According to the inside and outside of the heater in the vacuum vessel, the vacuum heat treatment furnace can be divided into internal heating furnace and external heating furnace.
1. Externally heated vacuum heat treatment furnace In this vacuum furnace outside the furnace can have ordinary air furnace, through the vacuum container heating, the workpiece side-heating. The heat treatment furnace has poor thermal efficiency and long cooling time. In addition, due to temperature difference between the workpiece and furnace, vacuum external pressure will also lead to deformation and damage of the furnace. Although the heat treatment furnace is cheap, it is not suitable for actual industrial production.
2. Internal thermal vacuum heat treatment furnace is a vacuum vessel with electric heater and insulator, the vessel itself is water-cooled. When the temperature is low, only the vacuum seal part is water cooled or not cooled. Compared with the external thermal type, the internal heat vacuum furnace has high thermal efficiency due to the workpiece facing the heating element. Thermal materials include electrothermal alloys (such as Fe-Cr, Ni-Cr, Fe-Cr-Al), Semimetals (SiC, MoSi2), and zirconium heaters (ZrO2).
3. Development trend and key technology of mold vacuum heat treatment. According to the forecast of American heat treatment industry in 2020 by American Metal Society Heat Treatment Society, American Metal Processing Research Institute and the Department of Industrial Technology of the United States Department of Energy, the future heat treatment industry should have first-class quality and produce parts with zero rate of change. Zero-dispersion is typical in the whole process. Energy utilization rate is raised to 80, working environment is good, clean and pollution-free. Standard closed-loop control system is adopted in production. Intelligent system control determines the performance of the product. The result of comprehensive technology reduces the process time by 50 and the cost by 75. All these ideas provide a broad stage and opportunity for the development of vacuum heat treatment technology. Vacuum heat treatment accounts for 15% of the current heat treatment production in the United States. This trend will be further increased in the future.