Estimating break-away force for an interference fit?
Estimating break-away force for an interference fit?
(OP)
I have a 45mm ball bearing shrink fitting onto a 303 shaft.
The ball bearing has an ID of 45mm at P6 tolerance.
The shaft has an OD tolerance of k5 as recommended by the bearing manufacturer (SKF).
This makes for an interference of:
maximum = 0.013mm
minimum = 0.002mm
How can I estimate the torque to break away this interface?
What should I use for friction coefficient?
steel-steel = 0.80?
Are there tables for these kinds of fitments?
Thanks.
The ball bearing has an ID of 45mm at P6 tolerance.
The shaft has an OD tolerance of k5 as recommended by the bearing manufacturer (SKF).
This makes for an interference of:
maximum = 0.013mm
minimum = 0.002mm
How can I estimate the torque to break away this interface?
What should I use for friction coefficient?
steel-steel = 0.80?
Are there tables for these kinds of fitments?
Thanks.
Beat to fit, paint to match.





RE: Estimating break-away force for an interference fit?
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Estimating break-away force for an interference fit?
where
f = static coefficient of friciton
A = 2*pi*r*L
Pc = given in the FAQ above
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RE: Estimating break-away force for an interference fit?
Typical mu for steel on steel is around 0.2-0.3. This is what I use when calculating press fits for bearings and it agrees pretty well with the measured insertion force.
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: Estimating break-away force for an interference fit?
ex-corus (semi-detached)
RE: Estimating break-away force for an interference fit?
or
http://www
These are usually simplifications of Lame's equation considering plastic deformation.
You must also consider the burst stresses and deformation consequences (ie if an internal (female) thread for a flange bolt is going to exist on an internal diameter of the shaft).
A lot of this is best done in FEA to confirm the calculator results.
Poisson's for steel: 0.3
coeff. friction steel: 0.2-0.3
(depending on surface finish, search online for data)
modulus of steel: 200Gpa
Yield: 50Mpa
(depending on carbon content/quality)
RE: Estimating break-away force for an interference fit?
I didn't know about the FAQ, that's pretty handy.
Greg & corus, the friction coefficient information is very helpful.
Gopher, I was actually just looking through the equations that calculator uses. This led me to the NTN bearing website, and this handy "Rolling Bearing Handbook"
htt
It looks like that has most of the information I need.
Thanks again.
p.s. I also just read the "rules" that mention performing internet searches and FAQ searches before asking questions. Oops! But then again, what else would we be talking about around here!
Beat to fit, paint to match.
RE: Estimating break-away force for an interference fit?
Tmax = 300Nm @.013mm interference
Tmin = 50Nm @.002mm interference
Tavg = 180Nm @.0075mm interference
Does that sound reasonable?
Beat to fit, paint to match.
RE: Estimating break-away force for an interference fit?
x/[Dc*[((Dc^2+Di^2)/(Ei(Dc^2-Di^2))+((Do^2+Dc^2)/(Eo*(Do^2-Dc^2))-((Ui/Ei)+Ui/Eo))]
Should it read?:
x/[Dc*[((Dc^2+Di^2)/(Ei(Dc^2-Di^2))+((Do^2+Dc^2)/(Eo*(Do^2-Dc^2))-((Ui/Ei)+Uo/Eo))]]
???
I attached a .JPG of the equation in question.
Beat to fit, paint to match.
RE: Estimating break-away force for an interference fit?
NTN = 29.2 Nm
Then I used the tribology calculator here:
ht
And I got:
Trib calculator = 29.2 Nm
Which makes sense since NTN equation assumes a steel shaft and a steel collar, so the Poisson's ratio's etc cancel out.
Beat to fit, paint to match.