Gravity-Sintering and Low-Pressure Pressing of Tungsten Powders
A limiting factor in the production of tungsten compacts by the conventional pressing and sintering technique is the cost and availability of pressure vessels larger than 18 in. in diameter. Two alternate methods of economically producing large-diameter tungsten matrices have been developed, i.e., gravity-sintering and low-pressure pressing. In gravity-sintering, tungsten powder of quasi-spherical shape and narrow size fraction is vibrated in a metal mold to a density comparable to those acquired by pressing, presintered to obtain handling strength, and removed from the mold and finally sintered. The process has no size limitations other than those of sintering furnace availability and is comparable in cost to the conventional process. A more extensive sintering schedule is required, however, because of the lesser sintering activity of the powder. Low-pressure compacting techniques have been developed to produce a highly uniform tungsten matrix. Although this process still utilizes pressure vessels, the low pressures required reduce the cost of equipment by a factor of four. The development of low-pressure compacting was accomplished by pressing tungsten powders of various sizes, shapes, and particle-size distributions. No variation in sintering activity was noted as a result of the lower pressure. A decrease in pore number and an increase in pore size was noted, however.
KeywordsCompressive Strength Sinter Time Sintered Density Tungsten Powder Powder Characteristic
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