Formula for 'pinch bolt joint'
Formula for 'pinch bolt joint'
(OP)
Does anyone know the formula or process for relating bolt tension to the nominal internal pressure when clamping a bore to a shaft using a pinch bolt.
I have looked through text books and can't seem to get the relationship to work. There must be a way of relating the bolt tension to hoop tension and therefore stress. From which it is possible to determine the internal pressure.
Any ideas??
I have looked through text books and can't seem to get the relationship to work. There must be a way of relating the bolt tension to hoop tension and therefore stress. From which it is possible to determine the internal pressure.
Any ideas??





RE: Formula for 'pinch bolt joint'
RE: Formula for 'pinch bolt joint'
I have divided the bolt tension by the Cross Secton area of the outer cylinder, this gives me a mean hoop stress If I assume this hoop stress is mid distance through the outer cylinder I can then determine the internal pressure maintaining equilibrium this is at the outer cylinder/shaft.
For simplicity it is reasonable to assume zero deflection of the shaft and that the fit is zero gap prior to bolt (pinch) load. I think this gives me a reasonable estimate.
Does this seem reasonable anyone??
RE: Formula for 'pinch bolt joint'
Andreas
RE: Formula for 'pinch bolt joint'
RE: Formula for 'pinch bolt joint'
The joint is best described as follows.
A component has a machined bore which fits over a shaft, for argument sake there is no difference between bore and shaft diameter and the shaft is solid. The component(which is cylindrical) has a slot machined through one wall in the axial direction. There are 2 lugs attached either side of the slot. A bolt is tightened through these lugs producing a reduction in bore diameter and hence producing a clamp load between bore and Shaft. The relationship I need to identify is the bolt tension vs clamp load or average contact pressure between shaft and bore.
I don't know what type of joint this is called.
RE: Formula for 'pinch bolt joint'
Let us say that a torque Mt is the outer force to withstand than we need a frictional-torque Mr which has to be produced by the clamping device (bolt). So the force pressing against the shaft has to be:
Fn > Mt/d/mu
d=diameter of the shaft
mu=friction coefficient between shaft material and component material
the Force in the bolt You need is:
Fb > Mt*l1/l2/d/mu
l1=distance between midpoint of shaft and its maximum outline point
l2=distance between midpoint of the bolt and mamximum outline point of the shaft
surface pressure has to be controlled by:
pm = Fn/d/L < pzul
pm=surface pressure
L=length of bore the shaft fits in
pzul=allowed surface pressure for the worst material in the system
I think that is all You need for the calculation.
Andreas
RE: Formula for 'pinch bolt joint'
Can I clarify a few points
are l1 and l2 radial dimensions? and when you mention shaft outline dimension do you mean Outside Diameter?
For a given bolt load are you saying Fn=Fb*L2/L1?
In my calculations this always gives a smaller Fn than Fb, I thought pinch bolts work the other way round? You get a higher normal load for a given pinch load.
I think Fn> Mt/(d/2)/mu ?
Do you know of text where I can find this?
Chris
RE: Formula for 'pinch bolt joint'
the calculation is out of "Maschinenelemente" from H.Roloff und W.Matek, edition 1976, page 280/281. It is a German book dealing with all kinds of machine parts and their calculation.
Fn can´t be smaller than Fb because l2 is more than 2*l1 in the example drawing here. Send me Your email and I will make a pdf-file of the two pages for You. That´s better than any explanation.
Andreas
mail@waffentechnik.com