qty of dry ice to chill a gal of denatured alcohol?

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bndshardr

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Oct 16, 2013
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Long time lurker, first time poster. I've learned a ton just following threads, I very much appreciate the shared knowledge in this forum.

I'm embarking on my first attempt at heat treating a steel which requires a sub zero bath following initial quench. How much dry ice will i need to chill a gallon of denatured alcohol (currently stored in my freezer to minimize the temperature drop to full-cold). And, how long can I expect it to take to reach its coldest temp?

Also, how much additional dry ice will I need to add for two 11" X .070" blades, say, 3 cycles for 20 minutes each? I'll be quenching the blades in cold water prior to each dunk in the dry ice bath.

Thanks all!

bndshardr
 
Okay, well my blades are bathing for their first cycle, however they came out of the foil pretty ugly. Please help me figure out what I've got here.
AEB-LpostAust_zps535daf1e.jpg


The steel is .070 AEB-L from Aldo.

I wrapped the blades in foil, double folded all the seams, then placed them in my food vacuum to further extract any air that might be trapped inside the packages. They puffed up considerably, then collapsed when the vacuum was released. I checked for punctures but couldn't find any,,, so, into the 1950F preheated oven they went. My oven is roughly 9X9, so these 11" blades had to sit diagonally, with the handle closest to the door.

I allowed the oven to come back up to temperature, then gave them 15 minutes then plate quenched them. I had to do them one at a time since I don't have enough room for more than one.

Thoughts?

-bndshardr
 
It looks to me like you had a pin hole at the point. Happens some time. You'll get some scale and some decarb but nothing that won't grind out.


edit: the bit of color is a good thing. It's normal and will frequently be burned off if you had a major problem. The black burnt crud on the point is not a good thing, but not that unusual. Was it near a heating element? It didn't over heat did it?
 
That's good to know. I was afraid that I'd badly overheated the tip due to the close proximity of it to the heating elements in the oven. If that were the case, would it show up in hardness, or would it retain good hardness, but with poor grain structure?

I also have some ATP-641 that I really like for carbon steels, O1 and the like. Could I coat the blades and wrap them in foil or a belt and suspenders approach? The instructions for the ATP indicate it's good up to 2400 but I've heard complaints that it really doesn't hold up that well at the higher temperatures.
 
You may have overheated the tip if it was up on an element. In this case, whether it would show up on a hardness test is complicated, but short answer, probably not.

No, you shouldn't need any other gunk under the foil and it would screw up your plate quench. Double seamed and rolled foil pouch works best with nothing inside.
 
Then I probably had a bum seal. The folded end was very close to the point of the blade, and that could have fouled the seal on the foil. I pinched the seals in a mill vice, but couldn't get the entire roll in the jaws on the tip-end of the pouch due to the proximity of the blade.

I think in the future, I'll do my food vacuum routine on a pouch that hasn't been fully sealed, allowing the evacuation process to pull more air out of the pouches and crimp the joints through the plastic bags before opening them up.

'Preciate the help.

bndshardr
 
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