In order to improve the mould steel hardness, we can upgrade by hardening heat treatment process. In order to better performance after handling tool steel, we need to be cool at the hardening process. Now we introduce the five mainly cooling methods:
1. Tool steel single liquid quenching method. The mould parts steel or heated to austenitizing quenched into water, oil or other cooling medium, after a certain time to cool ( cooled to below the pearlite transformation temperature of the martensitic transformation temperature region or area ) taken air-cooled steel mold. As the mould steel cooling process is completed in a single cooling medium, called single liquid quenching method.
2. Tool steel double quenching method. As the name suggests, mould steel quenching process in both the cooling medium ( most commonly used is water , oil ) and with the completion. The cooling process is desirable, both rapid cooling pearlite transformation in the region, slow cooling in the martensite transition region. In practice, the mold is heated to a temperature of austenitic steel or parts quenched into the high temperature zone of the first fast-cooling section a medium ( usually water or saline solution ), in order to suppress excessive cold austenite pearlite transformation , when cooled to about 0 degree, quickly removed the slow cooling into the low-temperature region of the second medium ( typically oil ) . Since martensite and cooling under moderate conditions, which can effectively alleviate or prevent deformation and cracking, commonly known as water quenching oil cooling. This method requires a higher operating skills. Sometimes the understanding of the three media, that is, first water, oil, and ultimately air.
3. Mould steel jet quenching. Especially in large and complex workpiece thickness difference is large and die steel, in order to avoid excessive cooling uniformity of quenching stress, control the cooling process at different stages in different parts of the cooling rate metho . There spray liquid (water or an aqueous solution ), spraying ( atomized spray compressed air and water to parts of different parts ), gas quenching and other methods, the advantage of each temperature can be controlled in different media or different flow , pressure control and regulation cold -speed area; or change to a different number and location of nozzles can, cooling evenly. Currently in the mould vacuum heat treatment of the most popular high-pressure gas quenching.
4. Mould steel quenching method. Heated to a temperature of austenitic steel mold or workpiece temperature quenched martensite transformation temperature near the cooling medium ( commonly used for salt bath ), and stay for some time, so that the surface and center temperature gradually converge after remove the air-cooled, at a lower cooling rate to complete martensitic transformation, this method can significantly reduce distortion and improve the toughness of the steel mold, mould parts is one of the commonly used method of quenching. Die steel quenching temperature selection, there are two: One is to take the work piece to be treated steel temperature martensitic transformation start (Ms point ) above 10 - 30 degree, the other is selected Ms point 80 - 100 degree. The residence time of grading have to master, too short temperature uniformity was not able to achieve the purpose of quenching, too long may reduce the hardness and the occurrence of non- martensitic transformation.
5. Tool steel isothermal quenching. Heated to austenitizing temperature quenching tool steel workpiece is slightly higher than the temperature stays hot bath isothermal hardening steel by Ms point, the completion of the phase change to obtain a lower bainite or lower bainite and martensitic mixing body tissue. The purpose of this method can alleviate deformation and cracking, quenching stress small. Tempered martensite having similar strength and toughness .
Avoid mould steel deformation, cracking phenomenon, the cooling mold steel after quenching process, it is necessary, it would be difficult to deformation tool steel, under conditions of use with a suitable viscosity, non-flammable, explosive, non-toxic.
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