Sub Zero Treatment
Sub-zero treatments are performed in a chamber designed to carry out a range of processes where controlled temperatures down to – 150 Degrees C are necessary.
Some applications are:
- The Ellenite Process – a sub-zero alternative to multiple tempering of HSS at – 80Degrees C to – 120 Degrees C.
- Transformation of retained austenite in carburised or through hardened, high carbon, components at -80 Degrees C.
- Prevention of ageing of aluminum alloys at -40 Degrees C.
- Controlled shrink fitting down to -150 Degrees C.
- Stabilization of heat treated components and assemblies down to -150 Degrees C.
- Cryotreatment of steels down to -1
- 50 Degrees C for 24 hours or longer to promote carbide precipitation resulting increased wear resistance.
The unit uses liquid nitrogen (LN) as the refrigerant to give a wide range of treatment temperatures. LN from the storage vessel is supplied through an insulated pipe at up to 2 barg. It is sprayed into a duct on each side of the box. The liquid evaporates in the ducts before reaching the product in the work space thus avoiding thermal shock.
To enhance the heat transfer mechanism, a fan is used which rapidly circulates the cold gas. The temperature of the product is measured by a floating thermocouple which is attached to it. When the temperature controller detects that the set temperature has been reached the solenoid valve in the LN line is closed.
The set temperature is then automatically maintained by on-off control. The temperature of the gas in the compartment is controlled separately to ensure that it remains constant throughout the product cooling cycle.