Thread: Thermal shrink fit

Originally Posted by Michael G

Does the OD of the sleeve need to be smaller? (I was wondering whether due to the thickness of the sleeve the ID is expanding inwards)

Michael

Hi Michael,
Can't help with the problem but i am 99% sure that it doesn't matter how thick the steel is the bore gets larger. Cut the ring and flatten it out (in your head) then add 1% (just for easy maths) expansion.....the inside surface gets longer so the bore must get bigger.

Hi Michael,
There are tolerance charts for shrink fits. I always pack the shaft in ice before shrink fitting.

Phil

Micheal I have done this before, If I remember correctly machinery's handbook has a chart for your
interference size tolerances for the diameter you require.

200 C should be adequate and it also doesn't hurt to put the inner part in the freezer for a while.
Heating to red would probably distort your good work.

john

edit.... haha, phil you read my mind and typed faster, do you use two fingers ?

I think this is it Micheal

http://www.google.com.au/url?sa=t&rc...efDfxA&cad=rja

Originally Posted by Michael G

(I was wondering whether due to the thickness of the sleeve the ID is expanding inwards)

Michael

I had a chuckle over that one Michael. My old physics teacher would have slapped me over the head for saying something like that Don't you remember the old ring and ball on a chain thermal expansion exercise kids at school got to do ?

Metal holes always get bigger as they heat up - end of story.

I've sweated on plenty of stuff over the years and yes 5 thou is way to much for something that size. 1 thou should be enough if your measurements are right.

Best way is to heat the sleeve up and press it on. If it starts to bind just keep heating it some more and keep pressing. It will stretch on. You will have to machine it afterwards regardless, due to distortion.

Putting the smaller component in the freezer is a good idea, but you have to act fast when putting it together or it will lock half way on.

That method is great for replacing cylinder liners where you have two different metals where the outer expands more than the inner, eg steel and aluminium.

But when you sweat together similar metals it's not so easy as they have similar thermal properties and you won't get the same degree of clearance.

Sweating similar metals together also works better where the outer component (sleeve) is thick as it will not stretch and lose it's tension as much when it cools down.

You may be better off using loctite to hold a lightly fitting sleeve much the same way as for a Speedie seal.

Or given that bronze and brass have a higher coefficient of expansion than steel, make your sleeve out of one of those and it should stay put when everything cools down.

See the table at link below:

Thermal Expansion Metals

Cheers

Rob

Originally Posted by shedhappens

edit.... haha, phil you read my mind and typed faster, do you use two fingers ?

Yes John I have just graduated to two fingers. I tried to use my little finger on my left hand to hit the 'A' but kept hitting the caps lock which started me shouting. Dropped that one now and am back to two fingers.


One thing I also have done with shrink fit is heat the parts up in oil. The sparkies at work wired up a pot with a thermostat on it and it worked a treat.

Phil

interesting............what temperature roughly Phil ?

Originally Posted by Steamwhisperer

Yes John I have just graduated to two fingers. I tried to use my little finger on my left hand to hit the 'A' but kept hitting the caps lock which started me shouting. Dropped that one now and am back to two fingers.


One thing I also have done with shrink fit is heat the parts up in oil. The sparkies at work wired up a pot with a thermostat on it and it worked a treat.

Phil

Nice trick Phil, zero oxygen = zero oxide. Thats why vacuum furnaces where made for hardening, but they are a little beyond the average back shed.

Originally Posted by shedhappens

interesting............what temperature roughly Phil ?

Hi John,
I couldn't tell you other than number six on the dial (rheostat??)
It was too hot for welding gloves which is kinda' obvious.
I made the pot out of a piece of steel pipe about 6" diameter and had a coil in the bottom like from a jug.
About the only thing to make sure of was not to boil the oil and to suspend the piece to be heated on a piece of wire.
If the piece touched the side of the pot it would locally overheat in that spot.
Sorry I couldn't be much help. It's been a long time since I used a pot shrink fitting.

Phil

Originally Posted by Steamwhisperer

Hi John,
I couldn't tell you other than number six on the dial (rheostat??)
It was too hot for welding gloves which is kinda' obvious.
I made the pot out of a piece of steel pipe about 6" diameter and had a coil in the bottom like from a jug.
About the only thing to make sure of was not to boil the oil and to suspend the piece to be heated on a piece of wire.
If the piece touched the side of the pot it would locally overheat in that spot.
Sorry I couldn't be much help. It's been a long time since I used a pot shrink fitting.

Phil

I used to use a Birko hand held heating element which I immerse into the oil and stir/agitate the oil with.

I have seen an electric oil fryer do the same job for small items

and as phil says keep it off the bottom and certainly do not boil the oil...remember if oil is at right temp it could ignite...I think I recall that if you see smoke coming off the oil, it too damn hot????

For 0.71" to 1.19" for precision running 1.6 thou interferance , throw the shaft in a zip lock bag in the freezer, heat the sleeve ( oil is ok but leaves a residue on the steel ) an oven is better .
Work fast make yourself a jack lever press for pushing it on and it helps if you have 2 people . Do a couple of dry runs and slight taper on the shaft or sleeve at the end 5mm or so to help with alignment
There are sprays you can get from places like blackwoods ( not cheep though ) that help with press fits

Originally Posted by Ashore

Do a couple of dry runs and slight taper on the shaft or sleeve at the end 5mm or so to help with alignment

I'd concur with that generally, you want nice broken chamfers. What I tend to do is put a slight parallel undercut at the start of the journal, just size for size or transition at cold. That gives you a nice start so your collar starts & goes on nice and square. With out cocking or picking up.

Interestingly enough, I get less discolouration heating in oil than I do in the oven. Heat Shrink Collar's on spindle's to retain bearings are becoming really common. It gets around thread drunkenness, that you have issues with threaded retainer nuts. Generally they go on at 240 - 260 deg C.

If I was European I'd have an induction heater. I have an old (clean) Sunbeam Chip cooker that I fill with transformer oil I steal from my mates in the Laser industry. Put that in the middle of the floor, and take the fire extinguishers off the wall mounts in anticipation.

That transformer oil seems to have the viscosity of about kerosene or velocite # 3 or 5. You pull a hot part out of the high tech cooker, and it flashes off almost dry, so there's no oil dripping into my synthetic grease.

Regards Phil.

Thanks guys.
So far it looks like I

• Was way too hot
• Had the sleeve under size
• Forgot my physics
• Needed more workpiece preparation

For a simple job I'm feeling a bit underwhelmed by my success
I might have to give it another go in a few weeks time

Michael

Hello Michael,
I think the old timers used to say one thou. to the inch. Easy to remember. I have had success with the oven in the kitchen for shrink fitting but in more recent times I have used loctite and a sliding fit. There would be times where the loctite method would not be suitable of course.
Russell