Tungsten electrode material

Details Tungsten electrode material Tungsten electrode material

1994-12-30

1996-04-30

Sheehan, John

Alloys or metallic compositions

Tungsten base

420431, 75244, 75248, C22C 2704

Patent

active

055122400

DESCRIPTION:

BRIEF SUMMARY
FIELD OF INVENTION

The present invention relates to tungsten electrode materials with excellent arc ignitability and high wear resistance. For arc discharge electrode materials used for arc welding, high arc ignitability and wear resistance are required. Conventionally, for satisfying these characteristics, thoriated tungsten in which thorium oxide is contained in tungsten has been extensively used.
The above-mentioned thoriated tungsten is used for TIG welding, plasma welding, and plasma spraying, and though thoriated tungsten is material with excellent arc ignitability and wear resistance, it consumes excessively when applied for high-current density large-size plasma electrodes for melt-refining or high-temperature combustion, and a desired object is unable to be achieved. Conventionally, the use under atmospheric pressure has been most popular but in recent years, as welding technique is advanced, the use under severe conditions such as high pressure and reduced pressure has been increased, and conventional thoriated tungsten is no longer able to satisfy the requirements.
In addition, because thorium oxide powders which are used for raw material are radioactive material, it has problems of increased difficulty in procurement, increased costs, and severe control required for storage and handling by laws. In the application, thorium oxide is aggresively consumed and evaporates to create serious problems from viewpoint of health control of workers and air pollution. Therefore, it is an object of the present invention to solve the above-mentioned problems of conventional thoriated tungsten and to provide electrode material with more excellent capabilities.


DISCLOSURE OF THE INVENTION

In order to solve the above problems, research has been made on various components, and the research results have indicated that the material comprising tungsten to which lanthanum boride is added provides excellent arc ignitability and wear resistance. That is, the essential of the present invention is to provide tungsten electrode material that contains 0.01-1.0% lanthanum boride by weight and tungsten for the remainder.
The electrode material of the present invention is fabricated, for example, as follows. First of all, lanthanum boride powders are dry-mixed to the material metal tungsten powders until lanthanum boride powders are uniformly dispersed. The mean particle size of powders shall be, for example, 2-4 microns, while that of lanthanum boride shall be, for example, 1-3 microns. The powder mixture is press-formed in a conventional method in powder metallurgy and after sintering, the sintered compacts are subject to necessary processing such as swaging, drawing, and the like to make a desired electrode material. This electrode material contains lanthanum boride in addition to main component tungsten, providing excellent wear resistance and arc ignitability.
It is preferable to contain lanthanum boride in the range from 0.02 to 1.0 wt. % (same applies correspondigly to the following). If the content of lanthanum boride is lower than 0.02%, the performance would not significantly differ from that of pure tungsten free from lanthanum boride. If the content of lanthanum boride exceeds 1.0%, there is a problem that crack generation or breakage accidents frequently occur during manufacturing with the present level of powder metallurgy, and the percent defective increases. As the content of lanthanum boride increases, the melting point lowers and the wear rate tends to increase. Consequently, for application to big currents, it is preferable to keep the amount of lanthanum boride 0.02% or more but not exceeding 0.2%.
This tungsten electrode material can also be used for electrodes for plasma melt-refining, plasma electrodes for tundish, electrodes for plasma welding, electrodes for TIG welding, and electrodes for electric discharge tubes for various types of lighting.


BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a drawing describing the testing conditions of the present invention.
FIG. 2 is a graph showing the test results

REFERENCES:
patent: 4908182 (1990-03-01), Whang

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