Bell furnaces are used where workloads may be heavy, and when processing atmospheres need to be contained in a positively sealed system that does not leak.
Examples include Carburizing and Ferritic Nitro carburizing (FNC), or Gas Soft Nitriding (GSN).
There are two general types of bell furnaces, both of which are easy to match with material handling and furnace furniture requirements:
1) Horizontally and vertically moving bell with one or more stationary hearths and integral controlled cooling furnace (photo on the right)
2) Stationary vertically moving bell with horizontally moving hearth furnace (photo below of bell furnaces)
For these applications an electrically-heated system is preferable because there is no need for a costly retort. Further, because the heating energy is delivered directly into the process with no retort or radiant tubes acting as a barrier, an electrically-heated bell furnace is more efficient.