Quenching Oil
Quenching oil, one of the slowest cooling rate, can have two purposes in heat tempering processes. One purpose of quenching oil, is the hardening of steel after heating it to high temperatures. The other purpose of quenching oil is minimizing the formation of gradients (crystals) which can lead to cracking and hollows. Quenching oil has numerous characteristics that separates it from other heat transfer liquids. These include viscosity, water content, acid number, flash point, sludge formation, and the composition of additives.
Viscosity is the measurement of resistance a fluid has. Different oils can have different rates of viscosity and will move faster or slower depending on the concentration, age and temperature. Water content is derived from the amount of contamination found in the oil. If there is water in the oil, a cracking sound will be heard once it is heated. Oil contaminated with water can lead to soft spots, staining, and even fires.
Flash point is another characteristic of oils. Flash point is the temperature at which the oil produces gas. The gas at the specific flash point will not burn, but will ignite. Acid number is the analysis of acid properties a degrading oil. The by products can be measured using chemistry. Sludge is another characteristic of quenching oils. Sludge is created by oxidation degradation. The oxidation reactions are insoluble in the oil. Sludge can damage heat-exchanger surfaces, plug filters, and cause overheating. Oils can contain additives. These can be metal salts to accelerate the quench rate. Other organometallic additives can be added as well