Molybdenum crucible prepared by spinning method
Spinning is an advanced technology which combines the characteristics of forging, extrusion, stretching, bending, ring rolling, cross rolling and rolling. The spinning process mainly uses the feed movement of the spinning wheel to exert pressure on the metal blank rotating with the spindle of the machine tool, and the metal blank produces continuous local plastic deformation, and finally obtains the required hollow rotating body parts.
The advantages of preparing molybdenum crucible by spinning method are as follows: (1) In the process of spinning, the roller presses down the billet point by point and makes approximate point contact. The contact area is small and the unit pressure is large. It is suitable for processing with high strength and difficult deformation, and the power consumption is also greatly reduced. At the same time, the approximate point-by-point deformation will expose the defects existing in the blank itself, which has the function of self-inspection.② In the processing process, the metal grains of the billet are affected by three deformation forces, and the grains tend to be equiaxed along the slip plane of the deformation zone. The direction of each slip layer on the slip plane is consistent with the direction of deformation. The metal fibers remain continuous and intact, and the strength of the spinning products is improved.(3) In the spinning process, the roller has a leveling effect on the spinning metal while calendaring it. Therefore, the molybdenum crucible prepared by spinning method should be able to achieve higher dimensional accuracy and surface finish.④ Spinning processing is a kind of less cutting process, therefore, the material utilization rate is high, cost saving.
The research on producing molybdenum crucible by spinning technology has precedent in China. The pure molybdenum ingot is made by vacuum smelting method, and then the ingot is hot rolled into a slab, and the slab is spun by spinning equipment, and finally the semi-finished products obtained by spinning are surface treated, and the products meet the requirements are obtained. The whole process includes the preforming of strong spin and gap-spin, the final forming of two strong spin and the annealing of two times. Finally, the large size molybdenum crucible suitable for processing sapphire is obtained.
Although the molybdenum crucible has been successfully fabricated by spinning technology, it is still a certain technical difficulty. First of all, molybdenum exhibits high hardness and brittleness at room temperature. Brittle fracture is easy to occur during spinning at room temperature, so it must be heated and spun. The selection of heating temperature becomes a difficult point, the temperature is too low, can not reach the temperature required for plastic deformation, brittle fracture will occur; If the temperature is too high and exceeds the recrystallization temperature, the structure and properties of the billet will change and the energy consumption will be high. Secondly, there are two annealing processes in the processing period, which lengthens the whole production cycle. How to avoid the annealing process and shorten the whole process while ensuring the dimensional accuracy and strength of the crucible is another technical difficulty in the production of molybdenum crucible by spinning process. Finally, it is also a major technical difficulty to use the spinning method to prepare molybdenum crucible to understand the influence of wheel track, spinning pass and various technological parameters on the performance and dimensional accuracy of molybdenum crucible in the spinning process, so as to achieve accurate control.
