These contact flats improve definition of the point of load application and, particularly for spring stacks, reduce friction at the guide rod. The result is a considerable reduction in the lever arm length and a corresponding increase in the spring load. This is in turn compensated for by a reduction in the spring thickness from t to t’.

When calculating disc springs with contact flats and reduced thickness, the factor K₄ must be calculated using formula 6, and t replaced with t’ and h_o with h_o’ = l_o – t’ in the equations 7 to 16.

The reduced thickness t’ is specified in accordance with the following conditions:                                                                        

• The overall height lo remains unaltered
• The width of the contact flats is to be approximately 1/150 of the outside diameter
• The spring load for a reduced thickness spring must be the same at s = 0.75 h_o as for an unreduced spring

The dimension t’ is specified for those discs springs contained in DIN 2093. The mean factor t’/t is:

For other springs the factor for t’/t is dependent on the dimensional ratio δ and h_o/t from figure 6. The curves were calculated for disc springs with δ_OM = -1600N/mm². For springs with different stress s_OM, we would ask you to contact us on 01202 339559. 

As the overall height is not reduced, springs with reduced thickness inevitably have an increased flank angle and a greater cone height h_o’ than springs of the same nominal dimension without reduced thickness. Therefore, the characteristics curve is altered and becomes more curved. Figure 7 shows the characteristic curves for springs of the series A, B and C as per DIN 2093 with and without contact flats and reduced thickness.

         Figure 6 – click to enlarge