Mikey98118

Here is an example of what I mean about armature commercial forge manufacturers: "Our entry level model built with customary care and attention to quality and detail. It is meant to last years of use, not months. Please pay close attention to the steel thickness of other forges you may be considering - sheet metal forges don’t hold up well over time. The repetitive heating and cooling of the forge body during operation weakens the thinner bodies and causes them to fail. That is why we use full 1/4” wall material for all of our forge bodies." But the fact of the matter is that even coffee-can forges last for years, unless they are left out in the rain. Furthermore, the best material for a high quality forge body (shell) is stainless steel sheet metal; not 1/4" thick mild steel pipe! They employ a half brick as the forge floor, instead of high alumina kiln shelf, or high alumina cast refractory, and a single layer of ceramic insulation, instead of two layers. Do I think this manufacturer is a greedy evil dirt bag? No; what I think is that they are self-deceived about the wisdom of their design choices, and much to fond of their product. For they could have produced a far better forge for the same amount of time and money, if they actually had a clue.

I did mention "swiping" from you, right? Your good buddy, Dishonest John (us bandits all use masks and phony monikers).

Commercial Forge choices The subject of what forge to buy comes up on a regular basis. While the yes and no choices don't change very much between established brand names, the opposite is true about most forges being offered below the $400 (and shipping) range (Diamondback single burner model). The rest of the pack are mostly imported Chinese junk forges, or wanna be amateur manufacturers that do not matter, and are often worse than the China junk. They all come and go, with the single exception of Mister Volcano forges; these are actually worth considerably more than their asking prices. Best of all, is that their burner, or burners, are not only properly designed, but made of stainless steel. So, Mister Volcano burners are well worth transferring into that first home built forge, once you get up the nerve. beyond that comes Chile Forge; their forges, and their burners are worth every penny of their considerably high prices; that last part is the stumbling block for most amateurs; businesses can afford them. What about all those other commercial choices; I can't recommend any of them, that I know of. Is this a harsh judgement? Yes it is; so what?

Yes; I think the Fisher burner screens and drill stainless steelplates in flame retention nozzles work in similar fashion. Good one, Frosty; I will have to swipe that one. Only, I will change it to "legacy thingy."

Burner Portals: Once you build a burner, you need to install it in your forge or furnace, which brings us to burner ports. Some people just drill a hole in the steel shell and a matching hole through the refractory layers; but this does not provide support for the burner, or any way to fine-tune its aim. Most of us attach a short section of larger diameter pipe or heavy wall tube to the outside of the shell, and use six thumb screws, in two rows of three screws each, to trap and aim the burner. Note that: (A) Pipe or tubing can be arc or braze welded over gaps in sloppy fits, but silver brazing requires close fitting parts, when positioning burner ports at an angle, that requires grinding the entrance hole into an egg shape. (B) Larry Zoeller (Larry Zoeller Forge) uses a 1-1/2" by 4" long schedule #40 pipe nipple with two 1-1/2" conduit locking rings, and two 2" by 1-1/2" rigid conduit reducing washers to mechanically affix a burner portal (for his 3/4” burners) into a hole in the forge shell of his five-gallon paint can forge; the limitation is that this method can only be employed to position a burner port at right angles to the shell. (C) Jerry Frost came up with an excellent method of mounting his burners directly onto brick or refractory surfaces; he threads a pipe nipple into a floor plate; a simple and effective method that can be employed on any flat horizontal surface; he and his friends use a plate suspended between upper and lower threaded rods to mount burners horizontally in a vertical side wall of brick-pile forges, in a manner similar to method “A” above. Control of secondary air: Now let us discuss the induction of secondary air and unwanted cooling of the equipment. Even single combustion envelope burners can benefit from external cooling air if the burners penetrate extra thick insulating layers (more than 2"), or the burners are very small (3/8" or less), because internal cooling from the cold incoming fuel gas could be overcome during long heating cycles, under these conditions. Most burners have at least secondary flame envelopes, so some builders deliberately leave their burner ports unsealed, because secondary air induction (powered by the flame) is needed for complete combustion of their flames. Unfortunately, this usually leads to an overabundance of a good thing, because the flame becomes an even more powerful induction "motor" than a burner's gas stream makes. It takes energy to heat air, so extra secondary air becomes a drag on performance within the equipment; leading to as much as 20% heat reduction. Fortunately, you do not have an if/or choice to make. It is just as easy to control incoming air through the burner port as incoming air through the burner, using a sliding choke mounted on the burner’s mixing tube. Simply employ a washer brazed to a short thick tube, drilled, which is threaded for a thumb screw, pressing against the burner’s mixing tube. Once the burner is installed, this choke can be slid up against the portal tube's end, to seal the opening against heating from chimney effects, after burner shutdown, and slid closer or farther from the portal tube for secondary air control during operation. Is this more work? Obviously, but you should expend the additional effort; especially because it is an add-on project, which need not delay getting your forge up and running. Existing tin cans and paint cans make cheap and easy equipment shells, with built in bottoms, which makes them irresistible for most first-time builders of portable forges and furnaces. When someone mentions making a shell from light sheet metal and pop riveting it together for more convenient diameters, most of us just shrug off the suggestion. But recently I stumbled across double wall chimney inserts that are filled with...you guessed it; ceramic fiber. Naturally they are too expensive to be tempting, but they got me to thinking... Two different diameters of sheet metal forms, pop riveted together, could be filled with Perlite that is glued into a monolithic shape, with plain old water glass (sodium silicate), making a highly insulating and rigid furnace shell for a minor monetary outlay. And since such cylinders can be made into larger diameters than the usual shell sources, they could also contain an extra layer of insulation and still have plenty of room left inside the shell for hot-face and insulation layers. Of course, the builder does not need to make a tubular shape; this kind of shell would also lend itself nicely to oval and “D” shaped forges. Light sheet metal can easily be cut to any desired shape for front and rear faces. By making the outline and then cutting a larger outline 1/2" outside of, and parallel to it. Room is thereby left between inner and outer lines, to cut out tab shapes with a drill and rotary tool; these can then be bent 90 degrees. Holes can be placed through the tabs and the outer shell wall beneath, and the tabs can be pop riveted in place, strengthening the shell into quite a rigid form to add the insulation into; afterward, this form is little heavier than a simple tin can, but far stronger. Burner ports can be attached to the finished form by employing a hole saw, to drill through both walls at the desired angle, forming four drilled tabs on one end of the portal tube, shoving the tube through the holes from inside the shell, drilling matching holes through the inner shell, and employing pop rivets to hold the tube in place. Or, the tube can be silver brazed to the outer shell. With the portal tube penetrating the two separate sheet metal walls, so that burners can be held rigidly in position.

Hybrid flame retention nozzles A ring of small holes, surrounding a larger central hole, has long been used, successfully, in the flame retention nozzles on air/butane torch-heads. I believe, but do not know for certain, that this configuration is used to create long "pencil" flames from these nozzles, for pin-point heating of jewelry and electronic parts, for silver soldering and silver brazing; this is supposition--I could be wrong about all of this I have also seen it used, occasionally, on air/propane torch head-heads, where it does not work worth beans. I think the difference is input gas pressure. Butane cylinder pressures are much lower than propane pressures at the same ambient heat levels. The point of interest for you people, is that flame shapes and lengths can be modified with hole filled rings or discs, placed in the forward ends of of slide-over step nozzles. Although my memory is more than a little shaky, I seem to remember three different burners that people posted with different versions of drilled discs in their flame retention nozzles, which were able to control flames very nicely. The bottom line for all this jabber, is that there is more than one way to come up with a multi-flame burner head; as three different guys on this group have proven

I have contemplated this very thing for years, and have come up with two ideas concerning them; they were originally used on air/butane torch-heads. I think the reason is to greatly narrow the flame, for pinpoint heating. I have also seen it used, occasionally, on air-propane torch head-heads, where it does not work worth beans. I think the difference is input gas pressure. Butane cylinder pressures are much lower than propane pressures at the same ambient heat levels. Of coarse, I could be quite wrong in my assumptions...

The burner flames in your photo look pretty good, so I would not think that they are your problem. However, it is a simple matter to remove them from the forge, and ignite them outside of it, to settle whether the odd odor is related to them, or from volatiles cooking off within the forge. If you find that the odor is coming from the burners, then it is time to disassemble them, and check for oil inside of their mixing tubes.

The equipment shell: This is where most people start their construction plans. A sheet metal casing does more than hold refractory materials in place; it is also important as handy for mounting burner portals, exhaust doors, and legs (or carriages) on. Nothing stops you from using hard refractory materials to help brace a very thin shell from the inside, but the shell should be thick enough to provide a rigid surface to mount parts too, at a minimum. With pop rivets and/or silver brazing, even tin cans can be made to work as equipment shells. Of course, a few extra thousands of an inch thickness in the shell wall can save you a lot of work, when mounting hardware with sheet metal screws or pop rivets. A 1/8" thick steel shell, is way too heavy; think 1/16" thickness as a maximum; stove pipe is a lot thinner, and some people use it quite happily, with sheet metal screws or pop rivets. But the added thousandths of an inch in helium, Freon, or propane cylinders makes a convenient difference; the same holds true for vehical exhaust mufflers, or pots and pans. Caution: Aluminum beer kegs are not a good shell choice because they lose their temper at 400 °F (752 °C), becoming much weaker. Most forge and furnace shells reach 400 °F (752 °C) during normal use. This does not prevent you from using thicker aluminum structures as shells, but thin and soft makes a very bad combination. You can hinge one end of a tunnel, “D” or oval forge; or front wall of a box forge, to get increased control of parts handling (ex. Crucible tongs) or to make construction and repairs easier. You can hinge the top and bottom halves of a forge together, so that it can be used as a clamshell design. Forge shape is a matter of opinion and we all have one. The most popular shape around is the tube forge; these have become the proverbial "well-worn path"; unless employed in a forge/furnace combination, they are also out of date for anyone but jewelers and knife makers. Oval shapes have been around for more than twenty-five years, and are finally catching on because they are a great improvement on tube forges. Oval forges give more use out of their heated space than a tube shape can. The floor area in an oval forge will end up at least one-third wider than in a tube forge. As burner flames become hotter, the added room before your flame impinges on a wall has also become increasingly important. Most people face their burners down at an angle so that their flames impinge on a high alumina kiln shelf, or cast refractory floor in tube forges; kiln shelves are cheap, easily replaced, and very tough. Kast-O-lite 30 is semi-insulating, tough, and can be shaped to improve atmospheric circulation (flame swirl). The slickest homemade forge design that I have yet seen is an oval mini forge built from half a car muffler. Larger oval forges require sheet metal work, or more expensive containers. Note: advanced materials, such as homemade tile (made from zirconium silicate and Veegum T), or insulating half bricks, covered in Kast-O-lite 30, can allow forge burners to be aimed upward toward the far side of an oval or “D” forge. The burners should be positioned high on a side wall, and aimed at the far wall of a box forge. So, why not build a box forge? If you employ rigid materials, such as ceramic fiber board and/or insulating bricks, a box forge makes good sense. But curved internal and external surfaces make more efficient forges; internally, to encourage even heating from burner flames, and externally to promote better air cooling of the shell. Caution: When flames are turned up for forge welding, small forge interiors will become super-heated, all the way to their sheet metal shells. At this point, the ability of those surfaces to air cool becomes quite important! Then the air circulation around the bottom exterior of tunnel and oval forges has an advantage over “D” and box forges, with their flat bottoms. Brick pile forges have the advantage over box forges of changing shape and/or size, as needed; they are held together with steel angle and threaded round bar.

Kast-O-lite 30 insulating castable refractory can be troweled or cast in a 1/4” to 1/2” thick flame face layer, giving a large measure of thermal protection, along with mechanical armoring, in case you are moving crucible tongs in and out of your equipment, and against contact with heating parts ; it is use rated to 3000 °F; is alumina based for flux tolerance; contains mini silica spheres to provide insulating voids (and crack resistance); it weighs 90 lbs. per cubic foot (compared to 146 lbs. for standard cast refractory). Kast-O-lite 30 has been the favorite refractory for construction of home-built forges and casting furnaces for the last twenty-five years. This refractory hardens gradually enough that the edges of equipment surfaces can be scraped with a straight edge during the first hour of drying, so that those surfaces meet perfectly, allowing two-part forges and furnaces to be run with little flame leakage. Kast-O-lite 30 has a moderate insulating value of great importance for protecting secondary insulation from heat damage; when coupled with a re-emission (heat reflective) finish layer, it will greatly lengthen the working life of ceramic fiber insulation. Kast-O-lite 30 will stick to most materials. Use cooking spray, Crisco, or car wax on plastic or wood molds as a release agent. I have also used glass jars as forms, and then shattered them by heating to red incandescence, followed by a water quench, after the refractory cured. Cardboard and wax candles (used as molds) both burn away conveniently. Some vibration during casting will considerably smooth the casting’s surfaces. Heat reflective coatings: There are inconsistencies found in advertisements for "heat reflective" products; this is a legitimate term, if inexact. when advertisements go further, and label various refractory products as IR reflecting, they depart from reality. Yes, there actually are substances that reflect infrared energy; the most notable being gold, followed by silver and aluminum. But the difference between cause and effect is important. Actual IR reflectors are only useful as ultra-thin coatings on optical devices, such as light filters in welding helmets, or camera lenses. Re-emission coatings can be used to transfer heat more effectively through a crucible wall (as a thin coating), or to redirect energy, forming a heat barrier in thicker coatings; to illustrate the importance of the point, we will define a typical thin zirconia coating as one millimeter or less (.039") and thick coatings as three to five millimeters and up. The critical difference between a heat barrier and standard insulation is that the higher the heat level the more effective re-emission coatings become, while insulation typically loses efficiency—over time—as heat levels rise. Also, the thicker the coating the more effective a heat barrier becomes. Induction "furnaces" for instance, use crucibles made of nearly pure zirconia refractory, which is transparent to high frequency waves, but is so efficient as a heat barrier that with secondary insulating refractory between the electric coils and an inch or less of it outside the coils, a crucible becomes the furnace. The way a re-emission coating works, is that it absorbs heat so readily that it quickly becomes incandescent. Think of a thin layer of tiny zirconium oxide particles exposed to a high heat source, and radiating that energy in all directions; now picture another layer of particles next to the first, with still other layers behind them. Each layer radiates heat in all directions, but the heat source only comes from one direction, so at every additional layer some heat gets subtracted as it is radiated back toward the heat source. So, a thin re-emission coating will transfer lots of energy through the surface of a crucible wall, while the portion of heat it radiates back into the equipment is then re-radiated back at it, while a thicker coating on equipment surfaces reduces heat transfer that would otherwise happen through conduction. Re-emission coatings are a simple but elegant form of recuperative energy generation. By converting combustion heat to radiant energy emission, more combustion heat is retained on interior surfaces before the heated gas is lost out of exhaust vents, while heat loss through conduction is greatly reduced, with the added benefit of reducing heat stress on ceramic fiber insulation. Efficient heating equipment is designed so that radiant energy to does much of the heating, with part of the combustion heat saved up on the radiant surfaces, so that direct heating from a flame becomes only part of the heat on part surfaces. By the time your equipment interior reaches white heat, about half of combustion energy is directly heating metal parts, or a crucible, while radiant heat is doing the rest of the work. Hot-face coating materials: Plistix 900F is a powder consisting of 94% aluminum oxide, and 1.7% silicon oxide, with 1 to 5% aluminum phosphate as a binder; it is in many ways the premier example of a thin hot-face seal coating that is recommended for use on cast refractories and ceramic fiber blanket (but not over ceramic fiber board), it is a general sealant that also forms a thermal barrier for ceramic fiber blanket insulation; it air sets to form a hard surface. Basically, this product forms a smooth high alumina coating; its sole claim to form a re-emission surface is its finish smoothness, due to its small particle sizes. The smaller surface particles are the higher their emission percentages go, when coated on a heated surface. Kast-O-lite 30, when hand troweled in place, forms a very rough finish surface, with quite low emission percentages. A careful job of finishing it with a smoothed over surface of Plistix 900F, will increase re-emission considerably; on the other hand, coating a high alumina kiln shelf with it will produce little benefit. Plistix is sold as powder, and is mixed with tap water to a consistency of sour cream, then dabbed on from a disposable paint brush in 1/16” thick layers (each layer will coat 1.2 square feet per one lb. of powder). After application on a dampened surface, allow to dry slowly at temperatures above 60 degrees to a hard set. Post drying, fire the first layer and all subsequent layers can be applied with brush strokes; or applied by, and smoothed while it is setting up. Bring the coated equipment up slowly to temperature, to avoid cracking and/or pealing from thermal shock. Air dry and fire every layer before adding additional coats. Zirconium silicate (zircon) is about one-third silica, so it takes a thicker layer than zirconium oxide (zirconia) to do the same re-emission job, but then it is also far less expensive and much easier to employ. It is a fact that the smaller the particles of zirconia the greater the percentage of re-emission they create (as low as 68% to as much as 95%). The zirconia particles trapped in the silicon matrix of zirconium silicate powder are minuscule. Zirconia crucibles employ very crude particulates, and yet they are so effective as insulation that they become the entire furnace, when surrounded by a high frequency electric coil, and insulated by a further layer of loose zirconium oxide. So, the thicker the re-emission layer on equipment interiors the better—always providing you use it in a manner that will stay attached. Hot-face heat reflectors can be as minimal as re-emission coatings over ceramic board and rigidized blanket, or painted on a 1/2” thick layer of Kast-O-lite 30 cast refractory. But an armored tile of 5/32” to 3/16” thick, made of homemade zirconium silicate “clay” has become a superior option, thanks to Tony Hansen’s famous Zircopax formulas on digitalfire.com: https://digitalfire.com/4sight/material/zircopax_1724.html If you are willing to take responsibility for understanding and using raw materials, there are alternative choices, which beat the heck out of commercial heat barriers; not only costing less money, but often giving better performance at the same time. So called IR reflectors (re-emission coatings) will be of especial help in raising efficiency while protecting interiors of heating equipment. The most effective commercial heat reflection coating I have used, claims "up to" 90% IR “reflection.” But, "up to" can also mean as low as 68% heat reflection; it’s all a matter of zirconium oxide particle size. Being a naturally mistrustful type, I tried separating the colloidal content from cruder particulates in the top commercial product by spooning some of their thick mud into a partially filled water glass, and presto; the crude stuff fell out of suspension in the mixture, and immediately sank to the bottom of the glass. So, I mixed in as much more mud as would separate, and painted the thinned-out coating over a previously coated, and heat cured surface. My forge went from bright orange to lemon yellow incandescence with the same burner and regulator setting. So, if the colloidal particulates are so much more effective why have crude particulates in the content? MONEY! Stabilized zirconia: When it first came on the market, stabilized zirconia flour cost twice as much as the regular kind. Today, there are three different ways to stabilize zirconia, and the price has fallen to about one-third more than the regular kind; this is an important factor to keep in mind. What is commonly called zirconia "flour" is nearly 100% colloidal, and will give you the full emissivity benefit; but it is not cheap. Zirconium oxide flour is the most effective heat reflector available, but it changes its crystalline structure at yellow heat, from cube to hexagon and then back again during cooling, so twice a heating cycle, it also changes particulate size, which is very hard indeed on every other ingredient in a hard cast refractory; not so slowly turning them to dust. And so, manufacturers of high heat crucibles (and others whose products justify the added expense) employ stabilized zirconia, mixed with a binder to make tough refractories and coatings. For maximum re-emission with minimum fuss, chose stabilized zirconia flour. Zirconia re-emission coating: Published government sponsored experiments with zirconia coatings back in the nineteen-sixties tried several binders; the most successful was orthophosphoric acid (commonly called phosphoric acid); a readily available and inexpensive product that stays suspended in water; it has some interesting physical attributes. When painted unto a surface it is adhesive, and will hold zirconia particles suspended on heating equipment walls and ceilings; when heated, it polymerizes, as this acid forms esters. Thereafter it remains on the surface in a vitreous (glasslike) form at room temperatures, and becomes soft and very adhesive above 365 °F (185 °C) from then on. Mixed with zirconia flour this is a highly effective heat shield, but isn’t physically tough. On the other hand, it is also simple to repair. Zirconium silicate (powdered zircon crystal), is a substance that came into popular use, while manufacturers waited decades for reasonable stabilized zirconia prices. Zirconium silicate, consist of silicate and zirconium molecules mixed in a stable tetragonal crystalline structure; it makes an end run around the crystalline size-change problem. Both zirconium and silicate are very resistant to flame erosion; they combine to form a tough hot-face coating. Zirconium silicate starts melting and separating out into its two constituents at 4650 °F (2550 °C); finally, it is only about 75% heat reflective as thin coats (.040”). Zirconium silicate is reasonably priced; if mixed with a binder, you can build up thicker layers of it. Zirconium silicate re-emission coating: Zircopax 95% by weight to Veegum or bentonite clay 5%. Hot-face formula: This recipe came from a potter’s supply store. It has ingredients that physically toughen, resist strong alkalis, and reflect heat. The (ingredients (by volume) are: one-part alumina hydrate; one-part kyanite (35mesh); one-part Zircopax; half part Veegum T or bentonite clay. With an average heat reflection percentage, zircon does not appear to be the best choice for a re-emission coating, but its 75% heat reflection increases with every additional layer painted on a surface. If you want maximum protection for a hot-face layer, or the best high-emission coating for a crucible, stabilized zirconia flour, mixed with a good refractory binding agent (ex. calcium aluminate) makes the optimal choice; it is expensively purchased from a laboratory supplier, like Reade Materials. There are three kinds of stabilized zirconia available at present. Rather than its previous price of three times that of plain zirconia, they are only about one-third more expensive these days: Calcium stabilized zirconia (melting point 4892 °F (2700 °C) Hafnia stabilized zirconia (melting point 4892 °F (2700 °C) Yttria stabilized zirconia (melting point 4892 °F (2700 °C)

I totally agree with your term, and your reasoning. So, I will start including it behind my term (In parenthesis)

Insulation: It only takes a moment's comparison between heat lost through an exhaust opening with heat lost through forge walls to make it clear that insulating the forge, to slow heat loss is only half the battle. You are insulating the forge, to help super-heat its internal surfaces into high levels of incandescence; at least into yellow, and hopefully into white-hot ranges. An efficient forge is a radiant oven. The burner flame is best used primarily to create radiant heat transfer; rather than for heating stock directly; get that straight in your mind, or give up all hope of knowing what you are doing with forge design. Why? Because the choices you make about hard refractories, insulation, and heat reflective coatings, need to reflect the need to super heat the forge interior without destroying those materials. For many years, ceramic fiber insulation in walls and under the floor has consisted of two 1” thick layers inside curved forge walls, and single layers of ceramic board, with a further 1” layer of ceramic blanket between the board and shell, in box forges. Two one-inch layers of ceramic fiber insulation within of a hot-face layer is the minimum insulation that is normally considered adequate for heating equipment; one-inch of ceramic fiber insulation normally is not. How much insulation is adequate also depends on other factors, such as how small the equipment is, and how long the heating cycles are. In other words, circumstances can alter cases—but only somewhat. Even the cheapest grade of ceramic fiber blanket doesn't melt below 3000 °F. Product temperature ratings come from the level of heat the fiber will withstand without massive shrinkage; this should illustrate the importance of locking the individual fibers in more secure positions by rigidizing; it also demystifies the seemingly magic protection given by a relatively thin sealing coat of high-temperature refractory, capped by a heat reflective coating. When you exceed ceramic fibers use-rating, it rapidly begins to wither. Ceramic fiber products need both rigidizer and finish coatings to do well in today's gas heated equipment; this is because better burner and forge designs create much higher internal temperatures, than were common twenty years ago. Rigidizer is especially important if you want your insulation to last. On the other hand, between using 2600 °F (1427 °C) rated fiber insulation and rigidizer, you can toughen the insulation layers in your equipment enough so that it should stand up well to the heat that will leak past a high emissive coating (AKA heat reflector) and a thin hot-face layer like Plistix 900F® (rated to 3400°F; 1871 °C). Rigidizer also helps fiber insulation to mechanically support a thin flame face coating, or cradle a cast refractory layer. (A) You don't want to use thick ceramic fiber layers; instead of a single 2" thick layer; use two 1" thick layers. Ceramic fiber blanket can be easily parted into thinner layers via delamination, if you mistakenly purchase 2” thick blanket. (B) Rigidize each layer after installation, and heat cure it with your burner, before installing the next layer. (C) Form the burner openings before rigidizing each layer. Remember to leave burner openings just a little oversize so that they can be finish coated with a hot-face layer of something like Plistix 900F. (D) Dispense the colloidal silica rigidizer from a used cleaner bottle with a spritzer top unto horizontal surfaces, and heat-set the ceramic fibers in position, before rotating curved surfaces to position further areas for the same treatment. After firing, those surfaces cannot sag out of position. (E) Silica rigidizer is colloidal silica (just fumed silica, which remains suspended in water) and common everyday food coloring (to allow you to visually judge how far it is penetrating the ceramic wool); this water born product is easiest to dispense by spritzing. You can always pay through the nose for premixed rigidizer from a pottery supply if you prefer; I buy fumed silica through eBay and Amazon.com and sometimes get free delivery, because the product is so light. Morgan’s K26 insulating firebricks (distributed through Thermal Ceramics in the U.S.A.) have become a tougher alternative to ceramic board in box forges and a better alternative to ceramic blanket under floors in “D,” oval, and box forges; they are use-rated to 2600 °F (1427 °C), and are available from eBay and other online sources; legitimate shipping charges are small because these bricks are very light weight. Other K26 rated bricks are not anywhere near as insulating, nor lightweight; with the addition of a high temperature coating, like Plistix 900, or Kast-O-lite 30, these bricks can even be used as a hot-face layer in forges and aluminum casting furnaces. There are other improved insulating firebricks on the market now, but I am not familiar with them Morgan’s K26 insulating firebricks, and competing brands, can all be cut by hand with a worn-out hacksaw, but are more quickly cut with resin bonded cutoff discs. Do not use steel cutting resin bonded discs on brick, or resin bonded ceramic cutting discs on steel. Morgan’s K26 bricks can be holed with ordinary drill bits, but drill smoother with carbide tipped bits, or hole saws; unlike ceramic fiber products, they are semi resistant to hot flux. These bricks have become popular over the last few years, so their prices on eBay have effectively doubled, but now they can be purchased from more and more online sources, like High Temp Inc., at reasonable prices and shipping charges. There are several kinds of refractories used for hard firebricks, but only one formula was historically used for insulating bricks, until recently: that was the pinkish to yellowish bricks made by including a foaming agent in clay to make lightweight bricks that are use-rated to 2300 °F (1260 °C); you see them employed all too often in old gas forges, and electric pottery kilns. To call them friable is to completely understate their fragility; calling them future rubble is more to the point, when they are used in equipment with rapid heating cycles, like forges and casting furnaces. While the strength and durability of various insulating refractories vary widely, all of them have a good insulation value in environments that are at or above 2000 °F; but Morgan’s K26 brick equals that of ceramic fiber blanket products at these temperatures. On the other hand, their K26 bricks can provide some structural integrity, while the blanket can easily be shaped into curved forms and then rigidized into firm featherweight insulation, outside of the bricks. Perlite and sodium silicate. Perlite granules are easily bonded together into monolithic insulating structures, with sodium silicate; both will quickly melt, If you exceed 1900 °F (1038 °C); these materials do best as tertiary insulation, but can be used as secondary insulation outside of insulating firebricks, if you aren’t going higher than 2300 °F internal working temperatures. Perlite can also be filled into contained areas, such as beds below insulating firebricks, or between them and curved forge shells; it will carry considerable loads, and is perfect for filling up space between rectangular solids and curved container shapes, to keep you from needing to measure and cut other materials to fit; this material is extremely light. Sodium silicate is attainable online, and inexpensive bags of Perlite are available in the garden departments of large hardware stores (as it is used for a soil additive).

So, the practical difference would be that what is going on in the product is not calcining at all, but simply the silicon content partially melting in the voids? Because I have deliberately taken Kast-O-lite 30 up high enough to make the change. And have also taken the product up just long enough to only change the inner part of a casting furnace's wall; when it cooled off, you could see the difference between the inner and outer thickness; they not only had different hues, but their was a line between the inner and outer portions of cast refractory.

Forge Floors: If you do not plan to do much forge welding, laying down a Kast-O-lite 30 floor over ceramic fiber insulation (or Morgan’s K26 insulating bricks) will provide a floor that is tough enough, and more insulating than kiln shelves. For occasional welding, some people use a stainless steel baking pan, filled with the kind of kitty litter that is made from pure bentonite clay bits to shield the forge floor from welding flux, But frequent welding is certain to slop flux onto a forge floor. A kiln shelf, that is trapped in slightly oversized slots in the forge shell, will pay for itself with the ability to be easily slid out and resurfaced, once its top is fouled with flux. Once the flux cools into a hardened glassy layer, a flap disc can remove it with little effort, before the widening puddle slops over the shelf’s edge. Do not forget to where safety glasses, and a dust mask, while grinding away the flux. If you are also going to use a tunnel forge as a casting furnace, the kiln shelf can simply lay on the round forge wall, when your forge/furnace is in the horizontal position. Forge Shells: Variable shaped brick-pile forges can be mounted on a suitable (fireproof) surface, with nothing more than metal angles, and threaded round bar, to hold them together. “D” shaped, tunnel, and oval forges are best contained in Sheet metal shells. If the forge has sufficient insulation to keep its outer surface below 400 degrees Fahrenheit, aluminum can be used for its shell; otherwise, steel or stainless-steel is a better choice, because all aluminum alloys lose their temper at 400 degrees, becoming soft. Hex shaped forges (i.e., Modified tunnel and oval shapes) can employ noncombustible fireplace backer board as their shells. If you live in an area where sheet metal has become ridiculously overpriced, old appliances are another source of sheet metal. Coffee cans, car mufflers, propane cylinders, non-refillable Freon, or helium cylinders, and paint cans, all make satisfactory forge shells. Smaller “D” shaped forges were once made from mailboxes, but I do not think they are a worthwhile effort. Insulation: Layers of ceramic fiber insulation 2” thick (in two 1” layers) can be pushed into shape inside of steel containers, and stiffened with colloidal silica rigidizer. After firing, the stiffened insulation will adequately support up to a ½” layer of hard refractory, in the bottom third of a cylindrical wall while it dries. The next hour, the cylinder can be rotated, and a further third can be covered, and the final third can be covered in the third hour. Remember to thoroughly wet down the older refractory area, where the freshly spread refractory will blend to it, to ensure complete adhesion between the old and new layers. A double layer of insulation is usually used as the subfloor below forge floors. Note: fumed silica in water is also known as colloidal silica. Silica (silicon oxide) is the main ingredient in common glass. However, glass has a much lower melting temperature than pure silica, because lime and potash are mixed into it, for the express purpose of lowering melting temperatures (the lime), and promoting the process of melting (the potash). Fumed silica easily melts initially, because the powder’s particles are so small that it has a tremendous amount of surface area, to promote the melting process. After the initial firing, this silica becomes pure quartz glass, and remelting it would take far higher temperature (3,133 °F; 1,723 °C). This is why fumed silica easily melts (once) on the surface of ceramic fibers, to rigidize fiber insulation. And why it also works as one of the binders in some high alumina refractories. Working with castable refractory: There are several hard castable refractories used as flame faces in forges, and casting furnaces. So far, I think Kast-O-lite 30 serves best in both kinds of equipment. You can carefully drill, grind, and scrape it, as the refractory is still setting up; this goes well enough, during the first hour, but far less easily after the refractory completely sets. During the week of curing, the refractory continues to harden, very like concrete.” In fact, castable refractory is a form of concrete; what sets it apart is that the chemically locked water that remains after curing can be—CAREFULLY—steamed out of the finished form by firing. Concrete cannot be fired; it simply explodes when heated; this difference is due to what is used as the binder in concrete; Portland cement. Aside from firing, the more familiar you are at working with concrete the more you already know about working with castable refractory. The other difference is that refractory has no rocks used as filler material; instead, refractory has ground up chunks of alumina rubble (aggregates), which help to stabilize the refractory against thermal shock. Insulating refractories, such as Kast-O-lite 30, also contains silica (or alumina) spheres, to create insulating voids, which are also crack interrupters, along with calcium aluminate cement for a binder. It was Kast-O-lite 30’s resistance to thermal cracking that first made it popular among home casting enthusiasts twenty-five years back. We were already using Perlite to make our own semi-insulating hard refractory. Kast-O-lite 30’s resistance to cracking during thermal cycling could not be matched by other refractories. Mixing and drying instructions for refractory mixtures will be found on the 55-pound bag it originally comes in; but mixing and curing instructions are less likely to be included with smaller amounts purchased from resellers online. The most used refractory in heating equipment is Kast-O-lite 30, because it is use-rated to 3000 degrees Fahrenheit, not inclined to thermal cracking, lighter weight, and is semi insulating. Kast-O-lite 30 is known as a gunning refractory, which means that it can be flung on walls of large industrial equipment through special nozzles, rather than only being cast in place; the qualities that makes it good for gunning, also make it useful for spreading in layers as thin as ¼” by hand troweling, onto the inside of curved internal surfaces. Kast-O-lite has up to one year expected shelf life, if stored in a dry container at moderate room temperatures (50-70F); it should be mixed with no more than 20 percent water, and mixed for three minutes, then poured within ten minutes, into stout water tight forms for best results as cast forms. A small amount of vibration will improve the casting’s finish surfaces. Keep the casting covered with a damp towel during air curing, which takes between sixteen and twenty-four hours, and keep the casting above sixty degrees Fahrenheit while it is air drying, for a week, with the help of a small incandescent light bulb. The first thirty minutes of set up time is the most important, as the mix is changing from thick mud, into a solid. If you have cast horizontal mating surfaces for the upper and lower halves of a clam-shell forge, or vertical mating surfaces for the forge shell and door in a horizontal forge, you want to use the edge of a steel carpenter’s square, etc., to flatten the mating surfaces by scraping. If you did a good job of cutting and grinding forge shell’s edges for close tolerance, this is where it pays off. What if you did not? It isn’t too late to fix your mistake. Low places, which don’t meet up with mating surfaces can be filled in with Plistix 900F. Thoroughly clean, and then wet the surfaces where you lay the finish coat. Place wax paper over the top of the new layer, and then close the mating surface against it during drying and curing. The wax paper should come away from the dried surface easily; if not, just let it burn away during firing. High spots must be ground away. If you grind too far, just use the refractory coating to correct that mistake, too. Do not try to do the whole repair job at one time. Correct your mistakes one at a time. How much firing? Once the chemically locked water is driven out, is firing finished? No; most people consider this to be good enough, but without frequent firing during wet weather, the refractory can still slowly regain some water content from ambient air; necessitating the same careful fire drying routine you used during the initial firing, to keep the accumulated water content from cracking the refractory from internal accumulation of steam pressure; unless you take firing to the next step, which is called calcining. Basically, you heat the fired refractory up to yellow incandescence all the way through the form. It will begin on the inside surfaces (flame faces) and slowly soak through the refractory until it reaches its exterior surfaces (“cold” faces). Technically, calcining is the process of removing, by very high temperature (but below melting points), any volatile particulates, and finishing the oxidization of anything that can be oxidized, in a substance. Many of the constituents of a refractory mixture are separately calcined long before being included in the blend. But the cast refractory article may also be “calcined” at the melting point of glass to improve strength and durability, while making the refractory far less porous. One example of calcining would be fine porcelain, which is fired at higher temperatures for extended periods versus a ceramic coffee mug, which is minimally fired at much lower temperatures. One of the binding agents in most refractories is silicon. Some of the other constituents in many refractories are materials that contain silicon (like clay, which is likely to contain up to 40% silicon). When a fired refractory product is kept at high temperatures for an extended period, the silicon content begins to liquefy, gluing the other ingredients together more thoroughly, and filling in any micro gaps between refractory particles; effectively toughening and waterproofing the refractory. So, “calcining” is a word with a double meaning; its proper use is one thing, and the second use is closer to industrial slang. Despite all the good and honorable intentions of English teachers everywhere, industrial slang follows an extension of the ‘golden rule (“them what has the gold makes the rules”). In this case, “them what has the power makes the rules”). In other words, OEM sales departments choose what they consider proper industrial terms for their products. And, as with so many other lessons from the school of hard knocks, we can like it or lump it, but we are not going to change it.

Casting furnace lids: All these advantages can also be applied in casting furnace mode, if a round or hexagonal kiln shelf rest on an angle iron frame; it can be swung into position above the furnace and swung out of the way during crucible removal. A mall center hole in the shelf allows observation of, and metal to be added to, the melt; it also provides a rest for preheating metal, to make sure it is thoroughly dried before placement in the crucible. But the hot exhaust gasses will heat re-emission coatings on the plate’s underside into incandescence, causing energy to be radiated back into the furnace.

Exhaust opening size: The last aspect of flame management, is the internal atmosphere’s exit point. One thing backyard casters and blacksmiths both worry about is how large to make exhaust openings on their equipment. Too small and you have high back pressure killing burner performance; too large and you cannot retain enough heat to do your work. Of course, the closer to the "right" opening size your equipment is the stronger the forge or furnace can be built. Just don't confuse the right size for a “perfect” size. With burner output that can by varied (turn-down range), there cannot be any such thing as a perfect opening size. The right size is what is needed to accommodate the burner's highest output (the highest you are willing to take it to), without creating a buildup of backpressure in the equipment. Variable is the optimal opening size; all other dimensions can be outright wrong, but are seldom just right, with a variable burner flame; this is one of the many reasons for controlling exhaust flow with an external baffle wall, positioned beyond an oversized exhaust opening; thus, permitting the least heat loss through radiation, while maintaining optimal pressure of circulating gases in the forge. Note: It is smart to include a ring of hard cast refractory around the exhaust opening, which protrudes beyond the shell a little bit; diverting hot exhaust gasses away from the shell, where it would super-heat the metal. If you place a movable brick baffle wall in front of the forge, keep the bricks at a small distance from the exhaust opening (start with 1” of distance, and move farther or closer, to optimize internal pressure); this allows hot gases to move up and out, between the exhaust opening and brick wall, while generating heat from a re-emission coating on the near side of the bricks, and radiating it back into your forge. Keep the stock opening in the brick only as large as is needed to move parts through. This arrangement helps to slow the flow of expended gas in the forge interior to what is needed, and no more; as it gets close to the exhaust exit, the gas speeds up and through the opening; another desirable trade off. So, you are gaining hang time for the heated gas in the forge, and recuperative savings from emission of radiant energy; a win-win situation. A baffle wall also minimizes the impact of infrared and intense white light on your eyes and face, improving your health and comfort. Doors: While a movable brick baffle wall is simpler to construct, maximum part clearance will be provided with a hinged and latched forge door (stainless-steel toggle latches make a good choice). The door structure should contain built-in interchangeable baffle plates (cut from high alumina kiln shelves), trapped in a steel angle frame. A door also makes building the refractory structures inside of equipment much easier, and permits larger parts to be heated than would pass through a smaller exhaust opening. Best of all, it allows closely contoured movable internal baffles to be employed, which would not pass through an exhaust opening; this promotes the use of a single burner to heat small parts, saving money in tunnel, oval, and “D” forges, which are run by two or more burners; on these forge shapes, the door is a step up from an exterior brick baffle wall; it should include parts entrances (plates) with varied openings; for instance, with several plates cut from kiln shelves, which have different openings drilled and cut into them (for passing stock through); these can be exchanged, and held within a pocket structure on the door. These improvements do not all need to be seen to at once, so long as a hinged and latched door is bult onto the forge shell. On forge/furnaces, the door can be left as is, or can be attached to a single pin hinge, and revolved out of the way. Sliding doors: Some people prefer vertical or horizontal sliding doors, instead of hinges. People usually employ the new tougher insulating bricks as sliding doors. High alumina kiln shelves are seven times more insulating than clay fire brick, but not as insulating as the new insulating fire bricks, now being used as linings for pizza ovens and home fireplaces; but high-alumina kiln shelves are tougher at incandescent temperatures than the new bricks; this is a consideration for something you will end up shoving parts back and forth through. Exchangeable kiln shelves, with different part openings drilled and cut into them are fine, but building an elaborate system of exchangeable kiln shelf parts, to ape the ability of bricks to infinitely vary their openings, comes under the heading of "gilding the Lilly." The additional energy savings it provides, probably is not worth the effort. Make up additional openings in kiln shelve baffle plates sparingly. Diamond or carbide coated rotary burrs (and diamond or carbide coated hole saws) are the preferred way to drill holes in kiln shelves. Friction cutoff blades (safest) and diamond coated blades (only of small diameter) are the best ways to cut out straight lines between those holes. A hinged and latched door, can also work on a box forge. Yet, movable bricks, trapped in an angle iron, or structural channel frame, will be more convenient than a hinged door, for most box forges. Furthermore, steel channel frames work best, for sliding those doors up and down on woven wire, while, running pulleys, and counter balanced with lead weights. You want to coat the hot-face side of either kind of door with one of the re-emission coatings. You can use a formula of 95% zirconia silicate powder (crushed zircon) and 5% Veegum (or 5% bentonite clay as an alternative); this mixture makes a tough heat reflective coating. The ingredients should be available in ceramic supply stores. Zirconium silicate can also be mixed with fumed silica to make a tuff and heat reflective coating on hard refractories, or on ceramic fiber products. There are other choices, Like Plistix 900F, but none of them are easily purchased in other countries. Zirconium silicate and bentonite clay should be readily available in pottery supply stores, all over the world.

Burner placement: The first question asked about burner positioning should be why; not where. Burner positions are always dependent, but not primarily on best circulation of hot gases; that is a tertiary concern. Flame impingement should be your first concern. The point where a burner's flame is aimed must be physically tough, up to thermal stress, and as far from the flame tip as you can manage. If your insulation is only protected by rigidizer and a thin seal coat, the flame needs to impinge on a high alumina kiln shelf or an exceptionally tough high alumina cast refractory floor (ex. Kast-O-lite 30). On the other hand, if the equipment’s interiors have a 1/2" or so thick layer of such a refractory, and is finished with a heat reflecting coating (such as Plistix 900), wall impingement is no longer a big issue; it's just one more factor, to be balanced against others of equal concern. You also want it to avoid flame impingement on workpieces or crucibles. If top mounted in a tunnel or “D” shaped forge, you would want the flame to strike as far from the first surface it will impinge on as possible. In that case, I now prefer to aim the flame diagonally downward at the far edge of the floor, so that it continues up the opposite wall, away from heating stock. The burner should be mounted at about three o’clock position. If you intend to employ crucibles in such a forge, use two smaller burners, with the crucible positioned between their flame paths. But why would you use top mounted burners in a forge these days? Only if you have a thin finish coating over ceramic wool insulation, instead of a 1/2” thick hard refractory flame layer over the insulation, which is also coated with a heat reflecting coating, like Plistix 900. In most box forges, the burner was previously placed at the top. And the flame was aimed at the floor; the point of this was for the flame to impinge on the toughest surface that could be provided, so that weaker wall surfaces might be spared the ravages of flame impingement. High (purity) alumina kiln shelves, or high alumina-based refractories are one the most effective choices to employ as an equipment floor; this was the limitation for decades, but with better wall materials available at reasonable prices, this limit is fading; allowing burners placed high up on side walls, facing across the interior at the opposite wall, and passing over the work. The latest development in burner positioning is placing them low on the wall, or even in the floor, and aimed up and inward in “D” forges, and aiming across the top of oval forges; this requires cast refractory flame surfaces (with heat reflecting finish coats) in floor, walls, and ceiling. Circulation is also a concern; fortunately, this takes nowhere near as much encouragement as is commonly supposed. With today’s stronger burners, there is a natural tendency for hot gases to circulate within most forge and furnace shapes; including box forges. In fact, the only burner position that would greatly interfere with sufficient circulation of hot gases, would be with the flame aimed directly toward the exhaust opening! Note: Positioning burners near the exhaust opening provides a close second to the previous example of exceptionally bad planning. Mounting burner ports: Typically, a burner port (entrance structure) consists of a short steel tube or pipe with about 1/4” larger inside diameter than the burner flame retention nozzle’s outside diameter. This allows enough space to aim the burner somewhat within the portal. The burner is held in position and aimed, with two rows of thumbscrews; each row has three equidistant screws. One of the advantages of these screws is that they can hold a length of pipe or tube in place within the portal, and resting exactly where the flame is intended to impinge, while the portal opening is being ground into an oblong shape (to allow the tube to be aimed at a desired angle). This method ends up with a very close fit between tube and shell opening, to promote easy silver brazing of the port’s tube to the equipment shell. You are building a burner, so employ it to help construct its forge. Why use six screws to hold the burner? After all, commercial forges mostly use only three screws to hold their burners; some have only a single screw. You are not trying to maximize profit on a product, but to build the best forge you can. Six screws allow flame impingement to be moved a little way, if your construction is less than perfect. Alternatively, you can drill and mount a burner port in the shell with three bent flat bars and some pop rivets, or screws. Bracketing parts together can end up looking tacky if you do not manage to keep the shell opening tolerances close. Employing screwed brackets can also be a be a minor pain, if the burner’s port tube is positioned at an angle. Welding equipment parts, such as burner ports unto a thin steel shell, takes a wire feed welding machine and a learning curve. Some people are reworded with distortion in the shell, because of welding contraction; it only takes a little time to learn to run a wire feed welder, and somewhat more to learn to bridge gaps with one; but it takes a lot more time to learn where and how much to weld without creating distortion. Neither hard brazing (braze welding), nor silver brazing creates that problem. Hard brazing requires an oxy/fuel torch and some skill, or an air/fuel torch with propylene fuel, and considerable skill. Silver brazing can be done with an air/fuel torch, propane, and close attention to setup as the only skill. But most silver brazing alloys will not bridge gaps wider than 0.005”. However, some aluminum/zinc-based flux core soldering alloys, like BLUEFIRE Low Temperature Aluminum Zinc Alloy Brazing Rods, do bridge small gaps, melt at 728 °F (387°C), and can be used to bond aluminum alloys, stainless and mild steels, iron, bronze, nickel, titanium, zinc, copper, and brass. It works best when their Silver Copper Brazing Flux Powder is employed along with the filler rods (good on mild and stainless steels, silver and copper alloys, and other metals). Silver brazing by hand torch benefits from a lower temperature filler with broad melting ranges, such as Ufhauser silver braze filler A-54N (54% silver/ ), which has a broad elastic range (250 °F), and bridges minor gaps (up to 0.012”); it can be considered something of a capping alloy (capable of forming a weld bead), but if heated too slowly it may suffer from liquation (where the alloy separates into solid and liquid zones); it can only be remelted well above its normal brazing temperatures, afterward. For this reason, alloy A-54N should be heated rapidly through its melting range; it has a melting range between 1325 °F (dark red) and 1575 °F (bright red). If you are joining a thin shell from a tin can to a thicker tube, keep the flame mostly on the tube. This filler alloy has a good color match to steel. Reasonable care with a sanding drum or grinding stone in a die grinder or electric rotary tool, will easily produce a sufficiently close-fit in the joint between a burner portal tube and the forge shell’s opening. If you are silver brazing on stainless steel, I recommend polypropylene fuel gas (if you employ an air/fuel torch), and black brazing flux. Old car mufflers are zinc coated, and new mufflers are coated with an aluminum-zinc alloy. Silver brazing parts to this kind of forge shell will ensure lots of damage to the plating. Stay Brite silver solder may be employed afterward, if you don’t want to paint the forge shell. Some zinc-based soldering alloys are zinc-tin-lead (avoid these), zinc-tin-copper (excellent), or zinc-cadmium (use fume rated respirator with these and follow all safety guidelines to the letter). Note: The main ingredient in zinc flux is zinc chloride (follow safety guidelines listed on its container); it is the only ingredient in many of them; it tends to “tin” the surface of steel, rather than just cleaning it. If steel is freshly cleaned and power buffed with stainless steel wire wheels, it can be zinc soldered without flux, but why do things the hard way? Zinc’s melting point is 787 °F; comfortably below its boiling point of1665 °F. Zinc fumes are easily seen and smelled; avoid them. Unlike lead fumes, it takes a much heavier dose of zinc vapors to cause fume fever. Unlike lead, the body can tolerate a little zinc, but keep your dose tiny; none is best. No metal fumes are good for your lungs. Caution: All metals give off toxic fumes upon reaching their boiling points, and all are toxic; some are simply more toxic than others. Using zinc coated sheet metal or parts (such as old car mufflers) is okay, if you are careful about doing it. The boiling temperature of zinc (the point at which it makes fumes) is 1665 °F (bright red heat). Your forge shell should not get higher than one-fourth that temperature, during heating cycles. But you do need to be careful to keep the shell well away from the edge of the exhaust openings, by not cutting the openings in ceramic fiber, kiln shelf, or cast refractory next to the shell; see to it that there is at least ½” of distance between them. But zinc coated flame retention nozzles or mixing tubes need to be stripped of their coatings. There is no need to avoid zinc coated reducer fittings on a burner’s air openings. In other words, keep zinc away from part surfaces that may become incandescent. Note: Preheat temperatures should be kept down to 600 °F (315 °C on zinc coated surfaces, such as old car mufflers, to avoid damage to the existing coating on their surfaces, and to keep scale formation down on the steel; “tinning” the bare steel with a zinc chloride-based flux will help with this. Remove all residual flux with hot water and a clean rag after silver soldering. Larry Zoeller (of Larry Zoeller Forge) is credited for first mounting schedule #40 pipe to a forge shell with conduit locking rings; he calls it a “burner holder assembly.” If you are looking for fast and easy, he sells them for $25 and shipping from his website. Their main limitation is that they can only position burners at right angles. Ideally, the burner port’s tube should be completely external to the forge shell; in any case, it should not extend inside the forge further than is needed to secure a locking ring. A washer should be provided to slide back and forth on the burner’s mixing tube near the outside of the portal, so that it can limit how much secondary air the burner flame can induce through the gap between the burner’s mixing tube and the portal wall. A nut can be silver brazed onto the washer, so that a thumbscrew can keep it positioned at the right distance away from the portal edge; limiting secondary air into the forge to only what is needed for complete combustion, without lowering internal temperatures needlessly. Considering air introduced from the burner opening as no different than air from other openings is a sad mistake, since those other openings do not have fast flames to induce air into the equipment. Burner ports for brick forges may simply sit on the top of brick ceilings, for down facing burners; or be attached to a structure made of steel angle, and threaded rod, for side facing burners mounted high up on one of a brick forge’s side walls. Side mounted burners take a little more work, but pay it back in increased heat management.

Even with the best possible flame (which you can visually detect), there may be some excess superheated oxygen molecules, escaping the primary flame envelope (due to excess air induction). But any such oxygen molecules, which impinge on super-heated metal, will combine with it, to rapidly create scale, and to burn away some carbon content in ferrous metals. What this means is that every extra inch of distance between the flame’s tip and your work pieces (or crucible wall) is highly desirable. Hot crucibles are inclined to suffer damage in the presence of superheated oxygen, leading to spalling, cracking, and early crucible failure. It is an advantage to building a tunnel, oval, or “D” forge with the flame angled away from heating stocks (or aimed between the crucible and equipment wall, in casting furnaces); or with the ceiling at least far enough from the work (in box shaped equipment), to keep a vertical flame from impinging on heating stock; increased room for the flame is one of the reasons for including a plinth in your casting furnace. Since different burner designs create different flame lengths, and since they also vary by how far the burner is turned up, there can be no pat answer on the height of a box forge or plinth height in your casting furnace; these are judgement calls on the builder's part. Most people find little reason to turn a burner up full blast, so the flame can be measured for length at a maximum of 20 PSI, and that can be used for a good distance measurement. You want at least two-inches beyond flame tip, and any surface it impinges on; the longer that length the better. No practical forge can include further length for tertiary flames, so construct and tune your burner well enough to avoid making them. Crucibles are tapered at their bottoms and should be raised on plinths to help keep the flame from impinging on their bottoms, since most casting furnaces are cylindrical, with a burner placed low on its vertical wall, and aimed horizontally at a tangent between furnace wall and crucible wall. However, flame length is most important if your burners are top mounted and facing toward a forge’s floor. Some people mount their burners high up on a sidewall, and facing horizontally across a box forge or furnace, to get around early flame impingement on work surfaces; this helps prevents scaling on heating stock, and also lowers thermal damage on walls (which can be further away from the flame tip, for the same cubic inches when ceilings are lowered; a win-win use of space). Is an exhaust flame just the tail end of the burner's flame? It can be just that in equipment that is loafing along, with interior surfaces that are only at red or orange heat. But in a forge or furnace that is turned up into yellow or white heat ranges—no. In fact, the goal is zero output flame; just clear super-heated exhaust gases. When your forge or furnace is capable of radiant-oven performance, everything about the exhaust discharge changes. With the average forge or furnace, a small amount of blue exhaust flame has been considered normal—in the past. But in proper equipment, should you keep turning up the input flame beyond its ability to completely burn internally, you still won't get blue exhaust flames; some of the yellow-white “atmosphere” will overflow out of the exhaust, and complete combustion within a few short inches, but without a trace of blue or purple flame (which indicates a probable buildup of carbon monoxide in your shop). What is different? The forge or furnace itself is changing the combustion equation by super-heating any byproducts of the primary combustion envelope. How is this possible, since immediately after combustion, exhaust gas temperatures naturally decline? Intense radiant energy from incandescent surfaces is being bounced back and forth through those gases. The whole forge interior becomes an ignition point; not just refractory surfaces. Thus, secondary combustion is exponentially increased; ensuring that any leftover fuel from the primary flame envelope has plenty of time to completely burn off. If the equipment interior is red-hot, you should consider heat losses in combustion byproducts to be accumulate faster than radiant energy is being added. In yellow to white-hot forges, combustion losses are no longer faster than radiant energy gains. It is not possible to understand internal combustion processes in a modern forge or furnace as just a chemical process, because of added heat gain from highly radiating surfaces; such equipment is as much radiant oven as gas appliance. While exhaust flames from your forge can simply be the result of fuel that has not combusted because of fuel gas pressure being turned up too high, the more common cause of yellow exhaust flames is a large secondary flame (from a poorly designed, constructed, or tuned burner). I have noticed that fairly opaque yellow to orange flame can be created from some kinds refractory that are "cooking off" calcium from their binding agent; these flames will not abate until the process is complete. As the flame turns from yellow to orange, it becomes more transparent, and may even seem to sparkle in a manner reminiscent of fireworks, if the forge is running hot enough at the time. This does not preclude other colored flames, such as purple and blue from being present in the orange exhaust, but they are an indication of poor combustion, and must be ignored until the refractory finishes out-gassing. It is best to address one symptom at a time. Caution: Blue exhaust flames are a sign of a reducing forge atmosphere, which even a perfect burner will give off, if its air intakes are choked enough. Be aware that blue exhaust flames will be accompanied by carbon monoxide production. Carbon monoxide monitors are cheap and effective health insurance.

Burner flames and incandescent atmospheres inside heating equipment When looking at the flame from a good burner in a cold forge or furnace, it will appear much as it does out in the open air (a single blue flame envelope); but within minutes it will lengthen and become smoother in outline, as the equipment’s interior starts to super-heat; it will also lighten in hue (due to backlighting from incandescent internal surfaces), becoming more transparent. There will be little to no secondary flame within the equipment, even while it is cold; lesser burners will make more complicated flame envelopes, but this is the ideal; these facts also hold as true for multi-flame ceramic burner heads as they do for single flame burners. You need to remember that there are two different flames created within the average gas forge or furnace; the flame being input by the burner, and an internal incandescent atmosphere, which may extend to an output flame leaving the equipment via the exhaust opening. When blacksmiths discuss terms like dragon's breath, it is such an exhaust flame they are speaking of; a very different animal than the burner’s flame. Not that both flames aren’t equally important clues to burner performance, but they need to be treated separately for clarity. So, what amounts to a perfect exhaust flame? No visible flame at all. If we are speaking about the burner flame, straight blue from a single combustion envelope is the goal, but many older burner designs have a small white inner flame ahead of a blue secondary flame, followed by a darker larger and less substantial appearing blue and purple tertiary flame; these multiple flame envelopes come from combustion of byproduct gases with flame induced air through a burner port. Buy or build a good enough burner to see no white in the flame, and then tune it well enough to have little or no secondary flame, with zero tertiary flame. Then, control flame induced secondary air, with a sliding choke on your burner’s mixing tube. The next question tends to be "how dark a blue?" Different fuels give off different hues, and lean flames are always a darker blue than neutral flames in any given fuel. In fact, a burner can be run so lean that the primary flame turns purple. On the other hand, any slightest tinge of green in the flame is an unmistakable sign that it is way too fuel rich; such a reducing flame will also be pumping out lots of carbon monoxide. The simplest way to judge a neutral flame is that it’s blue is a lighter hue, and it has secondary flame; any darkening beyond that is from too much air; it is called a lean flame as it is thought to be lean on fuel as compared to air input; the technical term for it is “oxidizing”. In the end, you must tune a burner back and forth between rich and lean to educate yourself on what constitutes the most satisfactory flame from your burner; you can do this out in the open air, or in the equipment, while its interior is warming up. You can also get thin yellow and red streaks in a perfectly tuned burner's flame, due to breakdown products of oxidation from some alloys of stainless steel, mild steel, or cast iron in your burner’s flame retention nozzle. Flame nozzles of #304 stainless can put on quite a show that way; it is harmless. #316 stainless nozzles make fewer streaks and last longer. Fuel rich (AKA reducing) flames, all have secondary envelopes, and can range from the faintest tinge of green in a blue primary flame envelope (AKA flame front) to bluish green flames that are pushing so much un-burned fuel into your shop's atmosphere that you feel like gagging. If the burner’s choke is completely closed the burner will make a lazy yellow flame like burning wood. Neutral flames range from light to medium blue; they are neutral throughout this tint range for all practical purposes; what that means is, although their combustion chemistry is changing, you cannot appreciate the difference without calibrated instruments. So how can you know when blue leaves the neutral range and inters oxidizing? The answer is that you cannot without a fair amount of practice. Eventually, you will learn to compare the flames from your burner at one time and another, to tune it perfectly; until then, your best bet is to tune the flame from reducing, down to nearly zero secondary flame; and leave it there. What does this look like? There will be a discontinuous whisper of secondary flame, beyond the tip of the primary flame. Oxidizing (AKA lean) flames start just beyond medium blue, go through dark blue, and extend into reddish purple, in a single primary flame envelope. While learning to discern the boundary between neutral and oxidizing flames, it is helpful to use small pieces of fresh ground steel in the forge, how fast and how much it scales—in the forge—gives you a faithful test for your assumptions, as you self-educate about flames. Flame color isn't the only sign of how well your burner is doing. The amount of secondary flame is also an important indicator; the less secondary flame the better. There is such a thing as perfect performance, which includes no secondary flame. Perfection is often at war with the practical. A small wisp of secondary flame is often better than no secondary flame at all; this is because air/fuel flames fluctuate more than oxy-fuel flames, so the "perfect" flame is likely to be slightly oxidizing part of the time. Since a wisp of secondary flame will burn up completely in your forge or furnace, it is better than scale added on work pieces during heating, or oxidative damage to super-heated crucibles. It should go without saying that tertiary flames indicate poor burner construction, or a very bad job of tuning. So, what is the practical upper limit for secondary flame? Is there flame coming out of the exhaust opening? Then your burner is either tuned too rich, or its gas pressure is turned up far too high.

Certainly, by the idiots

Yes; he could by casually chilling at times.

Which brings us to what is possible in burner design versus what is as close to fool proof as possible. Because the biggest dummy in the world can always find a lawyer to claim that its all your fault that he hurt his poor little self!

The wall of solid safety advise, given in any how-to book that I author; ambulance chasers being what they are! Why do you think I refused to ever sell a single burner in all these years?

Well, I think the choice of tubing is a fine example of "circumstances alters cases" I used to avoid copper tubing, just to preserve the cold in the incoming air/fuel mixture, strictly as a safety measure, for small burners that are deeply impeded witin a forge. Howsomever, since I'm not authoring another book here, I probably don't need to stand with my back to a wall all the time.

If you continue leaning the flame with added air, it continues to darken. Rarely, is a burner capable of inducing so much excess air that the flame turns reddish purple; I have built two burners which could do so. The first was a linear burner, and the second was a high speed tube burner. On the other hand, heavily reducing flames, begin to have a tinge of green in them, which becomes more pronounced as the burner's incoming air is reduced. I remember a burner system in a Tacoma foundry that was burning so rich, it drove us out of the room...gagging! You too, can do these tricks, although, why would you want to?