My time is worth something... well so people tell me. I'm going to ask them to just pay for materials, as I'm using the forges to work out the kinks in a commercial design I'm working on.
I bought the "Kaowool Rigidizer" from Thermal Ceramics, and Thermal Ceramics "only" sell the Kaowool by the roll, however you can get Kaowool at any kiln or potter supply place, this is where I bought my first metre :-)
I did this test, get an oxy acetylene torch and point it at your Kaowool... it disintegrates very quickly, apply "Kaowool Rigidizer" to another piece of Kaowool, wait the 12 hours drying time (if you force dry, the Kaowool shrinks a lot). Apply the torch and nothing happens to the Kaowool, except it gets hot to touch. Apply some thixotic zirconium paint and heat is reflected back :-)
I couldn't get ITC100, so I got the rigidizer instead. Is ITC100 a reflector as well as a hardener or is it just a hardener. Kaowool Rigidizer costs $23 for 5 litres from Thermal Ceramics.
You can easily set up a car battery and a cheap inverter to run your blower when your "in the field"... I've done it, it's really not a big deal. I find the increased effeciency more than make up for the inconvienience.
Really, I think it's a matter of which is *more* inconvienient: filling up extra propane tanks, or running a blower. I haven't made any effort to measure it, but I get a lot more heat out of a blown burner than a venturi-style one. I haven't really tried to tune the burner to be totally effecient, either.
BTW, right now I'm running a poor-man's recuperative burner (w/blower). The recuperative burtner is loosly based on the Sandia recuperative one, just made with inexpensive Home Depot parts. Basically it's just a Riel-style burner run inside a "sleeve" of larger 2" pipe. The hot air from the forge rises up the "sleeve" and exits out a T- fitting. It's fairly basic, but seems to work well. If any one wants to know more I can send some pictures.
I'm not sure if it's the same or not, but a common rigidizer is colloidal silica. You can find it on the net. I got some in liquid form, from what I hear there is a colloidal silica powder sold as an additive for fiberglass resin.
I've been using the colloidal silica with good results. About the only problem with it is that it's very brittle. A little pressure and it cracks up.
I ended up buying a bag of fine-milled silica powder from a ceramics supply place and made my own colloidal silica by mixing it with water. Whatever didn't drop out of suspension in a week or so was decanted off to another jug. It's cheap and seems to work just as well as the expensive stuff.
The Kaowool Rigidizer contains a lot of colloidal silica, but the additives make the difference... I guess. At $23 AUD for 5 litres and no screwing around... I can afford that :-) Charles
I don't know about expensive, I use one 9kg tank (20 litres of gas) of propane in about 4 days solid effort running a 2 burner propane forge running at 15 psi. The same 9kg tank will last about 4 hours when running at 300kpa in a melting furnace. No air source, all naturally aspirated. To refill a tank costs $25 AUD, and refill 5 is free.
If I were to add air, I would definitely be able to get higher temperatures, with the cost of adding a lot more oxygen.
Getting complete combustion -- involving all available fuel with sufficient oxygen -- will get the highest theoretical temperature for that fuel. That is, the peak temperature of the flame.
A naturally aspirated burner will have a small range of operation where the fuel burns fully -- or is more 'finicky' to operate. This works well. Any time you vary the amount of fuel -- the pressure -- you have to adjust the draw of air. Pretty straight forward. You adjust the air to get complete combustion, adjust the amount of fuel for total amount of heat you want.
Similar with the blown air forge. The temp is pretty constant - just keep the blower providing enough air for complete combustion. Too much air will cool the resulting burn, but the adjustment is less critical than getting the naturally aspirated burner to peak temp.
A blown forge is capable of more heat. Both have the same peak temp with the same fuel. But the naturally aspirated burner has a limit to the amount of air it can draw, which limits the amount of fuel that can be burned effectively. A blown burner is also limited by the rate at which air and fuel that can be burned, but the blower can typically supply much more air than the naturally aspirated burner can draw, thus allowing more fuel to be burned effectively. With the typical air choke plate, a blown burner can easily be adjusted for very low pressure/heat operation, too.
A naturally aspirated burner could theoretically be built to burn any large amount of air -- at the cost of giving up operation at lower pressures of fuel. The Reil style burner often uses a choke to limit air draw, but stable operation at lower, choked-down air flow may be more difficult to set on the larger burners.
Blown burners may also have an advantage in forges with an open side, or open ends. They can create a larger peak heat region in the firebox, even with one or more sides open as with a farrier's forge. The naturally aspirated burner will be more susceptible, at lower fuel pressure operation, to movement of air around the firebox.
Designing the volume and shape of the forge, capacity of the burner, fuel selection, all work best when they are in the right range to suit the other components. For many larger firebox uses, two or more burners of either type can be much more flexible than a single, larger burner. Sometimes. It depends.
Compressor, like the compressor half of a turbocharger for a car. Snail housing into a manifold to the box, burners are just holes in the box wall. Choke down the inlet and the gas gets sucked out of the pipe and into the inlet. The impeller will put up about six pounds above atmoshperic ambient boost, just like a turbo in a car. It sure makes the gas meter spin when it's running full out. Regs? What are those? This is a 'hobby'. I can make 12 Large a year on a hobby here. There are stringent regs for coal, EPA and all that, but nothing for natural gas. All the gas company cares about is that I pay the bill on time. They love me.
BradK wrote: That was cool, Brad, you ain't messing around. :)
All I really do is heat treat so my setup with the blower and rather "open box" has worked out great. :)
But there has been a few times where I used the burner for "out of the box" stuff like pre and post heating welds and bending heavy steel parts... stuff like that. I have a bunch of different sized "double-heads" and a "single head" too.
Like Brad said, mine sure as heck ain't finiky about full blast or with the baffle all the way shut (for smaller heads than shown).
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The side-outlet-elbow there is a 1" with 3/4" elbows holding the screens. Since then I've screwed in a couple 1/2" reducer bushings with their own screens, right on top of the screens shown. I've had better luck heat treating my little pocket knife blades and springs with the smaller flames. Easy as pie to run it too, I just "close" the baffle and it leaks enough air to give me the flame I want. :)
To heat treat a butcher knife, all I have to do is take out the 1/2" reducer bushing and run it with the baffle sitting a little more closed than what's shown.
Not that what I'm doing is a direct use to anyone else... the whole thing is done by the seat of your pants... that's just where I'm "sitting" is all. ;)
Gday Folks, so the nice people at iforgeiron have put together a page "getting started in blacksmithing" with links to their forge plans etc. It may be of use for someone here.... ok thats me ;-)
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Oh my head is now spinning after all the posts :-)
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