What are the commonly used quenching media? What are their characteristics?

Commonly used quenching media are water, aqueous solution, mineral oil, molten salt, molten alkali and so on.

1. When tap water and clean rainwater are used as quenching medium, the temperature shall not exceed 40℃, and the water shall not be mixed with suspended substances such as soil or turbid substances such as soapy water, as well as rising bubbles.

2. Use 5%~ 10%NaCl or 5%~ 10%NaOH and 3%~5%NaCO? When aqueous solution is used as quenching medium, the cooling rate can be increased and the quenching soft spot can be eliminated after complete dissolution. After water and aqueous solution are used for a certain period of time, they should be replaced appropriately according to the decrease of refrigeration capacity, or filtered for decontamination, or new media should be added according to the formula ratio.

3. When oil is used as quenching medium of total loss system, the oil temperature is generally controlled at 30~80℃. Too low or too high a temperature will reduce the cooling rate. The highest oil temperature shall not exceed 80~ 100℃.

4. Quenching oil will age after long-term use. Aging kerosene has high viscosity and low flash point, which is not only easy to catch fire, but also has reduced cooling capacity and is not easy to clean after quenching. Therefore, after a certain period of use, it should be filtered, updated or supplemented with new oil.

5. When oil is used as quenching medium, the oil tank should have good smoke exhaust device and proper fire prevention facilities, and its efficiency and reliability should be checked regularly.

6. Gases (including air, inert gas and protective gas, etc.). As a quenching medium, it is suitable for cooling some high alloy steel workpieces to reduce melting deformation.

7. Do not directly cool the workpiece heated in chlorine bath with air to avoid molten salt reacting with oxygen in the air and corroding the surface of the workpiece. If necessary, the salt attached to the surface of the workpiece can be removed by "water explosion" and immediately taken out for air cooling.

Extended data

The life of water-based quenching medium is mainly affected by the type of medium. For example, the quenching medium of polyvinyl alcohol generally has a service life of less than a few months; PAG media can generally be used for several years.

External pollution also has a great influence on the life of water medium. Therefore, the maintenance and management of water-based media is more attention and more troublesome than oily media. PAG quenching liquid can be purified to prolong the replacement time of the whole tank.

Whether it is an aqueous medium or an oily medium, it will gradually deteriorate and be polluted in use. The gradual accumulation of metamorphic products and foreign pollutants will affect the performance of the medium. After a period of use, the whole water tank should be replaced. It is known that the service life of quenching oil at home and abroad is generally not more than three to five years, except for quenching oil for large workpieces, when a large number of ordinary small and medium-sized basic parts are treated.

If it is not decontaminated, the replacement time of the whole tank of PAG quenching medium is generally shorter than three to five years. When the whole tank is replaced, it can often ensure the quality of heat treatment, improve production efficiency, simplify management and reduce medium consumption, thus reducing production costs.

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