Simple one this 1

[eski1]

Hi
Just a simple question from a simple guy
If you heat a metal donut shape , like a gear does the internal diameter get bigger or smaller . For instance if you had a gear on a shaft does heating it make it easier to get of or harder .Or would it be easier after heating once the gear has cooled down
Cheers
Chris

 

[metengr]

eski1;
As heat is applied uniformly to a metal gear, the gear should expand in each direction, which means the bore will increase in size. This should enable you to remove the gear during the application of heat, if the gear was installed using an interference fit.

 

[ko99]

As someone on another forum mentioned, think about the material that was removed to make the hole - it would increase in size just as the hole would incease

ko (

http://www.ecooling.biz)

 

[25362]

Visit also
thread330-36510
thread404-54501

 

[thermcool]

Definately, heating the gear will make easy take off due to the thermal expansion of the material on application of heat.

 

[JStephen]

One of the tricks of removing stuck lugnuts is to heat the nut with a torch. In case impact wrenches, hammers, lug wrenches, and cheater bars in various combinations don't work.

 

[katmar]

The way something expands when heated is just the same as if you enlarged it optically with a lens. If you think of it this way it is easy to predict what will happen to any particular dimension.


Katmar Software
Engineering & Risk Analysis Software

http://katmarsoftware.com

 

[eski1]

Thanks for the replies
Do you get to a point when the heat has transfered to the shaft and that expands as well
Its just it seems in practice that heating it can sometimes make it worse

 

[Montemayor]

Although not educated as a Mechanical Engineer, I was blessed to be raised and trained as a Boilermaker before I became an engineer and later had the world’s greatest engineering mentor when I started out as one. I am pleased that metengr and katmar have expounded on the very important and practical points: It’s how evenly and where you heat an object that allows you to do so many important and critical mechanical jobs:

1. An interference fit (I think this term should be firmly imbedded in every engineer’s ROM) is how a new cylinder liner is inserted into a car engine, into a reciprocating gas compressor, into a hydraulic press, etc., etc. I consider this technique to be one of the most critical gifts that God or nature has given us to do the important engineering jobs we carry out in industry.
2. It is also the way a critical impeller or wheel is fitted onto a shaft, using the reverse thermal effect: you immerse the object into a bath of supercooled fluid – alcohol with Dry Ice added.
3. A millwright uses this method to fit a critical coupling or a gear (as has been inferred). In some applications alignment and stability is vital and the need to have a shaft and coupling/gear function as if they are one homogenous component is very important.

But with the same simplicity, a critical component can be damaged or totally deformed if an engineer does not take into consideration that the METHOD, TECHNIQUE, RATE, and CARE of the application. My wife knows this and often applies the same criteria when she has a difficult and frozen peanut butter jar with a screwed cap that won’t budge. She simply immerses the cap (with the jar upside down) into hot water and the result is that the cap evenly expands and she can easily unscrew it.

The important points to remember are those inferred by metengr and katmar: always apply the heat in an engineered, evenly distributed manner that will produce the reversible effect that you expect. Otherwise, you can easily deform or ruin an object. There are experienced and trusted experts who do this type of fit as their business because it takes craftsmanship and engineered care to do it successfully on critical equipment. If that is the application, those are the type of people who should do the job.

 

[logoslarry]

When I was in the Navy we used an induction heater to expand bearings to fit on shafts. If in a hurry cooled down with a CO2 extinguisher. Not the best way but it does work.

When heating gears, shaft couplings etc to remove them take your time and do it slow and easy. Keeping the shaft relatively cool helps.