I started a forge build today.  Picked up a helium tank 12" diameter and about 13" long (after I cut the openings).  Spent more time trying to get the pink paint off than cutting the openings.  

I also picked up a bed frame that's made from channel iron that's just wide enough to hold firebricks.  I think that will make excellent sliding doors once I get them welded. 

I have a 3/4 inch Frosty burner that I built almost a decade ago and never used.  I'll finally get to see if this will work inside a forge.  

 

Sorry Brian, for not responding earlier

To begin with, although you chose a helium cylinder, its dimensions are in the ballpark with the five gallon propane cylinders that hundreds of people have used over the last quarter century to build gas forges from. The only thing you will find necessary when using a 3/4" Frosty burner in this size forge, is to turn it down a little, so as not to melt your parts 

Don't forget to use two layers of 1" wool and not a single 2" layer.  The latter form fat rolls the likes of what you'd see on My 600 lb Life.   There's a Youtube video titled  something like "super insulated forge" or "world's most insulated forge."  You can find it.  It's the one with the Rube Goldberg style baffle pulley counter-weight contraption.  It's worth a watch.

Thanks Mike, I hope I built the burner well enough that I need to detune it.  

Yep MS, I have the Kaowool and plan on 2 1" layers with fumed silica rigidizer between layers and a littel extra at the bottom to make a flat floor. I also have the Kastolite for lining.  I don't have the kiln wash yet, but plan to get some soon.

Unfortunately I haven't been able to get to the shop and put any more work into it.  We've had grandkids since I posted this and it's hard to do any serious work with 7 and 8 year old over active boys.

 

Brian, Mikey said turn the burner down, NOT detune it. T burners have a pretty flat performance curve over a wide range of propane PSI so you can turn the pressure down at the regulator if you need less flame, or up if you need more.

Frosty The Lucky.

Ok Jerry, I didn't pay attention to terminology, point taken. I'll still need to tune it.  Thank you for the plans.   

I did get a couple hours to work on it today.  Welded on some feet and put it the first layer of kaowool.

Don't sweat it Brian, it's easy to misread something because "everybody" calls a thing whatever is popular at the time. Humans have survived hostile environments since before we were human because we are good at rapid pattern recognition, association and correlation. We recognize patterns, free associate them and draw parallels as naturally as breathing, we cant help it it's literally ingrained in our DNA. 

So, when Mike said "turn down" it associates closely with detuning because both words as applied to naturally aspirated propane burners effect the same and interact closely. How you tune a burner is often determined by your available pressure.

Sorry, I'm a talky guy and pointing out terminology as it applies to us is a hope of mine for having a positive influence on the craft.

Frosty The Lucky.

I'm so glad that you feel compelled to hold the line on terminalogy, Frosty, so I don't gotta 

 Mike.

Frosty The Lucky.

(so this isn't a post with JUST an emoticon and justly deserve moderation!)

3 hours ago, Frosty said:

 Mike.

woof, woof 

OK, since we're woofing around, it's a good time to get your opinions about burner placement.

I was thinking I would mount the burner on the side or slightly below the apex of the side curve and angle the burner up a little to have the flame impact the far wall at a slight angle to induce more swirl before it his the working area of the floor.  I thought this would also keep the burner cooler after the forge is shut off.

Something like this:

Is my thinking way off?  Should I go for a more traditional mount on the high side of the curve and aimed down at the far corner of the D in the vault?

I'm hoping to get time today to fire up my first coating of rigidizer on the first 1" of blanket and install the 2nd layer of kaowool.  Then on to the kastolite in a day or 2.

 

Do NOT aim a burner into a corner! The flame won't be directed in a uniform direction like a swirly, it "boils" out in random (bad) turbulence. It also increases back pressure against the burner inhibiting it's ability to induce combustion air. 

Aim it at the floor's near side, maybe 1/3 from the near or far corner OR upwards at a near tangent at the roof. You want the flame to impinge the roof at a shallow angle but it needs to impinge the roof. The flame conducts energy to the refractory liner which then re-radiates it to the forge chamber as IR radiation which is what heats your stock for you.

Direct contact of the flame on the work is an inefficient and ineffective method of transferring heat to your work. Sure your flame Will impinge on the work if it's aimed at the floor and you'll be able to see the flame shadow in a lower color of the floor itself. This doesn't mean the iron has absorbed the energy, it has mostly deflected it as turbulence. However the burner flame is the stronger flow force in the chamber and will carry the deflected turbulence with the swirl.

The "down" side of aiming the flame towards the roof being that the refractory will come to heat sooner where the flame initially impinges so the roof will heat up faster. However because there's nothing causing bad turbulence the roof will come to temp almost as quickly as the rest of the liner.

Six of one, half dozen of the other. Just NEVER aim a burner into a corner! Visualize aiming a good nozzle on your garden hose into a corner or heck, give it a try on a warm day.

Frosty The Lucky.

9 hours ago, Brian Hibbert said:

OK, since we're woofing around, it's a good time to get your opinions about burner placement.

When it comes to burner placement, what is best and what is worst is quite plain to see. Flames which are placed to allow and even encourage swirl in the forge atmosphere are best. Next in importance is positioning flames to travel the longest distance before they impinge on part surfaces. If you combine both factors, you the receive maximum benefit. Of course, you may need to sacrifice some of one factor to increase the other, with some forge designs.

So, what would be the worst choice? Well, how about mounting the burner in the middle of the back wall and aimed straight forward toward the front opening? Yes indeed, this will do a horrible job! Naturally, none of us are that stupid, right? The point here, is that if you'll just take a moment to consider such an absurdity, it makes something plain. If you will picture a burner flame's heat path, which may be as much as two feet, from a four inch long flame, positioning is no mystery. Take a little time to think things out. The more you think things through the more obvious forge design becomes.

So, what about doing things different then what us gurus claim is best? Let me just say that you can cheat and get away with it. Yes, indeed you can. Lets look at positioning a burner at top dead center and facing straight down toward your work on the forge floor below it...

Mikey says don't do that!!! I say place that burner at 10 or two o'clock and aimed two inches short of the far end of the forge floor for best performance, and I am (of course) quite right 

But, my best buddy had me build him a forge with top dead center facing down burner position for a special purpose; he wanted to heat 1/4" square stock in it to build hooks for horse harnesses, as a business, and he only wanted to heat them to red. He wanted to heat a lot of pieces at one time. He thought that this positioning would be his best shot at achieving his goal.

I built what he asked, and the forge and burner setup worked find and dandy...wait a minute, what happened to all my rules about burner positioning, huh? what kind of deal is this? Maybe Mikey ain't so smart as  he thinks, yeah?

Um...when backed into a corner, my advice is to cheat, whenever possible, so that is just what I did. The forge was built from a five-gallon propane cylinder with a Mikey burner placed top dead center facing straight down on his work pieces, which of course is a perfect receipt for building scale. What to do? He only needed red heat, so I used a 1/2" Mikey burner in that forge. All problems were solved.

But, what about swirl? The smaller burner size allowed a kind of double swirl, with the flames dividing toward either wall of the forge, as they impinged on its floor; not ideal, but workable.

It is nothing I would have recommended, but circumstances alters cases, and the customer is always right, right? You consider all factors and do the best you can, within the limitations imposed by the forge design...which is why you should very carefully look at the WHY of that design before putting ink to paper. Then, review that why over and over as you proceed. And should you find that your design "just looked cool" when it came into your head, stop; revise it while it is just a doodle on paper. Because a paper doodle will turn into an embarrassing mess when you attempt to make it real.  

Thank you both for your replies.  You are the 2 people who's opinions on this topic I value most.

I'll do what Mikey says is best, 2 o'clock with the burner aimed 2 inches short of the end of the opposite floor.  And I'll probably round the corner of the D  on that side (maybe both sides) to reduce the corner effect Jerry warned against.    

2" is pretty close to the 1/3 from the far wall in your drawing, I suggested. HOWEVER I'd forgotten about complete combustion benefits or I wouldn't have mentioned aiming the flame at the near side! My bad.

Frosty The Lucky.

That is the best position in a tunnel forge. However, the wider floor in a "D" forge presents the possibility of a little better positioning; that would be burners placed just above the floor, facing upward and inward. However, that improvement comes with lots of headaches. To begin with, the burner bodies will now be protruding out to the side and downward, which means that you need to change out a single larger burner for two or even three smaller (therefore shorter) burners, to insure plenty of distance from their air openings and whatever surface your forge rests on. It also means that the whole inner surface of the forge must be just as flame proof as only the floor is in other forges.

How much return for all that extra work? maybe seven percent; maybe as much as ten percent

We, the insane, will jump on that deal; practical people? Not so much.

9 hours ago, Frosty said:

2" is pretty close to the 1/3 from the far wall in your drawing, I suggested. HOWEVER I'd forgotten about complete combustion benefits or I wouldn't have mentioned aiming the flame at the near side! My bad.

Okay, so I started out the same way. It took maybe ten years before I would admit my mistake, and started to advise people to aim toward, but short of, the far edge of the floor 

8 minutes ago, Mikey98118 said:

Okay, so I started out the same way. It took maybe ten years before I would admit my mistake, and started to advise people to aim toward, but short of, the far edge of the floor 

That last paragraph was for you, Frosty. The system simply merged it into my previous post.

But I didn't make a mistake, I simply adopted and adapted a better machine. I've never made or seen anything that couldn't be improved, my own stuff especially. It's how I've done new things my whole life.

That was a good idea, thanks Mike.

Frosty The Lucky.