Just about everyone knows what a screw looks like and how it works. Ball screws are a little different, though. They are a type of mechanical linear actuator, meaning they convert rotational into linear motion.
How Ball Screws Work
In a typical ball screw, circulating balls travel and are recirculated through a thread form. There are several methods for recirculating the balls.
External ball nuts feature stamped tubes that pick them up from the raceway, while internal button ball nuts employ machined button-style returns that allow the balls to exit and then renter the raceway one thread up. Endcap return ball nuts utilize caps on the ends that are machined to pick up the balls as they exit the nut and direct them down holes bored transversely down the ball nut to a complementary cap on the other side that directs them back into the raceway.
As should now be clear, ball screws are much more complex than lead screws. They also feature more parts than similar motion actuators. As a result, the ball screw assembly must be manufactured with extreme precision to facilitate the movement of the bearing balls and reduce friction. This makes choosing a ball screw manufacturer that has a reputation for excellence in manufacturing a must.
Understanding Ball Screw Efficiency
Ball screws are excellent options for any application that requires high precision and minimal friction. They feature higher mechanical efficiency ratings than other types of linear actuators, with typical ball screws boasting 90% efficiency, compared to the 20-25% found in lead screws of equal size.
Understanding Ball Screw Accuracy
These linear actuators are classified using a convenient scale of accuracy grades that range from C0 to C10, with C0 being the most precise ball screws available. High-precision ball screws may be precise to 830 nanometres per centimetre.
Backlash is a common problem in lead screw and nut systems, but it’s easier to address with ball screws. The balls are often preloaded to eliminate movement between the ball screw and nut, which can be particularly beneficial in machine tool applications where expected loads are variable and can change quickly.
The efficiency, precision, and accuracy ratings required of a ball screw vary by industry and specific application. The ball screws used in CNC systems and semiconductor manufacturing, for example, must be extremely precise. Those found in modern cars’ power steering systems may not need to be manufactured to the same precision and accuracy standards, although efficiency remains a top concern.
Ball Screw Care
Because ball screws are so complicated, they require specific kinds of care and maintenance. They must be protected from contamination with dirt and abrasives through the use of enclosed working surfaces or positive pressure of filtered air when used in open enclosures. The ball screws may also need to be serviced occasionally by a trusted manufacturer.
How to Get Replacement Ball Screws
If a ball screw has sustained significant damage, the best option is usually to replace it rather than repair it. High-quality ball screws are available through some of today’s top industrial parts and protective equipment manufacturers, some of which also provide ball screw repairs and protective covers. Contact a reputable manufacturer to request a quote today.