Electric heating – Metal heating – By arc
Patent
1996-04-12
1998-03-10
Paschall, Mark H.
Electric heating
Metal heating
By arc
21912151, 2191215, 219 75, 31323151, B23K 1000
Patent
active
057264147
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a plasma torch that can be used in welding or cutting with a plasma arc.
BACKGROUND ART
A vast research and development effort for the technique of plasma arc welding has hitherto be conducted in a variety of technical fields because of its unique advantages. Thus, the plasma arc welding technique, when applied to a spot welding process, has been found to enable a large workpiece and a workpiece of complicated configuration to be dealt with by virtue of the fact that its welding operation can be carried out from only one side of such workpieces which are subjected to their resistance spot welding thereby. Also, the plasma arc welding technique, when applied to a seam welding process, has been found to possess a productivity that is several times greater than the TIG welding technique.
A typical plasma torch in the prior art is disclosed in Japanese Laid-Open Utility Model Publication No. Hei 01-135174.
Such a conventional plasma torch unit is, as shown in FIG. 1 of the accompanying drawings hereof, configured to include: a base body a that is constructed as a tubular electrical conductor, a chip c that is held securely to the forward end of the base body a and constructed as an electrical conductor having an opening b which communicates with an inner space of the base body a, an electrode positioning member d that is constructed as an insulator held securely to a base end side of the base body a, and an electrode rod e that is located along an axis extending through a central portion of the opening b of the above mentioned chip c by means of the electrode positioning member d. In at least a portion of the space that extends from the internal space of the base body a to the opening portion of the chip c, there are formed a first gas passage f for causing a plasma gas stream to flow along the electrode rod e and a plurality of second gas passages g that branch from the first gas passage f for passing the plasma gas stream as a swirling or vortex flow around the forward end portion of the electrode rod e.
Notwithstanding its foregoing construction, the conventional plasma torch has been found to be poor in its arc stability because of the fact that while a portion thereof in which the swirling or vortex flow has just been created allows that swirling or vortex flow to be sufficiently enough intensive, thus permitting a leak of the high frequency from the electrode rod e to be prevented, the swirling or vortex flow tends to be weakened at the forward end of the electrode e under the influence of a gaseous flow passing in its axial direction, thus not permitting a leak of the high frequency from the electrode rod e.
In order to obviate this difficulty in such a plasma arc torch construction, a need has been considered to maintain the forward end of the electrode rod e sharpened at all the times. It has been found that this requirement causes a cathodic point (or an anodic point) to be formed at the forward end of the electrode rod e which as a result is rounded as the time elapses, and hence results in a shortened life of the electrode as well as in an instability in the welding quality that is attainable.
A present inventor has conducted a durability test for a conventional plasma torch of the above mentioned construction under welding conditions which are set forth in Table 1 below and has investigated how the electrode and the nozzle are worn off and how the welding quality is altered with the lapse of time.
TABLE 1 ______________________________________
Nozzle Diameter 2.4 mm
Welding Current 90 A
Welding Duration 7 seconds
Plasma Gas Ar; 1.8 L/min
Shielding Gas Ar + 7% H.sub.2 ; 7 L/min
Standoff Distance 4.5 mm
Crater Treatment None
(After Heat Treatment)
______________________________________
As a result of the investigation, it has been found that the forward end of an electrode in its configuration commences deteriorating at the time at which first 100 spot welds have been completed and that the size of a molten pool which is an i
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Kitahashi Masamitsu
Kurokawa Iwao
Tokunaga Mikio
Tokynaya Hiroyuki
Kananen Ronald P.
Komatsu Ltd.
Paschall Mark H.
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