Shrink Fit Recomendations?

[spggodd]

Hi all,

I have little experience with Shrink Fits and was looking for advice on a particular application.

I have a shaft and gear arrangement, shaft and gear nominal dia = 76mm
The arrangement at its maximum operating limits is going to be transmitting 3700 Nm at 4500 rpm with no axial force.

I have been looking at

http://www.cobanengineering.com/Tolerances/ANSIForceFits.asp

and ANSI B4.2-1978 but I'm not sure how my application compares to thier descriptions.

Can someone advise?


Thanks in Advance
Steve

 

[kingnero]

Is there a reason you don't want to work with a shear key?
If I'm correct you're working with about 1.7 MW.

Google lame equations, you'll find plenty of info. even on this site.

You'll need to take radial expansion into consideration, as well as a bunch of other factors.
please share some more info for us to be of any help.

 

[spggodd]

Hi Kingnero,

Shear keys need to be very accurate in order to reduce fretting, inevitably fretting will occur though and the gear and shaft will deteriorate.
I think a shrink fit will be more reliable in the long run.

The application is a gearbox within a closed loop Helicopter Gearbox Test Rig.

I have googled the Lame Equations this looks like a good start for real detailed analysis.
Is there not a way to related a range of applications to a specific type of fit referenced in a standard like ANSI B4.2-1978?

Let me know if you need anymore info.

Thanks
Steve

 

[kingnero]

I'm located in Europe, so I have no idea about ANSI regulations or examples...

with those equations, you should arrive at a first proposition, which you'll need to check for radial expansion, thermal cycles, ...

some links in this thread:

http://www.eng-tips.com/viewthread.cfm?qid=266096

also, engineerstoolbox.com

there was a very interesting thread a while ago about a similar situation:

http://www.eng-tips.com/viewthread.cfm?qid=296062

 

[Cockroach]

In general you are talking 0.0003/0.0006 inches to an interference fit. The hub is typically heated slightly and then placed on the shaft and allowed to cool. Stresses introduced as a result of that interference can be analyzed by Thick Wall Pressure Vessel theory. There is website calculators which do this for you, and interference fit tolerances by class can also be found there or in the various threads in this forum.

Regards,
Cockroach

 

[chicopee]

Any ME handbook have excellent articles on shrink fit, however, I would not use this method. I would use Kingnero's comment on shear key.

 

[mfgenggear]

SPG

for very small parts!!
The length of the shaft required to press & or shrink fit, can become an issue.
if ratio of bore size to length of travel is excessive.
The bore & diameter of the shaft can get scratched or damaged.
The differential difference from cold & hot will seize the parts very quickly.
shrink fitting on small parts is a PITA. but can be done.
just expect higher cost for assembling. & lost parts from rejection.
also do the calcs for expansion of the hub from acceptable heating, & the
contraction of the shaft from freezing. -100 deg F form dry ice or -370 deg from Liquid Nitrogen. or acceptable method.
this will also dictate the limitation of the press possible with shrink fit.
at small dia's there is very little of both.

HTH

Mfgenggear
if it can be built it can be calculated.
if it can be calculated it can be built.

 

[jagad5]

Don't forget to account for stress concentration effects at the shrink fit interface. See Stress Concentration Factors by Peterson, 1974 edition, page 251.

Doug

 

[spggodd]

Thanks Everyone.
Jagad, I will try and get a copy of the book.