Production of Tungsten Wire

Producing tungsten wire is a complex and difficult process. The whole process must be strictly controlled by controlling the proper chemical composition to ensure the physical properties of the finished tungsten wire. In the production process, if you want to cut corners to reduce production costs, it will lead to poor performance of the finished tungsten wire.

Since tungsten filament has the highest melting point of all metals, it is impossible to obtain tungsten from ore by traditional methods. Tungsten is obtained from ores through a series of chemical reactions. The exact process will vary depending on the supplier and the ore composition, but after the ore is crushed, roasted or passed through a series of chemical reactions, precipitation and washing to obtain Ammonium Paratungstate (APT). APT can be sold directly or further processed into Tungsten oxide. Tungsten oxide is obtained by baking in a hydrogen atmosphere to obtain pure tungsten powder and water vapor. Tungsten powder is the starting point for the production of tungsten pressed products including tungsten wire.

From tungsten powder to tungsten wire, the following steps are required:

1. Molding Tungsten powder is screened and mixed. A fixed weight of powder is put into a stainless steel mold, and the powder is extruded into a single, but brittle, rod. Remove the mold.

2. Pre-sintering This fragile rod is placed in a refractory metal vessel and placed in a hydrogen sintering furnace. The high temperature causes the metal particles to continuously agglomerate together. During this process, the density can reach about 60% - 70%, and the particle size does not increase.

3. Fully sintered rods are placed into a special water-cooled processing unit. Electric current is passed through the rod, and the heat generated makes the tungsten rod about 85% to 95% denser. At the same time, the inner tungsten crystals of the rod begin to form.

4. The tungsten rod at this time is relatively strong, but it is still relatively brittle at room temperature. The tungsten rod can be made more ductile by raising its temperature to 1200°C to 1500°C. At this temperature, the tungsten rod can be extruded by hammer forging machines. The hammer forging machine is a device that reduces the diameter of the tungsten rod by regularly beating the tungsten rod with a die 10,000 times per minute. Typically, the diameter of the tungsten rod decreases by 12% with each beating. By extrusion, the crystal structure is pulled into a fibrous structure. But to improve the strength and flexibility of the finished product, the tungsten rod must be continuously reheated and the beating continued until the rod reaches 0.25 to 0.10 inches in diameter.

5. Drawing The extruded tungsten rod is about 0.10 inches in diameter, and then it is drawn through a wire drawing die to make the diameter thinner. The wire is lubricated and drawn through a carbide wire drawing die or a diamond wire drawing die. The precise size to which the final reduction is to be made depends on the precise chemical composition and the final tungsten wire to be used. When the tungsten wire is pulled, its fibrous structure will be elongated again, and the tensile strength will be increased accordingly. Sometimes the tungsten wire needs to be further processed to a finer diameter, even 0.005 inch.