Heating Sintering of Refractory Metal Intermediate Compound Powder
Vacuum sintering furnace is specially developed for the sintering of the third generation rare earth permanent magnet NdFeB. It can also be used for aging and magnetizing treatment of NdFeB permanent magnet materials, sintering and heat treatment of rare metals and their alloys, quenching and tempering of small workpieces and dies, etc. In order to meet the technological requirements of the treated materials, when heated, the upper and lower valves of the high vacuum sintering furnace are closed, the workpiece area is completely closed, and the heater is uniformly distributed around, 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 working environment is pure and there is no high temperature volatile matter pollution to be treated materials. When cooling, the upper and lower valves are opened, and the workpieces in the furnace can be forced to be cooled by air-cooled heat exchange system specially designed at the rear of the furnace. Generally speaking, the sintering process requires higher vacuum and temperature parameters of equipment, especially for temperature control. The maximum temperature difference is generally not allowed to exceed the given value (+3-5 C). The constant temperature range of the equipment is 650 (L)x 450 (W)x 400 (H) mm, the maximum temperature is 1300 C, the temperature uniformity is (+5 C), and the maximum heating power is 63KW (magnetic regulating capacity). Because of heating in vacuum, it has low heat loss, low energy consumption, low air leakage rate, clean working environment, good thermal insulation performance and fast heating speed. According to the characteristics of vacuum sintering furnace, a fuzzy controller based on 89C51 single chip computer is used to automatically detect and adjust the furnace temperature, so as to achieve the goal of uniform heating.
In vacuum and protective atmosphere, when sintering metals, ceramics and some refractory metal intermediate powders, in order to obtain materials with certain density and mechanical properties, two processes are generally adopted: pressure sintering and pressureless sintering. Pressure sintering process is to place powdery materials in high carbon dies in vacuum and protective atmosphere, and when heated to softening state at high temperature, pressure forming. This process requires a vacuum hot pressing sintering process to achieve. The sintering furnace has the characteristics of high temperature, high vacuum and high thermal pressure. At present, this type of furnace has not been stereotyped in China. According to the technological requirements for preparing boride ceramics, after more than one year's efforts, a vacuum hot-pressing sintering furnace has been developed by the author, and its application effect is good.
The vacuum hot-pressing sintering furnace has high working temperature, high vacuum, high pressure and good cooling conditions. Except for heating and heat preservation parts, all other 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 body and power supply, vacuum system, water cooling system and temperature measuring system.
(1) Furnace body is made of stainless steel, which is double-layer structure. It is divided into inner and outer barrels. Furnace bottom head is processed by spinning process. Because the force produced by the hot-pressing device is to be borne by the furnace body, the furnace body must have high strength and sufficient stiffness, and must not be deformed under external force and high temperature. 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 jack rod. The fixed seat of the dynamic compact soil package has good cooling conditions to prolong the service life of the seals.
(2) The furnace cover is composed of a furnace cover body, a lifting cylinder and an upper pressure head. The furnace cover is a double-layer structure. In order to withstand the pressure transmitted by the lower jack rod, it must have sufficient strength and stiffness. The lower end of the upper pressure head is in the high temperature zone when working, and must be forced to cool.
(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 the radiation heat generated by the heating element, so as to avoid damaging the insulation layer and the furnace body.
vacuum hot pressing sintering furnace