Question About Handling Dry Ice

i4Marc

i4Marc

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Oct 19, 2011
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Just a quick question about proper handling and precautions when working with dry Ice. I'm setting up to do a sub zero procedure for and AEB-L blade. Are there any particular precautions as far as handling the dry ice beyond wearing gloves? How small do you need to break up the chunks in order to get the most efficient slush? I'll be using denatured alcohol for the medium.
 
I typically try to keep it to at least 1 1/2" sphere-ish chunks, but really haven't seen much difference if I go a bit smaller or bigger. As long as it all doesn't melt (or rather evaporate) by the time the knife needs to come out of the bath, it should be ok.

No real precautions are required other than gloves. Oh, and look out for the alcohol boiling over when you add in the dry ice - add it in very slowly at the beginning!
 
Wear heavy enough gloves to protect your hands from the cold. Make sure they are dry.

I break the dry ice into chunks about the size of charcoal briquettes, which also makes a bunch of small bits and dust. The little stuff will quickly drop the temp of the alcohol, and the bigger chunks will last a few hours. There is no need to leave the blades in the DI slurry for more than 10-20 minutes. The austenite-martensite conversion is finished as soon as the blade reaches -100F, which would happen in a few minutes, but a little extra time won't hurt.

When the dry ice is all evaporated, let the pan sit for a while and then pour the alcohol back in the can. It can be used over and over again for sub-zero baths.
 
i4Marc said:
Just a quick question about proper handling and precautions when working with dry Ice. I'm setting up to do a sub zero procedure for and AEB-L blade.
Are there any particular precautions as far as handling the dry ice beyond wearing gloves? How small do you need to break up the chunks in order to get the most efficient slush? I'll be using denatured alcohol for the medium.
Click to expand...




The melted ice sublimates in to CO2 gas

If you are working in a small unventilated space, you can suffocate.
 
Dry ice is not particularly dangerous.

I bust it into smaller chunks in a plastic bag with a mallet.

An interesting effect of getting acetone very cold is it stops evaporating, so there are fewer fumes.

The dry ice can carbonate the acetone, so when you return it to the can be sure to leave the cap on loose overnight so you don't pressurize it.

Large volumes of acetone are a serious fire hazard. Don't do any of this in your home or near fire.
 
I'll tell you how I handle dry Ice when doing sub zero , I take the small left over pieces from crushing and drop them into a large glass of white wine...homemade sparkling white wine with a mad scientist twist ;0)
 
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Thanks guys. I will be using denatured alcohol instead of acetone. The procedure will be done in an open detached garage. I bought a red plastic 2.5 gallon gas can to put the used alcohol into. Any issues with alcohol in a plastic fuel container?
 
I was planning on using an old ammo can, and just leaving the alcohol in the can all the time. After doing a SZ quench I had planned on letting it sit open for a day or two so that any CO2 is gone, and then just putting the lid back on. Is there any concern with leaving the alcohol in the same container that you do the soak in? Also Stacy, I've been told that the SZ should be for 8-12 hours if using Dry ice and alcohol, but shorter if using LN because it gets so much colder. Is that incorrect? Will any damage be done by letting them soak for too long?
 
^^^ I was told the same, and have been meaning to ask Stacy (or someone else). My (long forgotten) theory of metallurgy agrees with Stacy's statement above, though. I usually just leave it in there overnight (I mainly only work on knives at night), but it would be good to know for future reference.
 
Leave the DA/acetone in the same container that you did the quench in, lay some saran wrap over it till it warms up to minimize evaporation and explosion hazard, Then use a funnel to put it back in the same container you took it out of, leave the top open just a tiny crack to let the CO2 out.... easy peasy

J. Hoffman, anything that can evaporate and explode should be put back into the same airtight container that it came out of, this will also give the firemen a heads up if your shop was to catch on fire
 
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The conversion is temperature driven, rather than time driven. You just have to make sure the steel cools all the way through.

Take a small cooler with you when you pick up the dry ice. It makes transport easier.
 
A freeze treatment (dry ice bath) is done to convert a larger percentage of RA into Martensite. It only takes a few minutes to accomplish this. LN does the same thing but a longer soak at the lower temps. of a true Cryo has the added benefit of forming ETA carbides.
 
12345678910 said:
The melted ice sublimates in to CO2 gas

If you are working in a small unventilated space, you can suffocate.
Click to expand...

While good ventilation is always required when handling gasses and solvents, I would not normally suggest having a tank of alcohol and dry ice inside the shop.

Here are some interesting facts about CO-2:
Normal air has about 0.04% CO-2
At 1% (25 times normal) you will start getting woozy.
At 10% ( 250 times normal concentration) you will suffocate.
It takes a lot of CO-2 to kill you.
CO-2 is 1.66% heavier than air, and will flow along the floor and exit through an open door. Unless the room is tightly sealed, CO-2 will dissipate fairly fast.
 
NEVER, EVER, put the dry ice in your pants.

Just kidding its safe.

Anyways I have never done my own heat treating and am interested in this thread, thanks for all the good info!
 
The only thing that you should store in a gas can is gas and your elbow ;0)

Over the years I have had 2 volunteer firemen work for me and both stated that flammables stored in wrong containers and propane cylinders hidden out of sight were the two biggest dangers in a garage/shop fire

The explosive potential difference between gas and alcohol is significant, a firefighter will treat them differently in a fire
 
Is there any problem/benefit to simply placing the blade between two pieces of dry ice? It seems it would allow a bit of a cooler temp (albeit perhaps only a few degrees) because it wouldn't have to cool the liquid medium...
 
bladsmth said:
While good ventilation is always required when handling gasses and solvents, I would not normally suggest having a tank of alcohol and dry ice inside the shop.

Here are some interesting facts about CO-2:
Normal air has about 0.04% CO-2
At 1% (25 times normal) you will start getting woozy.
At 10% ( 250 times normal concentration) you will suffocate.
It takes a lot of CO-2 to kill you.
CO-2 is 1.66% heavier than air, and will flow along the floor and exit through an open door. Unless the room is tightly sealed, CO-2 will dissipate fairly fast.
Click to expand...

The "nice" thing about dry ice is, though, unlike CO where you can accidentally inhale it, you definitely know when you inhale a lot of CO2. Experience from a previous job where they kept large insulated coolers of sort of dry ice - leaning down far into those to grab it off the bottom, one made sure not to inhale - it burns quite badly. For such, ventilation is certainly important. I will also emphasize the point about dry gloves - nice, thick leather gloves kept dry should be plenty of protection, but still try not to grasp pieces of it firmly for too long, as the cold will always transfer more quickly than you realize. Be safe, and enjoy your project!
 
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