How effective are materials for good wear in a dry-running air motor?

[Mike_In_Plano]

Hello,

I'm puzzling over the likelihood of building a dry-running air motor for 25khrs @5-20kRPM.

I'm considering whether a small gear pump arrangement would doe the job - it only needs to output 6 shaft watts, but I'm concerned about wear.

Standard gears are avalable in steel and delrin, and with a bit of searching, in ceramic. I'm wondering what would be a good combination of materials between the endplates and gear. It seems that the endplates would have to be under a bit of compression to ensure that the air leakage doesn't become excessive over time.

Does this seem a reasonable conjecture?

It also seems the endplates would be a complimentary material:
Steel vs teflon loaded delrin plate
Ceramic vs teflon loaded delrin plate
Delrin vs Hard steel

Finally, how would one go about accelerating wear testing?

Well, I guess that wraps it up (and then some :)

Best Regards,

Mike

 

[Unrest]

The bearing material makers often have data sheets showing wear rates. Tho it can depend on speed as well as pressure and countersurface material. They may just show a few data points and leave you to guess the rest.

I see Dupont has a lot of leaflets online about Delrin's wear characteristics.

I'm kind of amazed at running a gear pump so fast. You can't use a centrifugal pump? You'd avoid a lot of the sliding sealing surfaces.

 

[Enthalpy]

You have no single chance with a dry plastic bearing at 25,000/min. It would melt.

In case this is a matter of vapour pressure, some lubricants have an extremely low one. Use with plain bearings of sintered metal.

You may try with unlubricated ceramic ball bearings.

An other direction is magnetic bearings.

Or could you maybe use the pressurized air in a set of "aerostatic" bearings? Similar to hydrostatic ones, with big leaks, connected in series with your engine?

 

[Enthalpy]

Thinking again at the aerostatic bearing...

Let's imagine your engine can be a centripetal turbine (you didn't mention that). Then you might inject the air at the periphery, use some of its energy contents to rotate the turbine, and let the air exit through the shaft at the bearings, where the remnant pressure gives lifting and centring force.

Maybe it doesn't fit your needs, but it's puzzling.