How is Tungsten Wire Made?

Aug. 20, 2010 - PRLog -- In our daily life, the incandescent light are widespreading use. As we all know, the light must use the tungsten wire. However, do you know how the tungsten wire is made? The process of making tungsten wire is very complicated and difficult.The process must be tightly controlled so as to insure the proper chemistry as well as the proper physical properties of the finished wire.
If we have pure tungsten powder, how do we make wire?
Firstly, Pressing - Tungsten powder is sifted and mixed. A binder may be added. A fixed amount is weighed and loaded into a steel mold which is loaded into a press. The powder is compacted into a cohesive, yet fragile bar. The mold is taken apart and the bar removed.
Secondly, Presintering - The fragile bar is placed into a refractory metal boat and loaded into a furnace with a hydrogen atmosphere. The high temperature begins to consolidate the material together.
Thirdly, Full Sintering - Bar is loaded into a special water-cooled treating bottle. Electric current will be passed through the bar. The heat generated by this current will cause the bar to densify to about 85% to 95% of full density and to shrink by 15% or so. Additionally, tungsten crystals begin to form within the bar.
Besides, Swaging - The tungsten bar is now strong, but very brittle at room temperature. It can be made more malleable by raising its temperature to between 1200°C to 1500°C. At this temperature, the bar can be passed through a swager. Typically a swager will reduce the diameter about 12% per pass. Swaging elongates the crystals, creating a fibrous structure. Although this is desireable in the finished product for ductility and strength, at this point the rod must be strees-relieved by reheating. Swaging continues until rod is between .25 and .10 inches.
Last but not least, Drawing - Swaged wire of about .10 inches can now be drawn through dies to reduce the diameter. Wire is lubricated and drawn through dies of tungsten carbide or diamond. The exact reductions in diameter depend on the exact chemistry and the final use of the wire. As wire is drawn, fibers again elongate and tensile strength increases. At certain stages it may be necessary to aneal the wire to allow further processing. Wire can be drawn as fine as .0005 inches in diameter.
All in all, making tungsten wire is really complex. You must be careful for every step. Also, you must be very surprised a small bulbs unexpectedly also contains such complicated procedure.