Liquid nitrogen

[Garry Keown]

I have just bought 6 liter Dewar so I can get a better blade from the NitroV I will be using in place of the 12C27I had used up until now.

Three questions for those who use this for their blades.

Is there any advantage in having the Dewar in a insulated box filled with the likes of bean bag styrene (or similar

insulation) 

Is it any advantage to pre cool in standard freezer to bring them down from room temp first

Is there any advantage for carbon steels to the LN quench.

[Jerrod Miller]

The answer to all 3 is "technically yes, but negligible".  

 

With the caveat that the first really depends on the quality of the Dewar you got.  

[Brian Myers]

The Dewar is really there just to hold it at temperature, it won't stop the liquid nitrogen from evaporating over time. And a good vacuum Dewar will keep it at temp by itself. To truly store it requires it to be kept under pressure in special tanks that are way to expensive and dangerous for your average bladesmith to have around. Remember to have your workshop well ventilated, liquid nitrogen is always evaporating and pushing past the Dewar plug and it expands to a gaseous state just under 700 times its liquid volume. Because its odorless and colorless,  you could walk into a shop that has a deadly atmosphere.

 

Many smiths use a bath of kerosene or acetone that has been filled with dry ice because it reaches that -100F/-73C degree state that Nitro V needs, and doesn't really need special storage beyond a proper flammable liquid storage jug. When you're ready for cryo, go to your local Kroger, or whatever store in New Zealand carries it, and get a block of dry ice and go to it.

Edited September 23, 2020 by Brian Myers

[Alan Longmire]

2 minutes ago, Brian Myers said:

kerosene or acetone

 

Somebody once told me to use RV antifreeze with dry ice, as it is not flammable and doesn't evaporate.  Never tried it, though.  

[Brian Myers]

2 minutes ago, Alan Longmire said:

 

Somebody once told me to use RV antifreeze with dry ice, as it is not flammable and doesn't evaporate.  Never tried it, though.  

Hmm...I don't think so, but I have no experience with it. The data sheets say antifreeze freezes at around -30 to -50 depending on the type. But I just don't know lol.

[Garry Keown]

1 hour ago, Brian Myers said:

The Dewar is really there just to hold it at temperature, it won't stop the liquid nitrogen from evaporating over time. And a good vacuum Dewar will keep it at temp by itself. To truly store it requires it to be kept under pressure in special tanks that are way to expensive and dangerous for your average bladesmith to have around. Remember to have your workshop well ventilated, liquid nitrogen is always evaporating and pushing past the Dewar plug and it expands to a gaseous state just under 700 times its liquid volume. Because its odorless and colorless,  you could walk into a shop that has a deadly atmosphere.

 

Many smiths use a bath of kerosene or acetone that has been filled with dry ice because it reaches that -100F/-73C degree state that Nitro V needs, and doesn't really need special storage beyond a proper flammable liquid storage jug. When you're ready for cryo, go to your local Kroger, or whatever store in New Zealand carries it, and get a block of dry ice and go to it.

The reason I went withn the LN over the dry ice is that we can no longer get the dry ice locally. It has to be ordered from city 300 mile away and in larger quantities than we typically need while the LN is available by the liter from the welding shop where I go every week.

Edited September 23, 2020 by Garry Keown

[Brian Dougherty]

1 hour ago, Garry Keown said:

... while the LN is available by the liter from the welding shop where I go every week.

Wow, I would have given for that kind of access to liquid nitrogen as a kid 

It's just the opposite where I live.  I can get dry ice at my local welding shop for a few cents a pound, but LN is pretty much impossible.

[Garry Keown]

7 minutes ago, Brian Dougherty said:

Wow, I would have given for that kind of access to liquid nitrogen as a kid 

It's just the opposite where I live.  I can get dry ice at my local welding shop for a few cents a pound, but LN is pretty much impossible.

LN is about US$10 a liter here

[Alan Longmire]

16 minutes ago, Brian Dougherty said:

It's just the opposite where I live

 

Same here.  And we both live adjacent to universities with science-type stuff happening.   

 

Garry, we can get those 5-litre dewars here too, used for transporting certain biologicals associated with livestock breeding.  They will hold a full dose of LN for about three to four weeks if the seals are close to perfect.  

 

Both of the above are reasons why when I finally start using stainless for folders it will be very much a batch process.  Lots of blades and springs ready for HT at the same time, all out of AEB-L/12c27. Enough to fill the kiln.  I figure that way I can do enough parts in one day (harden, cryo in dry ice, temper) to keep me busy for months without having to go buy more cryo materials.  The AEB-L is fine with dry ice temps, the supersteels need the LN.