Drawing billet can be produced either by rotary forging or by rolling. The deformation of billet produced by rolling method is large and the structure is more uniform, which is beneficial to the later processing.
Tungsten wire is drawn from tungsten wire blank by "warm drawing" method. Firstly, the diameter was pulled to 1.3 mm by the chain drawing machine, and then the diameter reached 0.2, 0.06 and less than 0.06 mm by rough, medium and thin drawing respectively. As the diameter decreases, the heating temperature should be reduced and the drawing speed should be increased. The amount of trace deformation is generally between 10 ~ 20%.
Drawing adopts gas-air mixture heating, the temperature is 900 ~ 400℃.Carbide die is used for drawing the coarse wire, while diamond die is used for drawing the fine wire. Mold material, hole, grinding technology has a great impact on the quality of silk, the quality of graphite lubricant, particle size, ratio, coating method also affect the quality of silk.
The inhomogeneity of wire diameter is one of the main reasons for wire breakage in use. A deviation of 0.2 ~ 0.4 micron will greatly reduce the life of tungsten wire in vacuum tube. The diameter of the filaments can be determined by gravimetric method or vacuum standard current method. In the process of wire drawing, the deformation resistance increases as the diameter decreases (for example, the fracture strength of tungsten wire with the diameter of 0.1 ~ 0.3 mm can be as high as 350 kg/mm 2), and its plasticity also decreases correspondingly. In order to improve the reprocessing performance, it is generally necessary to carry out stress relief intermediate annealing. In addition, the electrolytic corrosion method can be used to process the wire into a diameter of less than 0.01 mm.
