LN2 treatment

Stromberg Knives

strombergknives.com
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Hi!

I've been using dry ice in my process for heat treating stainless, but it was cumbersome planning the procurement of dry ice since its lifespan is rather limited.

So, I've finally acquired a LN2 dewar for transitioning to a cryo treatment.

It's this kind of dewar: https://www.amazon.com/Taylor-Wharton-Aluminum-Liquid-Dewar/dp/B00OPOC3F2

I have a practical question, what would be the best way of exposing the blades to the liquid nitrogen?
 
Hi!

I've been using dry ice in my process for heat treating stainless, but it was cumbersome planning the procurement of dry ice since its lifespan is rather limited.

So, I've finally acquired a LN2 dewar for transitioning to a cryo treatment.

It's this kind of dewar: https://www.amazon.com/Taylor-Wharton-Aluminum-Liquid-Dewar/dp/B00OPOC3F2

I have a practical question, what would be the best way of exposing the blades to the liquid nitrogen?

It's easy, you leave the liquid nitrogen in the dewar and hang the blade inside the dewar from a wire. That's why you or I should say we get dewars with at least a 2" neck opening.

You got that exzactly dewar? If so I hope liquid nitrogen is cheep in your area. It has an evaperation rate of .23L/day which means without you using a single drop it will boil off all the LN in 108 days. May sound like a long time but my dewar has an everapation rate of .09L/day and it holds 20L. It keeps liquid for a very long time and I'm glad because it costs me around $60-$70 to fill it. My neck opening is 2-3/16" wide and it's plenty large enough for my work. The larger the neck opening the faster you loose LN. To put your dewar into perspective if you paid the same amount per L as I do then just having it sit there costs you almost a buck a day in the LN that boils off. I had a 10L Taylor dewar befor and it never seamed to hold liquid for very long. But I got mine used so I don't know how old and efficient it was compared to there newer models. Also another thing to keep in mind is that when you go to buy LN you don't just buy a little bit. Thy fill the tank and sell you the amount that the dewar is rated to hold. I have never found a place that will only sell you a little bit.
 
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I use 1/16 welding wire formed that hold 4 at a time. Check welding supplies or your artificial insemination places. REI industries charges me 1.35 a pound so most times I take my sons semen tank and my dewar and it comes out to about$50.00.
He has a 20 week tank and it keeps forever it seems.
 
I'm going on 3 months with my $200 chinese 10L dewar and it's still holding. While I wish it had a bigger neck (1.9") I'm pretty satisfied with it value-wise. On the other hand the drive to where I get it filled costs more than the LN itself.
 
I'm going on 3 months with my $200 chinese 10L dewar and it's still holding. While I wish it had a bigger neck (1.9") I'm pretty satisfied with it value-wise. On the other hand the drive to where I get it filled costs more than the LN itself.

I’ve got a 20l with a 1 7/8” neck. I agree it would be nice to have a bit over 2” neck, but it holds the LN for a bit over 5 months between fills. $115.00cdn to fill, and about a 3h round trip from my home to the plant.
 
It's easy, you leave the liquid nitrogen in the dewar and hang the blade inside the dewar from a wire. That's why you or I should say we get dewars with at least a 2" neck opening.

You got that exzactly dewar? If so I hope liquid nitrogen is cheep in your area. It has an evaperation rate of .23L/day which means without you using a single drop it will boil off all the LN in 108 days. May sound like a long time but my dewar has an everapation rate of .09L/day and it holds 20L. It keeps liquid for a very long time and I'm glad because it costs me around $60-$70 to fill it. My neck opening is 2-3/16" wide and it's plenty large enough for my work. The larger the neck opening the faster you loose LN. To put your dewar into perspective if you paid the same amount per L as I do then just having it sit there costs you almost a buck a day in the LN that boils off. I had a 10L Taylor dewar befor and it never seamed to hold liquid for very long. But I got mine used so I don't know how old and efficient it was compared to there newer models. Also another thing to keep in mind is that when you go to buy LN you don't just buy a little bit. Thy fill the tank and sell you the amount that the dewar is rated to hold. I have never found a place that will only sell you a little bit.

Yeah, I see your point. Unfortunately I had no choice regarding the choice of container. I haven't found an easy way of obtaining and transporting LN2 where I live. I ended up getting an agreement with an large industrial gas company here in Sweden.

This means I can only choose the size of the container, I chose the 25 liters, but I made sure the neck was wide enough for my larger blades, and it's 2.5 inches. So I rent the container and when it's empty (or rather when I call them) they come to my house and swap the unit for a filled one. I'm aware this isn't the cheapest way of obtaining LN2, but it's very convenient.

Knifemaking is just a hobby for me, but I enjoy doing as much of the process as possible inhouse, I don't like being dependent on external parties. I want to to be able to get stuff done in my workshop when it suits me, not others. ;)My suit day job make sure the cost isn't an issue.

Based on your answers it seems that hanging the blades from a wire is the preferred method, sounds good, minimal slop.

A couple of follow-up questions:

  • I read somewhere that the blade doesn't even need to be submerged for it to reach cryo temperature? Is this correct?
  • When do you guys fill your dewars? How small amount of liquid will still give me cryo temperatures?
  • How do you check your liquid level?
Since unnecessary waste is, well... unnecessary, I've also been tinkering with the idea of insulating the container, for a longer holding time. I had something like this in mind. It's made of 100mm EPS all around.

WjxNUkx.jpg
 
  • I read somewhere that the blade doesn't even need to be submerged for it to reach cryo temperature? Is this correct?
  • When do you guys fill your dewars? How small amount of liquid will still give me cryo temperatures?
  • How do you check your liquid level?

All great questions as I've been looking and found some great deals on used Dewars locally that look like new. I haven't pulled the trigger yet because I can only obtain LN about 1hour away from my shop. Actually after reading the responses I guess I'm lucky! I'm guessing there is no way to determine if a used Dewar has lost it's vacuum or is there? How do you guys transport your Dewar? I'm thinking you would have to make some container so you could strap it down securely as a tipped over Dewar could turn ugly real quick.

I also just recently saw the thread about Peters Heat treat with the video of the shop tour. They specifically said they custom made a LN container SO THEIR BLADES DON'T go into liquid! So I just figured I'd be ahead to not get my container full but then JT's post has me wondering about that.
 
I bought a Dewar like Kuraki's and just dropped it off at the Airgas branch 20 min from my work. I was surprised at how few places have LN.
 
I buckle mine into my car with a seat belt.

Hah, the gas company here in Sweden told me that if I were to pick it up myself they wouldn't fill it if I didn't pass inspection on both the container and the transport situation. Which meant the container had to be designed for transportation of LN2 and during transport it had to be separated from the driver/passenger, which in my case meant a trailer.
 
Hah, the gas company here in Sweden told me that if I were to pick it up myself they wouldn't fill it if I didn't pass inspection on both the container and the transport situation. Which meant the container had to be designed for transportation of LN2 and during transport it had to be separated from the driver/passenger, which in my case meant a trailer.

I'm an incredible danger to the public. Liquid nitrogen buckled in like a 5 year old, propane tank on it's side in the truck bed, carrying a concealed handgun and a 4"+ double edged knife and a switch blade. :D
 
Hah, the gas company here in Sweden told me that if I were to pick it up myself they wouldn't fill it if I didn't pass inspection on both the container and the transport situation. Which meant the container had to be designed for transportation of LN2 and during transport it had to be separated from the driver/passenger, which in my case meant a trailer.

Same here. Must be in the box of the truck, and must be a certified dewar.
 
I buckle mine into my car with a seat belt.

That's exzactly what I do. I bring a blanket and kinda wrap it. Then pass the seat belt through the handles and buckle her up tight. It's funny because I also normally have a big propane tank on its side and also carry a gun but it's my 1911 so I do t try and conceal it. Then for a knife I use the spiderco farid CPM10 monster.

Your post made me laugh becaus I was thinking to my self. Self should I tell them how I transport my dewar.
 
We haul our in the bed of the truck. Pretty lax around here..Get this, when the coal industry was really booming there was diesel mechanics and equipment mechanics in every other building..Welding shop suppliers all over(still plenty of those)..
We use to be able to walk into them with a igloo cooler and get all the LN we wanted to freeze bearings with for a few bucks.Ah the good ol' days... We just paid $120 to fill our 31L dewar. It has a 2 5/8" mouth so the evaporation rate is a little higher but real nice for kitchen knives.. We used dry ice for ever with no problems but I hated driving to the store only to find they were out and then having to drive 45 minutes away to find it somewhere else..So if it costs $120 every few months then that's ok to keep from running all over creation to find dry ice when you need it.
 
So guys, you seem to have extensive experience of handling this stuff.

What's your take on these?

I read somewhere that the blade doesn't even need to be submerged for it to reach cryo temperature? Is this correct?

When do you guys fill your dewars? How small amount of liquid will still give me cryo temperatures?

How do you check your liquid level?
 
I have to drive the same distance to get dry ice as I do LN so there's no question I may as well get LN that lasts months.
 
So guys, you seem to have extensive experience of handling this stuff.

What's your take on these?

I read somewhere that the blade doesn't even need to be submerged for it to reach cryo temperature? Is this correct? Correct, it doesn't.

When do you guys fill your dewars? How small amount of liquid will still give me cryo temperatures? When there's no more liquid. If there's liquid, it's cryo temp.

How do you check your liquid level? I look in there, boiling, gtg, dry, need to fill
 
Can you clamp blades before they go into the dewer? If you can't is that an issue? I have been clamping my kitchen knives to prevent warping in dry ice
 
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