Electric heating – Metal heating – By arc
Patent
1997-12-23
1999-07-20
Paschall, Mark
Electric heating
Metal heating
By arc
21912154, 21912148, 2191304, B23K 1000
Patent
active
059252677
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a plasma torch that is designed to effect a welding or a cutting operation for a workpiece while bringing a portion of the plasma torch in contact with the workpiece.
BACKGROUND ART
In a plasma welding or process, where the resulting weld or cut quality is of a prime importance, it has been known to be necessary to perform the operation with a plasma torch while maintaining the distance between a nozzle forward end thereof and a workpiece, i.e. a standoff, constant. Thus, a plasma torch has typically been employed having a member that is mounted to a body portion thereof and designed to surround a nozzle forward end thereof, and such a plasma torch has been configured in a construction as disclosed in Japanese Examined Patent Publication No. Hei 3-9902 and Japanese Unexamined Patent Publication No. Hei 7-16752 in the prior art.
And, in a conventional plasma torch as disclosed in the former publication above, it can be noted that a spring member composed of a material having a heat resistant property is externally provided on the body of the plasma torch to form a coiled spring thereon whose leg end, extending downwards beyond the nozzle forward end, can be urged to engage with a workpiece so as to cut the workpiece. In another conventional plasma torch as disclosed in the latter publication above, it can be noted that the end of a retention cap mounted to the torch end extends downwards beyond the nozzle forward end and is urged to engage with a workpiece so as to spot weld the workpiece with another workpiece.
In these techniques in the prior art, however, it is recognized that a member as provided on a plasma torch and urged to engage with a workpiece must be subjected to a considerably elevated temperature that is brought by a heat of the plasma arc and a heat conducted from the workpiece. Thus, even if such a member contacting the workpiece is composed of a ceramic material to constitute a cap as have been used for a plasma torch and so forth, the contacting member is found to be disadvantageous on account of the productivity and the running cost because it tends to be broken or cracked.
On the other hand, in a case where the contacting member is composed especially of a metal, such as copper, having a high thermal conductivity, the member that is naturally of a non-insulating body allows a high frequency electric current that may be brought about when a plasma arc is started to leak therethrough into the workpiece, thus giving rise to a problem such as tending to develop an abnormal discharge or to make a plasma arc hard to develop.
In order to resolve the problem arising from leakage of such a high frequency current, it has been proposed as disclosed in Japanese Examined Utility Model Publication No. Hei 2-39657 that there be provided, between the end of a body portion of the plasma torch and the end of an insulating cap disposed coaxially to surround its nozzle portion with a spacing through which a shielding gas is allowed to pass, a protective packing that is composed of an insulating material and arranged to surround these two end portions so that the high frequency current may not leak through the gap between the torch body and the insulating cap into a region of the workpiece.
More specifically, a plasma torch as disclosed in the above mentioned utility model publication makes use of a packing interposed between the end of a torch body portion of the plasma torch and the end of an insulating cap disposed to coaxially surround a nozzle portion of the plasma torch with a spacing that is traversed by a shielding gas, where the packing is composed of an electrically insulating and heat resistant material such as to prevent a high frequency current from leaking from a region of the plasma torch into a region of the workpiece, and hence to prevent a development of any abnormal discharge.
With the use of a plasma torch of such a construction to carry out a welding or cutting operation for a workpiece while bringing a portion of the torch (here the i
REFERENCES:
patent: 5183990 (1993-02-01), Enyedy
patent: 5416297 (1995-05-01), Luo et al.
patent: 5530220 (1996-06-01), Tatham
patent: 5620617 (1997-04-01), Borowy et al.
Komatsu Ltd.
Paschall Mark
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