for all you forge guys..

M

MCoughlin

Joined
Feb 1, 2005
Messages
471
Hi guys,

I recently started a welding apprenticeship and am currently building myself a forge long enough for a 32 " blade. My question is how far apart should I put the burners? I was thinking every 4". The chamber will be 4 x 4 x 32 and will have a door on each end with a separator half way down the length so I can use it as a smaller forge for smaller blades. That would however make for 8 burners. It will be primarily a heat treating forge for my carbon steel knives (hopefully swords eventually;)) for now as I am a stock removal maker but in the future I may use it to forge as well.

Mike
 
Even when forging a sword, you only heat 6 inches at a time. WIll be handy though for HT'ing.
 
Ifyou are planning on using it for HT make a big chamber for the flame, heavily insulated, and a smaller interior muffle chamber for nice even heating. Working on forging a sword if you have more than 4-6 inches hot, it's going to whip like a ribbon every time you move.

-Page
 
Both of the above are good advise.

I'll offer some other things.

First a 4X4X32 forge chamber is very narrow. That is a great size for a dedicated heat treat electric oven, but too small for a multi burner gas forge to run right.

Second, the chamber should be round, not square, especially for a HT forge. I would use 10-12" pipe with a 2.5" lining, (2" of Hi-Z wool with a 1/2" coating of refractory and ITC100) .That will give you a 5" or 7" chamber. That will allow a 2" or 3" muffle to be inserted with enough room for the gasses to exhaust.More on that later.

As far as the burner ports in a HT forge (or any forge ,really) there is no need for one every four inches. If the forge is to be controlled by a PID and thermocouple, then the whole forge will be allowed to heat up to the desired temperature and maintain its heat by the hot lining. This is where a poured refractory is good. It may take 30 or more minutes to come up to temp, but it will hold it evenly and well. Kaowool and a good heavy lining coat of satanite topped with ITC100 works well,too. A muffle for long blades is a real good idea.More on that later,too.

As to the burners:
If the forge was 32" long and the burners were 4" apart there would only be seven ,not eight. 0,4,8,12,16,20,24,28,32. You don't put a burner at 0 or 32". In practicality, 6" apart works fine.Five burners,spaced at 4,10,16,22,28 will work well. Putting a shut off valve in the manifold to disconnect burners 3,4,and 5 will allow you to turn them off for shorter work. Inserting an insulating slug ,(a 4-6" slug of poured refractory in a piece of pipe or a can will work fine),will shorten the chamber to 16". It shouldn't be air tight, just enough to close the chamber down , while allowing some exhaust gas to escape. Sticking a 24" stainless rod in the slug ,for insertion and removal, is a good idea.(remember, it will get HOT)

Making a second,shorter forge with one or two burner nozzles is a better idea.This forge can be used for forging and the long forge used for HT. Doing this will allow the long forge to be built with a dedicated muffle.

Now, about a muffle:
Use a heavy walled (schedule 80 or more) stainless pipe, 2-3" round, and about 10" longer than the forge. Put a 6" refractory (poured) plug in the back end of the muffle, and make a removable 4" plug (soft firebrick) for the front.This will seal the HT chamber fairly well to keep the oxygen down (but not air tight).Leave the rest of the soft firebrick sticking out to allow removal with tongs or insulated gloves.
Now ,this is important , you need to have enough exhaust porting in the burner chamber to keep the pressure down in the chamber.The exhaust port area should be about 5 to 10 times the burner port area. That translates to (for a five burner forge with 1" nozzles) a straight tube forge with a 7" chamber (no end doors) with a 3" muffle down the center (or a 5" chamber with a 2" muffle). Support the muffle about every 6 inches on some pieces of hard fire brick, to keep it centered in the forge chamber. The burner flames will circle around the muffle and heat it from all sides.The thermocouple needs to be in the muffle to read the exact temperature the blade is receiving.It can be inserted through a tube cast into the rear plug. Installing a dedicated thermocouple that is plugged into the controller is a good idea. It should be your best thermocouple, with a ceramic sheath.This is for the HT, less than the best is not good enough here. The thermocouple wiring at the end of the muffle should be well insulated from the exhaust gasses.

If you design the controller and fan with quick connect propane fittings (Darren Ellis) in the propane hose,and a union on the blower pipe, you can switch the controller and blower from unit to unit in a couple seconds.

I am building an ultimate controller setup in a tool box. It will have everything to run a forge or tempering oven built in it. Just plug in the peripheries (blower fan, propane,oven coils,thermocouple, etc.), and plug the controller into the AC and the propane tank. At the end of the day, it unplugs, closes up and is carried away to be safely stored. It can be quickly hooked up to a non-controlled forge on a visit or hammer-in (I always carry extra quick disconnect fittings).
BTW,Using thermocouple plugs on your thermocouples allows for them to be switched and changed easily,too. Buy a bag of 6 sets, so all the wires have the same plug.

Last comment - when you build a big forge ,don't scrimp.....this is a big tool, and should be the best you can build.Spending a little more will be money well invested. Using stainless pipe, it may last for your lifetime with a little care. The HT oven will put the soul into your blades. A bad HT will make the best forged/ground blade useless. Give your blades and yourself the best start possible.

Well, that is enough for you to think on for now.
Stacy
 
bladsmth said:
Both of the above are good advise.

I'll offer some other things.

First a 4X4X32 forge chamber is very narrow. That is a great size for a dedicated heat treat electric oven, but too small for a multi burner gas forge to run right.

Second, the chamber should be round, not square, especially for a HT forge. I would use 10-12" pipe with a 2.5" lining, (2" of Hi-Z wool with a 1/2" coating of refractory and ITC100) .That will give you a 5" or 7" chamber. That will allow a 2" or 3" muffle to be inserted with enough room for the gasses to exhaust.More on that later.

As far as the burner ports in a HT forge (or any forge ,really) there is no need for one every four inches. If the forge is to be controlled by a PID and thermocouple, then the whole forge will be allowed to heat up to the desired temperature and maintain its heat by the hot lining. This is where a poured refractory is good. It may take 30 or more minutes to come up to temp, but it will hold it evenly and well. Kaowool and a good heavy lining coat of satanite topped with ITC100 works well,too. A muffle for long blades is a real good idea.More on that later,too.

As to the burners:
If the forge was 32" long and the burners were 4" apart there would only be seven ,not eight. 0,4,8,12,16,20,24,28,32. You don't put a burner at 0 or 32". In practicality, 6" apart works fine.Five burners,spaced at 4,10,16,22,28 will work well. Putting a shut off valve in the manifold to disconnect burners 3,4,and 5 will allow you to turn them off for shorter work. Inserting an insulating slug ,(a 4-6" slug of poured refractory in a piece of pipe or a can will work fine),will shorten the chamber to 16". It shouldn't be air tight, just enough to close the chamber down , while allowing some exhaust gas to escape. Sticking a 24" stainless rod in the slug ,for insertion and removal, is a good idea.(remember, it will get HOT)

Making a second,shorter forge with one or two burner nozzles is a better idea.This forge can be used for forging and the long forge used for HT. Doing this will allow the long forge to be built with a dedicated muffle.

Now, about a muffle:
Use a heavy walled (schedule 80 or more) stainless pipe, 2-3" round, and about 10" longer than the forge. Put a 6" refractory (poured) plug in the back end of the muffle, and make a removable 4" plug (soft firebrick) for the front.This will seal the HT chamber fairly well to keep the oxygen down (but not air tight).Leave the rest of the soft firebrick sticking out to allow removal with tongs or insulated gloves.
Now ,this is important , you need to have enough exhaust porting in the burner chamber to keep the pressure down in the chamber.The exhaust port area should be about 5 to 10 times the burner port area. That translates to (for a five burner forge with 1" nozzles) a straight tube forge with a 7" chamber (no end doors) with a 3" muffle down the center (or a 5" chamber with a 2" muffle). Support the muffle about every 6 inches on some pieces of hard fire brick, to keep it centered in the forge chamber. The burner flames will circle around the muffle and heat it from all sides.The thermocouple needs to be in the muffle to read the exact temperature the blade is receiving.It can be inserted through a tube cast into the rear plug. Installing a dedicated thermocouple that is plugged into the controller is a good idea. It should be your best thermocouple, with a ceramic sheath.This is for the HT, less than the best is not good enough here. The thermocouple wiring at the end of the muffle should be well insulated from the exhaust gasses.

If you design the controller and fan with quick connect propane fittings (Darren Ellis) in the propane hose,and a union on the blower pipe, you can switch the controller and blower from unit to unit in a couple seconds.

I am building an ultimate controller setup in a tool box. It will have everything to run a forge or tempering oven built in it. Just plug in the peripheries (blower fan, propane,oven coils,thermocouple, etc.), and plug the controller into the AC and the propane tank. At the end of the day, it unplugs, closes up and is carried away to be safely stored. It can be quickly hooked up to a non-controlled forge on a visit or hammer-in (I always carry extra quick disconnect fittings).
BTW,Using thermocouple plugs on your thermocouples allows for them to be switched and changed easily,too. Buy a bag of 6 sets, so all the wires have the same plug.

Last comment - when you build a big forge ,don't scrimp.....this is a big tool, and should be the best you can build.Spending a little more will be money well invested. Using stainless pipe, it may last for your lifetime with a little care. The HT oven will put the soul into your blades. A bad HT will make the best forged/ground blade useless. Give your blades and yourself the best start possible.

Well, that is enough for you to think on for now.
Stacy
Click to expand...


Thanks for all the great info!
I was planning on putting the 1st burner 2" in on each end to completely utilize the entire 32" chamber so that way it would be 8 burners with heat to a full 32" without losing it near the doors. Unfortunately other than the roof of the forge the rest is almost complete. Right now I am a stock removal maker so hammering out a sword won't be happening...I am working on something stock removal method though. This forge will be for HT. I was going for a nice even heat through the forge which is why I figured every 4". The burner I have I believe is a 3/4" atmospheric. I based it on that. If I use 1" I see your point for sure. I was actually hoping to find something even smaller so I can regulate the temp a bit better. I only have a one burner forge now and it's hard enough to keep the temp in the 1450-1550 range without creeping higher and higher... I will find a piece of 1 x 3" rectangular pipe for my makeshift muffle.

Mike
 
Mike, you might try Don Foggs' site. I believe he has a little article for a simple single burner sword heat treat forge. Even if you're part way done with your build, you may get helpful ideas, and possibly save time and materials.

Best of luck, Craig
 
I'll just reiterate that for forging, it doesn't matter if the flame is straight down on the blade. but, if you HT a long blade with a hot flame directly on the blade every four inches it will be a mess.

The need to use a blown burner is also paramount in a multi burner forge. You can not take an atmospheric burner and split it into multi-ports. Each port would need its own injector and air choke. It would be a nightmare to try and balance for eight burners. It takes the gas pressure to draw the air in a venturi burner (atmospheric). With the pressure required for eight 3/4" burners the forge would be great for welding, but terrible for HT.
A blown burner can be split into a manifold and have multi ports much easier. The lower gas pressure will allow the burner to run at a whisper for controlled HT temps.

The flames really need to enter the chamber a tangent. Even if your forge has a square chamber, this will make it run better. If you have to re-design the top, it would be better than having a useless forge.
The chamber will get hot for three or four inches each side of a burner (or more). You don't need one every four inches....it is the hot chamber that should provide most of the heat to the steel in HT, not the direct flames.

Some engineering that you may want to consider:
The forge shape and design you are planning has several problems.
First ,the tunnel is too long for its width and height.
Second, and related to the first, with all those burners, the exhaust gasses have to escape the chamber tube. The ones on the end-no problem. The next ones - not much problem. The ones toward the center will create a huge pressure differential and do one of two things. They either will not burn right,or ( if the gas pressure is high enough for then to burn) they will blow the flames from the other burners out the ends. What you will have in effect is a double ended rocket chamber ( a slight exaggeration for effect). There is no way that small of a cross section of chamber will allow for a complete burn and a proper exhaust flow.

I know you are excited about building your own long forge, but there are reasons most folks learn on a smaller forge before taking on a major engineering task like a 32" HT forge. It may be cheaper to start over and re-design it than to make one that does not work.
I would recommend that if you are bound and determined to make this forge as is, you only use four burners, placed at 4",12",20",28". Angle them sideways (tangential to the chamber axis) about 30-45 degrees. Use a blown burner (much easier to build and run anyway), with a fan control. 3/4" will work, but 1" would be better (the cost difference should be less than $10-20 for the whole forge). Definitely use a mixing chamber in the manifold prior to the nozzle ( a double bell bushing 1" to 2" and back to 1"). All blown forges should have one for optimum efficiency.

Good luck,
Stacy
 
Wow. :eek: I gonna guess you know what you're talking about so I'm going to make it smaller. I haven't done anything to the top piece and the rest is just tacked together right now so with a little effort I can take it apart and go from there. What I have are (4)36" pieces of 1/8" x 8" and 8" x 8"x 1/4" end pieces with 4" x 4" chamber holes. I have 2" cerwool for the refractory. I want to at least be able to move to some bigger knives now(12"-14" blade type thing) and I want a nice even heat. What would you recommend for what I've got...if you've got the time... I will save the sword forge for later. I actually do have a pipe but it's 1/2" thick x 10" or 12"..I think. I don't have the means to cut holes in it though. No torch..yet. I'll start with something for larger knives for now.

Thanks for your help so far.:thumbup:

Mike.
 
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That pipe sounds perfect. It will allow for a round forge chamber of 6" or so. (one other thing I didn't get into was the difficulty you would have lining a 32" long 4" wide chamber. ) The refractory coating will be much easier to apply in a 6" chamber. As far as the holes are concerned, you can drill them with a carbide hole saw, or mark them and have a welder cut them with a torch. They don't need to be precision. Use a larger piece of tubing (pipe) to slip the burners into the forge . Tack weld these in place and once the whole assembly is aligned, weld them in place strong. Tap them for a set bolt to clamp the burner nozzle in place.(look at some forge plans to see what I mean). You can make the forge as long as you wish, but for your first forge, I would suggest about 10"roundX16"long.
Stacy
 
Stacy,

The burners I was thinking of using are the z-burners from "zoellers forge". They are 3/4" burners and need 350 cubic inches of space per burner. I did some calculating and I would need 4 burners for the chamber I mentioned. There are several pictures on his website showing these burners used in multiburner forges. :thumbup:

I have a few questions for you,

1. Should both ends of my forge be left open with no doors?

2. When you say exhaust ports are you talking about the open ends of the forge or a chimney type deal

3. How far from the one end of the forge should the 3" tube with the 6" refractory plug be positioned. I'm guessing it should not be plugging up the opening on the end of the forge because that would screw up the exhaust ratio. I'm assuming the removable plug end is the one you say should stick out of the forge to place and remove the blade during heating.


I was thinking of using some 1/2" round bar to hold the 3" tube in place. I could set it up so the bars and tube are bolted in place for easy removal for other projects where I might need more space than the 3" tube would allow for.
 
If you are going with the 4X4X32" forge chamber, then I would put no doors. If It will have a 6" or so chamber diameter, I would add end pieces with 3" or 4" ports This also makes it easier to use a muffle for HT).
If you are considering the option of making the 4X4X32" chamber length adjustable, I would use a 3" round plug (6" long) and just let it sit on the floor of the chamber. It should allow enough exhaust to get past. If that looks too big, make it 2.5" round.
Exhaust ports are wherever the combustion gasses exit the forge. Usually this is the ends. On a HT forge, or a salt pot, It is often through a dedicated exhaust port(s) (often referred to as a chimney).
Stacy
 
Sorry I forgot to mention I'm going to use that piece of 12" pipe I have. I am going to leave it the full 32" though. I will have a chamber about 28" x 8" inside with 2" refractory on the ends and walls. I've got the places marked where I'm going to cut the holes for the burner pipes 7" apart starting 5 1/2" from each end. This will allow for 2" of refractory material from each end of the forge and then 3 1/2" in from the refractory on each end is where the two outer burners will be. Is this too close to the ends? I figured I would try to space them evenly throughout the interior space.
 
This looks like a nice design with two burners.
http://www.zoellerforge.com/forge.html

This is the burner that I built.. http://metalcast.boorman.us/reil_1.html

My forge is made of hard firebrick and uses a single burner placed in the end, angled on a tangent to create a swirl. the interior is roughly 4.5"x4.5" and the length is adjustable by taking or adding brick to the top and sliding the end brick in or out.

I've HT'd 10" blade successfully with the single burner at about 4 PSI.

I should add that 10" is the longest blade that I've tried so far, I'm pretty sure I could do 12 - 14" if I wanted (I do, but I'm still working my way up).

a couple of pics of the forge and stand

stand002.jpg


stand003.jpg



stand001.jpg
 
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For those that are saying that you have to have a blown forge to get down low on the psi are incorrect as far as my setup goes. I have a round boddy forge with a single 3/4" sidearm burner, the chamber is approximately 5.5" diameter X 8" chamber, with a flat floor. The burner comes in at an angle that is pointed slightly down, and intersects at the roof wich makes for a verry even burn. I have a 1.25X2.5" vent both front and back and it will run right down to 1psi. I have made 2 atachements to my forge, both front and back that are insulated with wool, this allows me to heat treat up to a 20" peice with only the single 3/4" burner and 8" long chamber.
 
John,
Glad your set-up works well. I do doubt that you are getting an accurate reading on a venturi burner if the gauge says 1PSI (most of those gauges don't read accurately at all in the bottom range). More likely you are running about 2-3PSI. It should take a little more than 1PSI to draw the air in .

Extensions to the chamber will work if you give them time to heat up and they are well insulated. One of my acquaintances has a large vertical HT oven. It will do a 30" blade no problem. For swords longer than that, he has a extension exactly as you have described. He sets it on the top, and the oven now has a 40" HT chamber. The lid sits on it just as it did on the oven.

Stacy
 
I belive it to be at 1psi because at 0 psi on the gage there is hardly a flame, but its still stable. If I remember right I did some "port work" to the 3/4" pipe both on the inlet and outlet side I gave it a gradual chamfer, maybe that has something to do with it?
 
MCoughlin said:
Sorry I forgot to mention I'm going to use that piece of 12" pipe I have. I am going to leave it the full 32" though. I will have a chamber about 28" x 8" inside with 2" refractory on the ends and walls. I've got the places marked where I'm going to cut the holes for the burner pipes 7" apart starting 5 1/2" from each end. This will allow for 2" of refractory material from each end of the forge and then 3 1/2" in from the refractory on each end is where the two outer burners will be. Is this too close to the ends? I figured I would try to space them evenly throughout the interior space.
Click to expand...

This sounds ok I think, if your planning on using 2 layers of 1" ceramic insualtion or whatnot its actualy going to end up being over 2" thick. Remember you want the flame to follow the curvature of the forge to create a swirling action for even heat.
 
Cool. I'm going to by buddies fathers welding shop today to cut the holes. I'm starting to get excited now.:D Thanks for all your help. I'll post pics when it's done.

Mike
 
I want to add my voice to Stacy's on this one.

The forge, pictured was built using Stacy's design and input.

As stated above this is a big tool and a large project with many aspects to consider when building.

Because you are not building just another forge from someones already approved design; there is a lot of learning and listening to do as you build, that is if you want to end up with a usable forge.

Don't get in a hurry on this, take your time and you might amaze yourself at what you end up with.

This forge has a 24 inch length inside the chamber and is open on both ends. Most of the time I operate the three burners in the center and don't need the end two to have the interior at an even heat.

With Stacy's and many others helpful advice, I amazed myself.:D:thumbup:

Fred
vulcan_s+chariot+002.jpg
Vulcan_s+Chariot-performance+sheet_+003.jpg
 
john0270 said:
I believe it to be at 1psi because at 0 psi on the gage there is hardly a flame, but its still stable. If I remember right I did some "port work" to the 3/4" pipe both on the inlet and outlet side I gave it a gradual chamfer, maybe that has something to do with it?
Click to expand...

John,
Think about that answer. If there is a small and stable flame at 0PSI....where is the gas and air coming from???
At 0 nothing is going through the gauge....and that nothing can't be drawing in any air. It sounds like you are running about 2-3 PSI when you read 0.

Mike,
Fred's "Vulcan's Chariot" is superb,and was the result of nearly a years work and study. There were dozens of emails and redesigns. Fred already knew how to build a forge, but this size is a different thing. Also, note that it is a blown forge. A venturi (atmospheric) burner would not work very well in this type of arrangement, and HT would be nearly impossible.
The heart of this setup is my two-stage burner control design. Without it the forge would be a bear to regulate temperatures.With it a gas forge can regulate withing a few degrees.Do some searches on the old threads that Fred and I put out on that design.
I bet if Fred built another one he would make changes then,too.

Stacy
 
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