Ball screws serve an important role in many manufacturing applications. Though seemingly simple, ball screws assemblies can be very complex. Having a thorough understanding of how ball screw assemblies work is crucial when choosing a screw to meet your goals.
How do ball screws work?
A ball screw assembly is comprised of four main components: the ball screw, the ball nut, a ball recirculation insert or tube, and the ball bearings. Each plays their own unique role in helping the assembly operate.
The Ball Screw
The ball screw is the main driving component in a ball screw assembly. It usually has machined ends for mounting to bearings and a designated length that is required for travel. For most ball screw assemblies, the ball screw is rotated using a motor, which translates the rotation into linear motion.
Ball screws can be constructed from a variety of materials depending on the needs for the application, including:
- Carbon steel (1045),
- alloy steel (4140), or
- stainless steel.
Carbon steel is used most often, though alloy steels are often used for aerospace applications. Both carbon steel and alloy steel are case hardened on the surface to achieve a high hardness, but the core remains soft to allow strength in the core of the system.
Stainless steel ball screws have a significantly lower load capacity, and usually can’t be matched to a carbon steel system. Precipitating hardened stainless steels can be used, but they become brittle when hardened to that of a carbon steel.
The Ball Nut
The ball nut is crucial in allowing for linear motion within the ball screw assembly. Once straddled onto the ball screw and mounted, the ball nut will travel axially along the ball screw when the screw is rotated by a motor, creating linear movement. Some applications require for the ball nut to be rotated by the motor, allowing for the ball screw to travel, however this is uncommon.
Ball nuts at the PST group are often manufactured of an alloy steel, such as 8620 or 9310. These alloys are then carburized to reach the high hardness levels required of the application. Stainless steels can be used but face the same challenges of stainless-steel screws.
The Ball Bearings
Ball bearings ride inside the matching gothic forms of the ball screw and ball nut. They allow the ball screw assembly to travel smoothly and accommodate the required loads of the assembly.
Ball bearings are typically constructed of either chrome steel 52100 alloy or 440C stainless steel, both hardened to above HRc 60.
The Ball Recirculation Insert or Tube
The ball recirculation system allows the internal ball bearings to continually travel inside the ball nut through a recirculation insert or tube. The tube is either mounted to the inside or attached to the outside of the ball nut. As the ball nut is rotated, the ball bearings travel through the track. This allows the ball bearings to rotate from the end of the track to the beginning of the track, creating smooth travel throughout the system.
Ball recirculation systems are made from a wide variety of materials, such as carbon steels, stainless steels, plastics and more, depending on the needs of the system.
If you’re interested in finding a ball screw manufacturer to create the perfect screw for your application, experts at The PST Group are standing by to help. Contact us today.