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For many heat treaters, the use of oil gives the best vale based on a number of factors including1:
* Overall performance (cooling rate or quench severity)
* Economics/cost (initial investment, maintenance, upkeep, lite)
* Minimization of distortion (quench-system performance)
* Variability (controllable cooling rales)
* Environmental concerns (recycling, waste disposal)
One additional factor - performance over time - should be added to the list since we are always looking tor ways to extend the life of our quenchanta without sacrificing their performance. Let's learn more.
Relationship of Physical Properties of Quenching Oils to Performance
Quench oil should be routinely analyzed (quarterly, or monthly if heavily used) to determine its performance characteristics. The testing laboratory or oil supplier's report (Fi«. 1) should be carefully scrutinized as it contains information about the physical property characteristics of the oil. Oil analysis uses standard test methods (Table 1), but in order to gain deeper insights into the meaning of the test results, as opposed to just comparing them with previous results, we need to understand what each category is telling us.
Viscosity
Quenching performance is highly dependent on the viscosity of the oil. In general, viscosity increases as the oil degrades. Degradation can be in the form of oxidation, thermal breakdown or the preseme of various contaminants. Oil viscosity changes with nine. and the formation of sludge or varnish accelerates the process. Samples should be taken and analyzed for contaminants and a historical record of viscosity variation kept and plotted against a process-control parameter such as part hardness.
Water Content
One of the concerns regarding oil quenching is the presence of water in the quench oil. It is dangerous since, on quenching, water will form steam with a resulting volume expansion of approximately seven times. As the steam bubble rises out of the quench tank, its surface is coated with oil. As it exits from the furnace (usually under extremely high pressure), it is ignited at the burnoff, resulting in...