How to solve the problems faced by water-based quenching additive?
October 15, 2021
How to solve the problems faced by water-based quenching additive? Problems encountered in quenching liquid during quenching and suggestions for solutions 1. Quenching abnormality (1) Quenching abnormalities caused by aging of quenching medium The traditional view is that the false concentration of the quenching liquid is caused by the increase of the concentration of the quenching medium due to the contamination of foreign substances. However, through in-depth study of the quenching cooling process and PAG material properties, Texas Cisco found that this local temperature during the quenching process (relevant literature shows 250°C) too high causes the quenching medium PAG to decompose, and the chain length of the hydrophobic group/hydrophilic group in the molecular chain changes. The decomposition products with low molecular weight are oxidized into gas and escape, and the remaining chain scission products remaining in the quenching liquid no longer have the original characteristics of adjusting the cooling performance, and become non-effective components in the quenching liquid. Therefore, PAG after repeated high-temperature use is more of a hydrophobic base, and even becomes an oil phase that precipitates out of water, which will also cause uneven heating of the workpiece during the quenching process. The larger the workpiece produced by heat treatment, the longer the quenching liquid is used, the more obvious the aging of the quenching medium, and this aging can only be slowed down and is irresistible. Appropriately increasing the stirring to allow the heat released by the quenched workpiece to be transferred to the quenching medium as evenly as possible, and to reduce the time when the local temperature is too high, is an effective measure to solve this problem. Texas Cisco also scientifically adjusts the quenching fluid for this problem. The proportioning system has developed a quenching fluid with long service life and stable cooling performance. (2) Abnormal quenching caused by solubility change PAG quenching fluid is mainly made of PAG polymer, plus other auxiliary performance additives. In the quenching process of the workpiece, once the liquid temperature around the workpiece rises above the cloud point of the solution, the PAG polymer will dissolve out of the solution and be suspended in the quenching liquid in the form of fine liquid beads. As soon as the suspended PAG droplets come into contact with the red-hot workpiece, they adhere to the surface of the workpiece by its very good wettability to wrap the workpiece. PAG quenching medium relies on this coating to adjust the cooling rate, avoiding quenching deformation and cracking of the workpiece. After the workpiece is cooled down, the polymer adhering to the workpiece will re-dissolve into the quenching liquid, which takes time, and during production, the workpiece is often taken out of the quenching liquid without waiting for the polymer to re-dissolve cleanly. In this way, the content of PAG polymer in the liquid brought out by the workpiece is often higher than the content of the quenching liquid used. After a long-term and large number of workpieces are quenched, the relative concentration of PAG in the quenching solution will inevitably gradually decrease, while the concentration of other added components will gradually increase. Because only PAG has the effect of adjusting the cooling characteristics, the decrease in its concentration reduces the cooling characteristics of the quenching liquid.
2. Quenching liquid pollution (1) Internal pollution Internal pollution has the characteristics of being difficult to recover, and it has the following two sources: ① The high temperature causes the quenching medium molecular chain to break, which will lead to internal pollution. The broken small molecules oxidize into gas and escape, and the broken larger molecules no longer have cooling performance and exist in the quenching liquid, thereby causing the quenching liquid to be polluted. ②For water pollution, use high-purity tap water as much as possible to avoid mixing of Ca+ plasma. (2) External pollution External pollution mainly includes oxide scale, dust, oil, etc. brought into the workpiece. Oxide scale generally dissolves into the bottom of the tank, and its existence generally does not affect the concentration measurement and cooling performance. As long as it is filtered and removed regularly, normal production can be ensured. For external pollution, oil is more difficult to deal with. Oil pollution usually comes from the cutting fluid on the workpiece, the lubrication in the equipment and the hydraulic oil. Since oil has a lower density than water, oil generally adheres to the surface or emulsifies into an aqueous solution. The oil floating on the surface does not affect the cooling performance of the quenching liquid, but may hinder the operation and concentration measurement. When subjected to relatively strong mechanical stirring or when soap and washing liquid are brought into the quenching liquid, these oils are easily emulsified into the quenching liquid. The emulsified oil generally does not affect the concentration measurement value of the quenching liquid, but it will slightly increase the cooling rate at low temperatures. It may become smelly due to the decomposition of oil stains and bacteria, and the quenching liquid will turn black at the same time. Therefore, in the production process, it is necessary to try to prevent the oil from entering the quenching liquid, to maintain the cleanliness of the quenching liquid, and to remove the slick oil on the quenching liquid in time. 3. Bacteria growth problem Water-based quenching fluid is different from quenching oil. Due to the organic properties of the polymer quenching agent itself, it has to face severe bacterial growth problems. Texas Cisco research found that not certain types of fungicides can completely solve this problem. , It needs to be considered from the overall compatibility system of the quenching liquid to resist the growth of bacteria and enhance the stability. The growth of bacteria will have a very bad effect on the quenching liquid, which is the beginning of its unstable cooling performance. The main hazards are as follows: (1) Bacteria uses organic matter as raw materials and catalyzes chemical reactions to occur, changing and accelerating the aging of polymer water-based quenching agents and shortening the service life of quenching media. (2) Accelerate the cooling rate in the convection stage, resulting in unstable quenching quality. (3) It may block the filter system and affect the normal operation of the system. (4) The growth of bacteria may change the pH value of the polymer water-based quenching agent and the rust inhibitor in the consumption medium, thus affecting the cooling performance of the quenching agent. (5) The growth of bacteria will produce unpleasant odors, which will harm the surrounding environment and the operator's skin. In order to prevent the growth of bacteria, we should start with the following aspects: First, select quenching medium with stable quality. At present, there are many manufacturers of water-soluble quenching agents on the market, and the quality is very different. Learn more about the application status of some customers to ensure that the selected quenching fluid has good cooling performance. Second, once a problem arises, find a professional manufacturer to solve it. Don't hear the hearsay, adding some substances that shouldn't be added will backfire. For example, the pH value of the quenching liquid is reduced, and adding alkali is a common method used by some manufacturers, but the alkali can easily react with the PAG substance, changing the PAG structure, and affecting the cooling performance. Third, pay attention to the preparation of quenching liquid with high purity water, usually pay attention to stirring, circulation and cooling, and insist on regular cleaning every year. The problems and solutions encountered in the use of water-based quenching agents are summarized: (1) The abnormal quenching phenomenon of water-based quenching agent may be caused by the aging of the cooling medium and the concentration change. Therefore, the concentration change should be detected and adjusted in time. (2) Internal pollution and external pollution will cause major changes in the cooling performance of the quenching fluid. Therefore, the quenching fluid should be tested and pollutants removed in time to prevent deformation or even cracking of the workpiece. (3) Insufficient water, miscellaneous oil and circulation, lower pH value, and sundries deposits will cause bacteria to grow. Therefore, the water source should be strictly selected during the use of water-based quenching fluid, the miscellaneous oil should be removed in time, and a good circulation system should be controlled at any time. Monitor the pH value and adjust it to remove debris in time.
