Using dry ice...

Rick Baum

Rick Baum

Joined
Mar 14, 2000
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509
I can't afford a liquid nitrogen dewar so I'm going to have to get by for a while with dry ice. Everything that I have read says to put the dry ice in your container and then fill with your desired non freezing fluid (kerosene, acetone, alcohol). What would hapen if the fluid was in first? Would the dry ice explode kind of like pouring warm water into a glass of ice cubes only a little more violent? Also, I was thinking of making a more permanent solution to the vessel that would hold the dry ice and Kerosene. I have an old milk can laying around and I am thinking of covering the outside of it with some expanding foam insulation a couple of inches thick. Won't be pretty but should keep things cold. What does everyone else do/use for their dry ice treatments? Any recommendations on soak times etc.?

Rick
 
When I was using that method I used dry ice and acetone. Temperatures ranged from -75°F to -100°F. Its going to be hard to predict precisely what will convert the most retained austenite most effectively. Both temp ranges will, but it will be longer for the warmer one. You got to experiment since dry ice is little less technical. More time or cold won't hurt though. If you had a faster quench in HT, typically you need less freeze time in other words.

Whatever you do, DO NOT USE STYROFOAM unless you feel a need to make homemade rubber cement. Storing the dry ice in it is ok, but do NOT put acetone in it. Melts the styrofoam instantly.

I used a small picnic cooler you can buy at the grocery store. Fill with acetone. Not entirely. The dry ice goes in after. It will bubble violently if you put larger masses and quantity in, so you have to guess at how high to fill, so it won't overflow when bubbling. So, again experiment. Start with small pieces. Use a face shield, BBQ tongs and a pair of gloves. It won't make any difference if you put the acetone in after, except for safety. I.e. splashing. Actually, the pouring wears away the ice rather fast though. So better to do acetone first.

I know Rlinger uses the method a lot, he might chime in here with some words on what he does.

Some info. Good luck!
 
Thanks Epsilon. Did you have any problems with the acetone evaporating. The fumes must be terrible. I was thinking of using kerosene so that I could keep reusing it. Do you think that there is a potential for colder temps using acetone over kerosene? How much dry ice did you use and how long did it last? I'm just trying to figure out how much dry ice would it take for a 24 hr. or longer soak. Nice looking website by the way.

Thanks again,
Rick
 
I use the Dry Ice - Acetone mix myself. I fashioned a deep thermos bottle out of 4" galvanized furnace duct inside 6" duct. I MIG-welded the inside duct to a 12"x12"x 1/4" square steel plate for solidity, then the 6" duct outside of that. I stuffed it with pink fiberglass insulation and then welded up a ring to fit the gap between the two ducts. Once I was satisfied with that, I bent up a hanger to hang the blade from when dipping it.

This makeshift thermos is 18" tall, but I hope to make one to accomodate a sword someday.
 
Thanks Higgy. Sounds like a slick setup. Have you done any before and after testing with the dry ice soak? How long of a soak do you try to get?

Rick
 
I'm not sure how much it would take for 24 hours to stay at a constant temp at least. Hard to accurately judge. You'd have to keep adding ice or have a better control over temp loss. It WILL NOT stay at -100° for 24 hours just by making a one time application. Even with good insulation I doubt. An immersion temperature probe is a wise investment over guess work. Tells you a lot.

Typically I bought a couple bricks from the grocery store. I put one in and let it cease its bubbling to a manageable tangent. :cool: Then added usually one or two more. Then found a space for the knives to rest in the liquid. If you add more ice to the same amount of liquid, your temp will drop. My efforts tended to be at -95° to -100°F for the first few hours. It remained at -60° to -70°F after maybe 12 hours. Sort of a low tech ramping eh? Doesn't do anything actually. Anyhow, try that.
 
Baumr,
Oh and the smell aint too bad. Unless you spill it all over the Arizona room like I did. :p I dropped the lid down and left a small gap (like 1/16") by not locking it down. Kept it like that overnight.

Don't know about the kerosene acetone mix. Might want to ask a chemistry wise smith on that one. Not sure of any potential hazards.

The acetone alone seemed to be at least mostly the same amount the next day.
 
I'm here. I have used kerosine. I pour the kerosine onto the ice, not the ice into the kerosine. I have experienced nothing violent. If I think to do so I cool the kerosine before applying it. I have had trouble keeping styrofoam coolers because the kerosine eats them up. It takes a couple days but it destroys the styrofoam. I have lined the coolers with plastic. That has helped but I always seem to succeed in getting kerosine on the cooler.

The important thing about the media is that it does not freeze at dry ice temperature. All kerosine I have used so far has had a small amount of water in it. This causes it to become a little slushy but has not caused freezing about the blade, which otherwise would cause the blade to not cool to dry ice temperature.

I try to get about 5 pounds of dry ice per cryo and a pound or two more is better. I use as small a cooler to accomadate the bath. The less vacancy the better for longevity.

Next time I will try another media - salt instead of kerosine. I saw that written somewhere. Should work just fine. I have not used acetone and do not wish to because of its volitile vapors. I have a gas water heater and heat with gas.

I also put my cooler in a freezer. This, obviously, gives the dry ice longer life. You CAN NOT cryo at dry ice temperature too long. I try to get two days of cryo using dry ice. As the second day wains the temperature slowly rises. I do not pull the blade until bath temperature reaches above 0 F.. This helps to eleminate thermal shock. I am still not convinced I understand how those that dip their blades into a -300 F. dewar prevent thermal shock. To expedite warming after the ice has mostly evaperated I usually lift the cooler lid and place cooler in a warm area.

To cryo (age) tool steel (I do this for stainless too), I do a snap temper before the steel cools to below 125 F. after heat treating(s). I let it cool to at least 140 F. though before snap tempering. After snap tempering and steel has cooled to room temp., I place in dry ice bath. After cryo and steel has acheived room temperature, I do the full tempers. These tempers do not need to be done immediately but the snap temper should be done immediately upon finishing the heat treat(s)/quench(s) - as described above.

Roger
 
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