Plastic-plastic friction vs. plastic-steel friction

[gravesity]

I am redesigning a micro-hydro educational tool that is essentially a Pelton wheel runner spinning in a polycarbonate enclosure. Our current design uses a steel axle spinning inside a boss in the enclosure.

We're considering changing that to a polycarbonate axle so we can reduce our part count and simplify the design. I theorize that we are going to see more friction with the new design. I've tried to find representative friction coefficients on the web but can't seem to find what I need.

Presumably, resin manufacturers are reluctant to list specific coefficients for their materials, since friction varies with texture, etc., but I'm just looking for ballpark figures, for feasibility. So does anybody have representative dynamic friction coefficients for:

1) Polycarbonate - Polycarbonate, and
2) Polycarbonate - Mild Steel?

Bonus points if these values reflect the materials being wet!

In the absence of numbers, intuition-based responses are welcomed.

 

[MikeHalloran]

Polycarbonate on polycarbonate is not going to be very good.
Acetal on polycarbonate may be a better choice.
Also take a (close) look at the bearings using pointy axle ends on model railroad car trucks.



Mike Halloran
Pembroke Pines, FL, USA

 

[chicopee]

Is the wetness for lubrication and cooling?

 

[gravesity]

Hi Chicopee,

This is a water turbine; the enclosure is consequently full of water splash. No need for cooling, but any lubrication effects will be bonus.

Thanks!

 

[Pud]

Polycarbonate (unless filled with stuff) is probably just about the worst material for a bearing. PC on PC is probably the worst.

H

http://www.tynevalleyplastics.co.uk

 

[asimpson]

Check out IGUS for plastic bearing data. I know adding a bushing increases part count, but it is a simple and reliable solution.

 

[stanier]

Non metallic bearings have ben successfully made in Paxolin. A reinforced resin. This material is water lubricated.