Why Does Rapid Quenching Oil Age After Long Use?
2023-12-11
At present, rapid quenching oil still plays a dominant role in the cooling medium for heat treatment of fasteners. The increase in the use temperature of quenching oil will significantly accelerate its aging reaction speed. When the oil temperature is increased by 10°C, the chemical reaction speed is increased by about 2 to 4 times. In principle, the use temperature of quenching oil is 60 to 80°C. The heating and repeated contact of the quenching oil with hot workpieces, resulting in oxidation and aging of the quenching oil, are the biggest threats in production.
Long-term bolt and nut quenching operations have caused many complex chemical changes in the quenching oil, resulting in significant changes in the characteristics of the oil, and aging of the quenching oil, including the thermal decomposition of the quenching oil hydrocarbons to volatile components or gases and The oxidation of some compounds and polymerization of the oxidation products will cause the viscosity of the oil to increase, which is the mechanism of quenching oil aging. At the same time, the surface of the oil contacting the hot workpiece is heated to a higher temperature, causing oil chain scission and secondary reactions to generate decomposition products. The oxidized hydrocarbons are in a highly unstable state, and they will polymerize and form grease , And even serious consequences such as contamination of the workpiece and blockage of the pipeline. Obviously, attention should be paid to the oxidation mechanism of hydrocarbons during the use of quenching oil.
Why fast quenching oil ages after a long time of use? This is the main reason why quenching oil is constantly oxidized during use, and sludge and stains appear on the surface of the workpiece. As the use time increases, the oxidation of the oil becomes more and more serious, the viscosity further increases, and the sludge further increases. These all reduce the cooling performance of the quenching oil, resulting in soft spots or even hardening of the workpiece, and the metallographic inspection shows that Microstructure: In carbon steel, there is more flocculent ferrite; in alloy steel, the structure of lower bainite is present. At this time, the essence is that the quenching oil has been severely oxidized during use.
As the quenching oil is oxidized during use, the acid content of its carboxyl (the carbon, oxygen, and hydrogen COOH groups in SUO-organic compounds is called carboxyl) will gradually increase, so the acid value of the oil can be tested to measure its aging Degree. After quenching oil has been used continuously for more than 2 years, the acid value continues to increase. When the acid value reaches about 1.0 to 1.5 mgKOH/g, the rate of carboxylic acid generation is significantly increased. After the quenching oil is aged, the cooling curve is reflected in the shortening of the vapor film stage, the maximum cooling rate increases, the cooling curve moves to the upper right as a whole, the high temperature cooling rate accelerates, and the hardenability of the workpiece decreases. The acid value of 1.5mgKOH/g is a quantitative indicator of quenching oil aging, and it is also the basis for oil change. Generally, the oil should be changed after 1 year of use. The measures to prevent the aging of quenching oil are: the use of hydro-refined base oil and compound antioxidant can effectively improve the anti-oxidation performance of the oil. In order to improve the anti-aging performance of the quenching oil, the following should be paid attention to when using the quenching oil: If the oil is in a circulating state, it should be filtered in time to prevent water ingress. Don't change the oil partly. Try to reduce the use temperature of the quenching oil and reduce pollution.
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