Dry Ice and ????

Deweyknives

Deweyknives

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Nov 29, 2006
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I've read that people mix dry ice for Cryo [or sub-zero] quench with:

Acetone
Keroseen
Alcohol [Iso. or denatured??]

What do you use & why that mix?? Tell me about it if you have time.

What kind of bio-hazard is left after the dry ice has melted & what do you do with it??

After 10 years of carbon, I'm looking at stainless options. Located dry ice locally so 'here we go....' :)
 
Most commonly I've seen people mix it with Acetone. Not nearly as cold as a nitrogen cryo treatment but pretty damn cold.

Dry ice doesn't melt btw...it evaporates. I'm thinking that when it's in the mix and has "melted" it has evaporated out of the liquid and you're left with what you started with.
 
If you put a blade between two pieces of -109° F dry ice, the blade will become -109° F. Why would you need anything else in the mix? As long as enough metal is in contact with the dry ice you shouldn't need anything else. I've used rubbing alcohol, but the logic of it didn't make sense. I use a thick styrofoam cooler used to transport vaccines stuffed inside of a larger styrofoam cooler used to store steaks from those crappy steak companies selling out of the back of a truck. It's a total of about 4" thick and will keep 2 lbs. of dry ice for over 24 hours.
 
Basically you need a liquid that is relatively safe and doesn't freeze at -78C. Dry ice is just solid carbon dioxide so once it sublimates (it goes straight from solid to gas) it's gone into the air for good.

I think the only reason for the liquid is that it transfers heat much more rapidly and uniformly than air.
 
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I use acetone. I believe it has the lowest freezing point of the fluids mentioned. It "boils" a bit from the sublimating dry ice at first so you want to be careful to avoid a mess. I add a few chunks of dry ice and once it chills a bit I can add the rest without much drama. Obviously you want to use glass or metal with acetone, plastic will melt.

I get dry ice at the Harris Teeter here in town. A couple pounds will treat my usual 10 blade lot without any problems and is relatively inexpensive.

Once acetone is extremely cold it doesn't make a lot of fumes. However I still recommend doing this is a well ventilated area.

After the HT I simply pour the acetone back into the original container. I leave the lid loose a day so air can get in and carbonation can escape.

In my testing of some alloys with dry ice or full cryo I can not find any difference in edge retention from the special carbide formations you get with full cryo. And when you consider the thermal shock of liquid nitrogen on untempered martensite I think there may be an argument for the use of dry ice over full cryo.

A lot of steels will perform significantly better if quenched to sub zero as a part of the original quench. You want a continuous reduction in temperature all the way to Mf without long delays. Plates-> water-> dry ice.
 
Acetone presents a fire hazard.

The "boil" is CO2.

I've used acetone a lot in the lab going back to the good old days when safety precautions weren't as restrictive. Use in a well ventilated room and the fire hazard should be minimal.

Both the acetone, which is a pure compound-not a mixture, and the dry ice/CO2 should evaporate/sublimate leaving no residue to deal with.
 
I was going to do this and needed a couple gallons to fill my small "lunch box " cooler..........
Dang Kerosene is like $12 a gallon..........F that

I used gasoline...........

I know , I know.........

What a hazard it is.......

Dont be a waterhead and put it near the forge, or smoke around it. Just use a bit of common sense.

The S30V blades came out real nice , it took more than 5 hours for the dry ice to evaporate from the cooler.
That stuff holds and incredible edge.... I'm sold on the process for S30V.


YMMV , JMHO
Dwane
 
I was told a long time ago , if I was going to do the dry ice treatment to use kerosene , because of the volitility(?) of acetone or alcohol , and that it wouldn`t freeze but turn to jell. When finished I just return kerosene to container until needed again . That`s just how I was taught and continue to do it that way .
 
I use denatured alcohol. Once the dry ice sublimates and the alcohol comes back to room temp. I put it back in the original container and reuse it the next time I need it. I will be doing a batch of 20 blades tomorrow.
 
Remember that you can also use your kerosene as "flux" for initial welds on a damascus billet.;)
 
We did a thermometer calibration at work last week. We used a dry ice and isopropyl alcohol mix. It measured -77.8°C.

Ric
 
First:
The dry ice bath is a way to finish the quench for stainless steels. These steels do not finish the martensite transformation at room temp, but need to be taken down to far below zero - around -95F. This should be done in as continuous a line as possible. Short delays at room temp are fine, but it is all one single quench. An interrupted quench should only be interrupted for a short period of time.



I have a gallon can of denatured alcohol from the Big Box hardware store for $14. I re-use it after letting the dry ice sublimate. I shake the can a bit and leave the cap slightly loose for a day to let any dissolved CO2 get released.

I don't like the greasiness and smell of kerosene, and stopped using acetone because it is too volatile ( evaporates too fast). The can of alcohol is still about 2/3 full after a year or two of use.

I take the blades from the quench plates and cool with water to room temp. I put them in the room temp pan of alcohol and add the crushed dry ice. I use about three pounds to the can of alcohol (about $5 worth). It really only takes around ten minutes to bring the blade down to the Mf point, about -95F. I leave them in for thirty minutes to an hour, just to feel like I am getting my money's worth from the dry ice. The bath will last several hours, so if you are doing several batches of blades, you can cycle them in and out, or just add them as they are ready and leave the others in the bath.

Following the sub-zero quench, immediate tempering is required. Two cycles at temper for two hours each. There is no real benefit for doing a sub-zero between the tempers.



Cryo is different from Sub-zero, and the times and procedures are different. The above only applies to sub-zero quench.

Final comment:
A freezer, no matter how good, will do nothing to make the blade harder or tougher ( not even if it sits there overnight). It requires reaching the full Mf at -95F to get that gain.
 
I'm in agreement with Nathan on the LN shock, when I used it a lot (LN) I would
suspend the blades on a wire over the LN before immersion.
Now its frozen plates while still in the packet- just a few seconds and I cut the
packet open put the blades and springs back into the plates and clamp for a few
minutes this keeps things pretty straight. Immediatly go into the dry ice and alcohol
and i usually leave the blades in overnite. This whole process takes less time than
it does to type this.
Ken.
 
With cryo in LN, you need to either slowly drop the temp, or do a snap temper for 30 minutes to relieve some stress. Dropping the temp of a solid and hard object 400+ degrees in a few seconds can tear it apart.
 
bladsmth said:
Final comment:
A freezer, no matter how good, will do nothing to make the blade harder or tougher ( not even if it sits there overnight). It requires reaching the full Mf at -95F to get that gain.
Click to expand...

Do you just mean a regular home use frost free freezer? Is a -80C freezer ok? ( -112F ) Just asking because we use alot of -80's in labs down the hall from my office, and free for me to use when I need to. The cryo tanks we have are a little more tricky to use so I prefer to avoid them.
 
We had one of those super chillers at Virgina Chemicals for storing samples.

-80C is great for the quench finish, but the delay in getting the blade from the quench plates to the sub-zero freezer in the lab may be a bit of a problem. Ideally, it should be within minutes of the plates.
Of course if you have HT ovens at work, there is no real problem ( unless the boss is not a knife guy).
 
Been using kerosene, but, am going to go to alcohol as the kerosene really foams when you drop the dry ice in and it is too easy to foam it over.
 
Stacy,

Any thoughts on how much better LN is than dry ice (see Nathan's comment that they don't seem different to him)? I still haven't gotten around to getting a dewar ($), and dry ice is available about 5 minutes from my house.

Also, any thoughts on a bath versus just making sure the knife is packed in dry ice? The metal should conduct temp pretty well, but I worry a bit about warping with uneven cooling...
 
LN is far colder than dry ice, and will get the blade down into the cryo zone. You don't need that to finish the martensite conversion, but it does change the carbides. It is also more efficient than dry ice, as well as being reusable. The trade off is that it is more expensive, and requires a dewar. For the hobby shop doing a blade or two a month, dry ice is the way to go. For a shop doing a batch of stainless blades every week, LN is the way to go.

The metal being a good conductor of heat isn't the issue. Dry ice sublimates into CO2 gas. The stuff around it is air. Both media are terrible conductors of heat. The liquid is needed to insure a full and even transfer of heat from the blade to the medium ( cold does not go in....heat comes out). Just packing in dry ice is not a guarantee. It probably works, but probably isn't my favorite word. A few bucks worth of alcohol takes that word out of the equation.
 
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