scragging or presetting

After heat treatment each spring is flattened at least once. This reduces the overall height by means of plastic deformation. Tensile stress results on the upper side, which counteracts the compressive stress caused by subsequent loadings and so reduces the stress peaks. Further plastic deformation is thereby avoided during later loading of the spring.

According to DIN 2093 each disc spring must be scragged so that following loading equivalent to twice the spring force F (s = 0.75 h_o), the limit deviations for the spring force are not exceeded.