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Screw drives for machine building and automation

Screw drives for machine building and automation Ballscrew 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. By rigidly connecting to an adjacent construction, the ballscrew drive provides axial displacement or positioning of the component.

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. 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 offer a number of performance advantages. The drive can be subjected to uniform running with high efficiency and reliability. 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.

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. Engineers also need to consider temperature, sealing and lubrication. Protection against contamination can be provided, for example, by 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.

Screw drives are suitable for a variety of machine building, automation, handling and automotive engineering applications.

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.

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. 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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