Schaeffler has the three types ball screw KGT, roller screw RGT and the new design Planetenwälzgewindetrieb PWG on a complete portfolio and can virtually any application with stem diameters of up 6 80 mm use. tuned to the performance of the screws and in an equally wide variety matching Thrust bearings are available.
The ball screw drive KGT offers high dynamics due to the large spindle pitches, the low-friction running and the very high positioning and repeat accuracy. For ball screws, however, the pitch must be at least greater than the ball diameter. Very small slopes are therefore not possible. The roller screw RGT, however, does not have this limitation and is preferably used for small pitches. The planetary roller screw drive PWG (figure) closes the gap between RGT and KGT with spindle diameters from 5 to approx. 30 mm in the range of even smaller gradients from 5 mm to well below 1 mm.
Due to the very high number of rolling contacts, the PWG achieves the highest load capacity and rigidity compared to the other two types. The good internal load distribution and the optimized osculation between the contacting flanks ensures a relatively low friction.
The PWG, for example, generates an axial force of 0,75 N at a pitch of 40 mm of only 2200 Ncm. Consequently, even with small motors, very large axial forces can be achieved. Due to its high gear ratio and small installation space, the PWG can replace hydraulic drives. The integration of the electric drive is very simple possible via a feather key connection on the outer diameter of the spindle nut. Basically, the PWG is supplied preloaded and pre-greased without backlash. The mother of the PWG is provided with gap seals on the front sides.
The bearing of the screw drives transmits the axial forces of the spindle nut and guides them into the housing. Screw drives and their storage are therefore always to be regarded as a system. The choice includes single and multi-row axial angular contact ball bearings ZKLN (bore mounting) and ZKLF (flange mounting) as well as double-acting needle-axial cylindrical roller bearings ZARN and ZARF. An economical alternative is the ZKLR version, whose double-row angular contact ball bearings are pressed into a sheet metal cover. Specifically for vertical axes, the ZKLFA version has been developed with three rows of balls. Axial angular contact ball bearings type ZKLF and ZKLN are available in X-life design. The better track quality ensures lower friction and lower bearing temperatures. The lubricant is subjected to less stress, the grease service life and any necessary relubrication intervals are extended. For applications with the highest accuracy and rigidity, the ZARN (bore mounting) ZARF (flange mounting) needle-thrust cylindrical roller bearings are used.