composite and electrical non-conductive shafting and bearings

[rmetzger]

I have a project requiring the manufacture of two composite shafts and am looking for experience / information in the matter. One can be an off the shelf product as its just acting as a guide rod, the second will be a custom design as it slides along the first shaft and has a piston sliding along its OD as well. Has anyone had any luck with linear bearings operating on composites and any recommendations for shaft suppliers?

 

[sreid]

I have no experience with this but I have given it some thought because I once thought I had an application.

1) There are many suppliers of filiment wound composite tubes.

2) The shafts can be ground but there must be a polymer outer layer so there are not "fuzzys" from the filiment.

3) Plastic can be electroplated with metal.

4) Air beaing bushings from New Way Machine make for a completely non wearing bearing.

 

[MintJulep]

Do the shafts really need to be a composite? It would be much easier to provide a bearing surface on a monolithic plastic material.

A corollary to sreid's point 3 is that metal shafts can be coated with a plastic or polymer.

Does the shaft really need to be non conducting? Would it be sufficient to simply isolate it electrically? There are plenty of plastic linear bearings available.

How does a piston slide on the OD of something?

 

[rmetzger]

MintJulip

The shafts need to be non-magnetic and electrically non-conductive because of the high EMF fields they will be exposed to. Anything than can conduct induced electric current will be a problem - but no you are right, the shafts don't necessarily have to be composite.

The linear plastic bearings are not a problem (igus and the like), its the wear and mating with a non-metallic shaft that I'm unfamiliar with. All I've worked with in the past are coated metallic shafts.

The piston's bearing surface is a shaft that runs through the center of the part. It guides the motion of the piston as the OD has no bearing surface. Picture a disk with a concentric bore moving along a shaft as a result of a burst of pressure on one side. There are no outer walls required as the force to move the piston results from a magnetic pulse.

 

[sreid]

Perhaps this would be cheap to do some experiments. Teflon bushes for the bearing surface?

http://www.mgs4u.com/fiberglass-tube-rod.htm