PUSH FORCE CALCULATION

[uppili11]

CAN ANYBODY HELP TO DETERMINE THE FOLLOWING MORE PRECISELY:

HAVE A SHAFT OF 4 MM DIAMETER

ASEMBLING A COLLAR ON SHAFT WITH TWO DIFFERENT MATERIALS

BRASS AND STEEL
THE THICKNESS OF COLLAR IS 3MM

THE INTERFERENCE MAXIMUM BETWEEN BRASS COLLAR AND SHAFT IS 20MICRON
THE INTERFERENE MAXIMUM BETWEEN STEEL COLLAR AND SHAFT IS 4 MICRON

WHAT IS THE GENERAL METHOD TO DETERMINE THE PUSH FORCE UNDER ABOVE CONDITION

 

[desertfox]

Hi uppili
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

 

[uppili11]

thanks.will check and give you feedback

 

[desertfox]

Hi again uppili

The formula that I gave you earlier were for obtaining the force required to make the assembly at room temperature.
I would point out that now you have added a temperature range, at the upper temperature of 170degrees C I calculate
that the brass collar will be loose on the shaft as you have
insufficient intereference between the steel and brass.
Brass expands 1.45 times that of steel for the same temperature rise.

exp coeff of steel= 11x10^-6 /K

exp coeff of brass= 16x10^6 / K

where K=Kelvin

You need to base your intereference between your brass and steel shaft on your maximum working temperature.
I can perphaps help you further if you require, but I will need more information about exactly what your trying to achieve.

regards desertfox

 

[desertfox]

Hi uppili

Having re-checked my calculation it appears that there would still be some interference at 170 degrees C however
at this temperature the axial force required to move the brass collar along the shaft would be reduced.

regards

desertfox