EXPERIMENT

[nifez]

Hey guys gonna be doing a study into the effects of surface finish (abraided and non-abraided)on the frictional characteristics between aluminium 7075, and Polyurethane(1.4u)
in dynamic conditions.
Any info on experimental techniques would be greatly appreciated

 

[rnd2]

nifez
Dry or lubricated condition?

 

[nifez]

rnd2
Dry conditions

 

[rnd2]

Don't know your sliding speed range. Polyurethane won't handle high sliding speed and no lubrication. High speed as well as load can rapidly raise surface temperature above the mp of polyurethane. So you will need to pre- determine your load and sliding speed range. As a quick general background, hard surface -v- soft surface and what may happen at high sliding speed you might want to look at thread342-92753.
Assuming you intend to work with relatively light loads and slow to dead slow surface speeds, I doubt that surface finish will make a huge difference to dynamic friction, once bedding in has occurred.

 

[nifez]

Thanks rnd2 really appreciate that info, i cant see it having a big effect either.
Might as well be bold and ask you if you could suggest a speed range, got a presentation next week and am struggling to find any sources.
Thanks

 

[rnd2]

This website may assist with basic comparisons. It at least gives you a base friction co-efficient for natural polyurethane of 1.26 static and 1.14 dynamic according to ASTM 1894-90. Unmodified, not a good dry sliding material, but improves with lubricity additives, in this case 0.42 and 0.3 respectively and a useful direct comparison can be made, as apparently the same ASTM test standard was used.

http://www.fostercomp.com/specs/042501_Low_Friction_Urethane.pdf

Like many plastics, material characteristics vary as each manufacturer strives to develop properties to enhance their product.
Speed and load wise? Hmmm.
We are currently testing bone dry bearing material brand XXXX (not polyurethane).
Shaft speed is 44 rpm
Shaft dia. is 55mm
Bearing length is 110mm
Bearing load is 15 Kg
This load and speed is not particularly onerous for this particular material, and each 200 hour period the load will increase with 5 Kg increments until failure. BUT, I doubt that unmodified polyurethane could cope even at the modest 15 Kg load and shaft speed.
So, best guess, a continuous rotating shaft surface speed of approx 0.04 m/s, a bearing pressure of approx 0.052 MPa or 7.5 psi might be just be too much for natural polyurethane.
Hope that helps.

 

[EdDanzer]

You might want to compare a burnished finished to a ground finish.
The P/V value should be documented.