Tungsten molybdenum hot zone
Heat insulation screen of tungsten molybdenum furnace (including side screen and upper and lower cover screen) : Heat insulation screen is an important heat insulation component of high temperature vacuum tungsten molybdenum furnace. Molybdenum reflection screen and upper and lower cover plate can block and reflect the heat in the furnace. High purity, accurate size, smooth surface, convenient assembly and reasonable design of heat insulation components play an important role in improving the temperature field.
Generally, when the temperature of high temperature vacuum furnace is higher than 1100 degrees Celsius, tungsten and molybdenum materials will be considered as tungsten insulation screen and molybdenum insulation screen (including side screen and upper and lower cover screen) : As heat insulation components in the furnace, the key role of molybdenum and tungsten reflection screen and upper and lower cover plate is to block and reflect the heat in the furnace.
Tungsten molybdenum insulation screen is usually made by riveting, which can be butt or lap joint. Corrugated plate, U-shaped lattice or molybdenum wire spring and ring spacing can be used between each layer of screen, and fixed with molybdenum wire or tungsten wire card and screw.
The heat insulation screen is placed between the upper and lower heating areas of a metal sheet, through the ceramic ring fixed; The metal sheet is made of molybdenum or tantalum or tungsten. Because the metal heat shield is placed between the upper and lower areas, the metal surface is bright like a mirror at high temperature, which reflects the light well, and the heat transfer is mainly in the form of heat radiation in the vacuum environment. Therefore, the metal sheet plays a good heat insulation effect. Due to the metal heat insulation screen, the upper zone can be controlled at a relatively low heating temperature. Increasing the temperature in the lower zone will not cause the upper zone temperature rise, which can effectively improve the temperature gradient. It avoids the adverse effects of increasing the temperature gradient in the prior art, which leads to the increase of the upper region temperature, resulting in the element burning, the reaction between the alloy and the mold shell, and the degradation of the casting performance.
The tungsten zone starts nitriding at 600℃ in the air. Tungsten thermal zone in hydrogen containing medium, 250℃~950℃ will absorb hydrogen. Therefore, welding and heat treatment in tungsten zone should be carried out in vacuum or under the protection of inert gas, that is, the thermal process above 300℃ should be carried out under the protection of vacuum or inert gas or high temperature coating. When the equipment and container of tungsten thermal zone are exposed to the atmosphere, the application temperature should not exceed 230℃. Only when the equipment and container are not exposed to the atmosphere, the temperature can be properly raised. The tungsten zone should be protected by high purity inert gas like tantalum during welding, and it should also be protected by inert gas when the temperature is above 230℃. Fortunately, the tungsten zone weldment is cooled to 200℃ before the inert gas is stopped.
Tungsten heater Tungsten (melting point 3420℃) and molybdenum (melting point 2610℃) materials have high temperature resistance, low pollution, high temperature creep resistance and other characteristics. It also has high temperature resistance, low expansion coefficient, heat shock resistance, chemical stability and good electrical insulation performance, is widely used in the production of electrical light source device, semiconductor, semi-conductive communication devices, lasers, optical instruments, laboratory instruments, electrical equipment, medical equipment and high temperature corrosion resistant chemical instruments, chemical industry, electronics, metallurgy, building materials and national defense and other industries.
