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Quenching and heat transfer oils

Quenching oils

Quenching oils are oils formulated to serve as a fluid media in quenching operation.

Different quenching media provide a variety of cooling rates. When the fastest cooling rate is required water or brine solutions are used as quenching media. Air quenching produces the lowest cooling rate.
Oils are intermediate quenching media and they are ideal for quenching steels (oil-hardened steels, Tool and die steels).

Cooling rates obtained in oil quenching and the final hardness of the parts are determined by the specific heat of the oil: the higher specific heat of the oil, the greater hardness value may be obtained.
Oils providing relatively high cooling rates are called accelerated oils and used for parts having low susceptibility to cracks caused by internal stresses. Slow cooling rates obtained by non-accelerated oils are important in heat treatment of heavy parts, in which the surface hardening should be achieved when the core remains ductile. Oils are not used for quenching non-ferrous alloys (Aluminum alloys, Copper alloys).

Mineral paraffinic oils, vegetable lubricants (soy oil, cottonseed oil) or animal lubricants (fish oil, lard) are used as quenching oils.

Quenching oils possess the following characteristics:

  • High flash point (the lowest temperature, at which the oil vapors are ignitable);
  • Oxidation stability (low oxidation rate even at increased temperatures);
  • Controlled volatility (volatile components in oil produce stable vapor blanket in quenching);
  • Thermal stability (low degradation rate of the molecules as a result of heat.

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Heat transfer oils

Heat transfer oils are oils formulated to serve as a fluid media in closed and open liquid phase heat transfer systems.

Oil used in closed systems may be used at temperatures up to 550°F (288°C). The hot oil must not come into a contact with air because of the possible oxidation and ignition.
Maximum temperature of heat transfer oils used in open systems is limited by the value 374°F (190°C).

Heat transfer oils are used in the following applications:


Heat transfer oils have low volatility (prevents vapor locks in circulating pumps) and minimum change of viscosity over wide temperature range.
Other characteristics of heat transfer oils are similar to those of quenching oils.
Some of heat transfer oils may be used as quenching oils.

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Properties of some quenching and heat transfer oils

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quenching_and_heat_transfer_oils.txt · Last modified: 2012/06/02 by dmitri_kopeliovich
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