What goes where is all about the WHY

 Tunnel forges are today's most common shape for home construction, because of the variety of steel containers, which can be recycled for their use; they are also the easiest shape to swirl heated internal atmospheres in; and that is a convenient way to increase hang-time for those expensively super-heated gases (by lengthening their exhaust path). Cylinders also provide strong light shells, with good heat dissipation from ambient air currents around their bottoms; this greatly eases the problem of heat transference into supporting surfaces, such as your table.

However, tunnel forges do not make the best use of their interior spaces, and so they are giving way to oval and "D" shaped forges, which do a better job of it.

Box shaped gas forges have been around since long before tunnel forges started being built. Since they obviously provide far more usable room than tunnel forges, why did tunnel forges ever get  started? No; it wasn't just that paint cans were convenient. The gas burners that heat those forges got better (as in hotter), while their fuel cost rose considerably higher (propane versus the price of natural gas).

Furthermore, back in those "early days," people were concerned about even heating, which was a concern with box shaped interiors. However, hotter burners, better insulation, and re-emission coatings have pretty well ended those problems. Placing burners high up on one side wall, allows them lots of room to finish combustion before impinging on the far wall, and keeps them well above your heating steel, most of the time. If you want to heat up a bowl or helmet, top-down facing burners are the ticket. What then; do you need two different forges? No; you need to make removable refractory plugs to to cover extra burner ports, when they aren't being used. Then you can reposition your burners at will. But isn't that a lot of added work? Not if you actually have need of them.

Well, it kinda looks like we went full circle, yes? No; circumstances, and technical advances are always going to alter cases. The point is knowing why what needs to go where

                                                                    Choosing among commercial forges

There are three exceptions to everything I am about to state about commercial forges:

(1) Chili Forges, while expensive, are probably the best commercial forge available today; they are the first choice for any busy shop.

(2) Diamondback single burner forges are very likely the best dollar value in commercial forges; if you want your money's worth in the mid price range, you won't do better; they are fairly economical to run, get plenty hot enough, and will still be running when you retire to the golf course.

(3) An unknown English two burner box forge, which I saw demonstrated at the ABANA conference at Seattle WA back in 2006. I have never seen or heard of it since, which is a shame. I have no doubt it  is alive and well over there. If anyone knows of it, please speak up.

So, with the glaring exceptions out of the way, I don't think much of mid price range gas forges ($400 to $600); I find them to be generally over priced and underwhelming.

Which brings us to the obvious choices for a beginner's first forge; the low priced range. Since the best choice (Mister Volcano) has withdrawn from the market, you will have to choice from whats left; some of them aren't half bad; others constitute a complete nightmare. 

The ATkrou 200 single burner, double door forge ($140), would be my first choice amoung what is left; they use a an upside down "U" shaped sheet-metal body; its singe burner is centrally located, leaving the flame to impinge on its far wall between its two exhaust holes; this is critical. The two burner model has the flame aimed toward the exhaust holes; avoid the two burner model. On the plus side, the burner is a competent design, and the interior of the forge is a "D" shape; this will provide more usable space for your heating parts.

Various stainless steel oval forges come and go; I bought one, just to use its parts; at $139 dollars it was a good deal, even though I build burners and forges.

Nelyrho offers several different low priced forges and casting furnaces, with good burners, to choose from; you can find their site on Amazon.com, and peruse some of the best low priced equipment on offer.

 

Most of these forges call themselves forge kits; you must provide the finishing touches, like colloidal silica rigidizer, Kast-O-line 30 flame face, and even upgrade some of their hoses and regulators. Keep these things in mind, when choosing among various offers. Look for the best forge and burner, with the least accessories, because a lot of those extra goodies will need to be replaced right away.

The British manufacturer is likely to be Swan: website gasforges.co.uk 

You are right; it was Swan. Thanks, Tim.

                                                                                  Brick pile forges

When might a steel shell amount to silliness on a forge design? Let us discuss the why of box forges. Assuming that box forges started out as a way to accommodate straight refractory products like firebricks, ceramic fiber board, and high alumina kiln shelves, deciding on a box shape is no great stretch, right?

    And most of us don't want such expensive materials wrecked, so steel cladding comes quickly to mind. If you are running a busy steel shop, that makes sense. If that new forge is going to live in your studio, I would recommend just keeping gorilla types outside of locked doors; this will save wear and tear on a lot of other equipment too. Just post a sign saying "no brats allowed". Keep a whip and a chair handy; brats will not leave quietly.

Which brings us to what should sensibly follow in typical box forge construction:

(1) For most forge sizes: Morgan K26 bricks from Technical Ceramics for floor, walls, and ceiling, makes a sensible building material.

(2) Refractory cement to glue the ceiling brick into one piece, the floor into one piece, and each wall into one piece (six sides in all). Cementing the bricks together, makes your forge more stable, but hampers its ability to change size; so run your forge long enough to decide that its size and shape is where you want it, before cementing anything together.

(3) The thinnest high alumina kiln shelf you can find to cover the floor, or a small sack of Kast-O-lite 30, to cover coat flame impingement surfaces on the bricks.

(4) A metal plate, or hard cement board, over the ceiling bricks is a smart bet, only if the burner or burners are positioned there, and down facing. Or, use a metal plate on one side wall if burners, are mounted high up on it (and cross facing). It takes a metal cover to provide a surface to mount burner ports on vertical surfaces, or if your forge also has a hinged door.

(5) four sections of angle, and four sections of all-thread, with matching nuts and flat washers to allow the angle to keep the floor, ceiling, and four walls trapped together.

(6) A floor flange, pipe nipple, and six thumb screws to make each burner port used to mount each burner on the forge top, or side. Most people find a floor flange makes a good anchor for a burner portal on brick, or refractory surfaces.

(7) A good burner or burners, with valves, regulator, hose, and fuel cylinder.

(8) Four extra bricks (minus whatever bricks you left out of one wall to leave an exhaust opening in the front of the forge) to make a movable brick baffle wall in front of the exhaust opening.

(9) Plistix or some other finish to coat the ceiling, walls with, eventually.

(10) A large square pan, nearly full of Perlite from your nearest garden center to place the forge on.

Beyond these items there can be a long list of added items if you like, but it will all be add-ons This list is all you need to construct a basically hot, efficient, and safe brick-pile forge.

                                                    Two-Brick forges; maybe not

The first question to address in forge design is why; what do you plan to use it for? You can temper knife blades in them, forge small items like leaves, and forge jewelers punches in them; not much else. You can forge and temper small knife blades in them.

    Not only are two-brick forges small, but most people heat them with propane torches, which are only rated for 2,000 to 5,000 BTUs (British Thermal Units). A 1lb. cannister of propane only contains about 26000 BTUs. You will require one of the hotter torches, running full out, to accomplish anything; so figure on that cannister not lasting very long. Therefore, the next thing you need is an adapter hose, so that you can run that torch from a regular refillable propane canister.

Morgan K26 IFB (insulating firebricks; also called soft firebricks) were the first of the new insulating firebricks on the market, as far as, but there are several different varieties now; their most common measurements are 9” long by 4 1/2” wide by 21/2” thick, although they come in various thicknesses. These soft white insulating bricks should not be confused with hard yellow or orange firebricks, which are used in fireplaces and wood stoves; they are neither soft, light, or very insulating.

The new insulating firebricks are all light, highly insulating, and easily cut, ground, and drilled.

Plistix 900 F (use rated for 3400 °F (1871°F) is recommended over other re-emission coatings because it provides a smooth hard finish surface, to the rough ground or gouged out internal surfaces of the two insulating firebricks, and can be purchased in small amounts, from various sources on line, at reasonable cost.

    Here’s the bottom line. By the time you buy the torch, the bricks, the Plistix, and the adapter hose, you could make a coffee-can forge for about the same amount of time and money. But you will end up with a lot more tool. On the other hand, if you increase the amount of bricks to build a brick pile forge no larger than that coffee-can, you will have a more durable forge for your trouble.

I don’t use propane torches as forge burners but I do use propane torches. Flame king makes refillable 1lb cylinders. They make them in both shapes. You have to buy the refill adapter. They are awesome. Easy to fill. DOT compliant. Actually meant to be refilled unlike refilling the disposable cylinders.

If you go through a lot of disposable tanks, they will save you money and are worth the initial cost.

Do you have a small burner design in your book? Like maybe a .375 or .50 pipe for a coffee can forge?

I imagine you are meaning standard nominal size? Like 3/8 or ½ inch schedule 40 pipe.

Nominal size has different OD and ID than that call out size. There are charts if you want to know that data.

I built an actual ID 0.364” Mikey, it was tricky to build and finicky to run.

Assuming that you are referring to Gas Burners for Forges, Furnaces, & Kilns, the answer is no. The smallest burner in that book is 1/2" size; it can easily be turned down enough to be used in a coffee-can forge. But I prefer a 3/8" burner size for that job. So, you can ether settle for a workable 1/2" burner in that coffee-can forge, or listen to the picky-butt's preference for the very best possible choice...

4 minutes ago, Another FrankenBurner said:

I built an actual ID 0.364” Mikey, it was tricky to build and finicky to run.

How interesting. I didn't run into finicky until I built the 1/4" size

Others have built the 1/4" burner using air slots in place of rectangular openings, and they ran fine, with just that little bit of de-tuning. However, why bother to build a Mickey burner if you are going to de-tune it? Thus, I became interested in linear burners, which are much easier to build in miniature sizes, and run quite well enough in any size

0.364” actual ID is a ¼” nominal burner. Sounds like we had similar results.

While I haven’t found a practical use for it, I have built an 1/8” pipe version of my burner. Cute angry little flame.

The burner has the intake funnel so I suppose that puts it in the linear category.

8 hours ago, Another FrankenBurner said:

0.364” actual ID is a ¼” nominal burner. Sounds like we had similar results.

While I haven’t found a practical use for it, I have built an 1/8” pipe version of my burner. Cute angry little flame.

The burner has the intake funnel so I suppose that puts it in the linear category.

Yup. Nevertheless, so far, all vortex burners are linear, but not all linear burners are deserves the title vortex; yours do.

It is convenient to be able to braze weld mild steel parts to paint cans and coffee-cans.

A Tausom JH-1 MAP & propane torch, with swiveling stainless steel flame tube, can be used to braze mild steel sheet metal, tubing, and schedule #10 to #40 pipe (with the aid of brazing flux), using 70/30 brass brazing rod which has a 70-degree melting range and the steel at red heat—not 60/40, which only has a 10-degree melting range. Brazing with 70/30 filler will prove easy, when heated by MAP gas (propylene) and will handle minor gaps , but is much more work is needed, when heating with propane.

For stainless steel, a silver alloy with a minimum of 56 % silver, and black flux is needed, and no gaps larger than 0.005” can be bridged.

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.

                                                       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.

 

 

                                                                             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.

 

                                                             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. 

                                                                                      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.

                                                                                                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

 

                                                                 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.

                                                                                                  Avoiding flow limiters

Bureaucrats being what they are, some states took federally mandated over-fill valves as an opportunity to quietly add an internal flow limiting device to the OPD valve, on five-gallon and other small propane cylinders; when used on a barbecue grill, flow-limiters should not create problems; when used on other heating equipment (which all demand much higher flow rates), they cause major problems. Check with your local propane dealer to see if you live in one of these states, and avoid fuel cylinder sizes with internal flow limiters. Instead, keep your equipment and hose in good condition, to avoid leaks. Be careful not to crimp or accidentally cut a fuel hose, by positioning it out of harm’s way; running the hose through hooks along walls or from the ceiling is a simple way to keep it from damage. Stainless steel braided hose is armored against such damage.

It is wise to buy your hose from a local supplier, rather than on line. It is even wiser to avoid Amazon ‘deals’ on hose and regulator combinations; many of those regulators have built in constrictors, to reduce gas flow to barbecue grill volumes. A 0-30 PSI Fisher regulator only costs about five dollars more than the so-called bargains, and will run trouble free for decades.

"So, we see that circulation is a weak secondary concern, which should be balanced against other factors, such as how far the flame can go before impinging on first surfaces. With a hot-face wall that is only a thin coating, you must aim the flame to impinge on the cast refractory or kiln shelve floor. You would still want to avoid your work pieces, but would also want it to strike as far from the wall it will bounce toward as possible. In that case, I prefer to aim the flame at the near edge of the floor, with only enough angle to assure that it will bounce toward the far edge of the floor, and continue up the wall."

This statement came from my belief that what I observed to do very well, must be right; which was, of course, quite wrong

After several more years of noting people aim burners at the far edge of the forge floors, I must admit that it is the better choice. My original positioning worked so well, because the burner worked so well; not because my choice of position was best.

Fuel gases

Propane, butane, methane, and propylene are all LPG (liquefied petroleum gas) fuels; they are sold separately, and in various combinations, depending on area. Methane, while available in cylinders, is usually piped to homes and businesses, and is known as natural gas. Propane has been steadily replacing butane in the marketplace, because butane is problematic in cold temperatures. So, you will most likely be choosing between propane and propylene to heat your equipment. MAPP gas has been off the American market since 2008. What you find sold as MAP gas in canisters, is propylene.

    Both propane and propylene come in 16 oz. cartridges and in various sized refillable cylinders. Propane comes in a generous variety of cylinder sizes. Propylene cylinders are sold and refilled at welding supplies stores, and only come in two or three sizes from any given store. While propylene canisters cost about double the price of propane canisters, their fuel is only about one-third hotter than propane; a very poor deal. However, in refillable cylinders, propylene only costs about one-third more than propane; but, why choose it? You can turn your gas volume down, and simply have the added heat available at need. Is this worth the lack of choice in fuel cylinder sizes? Probably not for most of us. However, anyone who is also doing torch work will want that added heat available.

    Several states took advantage of the national mandate on overfill protection devices in refillable propane cylinders, to include flow limiters in most propane cylinder sizes. You can count on exchange cylinders to come with flow limiters. When used to run a barbecue grill, flow limiters cause no problems; but that does not hold true when such a cylinder is used to run a forge, casting furnace, or torch. If you cannot find a refillable propane cylinder in a size without a flow limiter in your state, and cannot buy a cylinder from another state (which does not use them), propylene cylinders do not have flow limiters.

    No matter how well designed your burner and heating equipment is, the limit on heating efficiency is tied to exhaust losses. Propylene, being one-third hotter burning than propane, can be turned down one third more than propane for any desired equipment temperature; reducing exhaust losses by one-third.