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In the normal test of the vacuum furnace, if there is liquid, a liquid evaporation process is required (the gas can be vaporized without heating under high vacuum), and the liquid can be vaporized by pulling the vacuum for a long time to reach a high vacuum ( Waiting for stability)
If you do not reach the target air pressure for a long time, you should consider the system and the Roots pump. You can directly measure the ultimate vacuum of the Roots pump (not connected to other systems). If it is intact, it is the sealing performance of the system.
- The water-cooling device, the furnace shell of the vacuum heat-treating furnace, the furnace cover, the electric heating component guiding treatment (water-cooled electrode), the intermediate vacuum heat-insulating door and the like are all operated under vacuum and heat. To work under such extremely unfavorable conditions, it must be ensured that the structure of each component is not deformed or damaged, and the vacuum seal is not hot or burnt. Therefore, each component should be equipped with a water cooling device according to different conditions to ensure that the vacuum heat treatment furnace can operate normally and has a sufficient service life.
- Using low voltage and large current: In the vacuum vessel, when the vacuum vacancy is within a range of several Torr to 1 x 1 -1 Torr, the energized conductor in the vacuum vessel will produce a glow discharge phenomenon at a higher voltage. In the vacuum heat treatment furnace, severe arc discharge occurs, burning electric heating elements, heat insulation layers, etc., causing major accidents and losses. Therefore, the operating 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 in the design of the electric heating element structure. For example, the tip parts should be avoided as much as possible, and the spacing between the electrodes should not be too narrow to prevent the occurrence of glow discharge or arc discharge.
- Most of the heating and insulating materials can only be used under vacuum: the heating and thermal insulation lining of the vacuum heat treatment furnace works under vacuum and high temperature, so high temperature resistance, low vapor pressure and radiation are proposed for these materials. Good effect, low thermal conductivity and other requirements. Anti-oxidation performance requirements are not high. Therefore, vacuum heat treatment furnaces widely use bismuth, tungsten, molybdenum and graphite as heating and heat insulating materials. These materials are highly oxidizable in the atmosphere, so conventional heating and heat treatment furnaces cannot use these heating and insulating materials.
- Strict vacuum sealing: It is well known that the vacuum heat treatment of metal parts is carried out in a closed vacuum furnace. Therefore, the original air leakage rate of the furnace is obtained and maintained, the working vacuum of the vacuum furnace is ensured, and the vacuum of the parts is ensured. The quality of heat treatment is very important. Therefore, a key issue in vacuum heat treatment furnaces 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 design of the vacuum heat treatment furnace, that is, the furnace body should be hermetically welded, and at the same time, as little or no opening as possible on the furnace body, less use or avoidance Seal the structure to minimize the chance of vacuum leaks. Components, accessories, etc., such as water-cooled electrodes and thermocouple-extracting devices, which are mounted on the vacuum furnace body, must also be designed with a sealing structure.
- High degree of automation: The degree of automation of the vacuum heat treatment furnace is higher because of the heating, cooling and other operations of the metal workpiece, which requires more than a dozen or even dozens of actions to complete. These actions are carried out in a vacuum heat treatment furnace and are inaccessible to the operator. At the same time, after some actions such as heating and heat preservation, the metal workpiece must be quenched in six steps and completed within 15 seconds. In such a rapid condition to complete a lot of actions, it is easy to cause the operator’s nervousness and constitute a misoperation. Therefore, only high vision can be coordinated accurately and in a timely manner.