Oven foil vs shielding gas

JTknives

Blade Heat Treating www.jarodtodd.com
Knifemaker / Craftsman / Service Provider
Joined
Jun 11, 2006
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Most of you know we do customer heat treating in my shop and with the move I have been thinking about coughing up the bucks to run gas in the oven. My thoughts are as such so correct me if I'm miss guided or off in left field.

We are coming to the end of my big foil roll and it's rather pricy to replace it (24"x100ft 309SS $500-$800). I don't inherently dislike foil but it's not something I look forward to doing. And sometimes we double wrap big blades as thy try and poke holes in single layers. I know it's hard to quantify a price per blade for foil but if each pouch was 3"x12" not including the folds (double folds on all seams) you would be looking at 400 blades from a 100ft roll. That's over a buck in foil for each blade. And you can't reliably wrap carbon steel blades. I do get blades that stick to foil making it a pain in the ass to remove and clean. I would also say your blade heat up time is slightly slowed but that's just a guess.

My thought is if I went to injected nitrogen a lot of the drawbacks of foil would be over come. Things like air hardening only, sticking, wrapping, cuts on fingers and high up front cost. I called my local gas suplyer and he will sell me a 228cf bottle of nitrogen for $250 and fills/exchanges are $34. Talking to Salem who runs gas he uses 5CFH to be scale free in his paragon. But that's argon settings which translates to 6CFH of nitrogen as it's less dense. So the same volume flow of nitrogen would be close to 4CFH of nitrogen if your using a argon flow meter. I know you will get a tiny bit of scale going from the oven to the quench oil/plates.

But all that aside if we just ran 5CFH of nitrogen that's 228/5=45.6 hours of shielding. Avarage high temp heat treating is 1/2hr so we are talking about 90 blades per tank. That's not counting carbon steel blades that are 5-10min each. If you just did those you would be 3 times that number. So to compare prices it would take 400foil/90gas=4.44 tank refills to do the same number of blades as the foil. That's 4.5x$34=$153 vs $500-$800 in foil. That's $153/400 .38$ a blade vs the $1.25-$2.00 a blade. With those numbers I could run double or triple that gas flow and still be cheeper.

I'm thinking I will seal around all the Metal sides with high temp silicone so it's as sealed as I can make it. But I have never used gas befor so this is all just speculation. Thanks guys.
 
I've heard varied results about gas in the oven, but most were not good. Don't use 309 foil on everything. 321 will work for most of your Stainless steels. Also, you don't usually need 24"wide stuff. 18" is cheaper and less waste.
 
I was getting sticking with 321 some times really bad with AEB-L and a few others. I know the papers say 321 is sapost to be good to 2k but I don't find this to be true.

I wonder if the negative results with gas is becaus thy are running argon and not enough of it becaus it's pricy.
 
My experience with GN2 has been all positive. Where I used to work the met lab did all the heat treating and I car pooled with the Tech that ran the process so he came over and we set up the system one afternoon. Yours is a business where each penny saved is a penny earned and I think if you switch you will streamline your process as you move ahead and find the savings in time not spent wrapping the blades and how much gas is actually needed per oven load.
 
the price of that foil alone scares me away from stainless :eek: gas sounds like the way to go.
 
The average person doesn't need 100 foot rolls and 24" width. Personally, I think 12" width is better for knifemaking in most cases, anyway.

321 HT foil runs less than $50 a roll of 12"X25'. That does 30 to 50 blades, depending on size.
It is a consumable, just like belts. Spending a dollar or so per blade on your HT is just part of the cost.
It is almost inconsequential when compared to a $10-$40 block of wood for the handle, or $10-$100 in steel.

I understand that JT is figuring this as a business expense on doing HT, where the dollar is a reasonable percentage, but for the average home knifemaker doing his own HT ... it isn't a big deal.
 
If a hobbyist makes 25-30 blades out of stainless per year GN2 is total overkill stick to foil. For what JT is doing he may do 30-50 blades in a week for customers and the time to wrap and unwrap plus price of foil might just shrink the profit to barely covering price of foil. He also has the added cost of LN2 for stainless cryo treatment it's all the little things that eat away at profit some can be added to the price as consumables but the cost is still there.
 
That's what I'm thinking. You start doing the math and it's amazing how everything adds up. This also gives me the option to oil quench stainless steels if needed. Another nice thing is there will be minimal decarb on the carbon blades so less prep needed for hardness testing. And cleaner carbon blades for the customers which is great. Most of my carbon steel customers are new knife makers and thy are doing the work by hand so it sucks hand sanding the scale off.
 
JT, I have no idea where you're buying foil, but Sentry's direct pricing is WAAAAAAYYYYY cheaper than wherever you're getting it from:

HEAT TREAT WRAP ----- Quantity: 1 2-5 6+


24” Wide x 50’ Long $158.00 $151.70 $145.40

12” Wide x 100’ Long 161.00 154.60 151.30

8” Wide x 100’ Long 108.00 103.70 101.50

6” Wide x 100’ Long 82.00 78.70 77.10



I'm almost positive it's 309, btw.
 
It's been a couple years since I've bought foil, but I recall even Tru Grit being a lot less than that.
 
Trugrit is $300 for 100ft plus shipping which I'm guessing would be around $50. Thy say there is flat rate in check out but I highly doubt it because of the length. But what is the time worth that it takes to foil wrap all the blades.
 
No doubt, man - just pointing out that your initial dollar figure wasn't really reasonable, that's all.

For what it's worth. I've yet to see a kiln that was 'gas injected' that wasn't built with that intention, that produced clean enough results, at least for my expectations. Maybe snag a small argon cylinder and try it first, before you go all the way only to find out it's not what you hoped for...
 
Over length charges on packages don't start until 42", even getting my roll of foil shipped to Canada was less than $50, and I bought some other stuff at the same time too.
 
Another thing worth considering is coil life in your oven... I can't say I've noticed my coils suffering from argon use yet, but they are pretty new still and I still use foil for single blades much of the time. Supposedly though, they get an oxide layer that protects them somewhat from deterioration, and the use of shielding gas and then being hit at temp with oxy opening the doors can weaken them over time... at least I believe that's how I've seen the problem explained here and there on the webz.
Other than that though, I'd think going with gas would be way better for you. Foil takes time, costs money, and as you say can be a real PITA to remove sometimes.
 
Another thing worth considering is coil life in your oven... I can't say I've noticed my coils suffering from argon use yet, but they are pretty new still and I still use foil for single blades much of the time. Supposedly though, they get an oxide layer that protects them somewhat from deterioration, eingand the use of shielding gas and then b hit at temp with oxy opening the doors can weaken them over time... at least I believe that's how I've seen the problem explained here and there on the webz.
Other than that though, I'd think going with gas would be way better for you. Foil takes time, costs money, and as you say can be a real PITA to remove sometimes.
My friend have industrial HT oven in shop. You can not see coil inside , there are some thin / ceramic I suppose / plates that cover coil . . .
 
Another thing worth considering is coil life in your oven... I can't say I've noticed my coils suffering from argon use yet, but they are pretty new still and I still use foil for single blades much of the time. Supposedly though, they get an oxide layer that protects them somewhat from deterioration, and the use of shielding gas and then being hit at temp with oxy opening the doors can weaken them over time... at least I believe that's how I've seen the problem explained here and there on the webz.
Other than that though, I'd think going with gas would be way better for you. Foil takes time, costs money, and as you say can be a real PITA to remove sometimes.
I'm glad you brought up the "Coil" deterioration because I recently replaced my coils after 5 years of service and I was somewhat surprised that the coils looked pretty good after removing them for inspection. The failure point was right at the last coil and beginning of the pigtail that exits the furnace...just broke...When I ordered the new coils I asked about failure possibility due to the inert gas shielding and the rep said that on my initial firing that the coils would get the oxidation layer and that the gas should not be an issue...
I fired the unit WITHOUT the gas on BTW just to break in the coils all looks fine for the 3 actual heat treat firings since.
 
Busto do you have any pictures of what your blades look like coming out of your oven? What CFH do you run with your shielding gas?
 
JT,
I will have to see if I have any coming out of HT...Also ones plate quenched if I have any of those also. Both Stainless/Carbon.
I run just a bit over 5 and just a hair under 6 SCFH(closer to 6) once I found the sweet spot I haven't touched the flow meter and I use a Matheson regulator with 1/4" stainless tubing to AN Flair fittings in and out to a Dwyer flowmeter 1/4" copper tube that I pinched the end in the furnace to give a flat spray and in front of the flat end I put a piece of soft fire brick with grooves filed to give a little better turbulant flow to disperse the gas.

The Blades are Clean with just a hint of color on occasion like you might see out of Foil Pack...NO STUCK FOIL...:)
 
That's what I like to hear :)
 
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