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QUICK FACT GUIDES FOR MACHINISTS
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GUIDES |
QUENCHING IN OIL Oil is used very extensively as a quenching medium as it results in a good proportion of hardness, toughness, and freedom from warpage when used with standard steels. Oil baths are used extensively for alloy steels. Various kinds of oils are employed such as prepared mineral oils and vegetable, animal and fish oils, either singly or in combination. Prepared mineral quenching oils are widely used because they have good quenching characteristics, are chemically stable, do not have an objectionable odor, and are relatively inexpensive. Special compound oils of the soluble type are used in many plants instead of such oils as fish oil, linseed oil, cottonseed oil, etc. The soluble properties enable the oil to form an emulsion with water. Oil cools steel at a slower rate than water, but the rate is fast enough for alloy steel. Oils have different cooling rates, however, and this rate may vary through the initial and final stages of the quenching operation. Faster cooling in the initial stage and slower cooling at lower temperatures is preferable because there is less danger of cracking the steel. The temperature of quenching oil baths should range ordinarily between 90 and 130 degrees F. A fairly constant temperature may be maintained either by circulating the oil through cooling coils or by using a tank provided with a cold water jacket. A good quenching oil should
posses a flash and fire point sufficiently high to be safe under the conditions
used and 350 degrees F. should be about the minimum point. The specific heat of
the oil regulates the hardness and toughness of the quenched steel; and the
greater the specific heat, the higher will be the hardness produced. Specific
heats of quenching oils are from 0.20 to 0.75, the specific heats of fish,
animal and vegetable oils usually being from0.2 to 0.4, and of soluble and
mineral oils from 0.5 to 0.7. The efficient temperature range for quenching oil
is from 90 to 140 degrees F. |
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