The heat treatment equipment process of coil springs mainly includes three processes: heating, heat preservation and cooling, and sometimes includes two key steps: quenching and tempering.
Heating : This is the first step in heat treatment by heating the springs to the proper temperature by using different heat sources such as resistance heating, high-frequency induction heating, salt bath furnace, etc. The method of heating and the choice of equipment depend on the material, size and heat treatment requirements of the spring. For example, for coil springs with large diameters, spring steels with good hardenability, such as 60Si2Mn steel, are selected to ensure that the entire section is completely hardened with high elastic limit and tensile strength. The heating temperature is usually 50-90°C higher than the quenching temperature, and the holding time is usually 10-15 minutes to ensure that the spring is evenly heated.
Heat Preservation : After heating, the spring needs to be kept at a certain temperature for a certain period of time to ensure that the internal structure of the spring is homogenized, this step is essential to obtain the desired metallographic structure and properties. The holding time and temperature control depends on the material and size of the spring.
Cooling: After holding warm, the springs need to be cooled quickly to achieve the desired hardness and tissue structure. The choice of cooling medium has a direct impact on the performance of the final product. Common cooling media include water, oil, polyvinyl alcohol, etc. For example, 50# mechanical oil is used as the cooling medium, and the oil temperature is controlled in the range of 20-60°C to inhibit the occurrence of the second type of tempering brittleness.
Quenching: Rapid cooling (quenching) to transform the structure of the workpiece and improve the hardness. The choice of quenching medium is essential to obtain the desired hardness and toughness. For example, a 0.5% polyvinyl alcohol quenching agent is used, which meets hardness and hardenability requirements while reducing embrittlement of the specimen.
Tempering: After quenching, the springs need to be tempered to adjust the hardness, eliminate internal stresses, and improve toughness. The choice of tempering temperature and time depends on the material of the spring and the desired properties. For example, the process specification for medium-temperature tempering treatment is (460-490) °C× (80-90) min, and the tempering is quickly cooled in water at the end of tempering to inhibit the occurrence of type 2 tempering brittleness.
Throughout the heat treatment process, the selection of equipment and the control of process parameters have a decisive impact on the quality and performance of the final product. Therefore, choosing the right heat treatment equipment and optimizing the process flow is a critical step in ensuring product quality.
