Fluid bed hardening

The use of fluidised beds, consisting of a suitable solid inert medium, such as silica or alumina powder, agitated by flow of the heating gas medium through the bed, has largely replaced salt bath hardening. As with salt baths, heat input to the work piece is equally rapid and the method is similarly labour intensive, although health and safety and environmental risks are negligible. The heating gas can be supplemented with the controlled addition of a hydrocarbon gas for carburising and ammonia for nitriding or in combination with a hydrocarbon gas for carbonitriding or nitrocarburising. Small components, particularly those with geometries which are difficult to treat in batch furnaces, due to the risk of masking, may be treated very effectively in fluid beds.