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Coefficients of friction Question
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Posted by: AdrianT

11/13/2006, 05:15:01

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Hi there,

I'd like to know what values for the coefficient of friction for steel sliding on steel one would typically use in the design of something. The value seems to vary quite a bit. From 0.74 (static) and 0.57 (sliding) right down to 0.15 (static) and 0.09 (sliding).

Another source says to use values for static friction between 0.6 and 0.15 and to use values for kinetic (sliding) between 0.09 and 0.6.

These are all used in the simple formula F = *N

But when it comes to rolling friction, there is another approach with, once again, varying values. F = f * W/R. W the weight of the cylinder, R the radius and f the rolling coefficient of friction. Sources say to use a value of f of 0.0005m for steel rolling on steel. Is this correct?
Yet another formula is F = Crr * g * m. Using values of Crr. I have not come across these before but I see there is an example of 0.0025 for train wheels, steel on steel. g being 9.81 and m the mass in kg. Does anyone know more about this formula?

Which of the above formulas would result in satisfactory results for rolling friction?
Any responses would be appreciated. Thanks

Cheers
Adrian








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Re: Coefficients of friction
Re: Coefficients of friction -- AdrianT Post Reply Top of thread Forum
Posted by: Kelly Bramble

11/13/2006, 07:55:32

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AdrianT, the coefficient of friction depends on many attributes. Surface roughness, flatness, surface area, weight or pressure between the plates or other. Depending on your design or functional requirements, a good practice is to use the estimated value limit. For example, if you are designing for a hyraulic actuator which must over come the friction between the two objects, then design for the highest coefficient of friction plus a FS.

Ultimately, none of your equations may be satifactory in determining an accurate coefficient of friction. If your can, I would test your particular application to determine the typical coefficient of friction.








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