heat treating difficulties

ScottRoush

ScottRoush

Joined
Jan 10, 2010
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Now that I'm forging, I decided to pack away my old ceramics kiln that struggled and struggled to get to critical temperatures. It struggled, but it made for a nice even heat.

I'm now trying to do my hardening with my propane forge and it ain't easy. My first couple knives were pretty small, so it wasn't so bad. Anyway... The forge is about 17" long and I have one venturi burner situated closer to the front to leave room for another down the line (if needed). Anyway... I've been having a hell of a time getting even heats for my hardening temps. I'm playing around with with a steel tube. but the tube gets unevenly heated as well.

So what is my best option? I'm sure that the best thing would be to buy a heat treating oven with a PID and everything... but what other options do I have?

I did just get some stuff to make an idle valve... I was hoping that by ramping the forge up to high temps, then bringing it down to idle I could do it right...

I also don't mind building another forge that is more specialized for heat treating... I saw something like that at a hammer in.... any thoughts on that??

Thanks...
 
Does your forge open at both ends? You can try to manipulate the direction of heat flow by forcing the forge to vent at the other end, you need to be careful to maintain about 4-5 times the size of the burner opening for exhaust, though.
Welcome to the world of the gas forge. They have their peculiarities. For what it's worth, I am in the process of building an electric oven for heat treating after 5 or 6 years of doing it in my forge.
 
Mossanimal,

"I know exactly what you mean"
My forge is a one burner too,
and I have to move the blades around to get an even heat treat.
I try to get the 'evenest' heat on the blade rather than the handle,
and have done 73 knives so far that way.

Masterbladesmith Dan a friend, said
"a one burner forge is fine for knives, even a foot long
if one just moves the blade and tests for non-magneticity.
If the blade is non-magnetic then quench."

Dan makes swords and has 4 burners on his forge.
But my skinners are short blades 2"-3" long
and my favorite design is less than 8" overall.
Don't worry about it...
Just be cool...
If they art non-magnetic...
then they are non-magnetic.
Quench them fast.


Lets 'git ignert' and go coon hunting.


JacktheKnife
Sandymay and Dukedog
http://jacksknifeshop.tripod.com/
 
IMHO your best bet is to dig that kiln back out. You will get a more consistent heat that is more accurately controllable. Personally, I'd never mothball a kiln and use a forge for HT. If your kiln is struggling to get to heat, it may be time to think about new elements for it (yes, they are a wear part). Take a look at Nick Wheeler's recent thread on his paragon kiln for some more information on element sizes and what they mean to you.

Take your time and get the heat treatment right. You can't rush quality...

-d
 
Here are something you might consider on your kiln. One of the problems with them is that most are way to big inside. You could get some more bricks and use them to reduce the volume, even it it means taking out the existing coils and replacing them after the adding the bricks. The bricks cut and work easily, and you could cut some to change the normal kiln hexagon into a rectangle cutting grooves in the new bricks to route new elements that match the grooves in the old brick that remains exposed. A new set of elements are not that expensive. I got some rolls of Kanthal from this place and made my own by wrapping the wire on a rod.

http://www.ec-securehost.com/PelicanWireCo.Inc./Bare_Resistance_Wire.html

You can get 50' of 14 gauge for $40 and make a 220v 20 amp (4400watts) element that will heat up a decent sized chamber fast and is heavy enough to last a while. 50' of 15 gauge is the same price and will make a 17 amp 220 (3740 watts) element. I personally tore my old kiln apart and reused the bricks plus some new ones and some kaowool to make a horizontal oven. Added a PID, thermocouple and SSR from
http://www.auberins.com/ and used that for control.
I made a nice welded box with a removable top with enough room for the camber and the bricks with an inch of kaowool on the outside the bricks for extra insulation and to allow the bricks some movement when they heat. I used stainless welding rod to pin all the bricks together. You could make a box pretty easy with some angle and some light sheet metal and bolt it all together if you don't weld.
IMHO a electric oven is way better for HT than a forge.
 
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thanks for the suggestions guys... my kiln is already a horizontal with front access. That is a great idea about reducing the volume inside... I will look into that..
 
I agree with the above. I have been doing HTs in my forge for a couple of years, but it gets frustrating. I make straight razors, and if the heat treatment is off, your face tells you. After junking way too many nice blades, I decided it's not worth it. The oven I ordered from Sugar Creek Industrial cost much less than I lost on all those bad blades.

I still love my forge, but for hardening the blades go in the oven from now on. :)

Josh
 
It is my opinion that heat treating in a forge requires constant attention and movement of the blade. A muffle didn't work well for me either and setting a blade down in the forge to heat will cause uneven heating and probably warping.

I start by heating up the ricasso and tang areas because when cold they are heat sinks, when hot they are a heat source. My burner was situated so that when I was heating the ricasso, the tip of the blade was sticking outside the back of the forge. For more even heating hold the blade so that either the spine or the edge is cutting through the flame. Regulate how fast or how slow you heat the blade by bringing it out of the forge in the early stage you can see what areas turn colors first and those are the areas you have to be careful of not overheating. never leave the blade idle in the flame for more than 1 second, keep stroking it through the flame - slow in the thicker ricasso and tang areas and fast in the thinner blade and tip area The forge should have enough radiant heat built up that the tip of the blade should almost never have to be subjected to direct flame from the burner. I HT'd a 28" katana blade in a 1 burner forge :)
 
Thanks a lot... What you describe is what I intuitively started doing... sort of. The main problem I was having had a lot to do with the blade design... a very skinny, thin tip that was prone to overheating...
 
Mossanimal said:
Thanks a lot... What you describe is what I intuitively started doing... sort of. The main problem I was having had a lot to do with the blade design... a very skinny, thin tip that was prone to overheating...
Click to expand...

Compared to heat treating in a kiln or oven, you might want to leave more meat at the edge and even more so at the tip, as necessary, to help avoid these kinds of issues.
 
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