Sub Zero

Cardinal Knife

Cardinal Knife

Joined
Nov 25, 2007
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340
I treated two .070 AEB-L kitchen knives over the weekend and had my first bout with performing a sub zero quench. I used Acetone and about 1lb of dry ice. I didn't know if I could use plastic so my tank ended up being a 12 cup glass coffee decanter. Readings were taken with a infrared thermometer off the surface.

Temps only dropped to about -57 and seemed to evap pretty quickly. I assume I need more dry ice?? And a larger pot? What do you guys use stainless culinary pot then insulate it around the outside?

Pre sub zero readings were around 61-62 avg and post sub zero were a bit higher with a couple 63 readings.

Thanks Chris
 
I use 5 lbs crushed to form a slurry. Good call not using plastic as the acetone may have dissolved it. I use a steel container even though i use denatured alcohol instead of acetone as I would be concerned about plastic getting brittle with the cold. Are you sure your thermometer can go lower than what it's reading?
 
Kevin McGovern said:
I use 5 lbs crushed to form a slurry. Good call not using plastic as the acetone may have dissolved it. I use a steel container even though i use denatured alcohol instead of acetone as I would be concerned about plastic getting brittle with the cold. Are you sure your thermometer can go lower than what it's reading?
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5 lbs wow, is that considered the norm? Not sure what the thermo goes down to. Why do you choose to use alcohol Kevin?
Chris
 
Cheap, works well, less fumes. I use 5 pounds because that's what it takes to get slushy consistency in my container
 
This is one reasion I love LN. I normally do a 24hr soak at -300 and it's nice having it on hand all the time. No need to run to the store to pick up $10 worth of dry ice to do one blade.

I would not trust a temp gun on these cold temps. You will use up some of the dry ice just bringing the liquid down to temp. What your after is getting the blade to dry ice temps, to do that you need to make sure there is enough dry ice in the liquid to keep it and maintain that temp. Think of it like a single ice cube in a glass of water. Takes a while to get the water temp down and it will melt befor the water hits 32°. But if you crush the ice up and make a slush of sorts your just about instantly at 32°. It's actually accurate enough to calabrate food grade thermometer.
 
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JTknives said:
This is one reasion I love LN. I normally do a 24hr soak at -300 and it's nice having it on hand all the time. No need to run to the store to pick up $10 worth of dry ice to do one blade.

I would not trust a temp gun on these cold temps. You will use up some of the dry ice just bringing the liquid down to temp. What your after is getting the blade to dry ice temps, to do that you need to make sure there is enough dry ice in the liquid to keep it and maintain that temp. Think of it like a single ice cube in a glass of water. Takes a while to get the water temp down and it will melt befor the water hits 32°. But if you crush the ice up and make a slush of sorts your just about instantly at 32°. It's actually accurate enough to calabrate food grade thermometer.
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JT, I'm just a hobbyist. Don't HT enough to advocate an LN setup.
 
Use at least 2# of DI and a quart of alcohol (or acetone). I use 5# of DI in about three quarts of denatured alcohol (it started out as a gallon). Use a metal pan of some sort. For small knives, a bread pan will work. For larger ones, a gallon coffee can will do. I like a long pan called a whole fish pan. An old autoclave pan is also perfect. Don't use plastic or glass. Both can shatter from the cold without warning and spill -100F slurry over the floor and your shoes. There is no need to insulate the pan of DI or place in a cooler. The transformation to martensite ends as soon as the steel reaches Mf ( around -90F), so a long soak does no more than a short one. The slurry will last for many hours sitting out in the air before all the DI sublimates.

Reading the temperature of a a sublimation atmosphere (the cloud of CO-2 gas and water vapor mist over the slurry) with a laser thermometer will not be accurate. You are reading a cloud of warmer gas and liquid surrounding the colder liquid. The best way is with a contact probeIn the liquid, the knife comes down almost to the temp of the DI in the slurry. This is usually around -90F.


BTW, most non-contact (laser) thermometers are not accurate at these temps, -40 to -50 is the lowest most read. I'll have to look at my laboratory pyrometer tonight, but I don't know if it even goes to -100 accurately.

Funny story:
When I was doing research at Virginia Chemicals, one of the PhD's wanted to super cool something, so he went over to the cryo lab and brought back a coffee pitcher with about a litre of LN. As he sat down at his lab bench, he set the frost covered pot down on the granite top just a little too firmly and the pot disintegrated into tiny pieces of glass ... as the LN ran over the edge and onto him. He jumped up and was standing there, holding the pot handle with no pot attached, and had a big wet spot on his pants. At first we all thought it had spilled on him and frozen his family jewels. Then we saw that it had fallen on the floor and his shoes, not his lap. It had scared the piss out of him ... literally!
Luckily, it didn't do any harm to his feet, but he had to go wash off his pants. He put on a lab coat and went back to work while we hung his pants outside to dry. I went over and brought back more LN in a proper transfer dewar.
 
Stacy E. Apelt - Bladesmith said:
Funny story:
When I was doing research at Virginia Chemicals, one of the PhD's wanted to super cool something, so he went over to the cryo lab and brought back a coffee pitcher with about a litre of LN. As he sat down at his lab bench, he set the frost covered pot down on the granite top just a little too firmly and the pot disintegrated into tiny pieces of glass ... as the LN ran over the edge and onto him. He jumped up and was standing there, holding the pot handle with no pot attached, and had a big wet spot on his pants. At first we all thought it had spilled on him and frozen his family jewels. Then we saw that it had fallen on the floor and his shoes, not his lap. It had scared the piss out of him ... literally!
Luckily, it didn't do any harm to his feet, but he had to go wash off his pants. He put on a lab coat and went back to work while we hung his pants outside to dry. I went over and brought back more LN in a proper transfer dewar.
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Thanks Stacy. Story scared me I was waiting for the part where it spilled on his crotch. Guy got lucky.
 
I just checked my $1500 lab laser pyrometer ... it goes to -58F. I checked the specs on a ferw other good ones, and they are also -58F.
 
I cut the top out of a rattle can, and the bottom out of another (spray bomb paint cans) and soldered them together. This gives me a tall
can. #3 of DI and denatured alcohol and I often still have DI left in it the next day. I've put it in a chest freezer on occasion and it seems
to help a little. The best thing for it seems to be a bean can over the top and the whole thing sitting in a 5 gal. bucket of sawdust. I have a
dewar and now and then use LN. For the $5 it costs for #3 of DI its hard to beat----- plus it gets me out of the shop for a ride.
Ken.
 
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