tion that previously required roller screws. Or the designer
can extend the life of the assembly by using the high-load ball
screw in a low-load application. That’s because the assembly’s
life is a function of the load capacity (see “L 10 Life Expec-
tancy Calculation for Ball Screws,” above).COMPARING BALL SCREWS
High-load ball screws are typically available with screws up
to 15-m long, with single or double nuts, and in standard sizes
up to 160 mm in diameter. Their dynamic load capacity tops
out at 1,440 kN.
Applications that stand to benefit the most from these new
ball screws include large fabrication and injection molding
machines, and industrial security doors and gates used inHigh-Load Ball ScrewsL 10 LIFE EXPECTANCY CALCULATION
FOR BALL SCREWSBEARINGS ARE OFTEN specified to give an “L 10 ” (or in some
countries, “B 10 ”) life. This is how long it should take 10% of
the ball screws in an application to fail due to classic fatigue
failure or, alternatively, the time at which 90% should still be
operating. The L 10 life of the ball screw is theoretical and may
not be its actual service life. It can be calculated according to
the following formula:
L 10 = (Cam/Load)^3
Where L 10 = Life expectancy (in millions of revolutions)
Cam = Dynamic capacity of the ball screw (kN)
Load(kN)GO TO MACHINEDESIGN.COMRoller screws consist of a set of recirculating rollers. Roller bear-
ings with grooved rolling elements have more total surface contact
area than balls. As a result, service life and load-carrying capacity
increases.