Tungsten wire is made from doped powders, that is, powders in which small quantities of potassium, silicon, and aluminum have been incorporated. Their purpose is to influence the recrystallized grain structure to reduce the creep rate at the high temperatures of incandescent filaments. The powders are consolidated under high pressure, sintered at high temperatures and worked by rolling and swaging to heavy rod suitable for drawing.
Tungsten wire drawing is accomplished by coating the wire with a graphite lubricant, heating to a red heat, and then drawing through tungsten carbide or diamond dies. The process is sometimes referred to as hot cold-working, which means that, while the wire is hot, the temperature is still below the recrystallization range. Accordingly, as the cross-sectional area is reduced, strength and ductility increase. The as-drawn wire at finished size subsequently may be cleaned, straightened, or annealed. Through various drawing methods and annealing steps. We produce different physical characteristics in wire of a given size. Our control of each manufacturing step from tungsten ore to finished wire assures reliability and reproducibility.
Tungsten metal is lustrous and silvery white in color, and does not occur naturally (it has an abundance of 1 ppm in the earth's crust). It is found in the ore Wolframite, a tungstate of iron and manganese, (FeMn)WO4, which is converted to the trioxide and then reduced to the metal by reduction in hydrogen (carbon cannot be used as the very stable carbide would result). Tungsten metal is relatively inert, resisting attack by oxygen, acids and alkalis, although it will react with fused, oxidizing alkali media. It has the highest melting point of all metals and, when pure, it can be worked with relative ease; however, the presence of impurities renders tungsten extremely brittle and, therefore, difficult to fabricate.
The high melting point of tungsten makes it suitable for use as electric filaments (e.g. in electric light bulbs). It is also the basis of a range of alloys containing tungsten, copper and nickel which are used for radiation shielding as they provide a 50% increase in density compared to lead. Tungsten and its alloys also find uses in military applications (e.g. armour and shells), as well as counter-balance materials. Tungsten carbide powder (with possible additions of titanium and tantalum carbides) along with nickel or cobalt powders, are compressed and sintered to produce cemented carbides. These products are used in place of high speed steel to form the tip of cutting and drilling tools, or for parts which will be subjected to heavy usage.