Sub zero treatment

Stromberg Knives

Stromberg Knives

strombergknives.com
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Jan 3, 2015
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I'm about to try out some sub zero treatment with dry ice.

What would be a good ratio between alcohol and dry ice? And how much of it would be enough for a couple of blades?

Thanks!
 
It's all depends on size of blades, and size of container. What you are looking for is a nice slurry of DI and liquid. If your blades are thin and laying on side it's VERY easy for them to warp in the mixture. It really seems best to hang vertically using a wire thru the tang holes and completely submerge the blade. It will take somewhere around 3 liters of alcohol for around 2 kg of ice.

Ken H>
 
I'm not sure about warp, Ken. I have done hundreds, most all very thin, and never had a warp. They sit in the bottom of a long stainless pan called a "Whole Fish" pan. I am sure hanging by the tang would be a good method if you had a tall enough and stable metal cylinder.

I use a gallon of denatured alcohol and 5 to 7 pounds of crushed dry ice.

I pour in the alcohol, add the DI a bit at a time (it foams a good bit as the temperature drops), mix with a wooden paddle, and let sit a few minutes, Then I set in the blades flat on their sides. I have put form one blade to 20 at a time.

When done with the sub-zero treatment, I let all the DI sublimate, then pour the alcohol back in the can ( labeled "SUB ZERO"). I put the cap on a bit loose to let any gas escape overnight. The next day when the alcohol is back at room temp, I shake the can well, release any pressure, and then tighten the cap. You can use it for years.
 
Thanks! I've got a gallon of denatured alcohol. And now I know how much DI i should get for each batch.

I have a ammo box with a rubber gasket under the lid that I thought about using. Maybe I could even store the alcohol in it between uses.
 
By the way, is it necessary to have a thermometer to measure the temperature of the slurry?

Or do you feel certain you attain the correct temps and doesn't bother?
 
A good slurry of DI and denatured alcohol will be in the -95ºF range - you can almost check your thermometer with it. Well, not quite a good test, but it will be close provided you've got a good slurry. Sometimes I will check the mixture, but other times I don't bother putting probe in mix.

The ammo can would store nicely, but not sure about adding the DI to the alcohol. Like Stacy, I've always put the DI in container, then added alcohol to get the slurry.

Stacy - How do you get the blades laying flat when putting blades into slurry? I tried laying flat, then laying with edge down and really had issues with warp on blades using AEB-L in <.090" range. Do you lay your blades flat in pan, then add DI and alcohol? I would think the blades need suspending in slurry so there is slurry all around blade?

Ken H>
 
Okay! Thanks, I like to be sure about things. So I'd like to measure the temp, but I can't seem to find a thermocouple that does less than -50 degC. I've been looking at eBay and almost every TC starts at 0 degC or at best -50 degC.

I've found some that start at -200 degC, but they are described as for EGR use. And the few I've found seem to have spade lugs, do you know if I could mount a type K male connector plug on it for use on a thermometer with type k TC inputs?
 
No need to check the temperature. The dry ice will make the slurry a constant temperature until all of it sublimates. It will be about -90F and hold that steadily for a coupe hours. The only thing that make a difference in the temperature is the type of alcohol.

It is like putting ice cubes in a glass of water. The water will be exactly 0C/32F until the last sliver of ice melts. Nothing you do will change it.
 
Sorry, haven't had the time yet. Have been using all spare time rearranging the workshop preparing for my new grinder. So I've just prepared the ammo box and alcohol. If everything goes as plan (which by experience is never) I hope to try out some heat treating of Niolox shortly (with the sub zero treatment).
 
HSC /// said:
any update on this from you?
thinking I might want to try this
Click to expand...

I did my first sub zero treatment this weekend. My setup was as described, I have one gallon of isopropanol alcohol in a ammobox with a small rack at the bottom. For the blades to stand on spine down. I then added the dry ice pellets.

After I'm done I just leave the lid open on the ammo box until the dry ice fully has sublimated, and then close the lid.

View attachment 678422
 
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