Service Life Calculations

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Endurance test of an ETA+ ball screw on one of the three test benches at Steinmeyer. Endurance tests for industrial ball screw normally are highly accelerated tests (using higher loads and higher speeds than in the actual application). For aerospace applications, tests simulate the operation of the screw in the aircraft or spacecraft, using same loads, speeds and (if possible) environmental conditions.

Impact of preload

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 ...
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Duty cycle

To calculate the impact of actual duty on the fatigue life of the ball screw, it is necessary to convert the varying loads F_i into a mean load F_m which will have the same effect on life as the actual duty cycle. This mean load F_m is therefore called "equivalent" load
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Fatigue life

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 C_a, when subjected to the mean load F_m ...
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Technical Tip

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.