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The cooling rate of oil is much less than water. Intermediate rates between water and oil can be obtained with a purpose-formulated quenchant, a substance with an inverse solubility that therefore deposits on the object to slow the rate of cooling. Quenching can also be accomplished using inert gases, such as nitrogen and noble gases.
Comparing air and water, air has vastly lower heat capacity per gram and per volume (4000) and less than a tenth the conductivity, but also much lower viscosity (about 200 times lower: 17.4 × 10 −6 Pa·s for air vs 8.94 × 10 −4 Pa·s for water). Continuing the calculation from two paragraphs above, air cooling needs ten times of the ...
The two important aspects of quenching are the cooling rate and the holding time. The most common practice is to quench into a bath of liquid nitrite-nitrate salt and hold in the bath. Because of the restricted temperature range for processing it is not usually possible to quench in water or brine, but high temperature oils are used for a ...
Once removed from the oven, the workpieces are often quickly cooled off in a process known as quench hardening. Typical methods of quench hardening materials involve media such as air, water, oil, or salt. Salt is used as a medium for quenching usually in the form of brine (salt water). Brine provides faster cooling rates than water.
Tempering was usually performed by slowly, evenly overheating the metal, as judged by the color, and then immediately cooling, either in open air or by immersing it in water. This produced much the same effect as heating at the proper temperature for the right amount of time, and avoided embrittlement by tempering within a short time period.
The quenching converts the billet's surface layer to martensite, and causes it to shrink. The shrinkage pressurizes the core, helping to form the correct crystal structures. The core remains hot, and austenitic. A microprocessor controls the water flow to the quench box, to manage the temperature difference through the cross-section of the bars.
Water is inexpensive, non-toxic, and available over most of the earth's surface.Liquid cooling offers higher thermal conductivity than air cooling. Water has unusually high specific heat capacity among commonly available liquids at room temperature and atmospheric pressure allowing efficient heat transfer over distance with low rates of mass transfer.
Quenching, in the context of pollution scrubbers, refers to the cooling of hot exhaust gas by water sprays before it enters the scrubber proper. Hot gases (those above ambient temperature) are often cooled to near the saturation level. If not cooled, the hot gas stream can evaporate a large portion of the scrubbing liquor, adversely affecting ...
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