【Haichuan Expands Horizons】Do you know how the rotors of large-scale equipment are heat-treated?

The rotors have all been placed in the PAG quenching tank.

PAG quenching agent is the most widely used and effective water-based quenching medium both domestically and internationally at present. Such quenching media began to enter China’s heat treatment industry in the mid-1980s. Due to its good performance in actual production applications, it was quickly adopted on a wider scale. There have also been cases where some factories initially used the method successfully, but after a while, at the same concentration, a small number of workpieces cracked during quenching ； If it is continued, the proportion of cracking will gradually increase as well. The cause of the cracking could not be identified, and ultimately it had to be taken out of service. The reason for this is the lack of understanding of the changes in PAG quenching fluid during use, which prevented appropriate countermeasures from being taken.

The PAG polymer in the quenching fluid is quite stable; under normal operating conditions, it hardly undergoes oxidative decomposition, nor does it react with any acids or bases it comes into contact with. So, where lies the problem? Changes in the PAG component: The cooling properties of the quenching solution are determined by the characteristics and quantity of the PAG component. Other additives that provide auxiliary properties have little impact on the cooling characteristics, and the changes in PAG polymers contained in the quenching fluid include both qualitative and quantitative changes. Changes in PAG amount: PAG quenching agent is made primarily from PAG polymer, along with other additives that provide supplementary properties. During the quenching of the workpiece, once the temperature of the liquid surrounding it rises above the cloud point of the solution, the PAG polymer dissolves out of the solution and remains suspended in the quenching fluid in the form of small droplets. As soon as the suspended PAG droplets come into contact with the red-hot workpiece, they adhere to its surface due to their excellent wettability, forming a water-rich coating that wraps around the workpiece. The PAG quenching medium relies on this coating to regulate the cooling rate of water, thereby preventing cracking in the workpiece during quenching. Once the workpiece has cooled down, the polymer adhering to it dissolves back into the quenching solution. Re-dissolving takes time, and in production, the workpieces are often removed from the quenching solution before the polymer has fully re-dissolved. As a result, the PAG polymer content in the liquid carried away by the workpiece is often higher than that in the quenching fluid used. After long-term quenching of a large number of workpieces, the relative concentration of PAG in the quenching solution inevitably decreases, while the concentrations of the other additive components gradually increase. Because only PAG has the ability to regulate the cooling properties of water, a decrease in its concentration correspondingly reduces the capacity of the quenching fluid to adjust these cooling properties. Therefore, the more thorough the resolubilization, the slower the relative decrease of other additive components. That is, the faster its cooling rate is, the more stable it is. Changes in PAG quality: namely the oxidative degradation of the active components of PAG. The PAG polymer in the quenching fluid is quite stable; under normal operating conditions, it hardly undergoes oxidative decomposition, nor does it react with any acids or bases it comes into contact with. It is only oxidized and decomposed under conditions of high temperatures above 250 degrees along with the presence of oxygen. During quenching, most of the polymer film adhering to the surface of the workpiece can remain at a temperature not higher than its boiling point due to the vaporization of water within and around it; however, the layer in direct contact with the workpiece surface can still reach higher temperatures and undergo oxidative decomposition. The oxidation products with low molecular weight escape as gases, while the rest remain in the quenching solution. Chain scission occurs under high temperature and mechanical shear, yet it remains intact. This portion of PAG will no longer serve to regulate cooling performance, and will exist as an inactive component in the quenching solution. The higher the concentration of the quenching fluid, the thicker the polymer film that forms on the surface of the workpiece during quenching, and the more of this decomposition occurs. The greater the volume of material processed through heat treatment, and the longer the quenching fluid is used, the more of this decomposition and residues there will be.

For quenching, there are those treated with vegetable oil, and those treated with water for tempering. I think this term is called “quenching and tempering”, right?

I just saw it too, and it feels amazing