I need to get an interferance fit on some steel parts and need a >400 degree F differential to get a slip fit at assembly. The outside part will be heated in a 300 degree oven, I don’t want to use a higher temp. so it doesn’t affect the temper of the steel.
Web searchs refer to using acetone or alcohol with the dry ice to cool the internal part.
The liquid is used to speed heat transfer to the steel part, if I understand it.
The whole point is to use a low boiling point liquid so there is nothing safer I could subsitute?
tell me this isn’t for a vacuum pump for a general aviation engine.
When I was a machinist we would use liquid nitrogen for doing interference fits. It’s about -320 degrees F, which would be pretty close to your 400 degree delta T.
Nope, barrel for a German battle rifle into the trunion.
Many assembly procedures refer to press fitting the barrel further and further into the trunion until the bolt gap is achieved. My problem is the the working surface of the replacement barrel is not a ground surface, but a lathe turned surface. I don’t think I can adjust the assembly after test fit due to the friction.
Dry ice acetone is better. It gives a theoretical temperature of about -78˚C, but in practical experience I only got about -72˚C in the flask I was cooling. I suppose dry ice methanol would work the same. You can get mixtures that go lower. I successfully used a liquid nitrogen hexanes mixture to get -105˚C. In this case, rather than relying on the sublimation of dry ice, it is the slurry of frozen and liquid hexanes. It is more difficult to maintain, since you have to constantly and carefully add liquid nitrogen. Too much, and you freeze the hexanes, too little and it all melts.
What exactly is wrong with dry ice and ethanol? I’m not sure what you could use that would be safer… If you’re not in a hurry, you can just pack the part in dry ice alone. Then there won’t be any flammable solvents, if that’s what you’re worried about.
I think the trouble with ethanol would be water content. Actually, I’m not sure anymore why we always used acetone. Acetone is definitely the standard.
Actually, if you are interested, there is a whole list of these mixtures in The Chemists Companion. This is quite possibly the most broadly useful book for practical chemists, and that is probably the most useful page in that book. Some of the proposed mixtures are better than others though. Theoretically, you can get down to about -20˚C with just salt and ice, but in practice I’ve never seen it work, and we really tried. Also, the HMPA/Liq N2 mixture is probably best ignored since it might kill you, and IIRC, several of the proposed mixtures are comically expensive. Still, there are some real gems in there if you want to control to a specific temperature range.
I have put bearings on shafts, and jack shafts on base shafts that the room temp ID was 3 thousands less than the OD with just dry ice and a heat source.
What we was crush the dry ice and put it in a large rag. Wrap the dry ice in the rag around the shaft and tape it into place. Heated up the jack shaft. The main shaft had a mark on it indicating full penetration.
When everything was ready. One man grabed the jack shaft out of the heat source, second man removed the rag with the dry ice, The first man then aligned the jack shaft with the main shaft, and then the third man using a large brass hammer slams the jack shaft home. There is only one try and you have to get it right.
But we never used any liquid. Having enough dry ice and wrapping it tight worked for us.