Who What and Where for a good, safe Dewar???

Lerch

Well-Known Member
Hi all

well i thought i had me a dewar so i could finally start LN cryo treating but when it arrived today i realized that it would not be adequate. the top was extremely loose fitting and was not intended for storage, just holding briefly

I am need a dewar i can use to store LN in for as long as it will last and i can transport roughly 20 miles by personal truck. My knife shop is in my houses garage so i need to know what will be safe and will take a determined person to get open. I have a 1.5 year old son who is never allowed in my garage, but i wanna be as safe as i possibly can. I need something with a good screw on or latch down lid, if i could install a lock even better.

also when LN cryo treating is it important to submerge the handle of the knife, or only the blade. I figure i need a dewar that is 12" deep and roughly 4" internal wide

any help would be awesome, my cousin is trying to get me to use a 25 quart Yeti ice chest since they are virtually air tight but i dont know how safe that would be. they are lockable.

thanks
steve
 
Lerch,

Before you run out and buy something to store LN in, you may want to do a little more research first. My first call would be to where you think you are going to buy the LN from and see if they will even sell it to you. They absolutely will not put it in a 25 quart ice chest. Some things you should know:

-LN is approximately -325 degrees and will extremely burn any skin that comes into contact with it, including eyes.
- LN can not be stored in a sealed container, it must be able to vent off the gas pressure as the liquid boils. If it can't vent, the container blows up.
-Just because you find a dewar on fleabay, does not mean it is any good. The way a dewar works is by trapping a vacuum between the inner and outer containers (like a thermos) and that vacuum will degrade over time. If the one you buy has lost its vacuum, the LN will boil off very fast. By the way, ALL dewars lose vacuum at a certain small rate even when new.
-The smaller the dewar, the faster the rate of LN loss will be.
-Caps for a dewar are usually a foam plug with slots cut down the sides to allow venting of pressure while still allowing some insulating factor.
-You want a dewar with a large enough neck opening to allow the widest blade you are going to make to pass thru.
-You want a dewar deep enough that you can get the entire length of the blade in it and still put the plug in. If you leave a tang sticking out of the LN into open air, it acts as a radiator and helps to boil off the LN faster.
-Most dewars that you will be looking at will not be anywhere near childproof. Some have lockable lids, but if knocked over they will still spill NL out.
LN gas vapor is heavier than air and will displace oxygen in low lying areas. Personally, I would not recommend storing it in your house, even in an attached garage. Proper ventilation of the storage area is a must.

Last but not least, unless you have a proper digitally controlled heat treating oven and are working with stainless steels, I wouldnt worry even about cryo quenching the blades.

Brad
 
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