Formula for force requred to extract a bushing from a pulley

[MaddMax]

Hi,
I am looking for a formula to calculate the minimum force required to pull a press fit bushing from a pulley.
Thx,

 

[israelkk]

This depends on the actual fit which is the result of the dimensions and tolerances of the bushing and the pully's bore. It is also depends on the material combination of the bushing and the pulley which determine the coefficient of friction between the pulley and the bushing. Without this information there is no way to calculate the force.

 

[MaddMax]

Clarification:
I have the dimensions for the interference fit(0.0005in) and a good estimate of the coefficient of friction(u=0.20) as well as the nominal dimensions of the bushing and pulley. I just can't find the formula to calculate the force to pull. Assuming I have the interference & the coefficient of static friction, what would be the formula for force required? Would I just calculate the pressure(P) and divide that by the area(A) to get the force(N) and plug that into the formula for the Friction force(F) F=uN?
Thanks

 

[israelkk]

Any machine design book such as from Shigley or the Machinery Handbook has the formula. If you can calculate the force then "Multiply" it by the circuferential area and then by the friction ciefficint.

 

[desertfox]

Hi MaddMax

Here are the formula you need:-



Pa= f*3.142*d*L*Pc

where f=friction coefficient
Pc=contact pressure between the two members
d= nominal shaft dia
L=length of external member.
Pa= axial force required to interference fit
to calculate Pc for a given interference use the formula:-

Pc=x/[Dc*[((Dc^2+Di^2)/(Ei(Dc^2-Di^2))+....................
((Do^2+Dc^2)/(Eo*(Do^2-Dc^2))-((Ui/Ei)+
Ui/Eo))]



where x = total interference
Dc=dia of shaft
Di = dia of inner member(this is zero for solid shaft)
Do= outside dia of collar
Uo=poissons ratio for outer member
Ui=poissons ratio for inner member
Eo=modulus of elasticity for outer member
Ei=modulus of elasticity for inner member

This formula for Pc will simplify if the materials are the same.
Hope this helps

regards desertfox

 

[ccw]

It is not clear from your requirements if you are looking for the minimum force, ie. the dependable no slip performance of the bushing restraining forces, as one might consider if using the pressed bushing for a thrust bearing or combination thrust and journal; or if one needs the force to size a ram to extricate the bushing. If the latter, then it seems a simpler equation would be:

Fram = (greater than or equal to) pi*D*H*Shear.

where pi = 3.14
D = O.D. of bushing
H = length of contact engagement in pulley
Shear = ultimate shear stress of bushing material.
particularly if the bushing material is softer than the pulley parent material.

 

[MaddMax]

Great stuff, thanks all