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I Forge Iron

Looking for a REALLY hot and efficiant fire!


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Your forge volume is too great for the number of burners. Judging by the colors I'd say you need two more or double the size of the ones you have. A 1" burner is 2x the output of a 3/4" burner.

Changing the jet size will only be an educational experience for you, which I don't discourage mind you but it won't make your burners run hotter. With one notable exception living in Grass Valley won't invoke and that's altitude.

Mike, Ron Reil, Myself and a number of other guys have played with jet size a fair bit. What seems to be the general result is a little change doesn't make a difference a simple change in primary pressure won't duplicate. (PSI) Change jet size very much and it just won't burn right.

I'd suggest you either build two more 3/4" burners or two 1" burners or make a movable rear wall like Ron Reil did to reduce your forge's volume to suit your burners. Raising the floor is another I just thought of.

The general rule of thumb is 1 ea. 3/4" burner for every 300-350 cu/in volume. Guys who need to make consistently good welds up the ratio to 1ea. 3/4" burner for every 250-300 cu/in volume.

Nice looking forge by the way.


Edited by Frosty
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Thanks frosty!
I was hoping you would way in. From some of your earlier posts about hot fires, you sound like a man with experiance. Your observations confirm that.
If I understand correctly, a bigger burner chamber is better than bigger jet or more PSI. PSI and intake (combustion air) adjustment will deliver the desired affect.

I don't know if you could tell from the pics, but I made the mounting ports out of 2"

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I'm not sure just what you mean by a burner chamber so I'll list the terms I use.

The tube is the pipe that leads into the forge. It's length should be 8-9 x the diameter at the throat. (your 3/4" burner should have a tube about 6" - 6.5" long. 14" is WAY too long. Try shortening your tubes before you redesign your forge or build another set of burners.)

The throat is the narrowest part of the burner tube usually where it connects to the assembly carrying the air intake(s).

The air intakes or intakes are the holes, slots, open bell, etc. where the induced air enters the burner.

The jet is the orifice that delivers the primary, in our case propane.

What I was saying is before you go and try redesigning one of Mikey's burners you should get your other ducks in a row. I over explained it and confused the one important issue.

You need to have the correct amount of burner for the amount of forge volume. Period.

If you built Mike's burners correctly one is more than enough to bring 350cu/in of volume to welding heat. Nothing you do NOTHING will get more BTUs out of one than it can deliver. You can't get 10gls out of a 5gl bucket so to speak.

You'll need a 0.045" tip for a 1" burner and it'll run at a little higher psi but it'll induce air easier so it all works out.

Properly built one of Mikes burners should require little if any adjustment once tuned. I've never looked at his plans but I'm a bit surprised to hear there're soldered joints.

Did you mention how large your forge is? I forget.


Edited by Frosty
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Thanks Frosty-
Yeh, he calls for brazed joints. I used solder because thats what I had...

Mike's tubes are 12" long with about 4" dedicated to slotting for air intake, leaving about 6" for mixing. I said 14" because thats how much sticks above the forge including jets, valves etc. I would like to reduce that for safety's sake. I'm thinking I will go with "bell" type air intakes. Do you know of any good plans?

What do you think of ITC-100?

Being the cheep **** I am, I'm always looking to get 10 outa 5.
Given that I've only run the forge about a dozen times mostly between 5-10 PSI, I bet if I turn it up, I'll get to weld heat. I just seams to me, at some point the air-fuel mixing with be reduced because of the small tubes. On the last forge I built, paturned after a ferriors forge, I made a (I forget what it called) ring inside the tube to cause turbulence to aid mixing.

Edited by steve sells
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Interesting, I'll have to borrow a copy of his book and maybe haze him over that one.

By bell type intakes are you referring to a linear burner like Ron Reil's? If so you aren't going to be as happy with the performance. Mike's are ejector type inducers and about 30% more efficient so it's a lot easier to get them tuned.

One of the beauties of a properly tuned inducer is how flat the induction curve is. Meaning that the air : fuel ratio varies very little from min to max psi on the primary.

Oddly enough and something I wasn't able to convince Ron of is the lower the primary psi you design an inducer to operate with the more it changes as you increase psi. Induction will increase with psi, not decrease.

Proper mixing is another issue that suffers with a low primary psi design. Propane and air do not mix easily but it can be corrected by making it turn a corner. Use a bell reducer to increase the dia of the tube one size and put on a 90 elbow and another short nipple of the increased dia. then to the forge. You need to increase the dia a little to make up for the increased back pressure of turning the corner. you will of course have to retune it afterwords. The length to dia. ratio applies for each length of nipple.

The ring is called a "flame holder" and what they do is cause a pressure differential between the tube and the exit nozzle. (More accurately it increases the pressure differential.) Anyway as the mix hits the flame holder's restriction it backs up behind it and then accelerates as it passes through but at lower pressure. There can be a cavitation pocket down stream from the flame holder if it's made from the "right" stock. ("Right" in this instance means "right" to make cavitation pockets rather than it's the right material to use.)

The 12 : 1 flare being installed on the end of some designs is a far more efficient version and is not a flame holder though it does much the same thing. What happens is as the fuel air mix exits the straight tube and enters the flare it is forced to expand to fill the same volume and slows accordingly. Where a flare is far superior to a flame holder is it increases induction by lowering back pressure where a flame holder increases back pressure. The lower the back pressure and better the induction the more stable and efficient a burner is.


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I just looked at Ron Reil's burners and see what you mean about adjustability, as in not alot! I like the sturdyness though.

What do you think about the Hybrid burner made by Rex Price?

They seem to be an advanced version of Micheal Porter's.

One of the issues I think I'm dealing with in my forge is a flame that is not fully neutral. My sleaves are wide open and I'm still sending a little yellow flame out the top of the forge opening. Is the bigger "mixing" chamber on Rex's design going to alow for better air fuel mixing? Also, I think my version of Mike's design, being built intirely by hand, with hand tools, files and ill fitting off the shelf pipe, etc. doesn't allow for good fine tunning. Aiming the gas stream seems to be important as well as proper air/ fuel ratio. It also looks like Rex has a shorter section for his slits because of the increased diameter of the pipe.

Thanks again Frosty for all your input!

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This pic shows the burners pretty well. One of these days I'll get a shot of everything lit up and glowy.

The Rex "hybrid" burners are some of Mike's early designs, his type 4 I think, you'd have to ask him to find out for sure. He designed the burners Rex builds some time before he finished his first book.

If you're getting yellow flames it's running way out of tune.

#1 Make sure the jet is aimed straight down the tube, it's probably the single most critical element to getting one to operate properly. An easy way to check is to hook it up to a water line, hang the burner straight down and turn the water on. The stream should exit the tube dead center.

#2 If the jet's aligned try moving it farther back from the throat. This will usually result in more air being induced. However if it's too far back it won't induce properly either so you may need to move it forward. Experiment around.

#3 Make sure the jet isn't partially blocked. There can be crud left over from manufacture in any component from the prop tank to the jet itself and being the smallest opening it'll plug n the jet. Just a little bitty shaving can disrupt the flow enough to ruin induction.

If you built it to Mike's specs it'll work once tuned and there are a limited number of things to go wrong.



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Hot Damm! Or is it Damm Hot? Looks like you can cover a lot of steel with that burner configuration... I'm assuming you have the loose brick sides for unlimited variations for access and heated space size? Very Nice indeed!!
I like the jack for holding the top while you possition the walls

Tell me a little about how your burners work. Doesn't look like you have much in the way of adjusting for tune. Lots of trial and error? I like the sturdiness of the all pipe fitting system. Thats what appealed to me about the "bell" type. It looks as though you have 5 or 6 to 1 combustion air to tube diameter? Have you found, as I have, that the burners on the end of the manifold get more fuel than the 2 in the middle?

The two weakest links in my burners are the way the jets are held/aimed in place. Easy to adjust but easy to knock out of adjustment as well... Also, the slots are a little on the weak side. Not a forge to throw in the back of the truck for a hammer-in.

Thanks for all your patients. I think the prudent approach would be to tune up the burners I have. I will also rebuild the "weak links" mentioned above before I venture into making "new" ones. Great excuse to learn and at the end of the day, I will have burners for another forge or furnace and a better understanding of the dynamics.

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Thanks and yes, flexibility for the minimum foot print was what I had in mind. A number of years ago, on theforge list, a fellow smith Ralph Sproul and I started brainstorming a variable volume forge starting with a clamshell. Neither of us liked the way the smith gets roasted when you open a clamshell so we hashed away, talked , swapped sketches, etc. and came up with this general design. Ralph's is different in execution but the same in principle.

There's a refractory table and matching lid on a jack. The sidewalls can be configured as necessary.

No, my burners all receive the same amount of gas, the manifold pipe is more than twice the diameter and well more than 4x the capacity so there's no significant difference.

The air intakes on mine are just under 2.5x the tube's cross section. Tuning them is a matter of carefully aligning the jet and trimming it till it burns properly. After than you just turn it up or down as desired.

These do NOT burn as well as a Rex or Porter. Their flame is a bit more symmetrical than a Sidearm and so easier to tune and are quite a bit more efficient than a linear like an EZ.

I've tried making them with a cross so they'd be as easy to build as a Sidearm but so far haven't liked the results.

The burners on my forge use thread protectors on the ends as sacrificial "flares" just a step up in diameter to act as a partial flame holder and improve induction a bit. The improvement in induction just balances out the loss of efficiency the sudden increase in diameter causes due to turbulence. I LIKE a little carefully introduced turbulence though, it aids mixing the air/fuel. A little too much though and all you'll get are backfires.

Anyway, I used a couple hole saws to cut large "washers" from some 16ga. steel and tacked them to the thread protectors to be the mounts. My burners rest on the washers and are held in place by the copper tubing fuel line.

The "washers" are also welded on at a little bit of an angle so I can direct the flame about 10* in the forge chamber. Slipping a bit 16ga. under one side tips them back to vertical or can tip them as far as 20* or so.

Once you have a reliable set of working burners you can't lose much by experimenting. If on the other hand you don't have a set of working burners you don't have a lot of choice but to experiment. Eh?


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I finally had a chance to figure the volume of my forge interior. I came up with 710 Sq Inches. Using the 250 Sq inch per 3/4 burner number (used for forge weld type heat) it looks like I need to up-size my burners to 1 inch.

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Once you get your Porter burners tuned you'll be able to weld in that volume. If not simply put a little bulk material in it in an out of the way place to take up 100-150 cu/in. Ron Reil uses a sliding refractory rear wall, it even has a small pass through opening in it.


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