Shrink Fitting

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BRIAN

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In the next month or so I will be fitting the bronze valve cages into the aluminium heads on my Five cylinder radial engine. I have a electric hot plate that I have used for fitting bearings very successfully, to heat the head and I am thinking of freezing the cages with Plumbers freezing spray but I have no experience using this spray.
Has anyone used this product??? I understand from safety literature that the liquid Leaves the container
at -50° c So it seems ideal for cooling my small pieces of bronze. but more knowledge would be a great help.

Brian.
 
An alternate consideration.

The sublimation point (turns from solid to vapor) of dry ice is about -78C. A dry ice acetone bath is commonly used to chill things in laboratories and will go down to -78C. It would provide a more consistent temperature than trying to chill with a spray. You may be able to get dry ice locally. Dry ice can also be made from carbon dioxide welding gas. The tank would be tilted to have liquid escape instead of the gas and usually is vented into something like a cloth bag. The evaporation of the liquid will form the dry ice in the process. There are also special tanks with a siphon tube running to the bottom so you don't have to invert the tank.

Check Wikipedia for more information.
 
lot's of interesting suggestions. Never knew that plumber spray was available...

I would just put the parts in my freezer.

David
 
Just looked at Wikipedia. In addition to acetone, ethyl alcohol (grain alcohol) or methanol (wood alcohol) will also work.

Both of these should be available from paint dealers.
 
I always heated up one part in the oven (when the wife is out ) and put the other in the freezer the night before.
 
Don’t know your interference fit spec. I don’t bother with all the running around and extra costs. I just throw the stuff in the freezer. And use a map torch, my hot plate or oven. Sometimes, I just apply the heat. Works for me…Dave.
 
Just a general cautionary note for anybody who plans to cool bearings this way ...

It won't really apply to Brian, who's inserting bronze valve cages into engine heads. But soaking bearings in dry ice/acetone or other solvent may well dissolve out the lube. Likewise, I'd advise caution with plumber's freezing spray. It may well be one of the Freons, or maybe butane, any of which are also an excellent grease/oil solvents.

If you're cooling bearings, you might want to do a trial run with an extra one, to check for lubricant loss. If you want to use dry ice, it might be easiest to simply lay the bearing directly onto it. Or else, just use your home freezer.
 
If the parts you need to shrink are thin walled, and not large mass, the simplest way is just the home freezer. If your need for interference is too great for that high a temperature, and you cannot heat the mating part enough for some reason, most drug stores and the Walmart ilk carry wart removal kits which use (usually) propane and dimethyl ether to achieve cryogenic temperatures. I believe it would be cheaper than the plumber's spray, unless you have quite a few parts to do. If there were many, and the freezer would not work, dry ice and acetone (mentioned above) will shrink the part about as much as anything else. Yes, LN2 is colder, but the dimensional difference between it and solid CO2 and acetone are minimal.
I have a dry ice generator, and use it once in a while, but works best with the siphon tube cylinder also mentioned already. It doesn't seem very efficient to me, so if I only need a small amount, I just go to the ice house. I'm not going to get a cylinder just for a single fit, for example. Most sell it by the pound.

Or if you know someone in the fire extinguisher service business, talk to them about some expired, but still pressured up CO2 extinguishers. Chilled many a 6 pack with them. Instantly.
 
setting your part on top of dry ice works fine.built jet engines every day this way...that and big ovens for expanding
 
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