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.
