Water in quenching oils can be very dangerous, and even more so when martempering using oils at temperatures above 212oF. Where does water come from? Generally it is from condensation due to the heating and cooling cycles the oil goes through. The colder the climate the worse the problem can be if the quench tank is sitting on a cold floor. Water in oil generally collects and settles to the bottom of the quench tank, but can also become emulsified in a circulating tank. If the oil is stagnant, or not circulated, the red hot parts in the bottom of the quench basket can be quenched in water, which in turn can cause non-uniform hardness, improper as-quenched hardness of the parts, and very often cracks will also occur from the faster quench. If the water level is high enough that red-hot parts cause the water to boil, an explosion can take place from the large amounts of steam that is formed.
A larger amount of water can exist with less chance of explosion, in a tank with circulating oil because the steam cannot form; however, it can create foam. However, foam is also a very dangerous fire hazard since oil foam can catch on fire very easily.
It is generally a good practice to check your quench tank every 6 months to make sure your water level is under control. The best method is to pump the quench oil out and observe the mixture at the bottom of the quench tank. You will be looking for water, muck, dirt or any contamination which, if found, should be removed and disposed of properly. Muck and sludge in the bottom of the tank also can affect the effectiveness of the hardenability of the oil. If the oil becomes emulsified, it cannot be salvaged and must be replaced.
Another quick method is to attach a long handle to a shallow container which you lower to the bottom of your quench tank. It must go deeper than the bottom of your quench basket, and by removing it slowly and carefully, you can bring a sample of the bottom of your tank to the surface.
COPYRIGHT © April 2007, by Advisor In Metals
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