DISCHARGE ELECTRODE MATERIAL

Abstract: Disclosed is a discharge electrode material essential­ ly made of yttrium oxide and blended with rhenium or ruthenium. This electrode material is used as the elec­ trode for air plasma cutting, electrode for plasma spraying, and others, and it is excellent in heat resist­ ance and oxidation resistance, and its wear resistance is more than twice as high as that of conventional electrode materials such as zirconium and hafnium.

Description: Background of the Invention Electrode materials usable in cutting of metal materials in an oxidizing atmosphere such as fresh air and oxygen atmosphere are limited to only few metals such as hafnium and zirconium. Aside from them, there are various electrode materials excellent in conductivity and heat resistance, but they are consumed too fast to be used in an oxidizing atmosphere and are not practically usable. Hafnium and zirconium are extremely expensive, hard to obtain, and the cutting cost is very high. Recently, in addition to the improvement and diversification of the cutting equipment, automation and robotics are rapidly promoted for the purposes of saving labor cost and mass production, but development of cutting equipment is limited by the delay in improvement of electrode material. An yttrium oxide electrode material to which rhenium is added is known from Transactions of J.W.R.I., Japanese Welding Institute, Vol. 16, No. 1, June 1987, pp. 215-216. Brief Summary of the Invention It is hence a primary object of this invention to present a discharge electrode material capable of obtaining a high performance at a lower cost than the conventional electrode made of hafnium or zirconium, and this electrode material is essentially made of yttrium oxide, to which ruthenium is added. Of this component of the electrode, ruthenium has a high melting point, and is excellent in oxidation resistance, in particular, high temperature oxidation resistance. Besides, yttrium oxide is particularly excellent in discharge characteristic, and by combining ruthenium and yttrium oxide at a proper ratio, it is possible to keep a stable discharge performance while minimizing the oxidation and heat consumption. In the electrode material made of ruthenium and yttrium oxide, the preferable content of ruthenium is 40 to 98% by weight, and the content of yttrium oxide is preferably 60 to 2%. This electrode material is an alloy of yttrium oxide with ruthenium, but traces of other elements may be added as far as its characteristic is not sacrificed. This electrode material may be fabricated, for example, with the following method. First, to the starting material of ruthenium powder (for example, having a mean particle size of 15 to 20 µm), yttrium oxide powder (for example, having a mean particle size of 5 to 6 µm) is added and blended, and the obtained mixture powder is pressed and formed into a desired shape. The obtained compressed powder is sintered according to a known method to obtaine the desired electrode material. This electrode material is excellent in availability in comparison with the conventional zirconium or hafnium, and possesses a wear resistance of about two or three times higher when compared with them, and it can obtain a stable arc characteristic. This electrode material can sufficiently exhibit its characteristics for use in air plasma cutting, plasma spraying, heat resistant and oxidation resistant services, and others. Brief Description of the Drawings Fig. 1 and Fig. 2 are explanatory drawings of a testing equipment, and Fig. 3 is a graph to express the relation between composition and wear resistance. Detailed Description of the Invention This invention is described in further details below by referring to its embodiment. Ruthenium powder with mean particle size of 15.0 um and purity of 99.9%, and yttrium oxide powder with mean particle size of 5.7 µm and purity of 99.9% were dry-mixed for 30 minutes by means of a shaker-mixer. A binder was added to this mixture powder to granulate it. Obtained grains of mixture powder of ruthenium (Ru) and yttrium oxide (Y₂O₃) were pressed in a mold to become compressed powder of 2 mm in diameter and 4 mm in length (compressed powder density 65 to 75%), and it was presintered in hydrogen steam (500°C for 15 minutes) and sintered (2,100°C for 30 minutes) by conventional method, and an electrode material made of a sinter of 1.8 mm in diameter and 3.5 mm in length was obtained. The obtained electrode material was press-fitted into a copper-made chip holder to be used as the cathode, and a water-cooled copper plate was used as the anode, and an arc test was conducted by using the test apparatus shown in Fig. 1 and Fig. 2 to measure the consumption. In the drawings, numeral 1 is a torch, 2 is an electrode, 2a is an electrode material, 3 is a water-cooled copper plate, 4 is a cutting power source, 5 is an air regulator, 6 is a compressor, 7 is a nozzle, and 8 is a plasma arc. The results are shown in Fig. 3. The test conditions in Fig. 3 were a current of 25 A, a voltage of 95 V, an air pressure of 3.5 kg/cm², and a duration of 5 minutes. The consumption is expressed in cubic millimeters (mm³). As understood from Fig. 3, the electrode material of this invention is small in consumption as compared with the conventional electrode materials made from zirconium or hafnium. The preferable range of chemical composition is, as is clear from Fig. 3, 40 to 98% for ruthenium, or more preferably 50 to 96%. Fabrication of this electrode material is relatively easy, and there is no problem in the availability of the materials. In this electrode material, a stable plasma arc was obtained, and the consumption was small, and the cut section was straight and smooth when used as a cutting electrode, while the cutting width was small and the cutting speed was fast.

Claims: A discharge electrode material excellent in heat resistance and oxidation resistance substantially composed of yttrium oxide and ruthenium. A discharge electrode material as set forth in claim 1, wherein the yttrium oxide content is 60 to 2% by weight, and the ruthenium content is 40 to 98% by weight.

Inventors: MAENO, YOSHINORI, MATSUDA, FUKUHISA, MIKITA, HIROSHI, UMEZU, SADAO, USHIO, MASAO
Applicants: TOHO KINZOKU CO., LTD.
Application year: 1988
Main classification: H05H1
IPC codes: C22C1, C22C27, H05H1, B23K35, H01B1, C22C29, C22C32