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Mikey98118

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The why-for of burner positions

Forget about where people think they should put a burner in a tunnel forge. The whole point of oval and "D" shaped forges is their wider floors. The more time an incoming flame spends impinging on a tough floor area, the easier that flame is going to be on the much more tender forge wall and ends. So, aim your burner much further down then usual; aim it at an more horizontal angle (more like four o'clock).

In a tunnel forge, the burner(s) well usually be positioned near the forge top, and aimed at a steeper angle downward at the floor then you would get positioning it straight in from the forge shell, so that it should be aimed gently inward aimed (at 10:30 or 1:30) to impinge toward the near edge of its narrow floor; about one-third the way in.

One exception of this would be a top dead center aim at the center of the floor, which is preferred by some people who run small forges at lower heats, when bending thin parts (1/4" and under).

The bottom line is that you want to think why you aim your burner in a given direction.

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Very new to forges and thank you for all the great info. Been taking notes on this thread and the burner.

I have a need to heat long pieces for treating. I am looking at a forge that is around 30-32" long running 3 or 4 burners.

I am looking for any input of design considerations for a long forge that may not have been already discussed.

Also, if I am right, the metal will take longer to heat at the ends in a forge. So how much longer, if any, should the forge be then your material? Need to bring the whole piece to critical temp.

Edit: Not sure i understand the disadvantage thick wall outer frame (Say pipe) over something thin like a tank.

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Have you looked into high temp Salt Pots as a way of heating?  Swordmakers use them to heat long delicate items to uniform temperatures with minimal decarb and scaling. (Though the one I worked under had a custom built vertical electric furnace with computerized controls, ramping!, and provision for inert atmosphere to severely limit decarburization and scaling during heat treat.)

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"Edit: Not sure i understand the disadvantage thick wall outer frame (Say pipe) over something thin like a tank."

So for as the forge's performance is concerned there is no disadvantage; we speak out about guys using without thinking first, because there is no advantage; I speak out against using it without reason because most guys will have to move several times in the coming years, and everything oversize and/or overweight becomes a severe handicap at such times.

T. M.,

Salt as a transfer medium for heat treating sounds like an excellent idea.

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I have both thin wall and thick wall propane forges; thin wall is much easier to move around and the thick wall has been very handy as I welded a piece of sq tubing to each side and slid a piece of 3/8" sq stock with the end bent into an L and so have a 3rd hand  to hole longer stock in the forge. (the cross piece of the L are arranged with one on the front and one on the back)  Of course teaching folks not to touch the third hand with their hands is a necessary task...So each variety has things they are better at that the other type...

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"If life give you lemons, make a cannon that fires lemons!"  

Both of mine were from Forge building workshops done by SOFA.  I don't think I will wear out the heavy walled one---it was made from welding gas tank, (probably Oxy)  The other one was made from grain auger tubing which is fairly light and has scaled through near the burner in less than a decade!

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Their ain't no sucha thing as "standard" hard firebricks anymore!!!

It is understandable that people who have easy access to "hard" firebrick don't want to bother with refractory mixes; and it is just as obvious why people who have mixed a castable refractory already see it as utterly superior to old style--clay based--hard firebricks. They are old technology. Various castable refractory formulas are available in brick form nowadays. Such high tech bricks will only grow in market share, and will probably displace castable refectory as the main choice for tough hot face layers. We need to keep an open mind about this stuff.

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  • 2 weeks later...

So why, after several thousand years, is good old clay not good enough anymore? there are various kinds of clay, and some are better than others. But the purest clay consists of aluminum oxide and silicon oxide; two main stays of of high temperature ceramics. The problem is in the percentages of silicon. A good clay will still have about 40% silicon. High purity alumina refractories start with half that much silicon, and run as low as 1%. Silicon makes a great binding agent, but it also transmit heat better than any other refractory ingredient.

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 You cannot use a standard set of torch tip cleaners with gas jets for 3/8" and smaller burners, which use .022" and smaller orifices. Tip cleaners only go down to #72, which is .025”. Instead you need stainless steel piano wire for deburring and cleaning such small capillary tubes, by poking them through the cut and sanded end of the capillary tube from its finish end, and then running them back and forth until the cut end is smoothed: http://ziggystubesandwires.com/Wires  

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Various videos of  ribbon burner forges I have seen lately have confirmed a long held suspicion that nearly all of our opinions, including some of my own, about burner noise in equating to forge noise out is...

BUNK!!!

 

For years I have built high speed naturally aspirated burners that ranged from quiet to fairly loud, depending mostly on how high they were turned up, with minor variances in only a couple, do to harmonic effects-- that is, out in the open air. When burners were placed in forges and casting furnaces, all of them became much quieter; some turned whisper quiet. I have noticed a similar range of output decibels in fan-blown burners.

I have been hearing repeatedly how quiet ribbon burners are, and especially with factory built units that seems to be true; and they should be, since a ribbon burner tends to make very little sound in the first place. But I have also listened ribbon burner forges that are every bit as noisy as any other kind I ever heard. My conclusion is that most of the noise we hear coming out of a forge, is created by the forge; not by its burner.

This shouldn't come as any surprise, as sound waves travel in straight lines, and the flame path most of us choose for our burners are circular. Furthermore, even the harder refractory materials tend to sound dampening; it should have been blindingly obvious that most of the noise coming out of our forges had to be generated by something other than the burner flame. What other culprit is lest? Well, there is still a lot of gas movement within the forge...but my money is on the rush of exhaust gases out of the forge; they are as dynamic as the nozzle gases, and have almost nothing left to dampen their sounds...in most forges.

However, just because your forge and burner are already built, doesn't mean you're struck with a noisy bit of equipment. Sound waves from the exhaust port also have to move in straight lines.  A baffle plate in front of the exhaust opening will bounce sound waves back into the forge just as efficiently as it reflects radiant energy back in there.

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Yeah? Will how come the output sounds moves up and down exactly in time with the burner; why is that, then? Even as the burner's original flame sounds are being dampened by the forge, the decibel output that the forge is making increases and decreases directly in proportion with the input combustion gases and resulting exhaust gases increase and decrease.

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  • 2 weeks later...

Ok so im a total noob at this. ive just finnished cleaning up a length of rail track for an anvil, got some basic tools and now i need to build a forge. No one sell coal where i am so gas forge it will have to be. I know next to nothing about gas heating/exhaust/volume ect.... could someone please send me a design for a simple gas forge that will get me started on the cheep?

 

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Sort of skipped over using real chunk charcoal that is available most places in the world and was what was used for the first 1500 years or so of the iron age and is still used now in many places---both viking era pattern welded swords and Japanese Katanas were forged using charcoal. (NOT briquettes!)

Anyway Wayne's a good place to get a starting point for propane.

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Why construct miniature burners at all?

There aren’t a lot of people longing for a micro forge or casting furnace, but there are a few. There are plenty of people who want to get hotter flames from air-fuel torches than is available from commercial models; and they tend to be part of the same crowd that is looking to power compact heating equipment. In the face of rising energy prices, many other people are looking to maximize equipment efficiency as much as possible.

    Naturally aspirated burners have large turn-down ranges. So, it would appear that a wide selection of burner sizes isn’t needed; and so far as it goes, that’s true. But, efficiency is about more than how well fuel burns.

    There is another factor to get control of, and that’s the velocity of a burner’s exhaust. It’s easy to see what goes wrong when there is too much or too little exhaust capacity built into the equipment. It’s less obvious what goes right when you get superb control of its internal flame velocity; That's because doing so involves balancing two distinct combustion issues; they are flame and exhaust speeds. Fast flames burn hottest, but fast exhaust wastes heat.

    The reason burners are aimed on a tangent in compact heating equipment is to force their combustion gasses to swirl around inside its interior, creating a longer distance from burner(s) to exit. A longer exhaust path increases the gas’s amount of "hang time.” That seems quite obvious doesn't it? What isn't so clear is that most of that increased time isn't made by hot gases running a little farther at a given velocity; it’s provided through a considerable drop in velocity over that added distance; this happens because, while they are traveling fast, the gas molecules don’t have much mass. Flames passing through the equipment create drag from turbulence. Multiple smaller flames create more turbulence, and therefore more drag than a single larger flame; this is the whole point behind ribbon burners. Unfortunately, the smaller the equipment the poorer the fit ribbon burners make.

     The smaller flames of a pair of 1/2" burners will lose velocity much faster than a single 3/4" burner in a five gallon forge, greatly increasing efficiency; because they can be turned up faster/hotter without producing a tongue of fire out of the equipment's exhaust opening. But, what about the guy who wants to build a two gallon knife maker's forge? He is going to need two 3/8" burners, instead of a single 1/2” burner, to do the same trick. The guy who wants to forge hand tools in a coffee-can forge is going to need two 1/4" burners to do so with top efficiency.

    But why can’t a little canister mount air-propane torch simply be stuffed into a miniature forge or casting furnace, as is? Most of those torches have brass heads, which will melt when sealed well enough within heating equipment to prevent excess secondary air from being introduced through the burner opening. The few torches with stainless steel “heads” (actually, just thin wall stainless steel goose necks), will rapidly oxidize away under those conditions. If the torch is kept safely outside of the burner port, its ability to heat anything falls off sharply.

    Using one of these torches with propylene for brazing in the open air falls into the rapid oxidation trap, because of the fuel's much greater heat. Propylene can be purchased in regular industrial cylinders at your local welding supply store for about one-third more cost than propane, instead of three times propane’s price in 16 ounce canisters from a hardware store, but most commercial air/gas torches aren’t set up to withstand the flame temperatures of propylene very well, even if they are "rated" for it by the seller.

Heavy wall stainless steel flame nozzles, and longer mixing tubes are needed to withstand higher temperature fuels and sealed placement in heating equipment.

Reality check: This doesn't mean that a single 3/8" burner, placed deeper within the coffee-can furnace won't work perfectly well for lots of people, if turned down; ditto to single burners in most forges; this information exist to show you the how of things, the why of them, and how much effort you put into the equipment you build is strictly your decision; just make with your eyes wide open.

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Even if propylene only costs one-third more than propane in commercial cylinders down at your local welding supplies store, doesn't that still offset its third-higher flame temperature? Ask that question to anyone struggling to get their heating equipment to working temperature, and see their eyes roll up. It is true that you need to guard more carefully against overheating the equipment than you do with propane, but that is what the controls on your torch or burner is for. 

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On 1/13/2017 at 11:03 AM, ThomasPowers said:

Sort of skipped over using real chunk charcoal that is available most places in the world and was what was used for the first 1500 years or so of the iron age and is still used now in many places---both viking era pattern welded swords and Japanese Katanas were forged using charcoal. (NOT briquettes!)

 

Interesting, Thomas.  I often forget that as someone who started in non-ferrous metals, charcoal blocks were/are used in forges.  Lot's less impurities when it comes to coal or even coke.  In jewelry, we use charcoal blocks for all manner of soldering, annealing and it provides a great reducing atmosphere which lends itself well to most metals.  I'm guessing it is the same qualities that are great for the blacksmith's craft.  

On 1/17/2017 at 4:50 PM, Mikey98118 said:

Even if propylene only costs one-third more than propane in commercial cylinders down at your local welding supplies store, doesn't that still offset its third-higher flame temperature? Ask that question to anyone struggling to get their heating equipment to working temperature, and see their eyes roll up. It is true that you need to guard more carefully against overheating the equipment than you do with propane, but that is what the controls on your torch or burner is for. 

Hmmm, I would like to try out propylene gas, but definitely don't want to damage a nozzle in the process.  It's good to know that propylene can be purchased at welding supply stores.  Pardon the pun, but I may have to give that gas a whirl!  

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Wow, I don't check the thread for a few days and there's a bunch been talked about to catch up to. 

Mike the sound a burner makes is as much a function of the way it's burning as it is to a type. Some burners are soft when properly tuned and shriek if turned up others roar. I think multi orifice burners are quiet because the noise generated by the explosive combustion of fuel air mix is spread over many sources. This results in a lower amplitude per orifice and there is probably more than a little interference cancellation going on. Of course the second part of that is a WAG on my part. :ph34r:

Sound reflects like any wave so being contained in a forge doesn't necessarily damp it, heck it could act as a resonator if it were built just so. 

Here's something I haven't seen mentioned, a soft surface doesn't reflect sound waves nearly as efficiently as a hard one and we all know what happens when we get stuff REALLY hot. Yes?

Just some thoughts.

Frosty The Lucky.

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Dragon's Breath

The first time I heard that term was seventeen years ago; I thought it just concerned the withering blast of of exhaust gases coming from our forges; something to be dodged or redirected; child's play. The tiny amount of carbon monoxide rich blue flame leaking from my exhaust was so concerning that I invented a whole new series of burners to stop it cold. But in my mind they were two separate issues. In fact whatever comes out of the exhaust is one issue, and it isn't a straightforward one these days. Many of us are creating such high internal temperatures that we aren't certain just what all may be in our exhausts.

But a recent argument about a guy over his horrible excuse for a burner ended up with me observing the same overwhelming amount of "dragon's breath" spewing from his exhaust as some of the newest ribbon burners, with their excellent heat coming from competent looking flames. Conclusion? When all is said and done exit flames mean carbon monoxide period; all else is beside the point!

There are many safety issues that we ignore, at times; some of us more than others, and when we do it's clear we are taking a chance...that is except for ignoring CO. If you are making carbon monoxide, then you are exposed to it; the only question is how much. It is hurting you; how bad comes down to how much we make and what we are doing to divert it from the air we breath. If your forge has a tiny little intermittent blue flame peaking out of the exhaust, than maybe working outdoors or creating a cross breeze with an area fan is enough protection...maybe. But if your forge is blasting out big time "breath" you need to address that very serious problem--fast.

 

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Holding ceramics in place inside of a steel shell; less is more

Nineteen hears back I was just picking up how to keep cast refractory and ceramic blanket insulation in place within steel shells. All the industry standard products offered today were around back them. And the solutions guys are still dreaming up now were occurring to others back then. Everything professionals came up with back then, and still do now have the same problems; they are way overdone. The professional stuff is designed to keep large walls and suspended ceilings in place; you don't need anything like that to keep a square foot or less of material in place. Amateurs often run bars inside of refractory that could hold up the weight of cars! All it end up doing is transferring more heat out of the forge via its shell, and promoting cracks in the refractory. Metals heat up faster and increase in size more than refractory; when it is surrounded by incandescent ceramic materials it just makes problems.

No matter what the shape or size of your forge is, it has a hot face inner side and a cold face layer. You want any metal within the forge near to the cold face. By drilling holes all over the shell, and plugging them with short screws, or pop rivets. you can provide all the anchors you might want without creating cracks in hard refractory when the contents heat up; they can be held just fine by fiber insulation if it has been rigidized.  forges provide all the anchoring you need by surrounding its contents in in a rigid shell. If you have a two part forge, the upper portions content can be suspended with more anchors, rather than large ones. 

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Zirconium dioxide ZrO2 (AKA zirconia) has three phases: monoclinic crystal structure (rectangular) at less than1170 °C , tetragonal crystals between 1170 and 2370 °C  and cubic crystals above 2370 °C. The transition between the first and second phase creates enough expansion to prevent it being used in hard refractory products, unless it is stabilized in the cubic form, or in its more industrially useful partially stabilized tetragonal form.

A small percent of calcium, yttrium, or magnesium oxides can be used (in high temperature industrial processes) to partially stabilize zirconia; cerium oxide can also be used, but is too expensive for the purpose. Further high temperature manipulation can form fully stabilized zirconia (cubic phase), but adds further expense.

 

Zirconia has very low thermal conductivity, yet has very high luminosity when incandescent temperatures are reached. These two facts combine to make it a preeminent heat barrier. Because of the high luminosity it can be used as an effective method of heat transference on high temperature casting crucibles, when applied in very thin coatings (.004” or less), and yet thicker coatings can be used to “reflect” heat through re-emission, while providing insulation that only improves as heat levels rise. When it comes to various heat barrier coatings, very fine particles of zirconium is wanted, because the finer the particles the higher re-emission percentages go.

 

Zirconia refractories and ceramic products provide high resistance to chemical and mechanical erosion. Zirconia ceramics have very high resistance to crack propagation.

Zerconium silica is also used as a heat barrier.

 

Government sponsored experiments in the nineteen sixties showed that phosphoric acid was able to hold plain (not-stabilized) zirconia onto heating surfaces despite phase change resizing; it was an important find—back then. But, stabilized zirconia is much cheaper than it was in the past, and so this more expensive product is the better choice for tough heat barriers, and nowadays for inclusion in high alumina castable refractory.   Since the refractory makes a very large layer of super insolation, some zirconia refractory products, sucn as large crucibles, contain very large particles of grog Fine particles of stabilized zirconia are used in thin high tech crucibles, and as a covering on refractory’s hot faces. Zirconia based refractories, and alumina ceramics with stabilized zirconia included are famous for thermal shock resistance and resistance to erosion from incandescent liquid metals.

 

Note: Drying can produce up to 4% shrinkage in slip cast zirconia refractories, and firing at 1900 °C will produces up 15% further contraction; a factor to be considered when planning structures made of it.

Zirconia also comes as stabilized ultra-high temperature porous insulating brick.

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Brick Pile Forges & the KISS Principle

 

Big or small; short or long? Forges don't always have to be this way or that. Making temporary structures and changeable shapes are what brick pile forges are all about. The concept is simple, but keeping the follow throw that way is easy to lose sight of.

    I believe that brick pile forges are the city dweller's best answer to coal forges as backups for the occasional large project; they aren’t efficient or highly portable, but they allow you to build you’re your primary forge small enough to be both.

    Its called a "brick pile," and  that’s what it looks like when not set up for use, but those bricks need some support when they are functioning as heating equipment. It is natural to think of enclosing them in a metal box, as though the forge was a permanent structure. Using thread stock and steel angles to hold it together is a better idea. I would add that some flat washers and springs on one side of the thread stock will only improve it.

    This kind of forge also needs to be set on something that is flat, insulating, and fairly fire proof. Hard cement boards are used as fire barriers between wood stoves and home walls, and are easily found in larger hardware stores; place one or two layers of it between the bricks and support structure you choose to temporarily place the forge on.

    Burners resting on temporary refractory surfaces need some help staying in place, and at the right depth in the brick. Rows of three thumbscrews can be mounted in cut sections of pipe nipple, which are then screwed into floor flanges to hold burners placed on top of holes for burner ports. The flanges can even be attached to flat bar, and connected to the angle superstructure for placement on vertical surfaces.  

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I only have a couple thoughts to add to Mike's post about "brick pile forges." They should only be temporary appliances. I use them for public demos as an example of not needing something special to try blacksmithing, Even a used propane forge usually runs a couple few hundred $ and a lot of folk only want to give it a try and see if they want to get into it. $50 - 60 in fire bricks, $50 in plumbing parts and gas fittings and "borrow" the tank, hose and reg from the BBQ falls within most folks "reasonable" cost range.

As an experienced smith a brick pile forge is something for heating specialized shapes that won't fit a "regular" forge. They're also a good way to experiment with forge shapes,  sizes, burner placement and number without going to the expense of building permanent forges that might not do the job.

Okay, I think Mike and I are on the same page so far just saying it a little differently.

The table for a brick pile is important, flat, heat resistant and insulated. Cement board works a treat but I use spacers to support it and let dead air insulate. It needs more air space than behind your wood stove or IR radiation will overheat the table, I find laying brick flat works well enough on my rolling steel cart. The steel cart gets hot as a pistol under the pile but it's thin sheet steel and air cools well enough to not warp. Another factor is how it's heated, IR radiation heats it evenly over a large area so it expands evenly over a large area and that area is exposed to open air beneath.

Whatever you use as a deck to assemble a brick pile forge it needs insulation and it needs to be rigid enough to support the pile and work. I know that seems obvious but if you've missed the obvious as often as I have you'll get it.

Frosty The Lucky.

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