Equivalent Load

The mean or equivalent load is calculated using the above equation.

q_i Time percentage
n_i Speed (rpm)
F_i Thrust (which may need to be modified - due to preload - first)

The service life estimate obtained from ISO / DIN calculations represents a dependable method to predict useful life of a ball screw under the conditions and for the duty cycles found in most machines. Other necessary conditions include proper lubrication, suitable protection from contamination, and operation of the ball screw at temperatures not exceeding 70° C.

Should the calculated life fall outside the range mentioned on the following page, or if there are special requirements or unusual conditions, please contact our application engineers.

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By definition, the dynamic load capacity is the load at which the ball screw will reach a useful life of 1 million revolutions.

More accurately, this means 90% of a sufficiently large number of identical ball screws will reach this useful life. This life is designated as L10 and is usually the basis for ball screw selection in normal machine design. For higher reliabilities than 90%, an additional correction factor must be applied. In regular machine design, such higher reliabilities are normally not needed because there are much greater uncertainties, for example in the estimate of thrust.