Vacuum is one of the approaches to protect heated parts, furnace inside body (such as heating element) or both of them, from negative influence of air atomosphere. For example, in manufacturing process of carbon fibers, there is an step called “Carbonization”. As carbonization require high temperature, therefore air atmosphere shall be avoided during this process. Another example is induction graphite furnace. This furnace uses graphite as the sucebtor of induction current and carbon felt as insulation material. Both graphite and carbon felt shall not be exposed to air atmosphere at temperature higher than 400°C.
The vacuum inside the furnace is maintained by vacuum pumps. Depending on the furnace size and application, a single or combination of mechanical and roots, diffusion and turbo-molecular pumps maybe used.