My new Gas forge

[Robert Simmons]

Well it has been a long road to get started. At times I have felt so frustrated I had been tempted to throw in the towel. I tried a dozen burner designs and had a hard time with the blown burner designs working properly and staying lit. Perhaps that was a function of altitude or the need to have the burners be small. I also had Venturi burners that couldn't do much more than bake a cookie in the forge. Eventually I hit on a winner.

I originally cast the forge to be powered by three Venturi burners and made it so you could pass through stock or even reduce the size of the forge with fire bricks. Hence I had three burner holes with 1 3/8 inside diameter. However it quickly became apparent that this might not work. The Venturi burners had a bit of trouble burning completely and were just too slow to heat. The solution was a hybrid one. The main burner, in the middle, is a Venturi burner based on my black iron pipe burner with a flame stabilizer instead of a flare. The diameter of the burner pipe is 1 inch inside and it has a 1/2" inside diameter pipe welded inside in the direct center as a flame stabilizer. On the two remaining holes we have air feeds. So while the burner is Venturi, the forge can be and usually is blown. The idea is that the blower (hairdryer for now but blower when I get the cash, is mounted in the pipes and the T junction splits the stream to the front and back pipes. This feeds raw air into the forge which massively increases the heat output of the single venturi burner. Using this design I can get it glowing in about 15 minutes with 5 to 10 psi of propane coming through the Venturi. I plan to add ball valves so I can control the balance of air feed directly. I also thought it might be better to use some 45 elbows and try to avoid having the air stream take 90 degree bends but I am not sure that is necessary, I tried gate valves but the problem is I cant see the position of the valve from the outside so ball valves seem a better fit. I would also like to get some hard brick for the floor instead of the soft but my ceramics supplier is fresh out.

I am working on a dedicated table for the forge. Right now it is sitting on my heavy duty welding table (that thing could hold a car if you could get it up there). I want to put a roller holder out front that can be adjusted for length (sort of like trailer hitch style) with a pin through a pipe for a roller. I also need to weld some brick supports that can wrap around and hold a fire brick in a more elegant manner than stacking them like blocks. Another thing I would like to do is weld some 3 inch wide fins in a radial pattern to act as a heat sink on the top and sides as the metal shell stays hot for hours. Finally I want to increase the ITC100 layer to about 1/8th inch thick with perhaps another ITC coating over that for heat retention. Right now the floor has no ITC100 but that will come about.

Anyway comments and suggestions are appreciated. I would like to also thank all the people that helped me out and offered encouragement even when I was frustrated beyond belief.

[Nakedanvil - Grant Sarver]

Certainly shows that your atmospheric burner is unable to pull in enough air. You could drill the air holes out bigger and see what that does. Also, you could hook gas up to the other two and not open that up until the forge is hot. Interesting that it's working well that way, I'll have to file that away. Glad you're hot at any rate, good show!

OBTW: I know it's not elegant, but stacked bricks work well. Steel frame get warped beyond recognition pretty fast.

[kcrucible]

Certainly shows that your atmospheric burner is unable to pull in enough air. You could drill the air holes out bigger and see what that does. Also, you could hook gas up to the other two and not open that up until the forge is hot. Interesting that it's working well that way, I'll have to file that away.

Basically the furnace itself is a combustion chamber being fed from a pre-ignited stream. As long as there's enough time to finish combustion before the gas exits the chamber it should work just fine, otherwise you'll be wasting a little fuel. So with that in mind, reducing the air via the valves, etc, may increase efficiency.

I agree with the air holes comment. Seems like it should be sufficient, but the small holes may have too much air-drag to pull well. Bigger holes have a better air/surface ratio. Ron Reil, Michael Porter, and Rex Price all seem to be agreed that good sized slots are better than holes.

Finally I want to increase the ITC100 layer to about 1/8th inch thick with perhaps another ITC coating over that for heat retention.

I don't know that more ITC100 will help much. My understanding is that it's basically an IR-reflector, not an insulator. Think of it like a space-blanket... the foil keeps people warm by reflection, not insulation, and thickness has nothing to do with it. It'd probably just be a waste of money.

I wouldn't put anything over it either as is may completely negate the reflective qualities of ITC100.

One other tidbit I read about recently... over time your forge may get less efficient as scale, soot, etc, start covering the ITC. Cleaning it and/or repainting improves things dramatically. The guy doing this re-painted half the forge and fired it up to test out the theory. The difference was apparent.

[Robert Simmons]

Basically the furnace itself is a combustion chamber being fed from a pre-ignited stream. As long as there's enough time to finish combustion before the gas exits the chamber it should work just fine, otherwise you'll be wasting a little fuel. So with that in mind, reducing the air via the valves, etc, may increase efficiency.

I agree with the air holes comment. Seems like it should be sufficient, but the small holes may have too much air-drag to pull well. Bigger holes have a better air/surface ratio. Ron Reil, Michael Porter, and Rex Price all seem to be agreed that good sized slots are better than holes.

I calculated that the total area of the air holes in the pipe exceed 200% of the area of the bell reducer itself. As for drag, that could be a good point, I dont know. The burner works like a champ out of the forge, its only in the forge that it suffers burning rich but when I dump raw air into the forge, it works like a dream. It seems similar to a link someone sent me in the process showing furnaces that worked by dumping air and gas separately into the chamber and igniting them individually. However this would be safer because even if the burner burns rich, it still burns off the vast majority of the propane.

I don't know that more ITC100 will help much. My understanding is that it's basically an IR-reflector, not an insulator. Think of it like a space-blanket... the foil keeps people warm by reflection, not insulation, and thickness has nothing to do with it. It'd probably just be a waste of money.

I was referring to the ITC-296A as described at the following link:

http://www.budgetcastingsupply.com/ITC.php

ITC 296A Ceramic Top Coating is a high purity ceramic top coating that resists deposits from firing gasses and from contact with molten metals. Increases energy efficiency by reflecting heat back into the furnace or back into the melt. Helps to reduce contamination of subsequent firings from the by products of the previous heats. This material is applied over the base coat of ITC-100, ITC-200EZ or ITC-213.

I applied the ITC-100 like frosting a cake thin. It took a bit of effort but we got it done. The problem is the surface isnt really smooth, being very much like a cake. Another layer might allow me to get it polished smooth which might help reflectivity.

One other tidbit I read about recently... over time your forge may get less efficient as scale, soot, etc, start covering the ITC. Cleaning it and/or repainting improves things dramatically. The guy doing this re-painted half the forge and fired it up to test out the theory. The difference was apparent.

That is why I was thinking of the ITC-296A.

[kcrucible]

I applied the ITC-100 like frosting a cake thin. It took a bit of effort but we got it done. The problem is the surface isnt really smooth, being very much like a cake. Another layer might allow me to get it polished smooth which might help reflectivity.

I see.. hmmm. Not so much a thickness thing as an angle thing. Most angles it probably wouldn't matter much. Eventually they'll bound around the chamber and hit the metal again. If you have some frostings that direct the surface toward your doors that would be less than ideal. So... maybe worthwhile? Maybe someone has hands-on experiance with maybe it makes a difference.

That is why I was thinking of the ITC-296A.

Interesting. It must be invisible to InfraRed so that the ITC-100 keeps working, but provides a physical barrier layer like clear-coat for paint. I guess that's another thing for me to think about.

[Robert Simmons]

Well I now have a video up of the forge in operation. Let me know what you think.

[kcrucible]

Robert, check out page 385 of this book...

http://books.google.com/books?id=cCJ_YyAEqnQC&pg=PA362&lpg=PA362&dq=flame+stabilizer&source=bl&ots=Zmbx0gF-x_&sig=GK-l-lgCQpMoadoNGzoe2QhrKRU&hl=en&ei=WxhoTJbmC4OglAfunpGfBQ&sa=X&oi=book_result&ct=result&resnum=2&ved=0CBsQ6AEwATgU#v=onepage&q=flame%20stabilizer&f=false


Seems to be basically what you ended up with.

[Robert Simmons]

Robert, check out page 385 of this book...

http://books.google.com/books?id=cCJ_YyAEqnQC&pg=PA362&lpg=PA362&dq=flame+stabilizer&source=bl&ots=Zmbx0gF-x_&sig=GK-l-lgCQpMoadoNGzoe2QhrKRU&hl=en&ei=WxhoTJbmC4OglAfunpGfBQ&sa=X&oi=book_result&ct=result&resnum=2&ved=0CBsQ6AEwATgU#v=onepage&q=flame%20stabilizer&f=false


Seems to be basically what you ended up with.

Yeah sort of. Its a direct air supplement to a burner. In the old days they woudl actually not mix the gas and air til they hit the burner but that suffered from safety issues. I do a bit of both in this forge. I can crank up the PSI and get a ton of heat out of it. What I really need now is a good blower but all things in due time.

[Nakedanvil - Grant Sarver]

In the old days they woudl actually not mix the gas and air til they hit the burner but that suffered from safety issues.

Where did you see that? What safety issues? Maxon blowers I've had from the twenties had a connection for the gas to be fed directly into the blower. Same way I've done on many forges.

[kcrucible]

Certainly shows that your atmospheric burner is unable to pull in enough air.

After my experiment with the flame holder, I suspect that this is Robert's problem too. It seems like the flameholder is choking back gas velocity, limiting the venturi action. The result is that a lot of unburned gas enters the chamber, so needs a lot of additional air pushed in to finish combustion.


I think this choke-back effect is why Ron Reil said he'd never use a flame holder.

http://www.craftkb.com/Uwe/Forum.aspx/blacksmithing/1/propane-burner-question

RONALD S. REIL
...
as much of an advantage when
you consider what you lose by using them. That is the same reason I don't
have flame-holder designs on my site. They work too, but why have a 3/4"
burner tube and not get all the output it's capable of delivering.

[Robert Simmons]

Where did you see that? What safety issues? Maxon blowers I've had from the twenties had a connection for the gas to be fed directly into the blower. Same way I've done on many forges.

I was reading an article linked from the replies to one of my threads on the history of propane burners. The problem apparently is flashback which can happen if there are no flashback devices and pressure in the furnace exceeds that of the gas pressure. It doesnt so much apply to forges I guess. I was just basically talking aobut what I read.Anyway, with a good blower I think this forge would just roar. I am wondering though about back preddure on the blower when the gate valves are closed but I suppose a relief valve based on air pressure could be rigged. I dont mind fryong a 10$ hair dryer but a 100$ blower is another issue.

[Robert Simmons]

After my experiment with the flame holder, I suspect that this is Robert's problem too. It seems like the flameholder is choking back gas velocity, limiting the venturi action. The result is that a lot of unburned gas enters the chamber, so needs a lot of additional air pushed in to finish combustion.


I think this choke-back effect is why Ron Reil said he'd never use a flame holder.

http://www.craftkb.com/Uwe/Forum.aspx/blacksmithing/1/propane-burner-question

Actually my problems were gas velocity exceeding flame front velocity and flameout. If the velocity had been too slow a smaller jet would have solved it and I would have had the flame in the tube which I never did.

I am no expert on fluid dynamics but when you consider only 28.9% of the air is burnable oxygen and the blower increases all air products, it makes a heck of a lot of sense. I know when I had the burner singing fine outside the forge, I got a rude surprise when i put it into the forge. Introducing extra air separately solved the situation. You may not believe me but that is what I observed.

[kcrucible]

Actually my problems were gas velocity exceeding flame front velocity and flameout. If the velocity had been too slow a smaller jet would have solved it and I would have had the flame in the tube which I never did.

I am no expert on fluid dynamics but when you consider only 28.9% of the air is burnable oxygen and the blower increases all air products, it makes a heck of a lot of sense. I know when I had the burner singing fine outside the forge, I got a rude surprise when i put it into the forge. Introducing extra air separately solved the situation. You may not believe me but that is what I observed.

I was referring to the slow tube velocity not allowing enough suction to pull in enough air back when you were doing strictly natural aspiration. The exit velocity/stable flame is a seperate matter, though intertwined somewhat. It's tricky.

For my burner, for example, at high velocities I had good flame color... good mix of oxygen/fuel, but I couldn't keep it lit. At lower velocities (without a flame holder) I had burn-back. When I added the (admittedly bad!) flame holder, both the exit velocity AND the tube velocity decreased, causing my air/fuel mix to run quite rich even though it was stable. Now without the flame holder (that constricted the tube signifigantly) and a different way to reduce exit velocity that doesn't impact tube velocity signifigantly the mix is better, though still not perfect. I've got a little more tweaking to do.

I have no doubt that my burner with fan grill would have worked in a forge with the additional hair-dryer blower just like yours did. At that point I was getting a lot of fuel, a stable flame, just not enough air. Adding more air would have fixed the problem I'm certain. I'm just working on eliminating the need for the extra blower (hopefully.) It's been done before, so I'm sure I can get there with a bit more tweaking.

Unlike your situation, where you just want to get to blacksmithing, I'm finding the experimenting and tweaking quite entertaining.



If you ever get back around to experimenting, I just found this:


http://www.scribd.com/doc/24451217/Space-Heating-Handbook

Burner Operation at High Altitude. In burners operated at atmospheric pressure, altitude is an important factor because in- creased altitude causes air density (weight) to decrease (that is, the air becomes “thin- ner”). At high altitudes, therefore, the lower air density (less oxygen per cubic foot of air) results in combustion effects that are different than those at normal alti- tudes. For this reason, the heating system designer or equipment buyer should specify the altitude of the location where the heater will operate, if it is significantly above sea level (2000 feet altitude and higher is considered “high altitude”). The manufacturer can then make adjustments in orifice sizing to accommodate the less dense air.

So maybe part of your solution, if wanting to eliminate the blower would be to drop down a tip size because of the leaner air? That would probably reduce BTUs, but could have multiple flame jets instead, and not need power/blower at all. Edited August 18, 2010 by kcrucible

[tlreif]

Hey Robert. I was reading your post and I think the reason that the burner works great out of the forge, and not in it is the hole that you cast needs to follow the 1:12 taper. It looks to me that the wall of the forge is 3 to 4 inches thick. the opening by the time it get to the forge chamber should probably be at least 3 inches maybe more. Im not a math guru but you get the idea. The forge shell you have poured looks nice. I believe if you opened up those holes you would be surprised at the results. I haven't tried my burners at altitude but Im betting they would work great. Also for the forge floor I would get a piece of kiln shelf for that. I use them in mine and they work well. You can insulate under it with kaowool and you wont lose the heat that regular fire brick will suck out.

[tlreif]

oops one more thing. I dilute the itc 100 so that it is pretty thin. then I paint it on with a paint brush. the result is a smooth finish and an efficient forge! You can always paint more than one coat.