Keywords: PAG, nonionic polymer, quenching fluid, cooling, characteristics, Oxidative,

　　PAG quenching agent is made of specific polyether nonionic polymer (PAG), compound additives that can obtain other auxiliary properties and appropriate amount of water. In use, there are two main types of changes that may occur in the quenching fluid: one is the change in its cooling performance, and the other is the change in its anti-rust and anti-corruption properties.
　　The cooling characteristics of the quenching fluid are determined by the nature and quantity of the PAG component therein. Other additives providing auxiliary properties have little effect on the cooling characteristics of the quenching fluid. The change of PAG polymer contained in quenching liquid includes the change of quantity and the change of quality.
　　1. the change of polymer content in quenching liquid.
　　In production, the amount of polymer will be reduced when the workpiece is carried out and decomposed by high temperature oxidation. During the quenching process, the temperature of the liquid around the workpiece rises, and the PAG polymer is dissolved out of the solution and adheres to the workpiece surface in the form of a water-rich coating by its wettability, thereby adjusting the cooling rate of the workpiece. After the workpiece is cooled down, the polymer adhering to the surface of the workpiece will dissolve back into the pantom fire liquid. It takes a certain amount of time to dissolve back, and in production, the workpiece is often taken away from the quenching liquid without waiting for the polymer to dissolve back clean. Therefore, the PAG content in the liquid brought by the workpiece is often higher than the average concentration of PAG in the quenching liquid used. After long-term and large-scale quenching, the relative concentration of PAG in the quenching liquid must gradually decrease, while the relative content of other additive components will increase. Therefore, the more fully the backdissolution, the slower the relative reduction of the PAG component in the quenching liquid, I .e. the more stable its cooling characteristics.
　　2. Oxidative decomposition of PAG.
　　The polymer used to prepare PAG quenching fluid has high chemical stability and does not react with general acids and bases at room temperature. It is oxidatively decomposed only at a high temperature of 250°C and in the presence of oxygen. During the quenching process, most of the polymer film adhered to the surface of the workpiece can be maintained at a temperature not higher than the boiling point of water because of the vaporization of the water in and around it, but the part close to the surface of the workpiece may still rise to a higher temperature and oxidative decomposition occurs. Oxidative decomposition products of low molecular weight run away as gas, and other parts remain in the quenching liquid. The chain scission products of PAG that occur at high temperature and mechanical shear and remain will no longer have the original ability to adjust the cooling characteristics, and become inactive ingredients in the quenching fluid. The greater the concentration of the quenching liquid, the thicker the polymer film formed on the surface of the workpiece during quenching, and the greater the amount of this decomposition. The greater the yield of heat treatment production and the longer the quenching fluid is used, the more this decomposition and chain scission residue will be.

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