Plants using PAG quenching media are commonly encountered such as: 1. Why should the concentration of quenching liquid be gradually increased in long-term use to ensure that the workpiece is not quenched? 2. Which concentration measurement method is most effective? 3. How to reduce the consumption of quenching agent? 4. Can the quenching liquid be blackened and stinky? 5. There is no way to do the decontamination update of the contaminated quenching liquid. In fact, such problems are closely related to changes in the quenching fluid. Therefore, to understand and solve such problems, we must start with understanding the changing rules of PAG quenching liquid in use. The PAG quenching agent is made of a specific polyether nonionic polymer (PAG) plus a composite additive capable of obtaining other auxiliary properties and an appropriate amount of water. In use, there are two main types of changes that can occur in the quenching liquid: one is the change in cooling performance, and the other is the change in properties such as rust prevention and anti-corruption. Since the purpose of using PAG quenching agent is to adjust the cooling characteristics of water, the following will focus on the changes in cooling characteristics, only to mention the rust and anti-corruption issues.
First, the change of PAG components
The cooling characteristics of the quenching liquid are determined by the characteristics and quantity of the PAG component therein. Other additives that provide ancillary properties have little effect on the cooling characteristics of the quenching fluid. The change of the PAG polymer contained in the quenching liquid includes two parts: the amount change and the mass change.
1. Change in the amount of polymer in the quenching liquid
In production, the removal of the workpiece and the high temperature oxidative decomposition will reduce the amount of polymer. During the quenching process, the liquid temperature around the workpiece rises, and the PAG polymer is desolvated from the solution and adhered to the surface of the workpiece 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 is dissolved back into the quenching liquid. It takes a certain time to dissolve back, and in the production, the workpiece is often removed from the quenching liquid after the polymer is dissolved back. Therefore, the PAG content of the liquid brought out by the workpiece tends to be higher than the average concentration of PAG in the quenching liquid used. After long-term, large amount of quenching, the relative concentration of PAG in the quenching liquid will inevitably decrease gradually, while the relative content of other additive components will increase. Therefore, the more complete the remelting, the slower the relative reduction of the PAG component in the quenching liquid, that is, the more stable the cooling characteristics.
2. Oxidative decomposition of PAG
The polymer of the PAG quenching liquid has high chemical stability and does not react with ordinary acids and bases at room temperature. It is only oxidatively decomposed under the conditions of high temperature above about 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 the moisture in and around it is vaporized. However, the portion immediately adjacent to the surface of the workpiece may still rise to a higher temperature and undergo oxidative decomposition. The oxidative decomposition product having a low molecular weight runs away as a gas, and the other portion remains in the quenching liquid. The broken chain products of the PAG which are broken under high temperature and mechanical shearing will no longer have the ability to adjust the cooling characteristics, and the non-active components are present in the quenching liquid. 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 such decomposition occurs. The greater the yield of heat treatment production, the longer the quenching liquid is used, and the more this decomposition and chain scission residue.
Second, changes in non-PAG components
1. The qualitative change of non-PAG components
The additive component has no reverse solubility and is always distributed evenly in the solution. In addition, its concentration is low and is less affected by high temperature. Therefore, the amount of deterioration in production is also small, and the deteriorated product is substantially non-volatile. The qualitative change of the additive component usually only reduces the auxiliary properties such as anti-rust and anti-corrosion of the quenching liquid and defoaming property, and does not substantially affect the cooling performance of the quenching liquid.
2. Changes in the amount of additive components
As mentioned earlier, in the liquid taken away by the quenched workpiece, the relative concentration of the PAG component tends to be higher than the average value of the quenching liquid. Therefore, after a long-term use of the quenching liquid, the relative concentration of the additive components is always higher than that of the newly formulated one. However, quenching agents that are supplemented in production typically have a fixed proportion of components. Thus, the longer the quenching liquid is used, the larger the quenching amount, and the more the quenching agent replenishing amount, the higher the relative concentration of the additive and its deterioration residue in the quenching liquid. Conversely, the lower the relative concentration of the effective PAG component.
3. Tap water contains soluble matter accumulation
Tap water is added to the tap water to form a PAG quenching liquid, so tap water is also a component of such quenching liquid. In production, tap water is easily volatilized and needs to be replenished frequently. Tap water is not distilled water, which always contains a small amount but a lot of substances other than water. In use, after the water evaporates, the non-volatile matter originally dissolved therein will remain. As a result, the concentration of these solubles in water and their soluble metabolite residues in use is increased. These substances accumulate in the water and the concentration will be higher and higher. Over time, some get saturated, and more parts go into the sediment.
4. Alien pollutants
In addition to the quenching agent and water, the quenching liquid will inevitably bring in other substances in the production. Such as the scale of the workpiece, as well as the soluble and insoluble substances commonly found in the field. Some of the insoluble materials form sediment, and some are suspended in the quenching liquid. The soluble matter also becomes a component of the solution and increases the concentration by accumulation. These soluble and insoluble foreign materials constitute foreign contaminants in the quenching liquid. The foreign pollutants do not substantially affect the cooling characteristics of the quenching liquid, but the soluble matter therein increases the refractive index of the solution.
Next page
Tapered roller bearings refer to radial thrust rolling bearings with tapered rollers as rolling elements. There are two types: small cone angle and large cone angle. The small cone angle mainly bears the radial and axial combined load based on the radial load, and is often used in pairs, installed in reverse, the inner and outer seat rings can be installed separately, and the radial and axial clearance can be adjusted in installation and use; The large cone angle mainly bears the axial and radial combined load based on the axial load, and is generally not used alone to bear the pure axial load, and can be used to bear the pure radial load when it is used as a pair configuration (the end of the same name is relatively installed). The ability of a single row tapered roller bearing to withstand an axial load depends on the contact angle, i.e. the outer ring raceway angle, the greater the angle, the greater the axial load capacity. The most widely used tapered roller bearing is a single row tapered roller bearing. In the front wheel hub of the car, small double row tapered roller bearings are used. Four-row tapered roller bearings are used in heavy machines such as large cold and hot rolling mills
Tapered Bearings,Bearings 7212,Low Noise Bearings,Tapered Roller Bearing
Hebei Fangqiang bearing manufacturing Co., LTD , https://www.fangqiangbearing.com