Ball Screw Technology Turns on Innovations

By Kyle G. Fedorcha

December 11, 2006

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Ball screws convert rotary motion into smooth, accurate, and reversible linear motion and can often serve as the most efficient and cost-effective choice for linear drive systems. These anti-friction devices enable precise positioning of moving parts in a wide range of applications for the automotive, aerospace, injection molding, instrumentation, medical, and machine tool industries, among others.

Over the years ball screws have given competing technologies a run for their money. In general, ball screws will perform more efficiently than sliding screws (which generate more friction); cost less than complex hydraulic or pneumatic systems; and offer longer life, higher load capabilities, and maintained precision compared with belt, cable, or chain drives. Innovations in ball screw technology have expanded interest and designers are taking notice.

Ball Screw Basics

Ball screws consist of a screw shaft, nut, balls, and a ball recirculating system. Components are usually made from various hardened or stainless steels.

Their configuration consists of a shaft with precision ground or rolled concave helical groove (acting as the inner race) and nut with internal grooves (acting as the outer race). Circuits of precision steel balls circulate in the grooves between the screw shaft and nut.

Depending on the application, either a rotating screw shaft or nut will then translate in a linear direction. The ball screw has a natural ability with a high efficiency to convert about 90 percent of a motor's torque into thrust, which results in minimal mechanical wear and constant performance throughout the life.

Ball returns are designed to create smooth and efficient recirculation of the balls from the end of their load-carrying path back to the beginning to complete the circuit.

Ball screws have been developed both in inch and metric dimensions. Preloaded and non-standard sizes, configurations, and special materials, including composite inserts, extend the possibilities.

Application and Operating Issues

When evaluating ball screws for an application, the first rule of thumb is to understand that a solution for one application may be inappropriate for another.

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