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Movable Chamber for Cooling Parts with Liquid Nitrogen

Movable Chamber for Cooling Parts with Liquid Nitrogen

Movable Chamber for Cooling Parts with Liquid Nitrogen

Hello all,

I am seeking some advice to modify a parts cooling chamber I have designed, and determine the best material type for the job. We press fit many bushings and bearings at my place of work, and utilize liquid nitrogen to shrink these down for an interference fit.

before my involvement, assemblers were using a shop-built cryogenic chamber made from a corrugated drain pipe, plastic inserts, and expanding foam between, all covered by a plywood lid, to provide some insulation. The main issue is the plastic lining is prone to cracking due to the extreme temperature differentials, going from room temperature to -196C in an instant. The leakage, aside from being a waste, was also a serious safety hazard, and there was not a safe way to retrieve the parts without dipping a glove all the way into the chamber, or using a prybar to catch a part.

Knowing safety was a top priority, I designed a replacement cart that had adequate insulation all the way around the central chamber (over 2" of expanding foam on all sides, including the base), and was designed to be mobile to take it around the shop. the chamber also has a "fryer" basket inside to hold bushings and easily be lifted out without the need for dangerous contact. I used a thick-walled low carbon steel tube and a 1/2" plate welded together to make the chamber, not expecting the 1/2" walls to be much of an issue from a heat transfer perspective, and this was mainly done as a cost-cutting measure to use any materials we have on hand. That was a pretty foolish assumption on my part.

After completion, I was notified that it was taking much more liquid nitrogen to have it eventually condense into a liquid in the chamber to cover the bushings, as much as half the Dewar we have. While the design proved to be safer, the costs of excess nitrogen spent are now at a level of concern, not to mention the reluctance for the assemblers to utilize it as it takes much more time to work with.

I am seeking some design advice, as I had never seen another firm design something of this sort, could not find anything similar available for order online (aside from large ice chests & coolers which theoretically could work, but could just as easily crack like the old chamber), and have not had prior experience working on something like this. The nice thing is the chamber itself is designed to be removable and replicable, and we would like to reuse the cart portion. I am looking for a round chamber no larger than 16" in diameter, and 10" tall (the height doesn't exactly matter, we can cut down the height to make it fit if need be, or work around it).

Thank you in advance.

RE: Movable Chamber for Cooling Parts with Liquid Nitrogen

We used a foam ice chest, built a wooden box to protect and support the outside, and then hung perforated SS baskets inside of it.
Cutting notches in the plywood and foam to allow the baskets to sit low enough for the lid to fit snugly.
We got the baskets from a restaurant supply store.
Just don't let it sit around with LN in it for too long.
If you open it an see a blueish tint, take it outside and let it all evaporate.
The blue is LOX.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

RE: Movable Chamber for Cooling Parts with Liquid Nitrogen

The issue would seem to be the heat capacity in your steel tube.

Try using much thinner stl stl sheet or aluminium. Both are pretty good with cryo materials.

The thinner the better.

Try air ducting or similar.

Or a large pot.

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