Electric heating – Metal heating – By arc
Patent
1991-12-03
1993-01-05
Paschall, Mark H.
Electric heating
Metal heating
By arc
219119, 219121, 219 49, 21912148, 219123, B23K 900
Patent
active
051773384
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a cathode structure of a plasma-arc torch that is available in cutting and welding of metal, and more particularly to a cathode structure of a transition type plasma-arch torch, wherein in order to remarkably reduce a consumed amount of cathode material, a cooling effect is enhanced, and also within a bottom surface of a cathode movement of a discharge point is made possible.
TECHNICAL BACKGROUND OF THE INVENTION
As a cathode structure of a plasma-arc torch in the prior art, a rod-shaped cathode structure and a buried type cathode structure are known as shown, for example, in "PRAZUMA SETSUDAN NO KISO TO JISSAI (Fundamental and Practice of Plasma-arch Cutting)" (in Japanene) edited by NIHON YOSETSU KAI (Society of Welding in Japan) (published Dec. 1, 1983 by KOSAIDO SANPOH SHUPPAN, page 48).
The rod-shaped cathode is a cathode mainly making use of inert gas such as argon, nitrogen, hydrogen, etc. as a working gas, and it is employed in a torch having a relatively small capacity, whereas the buried type cathode is a cathode wherein kafnium, zirconium or the like is buried in a tip end portion of a water-cooled copper pipe, and it mainly makes use of an oxidizing working gas such as oxygen, air, etc. and is employed in a torch having a relatively large capacity.
In addition, with regard to a cathode structure of non-transition type plasma-arc torch, in the case of large-capacity torches, cathodes having various shapes and structures have been devised. For instance, besides the above-mentioned rod-shaped or buried type cathodes, cathodes having a ring-shaped or hollow type (hallow cathode) structure have been used.
In common to the transition type and non-transition type plasma-arc torches, one big problem is abrupt consumption of a cathode and a nozzle accompanying the generation of plasma arcs. Especially in the case where oxidizing gases such as air, oxygen, etc. are used as a working gas, their life would become extremely short, and as a cathode, the life is so short that it becomes necessary to be replaced at an interval of about 0.5.about.3 hours.
Heretofore, because of the necessity of frequent cathode replacement works due to such a short period of life of the cathode, for instance, version to numerical control (NC) of a plasma-arc cutting machine and a plasma-arc welding machine as well as popularization of these machines are remarkably lagging.
Now, it has been well known that among the heretofore employed cathode structures and working gas feed systems in the transition type plasma-arc torches, there are an axial flow type and a swirl flow type. And in these plasma-arc torches of either axial flow type or swirl flow type in the prior art, a discharge point exists always at the center of the cathode, and as the time when a plasma arc is generated elapses, consumption of the cathode proceeds remarkably from its central portion.
As one method for resolving the problem of abrupt cathode consumption, it was devised by the inventor of this application to continuously move the discharge point on the cathode surface to a new position during generation of a plasma arc. The device is disclosed in Japanese Utility Model Application No. 60-130799 filed on Aug. 29, 1985. The cathode structure of the transition type plasma-arc torch based on this device is the structure shown in FIG. 1 of the accompanying drawings.
In FIG. 1, reference numeral 10 designates a cathode holder, and to the bottom end portion of this cathode holder 10 is mounted a cathode 11. The cathode 11 is provided with a hemispherical concave surface 12 on its bottom surface. In addition, the cathode holder 10 is provided with a generating device of lines of magnetic force 13 such as a coil, a permanent magnet or the like, and this generating device of lines of magnetic force 13 is disposed above the cathode 11 coaxially therewith. In the case where the generating device of lines of magnetic force 13 is a coil, a D.C. coil is used. Reference numeral 14 designates a nozzle for
REFERENCES:
patent: 3610796 (1971-10-01), DeCorso et al.
Kabushiki Kaisha Komatsu Seisakusho
Paschall Mark H.
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