Mikey98118

Flame retention nozzles Details of burner construction depend on how fast and how low pressure the flow of fuel gas and air down the mixing tube is into the flame chamber made by the nozzle; and these factors hang on the overall design of a gas burner. There are two functions of flame nozzles; the lesser (but still important) of them is to provide a low-pressure area barrier before the mixing tube; thus, providing a safety factor by reducing the ability of flame to burn-back down the tube into the burner. The greater function is, by reducing pressure in the nozzle it helps "glue" the flame in place. Expanding gases from combustion creates forward pressure, which can blow the flame away from the end of the burner, blowing it out: all there is to stop that is the counter pressure of ambient air beyond the flame envelope (AKA pressure front). What air pressure? Only the difference between surrounding air and the lowered pressure of a partial vacuum formed by the drop in mixture pressure, which is made by the increased internal diameter in the nozzle area; this is assisted by the partial vacuum formed by a vortex in newer burner designs. There is an additional factor gained by flame nozzles; the ability to partially "suck" the flame back into the nozzle area, super-heating the nozzle into incandescent temperature; creating a large second ignition surface to add to the flame front that ignition usually tends to burn back toward the flame retention nozzle from. Finally, there is a synergistic motor affect created through the ability of flame nozzles to allow combustion rates to be greatly increased. Just as we are aware that the gas stream at the burners other end entrains air into the mixing tube by induction (Bernoulli's Principle), the flame itself can become, in effect, a second induction motor, speeding up mixture flow even more within the burner. But the flame also becomes a powerful induction motor on the outside of the burner, causing a lot of secondary air flow passed an entrance way, which should therefore be partially or fully closed (depending on burner design), to stop or slow secondary air, as needed. Intense burners require slide-over stepped flame retention nozzles (AKA flame retention cups); the simplest of these consist of a spacer ring, and outer tube, held in place by one to six socket set screws. The main job of the spacer ring is to keep the nozzle’s outer tube centered and parallel to the mixing tube. But, why stepped instead of tapered nozzles? Unless you have a metal spinning lathe, changes in taper angles, which are needed for changes in mixture flow is going to somewhat arduous to manage correctly; therefor, they will not be. The pitiful examples of tapered nozzles on commercial burners, prove this point. Exchanging wall thicknesses on pipe and tubing a few thousandths of an inch, to accommodate flow changes in burner designs is much esier. Cutting a longitudinal slit in the pipe or tubing being employed as a spacer tube, allows its diameter to shrink or expand as needed, within the flame retention nozzle’s outer tube, which increases the choices of suitable pipe and tube; it also allows the spacer ring to be contracted around thin wall mixing tubes, which would otherwise be dimpled by direct contact with set screws; this increases choice in usable parts, as most sausage stuffing tubes have thin wall tubing. Note: It has been repeatedly proven that an air gap between the outer tube and the spacer ring, or between the ring and the burner’s mixing tube (of up to 1/16”) does no harm, if you are willing and able to use six set screws to center the outer tube, and keep it parallel to the mixing tube. Due to the ridiculously high cost of small orders in stainless-steel pipe and tubing, as their sizes increase beyond 3/4”, mild steel pipe nipples, should be substituted for stainless-steel to make mixing tubes and spacer rings in the larger burner sizes. Schedule #40 pipe nipples of various lengths are available in hardware stores, and longer length pipe nipples are available in plumbing supply stores. Because cutting fees make 1” long parts used as as spacer rings, and approximately 2” to 4” long parts used for the flame retention nozzle’s outer tube nearly as expensive as 12” lengths), they should be cut from male pipe nipples (mild steel for spacer rings, and stainless-steel for outer tubes) to become far less expensive versions of flame retention nozzles; this can drastically reduce the costs to build your burner. This choice will produce slide-over step nozzles, which work every bit as well as nozzles that are built from lengths of tube and pipe, but which will not last quite as long, because the nozzle’s outer tube can only be made of #304 stainless, instead of #316. Note: These nozzles are kept in position with stainless steel socket-head screws. Do not use mild steel screws; they will freeze in place after a few heats. It takes months to wear out a flame retention nozzle, but they are disposable parts, and frozen screws must be drilled out. The outer tube should overhang the mixing tube by 0.125” longer than its inside diameter. The spacer ring should be 1” long, so that additional inch is added to the length of the outer tube. The nozzle is kept in position on the burner’s mixing tube with as little as a single screw, or as many as six screws, depending on how well it fits up to the mixing tube. Caution: Stainless steel flame retention nozzles on a good burner design, will get to yellow heat in ambient air, if you burn propylene, and will quickly melt down in a forge. The same nozzle will get to orange heat in ambient air, burning propane, and will melt down in a forge, if they are not recessed at least one-inch into the burner portal; do not position them close to the forge’s swirling super-heated atmosphere!

Merry Christmas, all.

Investment casting ceramic slurry If you don’t wish to pay for a large bag of investment slurry to coat ceramic blanket with, you can make up your own formula, which is good for up to eight layers; it consists of colloidal silica, which becomes a liquid binder for the dry particles in the slurry, and then acts as a fluxing agent at high temperatures, aiding the silica powder to bind together); 200 to 350 mesh fused silica powder (which is a non-reactive and thermal shock resistant filler); mix bentonite clay into the fused silica, before mixing it into the colloidal silica, to help keep the fused silica from settling out of solution; zircon flour (zirconium silicate). Slurry mixture component ranges by volume are: up to 24% colloidal silica (30 to 40% fumed silica in solution with water, by weight); between 13 and 35% 200 to 350 mesh fused silica powder; between 15 and 35% Zircon flour; up 17% bentonite clay. When used for investment casting, other components, such as silicon carbide, latex, and corn starch may be added; but are not deemed necessary for use in a refractory coating. Heat-cure the coatings at orange incandescence; 1832 °F (1000 °C).

One of the problems that remain with all this equipment is the delicacy of their speed control circuits; if you do not want them to burn out, do not run the motor slower than half speed. Aft this circuit dies, because you ignored this warning, you can bring the dead tool back to life, by cutting out the speed circuit, and replacing it with a length of wire. Your tool will only run at full speed thereafter, but that beats a dead tool.

From mini 12V angle grinders to rotary tools About three years back, Milwaukee came out with a 3" battery powered angle grinder, which they had built in China; it was a ridiculously overpriced and glitch filled design--since then the design as been improved, and it is only seriously overpriced. In the meantime, other China OEMs redesigned their own versions of that tool, which are marketed for around $50. Their tools feature 12V interchangeable batteries and high torque brushless motors. The main point of these tools isn't grinding, but surface cutting. I have wondered every since then, when the Chinese would make the obvious move, and come out with the same combination in a rotary tool, so that a battery powered rotary would finally be practical. There are now such rotary tools advertised on Amazon.com, by three different manufacturers; none of them feature a brushless motor, yet. But this upgrade is only a question of time; in the meantime swapping out the motor is just an additional twenty bucks and some wiring work

The two-brick forge The two-brick forge is merely chiseled out of 2600 °F or higher rated insulating firebricks; since the bricks are wider than they are tall, carving out two halves of a cylindrical shape is ill conceived; it is just as easy to carve two halves of an oval into the bricks; creating a larger chamber to work in. It is also best to leave one end of the hollowed-out longitudinal tunnel closed. Drill the hole for your burner two-thirds of the way toward the forge’s closed end, and slanting upward a little bit, to encourage the hot gases to swirl its way toward the forge’s open end. The hole should be about 1/8” larger diameter than the burner’s flame retention nozzle, to keep the nozzle’s expansion from cracking the brick, during heating cycles, and to provide a little secondary air, which propane torch-heads burners need to complete combustion in the forge. Seal the brick’s internal surfaces with Plistix 900, so that they will last much longer, and the forge will get hotter. The torch-head should be of the dual-fuel type, even though burning polypropylene fuel gas (wich is still misnamed MAP gas), in such a small forge will quickly destroy the brick. Nevertheless, dual-fuel torch-heads mostly use stainless-steel flame retention nozzles; this is what you need. The flame retention nozzle must be tightly encased in a stainless steel tube or pipe, to slow high-heat oxidation losses, and to keep something remaining for use as flame retention nozzle, once two-thirds of the original thin flame retention nozzle vanishes out the forge’s exhaust opening; it will happen. Brick pile forges Box shaped forges are the logical choice, when you use Morgan K 26 insulating firebricks from Thermal Ceramics, or ceramic board insulation in a forge. If you employ re-mission coated, 2700 °F rated hard ceramic board as the flame face material, with ceramic fiber blanket for secondary insulation, then a sheet metal shell is needed. If you choose 2600 °F insulating firebricks, nothing more than four threaded rods, five pieces of steel angle stock, and a threaded “U” bolt (to hold a burner) are needed, to trap “brick pile” forges together, or furnace cement, Plstix 900, etc. to glue the bricks together for a mini-forge. Threaded rod, and metal angles can be used to create box shaped forges of any desired size. Once, you feel confident that the size and shape is satisfactory, both the forge floor and top can be permanently stuck together with refractory cement. The side wall bricks should be left loose, but trapped, so that your forge remains variable in height. Mount the burner’s facing holes in one side wall, facing across to the other wall, and aimed slightly upward; they can be attached to vertical angles, which are in turn attached to horizontal threaded rods running between the top and bottom angles that keep the bricks in the forge walls trapped together. Threaded “U” bolts are the simple way to hold burners in position on the vertical angles.

It should not need pointing out that you can mix and match detail about all three forge sizes with any of the others.

Fine tuning the forge or furnace: Fine-tuning burner performance completely is usually done while running it in its intended equipment, and only after adding finish coatings, and a front baffle plate or brick wall for an adjustable exhaust opening to the forge, along with an adjustable secondary air choke installed on the burner’s mixing tube. These things are needed to raise internal temperatures high enough to better judge flame performance. Sounds backward, doesn't it? But the thing is that perfect evaluation only comes in equipment that has been turned into a radiant oven. Even as the burner’s flame is best judged in a cold forge, final evaluation of the burner’s effects of forge performance is judged by looking at the exhaust, and the level of incandescence on internal surfaces. The burner is merely part of the forge; if performance only revolved around the burner, most of what we have learned about constructing heating equipment would be "gilding the lily”—It is not. Back when I was still writing Gas Burners for Forges, Furnaces, and Kilns, I raised the temperatures in my forge enough that it changed from orange to lemon yellow, merely by refining the high-emission coating it was painted with (separating crude particles from its colloidal grade particles, using water). I A few weeks later, lemon yellow jumped up to yellow white by stopping all secondary air from entering the burner port; this can be further refined with the addition of a sliding secondary air choke on the burner's mixing tube. t has been stated that good burner performance is a delicate dance of different effects; ditto for the equipment it heats. The Two-gallon mini-forge Two 3/8" burners, mounted in a typical mini-forge; these are usually built from a two-gallon non-reusable helium cylinder (sold for inflating party balloons), or an empty non-refillable Freon cylinder (used by HVAC companies). So far as I know, Ron Reil first posted one of these forge sizes to the Net, back in the nineties. By law, empty non-refillable cylinders must be properly disposed of (which costs money), so they are not hard to talk businesses out of, once you explain what you want to do with them (they are only concerned about the chance of their being refilled). This size forge can be run from a single ½” burner, but two 3/8” burners give even heat, and can be used to turn this into a forge/furnace, like the coffee-can forge; or, they can be used to partition the forge, like the five-gallon model further on. Either way, the extra work to build and mount two burners will be handsomely repaid. A more recent variant on two-gallon tunnel forges, are mini-oval forges; these were first made from truck mufflers that were cut in half. But stainless steel oval trash cans can be made to serve with far less effort, for superior results; they should be run from two 3/8” burners, placed one-third of the way from its ends, and aimed up and toward the forge’s far side. Another variant on two-gallon tunnel forges is a two-and-a-half-gallon forge, shaped like a “D” laying on its side; these are made from one half of a five-gallon propane cylinder, cut lengthwise; this half has an exhaust opening cut into its front end, is lined with refractory, and rests on a 4” to 6” high steel pan. This pan is filled with various refractory layers; the additional height allows the bottom 2” of the pan to contain inexpensive Perlite, with tougher insulation layers of ceramic wool, etc. between it and the flame face. Where and what kind of burner or burners will be mounted varies from builder to builder. Five-gallon forges Five-gallon propane cylinders were used for most of the early home-made gas forges and casting furnaces; they are still the most popular container size for “tube” and “D” shaped forges; these forges are at their most efficient, when heated with two 1/2” size burners, placed low on the wall, but a little higher than the forge floor; aimed up and inward, so that the flame has the longest possible path to combust all oxygen in its induced air, before it can impinge on heating metal parts. With the burners placed at one-third the distance to the rear and forward ends of the cylinder. The far burner can be shut down, and a movable refractory baffle, placed midway between the burners, portioning off one-half of the forge, to save fuel, when heating small parts. This strategy works best on forges with a hinged and latched exhaust opening. Some people prefer using five-gallon paint cans, instead of discarded propane cylinders as shells. Five-gallons is the favorite size container being used for casting furnaces.

Drilling holes with rotary tools for 10-32 taps that are being used on small flame retention nozzles to thread holes for their socket set screws cab be done, if you are careful; these taps call for a #21 numbered drill bit, which is 0.1563” diameter; this is 0.030” larger diameter than the 1/8” shank limits of rotary tool chucks, so you need to enlarge the holes left by a 1/8” cobalt drill bit. Drill, and then file or grind, at one-half speed in a rotary tool. Enlarge the hole a little bit with a diamond coated rotary burr (safest) or a 1/8 single cut tungsten carbide rotary file (fast but tricky). You are removing only 0015” all the way around the hole’s periphery. So, you want a tool that works smoothly, and slow enough to keep control of the process. Swing the diamond coated burr lightly around the hole, and check to see if a taper tap will thread in the hole easily. If not repeat enlarging and checking. Be sure to keep track of how many passes produce the desired result. It is wise to perfect your technique on scrap tubing, before enlarging holes in your flame retention nozzle parts—especially if you choose to employ the rotary file.

Right there is all the difference between reading and doing. Without trying things out...

The short answer is yes. Amazon.com is a large marketplace. If you are able to tell good from bad products in that market, it is a useful choice; otherwise NOT!!! As to why we suggest 0-30 regulators over 0-20 models; it is just a matter of "just in case." I mess around with low volume higher pressure burners, and never need more than 20 PSI. In fact, most people spend most of their time at 12 to 15 PSI, even when welding in their forges. As to 0-60 regulators; the only time I ever use one is when I am testing a new burner design; and that is only to determine its safety limits.

Fine tuning the forge Fine-tuning burner performance completely is usually done while running it in its intended equipment, and only after adding finish coatings, and a front baffle plate or brick wall for an adjustable exhaust opening to the forge, along with an adjustable secondary air choke installed on the burner’s mixing tube. These things are needed in order to raise internal temperatures high enough to better judge flame performance. Sounds backward, doesn't it? But the thing is that the best evaluation only comes in equipment that has been turned into a “radiant oven.” The burner is merely part of the forge; if performance only revolved around the burner, most of what we've learned about constructing heating equipment would be "gilding the lily"; it’s not. Clear back when I was still writing Gas Burners, I raised the temperatures in my forge from orange to lemon yellow, merely by refining the high-emission coating it was painted with, from the stuff that came out of the jar to colloidal grade particles. I A few weeks later lemon yellow jumped up to yellow white by stopping all secondary air from entering the burner port; this has been further refined by the addition of a sliding secondary air choke on the burner's mixing tube. t has been stated that good burner performance requires a delicate dance of several factors; ditto for the equipment it heats.

People choose a variety of materials for the flame face layer; some merely toughen ceramic fiber blanket with rigidizer (colloidal silica; fumed silica suspended in water), and then add a thicker coating than normal of sealant and heat reflector over it. The point of this choice is immediate heating to very high internal temperatures. If time and fuel are at a premium, this is the way to go. If you want your equipment to last for years without the need to replace its refractory layers, a ½” layer of Kast-O-lite 30 is advised for a flame-face. Even rigidized ceramic fiber products still need to be sealed for safety. Furthermore, many of the coatings used for sealing provide a tough surface layer that holds high-emission coatings from peeling away from the fiber’s surface; an irritating problem that results from spreading some coatings directly on fiber blanket (especially when it is not rigidized first). Just as not all sealants are rated as high-emission, not all emission coatings are effective sealants, so you need to review the better-known products. There are also products, such as one shell coating for mold castings (consisting of zirconium silicate and fumed silica) which works quite well for surface sealing, and for heat reflection. I recommend this for those who do not want to include a flame face layer of Kast-O-lite 30. ITC-100: This is strictly a high-emission coating (not suitable for sealing); Twenty years ago, I found that deliberately separating it by adding more water to a small amount in a water glass, caused the non-colloidal particles to separate out, refining the coating, and greatly increasing its emission of radiant energy. My forge went from orange incandescence (when coated by the original product) to lemon-yellow, with just this change. I am not sure ITC 100 has the same ingredients today. You can make a better formula, for less money than this product now costs. 100% colloidal zirconium flour can be purchased from various online sources, and mixed with phosphoric acid from your grocery store, to make a high-emission coating, rated above (rather than “up to”) 90% “reflective” of radiant heat. None Stabilized zirconium dioxide (ZrO2; AKA zirconia) has three phases: Mono-clinic at less than 2138 °F (1170 °C), tetragonal between 2138 °F and 4298 °F (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 useful partially stabilized tetragonal form. A small percent of calcium, yttrium, or magnesium oxides can be used to partially stabilize zirconia; cerium oxide can also be used, but is too expensive for this homebuilt equipment. Further high temperature manipulation can form fully stabilized zirconia, but adds further expense. Zirconia has very low thermal conductivity, yet 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 (.040” 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 are desired, because the finer the particles the higher re-emission percentages go. Government sponsored experiments in the nineteen-sixties showed that phosphoric acid was able to hold 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 some castable refractory crucibles. When used as a refractory; clumps of it are also used as insulation between crucibles and wire windings in induction furnaces. Zirconia based refractories, and alumina ceramics with stabilized zirconia included are well known 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 3452 °F (1900 °C) will produces up 15% further contraction; factors to be considered when planning structures made of it. Zirconia is available for use as grog, and is an effective loose insulation for very high heat environments (think of it as like Perlite on steroids). Zirconia also comes as stabilized ultra-high temperature porous insulating brick. Zirconium silicate: Many hobbyists concoct a tough sealant coating that is also a high-emission product; they purchase zirconium silicate flour from a pottery supplies store, and mix it with bentonite clay powder; this is practical, because it does not go through phase shifts. Zirconium silicate, while very tough is only rated at about 70% heat reflection; it is also very resistant to borax, and an economical choice. Zirconium silicate can be either a coating or a hard refractory layer, depending on the amount of bentonite clay, etc. it is mixed with. One of the hobby blacksmiths on IFI makes a slurry of Zircopax (a brand of zirconium silicate) mixed into to colloidal silica (AKA fumed silica) and a little water; he also uses this mix for shell casting; he suggests mixing it to about the consistency of latex paint, in a clear lidded jar. The Zircopax will settle out, once you stop stirring every few minutes, and cake on the bottom of the jar, with the silica and water remaining in solution over it; until it is broken up with a butter knife, and thoroughly remixed back into solution. When combined with silica as a binder, I believe the overall performance of Zircopax in thicker layers will prove to be considerably higher than 70% heat reflective, since the other part of its molecular structure is clear natural silicate, which will pass light rays with very little interference, and since its re-emissive mechanism is radiance, I believe its overall performance in thicker layers will prove to be much higher than it is rated for. Remember that each layer must be fired before the next layer is painted on. Tony Hansen, of Digital Fire fame, uses Zircopax as both a coating and a solid refractory, very like clay, but good to very high temperatures, and highly insulating; two qualities that mere clay lacks. Mr. Hansen mixes it with Veegum T (a smectite clay) as a binder and plasticizer. A mixture of 97% Zircopax and 3% Veegum can be molded into structures, as easily as potters clay. A mixture of 95% Zircopax and 5% Veegum provides a hard tough heat reflective coating for other refractory structures. Mr. Hansen has also created his own 5mm thick (just over 3/16”) kiln shelf, which he states “will perform at any temperature that my test kiln can do, and far in excess of that.” It consists of 80% Zircopax Plus, with 16.5% #60 to #80 grit Molochite grog, and 3.5% Veegum T; he states that the mixture is plastic and easy to roll out, with 4.2% shrinkage, with 15.3% water added, but suggests that you dry your forms between sheets of plasterboard, to prevent warping. Firing to cone 4 produced 1% shrinkage, and left his shelf only cinder bonded. Firing to yellow heat will produce further shrinkage, but strengthen the final product; this has about the same thermal shock resistance as high-alumina cast refractories. Avoid uneven heating by setting your forge or kiln up to work as a radiant oven. Read about Zircopax at: https://digitalfire.com/material/zircopax Read about Veegum at: https://digitalfire.com/material/1672 Plistix 900 F is a 94% corundum aggregate and matrix, with a phosphate bond; it can be either a coating or cast refractory, depending on the amount of water used; it is use rated to 3400 °F. This product can also be used as a firebrick mortar. Matrikote 90 AC Ceramic Coating (one of the product line from Allied Minerals) is a very tough hard fine grained high alumina refractory coating containing 90.4% alumina, 1.5 silicon dioxide as a vitreous(glass-like) binder, and 2.7 % phosphorus oxide as a polymerizing binder. Matrikote is good to 3000 °F, and would prove useful as an inner layer between outer coatings of higher use temperatures and rigidized ceramic fiber products. Satanite is probably the best-known refractory mortar that is also used as a hard coating/sealant over ceramic fiber board; it is use rated at 3200 °F, and is easily purchased in small quantities through knife making suppliers. But refractory mortars are not recommended as flame faces, so plan on using a different finish coating on interior surfaces; It is excellent on exterior surfaces. Sodium silicate is a white powder that dissolves in water; it is usually sold in bottles, with the water already added; it is commonly used to glue the little bits of Perlite together into a solid layer of tertiary refractory insulation, as both products melt at about 1900 °F. Sodium silicate is also used to glue refractory fiber products unto other surfaces, like the inside of forge shells (containers). However, when used this way, ceramic blanket should be rigidized completely through all layers, to keep it from de-laminating, and falling away from the glued surface over time. So, why use it at all then? Sodium silicate hardens through contact in the carbon dioxide in air; it does not need firing to work; fumed silica rigidizer must be fired.

When it comes to a layer (or layers) of thermal insulation, your choice should be dictated primarily by what is available at a reasonable price, if the insulation you choose can withstand your intended heat levels. Obviously, fiberglass batting will not do. Perlite (use rated to 1900 F) is not sufficient for use as a secondary layer of insulation; it must be relegated to a tertiary layer, unless it is only meant to leave air voids in castable refractory; then it is still relegated to a secondary layer, below a pure refractory flame face layer of 1/2" thickness. Perlite was used this way, quite successfully for years by hobby metal casters; it was mixed into Kast-O-lite 30 castable hard refractory; this is because it is an insulating refractory to begin with. Normally, ceramic fiber board is employed in square structures, and ceramic blankets is the logical choice for curved surfaces; this is a convenience—not a necessity. The smaller the equipment the more precious internal space becomes. One-inch-thick fiber board has the insulating value of two-inches of ceramic blanket. In miniature equipment, the increased expense and labor needed to use ceramic fiber board is a smart choice. Must you cut the board on complementary angles, to avoid gaps? No, but you do need to cut strips of board narrow enough to keep the wedge-shaped gaps small. The insulation from all these products depends on tiny air gaps within the material, for insulation. So, very small wedge-shaped gaps will not cripple the ability of the board to insulate. Or, fill wider wedge-shaped gaps with refractory cement, to reduce the number of strips you must cut. But do not attempt to use left over cement for a flame face layer; it will not work for that purpose.

That would be like comparing apples and oranges, as Venturi refers to the air entrance and burner body's shape, while Ribbon refers to a form of multi flame burner head, versus a (single) flame retention nozzle.

I don't think you are. For instance, what's behind all of that new looking rust on the outside of the burners? I can think of zero good reasons for such a rapid build up, and have never seen the like. Anyone in the viewing audience have a clue what's going on? I suspect that there is some source of water vapor that the burners and work pieces are being exposed to. Did you finish drying out the forge, before trying to heat steel up in it? You did at least drill on 1/8" drain hole in the bottom of the forge shell, right? "on"? Perhaps "one" would be a better move?

While the flames are a little washed out by ambient light levels, what I can see of them looks pretty good. Furthermore the tint of their blue color is not dark enough to indicate heavily oxidizing flames. It looks like, the answer to your problem isn't going to be very straight forward Thus, I must defer to Frosty to provide your answers No, no, Frosty. Honestly, there is no need to thank me for this. Why, I was glad to help out Also, the photos show a secondary flame envelope; this pretty much excludes the flames being oxidizing.

That gas orifice looks pretty big already. Before you go any further, how about posting a photo of the flames your forge is putting out now.

When it comes to a layer (or layers) of thermal insulation, your choice should be dictated primarily by what is available at a reasonable price, if the insulation you choose can withstand the heat. Obviously, fiberglass batting will not do. Perlite will not do in secondary insulation; it must be relegated to a tertiary layer, unless it is only meant to leave air voids in castable refractory; then it is still relegated to a secondary layer, below a pure refractory flame face. Perlite was used this way, quite successfully for years, when mixed into Kast-O-lite 30 castable; this is because it is an insulating refractory to begin with. Normally, ceramic fiber board is employed in square structures, and ceramic blankets is the choice for curved surfaces; this is a convenience—not a necessity. The smaller the equipment the more desirable internal space becomes. One-inch thick fiber board equals the insulating value of two-inches of ceramic blanket. In miniature equipment, the increased expense and labor to use the board becomes a reasonable choice. Must you cut the board on complementary angles, to avoid gaps? No; but you do need to cut strips of board narrow enough to keep the wedge-shaped gaps small. The insulation from all these products depends on tiny air gaps within the material. So, very small wedge-shaped gaps will not ruin the ability of the board to insulate. Or fill those gaps with refractory cement.

After the burner portal tubes have been installed, it becomes time to install four individual legs, to hold a forge up a few inches above whatever surface it is sitting on. Another four legs need to be added at the rear face of forge/furnaces to hold the shell well above the sand filled steel pan, that it sits on, during casting. Or, build a carriage made from a bent 3/16” steel rod, which does the tasks of both sets of legs. Building the carriage is no more work than drilling eight holes and mounting eight long bolts in the equipment shell. All it requires is: (1) A nine foot long 3/16” steel rod. (2) Eight 10-24 nuts. (3) A 10-24 die to run threads on the rod ends with. (4) Two vice grip pliers to bend the rod into various right angle turns with. after heating it to red heat with one of the equipment’s burners. (5) A 3/16” chainsaw rotary file, to prepare the ends of two braces for silver brazing. (6) Silver braze filler and flux. Since you are just silver brazing on mild steel, 45% silver content and white borax based flux is fine for this job. Find the center of the rod, and make a mark 6” on either side of it. Heat and bend the rod at right angles at each mark, creating a “U” shape. After it cools, sit the “U” shape on a flat surface. Heat and bend down whichever leg of the “U” is raised up out of a flat plane. Make a mark 16” down each leg of the “U” from the cross bar. Heat and bend each leg up at right angles. Now, make a mark at 12” down each leg from the bends you just made. Heat and bend each leg up again. With the carriage lying flat between the second and third set of bends, so that the first “U” and the two ends of the legs are pointing up, lay books or boards in place to support the forge/furnace shell about 4” above the rods, and next to the shell’s open end. Male sure that the burner portals are positioned correctly, before going any further. Heat and bend the rod ends inward at an angle toward each other. and mark where you want to drill two holes for the forward end of the legs to penetrate the shell, after the excess material is cut away from them. Move the shell over beside the books or boards, and place first one mark, and then the other against the corner of your pile; mark a line down the from where the front holes will be, to the bottom of the shell, make cross marks 1-1/2” from the bottom face, to mark where the rear holes will be. Drill all four holes, and replace the forge/furnace back on the pile. Mark legs a little long, and then cut off the excess rod ends. Thread the end of the legs for a distance of 1-1/2”, and run a nut all the way to the end of the thread. Then, heat the bends in both legs at the same time, and re-bend them so that they slide through the holes. After the carriage cools down, screw a nut unto the end of each leg, and then screw the outside nuts up, as tight as it will go against the shell. Now, thread the two cut off pieces of rod the same as you did the two leg ends. Run a nut on each one of them a little further down the thread then is needed to allow sufficient thread for the inside nut, and push them, one at a time, through a rear hole, and swing them up against the carriage, make a mark for cutting that will leave an extra 1/8” or more of length, and cut off the rest of the excess on each piece of threaded rod. Now grind a round groove, using a 3/16” chainsaw rotary file into the ends of the rods, so that they will stay in place, without a gap; trapped between the carriage and shell, during silver brazing. Flux each joint, heat, and silver braze the two braces in position. Screw on the inside nuts, and screw the outside nuts tightly against the shell.

I agree with Frosty. If it was just a simple cylinder shape, you could get away with heating it up as is. However, you have three different hard right angles in this casting, which is not advised. Thus, you don't want to press your luck any further.

The burner ports are placed at a third the distance from the forward (top) opening, and rear (bottom) face of the forge/furnace; they consist of pipes or tubes large enough for the burner’s flame retention nozzles to pass through easily. Six socket set screws are screwed into them in two circles of three equidistant places. This arrangement secures them in place, and permits minor adjustment in aiming. Socket set screws are employed, rather than wing screws, so that the screws can be adjusted even when hot. Lots of people just use hex bolts, but that requires the use of a wrench. A small Allen wrench is easier to employ, and you while probably need this wrench to adjust the burner, anyway. By using the same size socket head set screws on the forge/furnace as used on it burners, the number of tools you must purchase is reduced. The next question is how to secure the burner ports to the forge/furnace shell. Stainless steel cannot successfully be welded by anything but welding rod or wire fillers dedicated to this task; welds made with the wrong steel alloy will crack, sooner or later. So, braze welding (which requires an oxy-fuel torch for most), silver brazing (which does not tolerate gaps over 0.005”), or silver soldering (which can bridge some gaps with expensive filler alloys), are your choices, for thermal joining; each choice has its limitations. However, the burner port tubes can be screwed onto the shell. You start by cutting a hole for each burner portal in the equipment shell, with a hole saw. Next, the pipe or tubing that is later to be cut into burner portal tubes, is placed in a hole, and a short line is marked on the shell, at it top and bottom areas. The tube is removed and a 1/16” elongation is ground into both areas. The tube is replaced, so top and bottom lines can again be marked on the shell; then another 1/16” is ground away. Repeat this operation, gradually changing the opening from a hole into an oval shape; this allows the burner portal tube, to be aimed at any desired angle, while maintaining very close tolerances between shell and tube. Once you have determined that the angle is optimal, the opening is ready to receive a burner portal tube. At this point you must decide to silver braze, silver solder, or screw the portal in position. If you opt for thermal joining, cut the tube along this first line, and proceed to use the tube’s other end to prepare the shell and tube for the second burner portal. If you opt for screwing, slide the tube into the opening 1” deep at the top of the tube or pipe, and ink mark the tube where it intersects the shell. Also mark a longitudinal line on the portal tube, with a matching line on the shell. Repeat this process on this tube end’s bottom area. Now, mark a second line where the tube and shell meet. Remove the tube and mark cutting lines on both sides of each longitudinal line on the tube. Cut into all four lines from the tube edge to where they meet the shell’s matching outline. Then, cut away the oval lines between the four longitudinal cuts, and remove the two portions of pipe or tube, leaving a tab at the top and bottom of the portal tubes. After the portal tubes are cut to length, these tabs will be bent, to match the angles of the shell, and the portal tubes will be pushed into position from the inside of the shell. The top and bottom lines on the shell show you where to drill holes screws, which will hold the burner portal tubes tightly in position against the equipment shell.

This is the main reason for running two 3/8” burners, rather than to two ¼” burners. The larger burners can be turned-down for forge work, while a single 3/8” burner can be turned up enough to heat gold or brass well into pouring temperatures. Surprisingly, 3/8” burners are much easier to build correctly than ¼” burners; this is mainly do to the gas orifice. The smaller the orifice the greater the difference between a desired orifice diameter and what may be available. All the other differences between what is best and what is available in part dimensions become exaggerated in miniature burners, too. But exact gas orifice sizes are the central aggravation.

Printer Nozzle Gas Orifices The gas orifice on a naturally aspirated burner must closely match its diameter in relation with the diameter of the narrowest point of constriction, no matter what the inside diameter of a burner’s mixing tube is. On 3/4” and larger burners, this is best accomplished with a MIG contact tip. On burners 3/8” size and smaller, 3D printer nozzles have every advantage over MIG tips (even with capillary tube trapped in them as precise gas orifices); this is because the greatly increased friction of the gas molecules through smaller orifices make it necessary to shorten the length of capillary tubes down to that of printer nozzles. So, in smaller burners, capillary tubing used for gas orifices give little advantage, while printer nozzles are cheaper, more easily acquired, and far simpler to mount. Right in the middle of these ranges are 1/2” burners, which can benefit from a correct size and length of capillary tube in a MIG tip, but with printer nozzles do nearly as well (with less work and expense). MK8 Ender 3 extruder nozzles are available through Amazon.com); they have M6x1 male thread. The markings on each of these nozzles stands for the orifice diameter in millimeters: 0.3 (millimeter) is 0.0117” orifice diameter is a good gas orifice size on a 1/8” burner. 0.4 (millimeter) is 0.0156” diameter is a good gas orifice size on a 1/4” burner. 0.5 (millimeter) is 0.0195” diameter is a good gas orifice size on a 3/8” burner. 0.6 (millimeter) is 0.0234” diameter is a barely workable gas orifice size on a 1/2” burner. 0.7 (millimeter) is 0.0273” orifice diameter is a suitable gas orifice size on a 1/2” burner, but a capillary tube can be tuned for performance by varying its length; thus, the right orifice diameter capillary tube can give a little better performance than just a printer nozzle. Printer nozzles generally have M6x1 thread, but there is another difference to look for; they have grown longer. The latest models feature 5/8” of thread length; this is important, because you need the gas orifice to run parallel to the axis of the gas tube. The older printer nozzles had as few as three threads, which were far harder to ensure a proper aim with.

Coffee-can forges There seems to be some confused ideas about coffee-can forges being a cheap and easy way to get into blacksmithing. What they are is an economical way to forge small parts, after the forge is built. C-C forge construction provides some economy of scale. You can find ceramic wool blanket offered in squares that are large enough to work in a C-C forge, so you spend less money for it. Castable refractory can be purchased in five-pound bags; these still make smart choices; but the significant savings come from minor fuel use. This equipment is also highly portable and compact, for those with limited space. For jewelers, they can be used to forge chasing tools, or small hammers; and also employed as a small casting furnace. Primary insulation layers made of mixtures of Perlite and water glass (sodium silicate) are going to melt in short order, if you heat the forge up very far; only employ perlite and sodium silicate in tertiary layers of insulation, with ceramic wool between it and, a primary layer of high heat castable refractory. Perlite and furnace cement are going to break down more slowly, but they still cannot hold up to direct flame impingement. You could mix Perlite and castable refractory as a secondary insulting layer, but then you would have spent enough money to buy that square of ceramic wool blanket. The infamous plaster and sand 'refractory formula' is such a major heat sink that you will want to throw your forge in the garbage can, before this so-called refractory even has a chance to crack apart! The second “cheap and easy” idea about C-C forges is that you can simply run them with canister-mount torches. There are high priced dual-fuel (meant for propane and propylene) torch-heads that have stainless steel flame retention nozzles, but those nozzles are so thin that they quickly oxidize away in the super-heated environment inside of a forge. Most propane torch-heads have brass flame retention nozzles, which will melt inside of a forge. So, the torch cannot be placed in a sealed burner port. Instead, it can only be placed in an oversized side hole, if its flame is weak enough, or aimed toward the hole from outside of it, if it is one of the hotter burning models. Either way the torch is either destroyed, or is under powered; the usual answer for this problem is to replace propane with propylene fuel canisters, at twice the price! A better choice is to push the thin-walled stainless steel flame retention nozzles, of dual-fuel torch-heads into a thicker walled stainless steel tube, to protect them from high heat oxidation losses. Then place the protected flame retention nozzle into a forge’s burner orifice. To prevent oxidation losses on the nozzle’s outer surface, the flame retention nozzle must be interference-fit into the stainless steel tube; no air gap between these two parts can be permitted. If you are going to all the trouble to build a burner (and you certainly should), you want it placed in a forge that is worthy of it, right? Now you have another problem, because a 3/8" burner is the largest size you can use in a C-C forge; by the time you have constructed it, you will not want to waste it in a cheaply built tin can forge. So, you might decide to spend a little extra to use a stainless steel container. 3 lb. coffee-cans (used for years as coffee-can forges, and by others as casting furnaces) are about equal in size to 1 gallon paint cans, or #10 tin cans, or some of the taller four-quart stainless steel kitchen pans. The main difference between a tube forge and a casting furnace is that the forge is positioned horizontally, and the furnace is vertical. With a little added work on its legs (to keep it up above sand box level in furnace mode), and the addition of an emergency drain hole at the bottom to let liquid metal escape into a metal sand box (in case of crucible failure), a forge, with a door that revolves out of the way, can be made to do both tasks well enough. One of the hard facts of equipment design is that there is no free lunch. Everything is a tradeoff. Being able to cast and forge in one piece of equipment must be paid for with some limitations on what can be done with the door and the forge floor; the larger the forge, the more serious these limitations become, but in a coffee-can forge/furnace the limitations are minor, because its capacity to heat work pieces for forging is limited to begin with. Thus, the lack of a flat floor section presents no problem. Another limitation in forge/furnace design is burner positioning. While the flame can be pointed in several ways in a forge, the flame in a casting furnace is aimed to impinge on the furnace wall as far away as possible, without directly impinging on the crucible (since flame impingement on a crucible promotes early failure). If the flames in a forge were aimed this way, they would not burn for a long enough distance before impinging on work pieces, if the burners should be pointed downward, toward the floor area. In these days of greatly improved castable refractories, it is better to aim them upward and slightly inward, to ensure the longest possible exhaust path in forges, while keeping the flame off of any crucible’s wall. Also, the use of two burners will change from a smart choice into a practical necessity, when the forge doubles as a casting furnace; so that the burner toward its rear can be run alone while the forward burner, which now becomes the top burner, can be shut down.