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Number of burners for gas forge?


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I have been reading Michael Porter's great book on burner and forge design.  I am going to build his basic 25-gal propane cylinder forge.  His basic design calls for a 1/2" burners for forge diameters up to 6", 3/4" burners up to 9" dia, and 1" up to 12" dia. 

For evenness of heat, would it better to use, for example, two 1/2" burners instead of one 3/4" burner? 

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Welcome aboard MP, glad to have you. If you'll put your general location in the header you might be surprised how many of the IFI gang live within visiting distance.

Surely 25 gal. is a typo, it'd be a huge forge and take probably at least 6-8 3/4" burners. A 20lb./5gl. tank is much more reasonable size.

I talked to Mike about how he states forge size but that was long after he published.

The metric for burner size, quantity and placement is 2 fold. First if chamber volume. A 3/4" burner will bring a 300-350 cu/in volume to welding heat IF it's reasonably shaped. The other factor is chamber shape a long narrow 300 cu/in. works much better with more but smaller burners.

A 1/2" burner is good for about 1/2 the volume of a 3/4" burner and a 1" burner works well in 700 cu/in. Provided it's a relatively a spherical or cubic volume,  WITHIN REASON.

Frosty The Lucky.

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Thanks, Frosty.

Yes, you are correct - it was a typo.  Can you imagine a 25 gal forge?  We could do trucks for freight railcars!

I am in Central Oregon, and have changed my profile to indicate that.

Are you the Frosty who I have seen associated with burner design?

 

 

 

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I have a friend who works where they use railcars to move stuff into their forges. 25 gallons would only be a bit over 3 cubic feet (8 gallons per cubic foot of water) not an especially large forge for industrial work and I've used larger ones used by professional artist blacksmiths.

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I have seen a number of your posts, Charles.  I like your commitment to normal aspiration.

 

Where can I find a design for this T burner, and how does it compare with the burners Michael Porter shares in his book?

 

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Hey, I resemble that guy!

Mikes type 5 burner is better on a few counts, most significantly it's less susceptible to breezes than the T and it's more efficient an inducer. The down side is how much basic shop skill you need, the Porter burners are a much more precision intense build. The T requires a straight hole in the center of the T threaded so the mig tip jet is aimed straight down the tube.

Mikes work better, closer to commercially made burners but take quite a bit of time and you need to get it right. Good burners though worth the time. I'm just lazy.

Frosty The Lucky.

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  • 2 weeks later...

Two 1/2" burners on a five-gallon forge will give more even heat than one 3/4"; on the other hand, the single burner will heat up most of the forge just fine, and produce less heat loss for gas used; why? Because of the kiln shelf in my design. Leaving the outer inch or two of the forge at a lower heat means less conductive loss via that shelf. Some people use a thin brick and don't extend it outside of the forge, but this makes a weak construction choice. In my next portable gas forge, the kiln shelf will extend even further outside the steel shell. this will be done in order for it to hold a sliding baffle plate, and will be featured on an oval forge, instead of a tube forge.

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MP,

When it comes to installing burners in a gas forge, they are interchangeable, so nobody says you need to build one of my burners, to begin with; not even me. The burners being sold on eBay at present are bargain priced and work reasonably well; there are many other choices as well. You don't have to build a Mikey burner to get your money's worth out of the book. Life is about choices; therefore options are a very fine thing. Of course, you probably will build one in the end :-)

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Ashbury did some experiments and found that a 1" burner was more effecent, BTU produced and fuel used, he also found that a 12" diamiter forge body with 2" of insulation was more effecent. He built 9" wide by 12" diamiter forges with 1" burners for the school he was working with. Now his article nither tells me what tyoe of burner or what school...

but it dose say that the distance the flame travels befor hiting an ubstruction matters, to close to the floor/wall and the fuel is not compleatly consumed. 

Some one with more practical gasser building experiance may have better experiance. 

 

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Requiring a long distance to consume the fuel completely is a sign of an inefficient burner. The larger the diameter of the tube and the more room there is for the fuel air to not mix. The fuel stream tends to channelize in the center of the air flow and because of it's nature propane doesn't mix easily anyway. If you've seen the machinations Lyle at All States did to get oxy propane mixed for an efficient torch you'd know what I mean.

I've only ever used one of Mike's burners once let alone had one to play with so I don't have a valid opinion about a ratio of increased or decreased efficiency depending on tube dia. Mine are a pretty straight up geometric change depending on the tube's cross section area. 2x the area, 4x the output.

A 9" long 12" dia. shell with 2" refractory is only 432 cu/in volume. A properly tuned T burner would melt the Kaowool out of it in the first 20 minutes regardless what kind of kiln wash you used. It doesn't speak well for his burners or test methods.

A single 3/4" T would be a LITTLE under powered in that forge but not much, an extra layer of Kaowool under the floor and it'd be golden.

Frosty The Lucky.

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Oh good grief you guys are in for it now. Mike is as long winded as I am and we have a little history of banging ideas and hypothesis off each other. We've had some good, REALLY good disagreements, been win wins every time. :lol:

Frosty The Lucky.

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9 hours ago, Mikey98118 said:

MP,

When it comes to installing burners in a gas forge, they are interchangeable, so nobody says you need to build one of my burners, to begin with; not even me. The burners being sold on eBay at present are bargain priced and work reasonably well; there are many other choices as well. You don't have to build a Mikey burner to get your money's worth out of the book. Life is about choices; therefore options are a very fine thing. Of course, you probably will build one in the end :-)

Mikey -

Definitely intend to build rather than buy.  I've always believed that is the best way to learn something.  Think I will do the two 1/2" burners.  Like you said, though, regardless of which path I take, I have already gotten tremendous value out of your book.  Thank you very much for writing it, and for taking the time to respond to my post.

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You're welcome, MP.

Hope you've been following along recently on all the gas forge discussions, If so, you'll already know that you want to buy extra MIG contact tips and insert .028" inside diameter dispenser needles into them. You will then have the ability to fine tune the forge even further; not that you won't also want a pair of .023 MIG contact tips with the original .031" holes left as they are, to give a slightly softer flame for forge welding.

What you will not have heard, because it is only mentioned in the updated version due out next year, is that I've modified my original advise about employing 4-1/2" angle grinders for all the work, to include hand held rotary tools for cutting out the air openings. In 2004 these tools and their accessories were just too expensive for most of the starving artists the book was dedicated to; today this isn't true. If you feel that both tools are too great an expense, choose the rotary tool over the angle grinder. Also Dremel's 1-1/2" spring loaded EZ mandrel, unlike much of their overpriced stuff, is worth every penny on this kind of work.

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I just knew if I could get Frosty to talk about brick pile forges something good would come up, and sure enough someone responded to his comment about painting the bricks with kiln wash with a better finish coating. Mentally, I hugged that idea to me and ran around in gleeful circles with it. Obvious; yes, but all good ideas are obvious...after someone else points them out! This little detail would make all the difference in how long insulating fire bricks last, and would create a tough enough surface that ITC 100 could be painted on one face to further increase efficiency.

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Oh great if it gets out at the coffee shop I have guys running in gleeful circles . . .  the expressions might be entertaining. Hmmmmm.

I've moved on from ITC-100, it's too expensive and not durable enough. The kaolin clay is too high a fire ceramic to vitrify and fix the zirconium to the forge walls so it abrades off faster than I can afford to freshen up. My latest experiment is sifting the coarser material from the high alumina refractory I used for the inner liner in the new forge and mixing the sifted cement element 1pt-2pts Zircopax flour.

The cement element from the castable refractory doesn't require initial firing to form a concrete hard 3,500f surface so I think it has a good probability of being a MUCH better matrix for the zirconium flour than kaolin clay.

Why I'm going to the trouble to experiment with and mix my own high zirconium kiln wash is simple. Last I checked ITC-100 was in the $136.00 / pint (1lb can water included) plus shipping. A little checking and Seattle Ceramic Supply (I think that's the name) flat rate mailed us Zircopax and the dry powder cost us $3.26 lb. shipping included. I think I should have gone with fine sand rather than flour but I'll see.

Frosty The Lucky.

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Charles, quoting an article. passes on the author's statement that  "...the distance the flame travels before hitting an obstruction matters, too close to the floor/wall and the fuel is not completely consumed. "

I don't find this to be so; in fact, once the forge interior becomes yellow hot any decent burner design should put out flames that are completely consumed, obstruction or no.

What does commonly go wrong when sufficient distance isn't provided, is that any super-heated oxygen molecules escaping the primary flame envelope will cause a lot of scaling on work surfaces before they are consumed in secondary combustion within the forge. The simple solution  for such a problem is running a reducing flame; of course, that can lead to other complications...best to design both forge and burner as well as you can, and only employ educing flames when they are the best option for the job you're doing :-)

Tunnel forges normally have down facing burners set at about a twenty degree angle to promote swirl, instead of top dead center, which is also found, but is far less common. Nearly every gas forge has a kiln shelf or hard fire brick floor that the burner is aimed toward in order to spare ceramic fiber insulation from direct flame impingement. But what would happen if each burner were facing upward at a twenty degree angle against a cast refractory flame impingement ring, so that there was loads of distance before it hit the work? This would also end the so called "chimney effect and greatly reduce interference from back pressure through buoyancy. Shall we discuss this possibility? I plan to use it in my next portable forge.

 

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