US3546422A - Device for plasma arc treatment of materials - Google Patents

Description

United States Patent Inventors Appl. No. Filed Patented Priority David Grigorievich Bykhovsky, Konjushenny pereulok, [/6 kv. 18; Alexandr Yakovlevich Medvedev, Ulitsa Kalyaeva, 3, kv .17; Yakov Vull'ovich Rossomakho, Ulitsa Treloleva, 32, kv. l4; Valery Alexandrovich Koss, Ulitsa Besstuzhevskaya 11, kv. 56, all of Leningrad, U.S.S-.R.

Feb. 11, 1969 Dec. 8, 1970 Feb. 15, 1968 U.S.S.R.

DEVICE FOR PLASMA ARC TREATMENT OF MATERIALS 4 Claims, 1 Drawing Fig.

U-S-Cl. 219/121, 219/75 lnt.C1. 3231:9/26

Field ofSearch 219/74, 75,

\ \IQ K Primary Examiner.l. V. Truhe Attorney-Holman, Giascock, Downing & Seebold ABSTRACT: A device for plasma-arc machining of materials in active media, preferably for cutting metals, wherein the cathode holder and cathode are separated by a gasket which increases the cathode life up to 6 hours at an allowable arc current of up to 350a. The gasket material is inert with respect to the cathode material (zirconium) and the cathode holder material (copper or copper alloy) and is preferably selected from the following: tungsten, tantalum, molybdenum, niobium, vanadium or chromium.

PATENTED DEC 8 I970 *WIL DEVICE FOR PLASMA ARC TREATMENT OF MATERIALS The present invention relates to devices for plasma-arc treatment of materials and more particularly it relates to the devices for plasma-arc treatment of materials in active media, preferably for cutting metals.

The device can also be employed for surface fusion, for example for the removal of a defective surface layer from castings and cast products or for the correction of such local defects as cracks, pits, scabs. The invention can also be used for heating chemically active gases and their mixtures and for the thermochemical surface treatment of metals, e.g. nitriding, case-hardening and similar processes.

The present invention'can be used both with and without additional protection of the cathode assembly.

Known in the art is a device for plasma-arc treatment of materials in active media, preferably for cutting metals, comprising a cathode holder made of copper or a copper base alloy, and accommodating a zirconium cathode. The cathode holder is connected, via an insulting bushing, with the body accommodating the nozzles which stabilize the arc discharge.

A substantial disadvantage of the known device is an extremely short service life of the zirconium cathode (not over 4 hour) at are currents of 250.

One of the main causes of excessive wear of the zirconium cathode is deterioration of the thermal and electrical contact between the zirconium cathode and the copper cathode holder. The temperature on the contacting surface between zirconium and copper reaches 700 1 ,000 C. The diffusion processes at such temperatures produce intermetallic compounds at thepoint of contact between copper and zirconium, these compounds having a-farlower heat and electrical conductivity than copper or zirconium. The layer of intermetallic compoundinterferes with the withdrawing of heat from zirconium which leads eventually to its ultimate destruction.

An object of the present invention is to eliminate the aforesaid disadvantage.

The main object of the present invention is to provide a device. for plasma-arc treatment of materials in active media, preferably for cutting metals, whose cathode would be more wear resisting as compared to the known device at arc currents of250 a. and above. i

This object is accomplished by providing a device for plasma-arc treatment of materials in active media, preferably for cutting metals, comprising a cathode holder made of copper or a copper base alloy with a zirconium cathode.

According to the invention, the cathode holder is separated from the cathode by a gasket made of a material which is chemically inert with relation to both zirconium and copper.

Now the invention will be described in detail by way of example with reference to the drawing (which shows schematically a device for plasma-arc cutting of metals in active media).

The device for plasma-arc cutting of metals in active media consists of a body 1 accommodating a cathode holder 2 and a nozzle 3 with a central passage 4 intended to stabilize the arc discharge 5.

To prevent formation of a double arc in case the nozzle 3 accidentally comes in contact with the work 6, or to increase the total length of the stabilizing central passage 4, there may be installed at least one more nozzle 7 (shown by dotted lines in the drawing).

The cathode holder 2 made of copper or a copper base alloy, is fastened in the body 1 by means of the insulating bushing 8, and is cooled by the coolant supplied through a pipe 9 installed inside the cathode holder. The nozzles 3 and 7 have passages 10 and 11 for the supply of coolant.

lf a number of nozzles are used, they are separated by an insulating gasket 12. The coolant may be either water or gas. The body has a hole 13 for the supply of plasma-generating gas, e.g. air, nitrogen, oxygen, or mixtures containing nitrogen and oxy en.

Pressitted into the cathode holder 2 (flush with it) is the zirconium cathode 14 separated from the copper cathode holder 2 by the gasket 15 which is made of a metal which is inert both to zirconium and copper (tungsten, tantalum, molybdenum, niobium, vanadium, chromium).

The thickness of this gasket should be sufficient to rule out the diffusion of copper into zirconium. For instance, at temperatures up to l,000 C. the thickness of the gasket may be l0- mm.

The zirconium cathode 14 can be separated from the copper cathode holder 2 by the gasket 15 using one of the following methods: by electrodeposition of one of the abovementioned metals or their compounds on the cathode 14, or by vacuum spraying of these metals on the cathode 14 or cathode holder 2. The separating gasket 15 can also be fitted into the cathode holder by a mechanical method.

The cathode holder 2 is acted upon by a negative potential while the work is under the positive potential. The are discharge 5 burns between the zirconium cathode l4 and the work 6, passing through the stabilizing central passage 4 in the nozzle 3. If the nozzle 7 is used, the arc discharge takes place between the cathode 14 and the work 6, passing through the stabilizing central passages 4 and 16 of the nozzles 3 and 7, respectively.

The tests of the claimed device have revealed that the allowable arc current has been increased to 350 a. with a simultaneous extension of the life of the zirconium cathode to 6 hour.

We claim:

1. In a plasma generator having a central cathode holder and cathode, an annular cavity between the cathode holder and a housing, plasma generating gas inlet means to the cavity, at least one central nozzle between the cathode and a workpiece, and a power source, the improvement consisting in that a conductive metallic gasket is interposed between said cathode holder and cathode, said cathode being made of zirconium, said cathode holder being made of a metal selected from the group consisting essentially of copper or copper alloy, and said metallic gasket being made of a metal which is inert to either said cathode or holder with regards to forming intermetallic compounds therewith at operating temperature.

2. A plasma generator as claimed in claim 1 wherein said cathode holder and central nozzle have coolant passages therein.

3. A plasma generator as claimed in claim 1 wherein said gasket is made of a metal selected from the group consisting essentially of tungsten, tantalum, molybdenum, niobium, vanadium or chromium.

4. A plasma generator as claimed in claim 3 wherein said operating temperature is approximately 1,000 C. and said gasket is approximately 10- mm. thick.

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