Effect of surface finish on coefficient of friction
Effect of surface finish on coefficient of friction
(OP)
I am looking to bolt two steel surfaces (A36) together. Most charts I have found show a static coefficient of friction of .74 for clean and dry sufaces. The surfaces will be subjected to heavy loads that would cause the surfaces to slide against each other. I am limited by the number fasteners that can be used to bolt the surfaces together because of space limitations.
The question is, to what degree would sand blasting (making the surfaces rough)increase the coefficint of friction compared to say s 63-125 micro inch machined surface?
The question is, to what degree would sand blasting (making the surfaces rough)increase the coefficint of friction compared to say s 63-125 micro inch machined surface?





RE: Effect of surface finish on coefficient of friction
In reality, the friction coefficient varies widely. In fact, environmental factors (like relative humidity, accidental contamination, etc.) cause variations that are much larger than that caused by surface roughness.
If there will be no lubricants (water, oil, paint, etc.), then you could use 0.2 as a minimum design number. If there are any lubricants, you should use 0.1 as the minimum.
Of course, you can conduct your own testing. It could be as simple as dragging an object with known mass across the other surface with a fish scale. There is an ASTM standard for this, ASTM G 115 Standard Guide for Measuring and Reporting Friction Coefficients, available at:
http://www.astm.org
Regards,
Cory
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: Effect of surface finish on coefficient of friction
Thanks
RE: Effect of surface finish on coefficient of friction
http://www.esk.com/Products/Ekagrip.asp
Regards,
Cory
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: Effect of surface finish on coefficient of friction
TTFN
RE: Effect of surface finish on coefficient of friction
Nick
I love materials science!
RE: Effect of surface finish on coefficient of friction
Probably not much. Machined surfaces of those typical values can include Planing, shaping, drilling, chemical milling, EDM, broaching, reaming and turning... to name a few.
So really, what size shot in the blaster being a variable, you are not going to gain anything noticeable.
Charlie
www.facsco.com
RE: Effect of surface finish on coefficient of friction
This may be even more pronounced on a joint that is subjected to repeated assembly/dissasembly cycles.
If you really need to know, test your application. Do not rely on handbook values. You don't know how they compare to your application.
RE: Effect of surface finish on coefficient of friction
As Corypad suggests, use a coefficient of friction that is recognised. For in-service conditions a value of about 0.1 is generally used, though what the source is for that I don't know.
corus
RE: Effect of surface finish on coefficient of friction
what is edm ?
RE: Effect of surface finish on coefficient of friction
The italian code (but I guess that similar rules exist in other codes) allows for taking two levels of friction:
0.3 for not specially treated surfaces and for site assembled joints
0.45 for white metal sandblasted surfaces, exempt of any dirt and well done as far as planarity and parallelism are concerned.
Bolt tightening must be to 80% of yield and a coefficient of safety of 1.25 (only) is applied to the calculated transmissible load.
prex
http://www.xcalcs.com
Online tools for structural design
RE: Effect of surface finish on coefficient of friction
Electrical Discharge Machining
Regards,
Cory
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: Effect of surface finish on coefficient of friction
nice to know
RE: Effect of surface finish on coefficient of friction
RE: Effect of surface finish on coefficient of friction
The USA equivalent to his data is from the Specification for Structural Joints Using ASTM A325 or A490 Bolts published by the RCSC, and available at:
ht
It lists three Classes: A, B, and C. Class A is uncoated clean mill scale steel surfaces or surfaces with Class A coatings on blast-cleaned steel, with a mean slip coefficient of 0.33. Class B is uncoated blast-cleaned steel surfaces or surfaces with Class B coatings on blast-cleaned steel, with a mean slip coefficient of 0.50. Class C is roughened hot-dip galvanized surfaces, with a mean slip coefficient of 0.35.
If you want to use surface roughness to improve slip resistance, you really need to test your actual parts and conditions.
Regards,
Cory
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: Effect of surface finish on coefficient of friction
taking a 63 or 125 finish and sandblasting it?
Wouldn't it get finer and smoother?
RE: Effect of surface finish on coefficient of friction
-Andy
RE: Effect of surface finish on coefficient of friction