Determining force from displacement on a polyurethane roller

[lardlad00]

Hi all,

I'm working on designing a pinch roller system, and I'm having some trouble deciding how to hold the two rollers together. One roller is 1.5" knurled stainless steel and the other is 1" steel roller with 1/4" of 80A polyurethane bonded to the surface. I would like to use a cam system so that when a lever is turned, the two ends of the polyurethane roller are both pushed down to the steel uniformly. However, I don't know how far to push them. Does anyone know of an equation or another way to determine how much displacement is needed to create a certain normal force, so that I can decide on the design of my cams? I'd like to be able to show my reasoning instead of just guessing at 1/16" or so. Thanks in advance.

 

[sreid]

Would it not be better to spring load the rollers together? You can then control/adjust the pinch force.

 

[lardlad00]

Well, that was what we first tried. The configuration of the whole deal makes springs non-ideal. We're actually having a hard time getting the springs to hold it down tight enough. There's just too much stuff in the way to get a good enough lever on the roller. Thanks for the idea though.

 

[gfbotha]

The knurling is difficult to take in consideration but luckily the effect thereof is likely to be small.

You need to get the modulus value for the PU (I estimate it to be near 8.5 MPa).

One could then probably do some very crude calcs based on F=k.x (there also are Hertz contact stress formulas for cylinders but they are not really convenient for your application).

I would rather opt for FEA in order to get to a F vs disp result. For FEA purposes I estimate poisson's ratio near to 0.495

 

[GregLocock]

http://www.iop.org/EJ/abstract/0508-3443/12/7/305

Cheers

Greg Locock

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