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Conventional process of tungsten wire production

Ammonium secondary tungstate (APT) is the main raw material for tungsten wire production.The general process is to roast the auxiliary ammonium tungstate in the air at about 500℃

Tungsten trioxide, or slightly less blue tungsten oxide in hydrogen at around 450°c.To make an incandescent filament, tungsten requires a mixture of small amounts of potassium oxide, silicon oxide and alumina tungsten trioxide or blue tungsten oxide, all of which add up to less than 1%.This is the tungsten doping process invented by bartz in 1922.The doped tungsten oxide was reduced to metallic tungsten powder by hydrogen.The reduction process is generally divided into two steps: the first step is to reduce to tungsten dioxide (brown tungsten oxide) at around 630℃, and the second step is to reduce to metallic tungsten powder at around 820℃.The purpose of the two-step reduction is to make full use of the added potassium and control the size of the powder.The resulting doped tungsten powder is pressed into a special mold to make a thin square strip.When the square rod is electrified in hydrogen, the density of the sintered tungsten strip can reach more than 85% of the theoretical value after self-resistance heating and sintering (the temperature is about 3000℃).The tungsten strip is processed into a tungsten strip with a diameter of about 3mm by rotary forging, and then processed into tungsten wires of various thicknesses by die drawing.For example, the diameter of the filament used in the 220 v and 15 w incandescent lamps is approximately 15.M, and the 10000W bromine tungsten lamp USES a tungsten wire with a diameter of about 1.25mm.The diameter of thin tungsten filament such as 220 v and 10 w incandescent filament is approximately 12.M shall be made from electrolytic corrosion.

When the diameter of tungsten wire reaches the micron level, it is difficult to accurately measure its diameter with traditional calipers.Therefore, internationally, the diameter of tungsten wire less than 0.2mm is usually expressed by the weight of the cutting length of 200mm filament segment.For example, the tungsten filament diameter of a 15W incandescent lamp can be expressed as 0.679mg/200mm.

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