(1) Strict vacuum sealing: It is well known that vacuum heat treatment of metal parts is performed in a closed vacuum furnace. Therefore, the original leak rate of the furnace is obtained and maintained to ensure the vacuum degree of the vacuum furnace. The quality of vacuum heat treatment is of great significance. Therefore, a key issue of the vacuum heat treatment furnace is to have a reliable vacuum sealing structure. In order to ensure the vacuum performance of the vacuum furnace, a basic principle must be followed in the structural design of the vacuum heat treatment furnace, that is, the furnace body should be air-tight welded, and at the same time, the furnace body should be opened or closed with as few holes as possible. Sealed structure to minimize the chance of vacuum leaks. The components and accessories installed on the vacuum furnace body, such as water-cooled electrodes and thermocouple lead-out devices, must also be designed with a sealed structure.
(2) Most heating and insulation materials can only be used in a vacuum state: The heating and insulation linings of vacuum heat treatment furnaces work under vacuum and high temperature. Therefore, these materials have been proposed to be resistant to high temperatures, low steam pressure, and radiation. Good effect, small thermal conductivity and other requirements. Anti-oxidation performance is not high. Therefore, the vacuum heat treatment furnace widely uses tantalum, tungsten, molybdenum and graphite as heating and thermal insulation materials. These materials are extremely susceptible to oxidation in the atmosphere, so conventional heat treatment furnaces cannot use these heating and insulating materials.
(3) Water-cooled devices, furnace shells, furnace covers, guides for electric heating elements (water-cooled electrodes), intermediate vacuum insulation doors, and other components work under vacuum and heat. In such extremely unfavorable conditions, it is necessary to ensure that the structure of each component is not deformed or damaged, and the vacuum seal ring is not overheated and does not burn. Therefore, each component should be provided with a water cooling device according to different conditions to ensure that the vacuum heat treatment furnace can operate normally and have a sufficient service life.
(4) Use low voltage and large current: In a vacuum container, when the vacuum degree is in the range of several Torr to 1xlo-1 Torr, the current-carrying conductor in the vacuum container will produce a photodischarge phenomenon at a higher voltage. In the vacuum heat treatment furnace, arc discharge will be severely caused, and the electric heating elements and heat insulation layers will be burned, causing major accidents and losses. Therefore, the working voltage of the electric heating element of the vacuum heat treatment furnace generally does not exceed 80 to 100 volts. At the same time, effective measures should be taken when designing the structure of the electric heating element, such as avoiding pointed parts as much as possible, and the spacing between the electrodes should not be too small and narrow to prevent the occurrence of glow discharge or arc discharge.
(5) High degree of automation: The reason for the high degree of automation of the vacuum heat treatment furnace is that heating, cooling and other operations of metal workpieces require dozens or even dozens of actions to complete. These operations are performed internally in a vacuum heat treatment furnace and cannot be accessed by the operator. At the same time, some actions such as the end of heating and heat preservation, the quenching process of metal workpieces requires six or six actions and should be completed within 15 seconds. To perform many actions under such rapid conditions, it is easy to cause operator tension and constitute misoperation. Therefore, only a high degree of eye movement can coordinate the movement accurately and timely according to the procedure.