Plasma torch for cutting use with nozzle protection cap having a

Details Plasma torch for cutting use with nozzle protection cap having a Plasma torch for cutting use with nozzle protection cap having a

1993-08-18

1995-02-28

Paschall, Mark H.

Electric heating

Metal heating

By arc

21912151, 21912148, 219 75, 21912149, B23K 1000

Patent

active

053939522

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD OF THE INVENTION

The present invention relates to a plasma torch utilized for a plasma cutting machine.


BACKGROUND OF THE INVENTION



First Prior Art (Water-cooled Torch)

This includes a torch of the type utilized for a plasma cutting machine in which an electrode and a nozzle are cooled by cooling water. In this type, the electrode is attached to a body of the torch, to which the nozzle is attached through a gas jetting port for jetting an operation gas by gyrating about a periphery of axes of an insulating member and the electrode. Portions of the nozzle, except for the front end including a nozzle orifice of the nozzle, are covered, and a nozzle cap for fixing the nozzle to the torch body is screwed with the torch body. In this structure, the cooling water after cooling the electrode passes a cooling water passage formed inside the torch body, then through a space defined by the torch body, the nozzle and the nozzle cap to cool the nozzle and then returns again to the cooling water passage formed to the torch body.


Second Prior Art (Nozzle Protection Cap in Air-cooling Nozzle)

In a plasma torch, at a time when a front end of the nozzle is exposed, there is a fear of damaging, in a welding operation, the nozzle by a fused metal (dross) blown up to the nozzle at a time of carrying out a piercing operation (cutting operation for forming a hole) to a thickened plate at a cutting start time, or there is a fear of damaging the nozzle due to an inaccurate discharge, called a double-arc, caused by the contact between the nozzle and a workpiece to be cut. To obviate these fears, in the air-cooling nozzle, a metallic nozzle protection cap electrically insulated from the nozzle is provided for protecting the nozzle front end portion, and also, the gas cooling the nozzle passes, as it is, the space between the nozzle and the nozzle cap to thereby blow off the blown-up fused metal. This nozzle protection method is disclosed in U.S. Pat. No. 4861962 (Hiper: Filed on Aug. 29, 1989).


Third Prior Art (Nozzle Protection Cap in Welding Torch)

As in the above Second Prior Art, Japanese Patent Laid-open Publication No. 53-119753 (HITACHI SEIKO: Filed on Mar. 30, 1977) discloses a plasma welding torch having a structure in which a metallic nozzle cap electrically insulated from the nozzle is mounted to the periphery of the nozzle and a secondary gas is blown between the nozzle and the nozzle protection cap.


Fourth Prior Art (Inclination of Cut Surface due to Gyrating Air-Current
Effect)
In the plasma cutting, in general, a front side of a cut groove (kerf) is wide and a rear side thereof is narrow, and for this reason, the cut surface does not provide a perpendicular surface and has an inclination.
On the contrary, it is known that, in the plasma torch in which an operation gas is gyrated around a periphery of the axis of an electrode for stabilizing an arc to thereby jet out the arc, the cut surface does not provide a bilaterally symmetric surface and provides an asymmetric surface. By utilizing these phenomenon, in a condition that a front kerf width is wide and a rear kerf width is narrow, a perpendicular cutting can be done with respect to only one side surface to be cut by gyrating the operation gas, which technology is disclosed in "Welding Technology", Vol. 6, Jun., 1988.
In the above respective prior art, the following problems have been provided in points of (1) protection of nozzle, (2) contraction of plasma arc due to secondary gas, (3) temperature rising of nozzle protection cap, (4) adjustment of gyrating air and (5) electrical corrosion of a cooling water passage surface.


(1) Protection of Nozzle

In the plasma cutting, when a piercing working (hole formation cutting) is carried out to a thickened plate at a cutting operation start time, a fused metal (dross) blown up to the nozzle is stuck to the nozzle, which may result in the causing of a fuse damage to the nozzle or in the causing of an inaccurate discharge, so-called double-arc, in contact of the nozzle to a workpiece to be

REFERENCES:
patent: 3204076 (1965-08-01), Browning
patent: 4125754 (1978-11-01), Wasserman et al.
patent: 4341947 (1982-07-01), Komura et al.
patent: 4389559 (1983-06-01), Rotolico et al.
patent: 4521666 (1985-06-01), Severance, Jr. et al.
patent: 4861962 (1989-08-01), Sanders et al.
patent: 4954688 (1990-09-01), Winterfeldt
"Welding Technology", vol. 6, Jun., 1988, pp. 115-121.

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