Controlling working gas flow rate and arc current level in plasm

Details Controlling working gas flow rate and arc current level in plasm Controlling working gas flow rate and arc current level in plasm

1994-04-21

1995-06-13

Paschall, Mark H.

Electric heating

Metal heating

By arc

21912139, 21912154, 21912155, 21912157, B23K 900

Patent

active

054245079

ABSTRACT:
A plasma arc cutting machine which utilizes oxygen as a working gas is controlled to provide: a long electrode life without serious electrode wear even if the starting operation of the arc is repeated frequently; a smooth transition from a pilot arc to a main arc even when a thin plate is cut; and a low noise characteristic. 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.

REFERENCES:
patent: 4816637 (1989-03-01), Sanders 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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