Rigid coupling design - friction of bolted shaft flanges 3

[crazyjpeters]

I cannot seem to find an answer anywhere, so I'm hoping some bright individual will be able to enlighten me.

I'm analysing a large machine shaft coupling, which is a bolted flange design, clearance bolt holes (not fitted bolts), where torque is to be transmitted through friction of the faces. This is augmented through a friction modifier (more on this later).

Can anyone point me to a formula which calculates the torque capacity based on number of bolts, bolt force, type of coupling material (static friction factor), etc.

The only meaningful formula I can find is supplied by Loctite, but I'm not entirely sure it is correct. It is stated as follows:
Torque capacity = Mechanical contribution + Adhesive contribution, with details on their website at:

http://loctite.fast.de/wwdh/us/i143ch08.htm

I know I've seen a similar formula without the adhesive contribution, but can't seem to locate it.

I'm up to my eyeballs in formulas and handbooks that seem to ignore friction of bolted joints as a torque transmission tool. Apparently fitted bolts are the only way to do it, so my machine is destined to end up failing.... :-(

 

[rb1957]

agreed, a longer bolt stores more energy, but that doesn't seem to affect this design app ... i'm assuming crazyj is bolting together two flanges, a relatively solid, inflexible joint (not an app where the bolt will be releasing this internal energy "like a leaf spring")

 

[desertfox]

Hi rb1957

Yes I agree with you in this apparent application maybe the OP can shed some light on what he means

 

[crazyjpeters]

Whoa, you guys don't need to analyse it for me, but thanks for the good discussion.

The OEM actually hasn't left much of a SF by my calculations, but then this is actually a francis turbine mounted to the other end of the coupling, and there is a fairly large upward force generated, which should create even greater friction.

It's in service already, and everything seems to be working fine, so this is really just an excercise.

 

[rb1957]

not so sure an "upward" force creates more friction ... how is the flange oriented (horizontal/vertical) ?

but you're happy so that's good enough for me ...

 

[desertfox]

Hi crazyjpeters

Were not trying to analyse it for you, you're quite capable of doing the calculations, however if all the informaton you have is given in one or two posts we can advise you and point out possible problems but we need the full story.
If the studs/bolts see axial load as well as torsion then your comment on longer studs may well be valid although if the OEM designed the original fixings then its probably not a problem.

How long as it been in service? it might fail shortly quick fixes usually come back to bite you and from your previous posts that is what it seems to be.

desertfox

 

[tbuelna]

crazyjpeters,

There are some design/analysis standards for your particular situation. A common one is VDI 2230.

Here's a link to a summary of VDI 2230:

http://www.hexagon.de/rs/review design guideline VDI2230fda.pdf

 

[hydtools]

tbuelna, please call your reference what it really is; a guideline, not a standard.

Ted

 

[tbuelna]

Ted,

Thank you for your correction. It is indeed a "guideline" and not a "standard".

Just as instructive for crazyjpeters none the less.

Terry

 

[hydtools]

None the less.

Ted