Spinning technology of molybdenum crucible
Molybdenum is a rare metal, an important non renewable strategic material, and an important basic material for realizing national modernization and building modern national defense. Molybdenum is a non renewable resource. With its increasingly extensive application, the demand is increasing, and its price is getting higher and higher. Therefore, it is of great significance to use advanced forming methods to further process molybdenum materials in order to save materials and improve efficiency. In this paper, the crucible forming technology is studied. The traditional forming methods of molybdenum crucible are: powder metallurgy, machining, riveting, welding and hot stamping. In these traditional forming methods, machining molybdenum crucible wastes materials and has low efficiency; welding and riveting crucible accuracy is poor; stamping crucible forming is complex, low efficiency, high cost, and only simple simple parts can be formed. The molybdenum crucible formed by spinning can greatly improve the material utilization rate and high forming efficiency. It can also realize the forming of molybdenum crucible with irregular shape, variable wall thickness and flange edge at the mouth.
1. Performance analysis of Mo
Molybdenum is a VB group element in the periodic table. Its melting point is 2620℃ and its coefficient of linear expansion is one of its remarkable characteristics (5.8 ~ 6.2) × 10-6, which is only 1/3 ~ 1/2 of that of ordinary steel. The thermal conductivity of molybdenum is several times higher than that of many superalloys. Molybdenum has high elastic modulus, which is one of the highest elastic modulus metals in industry. It is less affected by temperature. Even at 800°C, it is still higher than that of ordinary steel at room temperature. Molybdenum has good elongation property and can be processed into thin foil and fine wire. The brittle temperature of molybdenum is near room temperature.
2. Design of spinning forming scheme
Since the plastic brittle transition temperature of molybdenum is near room temperature, the plasticity of molybdenum is very poor at room temperature. Therefore, heating spinning method should be adopted for molybdenum crucible. The key starts to oxidize at 300C, and a thin oxide film is formed on the surface. The oxide evaporates at 600 ~ 700℃ and oxidizes rapidly when it is higher than 700℃. Therefore, the heating temperature of molybdenum crucible should be controlled at about 600C. The spinning forming of small wall thickness molybdenum crucible parts can be realized by using the better elongation property of molybdenum. In view of the above analysis, the molybdenum crucible is formed by heating and spinning, and the temperature is controlled at 600±20℃. The molybdenum crucible parts are thin-walled cylindrical structures with small taper and variable wall thickness, and the mouth is provided with conical flanging. Because of the taper of the part, it is difficult to control the forming precision. First, the cylinder with thick wall and equal wall thickness is formed by conventional spinning, then the cylindrical part with variable wall thickness is formed by strong spinning, and finally the final part is formed by conventional spinning.
