Quantifying the effects of grease on friction factors

[bmmrfn]

I am a recent graduate, and while I do have internship experience performing structural analysis I am rather new to the industry. My problem is that I have a joint connecting two cylinders and need to find the friction between the two surfaces to perform the analysis. I know the two materials and have found the friction between them. Yet the joint has grease applied to each mating surface and I am having trouble estimating the effects this grease has on friction.

Any standards or analysis that would get me moving in the right direction would be greatly appreciated.

Regards

 

[MintJulep]

Test it.

Gravity and a tilting table are all you need.

 

[GregLocock]

Yes.

Friction is one of engineering analysis' dirty little secrets. Oftentimes you'll get away with using the worst case book value. One day you'll do that and make an expensive (or dangerous) mistake. So, you end up measuring it.

Most recently I can think of a 2 million dollar recall that was due to a friction estimate that was incorrect.

If it is impractical to measure it run the analysis at 0.1, 0.3 and 1 . Take the worst of those three. Be aware that those are not the bounds of frictional behaviour, but you are dead unlucky to go outside them with steel, oil, water wood and crude plain bearings. Obviously designed bearings, or anything involving water and ice, or air, can be much less, and anything involving rubber can go much higher.


Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[chicopee]

Get yourself a Machinery's Handbook and you will find the coefficients of friction that you are seeking. For lubricated surfaces the numbers will range from .04 to .35 depending on material. If you are looking for formulae on disk friction get a statics and dynamics book.

 

[CoryPad]

Here is a good introductory standard that references many other standards to perform testing:

http://www.astm.org/cgi-bin/SoftCar...astm.org/DATABASE.CART/REDLINE_PAGES/G115.htm

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[bmmrfn]

Thanks for your input, I have been reading these forums during college trying to gain knowledge and now that I can make posts it is a great resource to have.

Thank you.

 

[Shmulik]

http://www.roymech.co.uk/Useful_Tables/Tribology/co_of_frict.htm