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The invention relates to a molybdenum crucible with large length-diameter ratio and a spinning method thereof

  • Mosten
  • 11 Nov

Sapphire crystal (A-Al203) is a kind of high temperature resistance, wear resistance, corrosion resistance and light transmission band wide quality optical functional materials, or the most widely used oxide substrate (mainly used as semiconductor substrate and large-scale integrated circuit substrate) materials, can be used in microelectronics - optoelectronics technology, military, aerospace, communications, medical and other fields, has a wide range of applications Scene.

At present, there are many methods to make sapphire single crystal, such as bubble growth method, Cheshire crystal drawing method, guided mode method, heat exchange method, temperature gradient method, crucible descent method, cold core shoulder micro drawing method and so on. Among these methods, high quality molybdenum crucible with small diameter and large aspect ratio is needed to grow sapphire single crystal by heat exchange method.

Molybdenum is a refractory rare metal with a melting point of 2620°C and a strong interatomic binding force that makes it strong at both room temperature and high temperature. Molybdenum has excellent physical properties such as small expansion coefficient, large electrical conductivity and good thermal conductivity. These excellent properties make molybdenum and its alloy in metallurgy, glass, ceramics, military equipment, high temperature machinery and other fields have a wide range of applications. As a kind of molybdenum material, molybdenum crucible is widely used in the process of rare earth metal melting and glass melting.

At present, molybdenum crucible production methods mainly include the following: plasma spraying method, casting method, stamping method, welding method, sintering method, etc. But plasma spraying is particularly wasteful and expensive. The casting method is complicated and requires a large number of moulds, and the melting point of molybdenum is high, so the melting needs a large amount of electric energy. The stamping method has a good effect on the crucible with large wall thickness, but it is difficult to realize the crucible with large size and thin wall. The crucible welded by welding method is easy to crack at the weld in the process of use, which reduces the service life of the crucible; The density of sintered molybdenum crucible is low, and there will be holes in the sintering process, which reduces the strength of molybdenum crucible. The service life of existing sintered molybdenum crucible is short, generally not more than 30-40 hours, and the sintered molybdenum crucible should have a processing margin during the sintering process, which requires mechanical machining and shaping after sintering, and the process is complicated. Spinning is an advanced method that integrates the characteristics of forging, extrusion, stretching, bending, ring rolling, cross rolling and rolling, etc. It is suitable for the processing of thin-wall vessels with large length-to-diameter ratio. However, because molybdenum is a refractory metal, it is more difficult to spin compared with ordinary metal. Ordinary spinning method is generally a molybdenum crucible with a larger diameter and a length-to-diameter ratio of 1-2. In the process of ordinary spinning, it is easy to cause defects such as peeling and delamination of products, which affect the qualified rate of products. Molybdenum crucible with large aspect ratio cannot be prepared by the existing spinning method. For molybdenum crucible with small diameter and large aspect to diameter ratio, the existing ordinary spinning method is not competent. The life and quality of molybdenum crucible with small diameter and large aspect to diameter ratio have been restricting the production of sapphire single crystal.

The invention relates to a spinning method of a molybdenum crucible with a large aspect ratio. The rolled molybdenum sheet is composed of isotropic fine fibrous structures and some recrystallized structures. Good ductility, creating conditions for spinning; Compared with alloy molybdenum plate, the pure molybdenum plate is easier to deform and has better ductility than alloy molybdenum plate. The use of water knife cutting board material, can avoid mechanical cutting caused by local heating which affects the internal grain size distribution of the entire plate, In the early stage, the plate is deformed by ordinary spinning, and the inner wall of the plate is close to the outer surface of the spinning die, forming a cylindrical structure. In the ordinary spinning process, the spinning pass and the pressing Angle of each pass are strictly controlled, the appropriate working curve is selected, the reasonable feed speed, the spindle speed and the appropriate spinning wheel are set, and the molybdenum plate is avoided in the spinning process due to the inappropriate spinning process Internal cracks; Then, the side wall of the initial spinning part formed by ordinary spinning is thin and elongated by the strong spinning with multiple passes and small pressure, and the defects such as cracks in the material are avoided at the same time. Finally, the molybdenum crucible with small diameter and large length-diameter ratio which cannot be prepared by the existing spinning technology is prepared. The whole processing method is simple, convenient to operate and low cost the life of sintered molybdenum crucible with large aspect ratio is greatly improved, which is of great significance for the production of molybdenum crucible with large aspect ratio.