Is it safe to assume, (like for non-blown autos, and house fu\rnaces), that one loses 3 percent efficiency per 1000 foot of elevation? So one at 5300 feet above sea level, would have to scale back the rule of thumb that a 3/4" burner will serve 350 cubic inches of forge? So at that elevation, a 3/4" burner would be good for about 294 cubic inches? One of those 5 gallon paint can forges reduced to 5" dia. X 15" long=294. Should work????? right? . . . .Also, if one built a forge slighly oversize, and then placed a firebrick (say, 2X4X6 ) inside the cavity, to reduce the volume by 48 cubic inches, would that work? IAT. . .
Looks like that at this altitude (5300') I'm limited to a coal forge. Or spending much $$$$ for propane everyday. Like $20/day for for an atmospheric forge.. . .(blown forges are too noisy for a city).... I have to look into a real small propane forge...2.5" diameter by 12 inches (60 cubic inches)...and well insulated...maybe a 1/2" burner. I have coal available, but I have never tended a forge fire. So I imagine I would be doing more fire tending, than metal forming. If I'm lucky enough to even get the coke formed..
Dunno where that tidbit comes from, but the ones I have built and been around were still quieter than a handcrank blower on a coal forge.
If you use a gas powered leafblower to push the air, maybe, but you really gotta do some more research. Get out to more hammer-ins or something like that.
Any smithing or knifemaking groups near you?
Aside from that, if you think that the neighbors are gonna get wierd on your ass fo a little noise coming from the shop (and it will be the hammering that they will hear, then), they will get RIGHT bent when they see the plumes of snotty yellow smoke from the coal coking off!
Tending a coal fire is nothing really, once you get it figured out. Good coal will make a heck of a difference, too. Find some decent metalurgical coal if you can.
Say I made a forge from a 5 gallon bucket, and used a 3/4" burner. Then at this altitude of 5300 feet, with a blower on the burner, I could get enough 'quiet' heat to do (try) some smithing. I could even capture waste heat off the forge with a shroud, and 'pump that to the burner. Then with a 3/4" burner, at this altitude I could have the
350 cubic inch forge. I read where one man used a solenoid valve on his gas line, so if the fan lost power, the fuel would shut off... sounds safe. As you can tell, I'm a newbie. No smithy near me that I know of. There may be one 35 miles away that I plan to check on when the snow gets below my butt.
Admittedly, this was a few years ago (well, alright, ten). I was living at 5000 feet and measured how much propane my two burner forge (8" dia. x 18" long) consumed. It came to $1 per hour. So your estimate doesn't sound unreasonable.
I'm not sure what altitude has to do with it--for a well tuned forge, it takes the same amount of propane whatever altitude you're at.
I'm using a 5 gallon bucket with 2" insulation and a single 3/4" Reil burner (atmospheric). When I lived in Colorado at 5000', it worked just fine. I wouldn't use a single burner with any larger interior volume though. No solenoid either.
I generally don't leave my forge running if I'm not in the shop.
Steve The snow was f>Say I made a forge from a 5 gallon bucket, and used a 3/4" burner.
You really need to check your math there. You are way off. I don't know how well a venturi burner works at that kind of altitude but I would think a 3/4" burner would work fine on that size of a forge chamber. What you really need to look at is how well it's insulated. Folks do heat treating in 50 gallon barrels with a single burner of the size you are talking about. How good is your burner and how good is your insulation? Those are the things you should concern yourself with. My forge is about 8x24 inch inside with a T-Rex 3/4" burner and I don't even have to try hard to pull 2000F. Noise is not even a consideration.
If you weld, these are pretty simple. The burner jet mounting is put in place with a mandril I made. The mandril is a 3/4" piece of pipe with a rod sticking out one end that is the same OD as the 1/8" brass pipe I use for gas. There is a larger diameter stop on it. I screw on a 1-1/2" to 3/4" bell fitting, drop the jet mounting over the rod and weld on the supports. This way I don't have to worry about alignment. A lathe helps making this stuff too.
To mount the burner to the forge body, I run a piece of 1" x 3/16" up the side of the forge, welded in place. The last 4" or so is bent at an angle so that the burner will point at the center of the forge floor (you can eyeball this and bend it cold to fit). You may have to tweak the angle, don't use 1/4" thick stock. Use U bolts to mount the burner (buy the right size (measure!)).
Be sure to make the tables outside each end of the forge large enough. I like them about 20" long and 6" wide. You can also run tubing along the sides of the forge. If you mount two tubes carefully parallel you can then make a sliding support for longer pieces.
If your insulation on the forge is good enough you can heat it with mapp gas. besides you're math sucks. or mine does. whatever. IF... you are serious - build a heat chamber. Start with (ins/kao/whatever)wool, two inches thick, since you are worried about your torch having the required balls and if you really want to conserve the heat, coat the inside with ITC. Keep the access opening small - but not air tight. the exhaust resistance should be less than the pressure of the gas and air going in. Get a torch that kicks out a blue or green flame going into it and fire it up. All that flame and heat soulds so intimidating and complex to folks when they don't have the experience of it. After first blush it's so simple and uncomplicated you will wonder what the problems were.
A 5 gallon bucket is HUGE for a forge. A guy could go broke stuffing enough refractory into it to get the inside space down to a decent size.
To the plus side of that, one could use a couple different types of refractory and end up with a small enough working area, and have a minimum of heat escaping through the sides. Of course, with the right refractory, you could get the same results in a forge that was far smaller, too. EG using some ceramic foam and ceramic fiber with a liberal coat of ITC-100, would put you a bit ahead of a firebrick or castable refractory liner, but at far higher cost.
My forge is mostly plumbed with salvaged BBQ fittings and line. The reg has been butchered in order to adjust the flow, and there are no safety features other than a ball valve shut-off and the valve on the propane tank. It does not get left running unattended. It does not worry me to be without the safety stuff, but your mileage may vary somewhat on that.
If you want to try a blown burner, get it out of your head that you should be comparing same size burners. A naturally aspirated burner will be much smaller to get similar flows. The blown burner on mine is made of 2 inch pipe fittings and nipples from the hardware store, and it works very well. I made no efforts at theoretical perfection when I made mine, and built a set of nested pipe sections into the hot end of the assembly as a flame spreader and keeper. Works great. The naturally aspirated burner that i made for it was of 1 inch pipe and worked OK as well but I found that the blown one met my needs and have not reinstalled the other one.
I made my forge too large, and it is all castable except the floor liner which is a half-split hard firebrick. When I get around to making another, it will be far smaller, and I will not bother to put a hole in the back for long peices, as I can lay them across the front of the forge and get the same heat. I have not welded with this forge, but have burnt a few peices badly enough that I have no worries about it's capabilities.