Liquid nitrogen question

Outdoor Gear Dad

Outdoor Gear Dad

Joined
Jun 1, 2019
Messages
211
Hello BF!

I have been doing a subzero quench up till now with dry ice and denatured alcohol. Thinking about switching to LN and doing Cryo. Couple questions. Will I notice much of a difference in the outcomes? What’s the advantage?

also where do y’all buy LN from and how long will it last in the dewar before I have to replace?
Thanks!
 
I think another good question is how much are people paying for LN. Last time i checked i was quoted 15 dollars a liter which seems ridiculously high.
 
Prices vary by where you are buying and even within the same place can have different tiers depending on how “valued” a customer you are. You can call around and ask how much for 10 liters, you don’t need a dewar to check prices. The best part of liquid nitrogen is convenience, it needs to be filled every 2-3 months but otherwise it’s ready to go whenever, no setup time.
 
I was quoted about $10 a liter.... they ask you - do you have an account?
no, so I open one... still $10 a liter

then I go with my friend who has been buying LN for a long time and use his account,
he pays under $2.50 a liter at the same place....he's been buying more often and for a long time
 
Larrin said:
Prices vary by where you are buying and even within the same place can have different tiers depending on how “valued” a customer you are. You can call around and ask how much for 10 liters, you don’t need a dewar to check prices. The best part of liquid nitrogen is convenience, it needs to be filled every 2-3 months but otherwise it’s ready to go whenever, no setup time.
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I am only a hobbyist knife maker and usually am only heat treating at the most 5 blades at a time. So what size dewar do you recommend and does it really last 2-3 months? How do you know when to replace it?
 
I have a 20l dewar, and it lasts me 5 months between refills. I have a friend at praxair, so I get it filled free now. Most I paid was $145.00 CDN.
 
The advantage is always having it available. In canada I can only get dry ice during business hours during the week so I was doing knives in batches. Now that I ln on hand I can heat treat a knife when ever I want. I use AEBL and s35vn so i have not noticed any performance difference.
 
I use a -45 freezer in my shop, but would be interested in getting things colder as even lower temps are recomended in most data sheets, and by knowledgeable people like Larrin. The -45 freezer is very practical though, and it also allows me to keep the blades clamped during freezing (to try and reduce any warp, maybe overkill though?).
LN2 seems more practical than dry ice, since you can keep it longer in the shop. However for me, I only HT maybe once every 6 weeks, the evaporation and cost of refill (appr USD 10/L) would stress me a little.
One option is a new Chinese ULT freezer at around USD 2200. The cost of LN2 is gonna add up to that over time. But then again an ULT freezer has something like a 8-10 year service life according to some sales reps I've talked to and they need maintainance and service during those years. So, maybe not the best for a hobbyist.
One option I've looked into, that eliminates evaporation issues and technical problems, is to rent (buying is usually not possible) a 15-30 L CO2 gas tank and make your own dry ice when needed. I did some calculations and for me cost would be about the same as for LN2 in the long run. It won't get you as cold as LN2, but I don't think that temperature difference will make or brake it for me as a knife maker.
 
Outdoor Gear Dad said:
I am only a hobbyist knife maker and usually am only heat treating at the most 5 blades at a time. So what size dewar do you recommend and does it really last 2-3 months? How do you know when to replace it?
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I have always sent them to Paul Bos HT at buck knives. For HT with liquid Cryo treatment and Paul Farmer knows what he’s up to. You get them back with three RC pin marks and your Average range of Hardness.. I’ve been happy with them since 97...
 
@Dad: Here's a thread I started a couple weeks ago on your question about cost.
https://www.bladeforums.com/threads/i-got-a-ln-dewar.1734963/

On the question of dry ice vs LN, I'm not totally sure but I do think LN "might" give a slight edge in performance. I don't see why since the RA conversion seems to take place around the dry ice temperature.

On the question of price to fill, note the difference I found, $5.50 (taxes included) so 50¢/liter at best and $6/liter the highest price, which happened to be the closest to me.

LN seems to be most available at welding supply shops in this area.

How long my 10 liter dewar is going to last? No idea. Manuf says 60 days if it's not disturbed. I'm disturbing my dewar lots - bet I've used over a liter making ice cream :) freezing grapes to watch them shatter like glass.
 
For the hobbyist knife maker would a smaller dewar make sense of should I just save up and go for a big boy. Like I said I am heat treating maybe 5-6 blades every couple weeks.
 
If I ever get a dewar (I am a hobbyist too) I want some with a throat diameter and depth that can take large chefs as well.
 
that was the kicker my chefs were over 2 inch wide and you go from 2 inch mouth to 3.75 as std sizes i went with 20l big mouth i try to plan large batches so i can get 2 "loads" per fill 40-50 blades
 
I don’t know ... dry ice is not all that cheap either ... and it does not last... so you will basically need to buy new every time you HT. at some point (Frequency of doing HT) the math will Say that LN is cheaper. It sure seems like it is more convenient.

SCANIAMAN: when you do cryo, do you need to fully immerse the blade in the nitrogen, or just make sure there is a reasonable amount in the bottom of the dewar?
 
On some steels, I get one Rc point higher with LN over dry ice. Others, no difference.
 
Outdoor Gear Dad said:
For the hobbyist knife maker would a smaller dewar make sense of should I just save up and go for a big boy. Like I said I am heat treating maybe 5-6 blades every couple weeks.
Click to expand...
Depending on where you are at, and what you have to pay for LN I expect you'll find LN less expensive than dry ice. As mentioned I got the 10 liter for $200, a 20 liter was going to be $400 (or more) https://www.ebay.com/itm/111691518245 as one source.
 
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