Refractory metal intermediate compound powder heating and sintering
Vacuum sintering furnace is specially developed for the third generation of rare earth permanent magnetic materials NdFeB sintering, also can be used for NdFeB permanent magnetic materials aging and magnetic processing, rare metals and their alloys sintering and heat treatment, small, mold quenching and tempering. In order to meet the technological requirements of the material to be processed, the upper and lower valves of the high vacuum sintering furnace are closed during heating, the workpiece area is completely closed, and the periphery of the heater is distributed, so the heat loss is small and the temperature is even. Because the hot area material selection molybdenum, ceramic fiber stainless steel material, the workpiece environment is pure, no high temperature volatile matter pollution is processed material. When cooling, the upper and lower valves are opened, and forced gas circulation cooling can be carried out on the workpiece in the furnace through the specially designed air cooling heat exchange system at the back of the furnace. In general, the vacuum degree of sintering process on the equipment, the temperature parameters such as the demand is higher, especially the requirement for the temperature control is very strict, maximum temperature difference are generally not promise more than the given value plus or minus 3 ~ 5 ℃. This equipment is constant temperature area size of 650 (L) x 450 (W) x 400 mm (H), the highest temperature 1300 ℃, the temperature evenness + / - 5 ℃, maximum heating power of 63 kw (magnetic capacity). Due to heating in vacuum, it has small heat loss, low energy consumption, low air leakage rate, pure working environment, good heat preservation performance and fast heating speed. According to the characteristics of vacuum sintering furnace, the fuzzy controller which is composed of 89C51 single chip microcomputer is used to automatically detect and adjust the furnace temperature to achieve the purpose of uniform heating.
In vacuum and protective atmosphere, two processes are generally adopted to obtain materials with certain density and certain mechanical properties by heating and sintering metal, ceramic and some refractory metal intermediate compound powders. That is, pressure sintering and no pressure sintering. Pressure sintering process is the powder material placed in a vacuum and protective atmosphere of high carbon mold, high temperature heating to the softening state, pressure forming. This process requires a vacuum hot press to achieve. The sintering furnace has the characteristics of high temperature, high vacuum and high thermal pressure. At present this kind of furnace type has not seen the finalizing product in our country. According to the technical requirements for the preparation of boride ceramic materials, the author developed a vacuum hot-pressing sintering furnace by himself after more than a year of efforts, and the application effect is good.
The working temperature of the vacuum hot pressing sintering furnace is high, the vacuum degree is high, the pressure force is large and the cooling condition is good. In addition to heating and insulation parts, the rest parts of the furnace body are strongly cooled, which puts forward higher requirements for structural design and manufacturing accuracy.
The vacuum hot pressing sintering furnace is composed of furnace body, furnace cover, heat preservation barrel, hot pressing device, heating element and power supply, vacuum system, water cooling system and temperature measuring system.
(1) the furnace body is all made of stainless steel, which is double-layer structure, including the inner and outer barrel body, and the bottom sealing head of the furnace is processed by spinning technology. Because the pressure device produced by the furnace to bear the force, the furnace must have a very high strength and enough stiffness, in the external force and high temperature must not be deformed. The center line of the fixed seat of the dynamic sealing device at the bottom of the furnace must be perpendicular to the flange on the furnace body to ensure the straightness of the movement of the lower jacking rod. It has good cooling condition to extend the service life of seal.
(2) the furnace cover is composed of the furnace cover body, lifting oil cylinder and upper pressure head. The furnace cover is double layer structure, it must have enough strength and rigidity to bear the pressure from the lower push rod. The lower end of the upper pressure head works in a high temperature zone and must be forced to cool down.
(3) heat preservation barrel is composed of heat insulation barrel, reflection barrel, heat insulation layer and barrel body, respectively made of graphite, molybdenum sheet, graphite felt and stainless steel. The reflector barrel made of molybdenum sheet mainly resists the radiant heat generated by heating elements so as not to damage the insulation layer and furnace body.