Plasma arc cutting machine with variable constant current source

Details Plasma arc cutting machine with variable constant current source Plasma arc cutting machine with variable constant current source

1995-01-31

1996-04-09

Paschall, Mark H.

Electric heating

Metal heating

By arc

21912154, 21912156, B23K 1000

Patent

active

055063845

ABSTRACT:
A first stop valve (4) is connected in parallel with a serially connected second stop valve (7) and a gas flow regulating means (6) between a supply of working gas and a plasma torch (1). In response to a start signal S.sub.T, the second stop valve (7) is opened so as to supply the working gas at a small flow rate Q.sub.P to the plasma torch (1) via the gas flow regulating means (6). After a pilot arc is started, the first stop valve (4) is gradually opened so as to gradually increase the flow rate of the working gas from the small flow rate Q.sub.P up to a normal flow rate Q.sub.M, and at the same time, the pilot current is gradually increased from an initial pilot current level I.sub.S to a pilot current level I.sub.P, corresponding to the gradual increase in the flow rate of the working gas up to the normal flow rate Q.sub.M. In response to a stop signal S.sub.P, the arc current is gradually reduced from the cutting current level I.sub.M to a lower level I.sub.D at which the main arc (13) is extinguished. A resistor (12a,12b) is connected in a current path between a constant current source (8) and the plasma nozzle (1a), with the current source (8) having a plurality of switchable current levels and the resistor (12a,12b) having a corresponding plurality of resistance levels, whereby the nozzle-workpiece voltage can be maintained substantially constant.

REFERENCES:
patent: 3809850 (1974-05-01), Saerger, Jr.
patent: 4816637 (1989-03-01), Sanders et al.
patent: 4839499 (1989-06-01), Kotecki et al.
patent: 5017752 (1991-05-01), Severance, Jr. et al.
patent: 5070227 (1991-12-01), Luo et al.
patent: 5166494 (1992-11-01), Luo et al.
patent: 5235162 (1993-08-01), Nourbakhsh

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