the operation of the conventional example. , FIG. 6 is a block diagram showing the control system. DESCRIPTION OF SYMBOLS 1...Torch, 2...Pilot arc, 3...Plasma arc, 4...Workpiece, 5...Main electrode, 6...Nozzle electrode, 7...Start switch, 8...Control circuit, 9
...Main power supply, 15...Plasma arc detector for detecting plasma arc disappearance, 23...Pilot arc generating means (10...Pilot arc power supply, 11...
high frequency generation circuit, 12... pilot arc detector, 20... changeover switch, 21, 22... current limiting resistor).

Claims (1)

[Claims] 1 A means for generating a pilot arc is provided between the main electrode and the nozzle electrode surrounding it, and with the help of this pilot arc, a plasma arc is started between the main electrode and the workpiece to cut the workpiece. The device includes a means for detecting the extinction of the plasma arc and a method necessary for restarting the plasma arc after the extinction of the plasma arc, provided that the extinction of the plasma arc is detected by the means and a start switch is operated. The output of the pilot arc generating means is controlled so as to generate a pilot arc of a predetermined current value, and to stop the pilot arc during plasma arc generation or to limit the current value to a low current value necessary to sustain the pilot arc. 1. A plasma cutting device characterized by comprising a control circuit for cutting.