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Sam Salvati

heat treating furnace design

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Would this work? 1" thick inswool/kaowool coated with satanite refractory all around the inside, burner port at one end, with a fire brick in fornt of the flame to disperse/baffle the heat, with the blades never extending over the firebrick and flame itself. ID is 10 inches, would this be suitable for heating blades nice and even to the proper temperature? I would use just the PSI valve to control the heat with a thermocouple to measure how hot inside it is and control it from there.

heat_treating_furnace_design.JPG

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Sam,

 

A design like that tends to breath fire straight out the door at you. In fact, around here the design is called a Dragons Breath forge. Instead, I would go for a more conventional side burner and use a sacrificial piece of pipe in the forge. The pipe extends out the doors on both sides. The burner heats the pipe, the pipe heats the blade, and the blade is never in the direct flame. After a while the pipe scales up so bad you burn holes in it, then you just replace the pipe.

 

You can put a piece of paper in the pipe to burn up excess O2, or even a squirt of WD40. If you luck out and find a piece of stainless pipe, that will last a long time. Don't use galvanized what ever you do. Even black iron pipe works, but a piece of square tube means you can place your blades spine down to heat. If you weld half-moon keepers on the ends of the pipe, you can fill it with sand, which keeps the spine cooler than the edge for edge quenches, and holds the blade upright nicely.

 

Geoff

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Thanks Geoff! I am not so much worried about scale, or dragon's breath (get that with gas forges anyway).

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Sam,

 

1" inch ceramic blanket should be sufficient. You shouldn't need ITC. 10 inch ID could be a problem. A bigger diameter will be better to equalize the temperature inside the chamber but there will be some tapering of the temperature towards the ends of the chamber. I have not been able to fix that issue with my own and it may have to do with using one single venturi burner coming from one end. I have two openings in mine. One on each end. One to put the sword in. The other as an exhaust. That way I avoid all the hot gases coming out from the opening where I need to work.

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Cool Jesus i was mainly designing after Don's and your designs, thanks. I figured the brick in front of the burner would help disperse things a bit more, but i can go bigger (best friend's a plumber so water tanks are easy to be had), or even go to the 55 gallon drum. I'll have to try the two opening idea, would help with the facefull of flames:). Thanks Jesus.

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I'm thinking of building one of those from an old water tank I've got when I come home from Africa in January. I'm thinking of using both my T-Rex burners on it, but in stead of running them in from the ends I'm going to try to run them in from the sides and hot spot them towards the centre of the furnace floor. Since I'll be using two burners I recon I should be able to get the right temperatures at lower pressures than with only one and get a more even temperature.

 

It sounds good in my head, anyway.

 

Hey, Sam! What do you say to a furnace build off?

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I'm thinking of building one of those from an old water tank I've got when I come home from Africa in January. I'm thinking of using both my T-Rex burners on it, but in stead of running them in from the ends I'm going to try to run them in from the sides and hot spot them towards the centre of the furnace floor. Since I'll be using two burners I recon I should be able to get the right temperatures at lower pressures than with only one and get a more even temperature.

 

It sounds good in my head, anyway.

 

Hey, Sam! What do you say to a furnace build off?

 

 

Quite likely you will get a hotter middle section in that way.

I only need about 4 psi to get a 15 I.D. by 55 inch long forge to temp with a single T-rex.

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Actually I'm wasnt thinking of mounting the burners at even distances from the furnace ends, one's going to be quite close to the main door and the other will be slightly passed the middle of the furnace. This way I think I'll get a proper heat in tang area in stead of the tip and also make it more suited for shorter blades.

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Leif, that might work pretty well.

 

Jesus, maybe the problem is why the 55 gallon drum is used like Don's? Would more ID mean less hot spots and more even heat throughout?

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I think so. Larger ID will help equalize temps inside the forge as I said before.

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Just curious, Jesus. How long time does your furnace need to heat up?

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Hmm so the 55 gallon drum should not be much worse, now just have to find enough ceramic blanket to cover the ID of a 55 gallon drum.......

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g'day all, how well do gas ht ovens with the sacraficial pipe hold set temp? do you need a gas solenoid linked to a thermocouple to really hold set temp well or can you achieve this just by adjusting the burners? thanks.

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Hey again guys. i got to thinking about the tube in the forge/furnace design, and could an alternative to the salts or jus tplain tub ein a tube with end caps be Sand? Sand would surely even out the heat, with a venturi effect going all around the tube of sand.

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Hey Sam, all your ideas have merit and may be worth your time if you want or like fooling around with such things. You'll learn a lot that's for sure. I believe Don Fogg messed around with glass beads and perhaps sand at one point. I can highly recomend the 55 gal. drum forge though. It comes up to temperature reasonably fast with even just the little 12 cfm blower/burner, faster of course with more agressive burners. The little blower at least in my forge does have problems reaching higher heat treating temps for some reason but has no problem with the 1400 to 1500 degree range, with over 1500 being the problem. I have noticed about a fifty degree swing in temp in mine with the hotter end being the one opposite the burner but the front three quarters is very even in temp. I've discussed this with a couple of buddies and we came up with the idea of a baffle of some kind perhaps midway down the forge but I don't think any of us ever bothered to install one. Just for covenience the drum forge is a quick and easy build which is important to me, it works nicely and seems to develop a neutral atmosphere with little adjusting, I use it for regular knives as well as longer blades. Jesse Frank even stands his on end at times when heat treating the wider and thinner European style sword blades as they can get quite floppy at heat treating temps. I don't believe this is as much a problem with more robust styles like katana and since they hold a good even temperature over time they work well for soaking at the lower austenitizing temperatures. Jesse has also had good luck using venturi burners in his, somehting I've been meaning to fool around with in mine. I do like Jesus' version made from the hot water tank with an agressive but highly adjustable venturi burner and if I made another heat treating forge it might just be along those lines. All in all it's the bigger chamber that seems key to developing a more even temperature.

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Ok thanks Guy, i was kinda figuring i would end up building the 55 gallon drum one. I am going to try a small knife size version of the sand tube, to not waste alot of time and money yet still see if it is plausible.

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Sam I encourage you to experiment and take any advice from me with a grain of salt since I haven't even cranked up a forge in over six months! That may change soon, Jesse Frank needs to do some heat treating so we'll be heating my drum forge up maybe next weekend.

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Nah no worries Guy, i understand where you are coming from exactly. Why reinvent the wheel when there is a perfectly good wheel already? I just like to experiment:D, i think one of my ancestors must have gotten busted snatching and reanimating bodies from the graveyard or something.

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