Contact arcing and transfer arcing

Plasma arc cutting generally has two ways to start the arc:

1. Contact type: the nozzle insulated from the pole pin is attached to the workpiece (connected to the positive end of the cutting power supply), and then the high-frequency high-voltage current is applied to the electrode needle (tungsten needle) connected to the negative end of the power supply, so that the pole needle discharges the arc. The arc forms a plasma arc under the action of voltage, air pressure and magnetic field, and maintains the plasma arc stable combustion by a large current, and then raises the nozzle slightly (avoiding the hot workpiece from damaging the nozzle) and starts cutting.

2. Transfer arc type (dimensional arc type): the positive end of the power supply is connected to the nozzle through a certain resistance and relay switch, so that an arc is formed between the pole pin and the nozzle (the arc is small due to resistance current limiting), and then The nozzle is close to the workpiece directly connected to the positive end of the power source, and a more energetic arc is formed between the pole pin and the workpiece. The arc is compressed to form a plasma arc, and the connection between the nozzle and the positive end of the power source is disconnected to start cutting.

The transfer arc cutting method can prevent the arc from damaging the nozzle under the action of air pressure. This method is suitable for high power cutting machines.

The cutting machine uses a plasma arc. The generation of the plasma arc is a combination of voltage, air pressure and magnetic field. Therefore, the output of the cutting machine requires a higher voltage (generally 100~180V) and a smaller current (generally 30A~160A).

Thus, the technical parameters of the cutting machine are changed relative to the welder:

1) The main transformer turns ratio becomes smaller to obtain a higher output voltage;

2) Slow (slow) start-up time becomes longer to ensure gas supply and air pressure;

3) The feedback gain becomes smaller, and the feedback op amp gain is changed from open loop gain to closed loop gain;

4) The duty ratio becomes larger (more than 90%) to obtain a higher output voltage;

         5) The impedance of the reactor becomes large to prevent high-frequency interference and ensure reliable shutdown of the control relay