Friction coefficient between SS and PTFE

[Patafian]

Recently I came across a couple of pipe stress calculations with very low friction coefficient used for SS on PTFE pad.
Those coefficients varied from 0.05 to even 0.01. I started to look what teflon sliding pads vendors reccomend in their specifications.
I found one German producer who gives eksperimental coeff. 0.016 and design 0.017 for surface load 25 N/mm^2. For lesser looads coefficient is of course higher and ends with values 0.045 experimental and 0.06 design for loads 1.5 N/mm^2.

I never used friction coefficient less than 0.05 in my calsc, so I'm a little bit confused.

What is opinnion of forum members.

 

[IRstuff]

see response from Q_Goest on

http://www.physicsforums.com/showthread.php?t=505767

however, the only data presented anywhere is ~0.04

and

http://wisdotresearch.wi.gov/wp-content/uploads/WisDOT-WHRP-project-0092-08-13-final-report.pdf

not sure how applicable this report is to your specific problem.

TTFN
faq731-376

 

[TomDOT]

Well, it's bridges again instead of pipeline - but there is a nice table in the AASHTO LRFD Bridge Design Specifications (Table 14.7.2.5-1) with different teflon types, temperatures, etc. The discussion starting at 14.7.2.5 is also useful.

 

[Patafian]

Thanks for for info.
I have no access to AASHTO Specifications.

IRstuff

Engineering ToolBox lists strange coefficients.
For example steel on steel - 0.8

Also here

http://hypertextbook.com/facts/2005/steel.shtml

I can't find familiar value of 0.3.

Am I in a parallel Universe???

 

[BigInch]

Quite possibly perpendicular.

"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek

 

[TomDOT]

Just noticed you're Mechanical. ASME members should have access to the AASHTO specs online through the e-Library

http://www.asme.org/about-asme/membership/professional-membership/asme-e-library

 

[IRstuff]

As they always say, "Your mileage may vary." Friction coefficients are highly dependent on the material and the surface properties, including contamination or purposeful coatings. Without doing an exhaustive analysis of the data, it's not possible to determine the applicability of any given set of values to whatever it is that you are doing. You should use whatever works for you, assuming you have real data to compare against.

Note also, numbers used in calculations are often unrelated to values that might actually be observed in real life. Your low value might be for a particular analysis case, be it worse or best. This will definitely be different than the published values, which are supposedly more like mean or median values.



TTFN
faq731-376

 

[stanier]

What you need to consider is that the coefficient fo friction is in the limit state. ie The surfaces are just about to move relative to each other. So your load may actually be higher than when the surfaces are moving. The coefficient quoted is generally when the surfaces are moving.

Teflon is a trade name. To support a load TFE needs to be filled with glass or other mineral. If not the TFE will extrude when under load. The composite has different values compared to pure TFE. This explains the variation in coefficient of friction quoted in industry.

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---B.B. King

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[TomDOT]

And all of these factors (plus temperature) is the reason I suggested a table rather than a single design value. The values in the AASHTO table range from .02 up to .65