Why Do Polymer Linear Bearings Have Grooves?

[Stormer]

TL;DR

What is the function of the groves in polymer bearings?

All polymer linear bearings i have seen have a lot of groves in the running direction (at least the ones for round shafts). Is this just to minimize the surface area in contact with the shaft to minimize the friction? Or do they have another function like clearing dust and particles? And why does not other plain bearings like oilite bearings have these groves?

 

[john.phillip]

You might find this video useful:

 

[Stormer]

You might find this video useful:

Not really... It is just an advertisement for a company that does not use slots that emphasized that it can take lager loads because of a larger surface area. It says nothing about why so many use slotted designs.

 

[Tom.G]

If you watched the video you should have noticed that YouTube suggested the Igus video as the next one up. I didn't bother.

Try watching that Igus video and you may be able to answer your own question.

 

[Baluncore]

I want to know why they use slots, and why the slots are so wide.
My guesses are;

1. Slots are there to provide a path for dust, dirt and wear particles to escape the system. But they seem to be much too big for that.

2. Polymers tend to have large coefficients of thermal linear expansion. The sectional area is more critical. Without some space, pressure would increase when the bearing material gets hot, so the bearing would lock.

3. The slots used are large, so more cooling air can pass through during periods of high activity. That air will cool the shaft and the polymer material.

 

[john.phillip]

I watched one ~50min long Igus webinar and downloaded their drylin linear bearings catalogue. My findings are the following:

a) They state in the video that heat is mostly transferred through contact (shaft and housing);

b) They offer +150 materials for non-metallic bearings and they tweak the composition in order to primarily achieve a desired PxV (Pressure x Velocity), and then the other required properties such as: coefficient of friction, wear, temperature range, dirt tolerance, contaminant tolerance (water, oils, chemicals), shaft material compatibility and others;

c) They call this design "Flute", "Ribbed", "Slotted" or "Padded";

d) They make one and only one claim for the design: it is dirt tolerant;

e) They explain how it controls dirt and dust through three mechanisms: The slot is large enough for some particles to pass through; The pads act as a wiper due to the high contact pressure; Assembly tolerance is tighter than for ball bearings;

f) The design came to be through the objective of replacing linear ball bearings, which led to the observation that linear ball bearings usually only contact the shaft mostly in 1 to 3 linear positions, thus it made sense for them to replace the chain of ball bearings by individual pads; however, the contact pressure would be generally high for the non-metallic material, leading to the addition of more pads in order to obtain the desired speed (PxV);

g) The adverts for the padded bearings in the catalogue show agricultural application, milling machine, saw mill and industrial equipment covered in powder;

h) They also offer the same variety of solutions for padless bearings, just like their competitor in the video I posted, thus it's not an "our" design vs "their" design competition, there are limitations for both designs.

Regarding your guesses:

1) It does mechanically work in the environments they show in the adverts but actual product life is unclear;

2) They offer a large variety of plain bearings, just as their competitors. Also, as shown in the video, PxV for padded bearings is reduced (mind you, PxV ultimately converts to W/m²). Many of the bearings in the catalogue are not a full ring for mechanical reasons, regardless of being plain or ribbed, but the closed bearings are still free to expand in the axial direction. Their rated PxV (W/m²) is a consequence of their thermal performance;

3) Contact is the primary heat transfer mechanism, thus having slots can be detrimental to heat transfer, but without calculations or analysis of a specific bearing, it is safe to state that any benefits to heat transfer remain undecided.

 

[Baluncore]

I watched one ~50min long Igus webinar and downloaded their drylin linear bearings catalogue.

Interesting, please post a link to the webinar.

 

[Tom.G]

As stated in post #4, it is also retrievable at the end of the video in post #2. Scroll the video to the end and the Igus video is presented as the next suggested thing to watch.

 

[john.phillip]

The post above contains the webinar I watched.