Service Life Calculations
In this step, we modify axial forces to reflect the impact of preload. The preload graph shows how internal forces in the ball nut are affected by external forces and preload ...
To calculate the impact of actual duty on the fatigue life of the ball screw, it is necessary to convert the varying loads Fi into a mean load Fm which will have the same effect on life as the actual duty cycle. This mean load Fm is therefore called "equivalent" load
The useful life L10 can be expected to be reached by 90% of a sufficiently large number of identical ball screws having a load capacity Ca, when subjected to the mean load Fm ...
Ball screws are normally loaded with axial forces. Service life is determined by material fatigue in most cases. However, in some applications, abrasive or adhesive wear may cause a loss of preload and thus be considered a failure of the ball screw.
In the ISO 3408 or DIN 69051 standards, the math used to estimate ball screw life is based on material fatigue only. This is generally correct, but if the loading is very low and mean speeds are very high, this method may return an erroneous life estimation which cannot be reached in reality. If your application falls within this category, please consult our engineers.