Like arc furnaces, and induction furnaces, vacuum furnaces are used in many applications. They are specifically used to protect heated steel and metal from negative effects of air. A vacuum is normally electrically heated. Vacuum furnaces are heated by electric resistance metals and made from ceramics, or graphite.
A vacuum furnace is surrounded by a vacuum during the processing stage. The absence of the air prevents heat loss from the product. The process uses convection to prevent heat loss and removes air and other gases that can contaminate the product. Convection is the amount of heat transfer by mass motion, when the heated fluid is caused to move away from the source. The warmer molten product will rise, while the cooler molten product will sink. Vacuum furnaces allow for uniform heating, low contamination and quenching of a product. The process can also be computer controlled.
When heating metals to high temperatures rapid oxidation occurs. Oxidation is the loss or increase of electrons in an atom. This can occur when molten product is introduced to air. The product now has a different chemical composition because the introduction of a new material. A common example is the rusting of iron. A vacuum furnace locks the oxygen or other gasses away.