Fully Ceramic Linear Bearings vs. Roller Bearings

I'm confused (easily done). Do you want a linear bearing or a rotary bearing?

First off a linear bearing and a roller bearing are not bearing for the same type of application. A linear bearing is design to move up and down the shaft in a linear direction not around the shaft in a radial direction as a roller bearing does. The linear bearing will have some radial movement but should not be used as such.

I have been fairly impressed with the performance of self lubricating (made of some specialty polymer) linear bearings from a company called IGUS, I believe their max operating temp is somewhere in the 160C range. There are MANY manufacturers making both roller and ceramic/polymer self lubricating linear bearings. Some things to take into account are the rod material, linear speed, loads, temp, contamination, moisture, among more. From my experience, choosing either a self lubricating polymer/ceramic bearing versus a standard roller all depends on your application. Contact some manufacturers and work with their engineers to help you decide what is best for your application.

Okay, I understand the difference between the two types of bearing now; but even so, logically there is no reason [that I can think of] why there can't be in effect a series of roller bearings [for radial loads] in one case that would do a similar job to roller bearings. Do they exist? If not, then this is going to be a very short discussion

Does anybody have any information on the reliability of full Silicon Nitride [Si3N4] roller bearings in the range of 25-45 mm external diameter, 10 mm roller length upwards?

There are linear bearings suitable for rotary as well. The radial loads, I think I remember, have to be moderate. I don't remember manufacturers, but you're on GlobalSpec; search away.

Bearings Reference Guide:

http://www.bearings.machinedesign.com/

Thanks the link. They only seem to do steel and hybrid. I'm in manufacturing heaven here in China The ceramic bearings in the picture are made in Shanghai. When I checked comparable bearings here, they were $25, in the US they were $69 and I bet the US ones come from China too

Presumably multiple balls are tougher than a long roller but obviously have less contact area.

The reason for using a roller bearing vs a conventional ball bearing is greater radial load capability, for the reason you mention (load spread out along a line rather than at a point). The linear bearings you show accept a radial load, and permit linear (axial) motion. They are not used for the same purpose as a roller bearing. Roller bearings should not routinely be subject to linear motion, and linear bearings should not routinely be subjected to rotary motion.

Ceramic roller bearings are available, as are polymer rolling element bearings. Torlon balls or rollers are used in polymer bearings where high load capability is required. Delrin is typically used where loads are lower. (Races can be aluminum or stainless steel.) 150C is probably too high for either Torlon or Delrin, however.

In any case, if you want the shaft to rotate, then you should be looking for a roller or ball bearing. (Needle bearings are a variation of roller bearing in which the rolling elements are long and thin. Often, a needle bearing does not have an inner race, and uses the shaft itself as the inner race: this usually means the the shaft material and finish must be more carefully designed.

Many thanks to the information.

I'm getting very close to finding the manufacturers of the best fully ceramic roller bearings in China, so I will be able to see what is available off-the-shelf and go from there. Hopefully the companies will be able to provide all the technical specification information needed to select the most appropriate bearings. If fully ceramics don't work in the design then nothing will! If they do work then it may be time to experiment with substituting cheaper hybrids or even those old-fashioned steel things