Heat treatment of Air Cooler Mould is an important proc […]
Heat treatment of Air Cooler Mould is an important process to ensure mould performance, which has a direct impact on the manufacturing accuracy of air cooler mould, the strength of plastic mould, the working life of mould, and the manufacturing cost of mould.
The heat treatment of air cooler mould is to exert the potential of mould material and improve the service performance of mould. The performance of the air cooler mould must meet the following requirements: high strength (including high-temperature strength, cold and hot fatigue resistance), high hardness (wear resistance) and high toughness, and also require good machinability, (including good polishing) weldability and corrosion resistance, etc.
The deformation of air cooler mould after heat treatment is generally believed to be caused by cooling, which is incorrect. For complex dies, the correctness of the heat treatment process often has a great influence on the deformation of air cooler dies. Comparing with the heating processes of some dies, it can be clearly seen that the heating speed is faster and larger deformation often occurs.
(1) The cause of deformation
Any metal will expand when heated. As steel is heated, uneven temperature (i.e. uneven heating) in each part of the same mould will inevitably lead to an inconsistent expansion in each part of the air cooler mould, thus forming internal stress due to uneven heating. At the temperature below the transformation point of steel, uneven heating mainly produces thermal stress, and uneven heating beyond the transformation temperature will also produce uneven microstructure transformation, which not only produces microstructure stress. Therefore, the faster the heating speed is, the greater the temperature difference between the air cooler die surface and the core, the greater the stress and the greater the deformation of the air cooler die after heat treatment.
(2) Preventive Measures
When heating complex dies below the phase change point, they should be slowly heated. Generally speaking, the vacuum heat treatment deformation of air cooler dies is much smaller than that of salt bath furnace heating quenching. Preheating is adopted, and one-time preheating can be adopted for low alloy steel moulds. For high alloy rigid moulds, secondary preheating shall be adopted.