Problems in the use of AQ251 In recent years, Donggang Company has used the quenching medium AQ251 produced by Houghton Company Shenzhen Branch to heat the 8.8 high-strength bolts below M16 (the conventional material is medium carbon structural steel: 35 steel, Run and leak.
AQ251 quenching medium use conditions analysis medium concentration too low low concentration is one of the most common causes of deformation and cracking. It is necessary to strengthen the concentration detection and make adjustments in time. Comparison of quenching tests of different concentrations of AQ251. Many users actually understand the effect of concentration, but for cost reasons, they are worried about the increase in concentration, which increases the consumption, that is, the increase in cost, so they are reluctant to increase the concentration.
In fact, because AQ251 has a unique reverse solubility, the solubility in water decreases with increasing temperature. AQ251 and water separation occur after a certain concentration of AQ251 and the solution are heated to a certain temperature.
In the quenching and cooling process, the reverse solubility of AQ251 can be used to form a thermal resistance layer on the surface of the workpiece. That is, the AQ251 quenching medium is in the cooling process. When the hot workpiece enters the medium, a layer of heat retaining energy; reducing the heat dissipation at the inlet and outlet ends of the drying chamber Amount; high-infrared fast curing and far-infrared radiation drying technology; low-temperature drying coating.
During the use of AQ251 quenching medium, the refractive index will decrease due to contamination and media aging. If the refractive index of the new liquid is still used, the concentration will be overestimated. For example, the refractometer reading is 3, the refractive index of the new liquid is 2.5, and the determined concentration is 3X2.5=7.5%, and if the refractive index of the actual solution is reduced to 1.5, the actual concentration is only 3XI.5=4.5%. The concentration is overestimated by 3%, which is very dangerous. Therefore, it is necessary to frequently check the refractive index of the refractometer.
AQ251 quenching agent has a unique reverse solubility. When a certain concentration of AQ251 solution is heated to a certain temperature, PAG and water separation phenomenon occurs. The workpiece is quenched and cooled in a medium with varying state of matter into three stages: a vapor film stage (723 ° C to 40 ° C), a boiling stage (4 ° ° C to 150 ° C), and a convection stage (about 150 ° C or less). When the workpiece is quenched in AQ251 medium, the speed is 162 ° C / s when the liquid temperature is about 50 ° C. After the temperature of the medium rises, the evaporation increases, the vapor film stage is greatly extended, and the maximum cooling rate is decreased, so the use temperature is mostly Below 60 ° C.
Low temperatures increase the rate of cooling and increase the tendency to crack and crack. For example, in the cold winter, when the quenching is started, the medium temperature is lower and the deformation is increased, so it is necessary to heat the medium to a prescribed temperature or increase the concentration to compensate. In the winter, the company will increase the use concentration by 2% and receive good results. Obviously, in order to obtain a stable quenching effect, it is necessary to maintain the temperature of the medium in a relatively narrow range, from 15 ° C to 30 ° C in summer and from 30 ° C to 40 ° C in winter. Therefore, it is necessary to equip with an efficient heating and cooling device, which is essential for the continuous mesh belt furnace production line.
The medium aging quenching and cooling process causes a rather harsh environment, and oxidative degradation, thermal degradation, mechanical degradation, etc., cause the PAG molecular chain to break and become shorter. Thereby the flow of the medium is made easier, that is, the viscosity is reduced. The convection stage cooling is closely related to the fluidity (viscosity) of the medium. The viscosity becomes smaller and the convection cooling rate increases. That is, at the same concentration, as the use process continues, the viscosity becomes smaller, and the cooling rate, especially the convection cooling rate, becomes larger, which increases the tendency of deformation and cracking. Therefore, it is necessary to continuously detect and control the cooling condition of the AQ251 quenching medium in use, and measure the cooling rate distribution with a cooling characteristic meter to ensure the stability of cooling in the convection stage.
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