Table of contents:
- Three screw drive types with specific strengths
- Planetary roller screw drive
- Axial bearings for screw drives
- Precise interpretation
Video: Screw Drives In All Force And Speed Ranges
Screw drives dominate in the feed axes of machine tools, in format adjustments, in portal axes or lifting axes. The replacement of hydraulic or pneumatic cylinders with a mechanical actuator also leads to a further spread of the screw drives. So come mechanical linear actuators such. B. also used in welding guns or small presses in assembly technology. This very wide range of applications can only be covered with a large variety of types of screw drives, especially with regard to the transferable forces and thus the realizable pitches.
Three screw drive types with specific strengths
According to Schaeffler, the strengths of the KGT ball screw drive include the high dynamics due to the large spindle pitches, the low-friction running and the very high positioning and repetition accuracy. With ball screws, however, the pitch must be at least larger than the ball diameter. Very small gradients are therefore not possible. The RGT roller screw drive, however, does not have this restriction and is preferred for small gradients. The planetary roller screw drive PWG is intended to close the gap between RGT and KGT with spindle diameters from 5 mm to approx. 30 mm in the range of even smaller pitches from 5 mm to well below 1 mm.
Due to the high number of rolling contacts, the PWG should achieve 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.
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Planetary roller screw drive
For example, the PWG generates an axial force of 2200 N at a pitch of 0.75 mm from 40 Ncm. As a result, very large axial forces can be achieved even with small motors. The PWG can replace hydraulic drives due to its large translation and small installation space. According to Schaeffler, the electrical drive can be easily integrated via a feather key connection on the outside diameter of the spindle nut. Basically, the PWG is preloaded free of play and supplied pre-greased. The mother of the PWG is provided with gap seals on the end faces.
Axial bearings for screw drives
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 considered as a system. Therefore, the wide variety of INA lead screws is also reflected in the axial bearing variants on offer. You can choose between single and multi-row axial angular contact ball bearings ZKLN (bore mounting) and ZKLF (flange mounting) and double-acting needle roller / axial cylindrical roller bearings ZARN and ZARF. The ZKLR version should offer a particularly economical alternative. The double row angular contact ball bearings are pressed into a sheet metal cover. The sheet metal cover has a wide flange that is screwed to the machine. The ZKLFA version with three rows of balls was specially developed for vertical axes.Axial angular contact ball bearings of types ZKLF and ZKLN are also available in the X-life version. The better track quality is supposed to ensure less friction and lower storage temperatures. The lubricant is less stressed, the grease service life and any necessary relubrication intervals are extended. ZARN needle-axial cylindrical roller bearings (bore mounting) ZARF (flange mounting) are used for applications with the highest accuracy and rigidity.ZARN needle-axial cylindrical roller bearings (bore mounting) ZARF (flange mounting) are used for applications with the highest accuracy and rigidity.ZARN needle-axial cylindrical roller bearings (bore mounting) ZARF (flange mounting) are used for applications with the highest accuracy and rigidity.
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Schaeffler wants to strengthen the industrial sector
Optimally selected and designed products should give Schaeffler customers a noticeable competitive advantage. The company provides the Bearinx-online Easy Ballscrew version especially for the design of screw drives. The software tool takes into account, among other things, the non-linear, elastic spring behavior of the rolling elements, the elasticity of the bearing rings, load-related pressure angle displacements and the real contact pressure when skewed, as well as the influence of the profiling of the rolling elements on the contact pressure. Design influences such as the connection of the bearing to the shaft, the shaft material, the lubrication and the degree of contamination are also taken into account.
The program provides the four common bearing arrangements for screw drives as preconfigured calculation models: one-sided fixed bearing, fixed / floating bearing, fixed fixed bearing (spindle stretching with locknut) and fixed fixed bearing (spindle stretching with shim). Bearinx-online Easy Ballscrew calculates the minimum static load safety and the modified reference service life for all bearing arrangements. For the fixed-fixed bearings, the spindle stretching force and the value for the effective spindle rotation by stretching as well as all assembly setting values are also output. An exchange of the calculation file with the Schaeffler engineering service is possible at any time. (sh)
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