Production Process

Generally, for the manufacture of valve springs, we can distinguish between two methods:  low temperature and high temperature processes, depending on heat treatment after coiling.

With low temperature heat treatment, the spring is submitted to stress free annealing after coiling in order to reduce internal stress on the inner periphery of the spring caused by the coiling process. However, this process is always a compromise between desired and required reduction of natural frequency after coiling and unwanted lowering of component strength by this type of heat treatment. A fundamentally different and optimized manufacturing process is spring tempering after coiling. With this process, the entire spring is heated to a temperature above AC3 after coiling and is then quenched. On account of the high process temperatures, all internal stress on inner periphery of the spring caused by the coiling process is eliminated. Subsequently, spring stiffness and ductility are set in a tempering process. Optimum spring material properties regarding stiffness, ductility and internal stress can be controlled with the spring tempering process.