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Dewar Question

Discussion in 'Shop Talk - BladeSmith Questions and Answers' started by Marc Cooper, Oct 9, 2019.

  1. Marc Cooper

    Marc Cooper Platinum Member Platinum Member

    Apr 7, 2019
    Hey All

    I am shopping for a Liquid Nitrogen Dewar and can't seem to find many with large neck openings.

    I have found one on Amazon that can qualify for free shipping. It only has a 2" neck but it has a 172 day storage life. I've modified a job site box with foam insulation to store it in to hopefully extend the life of my Liquid Nitrogen.

    Here is the link:


    For $130 more I can also get a 30 litre Dewar that has a 255 day storage life.

    Here is the link:


    Most all my blades are under 2" wide and under 12" long.

    Most all Dewars I see have specimen holders. Will this stop me from being able to submerge a knife on a piece of wire?

    Does this seem like a good Dewar?
    Last edited: Oct 9, 2019
  2. kuraki

    kuraki Fimbulvetr Knifeworks

    Jun 17, 2016
    You dont need to submerge the knife. An argument can be made that it's beneficial not to. It's cold enough in the dewer to do it's job even when you're down to 1/2" of liquid.
    Marc Cooper likes this.
  3. J. Hoffman

    J. Hoffman KnifeMaker / Craftsman / Service Provider Knifemaker / Craftsman / Service Provider

    Jan 1, 2011
    For some reasons the links don't work for me. Keep in mind that the LN life will quickly deteriorate when we use them the way we do. Putting warm or room temp blades in the dewar makes it evaporate quicker. I have a 47l and it usually lasts about 90 days. 4-5 heat treats. If you can keep the blades above the liquid, it will improve it's life span. The life span listed in an ad is going to be the life of the liquid if it's sealed and never opened.
    Marc Cooper likes this.
  4. Marc Cooper

    Marc Cooper Platinum Member Platinum Member

    Apr 7, 2019
    here is another link to the 30 litre one.


    My main concern is the specimen containers. Will these get in the way or should I just remove them permanently?
  5. J. Hoffman

    J. Hoffman KnifeMaker / Craftsman / Service Provider Knifemaker / Craftsman / Service Provider

    Jan 1, 2011
    The specimen containers come right out. I did get the links to work on my phone. The containers just hang over the edge of the opening and into the Dewar. I just make hangers that hold my blades and hang over the edge.
    Marc Cooper likes this.
  6. Joker66

    Joker66 Gold Member Gold Member

    Apr 20, 2014
    I have a 32 liter dewar that has a 2" opening. These are generally used for cryogenic storage of "biologic material".
    Mine has 6 specimen holders that are good for holding knives to be treated. It works well.
    I save up my blades and heat treat in batches to get the most out of my LN.
    Mine will usually last for a couple of months if not used much but will be gone after about 5 HT batches of 12-15 blades each.
    Keep in mind that the holding time is optimistic and is based on not opening the dewar as J. Hoffman said, and is the time until the LN is completely gone.
    Marc Cooper likes this.
  7. JTknives

    JTknives Blade Heat Treating www.jarodtodd.com Knifemaker / Craftsman / Service Provider

    Jun 11, 2006
    What dewars do you guys have? Mine is a 20l with a 2.16” opening (I think, I know it’s bigger then 2”). It’s evaporation rate is .09L/D. Now I don’t get that kind of life out of my dewar because I use it. But I use it a TON. I date my fills on the lid with a sticky note, 4-29 to 8-21 was how long the last full lasted. We have done hundreds of aebl blades in that time frame. But we pre cool the blades in a freezer first to knock off most of the heat that into the LN. And yes the blades don’t need to be in the liquid. Thy just need to be under the level of the foam plug. I posted awhile back about the temp of the gas inside a dewar and just under the foam plug it’s -300° if not colder. I have looked for the paper I found that talked about that but could not find it. Sorry to say a foam lined box is not going to gain you anything. A proper dewar does not absorb heat through the side walls. It absorbs heat through the opening at the top. This is why larger opening have higher evaporation rates. I would be VERY cautious of buying a cheep dewar as thy can put what ever evaporation rate thy want on it. I have all ways spoke out about my feelings on this topic. LN is expensive and your quickly going to waste it if your using a cheep dewar. I think I paid around $500-$600 for mine used and I got a good deal. I see these dewars on eBay and what not that are a few hundred bucks and thy come with an insulated blanket cover. Yeah stay away, that’s a HUGE warning sign. Your dewar should not be getting cold on the outside.
  8. 12345678910


    Jul 13, 2009
    The large opening is rare because the evaporation rates are faster in them.
  9. jdm61

    jdm61 itinerant metal pounder Knifemaker / Craftsman / Service Provider

    Aug 12, 2005
    When I was looking a couple of years ago, it was tough to find one with a neck larger than 2 inches or 50mm, which is 1.96. Jarod's 2.16 incher would be a 55mm. I have seen a handful bigger than that, maybe up to like 2.5 inches which would be perfect for most of our needs, even big kitchen knives in the 60mm range, but they were pricey. I think that I might have even seen one or two in the 3 inch/76mm range, but I may be wrong. The problem with any equipment is that the bad old days of the post crash era are long gone, so nobody is giving away. stuff anymore. I am seeing UGLY units being sold for the same or more than perfect ones were going for a few years back.
  10. Stromberg Knives

    Stromberg Knives strombergknives.com Knifemaker / Craftsman / Service Provider

    Jan 3, 2015
    This looks like a pretty well made tank. Made in the USA if I'm not mistaken. Doesn't look like the china stuff you see everywhere.

    It's 20 liters, the neck is 2.2" and has a low evaporation rate of 0.09 liters per day. It even has the Semen SafeTM feature. How bout that. :D


    The price seems reasonable for a quality tank.


  11. scott kozub

    scott kozub Gold Member Gold Member

    Jan 1, 2018
    Back to your original question about neck size. You can safely transfer to another container for larger blades. However the transfer of ln if you do this often will negate the savings of loss from a smaller neck.
  12. JTknives

    JTknives Blade Heat Treating www.jarodtodd.com Knifemaker / Craftsman / Service Provider

    Jun 11, 2006
    I have a big glass silvered vacuum flask for blades larger then 2”. Works like a charm as I only have to stick a little in it. Also if I’m doing a ton of aebl it’s much faster to use.

  13. Heli00


    Oct 19, 2017
    @JTknives , I can't see the pic. What brand is it and where did you get it from?

  14. JTknives

    JTknives Blade Heat Treating www.jarodtodd.com Knifemaker / Craftsman / Service Provider

    Jun 11, 2006
    I found it on eBay as thy are prohibitively expensive new. I think it’s 4200ml in volume. It’s tricky to fine ones that are deep enough for our needs. You can find some monster ones but by that point you might as well buy a cryo freezer which we are looking into. The bulk of our cryo is aebl. Once we get to the point where we are having to fill the dewar once a month we will switch to a large cryo freezer. I did the math and thy cost around $30-$60 to run per month. Which is not a whole lot but thy in and of them selves are quite expensive.
  15. butcher_block

    butcher_block KnifeMaker / Craftsman / Service Provider Knifemaker / Craftsman / Service Provider

    Dec 6, 2004
    my 20L has a 3.75 neck on it but i only fill it 2 3 times a year i plan for the shorter out gass time the only knives that dont fit in it are full on veg cleavers. fill is abot 90$ and i plan for 2 good sized batches and see if i can sneak in a 3 once and a while
  16. JTknives

    JTknives Blade Heat Treating www.jarodtodd.com Knifemaker / Craftsman / Service Provider

    Jun 11, 2006
    So your not holding liquid all year long. You fill when you need it?
  17. Stacy E. Apelt - Bladesmith

    Stacy E. Apelt - Bladesmith ilmarinen - MODERATOR Moderator Knifemaker / Craftsman / Service Provider

    Aug 20, 2004
    A tip for folks who don't have to drive far to get their LN Dewar refilled:
    Only fill it with what you need for the batch of knives you are planning on doing. Get a couple liters and do the HT. The LN will last a couple weeks , so plan your HTs during that period. Then set the empty Dewar on the shelf until the next HT time.
  18. Heli00


    Oct 19, 2017
    If in a pinch, could one just use a glass or aluminum container with a made up styrofoam cap?

    My dewar is only 10l and does not accommodate long-ish blades.

    Say, 0.5 l how long would it last in such container? I assume one needs to cryo for minimum one hour, or longer?

  19. Busto

    Busto KnifeMaker / Craftsman / Service Provider Knifemaker / Craftsman / Service Provider

    Jul 26, 2011
    Half a Liter is not going to last....LN2 is a Liquid that turns to gas when it's exposed to atmosphere...you spill a little on the ground and it boils off to gas immediately! The best Secondary Style Container would be an Insulated Thermos with a Wide Mouth and Fairly Tall probably 2 liter or Larger. You need the insulation for holding the LN2 at Cold Temperature and also to keep from freezing your body parts to the container. This stuff is BAD COLD think instant Frostbite!!! Also the Lid or Stopper for the Thermos must be left loose so that the container can OFF GAS a little again the Reason for Foam Plug in Dewars to regulate amount of Off Gassing.
  20. Heli00


    Oct 19, 2017
    Excellent, thank you!

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