The electrically heated furnaces are equipped with either resistance or silicon carbide heating elements, mounted externally to either a square or round metal pot holding molten media.
At elevated temperatures silicon carbide heating elements are prefered. The elements are made in one piece from high-density, high-purity, self-bonded silicon carbide.
For a round pot furnace helically-wound wire heaters are a common configuration.
Schematic view of Furnace with over - the - top mounted electrodes
Features include: 6" thick tile walls make the pot last for years. The removable electrodes can be changed without emptying furnace.
The use of large cross section electrodes assure long heater life and provides electrodynamic circulation for uniform temperature.
Furnace with submerged electrodes Operating temprature 850°C; to 1260°C; (1550°F to 2300°F) for Austenitizing
Submerged electrodes provides long life & trouble free service with periodic maintenance. Electrodes, embedded in the wall, below the salt line,are sealed against corrosive attack at the air-salt interface. The submerged electrode design also lends itself to economical 3 phase operation in deeper furnaces when 2 or more tiers of electrodes are utilized.
Isothermal Quench Furnaces
For Austempering & Martempering
Molten salt quenching for austempering or martempering requires a furnace capable of several functions, and the resulting designs are much different from salt bath furnaces employed in heating or austenitizing work.
Four primary factors should be considered for all Quench Furnaces:
1.Bath Temperature Uniformity
is essential for consistent metallurgical
properties. Internal heating of the bath can be accomplished electrically
by using either immersion heaters or electrodes. Gas-fired immersion tubes
can also be employed. It is important to automatically dissipate heat from
work being quenched by either internal or external cooling means. For light
duty, forced air or air/water can be directed to the exterior of the pot.
For heavy duty, controlled cooling is provided by internal coils, using
water or air/water injection.
2.Proper Agitation of the bath is necessary to remove heat quickly and efficently from the work.mConstant or variable speed propeller agitation provides a uniform flow through the workload being quenched.
3. To achieve optimum hardness and other physical properties, foreign bath contaminants must be removed. In most furnaces this is accomplished by a continuous filtering and automatic dumping. A common system like that supplied by AJAX Electric Company comprises a scoop-shaped filter basket connected to a driving cylinder mounted adjacent to the furnace wall, the basket is automatically raised up and out of the bath - automating chloride removal. Readily installed on new furnaces, the mechanism can also be retrofitted on existing salt baths.
4. For isothermal quenching of heavier sections, water increases quenching power. Small amounts of water added to a nitrate-nitrite salt drives vapor from the bath as hot work enters and gives a faster cooling rate. Both manual and automatic systems are available for adjusting the frequency and duration of water additions.