How Long Does your LN2/Dewar Last?

How long does your dewar hold a useable amount of liquid nitrogen?

  • 0-2 weeks

    Votes: 0 0.0%

  • 2-3 weeks

    Votes: 0 0.0%

  • 3-4 weeks

    Votes: 0 0.0%

  • 4-6 weeks

    Votes: 1 16.7%

  • 6-8 weeks

    Votes: 3 50.0%

  • More than 8 weeks

    Votes: 2 33.3%
  • Total voters
    6
tkroenlein

tkroenlein

Well-Known Member
I was discussing the price and details of supplying me with LN2 with a local supplier today. I've worked with this fellow a LOT, as he is the "old" hand there and I've dealt with him for the better part of 15 years on all of our gases and welding supplies. He's set up bulk O2, N2, argon and hydrogen at our facility, as well as worked out custom blended welding gases for some of our more proprietary welding processes. He *knows* gases.

I told him what I was after and what I knew about LN2's use for knife making (not much!) and he was surprised and even a bit "no way" when I told him how long some folks were reporting they held useable amounts for knife cryo.

So I just want to double check what I think I've understood up to this point.

Please vote and drop a comment in on your set up if you would, help me confirm what I've heard up to this point.

Thanks!
 
I borrow the dewar from my neighbor who raises purebred cattle. They use it to store collected semen for their breeding program(till they can get it to the LN bank). Do not remember the make.
 
How long a dewar lasts will depend a GREAT deal on how many liters (notice we're metric now) it holds. While a 20 liter dewar won't last twice as long as a 10 liter, it will last a lot longer.

You need more than 8 wks listed - I'm at 9 weeks today on a 10 liter dewar and as of last night it was still at -278°F. It is about empty, but still cold. Also depends on how often it's used, and what it's used for. I've sure at least a liter (maybe a tad more?) playing with the LN by dipping it out to freeze grapes and make ice cream.
 
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I went with "more than 8 weeks" because I'm really probing to see if there are folks that are only getting a few weeks out of theirs. Most typically I'm seeing most knife makers getting a couple of months +.
 
I polled for 8 weeks+. Mine holds 52lbs of LN, and I built a very special "box" for it. The box is just large enough for the tank, lined with 1" of foil backed insulation, and when the tank is in the box, I fill ALL the air space with vermiculite, up to the neck/opening.....and that is covered with a piece of R30 fiberglass insulation. It's been that way and working for 20+ years.

As has been said, many factors come into play with just hole long it lasts. Mine is in a temp controlled shop, with the heat set at 55F year round.
 
EdCaffreyMS said:
I polled for 8 weeks+. Mine holds 52lbs of LN, and I built a very special "box" for it. The box is just large enough for the tank, lined with 1" of foil backed insulation, and when the tank is in the box, I fill ALL the air space with vermiculite, up to the neck/opening.....and that is covered with a piece of R30 fiberglass insulation. It's been that way and working for 20+ years.

As has been said, many factors come into play with just hole long it lasts. Mine is in a temp controlled shop, with the heat set at 55F year round.
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Does that big monster thing still have a 2" bung?
 
Yes..... 2". At the time I purchased it..... it was about the only one I could find (that was PRE Amazon days). I've actually put it out there a couple of times for sale, or trade fro a smaller one....no takers. :(
 
So I've learned enough so far
EdCaffreyMS said:
Yes..... 2". At the time I purchased it..... it was about the only one I could find (that was PRE Amazon days). I've actually put it out there a couple of times for sale, or trade fro a smaller one....no takers. :(
Click to expand...
Probably no one can afford to fill it!

I was quoted $65 for 10L.
 
BobbyD said:
So Gene about how many knives Will you treat in those 8 weeks?
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It all depends on orders and how much time I have to work on knives. I think the most was 55 knives.
When I get my tank filled, I like to have a large batch profiled, holes drilled and ready to heat treat. From there, I just hang them up and they are ready to grind when someone orders them.

I have also had to heat treat a few for orders and only got 10 or 15 out of a fill.
 
An update on my 10 liter dewar - it's empty. Sat I checked and while it was still cold inside there was no liquid LN. My sister was here and I tried to pour some LN into a container to freeze chunks of apple to break, and maybe make some ice cream. Nothing but vapor would pour out, no liquid. That was 9 wks. I think somewhere between 8 and 9 weeks the liquid went away, but it was still cold enough inside to treat a small blade. I think I can count on 8 weeks and I'm happy with that.

I'm not sure about cost, this fill was $5.50 including taxes (50¢/liter) to fill. I'm expecting the next fill to cost more, maybe $9 or even $15 to fill. The most expensive place around was $62 including taxes. The only places I found to fill are welding supply places.
 
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