Growlers for Cryo - Recommendations?

[MTBob]

Thought I'd post this question to see if any of you have experience with using conventional Growlers (large thermos bottle) to store liquid nitrogen for Cryo treatment.
I'm doing a lot of stainless kitchen knives and have been using dry ice. Yesterday I discovered that the welding shop that sells both dry ice and LN has some customers that use LN on their knives and uses growlers similar to this.
Do any of you use LN in containers like this - or some other variation. I do not want to pay for a LN Dewar bottle, just too expensive.

 

[Taz575]

With Dry Ice or LN2, you do not want it in a sealed container, it goes kaboom! You won't get much LN2 in there and it will be gone very quickly.

If you are on facebook, check the marketplace for Dewars. You can sometimes snag them for cheap!

 

[Taz575]

If you are in Montana, check with ranchers and see if they have one they are getting rid of, or will let you borrow from time to time. They are used often to keep semen frozen to inseminate livestock, so if the MT is for Montana, check the local ranches!

 

[KenH]

Bob, note that is only 9.7" tall, so would have only maybe 6" of space for a blade. Also as mentioned N2 can't be in a sealed container. Nor should it ever be transported inside an enclosed car due to the escaping N2 vapors.

I think this is the item you're referring to: https://a.co/d/0tA9OrK note the little square with "up" arrow in the upper right corner of your image? Click on that it and gives the short URL to link to the Amazon page.

 

[Taz575]

Yeah, Even small dewars have a neck to them that a foam core plug fits loosely into. This helps it not splash out and is loose enough that pressure can't build up inside. Most dewars have a 2" neck opening and 2" wide kitchen knives typically don't fit. Some guys get a small LN Dewar and then pour it into a tray instead of dipping the blades into the dewar itself. Insulate the heck out of the tray! A 9x13 cake pan or bread loaf pan will work well.

I picked up a 32" Bar Speed Rail, lined it with several layers of heavy duty aluminum foil and insulated it with pink R30 insulation. I put a layer of insulation under the speed rail, then cut out for the speed rail to sit into the 2nd layer of insulation and then a lid with the insulation. Basically has a R30 insulation wrapped all around the Speed Rail. I will make up a wood box for it one of these days to contain the insulation and get the Speed Rail itself welded up so it's water tight and then get some smaller aluminum flashing trays made to fit into the speed rail so I can do shorter/wider blades that won't go into the dewar neck and not need to waste as much LN2 or Dry Ice/DNA slurry. This kept Dry Ice/DNA slurry with chunks of Dry Ice in it for several hours so I could do a sub zero on some 24" OAL Shechita I heat treated recently. I used like 10# of Dry Ice and a gallon of DNA. I checked it the next morning and the tin foil was still frosted up under the insulation, but there were no more chunks of ice left.

 

[KenH]

Most dewars have a 2" neck opening and 2" wide kitchen knives typically don't fit.

Many dewars have a 50mm opening which is 1.9685" or 1/32" less than actual 2". I find a 2" blade that's 1/32" less is no big deal, just list as a 50mm blade. In the real world I find it's much easier to get a 1.95" blade thru the opening.

 

[Taz575]

Yeah, I was doing some Shechita that were from 2" bar stock and they weren't close to fitting in! Plus the blades are 18" long, too long for the dewar. Big blades can be a PITA sometimes!!!

Lots of my kitchen knives are around 2.25" wide or a bit longer. People don't realize that the dewars have a fairly long neck, so even a long, skinny blade may not be fully submerged in the nitrogen. I need to stick a thermocouple down into the neck area to see the temp there, but I think it would take longer to get down to temp if it's not submerged. I read that the vapors are the same temperature, but I don't know if they will cool as efficiently.

Easier to do a pour into a tray for the big stuff for me! I will probably pick up a smaller dewar one of these days for when I need to do a pour instead of trying to pour from the larger dewar. Less waste, too!

My 18L Dewar is an Extended Hold Dewar. I filled it up on Oct. 15th or so and it's just going out now, and that is with boiling off a bunch by accident my first time using it. I did over 20 blades with it myself and my buddy borrowed it, too. It was the winter time, but it's a nice hold time! They use one at work and it's inside the Health Center in a room at 70 degrees and they use it for 2 months before having to re fill it. I am going to make a big insulated box for the Dewar, similar to the Speed Tray setup to keep it cooler during the summer months.

 

[KenH]

WOW - Oct 15th? That's almost 5 months! That's surely an extended hold Dewar. My el-cheapo 10L Dewar will hold around 6 to 8 wks with normal use. It's stored inside a climate controlled room so isn't exposed to hot weather.

I've checked the temp up in the vapors when dewar is over half empty and it's still in the -300°F range so the vaports are pretty cold.

 

[Taz575]

Yeah, I did my first heat treat batch on October 17th, and I picked it up a day or two before that.

When I was at work, I saw the dewar in the dumpster, so I was able to snag it out and just needed to buy a foam core for 20 bucks on eBay for it. It's a Wharton Taylor xt18 and it's rated for I think over 200 days static time and well over 100 days use time or something like that.

It's currently in my garage, but I may bring it inside in the box during the summer time. I try to heat treat in batches so I don't have to heat treat a couple here and there. That way I can fill it up before I'm ready to heat. Treat a bunch of blades and have it for a couple months to use. It came with the specimen holders and I can fit usually three to five blades in each of the holders at a time.

 

[MTBob]

Hey guys, great information, just what I was hoping to hear. I'm not sure what I want to do yet. But, there's a cattle AI outfit nearby and I'll stop over there and see if they have an excess Dewar bottles. If I find one, the neck size will be an issue for the knives I'm making that are in the 2 1/2" +/- range. But, using a Speed Rail (a product that I didn't know existed until now) would seem a good way to address this issue and could have lots of uses!

Related to this question - what are your thoughts on the added value of Cryo'ing with LN over dry ice on stainless, such as AEB-L or others? I've read L. Thomas articles where he says stainless will have increased Rc number and better carbide formation with LN, though only a marginal improvement. From a real world practical view point, are you seeing any notable difference between the two Cryo methods, LN or DI?

 

[Taz575]

With the speed rail, they usually have some gaps in the welding of them, so they're not watertight.

I'm not sure if they'll be much practical difference with a dry ice slurry immediately after the blades get to room temperature, or liquid nitrogen, or liquid nitrogen over dry ice. I dont know if anyone would really be able to tell in real world usage the difference between them.

Dry ice only gets down to -108 or so with acetone which is different than liquid nitrogen going down to -300. But again, I'm not sure if anyone would really be able to tell in use.

 

[KenH]

I agree with Taz, not sure there's any real world difference between DI and LN. It does "seem" like I get an extra 1/2 point, or maybe a full point extra R\c hardness with LN than I got with DI. I wouldn't bet more than a nickel on that though. Real world, not a big deal

 

[MTBob]

Dry ice only gets down to -108 or so with acetone which is different than liquid nitrogen going down to -300. But again, I'm not sure if anyone would really be able to tell in use.

It does "seem" like I get an extra 1/2 point, or maybe a full point extra R\c hardness with LN than I got with DI. I wouldn't bet more than a nickel on that though. Real world, not a big deal

That's what I'm thinking. I suppose one way of saying this: "Is the juice worth the squeeze" - particularly for a non-commercial hobby knife maker? Unless I can see a meaningful difference in using LN, why add more "stuff" to my already cluttered shop? I can see in a commercial world that adding LN to the heat treating cycle adds a bit of marketing sizzle that could be meaningful to some buyers.

 

[Taz575]

And remember, if we use a lower austentizing temperature, we have less retained Austenite. The RA adds some toughness to the steel as well.

Using a higher Aus. Temperature means higher hardness, but more RA which the sub zero helps reduce. If I'm going for 62 in magna cut, I can get there easily with a 2050 aus temperature, 340° temper and dry ice/dna. If I want 64 in magna cut I austentize at 2150 and cryo and temper the same.

 

[MTBob]

And remember, if we use a lower austentizing temperature, we have less retained Austenite. The RA adds some toughness to the steel as well.

Using a higher Aus. Temperature means higher hardness, but more RA which the sub zero helps reduce. If I'm going for 62 in magna cut, I can get there easily with a 2050 aus temperature, 340° temper and dry ice/dna. If I want 64 in magna cut I austentize at 2150 and cryo and temper the same.

If you work with it - What's your recipe for AEB-L?
Per L.T's recommendations - I've been Austentizing AEB-L at 1975, plain dry ice (no slurry), and 350 temper 2x2. I average about Rc 62 with that method. I've considered lowering the Tempering to 325 to bump the hardness a bit. Thoughts?

 

[Gliden07]

What is a good size for a Dewer for a low production shop?

 

[KenH]

I've been Austentizing AEB-L at 1975, plain dry ice (no slurry),

A slurry is really needed - just chunks of dry ice won't get the temp down nearly so well as a slurry. All those air pockets between the chunks (even crushed) have a negative affect on getting the blade down to the -100°F range.

What is a good size for a Dewer for a low production shop?

I would think 10 liters is about the smallest size to be useful, while perhaps 20L would be close to a max size? Not sure what the max size would be, just take more to fill it, and the larger size will last longer than a smaller size. Myself, I think a 10L is about right - easy to carry, at $300 shipped a "somewhat" reasonable price. Only costs about $8 to fill and last 6 wks or so. There are times when it might sit empty for a month or so before needing next refill. I try to profile several blades when I fill, then if I don't need more no point in having the LN sitting there evaporating.... Of course there's always the fun of freezing grapes for the grandkids to break on sidewalk.... AND making LN ice cream.

 

[MTBob]

I was doing some Shechita that were from 2" bar stock and they weren't close to fitting in! Plus the blades are 18" long, too long for the dewar. Big blades can be a PITA sometimes!!!

I have never heard of a Shechita knife until now. How fascinating to learn about this knife design and its use. https://thekoshercut.com/blog/the-shechita-knife/
From my uneducated view, it would seem the Shechita is similar in design to the Japanese Nikiri.
Thank you for mentioning it!

 

[Taz575]

Yeah, the ones in the picture on the blog are poultry sized. I have done some with 5" long blades and others with 18" long blades for cows.

These are 18" x 2" blades in 1/16" Magnacut, 62 HRC, 24" OAL. Customer wanted heat treated and rough ground blanks for his buddy to finish off and do handles on, so these are 120 grit on the blades and 36 grit on the handle flats.


Yeah, you really need a slurry to get it cold. Denatured Alcohol works well and you can re use it several times! I wish my 18L dewar was $8 to fill up; it's $12/Liter at the welding place! I need to call around and see if I can find it cheaper somewhere else.

I haven't heat treated AEB-L yet; the 2 blades I thought were AEB-L were actually 1095...lol. I usually ask for 62 HRC with AEB-L when I had Bos or Jarod Todd heat them for me, so 62/63 is right on! May be able to push it to 64 with kitchen knives though?

 

[Drew Riley]

I just bought a 35L Taylor-Wharton (model 35HC) Dewar off of eBay for right at $350 shipped to my door. It came with 10 sample holders that are perfect for holding the average sized blank (or multiple blanks for that matter) that I make, and has a neck opening of almost 5 inches.

It also came with a little 5 wheel dolly for rolling it around the shop. I'm probably going to head to my local welder supply this coming week to fill it with 20 or 30 liters, as I have a batch of 25 AEB-L neck knives to heat treat.

The nice thing about a larger dewar, is that the "fill" will last longer, but it also gives you room to dip larger pieces without having to fill up a different container.

FWIW, I also slightly modified a hitch mounted game hoist to load/unload it out of the bed of my pickup truck (it'll weigh around 100lbs when full) and I bought a small folding flat cart for about $40 for transporting in and out of the welding supply, as well as from my driveway to my garage.

Now, as far as the question of whether it's worth the squeeze.... well, that's a good question. For some it is, for some it isn't.
Back before Peter's raised their prices, I did the math on what it would cost for the heat treat setup I have now, and it was actually quite a bit cheaper to send them out. Even at todays pricing, it'll take me a pretty good while (and a lot of blades) to break even with what I currently have invested in tools and supplies and such.
Bos heat treat pricing is quite a bit better, and I'll admit, it gave me a lot of pause when considering if I wanted to start doing it all myself.

That said, at the end of the day, I'll have to do a little more work, spend a little more money, and arguably absorb a little more risk, but...
wait, why am I doing this again? hahahah

In all seriousness though, I will be getting a little more control over the process, turn around will be much faster, and I can have a lot more flexibility on whether I want to do 1, vs 100, and do things at my own pace. Also, if I want different hardnesses, or want to experiment a little bit, it's just nicer to have everything there at hand, vs waiting 2 week, a month, or sometimes even a couple of months for some blades to come back.