Mikey98118

I think that fan-blown burners will also be making a comeback. Since multi-flame ceramic heads, and also multi-flame ribbon burners have a much greater cubic area than typical flame retention nozzles, limited increased flow pressure is a positive, rather than a negative. However, the oversized fans of the past, being a great example of "too much of a good thing," will probably be replaced with 12V to 24V fans. All things in balance, is key.

Slide-over stepped flame retention nozzles I am not certain if Ron Reil pioneered slide-over tapered flame retention nozzles, or if someone else did; I first came across them on his burner pages. The taper amounted to about a 1/8" increase in diameter over a distance of 1-1/2". The increased diameter was in addition to about 1/8" increase in diameter from the inside to the outside of a burner's mixing tube. What made them so convenient was that one-half the increased-cross section was variable in length; this allowed burner flames to be tuned somewhat. Thus, the importance of sliding flame retention nozzles. The next innovation was stepped slide-over flame retention nozzles, made by inserting a short length of pipe or tubing, as a spacer ring between an outer tube and the burner's mixing tube; these were also designed to slide back and forth on the mixing tube, to vary width to length increases in flame retention nozzles. However, they increased air induction by increasing turbulence (in the form of drag over the internal shoulder). This design was also much easier for newbies to produce. The idea came to me, while looking at various butane and propane torch-heads. It is a good design, but hardly the be-all and end-all final design for flame retention nozzles. The old tapered nozzles still work best on slower flow burner designs, such as "T" burners. And multi-lame retention nozzles will probably dominate future burners. Progress marches on.

Well, we need to talk about this subject more. Small naturally aspirated burners are my particular rabbit hole, but I think fan-blown multi-lame burners will become the main stream.

Thanks, Latticino; that was good information. I used the unfortunate term "glory hole" just one time. The lady eventually got over it...and I never repeated that mistake! There comes a point when good manners trump politcally incorrect techncal terms

Latticino, back in 2000 I stumbled across Giberson, and bought his excellent little book. The only reason why I didn't buy his burners, was because he was into hot glass work, with much longer heating cycles. I had some doubts about how well his burner heads would hold up with repeated fast thermal cycling. However, Kast-O-lite ribbon burners seem to be doing okay in forges. Eventually, I think something very like his burner heads will end up as the standard burner in forges. Perhaps, with a little tweaking of what refractory is used to make them.

Efficiency is the whole point of forges The burners discussed on IFI, are primarily equipment burners. So, understand that heat management only begins with flame temperature. The reason burners are aimed on a tangent, is to cause their combustion gasses to swirl around equipment interiors; creating a longer distance from flame tip to exhaust opening. Obviously, a lengthened exhaust path increases the amount of the flame’s hang time, depositing more combustion energy on internal surfaces. What is not so clear is that the heat gained is not added by super-heated gases blowing an extra foot or two at high speed; it is due to their continuing drop in velocity over that added distance. Combustion gases begin to slow, as soon as they leave the flame envelope. The flames of two 1/2" burners will use the same amount of fuel to produce an equal amount of heat as a single 3/4” burner; but they will drop velocity much faster in a five-gallon forge or casting furnace, increasing efficiency, because their flames can burn faster/hotter without creating a wasteful tongue of fire out the equipment’s exhaust opening. Ditto for two 3/8” burners versus a single ½” burner in a two-gallon combination forge/furnace, or two ¼” versus a single 3/8” burner in a one/gallon forge/furnace. Because the parts and tubing these burners are built from cost less as their sizes reduce, it costs little more to make two smaller burners than a single larger burner; only the price of an additional funnel shaped air entrance is added on smaller burners, along with the cost of a second mixing tube on larger burners. When heating small parts, further efficiency can be gained by placing a temporary partition in equipment interiors; separating them into twin spaces, and shutting down the rear burner. This is something that cannot be done with a single large burner, which is centrally located. Combination forge/furnaces require the forward burner to be shut down during casting operations, so that its flame is not mostly wasted, from being positioned too high up the crucible wall. Multi-flame burners are the simplest way to produce high efficiency, in a first forge. I totally approve of them, even though my interests lie elsewhere.

Drilling and in threading stainless-steel Three-hundred series stainless tends to compress during drilling and/or threading, thus compacting its surface; this is a form of work hardening. What actually happens is the compressed surface becomes denser; this condensed layer begins to act like a bearing surface; dull cutting edges tend to ride on it ineffectually, instead of penetrating it, thus causing rapid heating of the cutting tool, which is why only very sharp drill bits should be used to drill stainless. The softer stainless alloys also tend to gum up tool edges, which then rapidly become dull. Stainless steel work hardens easily if a dull drill bit is used, if too little feed pressure is applied, or if drilling fluid isn’t used (tapping oil is perfect for this, and can be purchased in amounts smaller than a pint, but even kitchen oil is better than dry drilling). It only takes seconds to overheat a dull and dry drill bit in stainless, which rapidly results in melting temperatures on a drill bit’s leading edges, followed by transference of some of the bit’s high speed steel material to the stainless part’s surface; thereafter, no further drilling is possible, although the resulting mess can be removed with diamond coated burrs and patience. High speed steel lathe tools can suffer the same fate as drill bits. When a drill bit is about to exit the far side of a hole, feed pressure on the bit can cause the leading edges of its flutes to suddenly catch in the material’s thinning edge, and bind; small drill bits usually snap off at this point. To avoid breakage, ease up on feed pressure when you feel the bit “breaking through” the far side of a hole; this is true for any malleable metal--not just stainless steel. Larger bits may “grab” the part, causing it to spin around on the drill press, dangerously. It is generally a good idea to employ the drill bit recommended for a given tap in a given metal. However, the drill bit sizes listed in threading charts are normally meant for use on soft metals like brass or mild steel; they produce a 75% thread engagement. Only 50% thread engagement is recommended for stainleel-steel alloys, but the relatively few threads produced in most tubing/pipe products are under more than moderate stress at times; this makes the additional pressure on your tap, which comes along with an additional 25% thread engagement, a recommended burden, when using set screws in pipe or tube. But, threading through doubled layers of tubing or pipe used in some stainless steel burner nozzles is done with the recommended 50% thread engagement; also with schedule #80 pipe, when used as the nozzle’s outer tube. When schedule #40 pipe, or the equivalent wall thickness in tubing is used for a flame retention nozzle’s outer tube, but the threaded hole doesn’t include the nozzle’s spacer ring, it needs 75% thread engagement. “High-speed steel” drill bits are the cheapest grade of tool steel; if you are careful, you might get as many as four holes in thin stainless tubing before they need resharpening. “Cobalt” bits are made from high-speed steel, with cobalt added, for further hardening and heat resistance. When you can find cobalt bits with 118° points (standard angle for drilling ferrous metals) in the size you need, they are well worth their higher prices, in hardware stores; they are usually only available in fractional sizes. Cobalt drill bits can be purchased through Amazon.com for the same price as mere high-speed steel bits will cost at a hardware store. Look up any drill bit chart to understand the differences between fractional (fractions of an inch), wire sizes (adhering to wire gauge numbers), letter, and metric drill bit sizes; all of them are a few thousandths of an inch different from, than the closest size in one of the other classifications. The harder the alloy the more brittle it is; therefore, treat cobalt drill bits more gently than plain high-speed steel bits, and tungsten carbide bits more gently still; use light feed pressure on cobalt and carbide drill bits; do not forget the cutting oil, and they will serve you well. 135° split point cobalt drill bits also work well for drilling stainless steel; these bits come in a greater variety of sizes than 118-degree chisel point drill bits: including number and letter drill sizes. Because they are made for drilling hardened and stainless steels, hard bronze alloys, and titanium (all tough jobs), cobalt bits have thicker webs, leaving smaller clearances than standard bits; which means you will have to work more diligently at chip removal. One of the advantages of split point bits is that they do not tend to “walk” (move around on the part surface before penetration) like chisel points do. Try to buy American made M42 (8% cobalt) bits; most of the imported cobalt bits are only M35 (5% cobalt). If you look cobalt drill bits up on eBay (the drop shippers paradise), make sure the bits you choose really are cobalt. Amazon may be a better market for these bits. M35 bits are good enough for this work, but you can find M-42 bits in the desired size at Panamericantool.com. Note: Sets of tungsten carbide micro drill bits embedded in 1/8” mild steel shanks are available online for low prices, and also of tungsten steel. Tungsten steel will hold its temper up to 932 °F, and tungsten carbide is immune to tempering, but is quite brittle. Common high-speed steel bits lose their temper above 400 °F. Threading in stainless steel: The greater thread engagement (75%) needed on thin tubing walls, is one of the reasons you only want to use taper (AKA starting) taps; not plug or bottoming taps. The other good reason is that, unless you are going to start the tap in a drill press, (with the part trapped in a drill press vise, after drilling each hole, without moving the part), it is not likely that the tap will be started at true right angles. Starting taps will self-correct to that position if your aim is “in the ball park.” Plug taps will not. The way to tell the difference in taps is amounts of chamfer in taps are: Bottoming taps (1 to 1.5 chamfered threads); Plug taps (3 to 5 chamfered threads); and Taper taps (8 to10 chamfered threads). Lazy sales clerks and ignorant drop shippers are likely to offer plug taps in place of taper taps, so count those chamfers before buying. It should be obvious that stubbornly insisting on a tapered tap (even if you have to special order it), will return big dividends once you start threading in S.S. It is better to pay a premium price and/or special order a taper tap, than to try forcing a plug tap to work in stainless-steel. Another difference in tap designations are “straight” hand taps, and “spiral” CNC machine taps. Spiral taps have deeper groves for faster clearance of chips, and are therefore weaker than straight taps; take extra care with small spiral taps; there are other types of thread taps, but these two are the most likely types to be offered online. Start threading with your tap as close to right angles as possible, and only turn the tap until you can feel resistance suddenly increase (the “quarter- turn and reverse tool to break burr” rule of thumb is not adequate for stainless or high carbon steels); instead, you must back the tap off as soon as you feel a sudden increase in resistance to movement; as tjos indicates that the tap is starting to bind against chips, which need to be free to fall away from it. It does not matter how little progress you make before breaking the burr away from the thread end, and starting another twist; have the patience to follow this advice. You are going to be using small (and therefore easily broken) taps on these burners. Be liberal with your tapping oil, and back the tap out completely (in order to clean out collected metal chips) every full turn; dealing with a broken tap is even less fun than removing high speed steel layers left from partially melted drill bits. Should you break a tap off in the hole, gently rap back and forth on the protruding point outside or within the tube (with a rod, bolt, or piece of scrap metal), to loosen the embedded point or protrusion; then, try to back it out of the hole with pliers. Otherwise, you must grind out that piece of high-speed steel out with a diamond coated rotary burr. Once the partially threaded hole is cleared, try to continue threading it with a new tap; most likely this will work out well enough to accept a screw, but if there is not enough thread left to properly engage the screw, you must start over by drilling and tapping for a larger screw. Any malleable metal will form a raised area on both the outer and inner surfaces of the part, during tapping; #300 series stainless steel more so than other ferrous alloys. The inside face of threaded holes in the burner’s flame retention nozzle and other close-fitting parts must be sanded flat in order to keep proper fit. After sanding, the tap must be run through the threads again to “chase” them (to help clean out debris and get rid of burrs and/or deformed thread ends). Chasing and sanding the surfaces of tubes must be repeated back and forth, until all screws turn smoothly, and the part slides smoothly over other tubing.

Adding a locking screw If you plan to mount a burner in your forge, and if it will be top mounted, facing down; then it is wise to include a locking screw to any slide-over flame retention nozzle. After tuning the burner completely, drill a hole completely through the nozzle, spacer ring, and mixing tube, between two of the rear set screws on the flame retention nozzle’s outer tube. Thread through both parts, locking them together, and screw in a long set screw. Ink-mark the protruding portion of screw inside the spacer ring, and remove the set screw. Employ the nut and Allen screw to help as you grind away excess thread. Run the nut over the end of the screw, and reinsert the screw. The nozzle is now locked in position, against dropping off during thermal cycling, and your work is done.

Refractory cracking It seems like its "two steps forward, and one step back." But what is going on is just problems recycling, because "circumstances alters cases," over and over. Newbies will not be acquainted with thermal cycles creating cracks in hard cast refractory products, but twenty-five years ago it was a serious concern. Then along came Kast-O-lite 30, and that serious concern became history. However, some of us are experimenting with advance formulas for new hard refractories, and cracking problems have returned with them. So now it is time to dust off advice from the past, like avoiding sharp angles in refractory forms. Another suggestion from the past is to trap different refractory parts, instead of cementing them into a single form. The worry is that this will lead to the flame peeking though seams between those parts. But this is a minor concern, if the parts are surrounded by insulation. Why? Because the increased pressure of the forge's incandescent atmosphere, pushing those flames out, is minor. So, wrap them and trap them; don't cement problems in place

You will notice that the Frosty forge has the burner mounted so that the flame enters horizontally toward the top of his forge. The other guy had the flame entering at the bottom; giving little room for the fuel to combust before impinging on the work pieces. I have nothing against innovation. However, everything has a reason behind it in good forge and good burner design! The main point of horizontal positioning is to allow more room for flame combustion to complete before impingement with work pieces, than top mounted down-facing positioning provides. Placing the flame right next to the work does just the opposite.

Your numbers put it in the ballpark of a 3/4" burner, which would benifit from a .6mm printer nozzle.

You got me; yes, I meant .5 or .6. Between 0.020" and O.027" (approximately). The smallest MIG contact tip that I know about is for 0.023" welding wire, and its through hole is supposed to be 0.031" diameter. Cheaper import tips are often up to 0.033" diameter Why 3D printer nozzles? I am "gestimating" the size of that burner to be 1/2". I could be wrong. A typical mix of printer nozzles will have four or five different nozzle diameters (to cover my bet).

You bet, Frosty. The burner is a commercial reinterpretation of a Mikey burner; that makes it easy for me to know what is most wrong with it. What is it? The diameter of the gas orifice is way to large!!! This is why it is burning back into the mixing tube. What to do? Your present brass gas orifice needs to be replaced or rebuilt. I suggest rebuilding it. How? drill out that gas orifice way larger No; I didn't suddenly get even crazier. You need to drill out that center hole large enough to thread it for 3D printer nozzles. Then, buy a bag of nozzles (they're cheap), and the right tap. Why not use a MIG tip? I don't think you will find a MIG contact tip with a small enough through hole. I think you will find that this burner requires a 5mm (or 6mm) printer nozzle. I don't like the cross tube, which they use to anchor the burner at a given depth in the forge. However, there is very little that can be done about that. You need to get a bag of Plistix 900F to coat that forge's ceramic wool with. Rigidizer would be good too. Eventually, you will want to add a layer of Kast-O-lite 30 over the floor. Good luck. 111

Burners and Their Portals Occasionally, people complain that their burners are turning red, and then we on IFI need to help them understand why, before their equipment burns up. With many different burners in different forges, we can't provide any pat answers. However, if we look at what is suppose to be happening, you can get a clue about what your problem is. Essentially, burner ports are openings in the equipment shell, insulation, and flame face, which burners are placed in. To keep the burner in place, at the right depth in the short hole tubes, with a pattern of screws, are connected with the equipment shell. Ideally, the burner portal tubes are enough larger than the burner's mixing tube to leave 3/8" of space between the mixing tube and the portal tube all the way around it. Ideally, the burner has a sliding choke on the mixing tube, which allows your to control the amount of secondary air that the flame induces into the equipment, through the portal. Why? Because, as the forge heats up; heat from its interior is conducted, through the flame face, and through the layers on insulation. So, the burner is surrounded by incandescent material. If there is no space between the burner's mixing tube and the heated material, it is rapidly heated by conduction; only the incoming super cooled fuel gas and ambient air mix is cooling the burner, against all that conducted heat. If an air space is provided between the incandescent insulation and the burner's mixing tube, only radiant heat is transferred. Also the flame induces cooling air through the gap; not a lot of air, but reduction of heat transfer, and any increase in cooling is a good thing. So much for the ideal. Mister Volcano forges have no such air gap, and do fine; why? Their high speed tube burners provide way more cooling from their fuel/air mix than other designs; they are not alone. There are many other burners that are also capable of doing so. The other extreme is a so-so burner design, which also leaves no gaps between burner and forge opening. Consider these factors, and take warning, when others complain about this problem in the forge that they just bought.

Mixing tube hints Thermal cycling is quite hard on mild steel; far less so for stainless steel. It makes sense to use mild steel for every part possible in large burner sizes, since prices go up rapidly by size. While handier over time, the only part that is vital to use stainless for is the outer tube of flame retention nozzles. However, there is little difference in price of stainless and mild steel in small pipe and tube. Also, stainless steel pipe and tubing is generally better quality than its mild steel equivalence. Finally stainless steel metric tubing is much easier to match up closely with stainless steel funnels.

Occlusions in the gas orifice Why is it important to screw the gas orifice onto your burner's gas line? Construction debris must be thoroughly cleaned from your burner’s gas orifice during construction. But, after a short time, any debris in a gas hose, or lodged in valves and/or regulator will be blown into the burner’s gas orifice. After further time, propane (or LPG fuel mixtures) can leave residues of wax and/or tar in your burner’s gas orifice; especially in the orifice of small burners. How long that takes, depends on the quality of the fuel, and how small that gas orifice is. Whether the flame gets leaner for a while, bent off center, or reducing is just pure chance; it could go through all those stages. However, eventually the burner will be snuffed out, when the obstruction completely blocks off gas flow. Remove the gas orifice and blow air through it in the opposite direction of normal gas flow. If you have no source of compressed air, stuff a wire file from a set of torch tip cleaners through the orifice from the exit clear through its entrance. Poke the orifice one time only. You do not want the file to start enlarging the orifice. Try to catch the obstruction and have a look at it. Whether you see a little black tar ball, general debris, or insect remains, will tell you how likely the problem is to recur. A friend’s forge burner shut down after three weeks of running propane through it (from an especially cheap source); its gas orifice was thirty-0ne-thousandths of an inch diameter (an 023 MIG contact tip). A single poke through the burner’s tip with a wire file produced a tiny little black tar ball. A smith in Europe wrote that he found his gas system, and burner orifice lined with what he described as “greasy waxy stuff,” after a few months of forge use. However, how long it usually takes for propane to clog a gas orifice has more to do with gas orifice size, than propane quality. Orifice diameters on propane torch-heads are likely to be smaller than ten-thousandths of an inch; some as small as four-thousandths! Even better-quality propane can clog such a small orifice in hours. Easy removal for cleaning, is just one more reason for employing a 3D printer nozzle as the gas orifice in your small burner.

Propane adapter hose Propane extension hoses (AKA adapter hoses) are marketed to allow campers to run portable gas stoves on refillable propane cylinders, instead of the 16 oz. none-refillable canisters that backpackers prefer; some of them also allow you to do the same with canister mount torch-heads, which are a popular choice to heat two-brick forges. These hoses all have a QCC connector fitting at one end (which screws into your canister-mount burner). The hose’s other end may have a QCC connector fitting meant to mount on a canister, or a POL fitting for refillable cylinders. Even the hoses with QCC connectors on both ends are helpful, as they allow the burner to operate as a hand torch more easily, and to separate the fuel source from hot equipment by a few feet. There are hoses that include variable pressure regulators, and hoses of varying lengths. Hoses with stainless steel armor braiding are the best choice, whatever their length, for service near hot equipment (or in busy metal working shops). I don’t like standard heavy wall propane appliance hoses; they are stiff and overpriced. However, adapter hoses are not stiff, and have reasonable prices. Braided armor stainless steel propane hoses, are also available with 3/8” flare nut connector ends, which can be matched up to propane flare fittings available at some large hardware and appliance stores.

Although both kinds of spheres are available online these days, I don't mix my own refractory, so far. That will probably change this summer, as I begin constructing equipment for the next book burner book. And, while it is just book knowledge so far; I think at least one other guy on here has actually mixed the glass spheres into his refractory mix. It isn't a big leap, as similar voids have been created, employing Perlite in Kast-O-lite 30 for several years. One guy used a two-thirds refractory to one-third Perlite mix quite successfully. The glass spears should do the same job, with less increase of silicon content into the refractory during firing. I suspect that the simplicity of ceramic wool blanket, has held off this kind of experimentation from going forward in the last two decades, but everything always changes

Marrten, We have all failed to address the central point of your experiment; to produce a flame face material that is a hard, and re-emission layer; rather than a mere surface. I note that the burner in your forge does not look to be any advanced design, yet the exhaust opening appears as yellowish-white. I would surmise that it is above 2700 F. May we assume that it is also mechanically tough?

Employing used gas cylinders safely People who understand that heating equipment should be kept as light as practical concerns will permit, are naturally drawn to cylinders as material for equipment shells; they have enough thickness to provide support and some protection from impacts without adding excess weight (having already been engineered for maximum efficiency from their sizes). Clean food containers used for miniature equipment present no hazards, but gas cylinders can. Old five-gallon propane cylinders (twenty-pound barbecue grill size) have a wall thickness less than 1/16”, which makes them excellent candidates for recycling into tunnel forges and small casting furnaces, but they may have some propane content that isn’t already expelled. You need to connect your burner to the cylinder via a hose and regulator. Then light the burner, with the cylinder turned to a vertical-up position, using the burner to completely empty the propane tank of positive pressure. With the tank out in the middle of your back yard (completely away from ignition sources and/or combustibles), slowly turn the little bleeder valve on the neck of the main valve counter-clockwise; if no positive gas pressure is detected, continue unscrewing the valve until it comes off, and then squirt dish-washing detergent into the tank. Fill the tank with water until it starts spilling out the top hole, and let the tank set for a few days. After the tank is emptied, start your layout work on its bottom end. Turn the tank upside down, so that it rests on its protective collar, and cut your bottom opening (if any), being careful not to let the cylinder fall on your feet. Remove the protective ring, and lay out the cylinder’s top end. The rest of your work is now safe from flammable threats. A friction wheel or toothed saw should be the cutting tool used—not a cutting torch. Freon cylinders: "When grinding wheels touch steel these days, your work is quickly past But when they cut into a tank the steel is turning red Which means it's more than hot enough to make a nasty gas Breath not the fumes or you will find yourself quite sick in bed." Traces of fluorocarbons can remain in old refrigerant cylinders. After removing their valves, wash them with hot soapy water, and then let the cylinder soak for a few days before doing any kind of hot work on them, including abrasive cutting. The various refrigerant gases all decompose when exposed to elevated temperatures from open flame or hot metal surfaces, creating a number of toxic gases and vapors. So, why use them at all? These one-use tanks are thinner than the walls of one-to-three-gallon propane cylinders. In fact their wall thickness is perfect for their size; thinner than any other cylinder wall, but considerably heavier than tin cans. What more could you ask? Well, non-refillable helium cylinders from party stores make no toxic fumes at all.

Well, I believe the glass spheres simply melt into the refractory mix, during firing. However, the amount of glass they introduce is insignificant; it should make no practical difference in use ratings. The point of alumina and zircon spheres, is that they add to the strength of cement mixtures. My thought is that, in a refractory "so what?" We aren't designing bridges

Threaded parts seldom seal gas tight; especially when exposed to full cylinder pressures, as in the case of most cylinder-mount propane torches. The common fix is to use Teflon tape that is rated for fuel gas as a sealant, but such tape is meant for relatively low pressures encountered in household natural gas lines. So, Teflon tape is not likely to work well on lines without a pressure regulator installed. Even then, they must be turned in the right direction to avoid unraveling during installation, and the tape must be kept away from the last two pipe threads to avoid Teflon shreds from migrating into the gas line; inescapably plugging up the gas jet. A surer method is to apply gas rated gasket sealant on the threads of the male connection (kept away from the last two threads on the fitting’s end). You can also employ gas rated thread sealant (AKA Threadlocker). If you disassemble the fitting later, be sure to thoroughly wipe off excess sealant from internal threads first thing, lest some end up inside the gas orifice. Always clean the gas system before assembly: Teflon shreds are not the only junk that can enter your gas system. Burrs from cutting, grinding, sanding and threading operations must be thoroughly cleaned from burner parts, and all lines and hoses cleaned out with compressed air, to avoid debris from accumulating in the small gas orifice of a burner. Debris could have collected in the fuel hose from the gas cylinder, if you rent cylinders from an exchange system, from junk in the hose, if you leave it off for a long time. Insects and spiders are attracted to fuel hoses, because of their stench of fuel vapor. Propane can leave a buildup of tar and wax in a burner's gas orifices; especially from poor quality fuel. The wrong kind of hose will rot out over time; only use LPG or multi-fuel rated hose. Never use acetylene hose! Never use air hose! Never use water hose! The Latest lab burners It is always fun to look into lab burners; their manufacturers keep right up to the minute. Over the years, I have seen my own ideas on air entrances, and flame retention nozzles appear in their design. Now, they also include linear burner funnel entrances, and wast waist mixing tubes; they've come a long way in the last two decades. Lab burners are actually harder to improve than our equipment burners, because they must output soft flames.

On top of the swelling and than contraction of the bentonite, which is simply an essential ingredient in this formula; expansion/contraction during thermal cycling was always a major problem in hard refractories, until Kast-O-lite 30 was introduced into the market. I remember what extremes old timers went to, in avoiding major cracking in their casting furnaces back in 2000, when I started hunting for "the right refractory" to use a the flame face layer in my own equipment. The difference seems to be mainly due to the addition of bubble spheres. The voids they leave behind, are suppose to interrupt cracks, before they can get very far. The resulting mini-cracks are suppose to provide stress relief; anyway, that's the theory

Good to see you back, Marrten. Thank you for the update. I seem to remember that Mr. Hansen mentioned considerable shrinkage in his own parts, during firing. So, it does not seem likely that any tweaking of ingredients will allow a rigid structure of more than single parts. Perhaps, the best path would be to fire each part, and then trap the whole assembly within some outer layers of rigidized ceramic wool. Possibly to even surround the rigidized wool within a structure of Perlite, which is glued together into a monolithic shape, with water glass? Maybe encased within sheet-metal? This sounds more complicated than it is, because the wool blanket encased part, could simply be slid into a metal box, and the Perlite poured in; then the water-glass poured over the Perlite, and the whole assembly allowed to harden. A small hole in the rear face of the box, which is temporarily at its bottom, could allow any excess water-glass to pour out, into a container for reuse.

You can choose to employ the burner you are building, instead of a torch; it will provide more heat, but from a brush type flame; this is less concentrated then the torch’s pencil flame, and will call for increased manipulation of the filler rod; this can be done, but is less convenient; on the other hand, propane fuel will work just fine with this larger heat source.