Heat treatment vacuum method

Update: 07-06-2021

Because the heating and cooling of metal workpieces req […]

Because the heating and cooling of metal workpieces require dozens or even dozens of actions to complete. These actions are carried out in a vacuum heat treatment furnace and cannot be accessed by operators. Therefore, the degree of automation of the vacuum heat treatment electric furnace is relatively high. At the same time, some actions, such as the quenching process of the metal workpiece after heating and holding, require six or seven actions and must be completed within 15 seconds. To complete many actions under such agile conditions, it is easy to cause operator tension and constitute misoperation. Therefore, only a high degree of automation can accurately and timely coordinate in accordance with the procedures.

The vacuum heat treatment of metal parts is carried out in a closed vacuum furnace, and the strict vacuum seal is well known. Therefore, obtaining and maintaining the original air leakage rate of the furnace and ensuring the working vacuum of the vacuum furnace is of great significance to ensuring the quality of the vacuum heat treatment of the parts. Therefore, a key problem of the vacuum heat treatment furnace is to have a reliable vacuum seal 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 airtightly welded, and at the same time as few or no holes are opened on the furnace body as possible, and dynamic sealing should be avoided or avoided Structure to minimize the chance of vacuum leakage. The parts 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.

Most heating and thermal insulation materials can only be used under vacuum. The heating and thermal insulation linings of the vacuum heat treatment furnace work under vacuum and high temperature. Therefore, these materials have requirements for high temperature resistance, good radiation results, and low thermal conductivity. The anti-oxidation performance is not demanding. Therefore, the vacuum heat treatment furnace widely uses tantalum, tungsten, molybdenum and graphite as heating and heat insulation materials. These materials are very easy to oxidize in the atmosphere, therefore, ordinary heat treatment furnaces cannot use these heating and heat insulating materials.

Water cooling device: The furnace shell, furnace cover, electric heating element, water cooling electrode, intermediate vacuum insulation door and other parts of the vacuum heat treatment furnace are all working under vacuum and heating. Working under such extremely unfavorable conditions, it is necessary to ensure that the structure of each component is not deformed or damaged, and that the vacuum sealing ring is not overheated or burned. Therefore, each component should be equipped with water-cooling devices according to different conditions to ensure that the vacuum heat treatment furnace can operate normally and have sufficient service life.

Using low voltage and high current: In the vacuum container, when the vacuum vacancy is in the range of a few Torr to lxlo-1 Torr, the energized conductor in the vacuum container will produce glow discharge under higher voltage. In the vacuum heat treatment furnace, severe arc discharge will burn down the heating elements, heat insulation layer, etc., causing major accidents and losses. Therefore, the working voltage of the electric heating element of the vacuum heat treatment furnace generally does not exceed 80-100 volts. At the same time, effective measures should be taken in the structural design of the electric heating element, such as avoiding sharp parts as much as possible, and the distance between the electrodes should not be too small to prevent glow discharge or arc discharge.



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