Forges 101

[Mikey98118]

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.  

 

[Mikey98118]

   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.     

[Mikey98118]

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.       

[Mikey98118]

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.       

 

[Mikey98118]

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.

[Mikey98118]

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.

[Mikey98118]

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

[Mikey98118]

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.

[Mikey98118]

                                                                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).  

[Mikey98118]

Merry Christmas, all.

[1forgeur]

You Too!

[Mikey98118]

                                                                    Fiber blanket needs rigidizer

Even the cheapest grade ceramic fiber blanket does not melt below 3200 °F. Product temperature ratings come from the level of heat that fiber products 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 conferred by a relatively thin coat of heat reflector, such as ITC-100. Ceramic fiber products need both rigidizer and finish coatings to do well in today's gas forge; this is because better burner designs and smarter forge designs create much higher internal temperatures than were common in the past.  

    Rigidizer is especially important, because if you want your insulation to last it must be prevented as much as possible from shrinking. On the other hand, between employing 2600 °F rated ceramic fiber insulation and rigidizer, you can toughen the secondary insulation layer in your forge or furnace enough so that it should stand up well to the heat that will leak past the high emission coating (AKA IR reflector) and thin hot-face layer (typically Kast-O-lite 30. Rigidizer also helps support thin seal coatings. There are products like Plistix touted as heat mirrors which make very nice surfaces on which to paint even more effective high-emission coatings.

    You do not want to use thick fiber insulation layers, which tend to ripple when placed inside of curved surfaces; instead of a single 2" thick layer of ceramic fiber, place the blanket in two 1" thick layers. Ceramic fiber blanket will easily part into thinner layers via delamination between layers. Rigidize each layer after installation, and heat cure it, before installing the next layer. Finish forming burner openings before rigidizing each layer. remember to leave them just a little oversize so that they allow the burners to be moved without suffering damage.

    Rigidizer is colloidal silica (just fumed silica, which suspended in water) and common everyday food coloring (to allow you to visually judge how far it has penetrated); this product is easiest to dispense by spritzing after you mix up your own. But you can always pay through the nose for it, already mixed with water, from a pottery supply. I bought my fumed silica powder through eBay and got free shipping, because its weight is negligible.

    Ceramic fiber products are so porous that water runs right through them, unlike solid refractory, which must be slowly dried out, and then gently heat cured to prevent damage from a buildup of steam pressure. So, ceramic fiber can be "cured as you go," which means that nothing prevents you from slowly rotating a layer of blanket on a curved surface, like a casting furnace or tube forge, spritzing the rigidizer unto each area that is laid flat by the weight of the liquid, using your burner (turned down low and constantly moving over the wet fiber), to stiffen the blanket into permanent shape, and then moving on to the next area at your convenience. After creating a smooth stiff surface inside the structure, you can install another layer over it, the same way.

    One of the joys about completely soaking the blanket through is that both layers will bond together. Any excess rigidizer that soaks into the first layer will run right over its fiber’s surfaces by capillary action, the same as it did the first time, causing no clumping to degrade the insulating value of the outer fiber layer.

    The whole process is nearly goofproof. But, it’s still possible for a complete idiot to burn himself with the escaping steam that will be created, during firing. If you turn a high-speed burner on at maximum while holding still over one spot, it is conceivable (but quite unlikely) that you could even melt a patch of fiber.

    What keeps Murphy’s Law from messing up your efforts? First, the fiber is partly alumina, and partly silica; the aluminum oxide pretty much prevents it from melting, while the silicon oxide content bonds beautifully to the colloidal silica in the rigidizer. Secondly, the individual fibers in the blanket are very thin, which maximizes capillary action of a liquid across their surfaces. During heat curing, the colloidal silica that has wet every bit of fiber becomes a permanent vitreous outer layer on them, which creates welded joints everywhere the fibers cross each other. This glass sheathing is permanent. More rigidizer applied over it simply adds another layer after the next heat. Glass (silicon) is heavy, yet a quart jar of foamed silica (the which forms colloidal silica in water) is so light that it is obvious that the plastic container is heavier than all its content; this is because colloidal silica particles are so small that the main ingredient in the jar is air. Their tiny size is also why the powder will melt unto the ceramic fiber surfaces, this one time, at red heat. Afterward it remains solid at yellow heat. Consequently, every layer of silica sheathing on the ceramic fiber remains so thin as to leave the insulating ability of the blanket unchanged, even after repeated applications.

Note: If you do not completely dry the rigidized blanket before coating the blanket layers with sealant, it can still create a steam pressure problem, damaging the final coating. So, drill a 1/8” hole in the bottom of the equipment’s steel shell, as a pressure valve, and seep hole.

 

You can buy colloidal silica rigidizer at some pottery supply stores, but being mostly water, it is not cheap to ship from online sources; in that case you are better off to mix your own. Commercial solutions usually contain about 1100 grams of colloidal grade silica per liter of water. A liter is just over one quart (just under 34 ounces), if you want to use a kitchen measuring cup. One easily found and economical source of colloidal grade silica is fumed silica, which can be purchased from eBay, Amazon.com, and many other suppliers.

    Unlike sodium silicate, this product must be fired to take a permanent set on the ceramic fibers. Never allow this or any other colloidal solution to freeze, or it will clump together, and be ruined. On the other hand, measuring amounts is not needed. Commercial solutions commonly contain thirty percent fumed silica in solution with water. If you make your solution too thick to spritz, just add water. Too weak? Add more fumed silica. Hard to determine how well it is penetrating the ceramic blanket? Add food coloring.

[Mikey98118]

                                                                                    Kiln shelves

Kiln shelves are mostly considered a topic of interest to potters, because they are normally found in electric kilns. What goes on in these kilns is that heavy loads of pottery are cured at high heats for several hours; which is why high-alumina kiln furniture, including shelves, are rated by cone numbers, rather than merely use rated by temperature. The bottom line is that these shelves are engineered for maximum resistance to slumping under loads at sustained high temperatures (up to 3000 °F)—not for insulation value, which for kiln shelves is considered counterproductive. In fact, high alumina kilns are the perennial favorites of small business users despite their simi-insulating status; not because of it. The most expensive kiln shelves are nitride bonded silicon carbide, because of their high loading capacity and low shelf weights, which are important factors in a pottery kiln. Both carbon and silicon transmit heat well, but that is a plus factor—In a pottery kiln; not in a blacksmith forge or casting furnace. Fast heat transfer, combined with a maximum use temperature of 2600 °F degrees make silicon carbide a poor choice.

    Mullite kiln shelves are made by fusing magnesium and silicon together; a use temperature of 2900 °F degrees compares well with high alumina shelves; it is noted for thermal shock resistance, but high alumina shelves or very good at that also. Mullite is a poor insulator, and not as strong as high alumina, but the product is an acceptable alternative to shipping costs, if high alumina isn’t locally available.

    Half-bricks (1” thick hard fire bricks) are only acceptable for whose who’s common sense is blinded by parsimony. High-alumina kiln shelves are seven times more insulating than clay firebricks, and far tougher under loads.

    A floor made of semi-insulating high alumina refractory, over ceramic fiber insulation, is an acceptable substitute for a high alumina kiln shelf, and perhaps even more advisable if you want your floor shaped; but it is nowhere near as strong as a high-alumina kiln shelf, and therefore not removable for power brushing spilled flux from. As is often the case, once you have a look at the facts, choosing between viable alternatives can be tough. You only need to leave a little extra width in slots built into a cylinder’s front exhaust opening for the kiln shelf to rest in, and it can be slide in and out over the insulation without worry. If you want to weld in your forge, choose a kiln shelf floor; if not, choose Kast-O-lite 30 for your floor. If you like spending money on fuel, choose a half-brick.

[Mikey98118]

Kast-O-lite 30 Li is, for very good reasons, the most popular castable refractory on the market. Therefore, ALWAYS do a word search to find the best offers near you. One seller will be offering five-pounds of it for $45 while another seller offers five- pounds for $17. 78. Look before you leap, or pay sucker tax. This product is even sold at Home Depot.  Kast-O-lite 30 is a light weight, semi-insulating, high-alumina refractory that is resistant to cracking from thermal stress, and use rated to 3000°F; it is suitable for use as a primary flame face layer, and be cast in two layers with a secondary outer layer mixed with one third Perlite, to increase its insulation value. What if you live somewhere that forces you to pay high taxes and ridiculous shipping fees to import the refractory? Simply choose a local high-alumina castable refractory, and add silica or alumina bubbles (little hollow spheres) to suit. One kind of spheres or the other should be available from suppliers of cement; they are used to reduce weight in cement structures.

 

Zircar Ceramics’ Bubble Alumina (not to be confused with alumina bubbles) is an extremely low-density insulating castable refractory consisting, principally, of high-purity alumina spheres, in a high-purity alumina cement binder, which is use rated to 3317°F (1825°C). Obviously, this refractory constitutes the best possible insulation, needing only the thinnest of flame face covering over it.

    I would suggest Plistix 900 F for a flame facing, and also as the cement binder of alumina bubbles, if you wish to mix your own bubble alumina refractory; it is use rated to 3400°F  

If you must import Plistix 900 F, choose a local high-alumina refractory; these are commonly employed in glass working equipment.   

 

[Mikey98118]

18V and 20V angle grinders can be a good choice for general cutting jobs on sheet metal, but not for making interior cuts for rectangular air openings in pipe and tubing; use 12V 3” angle grinders, or 15/16” discs in rotary tools for such delicate work. Cutting pipes, tubes, and angle to length, or cutting empty cylinders for equipment shells, is what these grinders are best at. So, why not use 120V angle grinders for these tasks? The race to market ever stronger grinders is the problem. 280-watts on a 3” cutoff disc, or 350-watts to spin a 4-1/2” cutoff disc should be the limit for safety. Obviously, a 7.5 amp angle grinder is complete overkill for surface cutting. Cordless grinders are about half the torque of 120V grinders. Furthermore, the latest 18V and 20V grinders feature speed control; allowing you to drop them down to two-thirds input, which is just about as close to perfect for cutting on sheet metal as you can get.

[Mikey98118]

The Bauer 20v 3" cutoff tool (available from Harbor Freight Tools for $50 (but the battery is another $50); this is a burlier version of the 12V 3” angle grinders (whether they are called grinders or saws depends on their primary use; they can all be used for both tasks). You trade handiness on delicate tasks for increased power; This is one of the latest models of stronger 3” tools. DeWalt, Works, and other brands are also selling 20V 3” cordless saws.

    What then is the point of this particular tool? After all, there must be a point to it, if competing brands are proliferating, right? Not necessarily. Lots of power tools are popular for a while, but don’t last the test of time; I don’t think these will either. their point is supposed to be sufficient power to be considered a practical workman’s tool, but light and handy for cutting. While it is considered hard to make an angle grinder too powerful (a view I totally disagree with), it is easy to make a saw overpowered and unsafe; this is because of the danger of severe kickbacks from overpowered hand-held saws. But high torque hand-held saws have been used for over seventy years. Yes, for cutting wood--not steel. The difference is positioning. If you plunge cut steel with a chop-saw, it can be done safely. If you put a friction blade on a circular saw, you can only cut steel safely, so long as you keep its shoe (the flat rectangular metal base) flat upon the work surface. But surface cutting is done free hand; this tends to create kickback. During this kind of cutting, too much torque in your tool is likely to be paid for with your blood. 18V to 20V motor are as strong as you want to try, when surface cutting.

[Mikey98118]

Back in the early eighties Makita started marketing lighter more portable power tools; they first came out with a 5" angle grinder, and then a 4" angle grinder the following year, within a couple more years 4-1/2" angle grinders were marketed by multiple manufacturers; at first, they were all knockoffs of Makita's 4" model, with a larger spindle. The advantage was that they could spin cheaper grinding wheels than the high priced Makita 4" wheels.

In the following thirty years 4-1/2" angle grinders have come dominate the market, which is good. Unfortunately, these grinders have steadily grown more powerful, which is dangerous...if you want to use them with a cutoff disc. Today, using such a tool for surface cutting has come down to "riding the tiger."

About five years back the Chinese came out with 3" 280-watt angle grinders, which were the right size and power for surface cutting steel parts, with reasonable safety. Alas, they were 220V, with made them unpopular outside of Europe and Asia.

Then, along came 3" 12V angle grinders, which are under powered, but at least reasonably safe to use for surface cutting.

18V to 20V angle grinders have at least reduced torque back to the level of the original Makita 4" angle grinders, but are still over powered for safe surface cutting.

But, some of the latest model 18V to 20V angle grinders are variable speed; these can now be used with reasonable safety for surface cutting, by reducing them to half-speed during cutting.

[Mikey98118]

So much for looking for surface cutting answers by painting by the numbers, like good little boys and girls.

    The only advantage to cutting with angle grinders is their safety handles, which stick out at right angles from the tool's body. Worse is the reason for cutting with them; to save money by using a single tool for two tasks.

    Supposing we cut through all the commercial baloney, and get down to what counts; the best and safest possible performance, during various surface cutting jobs--at a sane price. Various surface cutting, and cutoff tasks call for cutoff discs from 15/16" up to 3" with corresponding speeds from 25000 to 10,000 RPM, and torque from 160-watts up to 300-watts. So what you need to start with is a  medium strength die grinder. Variable speed is no problem with a DC motor; just plug a fan speed control into its cord, and plug the controller into the wall. You will nearly always be far better off using an external controller, and leaving any speed control circuit on the tool at full speed (effectively by-passed).

    A medium power die grinder (around 400-watts) is already more power than you want; thith a full power die grinder you will not be able to lower power enough for delicate work, without turning the tool down below half-power; a big mistake if you want that tool to last!

    Next, you want to build your own safety handle to mount on the tool's neck, at a right angle, to provide the same superior grip, which is all that allows people to "ride the tiger"

[Mikey98118]

So, what advantage is such a tool with 15/16" cutoff discs? Compared to a high power power rotary tool, such as a Black and Decker RTX-6 (220-watts), or a Votoer 260W(watts) rotary tool, none at all, with such a small disc. The point is that you can run them successfully in a die grinder. As disc diameters increase the added power of a medium strength die grinder rapidly comes into its own.

Nevertheless, we don't run with scissors, slap the junkyard dog, or cut with high power die grinders in our hands

[Brassa]

Hello all! Just received in the Mr. Volcano Hero forge. It does come with Satanite but was curious if I should go over that with Plistix before using it. I have never really forged before. I did make a knife from a RR spike in a horseshoe forge once at a friends. Just starting out and have read most of what is on this site (thanks for that!).

I noticed above about it getting cold and wondering if I can start forging when the ambient temp is about 30 degrees F?

Thanks in advance!

Brassa

[Mikey98118]

Covering the Satanite with Plistix is a very good idea.

The low ambient temperature will not prevent you from forging; it will cause a smaller cylinder to frost over faster, if the cylinder is kept outside, where it belongs. If the cylinder is used indoors, which I discourage, how fast a five-gallon cylinder will become covered in frost will depend on how warm your shop gets.

So what is bad about the cylinder frosting over? No, it does not necessarily mean that your burner will shut down; at least not right away. What will happen first is that the gas orifice will start spitting out bits of frozen fuel with the fuel vapor, and will start faltering. Eventually, the burner will cut out, until the cylinder wall can warm up a little bit.

[Mikey98118]

This is because the vaporization temperature of propane is –44°F. As the propane is bled off from the fuel cylinder, it creates a refrigeration affect, which cools the remaining propane in the tank. Ambient air warms up that propane by conduction through the cylinder's wall; this is why tanks that are low on propane freeze over much quicker than full tanks, even on a warm day; it is also why people gang two tanks together, thus doubling the amount of wall area, and delaying that fow tank freezing problem, while keeping cylidner sizes small enough to deal with easily

Also, hotter burners in more efficient forges greatly reduce the amount of propane per hour being consumed. Over the last twenty-four years I have noticed a steady decline in readers asking your question, as burner and forge designs have improved (hint, hint).

[Mikey98118]

To be fair, a Mr volcano single burner forge is a pretty good example of that progress.

[Brassa]

Thanks Mikey! Since I still need something to hammer on and a few tools, that gives me time. I appreciate your insight!

Brassa

[Mikey98118]

You are welcome.