Discussion on vacuum sintering technology of molybdenum bar
Since the great development of vacuum sintering technology in cemented carbide production practice in 1960s, vacuum sintering technology has also been applied in the field of tungsten molybdenum powder metallurgy. However, due to many reasons, the traditional vertical melting sintering method is still used by most manufacturers to produce molybdenum bars for wire drawing. Vertical melting sintering is usually carried out in bell jar type vertical furnace. The pre sintered molybdenum bars are placed between the upper and lower conductive column clamps. The cover is filled with hydrogen, and the molybdenum bars are directly electrified and heated. The maximum sintering temperature is 2300 ℃ ~ 2350 ℃, and the final sintering density is 9.2~9.5 g/cm3. Although this method has the advantages of fast heating, short sintering time and difficult bending, it has the following disadvantages: (1) lower temperature at the upper and lower ends, large temperature gradient and poor consistency of sintering density; (2) poor thermal insulation and sealing, resulting in high power consumption and hydrogen consumption, and high sintering cost; (3) the clamping parts at both ends (about 4%) need to be cut off for the vertical melting strip, and the yield is reduced.
With the development of China's material industry and high temperature technology, the high temperature furnace which can meet the sintering conditions of molybdenum bar has been gradually applied in production practice. This kind of high temperature furnace is mainly used for sintering tungsten molybdenum plate, bar and profile, while the molybdenum bar for sintering wire drawing is rarely used. In recent years, with the fierce competition in China's tungsten and molybdenum industry, some manufacturers have begun to use indirect sintering method to produce molybdenum bars for wire drawing in consideration of energy saving and cost reduction. However, hydrogen protection is still adopted and the energy saving effect is poor.
(1) The vacuum sintered molybdenum bars have good consistency of density, low impurity content, good wire drawing performance and better technical properties than vertical melting molybdenum bars.
(2) Vacuum sintering molybdenum bar has high yield, energy saving, hydrogen saving and sintering cost greatly reduced.
(3) Vacuum sintering technology is more suitable for the production of large billets, which creates favorable conditions for increasing the single axis weight of molybdenum wire, improving the comprehensive technical performance and developing spraying molybdenum wire. It is of far-reaching significance to change the operation form of billet in China.
