Dewar options

JTknives

JTknives

Blade Heat Treating www.jarodtodd.com
Joined
Jun 11, 2006
Messages
8,647
I have been doing a bunch of research of dewars as I want to get one that will fit me and my customers needs. I'm in the process of setting up my shop to do semi part time heat treating for guys here on the forum and wanted to add cryo to the options. The 2 dewars I have been looking at are high end brands and good quality. First one has a 2.1875" opening and holds 20L which I could most likely live with but don't know about customers. But this dewer has one amazing feature and that's a .09 L/day evaporation rate. The other one is the same brand but has a 2.5" opening and is 30L capacity but it's a an evaporation rate of .22 L/Day which seams to be standard for most good quality dewars.

Being that I do see my self using it all the time but I want to have it on hand at all times I'm leaning twords the more efficient (more pricy) one. But could I deal with the lower capacity and neck size.
Thanks guys for your help.
 
i got a 3.5 inch big mouth 20l cause of all the kitchen knives i do i needed the large opening. drawback of it is it has about 45 day life about the same as my old 10l 2 inch mouth
i work in batches and might don 50 blades in a day for HT so price per blade is not too bad and if i really push i can get a 2nd HT day in before having to refill
 
Butch what brand is your dewar, international cryogenics?
 
I bought a used Taylor Wharton 34hc off of eBay. It has a 3.6" neck and it's rated for 200 days I think static hold time. Working time 125 days. .17 evap rate. I filled it and had it filled again at 115 days and it still had some in it. I feel like it was the perfect fit for me.
 
That's what I was actually looking at but not many on eBay right now.
 
As far as the Dewar, I would get the 20L with the 2.1" neck. As far as doing H/T for other people, I've done a bit of it and I'm here to tell ya if you're thinking of doing it for the $$, DON'T. You'll have to charge $20 per blade to make it worthwhile. Its totally your choice but don't say I didn't warn ya. LOL

Feel free to call me if you wanna discuss the headaches & pitfalls.
 
I'm kinda heavily leaning twords the 20L with the 2.1875" neck. If I have to so something larger I could pick up a flask. But the .09 evaporation rate is hard to pass up. That's 222 days for 20L or 100 days for half tank. And considering the air (nitrogen) space above the liquid sits right around -300 you don't have to be submerged any way. Which considering a warm blade in liquid boils off a lot of nitrogen.
 
You know I've been looking into the same thing and actually one of my buddies was telling me u can use a liquid oxygen tank, just pull all the gauges and cap it... Most places throw them away once the gauges fail so u can find them free


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In doing cryogenics at Virginia Chemicals, we used heavily insulated Dewars to store the LN and more manageable Dewars to hold it in use.

Get the 20L long storage Dewar. Then, use a Dewar flask that is tall enough for the knives you will do. A 2-3L flask would be big enough for any knives. You pour the LN into the flask, do the cryo, and pour it back in the storage Dewar. A good metal funnel with a wide spout is a good idea when transferring the LN.

You can buy one on eBay for a couple hundred, but you can make one that will do for our purposes for a fraction of that.

A fellow as inventive as you are can just weld up a stainless tube that is wide and tall enough for doing cryo, and insulate the heck out of the outside of it.

One option would be to place the welded up cryo tube inside a large PVC pipe. Lets say you make a 3" by 26" tube. Take a 12" by 26" piece of PVC pipe with the bottom closed off, and put 6" of Styrofoam or other firm insulation in the bottom (poured urethane?). Set the tube on that and fill around it with more foam. Urethane would be great here, but rings of Styrofoam would be just fine. That allows a 20" blade to be cryoed. The extra 6" of tube sticking out is the unfilled zone and makes filling and emptying easier. Make Styrofoam cap to fit over the top of the cryo tube, and make a Styrofoam ring that sits around the extended tube when in use. Screw some handles on the PVC to make it easy to pick up and move. You should be able to do cryo in that and easily pour the LN back and forth. This whole 2L Dewar will be made to do knives, and cost maybe $50-75. No good for long term storage, but great for doing cryo.

If you decide to build one, I have a few other suggestions that I will pass if you send me a PM.
 
I'd like to see you make your own, and tell us how to do it, just to stay away from the Chinese shtuff!!
 
Out of curiosity how much are you guys paying to fill a tank? I got a great deal on my Dewar, and it's on about six weeks right now and still cold. My old one would loose 30l in a day or so.
 
My new dewar if it truly gets its rated loss rate would be 30-32weeks of hold time from full to empty.
 
Don't really expect the rate advertised. A really good tank has about 100 days. The loss goes a bit faster as the tank gets emptier, IIRC.
 
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