friction coefficient

[trentar]

Hallo, does anybody knows where to get friction coefficients for different materials used in design (PTFE; PP; PVDF; PFA; TEFLON; VESPEL) or how to calculate them? Suppliers do not give a lot of data,..is there a theory behind to estimate friction coefficient? thanks in advance!

 

[cloa]

Very difficult area when its plastics in contact with anything else- you need the material in contact with the plastic to get some sort of value.

 

[Walterke]

If you ask your supplier he may know.
You can find a lot of charts on google but most of the time they give something like "0.01-0.3" so that's not really helpful.

There are some easy ways to test it though, so maybe you could ask some samples and try them out.

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[imagitec]

Testing.

 

[MintJulep]

they give something like "0.01-0.3" so that's not really helpful.

There are so many variables that are range is the best you are ever going to get.

If you are designing something that relies on friction to work properly, then you need to do your own testing to get your own range.

You need to make sure that your design will work over the full range of possible values.

If you are relying on friction, and you do your design calculations using only a single value of mu, your design in guaranteed to fail.

 

[Cockroach]

There is considerable variation in plastic properties, not to mention coefficient of friction(s). These are thermally dependent and heavily related to quality of the surface finish on the mating parts. So yeah, testing would be appropriate.

You can get some ball park answers from the various websites or vendors pumping out plastics. AT Plastics is one that comes to mind.

Good luck with it, very tricky application.

Regards,
Cockroach

 

[Tmoose]

DuPont seems to be willing to assign values for u for several combinations here, but as others said, I'd not be willing to bet heavily on their absolute accuracy.

http://plastics.dupont.com/plastics/pdflit/europe/delrin/DELLWLFe.pdf

First time I'd seen a "squeaking noise" rating, but maybe I just never looked.

 

[GregLocock]

Any contamination of the surface with water or dirt or squashed spiders will have a big effect on mu. For instance dry PU on PU is up around 1, when I did the experiment which took about 5 minutes. I then sloshed water and kerosene around (it was for a shipboard system) and got a result of less than 0.2.

If your results are at all criticially dependent on the number I think a test is important.



Cheers

Greg Locock


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[KENAT]

Another vote for testing.

Even if you find numbers there are so many variables in the real world that it's difficult to have much confidence that your real world application will match nominal values.

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[chicopee]

If you can do a search on chemical and mechanical engineering periodicals, these values will be published. Also check out some of the latest editions of the Machinist hanbook as there is substantial info on the types of plastic that you mentioned.

 

[izax1]

Yes, definitely testing of you own application if your design relies on friction. And even then, I would apply generous Safety Factors. It is not likely that you will be able to repeat your friction test data. Friction is one of the black holes of mechanical engineering. But with careful design and understanding the limitations, it can be done.