Trying to figure out appropriate forge size for burner- any help appreciated!

On Sat, 02 Dec 2006 17:48:20 +1100, Chilla


Thanks Charles-
I think I may have come up with something similar enough to that to work- instead of stacking the side bricks on end, I put them all on their faces, with the two bricks in the middle layer 1" apart. Then I put a partial brick on the back end to close the chamber, and tied the stack together with bailing wire. That made a chamber that was 9"x1"x1.25". Luckily, I had a masonry bit long enough to drill the 4.5" through one of the side bricks, and just put the torch right in the end of the hole.
It took about an hour to get really good, but after that, it was able to take a cool bar to a bright red-orange in about 3-4 minutes. It would do that right away, but it took a lot longer. Never got much hotter than that, but that was plenty. What was really nice about that vs. a single hollowed brick was that I was able to reheat the sheep's nose tool I was making after getting the angle and hook established by carefully sliding one of the middle bricks over a little to enlarge the chamber.

Not sure I understand this- is the bore the chamber radius, and the length the length of the chamber? If so, I guess I got lucky!

I'll take a look for one the next time I'm at the hardware store, thanks!
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Prometheus wrote:

Sorry my bad, length of the burner tube to the diameter of the bore in the tube.
Regards Charles
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All firebrick is not the same. For "quick action" you want lightweight brick (feels almost like styrofoam). Fireplace brick is harder and heavier. Pottery supply is the typical source for the lightweight stuff. Point being, it takes time and fuel to get the face of heavy brick up to temperature, and heavy brick does not insulate as well (it does, however, hold up to abuse better, such as having logs tossed at it)
BUT...
You don't need to go get those, since you already have some brick, if you get one of the other trick materials - find your local pottery supply (or one on the net) and get some high temp insulating blanket (eg, kaowool), which you can use to line the inside of this forge (or a coffee can - the stuff is that good). There are also coatings you can use (eg, ITC-100) on the face of the stuff. The lightweight, highly insulating nature of the blanket material will mean the thing heats up a lot faster. But that will come later, as you're not in a state to spend money on it until after the holidays - OK.
For now, If you are primarily heating small chunks of drill rod, I'd restack the forgelet such that you have two brick laid flat, so it's 1.5 inches high, and perhaps set them 1 - 1.5 inches apart, so the space is more like 1 or 1.5 x 1.5 x 9 - if you need a little more width, make it a little wider. Given limited heat input, the less excess space (and brick face exposed to the heat) the better.
--
Cats, coffee, chocolate...vices to live by

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Your forge is plenty small. Your firebrick isn't the right stuff, as others have mentioned, but it should work a lot better than it is. I think your torch is at fault. What to do about it is the tricky part.
If you can post a picture or two, it may help us figure out what to do. Otherwise, you can try adjusting your burner. Try to figure out some kind of choke to reduce the amount of air. Try reducing the pressure (you are using a regulator?) and see what happens.
Here are some flame pictures:
http://ronreil.abana.org/richtolean.jpg
http://ronreil.abana.org/flame.jpg
http://ronreil.abana.org/sidef.jpg
http://ronreil.abana.org/burner2.jpg
They come from here: http://ronreil.abana.org/design1.shtml There are more pages on this site of interest--you could spend between now and Christmas reading it all.
The firebrick you have is probably intended to hold heat. This means it will be slow to heat up. A piece of 1/8-1/4" steel rod held in the flame will show rough heat changes a lot quicker than your forge body.
Larry Zoeller isn't answering my emails--has anyone else been in touch with him? I'm wondering if I'm getting nailed in a spam filter or something. Maybe he's on vacation.
Steve
Prometheus wrote:

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OK, it was my spam filter. Larry Zoeller is out there and responding. Ignore my last question.
Steve
Steve Smith wrote:

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wrote:

Unfortunately, photography is one thing I don't do- seems like the couple of times I bought a camera, I managed to break the things right away. Got sick and tired of throwing away $$$- so no pics.

The "neutral" flame best illustrates what the flame looks like out of the torch. It's not a terribly fancy one- just a standard one that screws to the top of a skinny propane tank and adjusts via a knob at the back.
I'll try to describe the setup in words- there may be something you can spot from the description alone.
The firebricks are layered to make a chamber that is about 1" x 1.25" x 9" long, with one brick stood on edge to block the back. Each brick has is 1.25" x 4.5" x 9". To direct the flame into the forge, I drilled a hole halfway down the nine inch length through the narrow part of the brick, so that the hole is 4.5" long. The nozzle of the torch is a tight fit in the end of the hole, and when looking into the opening of the forge, the flame comes straight out of the hole, hits the far wall, splits in two and swirls back along the top and bottom.
The torch nozzle is essentially a bit of bent pipe with no end on it. It does not have air holes near the tip (It just occured to me that that may be important, as the end is fitted into the hole.) I have been running it fully open.
What happens after the bricks begin to heat up is that glowing red spots about 1.5" wide gradually develop on the bricks themselves- first where the flame is coming through the hole, and then spreading to the top and bottom of the chamber shortly thereafter. As you can probably guess, the metal is most efficiently heated right on those spots.
At the mouth of the opening, there is a fairly consistant blue flame extending out about 1".

I believe it is- several hours after turning the forge off, the bricks were still very warm to the touch. They were sold as fireplace liners.
It worked well enough to make what I needed, so I suppose that might be where it's at for a little while. I got the boss to agree to let me take a little time to make a metal forge body with the equipment at work, so once I figure out how to make an appropriate burner, I can go that route and buy some of that kaowool and line the inside. Lots of overtime right now, especially with people missing work for the hollidays, so I might be able to get something more respectable together fairly soon.
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That sounds really good actually. :)
There's some talk about putting some sort of replacable fireproof brick on the bottom of the forge when you are welding, flux eats it up instead of your lining etc.
Not sure what type of brick tho. :/
I'll shut up now, ok? :)
Alvin in AZ (not a blacksmith just a blabber mouth)
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The one inch thick firebricks from the farm stores work okay for this duty. They are cheap and easily replaceable. Some people lay them on top of the kaowool at the bottom. That's where I put the joint anyway. Some people put the firebrick on the bottom of the forge first and then run the kaowool up to it. If you make the "pipe" forge that's on my website, the pipe is 18 inches long, so two of those 9 inch long firebricks fit without trimming.
>
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>
http://www.spaco.org/gsfrgdrw.jpg
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Pete Stanaitis -----------------------------
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I'm trying something different on the forge I'm making this winter. I cut my tube into a half cylinder and I'm going to lay it on a flat floor of brick. I'm thinking (hoping) that coating the Durablanket with Satanite will make it rigid enough to stay up. The edges will have a small piece of angle to hold the Durablanket.
Steve
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Prometheus wrote:

Ah, there we have it, I was wondering why you needed a masonry bit to cut the brick, a K26 fire brick can be cut with spoon. Buy 1 K26 fire brick make a hole through the centre, and a hole in the side for your propane hand torch (small blue bottle bernzomatic or something similar at a guess). Wire around the block in front and back and run two wires around the length of the brick.
1 K26 costs $8 AUD, so probably $5.50.
You will definitely be able to work faster, get higher temperatures and the gas economy will be better.
The brick will eventually degrade, and the wires help stop that a little, but if cost is the issue, this is definitely the way to go for knives and small tools.
Regards Charles P.S. Just to confirm how well this simple idea works, I used 1/2 a K26 and a 250g crucible to melt 90/10 bronze in about 5 minutes. Powered with a propane hand torch.
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Yep. The object isn't to make heat: That's easy. It's to keep the heat where you can use it.
There are variations of propane forges and kilns all over the net, from bean can or one brick size, using ordinary propane torches to monster furnaces that can melt pounds of bronze, using burners maybe more suited to industrial tasks. :)
I built my two-burner tube forge from plans on Dave Wilson's site.
http://www.flash.net/~dwwilson/forge/forgeplans.html
I built the Plan 2 forge.
It's served me well for somewhere around ten years with only minor repairs like relining now and then. I've welded no few pattern welded billets in it. When I quite making long things, I turned off one burner and blocked one half of the forge with some Kaowool blanket. Still works fine.
If I decide to play a bit, I'll see about building a lighter version or maybe a toaster forge this Winter.
--
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Oh, bring back that old continuity.
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I misunderstood. I was picturing a large weed burner. You're right, your burner is undersized compared to the volume, and the heavy firebrick isn't helping matters.
This is a burner that works great and is cheap and easy to assemble: http://ronreil.abana.org/design1.shtml#Reil If you weld, you can come up with better ways to hold the jet. Alignment of the jet with the burner bore is important. If money is easier than time, buy a sidearm burner from Larry Zoeller (see my other post). I'm using one of these burners in a forge 11" diameter (outside), 15" long with 2" of Durablanket S insulation and a flat floor (so it is a half cylinder inside). This works fine, but I wouldn't make a single burner forge any larger.
If you want to get a little fancy when you build a bigger forge, add an idle circuit to the gas flow. You should have a shutoff valve of course, from there you run two gas pipes. One goes thru a second shutoff to the burners. The other route goes thru a needle valve to the burners. Adjust the needle valve for the lowest pressure the burners will run at. Now you can switch between full bore and idle with the flick of a valve. You will need a regulator--most non-blower burners run in the 3-10psi range.
Another nice thing to do (I haven't tried this yet--I'm building a larger forge this winter) is to make air curtains at the open ends of your forge. This is a narrow stream of cool air, maybe 1/2-3/4" by the width of your forge opening. This is supposed to help reduce heating on stock sticking out of the forge (and your hands). You still need firebrick or doors. I'm going to use a crossflow (tangential) blower like this: http://www.herbach.com/Merchant2/merchant.mv?Screen=PROD&Store_Code=HAR&Product_Code=TM03BLR4713&Category_Code N
You should coat the wool products with something to seal the surface and keep particulates out of the air. Larry sells some coatings that are also IR reflectors (somewhat increasing your forge temp), but they're expensive. I use Satanite, which is cheap. You paint it on (glop it on?).
You need 2300F rated Kaowool (Durablanket S is the same rating). I usually buy the 3000F bricks. The fireplace type bricks will crack eventually from thermal stress. The high temp bricks won't, but they crack from being dropped. :)
Steve
Prometheus wrote:

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