Keywords: PAG, quenching liquid, quenching, water, tester, quenchant, cooling,

the reason for the change of PAG quenching liquid
　　The PAG polymer in the quenching liquid is quite stable and will hardly be oxidized and decomposed under normal use conditions, nor will it react with the acid and alkali substances encountered. Then, what is the problem? Later, after research, it was found that the problem mentioned above was essentially the problem of the method for determining the effective concentration in use.
　　PAG quenchant is mainly made of PAG polymer and other additives providing auxiliary properties. During the quenching process of the workpiece, once the liquid temperature around the workpiece rises above the cloud point of the solution, the PAG polymer is dissolved out of the solution and suspended in the quenching liquid in the form of fine beads. 1 the suspended PAG beads come into contact with the red hot workpiece, they adhere to the surface of the workpiece by their very good wettability, and wrap the workpiece with a water-rich coating. PAG quenching medium is to rely on this coating to adjust the cooling rate of water, to avoid the workpiece quenching cracking. After the workpiece cools down, the polymer adhered to the workpiece will dissolve back into the quenching fluid. It takes time to dissolve back, and the workpiece is often removed from the quenching liquid before the polymer is dissolved back clean in production. In this way, the PAG polymer content in the liquid carried out by the workpiece is often higher than the content in the quenching liquid used. After long-term quenching of a large number of workpieces, the relative concentration of PAG in the quenching liquid will inevitably decrease gradually, while the concentration of other additive components will gradually increase. Because only PAG has the effect of adjusting the cooling characteristics of the water, its concentration is reduced by the corresponding reduction in the ability of the quenching fluid to adjust the cooling characteristics. Since the general factory uses a refractometer to determine the total concentration of quenching liquid, the cooling speed of the PAG quenching liquid that has been used for a long time is faster at the same concentration, which is the cause of quenching cracking.
　　 The 1 way to solve this kind of problem is to improve the concentration detection method, and it is best to use the cooling characteristic tester to control the concentration. The 2 is to find that the quenching hardness of the workpiece increases, so as to appropriately increase the refractometer concentration of the quenching liquid to ensure that the workpiece does not crack.
　　In addition, in order to slow down the effective concentration reduction rate, you can try to extend the workpiece in the quenching tank immersion time, and the workpiece with the quenching liquid to do timely cleaning, and then the cleaning water supplement into the quenching tank. This also reduces the consumption of quenchant.
　　Because water is the first major component. Water is particularly volatile in heat treatment production. Therefore, the effective concentration measurement of water-soluble quenching medium is very important. The PAG quenching medium can be measured by the refractometer method, but it is not suitable for measuring the concentration by the specific gravity method. Because the measurement of different temperatures will affect the measurement results, with temperature compensation digital refractometer PAL-1 can ensure the accuracy of measurement. The polyvinyl alcohol quenching medium is not suitable for the specific gravity method, nor is it suitable for measuring the concentration by the refractometer method; therefore, it is difficult to achieve on-site concentration control. The concentration of the inorganic salt aqueous solution can be measured by either the refractometer method or the specific gravity method. All aqueous quenching fluids are suitable for concentration control with a cooling characteristic meter. However, the use of cooling characteristics to control concentration requires not only a cooling characteristic tester, but also related application technology and analysis capabilities.

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