do you do cold or cryo treatments?

hardheart

hardheart

Joined
Sep 19, 2001
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just wondering who uses either, and for what steels.

Also, is there really a reason to use acetone with dry ice for knives? I noticed the temp of the mix is higher than just the solid alone, and a flat blade should contact fully. If you let it sit overnight, wouldn't the temp of the blade should still reach that of the ice?
 
hardheart, out of curiosity, what is your info source that the temp of dry ice versus a dry ice/acetone bath are different? They should both be -78C. thanks.
 
It probably doesn't make any difference whether you use acetone or not.
 
While I agree with Larrin that they will both produce the same low temperature, you will get slighttly uneven cooling initially if you use pellet dry ice instead of blocks. Whether that sets up any localized stresses may be a totally moot point and not amount to anything. I wouldn't, however, just set the blade on the top of a dry ice block instead of sandwiching it.
 
hardheart said:
it says dry ice + acetone is -72C, dry ice alone -78.5C. I don't have a way to measure that low to check myself.
http://yarchive.net/metal/dry_ice.html
Click to expand...

Actually, the author says it's *F, which makes him wrong from the start; I assume it's just a common typo like we all make. All I can tell you is that if you search on the term "dry ice bath", you will see numerous references in Google that say unequivocally that the temperature is -78C both as is melting point (sublimation) and in a bath with either acetone or isopropanol. It's an accepted measurement in chemistry, verified thousands of times daily in laboratories during the normal course of working.

Not looking to argue at all, but from what I read in your posts, you prefer accurate information.
 
here's a few

fitzo - true, I'd like to try to find more accurate info, and I was kinda wondering how the mix could be warmer. If the temp was above -78, I was wondering how there would be any CO2 left in the acetone, since it doesn't become liquid.
 
heardheart, that table you posted links to a site my PC-cillin flagged immediately as "Dangerous". Might wanna close and re-open your browser to clear it. Might just be my paranoid AV, too.

There are a couple mixtures that produce warmer temps: http://www.vanderbilt.edu/AnS/Chemistry/Rizzo/stuff/baths.html I wouldn't recommend either for home use. :) Salt/water/ice will produce a subzero temp, as will ice/methyl (wood) alcohol, but only something like -10C. PITA to get them right.

In order for the dry ice solvent bath to remain at -78C, there has to be a decent enough amount of dry ice remaining to keep it cooled convectively. Like Ornitz' post stated on rec.metalwork, the liquid only provides complete contact with the cooled object. Stuff it between two slabs of CO2 and it will be fine.
 
hmm, that's strange, it's an image on imagevenue.com that I just scanned and uploaded from my copy of the Heat Treater's Guide.
 
Might just be one of the ads on the site...Trend Micro prefers over-reaction to under-, it seems. It said "hacker hazard".

I just checked it again, and didn't get the same warning. Had to have been the pop-up at that time. Sorry for any fearmongering.
 
Well I think we have figured out that there may be some diff in temps with acetone or not acetone.
Back to the question. What does it do to the steel . Is there an advantage to a dry ice cryo? and how soon should it be used after quench?
Please excuse any mis spelled or used words.
Take care
TJ
 
I use cryo on all air quench steels. It makes a difference of 1 - 2 RHC points - and although I temper to the same range, I know it has made a difference.

Rob!
 
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