Interference coupling hub removal - Heating device
Interference coupling hub removal - Heating device
(OP)
Could anyone recommend a heating device (maybe a jacket, belt, etc, and its manufacturer) for the removal of pump coupling that was installed by interference.
The first challnge is that the removal will be in the vicinity of highly flamable fluids/gas. The second challenge is that removal should be fast enough for pump rotor changeout (i.e a fraction of an hour).
I do appreciate responses.
The first challnge is that the removal will be in the vicinity of highly flamable fluids/gas. The second challenge is that removal should be fast enough for pump rotor changeout (i.e a fraction of an hour).
I do appreciate responses.





RE: Interference coupling hub removal - Heating device
RE: Interference coupling hub removal - Heating device
Typically inteference increases with shaft size and the force to pull it off will increase dramatically with shaft size. There are formula's that can tell you how much you have to heat to give a given expected removal force (depends on roughness, areas in contact, interference, and size of the pieces). Recently remvoing coupling with inteference fit on 10" shaft it was very difficult to remove even in the shop. We had to heat the coupling very rapidly (so shaft doesn't have time to warm). I can't imagine trying to remove that hub in the field near explosive gases.
You also need to consider if you pull on the hub what is providing the counterforce (don't pull against the machine)
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RE: Interference coupling hub removal - Heating device
p = Int_diam * E [1- (Rshaft/Rhub)^2] / (4 Rshaft)
where p is pressure, Int_diam is diametrical interference, E is Young's modulus, Rshaft is shaft O.D., Rhub is hub O.D.
Force would be
F = A*P*mu = (2*pi*Rshaft*L) P* mu
where mu is around 0.03 - 0.3 (use the max value to be conservative)
As a rough estimate of the force which would be required under uniform heating, you can assume the inner diameter of the hub expands at coefficient for steel ~ 6.5 micro-Inch per inch per degree F. Although you will probably not be lucky enough to heat the hub uniformly and not heat the shaft at all so make an adjustment...
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RE: Interference coupling hub removal - Heating device
Consideraion is being given to induction heaters, (akin to those used for installing bearings) , to rapidly heat up the hubs to about 120 deg C, and thereafter pull them out from the shaft.
The challenge is to get an induction heater with a configuration that can heat the hub quickly while on the shaft for removal without heating up the shaft.
Your suggestions are appreciated.
RE: Interference coupling hub removal - Heating device
RE: Interference coupling hub removal - Heating device
RE: Interference coupling hub removal - Heating device
Removing the hub without heat is, of course, a function of fit...i.e. how much interference. As previously mentioned, it is also a funtion of size. A large shaft, say >6", could be extremely difficult or impossible to remove without heat.
Use of heat requires heat input as quickly as possible. Typically a couple of large oxy/acetylene "rosebuds". The idea is to remove the hub before the heat reaches the shaft. This means you have to be set up properly and work quickly. When the hub starts moving during the pulling, don't stop the movement until the hub is removed. If you stop, it is likely that the hub will "freeze" and require allowing the parts to completely cool and before another attempt can be made.
As mentioned, stainless on stainless can cause big problems. Galling is likely.
While it doesn't help you now, my suggestion would be to convert to a tapered fit with a nut on the shaft end or go with a hydraulically fitted hub. Either of these setups should not reauire any heat for hub removal. We typically use the tapered shaft arrangement for between bearing pumps which require the coupling hub to be removed for seal or bearing work on the coupling end. We use hydraulically fitted couplings on larger turbo machinery.
RE: Interference coupling hub removal - Heating device
In this case you could fab a thick plate to match the bolt circle on your coupling, install it with a number of high strength studs or long bolts such that there is a large enough gap between this plate and the shaft to insert a short hydraulic ram or pancake cylinder ram. This will require some spacers behind the ram to advance it as the coupling is pulled off. Like any advice in here, use at your own risk.
"If A equals success, then the formula is: A = X + Y + Z, X is work. Y is play. Z is keep your mouth shut."
-- by Albert Einstein
RE: Interference coupling hub removal - Heating device
Mike Halloran
Pembroke Pines, FL, USA
RE: Interference coupling hub removal - Heating device
p = Int_diam * E [1- (Rshaft/Rhub)^2] / (2 Rshaft)
Note the change from 4 in the denominator to 2 in the denominator.
Lindenburg's EIT Reference manual 8th ed had 4 in the denominator.
Shigley's Mechanical design had 2 in the denominator.
Fieldings Programs for Rotating Equipment design had 2 in the denominator.
I double checked all were using radius, not diameter.
2 out of 3 wins. EIT Reference manual must have been wrong.
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RE: Interference coupling hub removal - Heating device
Also you can have the calculation done for you here:
ht
(Scroll down to "C5.13 Design of an interference fit (shrink-fit / press-fit / expansion-fit)")
They also have an adjustment for heating/cooling required during mounting.
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RE: Interference coupling hub removal - Heating device
We heat to remove couplings all the time.. saves scoring the shaft.. But.. the secret is lots of heat fast..The idea is to heat the coupling and not the shaft..Once the shaft heats up you loose the advantage.
Have a puller arangement that will pull the full length of the fit (you do not have time to re-position your pulling equipment.. Apply a "moderate" force and heat rapidly.. Keep heating for a few seconds after the coupling starts to move.. "then" apply more jacking power and you should have a clean removal..
Most folk just don't appreciate the size of the torche(s) to heat the coupling.. a cutting torch will not do it..
RE: Interference coupling hub removal - Heating device