Letter 5084

Aluminum bearing surfaces...hardening, ball bearings, Teflon? 

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I am working on an aircraft structure related problem and need some input. First, some general info. Imagine two thin 1/8" thick rings one inch wide (Aluminum), 33" diameter approx, one inside the other, concentric, with the inner surface of the outer ring bearing on the outer surface of the inner ring. Essentially, this is a bearing--they need to rotate around the common axis. I need a low friction (coefficient less than .2), minimal particulate, non-lubricated surfacant of some sort between them.

I have looked at Teflon coatings a little, but here is my concern: there is a fairly good potential of misalignment or thermal effects which would cause binding (not to mention whether these can even be machined round enough). If I were to groove both rings (and maybe thicken the rings and gap between so the surfaces don't directly bear on eachother) and insert ball bearings, what process would harden the aluminum grooves to accept the harder bearings? Input would be great! ly appreciated...

Rob Berger
- Tulsa, OK, USA

Hard anodize that is teflon impregnated might work. Chrome plating will last longer (my opinion) but is very hard to be uniform around sharp corners. Would probably have to be ground afterwards. My idea of best would be 0.0015 of electroless nickel, low phosphorous and heat treated. Boron EN is slightly better, but it costs more and there are less job shops that can do it.

If you are paranoid about lubrication, there are several shops that do Teflon-EN. This is entrapped tiny teflon particles in the EN matrix, so it does not "wear off". This will be a mid phos, but with the extra lubrication, it should not be a problem

James Watts
- FL

We have been having very good success depositing chromium nitride on aluminum surfaces. The coating adheres very well (can't be removed using standard scratch adhesion tests), has a hardness around 2200 HK, and can be deposited at temperatures as low as 120 C -- we put it on 7075 aluminum alloy and found no deterioration of the mechanical properties of the aluminum. In simple wear tests against a tungsten carbide ball it has shown to be around 100 times more wear resistant than 7075 aluminum. Our deposition system is large enough to coat your parts, if you wish to try it.

Jim Treglio
- Gardena, California

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