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Puffy Pouches

T

Taz

Knifemaker / Craftsman / Service Provider
Joined
Apr 28, 1999
Messages
2,606
I seem to always get puffy foil pouches when heat treating. I add a little baby powder so the foil doesn't stick, a small piece of paper towel to help remove any oxygen and I press the foil down around the outline of the blanks, then double seal all edges. But as soon as I put them in the kiln, they puff right up! Is is the paper towel or baby powder??
 
Probably the baby powder. if the ingredients include cornstarch (common) cornstarch will expand and swell during heating. Pure talcum powder does not.

From Dr. Google:

Cornstarch is a plant-based carbohydrate that is significantly more reactive to heat than talc.
  • Heat-induced degradation: When heated, cornstarch granules swell and burst, a process called gelatinization.
 
T Taz I have given up on any additives in the foil due to the same issue you mention. My latest, and best results, come from cleaning the steel thoroughly with alcohol or acetone prior to adding them to the packets, and making triple seams at the edges. Additionally, it's a good idea to wipe the internal side of the foil packet itself with the same alcohol or acetone to remove any contaminants. In general, I find if you keep all the metals clean, no additives, excellent seams to keep air out, and insure your not pokiong any holes (like with the sharp tip during sealing, the vacuum effect works very well....no more poofy.

Best,
John
 
Thanks guys! I will get some pure talk and try that! I am going to 2150 with magnacut, so I want to make sure the pouches aren't sticking at the higher temps.
 
SharpBits said:
Haven't they all switched to corn starch now after the lawsuits over ovarian cancer risks?
Click to expand...
They may have, I haven’t looked at the ingredients on bottles out there now. This bottle is pretty old. Johnson’s might not sell it anymore as pure talc but a quick google search shows it’s out there. I’ve been using it on CPM154 for years, I had the foil weld to the blade twice and never had anymore problems after dusting the before heat treated.
 
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I get puffy pouches when using baby powder, so I quit using anything. But I would also wipe the blade down with Wd40 first, then remove the excess oil, so the powder would stick. Not sure if it was the oil residue or the powder. I'd rather the foil weld to the blade than deal with puffy pouches. Just got through heat treating an AEBL knife and 10V. They had a bit of oil residue on them but I just lightly rinsed it off with water, no soap. The pouches didn't puff up, nor did they weld to the blade, they came out perfect.
 
Are you guys having issues with 309 foil welding to the blade?

I know I use to have issues with 321 sticking but once I went to 309 zero issues.
 
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