Classification used depends upon the scope of production and the nature of the business. While the science behind heat treatment remains principally the same, certain advantages can be achieved from particular oven and furnace types. As an example it is possible to carry out the annealing process in air furnaces, vacuum furnaces, and gas purged retort furnaces, amongst others. Similarly the surface chemistry process of carburizing can be carried out in a range of equipment types including batch and continuous atmosphere controlled furnaces, pusher furnaces, or vacuum furnaces. The range of furnace types is extremely diverse. So, if the furnace equipment type does not define the process, why should there be so many different options for users to choose from? For example: Automotive gears have been hardened and tempered for many years in standard gas carburizing and draw furnaces. Recent advances in Low Pressure Carburizing for these components in a vacuum furnace have brought advantages to production cycle integration and component quality. Aircraft components can equally be annealed in gas purged retort furnaces or in vacuum furnaces. The distinction often lies in the stage of the process, with annealing of raw or core material being carried out under controlled atmospheres, while finished components are processed in vacuum where there is a much greater need to maintain control of components shape, dimension and surface finish as well the material properties.
Other issues that influence the choice of processing equipment include:
The following gives typical examples of furnace types, but this is by no means an exhaustive list:
The following gives typical examples of process types, but this is by no means an exhaustive list: