Save the tri-wall for another project. Get a 16" piece of 9" to 12" pipe. Doesn't need to be heavy wall or any particular steel type.
Here are a couple of older articles I wrote on building a forge. The stickys has a place with more forge building info.
Old Thread 1
OK, Let's talk forge design:
No good forge will reach welding temps fast.....and a large one will be slower. A long thin forge chamber with a venturi burner will be very inefficient.
A 6" shell won't make a long forge. It will make a 10-12" long forge at best. Use a 10-12" pipe/shell for a long forge.
A small venturi burner won't reach welding temps efficiently ( or at all) in a large forge. Either use two burners or a large blown burner ( best idea). Burner angle, placement, and flame path is very important on a long forge.
A blown burner is really no less portable than a venturi burner. If there will be no electricity within 100 feet of where you will be forging damascus ( unlikely) you can use a 12 VDC blower and run it from you truck battery. On a welding forge the propane tank is more of a concern with portability that the burner. ( You need a large tank to avoid freeze-up - 100 pounds or larger is the norm )
Basically, a damascus welding forge is not (usually) a portable item. Lots of bad things happen to well fired refractory liners when bouncing around in truck beds.
For welding you need 2" of wool, 1/4" to 3/8" of satanite, and a good coat of ITC-100. These measurements are doubled to get the lining thickness. Thus a 10" pipe will have a 5" chamber.
For a robust and long life forge, a cast refractory liner may be a better option. Cast a 1" thick liner, coat the inside with ITC-100, wrap it with 2" of high-Z wool, and bundle that in a sheet metal shell.
This will take a good while to heat up, but is quite efficient once at temp. For HT this is a superb design.
Raising the gas pressure beyond normal won't make the forge heat up all that much faster. The thermal mass of the lining is the determining factor ,mainly.
A forge shell only needs to be a few things:
1) Metal....and round
2) Able to withstand 500-600F heat
3) Cheap
A trip to a scrap yard ,or a drive around town on trash day will bring many things up that will work. When your brain thinks
"FORGE", everything looks like a shell.
Many things will work that are free or very cheap:
Trash can or waste basket- preferably a plain steel can ( before anyone yells, "Not galvanized", remember that the shell won't be getting hot enough to burn off the galvanizing - but ,yes, it would be best if it isn't galvanized )
15 to 35 Gallon oil drum ( check you local car dealer or garage)
Used water heater tank or shell ( free from any plumber)
Used 25 gallon syrup tank ( check your syrup supplier for a damaged tank)
Piece of 24 gauge sheet metal rolled up and pop riveted into a cylinder ( this is how the outer shell of most cast refractory forges is made).
Old water main pipe ( check the water dept.)
Well shell (check the phone book under "Well Drilling"
Cut-off from a metal fabrication shop ( usually free if you explain what you want it for)
Junk yard, scrap dealer, trash dump.....all kinds of neat stuff shows up here.
........you get the idea.
Old Thread 2
I would recommend building one from either High Temperature Tools & Refractory (HTT&R) kits/supplies, or from scratch. Here are the basic things that will work best:
Ro
und shell - The shell should be as long as you want the forge chamber, plus two inches. A piece of 10" round by 22" long is good. That will build a 20" forge with a 5" chamber when done.
Insulation - Use 2" of wool. Either regular 2" thick wool, or two layers of 1" Hi-Z wool. The Hi-Z wool is worth the extra, IMHO. Use 1" Insulboard for the ends. No need for an outer end plate unless you want a shelf on the ports. If doing that just weld a piece of 2" angle iron across the ends when the lining is done and cured.
Refractory - 1/4"+ Satanite for the walls with a good coat of ITC-100 over that. Put a floor of bubble alumina down that is about 3" wide.
Burner - Build a blown burner with a good size burner tube. 1" is good, 1.25" is better. A 3" wide by 4" long mixing chamber is a really good idea on the burner. Burner flares are nice, but not mandatory. Having two burner tubes is a good idea on any forge over 16". You only need one blower for the unit. The burners should enter the chamber at the top and be on an angle to direct the flames along the walls ( tangential). Separate gas and air valves at each burner is better than a manifold. You can tune them to give an even chamber temp, and shut one down when not needed for forging if desired. The entire forge with a blown burner is $200 or so. If possible, use a blower motor that is able to be slowed down. Either a standard shaded pole type ( use a dimmer switch or cheap speed controller), DC, or 3Ph.
PID Control - If you go to the trouble of building a first class blown forge, it only makes sense that you will want to know the internal temperature. A PID ,TC, and Ceramic Sheath ( plus a few wiring parts) is all that takes. Cost is around $100 for good quality parts.
It is also only a few more dollars ( very well spent) to make the forge run automatically on PID control. The stickies have a section on that. It works super well. Keeping +/- 2 or 3 degrees in not uncommon. All you need to make it run on PID controlled is to add a propane gas solenoid to the gas line and a few more valves and fittings ( plus a few electrical parts). This will run about $100 extra.
So for $400-500 you can have the Cadillac of forges, or spend that amount on a pre-made forge with very limited capabilities.
From this you can add auto-ignition or pilot light, flame control to lower the forge flame when you pull the bar out to forge, and bring it back up when you put the bar back in for the next heat, etc.
TIP:
Take two lengths of 1/2" pipe and weld along the sides as slides for a pull out front work rest. Make the slide from two pieces of 3/8" round bar and a work rest welded across them. The rest should be at the height of the front port, so you may have to weld a couple pieces of square tubing or other bracing across the rods to get sufficient height. This will allow supporting work of all lengths. It is really useful for working long bars and things locked in tongs.
Some good build threads:
So after going through the stickys a couple weeks ago and finding all of the amazing plans for different PID controlled forges, tempering ovens, salt pot etc, I've switched gears fully to creating a really high-functioning PID controlled forge & heat treating oven. First off, thanks to other...
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I'm about ready to start building a forge. I want to do it right from the start so I don't have to redo anything in the future and I want it to last. I've been reading through all the stickys and think I have most of it figured out, but some of the pictures and diagrams are missing now. I have...
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