H.T. Question regarding O1

Thanks for all the great suggestions guys. I kind of like the idea of a muffle forge. What diameter and wall thickness of steel pipe do I need? Also, fow much room do I need between the OD of the steel pipe and the ID of the firebrick chamber? Should I have it suspended above the floor of the forge?
 
I slide a 3" pipe into my horizontal forge. I sit it up off the bottom with pieces of fire brick to get a nice swirl around the muffle pipe. I run the forge to get the whole thing up to a nice even temp then put in the blade. Bring it up to temp and soak. Quench and you have it. The id of my forge is 8" but smaller would work also.
 
thanks alot for all the great info yall are very gracious and very helpful. thanks
 
Smitty, any pipe is better than none, but if you can get one that has about 1/4 inch wall thickness, that would be ideal. You only need about an inch of clearance between the wall of the chamber and the pipe. If it is a close fit you may need to put a vent hole in the top for a better heat. You'll also want to put a hole at the back of the chamber so the pipe can pass through, which will leave enough space at the back of the muffle for a substantial wood chunk to create that contained reduction atmosphere inside the pipe, and give you plenty of time for a good soak. I usually plug the back with a small roll of thermal blanket (KAO wool), not too tight. You don't want to make the wood chunk too tight of a fit in the pipe either (like a plug), because there is the chance that pressure could build up behind the wood and shoot it out like a canon ball. However, as long as it's square or rectangle, (not round and tight), you are safe. The rolled thermal blanket plug at the back is also for safety. It would blow out fairly easy in case of any kind of explosion inside the muffle. I've been using a muffle furnace for about 10 years now and have never had an explosion, but thought I'd mention safety,... just in case.

Also, don’t use a galvanized pipe. They put out some real nasty fumes.

Yes, suspend the muffle above the floor, so the flame can swirl around it.

As a side note,... You can also use a muffle inside of an electric furnace for contained reduction instead of a foil envelope. It makes it faster and easier to pull the blade out when it’s ready to quench.
 
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Tai, how close is too close for the muffle to be to the coals if using a charcoal forge? When you say "thermal blanket" over the top, do you mean just a big piece of Kaowool or is there something else I'm missing?
 
Jackrabbitslim, If the coals are touching the muffle you will get cold spots. If the coals are say one or two inches away, you might get hot and colder spots. I think the ideal is to have them about 3-4 inches away for the most even heat. Of course you can also move the coals around and work with the draft and/or blast and type/size of wood or charcoal to even the heat out if needed.

Working with wood or charcoal does take a little more attention, skill and experience than gas, especially for longer blades,… but it‘s definitely very doable and may even have a few advantages depending on the circumstances.

Yes, the thermal blanket is KAO wool type refractory which also helps "muffle" the heat. I like the high density blanket 2400 degree, one inch thick, but be sure to leave enough space around the side for air to circulate. Two inches or so should be fine and also allow you to feed it some extra fuel as you go, if you need.
 
Excellent! That is just what I needed. I have been looking for a way to improve the performance of my current (charcoal) forge until I can afford to upgrade and this seems like just the ticket. Thanks, Tai.
 
I forgot to mention that Harbor Freight had some low end weed burners for around $20-$30. They are really a much better muffle furnace heat source for this kind of thing than the Bernzomatic type MAPP gas torches. The MAPP torches burn hot and tight, but the weed burners will give you a nice big bushy flame, just right for heat treating smaller blades, 4-5 inches, no problem... for the guys that want to go gas.

I have a gas (for small blades) and a triple tuyere charcoal set up for longer stuff.
 
Could you possibly post a picture of your charcoal setup? Sorry if this bugs anybody. I didn't mean to hijack this thread.
 
Here's what the triple tuyere charcoal set up looks like. The lining is wood ash.
Mufflefurnace015a.jpg


Here's the little gas muffle furnace, minus the weed burner. The weed burner doesn't go inside the side hole, but stays back a few inches and just blows in.
Mufflefurnace012a.jpg
 
Tai,

I love your fancy blowers on your triple tyeure. Is that all you are using or are those for other purposes???
 
Chuck, I use the two little fans and the hand crank blower, but once the heat evens out it's mostly just the drafts. The fans and blower just help give a bit more control. When doing the integrals for example, the bolster acts like a heat sink and the point tends to heat up much faster than the area nearest the bolster. So what I do is preheat the tang and bolster a little with the small gas furnace and then go into the charcoal furnace. I run it with a heat gradient at first, so it's a little hotter at the bolster area, by using one of the little fans, so whole blade heats up at a more even rate. Then it's mostly just using the drafts for a nice even soak. It makes judging soak times on the integrals a bit easier and is less likely to warp the blade while it's heating up.

Another nice thing about the ash lining and triple tuyere is that I can use one, two or three depending on the size of the blade and conform the ash to fit what ever size I want. This one is set up for about a 16 inch blade maximum not counting the tang.

I end up moving the fans closer and further, turning them off and on and using the central blower to help control the heating and soaking. It probably sounds difficult and looks a bit goofy, but with some practice it's really not hard to do and works great! :)
 
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I guess I should add that I can easily get a 10-12 inch blade with just the central tuyere. However, if the blade gets much longer than that the heat slopes off at the ends. That's where the other two tuyeres come in.
 
Very cool. I still do not go much over 12". I have gone to salt a pot and have little problem getting the whole blade evenly heated. Still does not solve all the problems but make it a bit easier.
 
The charcoal muffle also works pretty good for slow cooling. Sometimes all I need to do is plug the opening of the pipe with a roll of thermal blanket and let it cool down naturally. I can also add some wood periodically too slow it down even more.

If I really want a super slow cool down, I use a shorter muffle that will fit down into the ducks nest and rest on top of a nice bed of coals. Then I rake the hot wood ash over the top and cover it with the thermal blanket, leaving the tuyeres open.
 
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