Technical Characteristics of Vacuum Heat Treatment Furnace
(1) Water cooling device, furnace shell, furnace cover, electric heating element conductor disposal (water-cooled electrode), middle vacuum insulation door and other parts of vacuum heat treatment furnace are all working under vacuum and heating conditions. When working under such extremely unfavorable conditions, it must be ensured that the structure of each component is not deformed or damaged, and the vacuum seal ring is not overheated or burnt. Therefore, each component should be equipped with water cooling device according to different conditions to ensure that the vacuum heat treatment furnace can operate normally and has sufficient service life.
(2) Low voltage and high current: in the vacuum container, when the vacuum void is within the range of several torr to lxlo-1 torr, the energized conductor in the vacuum container will produce glow discharge under high voltage. In the vacuum heat treatment furnace, serious arc discharge will occur, burning electric heating elements, 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 electric heating elements, such as avoiding the parts with tips as far as possible, and the spacing between electrodes should not be too narrow to prevent glow discharge or arc discharge.
(3) Most of the heating and thermal insulation materials can only be used in the vacuum state: the heating and thermal insulation lining materials of the vacuum heat treatment furnace work in the vacuum and high temperature, so the requirements for these materials are high temperature resistance, low steam pressure, good radiation effect, small thermal conductivity, etc. The requirements for oxidation resistance are not high. Therefore, tantalum, tungsten, molybdenum and graphite are widely used as heating and insulation materials in vacuum heat treatment furnaces. These materials are very easy to oxidize in the atmosphere, so they cannot be used in conventional heat treatment furnaces.
(4) Strict vacuum sealing: It is well known that the vacuum heat treatment of metal parts is carried out in a closed vacuum furnace. Therefore, it is very important to obtain and maintain the original air leakage rate of the furnace and ensure the working vacuum of the vacuum furnace to ensure the quality of vacuum heat treatment of parts. Therefore, a key problem of 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 adopt airtight welding, and at the same time, the furnace body should be opened as few or no holes as possible, and the dynamic sealing structure should be used or avoided, so as to minimize the chance of vacuum leakage. Components and accessories installed on the vacuum furnace body, such as water-cooled electrodes and thermocouple export devices, must also be designed with sealing structures.
(5) High degree of automation: The reason for the high degree of automation of the vacuum heat treatment furnace is that the heating, cooling and other operations of the metal workpiece require more than ten or even dozens of actions to complete. These actions are carried out in the vacuum heat treatment furnace, which is inaccessible to operators. At the same time, some actions, such as heating and insulation, require six actions to complete the quenching process of metal workpiece within 15 seconds. In such a rapid condition, it is easy to cause tension of operators and constitute misoperation. Therefore, only high automation can be accurately and timely coordinated according to the procedures.