JPS635875A - Igniting method for plasma torch - Google Patents

Abstract

PURPOSE:To eliminate the influence to an object to be heated by a pilot arc by extinguishing the pilot arc when a main arc is ignited and impressing the pilot arc power source voltage on between an electrode and a nozzle just before the arc is extinguished to ignite the pilot arc and not necessitating the frequent high-frequency discharge. CONSTITUTION:In a state with the main arc M ignited between the electrode 2 and the object M to be heated, an ionized atmosphere layer 8 having conductivity where plasma gas G is made in an ionized state is formed around the arc M extending to the object W to be heated from the ignition 2 via the lower end of a nozzle 3. Then, only the DC voltage by a pilot arc power source 5 is impressed on between the electrode 2 and the nozzle 3 before the arc M is extinguished. In this way, the pilot arc P can be ignited without destroying the insulation between the electrode 2 and the nozzle 3 by high-frequency output of a high-frequency power source 6. Furthermore, it is prevented that the quantity of heat radiation of the arc P exerts the thermal influence upon the object W to be heated by extinguishing the arc P after the arc M is ignited.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a method of igniting a plasma torch.

(Prior art) A transfer type main arc is formed between the electrode of the plasma torch and the object to be heated, and this main arc can be used to perform various processing such as welding, cutting, melting, thermal spraying, and surface treatment of the object to be heated. This method has recently become widely adopted. In this case, it is necessary to ignite the main arc intermittently in the plasma torch in order to ignite the main arc on the object to be heated, which is continuously transported by a conveyor or the like. The main arc is ignited by igniting the pilot arc P between the electrode 2 and the nozzle 3 of the plasma torch 1 as shown in FIG. This is done by applying the voltage of the main arc power supply 7 to @ to form the main arc M between the electrode 2 and the object W to be heated. The method for forming the pilot arc P necessary for ignition of the main arc M is to superimpose the high frequency output of the high frequency power supply 6 and the DC output of the pilot arc power supply 5 a short time before the ignition of the main arc M. A method of applying the main arc between the electrode 2 and the nozzle 3 to ignite it, and extinguishing the main arc after igniting it;
There is a method in which the pilot arc P is kept in a continuous firing state, and only the main arc M is repeatedly fired and extinguished.

(Problem to be Solved by the Invention) However, according to the method of intermittently firing the pilot arc P in synchronization with the main arc M, the high frequency electric
The frequent high-frequency discharge caused by II6 has a negative effect on other control equipment and light electrical devices, such as radio wave interference, and since the electrode 2 is not heated at all when the main arc is extinguished, the cold electrode 2 is subject to thermal shock when it is re-ignited. In addition, an accident may occur in which the electrode 2 falls off.

In addition, in the case of a method in which the pilot arc P is kept in a continuous ignition state, the pilot arc P enters and exits from the lower end of the nozzle 3 due to changes in the flow of plasma gas G, etc., and the heat radiation amount of the pilot arc P changes due to this entry and exit. is superimposed on the amount of heat of the main arc M and given to the heated object W,
This has been the cause of welding defects in thin-wall welding, which requires strict control of the heating temperature of the heated object.

This invention solves the above-mentioned conventional problems, and is a plasma torch ignition method that does not require frequent high-frequency discharge, has almost no thermal effect on the heated object due to the pilot arc, and also prevents cooling of the electrode. The purpose is to provide

(Means for Solving the Problems) However, the plasma torch ignition method of the present invention is a plasma torch ignition method that intermittently forms a transitional main arc between the electrode of the plasma torch and the object to be heated. In,
When the main arc ignites, extinguish the pilot arc,
A plasma torch characterized in that a pilot arc is ignited by applying a pilot arc power supply voltage between an electrode and a nozzle immediately before the main arc is extinguished, and the next main arc is ignited by the pilot arc. This is the ignition method.

(Function) As a result of various studies carried out by the inventor in order to achieve the above object, in a state where the main arc M is ignited between the electrode 2 and the heated object W as shown in FIG. It has been found that a conductive ionized atmosphere layer 8 in which the plasma gas G is ionized is formed around the main arc M extending from the main arc M through the lower end of the nozzle 3 to the heated object W. .

Therefore, by applying only the DC voltage from the pilot arc power source 5 between the electrode 2 and the nozzle 3 before extinguishing the main arc M, the high frequency output from the high frequency power source 6 can be applied to the electrode 2.
The pilot arc P can be ignited without destroying the insulation between the nozzle 3 and the nozzle 3. Further, by extinguishing the pilot arc P after the main arc M is ignited, the amount of heat radiated from the pilot arc P is prevented from having a thermal effect on the heated object W. Further, from the time when the main arc M is extinguished until the next time it is re-ignited, the pilot arc P is ignited to prevent the electrode 2 from being cooled.

(Embodiment) An embodiment of the present invention will be described below with reference to FIGS. 1 to 4.

In the figure, 1 is a plasma torch, 2 is an electrode made of tungsten or the like, 3 is a cylindrical nozzle in which this R-shaped rod is fitted, and 1.4 is a cooling water passage formed inside the nozzle. Connected between the electrode 2 and the nozzle 3 are a pilot arc power source 5, a high frequency power source 6, and a pilot arc power switch S1. Further, a main arc power source 7 and a main arc switch S2 are connected between the electrode 2 and the heated object W.

Using the apparatus configured as described above, when starting a series of operations such as welding multiple objects to be heated using a plasma arc, the pilot arc switch S1 is closed as shown in FIG. 2 and the nozzle 3, and similarly to the conventional method, the high frequency power source 6 is operated for a short time t0 to superimpose the high frequency output H, and the pilot arc P is ignited. After this ignition, the main arc switch S2 is closed to ignite the main arc M, and from this ignition a short time 1. After (for example, 0 to 2 seconds), the pilot arc switch S1 is opened to extinguish the pilot arc P. The main arc M performs welding of the heated object W, and a short time t2 (
For example, 1 to 5 seconds before the pilot arc switch S1 is closed. Note that the high frequency power supply 6 is not operated at this time. As a result, the DC voltage V of the pilot arc power source 5 is applied between the electrode 2 and the nozzle 3.As shown in FIG. is formed, the pilot arc P is immediately ignited, and even if the main arc switch S2 is opened to extinguish the main arc M due to the completion of welding one object to be heated, etc., the pilot arc P will not fire. The ignition state is maintained. If the main arc switch S2 is closed when the next heated object W arrives at the arc irradiation position and the connection between the heated object and the main arc power supply 7 is completed, the pilot arc P is in the ignition state, so the main arc M fires immediately. After this ignition, the main arc M is created between the electrode 2 of the plasma torch 1 and the heated object W by repeating the extinguishing of the pilot arc, the ignition of the pilot arc immediately before the extinguishing of the main arc, etc. in the same manner as described above. formed intermittently,
This main arc M processes the object W to be heated. In addition, the operation of each switch S1, S2 and the high frequency power supply 6 in the above process is performed by a known control circuit using a timer.

The output voltage V of the pilot arc power source 5 necessary for igniting the pilot arc P in the above process.

The minimum value of varies depending on the magnitude of the current of the main arc M, and when the current of the main arc M is large, the output voltage V is low.
, can be ignited by . This seems to be because when the main arc current is large, the degree of ionization of the ionizing atmosphere layer 8 is accelerated. FIG. 4 shows an example of the measured value of the ignition voltage (minimum ignition voltage) at which the pilot arc can be ignited when the main arc current is changed using the same plasma torch.

(Effects of the Invention) As explained above, according to the present invention, the pilot arc is extinguished most of the time during ignition of the main arc, so the thermal influence of the pilot arc on the object to be heated is greatly reduced. Who? In addition, the pilot arc is ignited using the ionized atmosphere layer that forms around the main arc, and high-frequency discharge from a high-frequency power source only needs to be performed at the first ignition at the start of work, so there is no risk of negative effects such as radio interference. It can be significantly reduced. Furthermore, the electrode is heated by the pilot arc even when the main arc is extinguished, so
Cooling of the electrodes is prevented.

[Brief explanation of the drawing]

FIG. 1 is a system diagram showing an example of a plasma torch used in the method of the present invention, FIG. 2 is a sectional view of essential parts of the plasma torch shown in FIG. 1, and FIG. 3 is a time chart showing an embodiment of the present invention. FIG. 4 is a diagram similarly showing the correlation between the pilot arc ignition voltage and the main arc current. DESCRIPTION OF SYMBOLS 1... Plasma torch, 2... Electrode, 3... Nozzle, 5... Pilot arc power supply, 7... Main arc power supply, 8... Ionizing atmosphere layer, W... Heated object , P
...Pilot arc, M...Main arc.

Claims (1)

[Claims] In a plasma torch ignition method in which a transitional main arc is intermittently formed between the plasma torch electrode and the object to be heated, the pilot arc is extinguished once the main arc is ignited, and immediately before the main arc is extinguished. A method for igniting a plasma torch, characterized in that a pilot arc is ignited by applying a pilot arc power supply voltage between an electrode and a nozzle, and the next main arc is ignited by the pilot arc.