Surface reactions become less likely when the heating chamber’s atmosphere is strictly controlled as it is in a vacuum oven. When a complete or near-complete vacuum is created, convection, which is the transfer of heat between gasses and liquids, becomes impossible. The only transfer of heat in a vacuum happens as a result of radiation, and radiant heat is reliably even in its distribution.
Vacuum ovens have a number of advantages over other types of industrial ovens. In drying, negative pressure from the vacuum works together with the heat allowing drying to take place at lower temperatures than would otherwise be possible. Some laboratories use vacuum ovens for drying heat-sensitive materials. Vacuum ovens may be walk-in or truck-in batch ovens or smaller cabinet ovens.
The process of applying heat treatment begins with loading an item or several items into an oven. Unlike with other heat treating processes, the number of kinds of ovens available to heat treating technicians is limited; conveyor ovens are not suitable solutions in vacuum heat treatment.
Outside the confines of a vacuum chamber, atmospheric conditions cannot be maintained. Within the vacuum chamber, there would be no use for a conveyor as heat distribution is completely even throughout the chamber. The most likely variety of industrial oven in vacuum heat treatment contexts would likely be a batch oven if several smaller items were to be treated. In the case of a single, large item, a walk-in or truck-in oven would be suitable. The chamber would be sealed after loading the oven, and a vacuum would be created by pumping atmosphere out of the chamber.
Any variety of heat sources could be used to heat the newly evacuated chamber; gas-fired ovens and electric heat sources are both used to heat vacuum ovens. The product, once sufficiently heated, is sometimes quenched with an inert gas that allows the product to cool quickly. The gas is then evacuated through heat transfer equipment, and the product is ready to be removed from the vacuum chamber.