Salt Bath Furnace

Salt Bath Furnaces Points : Salt Bath Furnaces, Molten lead baths, Molten salt baths Roth molten lead and, molten salt baths are used for heating of steel in operations involving hardening, annealing, tempering etc.

Molten lead baths Molten lead is fast-heating medium and gives complete protection to the surface of the steel with a melting point of 327°C, lead may be used successfully from 370°C to about 870°C. Lead oxidizes readily with the formation of dross, making a dirty bath, and gives trouble because of the sticking of lead, and dross to the surfaces of the steel being heated. This can be overcome by suitable lead coverings such as wood charcoal, coke, carburizing compounds, salts, etc. The steel can he further protected from lead sticking to its surfaces by the use of a coating of a thin film of ‘alt or some other material which is applied to the steel before it is placed in the lead bath. Molten salt baths These baths have been found to be satisfactory for the, heating of many steel parts that are to be given heat treatments. They transmit heat quickly and uniformly and afford a protection to the steel during the heating cycle. Upon removal of the steel from such a salt bath a thin film of salt adheres to it giving Protection from air prior to the quenching, etc. Although ideal salt bath has not been discovered, if care is used in the selection of a salt and precautions are exerted in its use and maintenance good results may be expected.

1. Salts may be used for low temperature tempering. They usually consist of nitrates and ay he used in a range of temperatures from 150°C to 540°C.
2. Salt baths used in temperature ranges of 540°C to 870° consist mainly of sodium carbonate, sodium chloride, sodium cyanide and barium or calcium chloride.
3. In a temperature range of 980 C to 1320°C, salt baths are made from mixtures of barium chloride, borax, sodium fluoride and silicates.
4. Precautions should he observed in the use of salt baths in order to prevent violent reactions from mixing of certain salts. One should also be careful to prevent moisture from coining into contact with the fused salts. With the cyanide salts, precautions should be observed because of their poisonous nature.