Tank Furnace

Tank Furnace 

a furnace for heating materials in a liquid medium. They are used in heat-treatment shops to heat metal parts for hardening, tempering, normalizing, roasting, cyaniding, and case-hardening, and also for lead patenting wire and tape.

The most generally used mediums are chlorides and carbonates for heating to 700°-1300° C, nitrates for 160°-500° C, and oils for up to 250° C; molten metals such as lead, lead alloyed with tin, and silumin are also used.

The advantages of heating in liquid mediums compared with heating in ordinary furnaces are the rapidity and the uniformity of the heating and the absence of oxidation on the surfaces of the parts.

Tank furnaces are subdivided into internally fired and electric types. The internally fired tank furnace has a crucible made of high-temperature steel with walls 15-30 mm thick. The crucible is heated by a flame from a nozzle or burner.

Electrical tank furnaces are of two kinds: in one type the heat is generated in heating elements (for example, wire or tape types) located outside the tank (externally heated crucible), and in the other, the heat is generated in the liquid medium itself by current supplied to it through electrodes (internal heating). There are also tank furnaces that are heated internally by tubular heating elements located within the crucible lining. Externally heated electrical tank furnaces are similar in construction to internally fired tank furnaces (except for the crucible heating facilities).

The most common tank furnaces in industry are of the one- or three-phase electrode-salt type, which use as the heating agent molten salt that is loaded into a working chamber with a circular, rectangular, or hexagonal cross section, made of shaped fireclay bricks, or into a crucible of high-temperature steel. Electrical current of 6-24 volts is fed through massive steel electrodes directly to the salt. The most modern electrode tank furnaces have immersed electrodes. The electrical current passing through the molten salt causes its vigorous agitation and ensures uniformity of the temperature in the tank. Electrode tank furnaces are used for heating to temperatures of 40°-1300° C. The power for electrode furnaces is 20-100 kilowatts, and their productivity is 30-200 kg/hr.

REFERENCES

Rustem, S. L. Oborudovanie i proektirovanie termicheskikh tsekhov. Moscow, 1962.
Krylov, P. A. Elektricheskie solianye pechi i vanny. Moscow-Leningrad, 1962.

V. A. MOROZOV