Tue, 07 Aug 2018 02:23:22 +0000
Refractory metal heating and sintering
The vacuum sintering furnace is specially designed for the third generation rare earth permanent magnet material NdFeB sintering. It can also be used for the aging and magnetic treatment of NdFeB permanent magnetic materials, the sintering and heat treatment of rare metals and their alloys, the quenching and tempering of the small workers and the moulds. In order to meet the technical requirements of the processed materials, the upper and lower valves of the high vacuum sintering furnace are closed, the workpiece area is completely closed and the heaters are all distributed around the heater, so the heat loss is small and the temperature is uniform. Because molybdenum and ceramic fiber stainless steel are used as hot zone materials, the workpiece environment is pure and there is no high temperature volatile matter pollution. When cooling, the upper and lower valves are opened, and through the air-cooled heat exchanger system specially designed at the back of the furnace, the workpiece in the furnace can be forced to circulate gas cooling. Generally speaking, the sintering process requires higher vacuum and temperature parameters, especially the requirements for temperature control, and the maximum temperature difference is generally not allowed to exceed the given value of + 3~5. The equipment’s constant temperature area is 650 (L) x 450 (W) x 400 (H) mm, the maximum temperature is 1300 C, the temperature uniformity is + 5 centigrade, the maximum heating power is 63KW (magnetic capacity). Because of heating in vacuum, its heat loss is small, energy consumption is low, leakage rate is low, working environment is pure, insulation performance is good, heating speed is faster. According to the characteristics of the vacuum sintering furnace, the fuzzy controller composed of 89C51 single chip microcomputer is used to automatically detect and adjust the furnace temperature, so as to achieve the purpose of uniform heating.
In vacuum and protective atmospheres, two processes are generally used to heat and sinter metals, ceramics and some refractory metal intermediate compounds. In order to obtain a certain density and a certain mechanical properties, there are usually pressed and no pressure sintering. Pressure sintering process is to place powdered materials in a vacuum and protective atmosphere of high carbon mold, high temperature heating to the softening state, pressurized molding. This process needs a vacuum hot pressing sintering. The sintering furnace has the characteristics of high temperature, high vacuum degree and high heat pressure. At present, this type of furnace has not been set up in China. According to the technical requirements of preparing the boride ceramic material, after more than one year’s efforts, the author has developed a vacuum hot pressing sintering furnace successfully, and the effect is good.
The vacuum hot pressing sintering furnace has high working temperature, high vacuum degree, large pressing force and good cooling condition. Except for heating and insulation parts, all parts of the furnace 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, insulation barrel, hot-pressing device, heating body and power supply, vacuum system, water cooling system and temperature measuring system.
(1) the furnace body is all made of stainless steel, which is a double-layer structure, divided into inner and outer barrel body, and the bottom of the furnace head is processed by spinning technology. Because the force produced by the hot-pressing device must be borne by the furnace body, the furnace body must have high strength and enough stiffness, and can not be deformed under external force and high temperature. The center line of the fixed seat of the bottom sealing device must be perpendicular to the flange on the furnace to ensure the straightness of the lower ejector rod. The fixed seat of the dynamic soil sealing device has good cooling conditions to prolong the service life of the seal.
(2) the furnace cover is composed of a furnace cover body, a lifting oil cylinder and an upper pressure head. The furnace cover is a double-layer structure. It must have enough strength and rigidity to bear the pressure transmitted by the lower ejector rod. The upper end of the upper head is at high temperature and must be forced to cool down.
(3) The insulating barrel is composed of insulating barrel, reflecting barrel, insulating layer and barrel body, which are made of graphite, molybdenum sheet, graphite felt and stainless steel respectively. The reflecting barrel made of molybdenum sheet mainly resists radiant heat generated by heating elements, so as not to damage the insulation layer and furnace body.