Tell me about Dewars, what do you guys use for your cryo set up?

DeadboxHero

DeadboxHero

Joined
Mar 22, 2014
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Just getting my shop set up.
I've been looking at Dewars for cryogenics.

Dang man, kinda spendy haha.
Not sure why I am surprised.

Anyways, what do you guys use in your cryo set up. Just would like to get some ideas so I hopefully don't waste money on something that is not going to met my needs

Thanks
Shawn
 
I bought a 10L dewar off eBay, it was somewhere in the $2-400 range, can't really remember. I built a plywood box, put a layer of rigid foam insulation on the inside of it, and filled the rest of the space with two part castable urethane foam. In hindsight the hardware store spray foam would have been a lot cheaper. Just make sure you wrap the dewar in cardboard first, otherwise you'll never get it out again.

The box made a huge difference. It went from holding nitrogen for 3-4 weeks, to 2-3 months.

It's also worth shopping around town to find the cheapest liquid nitrogen. Praxair and air Liquide (Airgas) sell it here, air Liquide is $5 a litre, Praxair is $8
 
A good dewar is worth the extra money. LN here is around $3 a litre and mine hold 20. It's lasts a really long time. The larger the opening/mouth the faster it boils off. Mine is rated at an evaporation rate of .09 L/Day.
 
My dewar has a 2" mouth, and about the widest knife I make that would receive cryo is a 10" chef's knife, which just barely fits in.
I put a piece of stainless tie wire through one of the pin holes, and wrap it around a wood dowel. Sit the dowel over the mouth of the dewar to keep the knife from falling in.
I'm sure there are other ways, but it works for me.

Putting it in another container would definitely work, but I'm sure it would result in a fair bit of your nitrogen disappearing while out of the dewar
 
A couple questions to ask yourself are: what steel will I be using does it require cryo? How many will I be making at any given time(best to do in batches). Whats my investment in equipment and how many knives will I have to produce to get back my investment? The LN2 is a consumable like belts and epoxy you don't necessarily charge for 2 oz of epoxy used but somehow is wrapped in price of production. I have a wide mouth 30L dewar and over 2 months I will treat 50-75 blades sometimes less. If the dewar is $400 and you charge $5 per knife that's 80 knives to recoup your equipment investment.
 
Along with the Dewar you will need SS foil for wrapping the blades and Aluminum quench plates to draw off heat. I would get the 1" thick plates at least and 6-8" wide and longer than the longest knife you intend to build my plates are 1-1/2" thick 10" wide and 20" long and I can put multiple blades down during quench.
 
Very good advice on the quench plates. I've got 3 sets of them from each time thinking I'll never do a bigger knife.....

It'll be much cheaper in the long run to just buy plates 3-4" longer than your heat treating oven to begin with.
 
I got mine off of eBay, 20l about $750.00 CDN. It costs $150.00 CDN to fill. The LN lasts about 5 months.

Is it cost effective? Nope. But, if you like to do everything in house, it's worth it. I did a lot of testing with z-wear this spring, and it would have been cost prohibitive to send each test piece out. Not to mention, I was using non industry heat treat methods. Not all heat treaters will accommodate these types of recipies. If I was just looking to get regular heat treat done, sending them out would probably be more cost effective.

My dewar was advertised as a 2" mouth, but it's actually 1 7/8". It's a bit of an annoyance when I want a high heel on a chef's knife.
 
mine is a 20L and i got the wide mouth 3.75 inch so i never have to worry about how tall 95% of my knives are. i get it filled when i have about 40 knives ready and just plan on doing that batch and flipping into 20 or so more a few weeks later after that i use the LN in other ways like make icecream or fog or donate to the high school science lab (the kids loved the demo the teacher setup for them
 
DBH has settled in ! Trouble ahead !
Batch is the way to do it. Steels that respond well to cryo are the " super steels " like Crucible's CPM series. High tech with a good amount of alloying elements. The lesser steels don't respond much to cryo , little is gained . Remember that cryo is part of the HT not an add on done days later. Suspend the blade in the liquid lowering it gradually.
after about six hours gradually lift the blade out of the liquid , let it equalize at room temp .Then heat to temper of 300 - 400 F.
 
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