The coefficient of sliding friction of a screw drive results from the sliding pairing between spindle and nut. Other factors are the axial load, the pitch of the spindle and possible external lubrication. In order to achieve a high level of efficiency and to reduce the drive torque, it is essential to optimize the coefficient of sliding friction.
In principle, coefficients of friction are divided between static and dynamic values. The static value indicates the coefficient of friction, i.e. the breakaway torque to set the nut in motion. The dynamic value relates to a screw drive that is already in motion.
While the thread profile is mostly specified by the application, a great improvement can be achieved through the use of suitable sliding pairs.
The combination of an aluminum spindle with a plastic nut has proven to be ideal for small loads. In the high-load range, enormous successes can be achieved with whirled or ground spindles in combination with modern high-performance bronzes and lubrication.
The use of the right lubricant is still an essential factor for high-speed or highly stressed screw drives. The “junagrease spindle grease” was specially developed for the lubrication of screw drives (especially ball screws, trapezoidal threads and high helix threads). But the use of maintenance-free, i.e. unlubricated materials is also becoming more and more popular.
Junaspin is happy to help with the design. Thousands of test results are documented in our database. In addition to the pure calculation, experience from “real applications” and tests can also be incorporated.
Comparison of friction coefficients
|Spindle / nut||dry||Junagrease lubrication||dry||Junagrease lubrication|
|Steel / steel||0,30-0,35||0,09-0,15||0,15-0,20||0,05-0,10|
|Steel / cast iron||0,19-0,24||0,10-0,15||0,10-0,15||0,05-0,08|
|Steel / gunmetal||0,19-0,24||0,10-0,15||0,10-0,15||0,05-0,08|
|Steel / aluminum bronze||0,18-0,24||0,08-0,13||0,08-0,13||0,04-0,08|
|Steel / PA6.6||0,20-0,25||0,04-0,06||0,10-0,14||0,02-0,04|
|Steel / POM||0,20-0,25||0,04-0,06||0,10-0,14||0,02-0,04|
|Steel / plastic with optimized sliding properties *||0,18-0,23||0,03-0,05||0,08-0,13||0,01-0,03|
|Stainless steel / stainless steel||0,30-0,35||0,09-0,15||0,15-0,20||0,05-0,10|
|Steel / stainless steel||0,30-0,35||0,09-0,15||0,15-0,20||0,05-0,10|
|Stainless steel / gunmetal||0,20-0,25||0,04-0,06||0,10-0,15||0,05-0,08|
|Stainless steel / PA6.6||0,20-0,25||0,04-0,06||0,10-0,14||0,02-0,04|
|Stainless steel / POM||0,20-0,25||0,04-0,06||0,10-0,14||0,02-0,04|
|Stainless steel / plastic with optimized sliding properties *||0,18-0,23||0,03-0,05||0,08-0,13||0,01-0,03|
|Hard anodized aluminum / POM||0,16-0,20||0,02-0,06||0,05-0,08||0,01-0,03|
|Hard anodized aluminum / plastic with optimized sliding properties *||0,14-0,18||0,01-0,04||0,05-0,07||0,01-0,03|
* Average value of various sliding plastics