General Method For Producing Tungsten Wire
Most of the production of tungsten wire use the material of ammonium paratungstate(APT). The process is using the ammonium paratungstate firing into tungsten trioxide at about 500 ¡æ in the air,or slightly reducing to blue tungsten oxide at about 450 ¡æ in hydrogen.In order to produce incandescent tungsten filament wire,it requires incorporation of a small amount of potassium, silica and alumina in the tungsten trioxide or blue tungsten oxide.Total amount of them not more than 1%.This is the tungsten wire doping process.which is inventioned by Buzz in 1922.Tungsten oxide after the doping process reduced to metallic tungsten powder by hydrogen.
Reduction process is generally carried out in two steps:The first step is reduced to tungsten dioxide at about 630 ¡æ .The second step is reduced to metallic tungsten powder at about 820 ¡æ.The purpose of the two-step reduction is to make full use of the incorporation sodium and to control the power size.Doped tungsten powder thus obtained compressed into an elongated square bar in a special mold.Put the square bar powered in hydrogen,using self resistance heating (temperature of about 3000 ¡æ) method sintering.After sintered the density of tungsten bar can reach more than 85% of the theoretical value.This tungsten bar can be processed into tungsten rod at about 3mm by swaging method. And then processed into a variety of different thickness of the tungsten wire by mold drawing method
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