Ballscrew drives now include new rolled version

Paul Boughton

Schaeffler has extended its range of ballscrew drives to include a series of Transportation DIN standard ballscrews. This new series now completes Schaeffler’s comprehensive screw drives offering, which now includes ballscrew drives (ground and rolled), planetary screw drives, roller screw drives, as well as a range of ballscrew support bearings.

Screw drives are suitable for a variety of machine building, automation, handling and automotive engineering applications. Screw drives comprise a threaded spindle and threaded nut. Due to the rotation of the spindle, the nut moves in a linear manner along the spindle, converting the rotary motion of the drive into linear motion. A screw drive is rigidly connected to the adjacent construction, providing axial displacement or positioning of the component. The screw drive can be subjected to high dynamic loads.

Nuts are available in a flanged or cylindrical design and in the form of single or double nuts. Preloaded (double) nuts enable high positional accuracy and rigidity. The thread on the shaft is either rolled or ground. The threaded shaft can be driven by direct or indirect means and is supported on one or both sides – typically by locating/non-locating bearings.

Selection criteria for screw drives is based on a number of requirements including positional accuracy, rigidity, freedom from clearance/preload, load carrying capacity, speed, basic rating life, frictional torque, smoothness of running, and pitch.

In ballscrew drives, the load is transmitted from the spindle by means of precision, hardened steel balls to the nut. The nut (cylindrical or flanged) has a return system for recirculating the rolling elements. Ballscrew drives are able to offer high load carrying capacities and smooth, uniform running with high efficiency and reliability.

Schaeffler’s KGT range of ballscrew drives have a contact angle of 45°. External drive forces induce an axial force, which causes axial deflection as a function of the preload. In the case of preloaded single nuts, the preload is achieved by the introduction of oversize balls, resulting in four-point contact with the raceways.

Double nuts are preloaded by the use of a spacer, which sets the nut in an ‘O’ arrangement. In this case, the rolling elements are in two-point contact with the raceways.

Depending on the operating parameters and application, different requirements are placed on the accuracy of ballscrew drives. The KGT series is available in accuracy class T7 (52µm variation over a 300mm axial travel) as standard, with a class T5 (23µm) option also available. Other tolerances can be supplied in accordance with ISO 3408-3 (DIN 69051).

The KGT range of ballscrew drives can be used at operating temperatures from -10°C to 80°C. The screw nuts (KGF/M) are protected against contamination by either a gap seal or a labyrinth seal. For some ballscrew designs, a contact seal may be recommended. If there is a risk of dust or foreign matter entering the screw nut, additional sealing measures can be implemented.

Depending on technical, economic and ecological factors, lubrication is achieved using oil or grease. The screw nut is pre-greased as standard with a high quality lubricant. For re-lubrication, lithium soap or lithium complex soap greases with a mineral oil base is recommended.

Ball screw shafts (KGS) are available in diameters from 6mm up to 80mm and in lengths from 900mm up to 7600mm.

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