The dog days of summer are rapidly passing by. It is probably time for the prudent among us to get busy building their neat little garage heaters...er, I mean their gas forges and/or casting furnaces, before next winter arrives

I don't know about that, it was 100°F here with a breeze that felt like someone had opened the big blast furnace door.

Now we are under a severe thunderstorm warning, time to batten down the hatches.

I can't control the wind, all I can do is adjust my sail’s.~ Semper Paratus

I think day to day weather is becoming less predictable, but overall, seasonal changes will continue; but more extreme. Winter is still going to be winter; just more so

Naw Mike, the weather is just as unpredictable as it always has been in spite of computer modeling () we just don't remember the last forecast let alone our youth so accurately anymore.

Heck, the forecasters only average back maybe 10 years it seems. We've lived in this house 25 years now and we clearly remember -45f a few times and a couple winters ago all the forecasters on the news were talking about record breaking -15f cold snaps. I actually talk to one of the long time weather people now and then, we've kept in contact since one of Deb's born at the state fair pygmy goat kids completely upstaged her doing an interview. She doesn't remember me from Adam unless I mention the fair and goat kid, then we reminisce. They only read the prompters on camera and details like past weather is left to interns or . . .?

We and our dogs spent a few days at the far end of the road beyond N. Kenai. It's a great campground just back from the edge of a 70-100' bluff over Cook Inlet with a view of Redoubt Volcano across the Inlet. It was a little windy but sunny and warm, even hit the mid 60s! It's one of our favorite campgrounds, no hookups, hand pump water every 20 spaces or so and decent size spaces. It was a nice few days off, even if riding shotgun in Deb's RV with the dachshunds in my lap tends to REALLY make my knees hurt. Soooo we stop to stretch our legs and let the dogs run (ON leads) pretty often.

Frosty The Lucky.

That brought back memories of my first view of a live volcano (we were out to sea) in Alaska; it was billowing smoke sideways from the top, because the wind was blowing so hard. I hadn't thought about that in thirty odd years.

You must've been sailing along the Aleutian chain, there is almost always a volcano or two erupting at some level. I don't think Mt. Wrangel is visible from sea but it's always venting, steam, ash, and various sulfur compounds. Heck, almost the entire Wrangel Complex tends to vent pretty continuously. 

Mt. Shishaldin is a "moderately" active stratovolcano on Unimak isle. in the Aleutian chain and puts on a good show pretty regularly.

I'll have to ask Deb to send me pics 0f Redoubt if she got a good one, the ones on my phone are all foggy looking. The winds and clouds were putting on a good show the day we headed home, it looked like it was venting. Unlikely though, the shape tends to cause "interesting" air currents around it so you get big puffs of cloud rolling down the S. side like cotton balls.

Frosty The Lucky. 

 

I was in the Aleutians, working steel on a floating fish processor; it was a converted Liberty ship, served by their own trawler fleet. I spent months at a stretch working steel on their ships in the Aleutians, for five years; then they started getting their people killed, and I left; a few months later they managed to sink their newest factory trawler in calm waters, through sheer mismanagement.

Sounds about right. Exactly why I've never gone commercial fishing and ignored all the processor help wanted ads. I was here maybe 2-3 weeks and a crabber capsized, a trawler went down with all hands and a processor. . . caught fire maybe? People being swept or falling off boats wasn't uncommon either. 

Mismanaging a fish processor or "fleet" of boats is the norm for mid level corporate. Heck, same for construction companies that are headquartered outside. 

Ahh, nothing you haven't heard, seen or experienced so I deleted a few paragraphs of old fogey rant.

Frosty The Lucky.

 

What I found over the years, was that proper working habits make all the difference, when you're so tired that you can barely drive home after the shift. Some deals, like the fishing fleet, takes tiredness to a whole new level; then lack of good habits, combines with lack of sense, and stuff like cocaine ...what a sad mess!

Fortunately I never found myself working in conditions quite like a fishing fleet though road maintenance got close at times. When I was drilling we had a procedure we followed for most of what we did and so long as we did the job the same every time we had very few accidents and those involving equipment and tools not crew. Every job was different but we always knew what was going on, what came next, etc. etc. and if something changed we could hear, see, etc. it and not be surprised. 

There were certainly "THOSE" crew members though happily not many. Some were just a bit crazy, a few druggies and alchies. Happily in the mid 80s the Feds started random mandatory drug testing for GVT employees holding CDL licenses. Some folk got moved into positions that didn't require clean blood, some folks got pink slips. 

Wrecks involving commercial vehicles went WAY down.

Frosty The Lucky.

I paid little attention of druggies on the tools; I found them no more troublesome than young "cowboys" on the steel crews. However, cocaine brains making management decisions, was "a bridge too far," out at sea...

Or meth, it was a LOT more common than cocaine back when. I worked briefly for a paving company the owner's son handed out a couple whites at the morning huddle. We gathered at the lead man's pickup to get the day's "instructions" over coffee, doughnuts and a couple hits of speed.

That job lasted about 90 minutes, I didn't even try to collect my wages.

It wasn't the only time but it was the most egregious. The company changed names almost every year and last I heard had faded away.  

I really liked making grade on paving jobs too. Oh well.

Frosty The Lucky.

"Oh well" is kind of a drag...but it beats becoming a statistic

The wrong kind of statistic that is. After the second or third construction crew where meth was a morning supplement, "vitamin" as one guy called them I started interviewing jobs before I applied. Got some funny looks but stopped taking jobs for outfits looking for desperate employees. Those never turned out so well, a good construction company rarely has a high employee turnover rate. They were also the ones that asked you not to cash a paycheck till they got the money in the bank. 

Glad I don't have to deal with that anymore!

Frosty The Lucky.

 

On 8/24/2024 at 6:32 PM, Frosty said:

I started interviewing jobs before I applied. Got some funny looks but stopped taking jobs for outfits looking for desperate employees.

I stopped getting "jobs from hell," as I thought of them, once I learned better than to allow the department of unemployment to suggest places to apply

                                                                 Adjustable LPG pressure regulators

There are a whole lot of very bad propane regulators being offered online these days. On top of junk regulators that barely work, and/or leak, there are many regulators that were intended for barbecue grills, or camping stoves, that have  deliberately restricted flow; these will never be able to supply sufficient fuel to run heating equipment. Searching for "propane" regulators will bring them up in droves. Search for LPG regulators, to have any chance of finding something useful.

Fisher regulators (now Emerson Fisher) is a long time supplier industrial grade LPG equipment; their 0-30 PSI adjustable regulators (now 3-35PSI) cost about $55; that is double the price of junk regulators. But then, you end up with dependable equipment, rather than nasty problems.

 

Fuel gases

Propane (C3H8), butane (C4H10), methane (CH4), and propylene (C3H6) 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 called 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 16 oz. canisters, is propylene.

In general, the higher the number of carbon atoms to hydrogen atoms in fuel molecules, the hotter a fuel burns. However, propylene,  is an exception to this rule of thumb, because of double bonding between two of its three carbon atoms. The breaking of this bond provides an energy boost during combustion, in a similar manner to the double bonded carbon atoms in acetylene (C2H2), which also has the highest carbon percentage. However, acetylene is expensive, because it is dangerous (and therefore, more expensive to produce, transport, and store, due to high insurance costs).

    Both propane and propylene come in 16 oz. non-refillable cartridges and in various refillable cylinder sizes. Propane comes in a generous variety of cylinder sizes. Propylene cylinders are sold and refilled at welding supply stores, and only come in two or three sizes from most of these stores. While propylene canisters cost about double the price of propane canisters, their fuel is only about one-third hotter than propane; a sucker’s bargain. 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 greater 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 propane exchange cylinders to come with flow limiters. When used to run a barbecue grill, flow limiters cause no major 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 suitable size, without a flow limiter in your state, and cannot buy a cylinder from another state (which does not include flow limiters), remember that propylene cylinders do not have flow limiters.

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

Burner flames and incandescent atmospheres inside heating equipment

When looking at the flame from a good burner in a cold forge or furnace, it will appear much as it does out in the open air (a single blue flame envelope); but within minutes it will lengthen and become smoother in outline, as the equipment’s interior starts to super-heat; it will also lighten in hue (due to backlighting from incandescent internal surfaces), becoming more transparent. There will be little to no secondary flame within the equipment, even while it is cold; lesser burners will make more complicated flame envelopes, but this is the ideal; these facts also hold as true for multi-flame ceramic burner heads as they do for single flame burners.

    You need to remember that there are two different flames created within the average gas forge or furnace; the flame being input by the burner, and an internal incandescent atmosphere, which may extend to an output flame leaving the equipment via the exhaust opening. When blacksmiths discuss terms like dragon's breath, it is such an exhaust flame they are speaking of; a very different animal than the burner’s flame. Not that both flames aren’t equally important clues to burner performance, but they need to be treated separately for clarity. So, what amounts to a perfect exhaust flame? No visible flame at all.

    If we are speaking about the burner flame, straight blue from a single combustion envelope is the goal, but many older burner designs have a small white inner flame ahead of a blue secondary flame, followed by a darker larger and less substantial appearing blue and purple tertiary flame; these multiple flame envelopes come from combustion of byproduct gases with flame induced air through a burner port. Buy or build a good enough burner to see no white in the flame, and then tune it well enough to have little or no secondary flame, with zero tertiary flame. Then, control flame induced secondary air, with a sliding choke on your burner’s mixing tube.

    The next question tends to be "how dark a blue?" Different fuels give off different hues, and lean flames are always a darker blue than neutral flames in any given fuel. In fact, a burner can be run so lean that the primary flame turns purple. On the other hand, any slightest tinge of green in the flame is an unmistakable sign that it is way too fuel rich; such a reducing flame will also be pumping out lots of carbon monoxide.

    The simplest way to judge a neutral flame is that it’s blue is a lighter hue, and it has secondary flame; any darkening beyond that is from too much air; it is called a lean flame as it is thought to be lean on fuel as compared to air input; the technical term for it is “oxidizing”. In the end, you must tune a burner back and forth between rich and lean to educate yourself on what constitutes the most satisfactory flame from your burner; you can do this out in the open air, or in the equipment, while its interior is warming up.

    You can also get thin yellow and red streaks in a perfectly tuned burner's flame, due to breakdown products of oxidation from some alloys of stainless steel, mild steel, or cast iron in your burner’s flame retention nozzle. Flame nozzles of #304 stainless can put on quite a show that way; it is harmless. #316 stainless nozzles make fewer streaks and last longer.

Fuel rich (AKA reducing) flames, all have secondary envelopes, and can range from the faintest tinge of green in a blue primary flame envelope (AKA flame front) to bluish green flames that are pushing so much un-burned fuel into your shop's atmosphere that you feel like gagging. If the burner’s choke is completely closed the burner will make a lazy yellow flame like burning wood.

Neutral flames range from light to medium blue; they are neutral throughout this tint range for all practical purposes; what that means is, although their combustion chemistry is changing, you cannot appreciate the difference without calibrated instruments.

    So how can you know when blue leaves the neutral range and inters oxidizing? The answer is that you cannot without a fair amount of practice. Eventually, you will learn to compare the flames from your burner at one time and another, to tune it perfectly; until then, your best bet is to tune the flame from reducing, down to nearly zero secondary flame; and leave it there. What does this look like? There will be a discontinuous whisper of secondary flame, beyond the tip of the primary flame.

Oxidizing (AKA lean) flames start just beyond medium blue, go through dark blue, and extend into reddish purple, in a single primary flame envelope. While learning to discern the boundary between neutral and oxidizing flames, it is helpful to use small pieces of fresh ground steel in the forge, how fast and how much it scales—in the forge—gives you a faithful test for your assumptions, as you self-educate about flames. 

    Flame color isn't the only sign of how well your burner is doing. The amount of secondary flame is also an important indicator; the less secondary flame the better. There is such a thing as perfect performance, which includes no secondary flame. Perfection is often at war with the practical. A small wisp of secondary flame is often better than no secondary flame at all; this is because air/fuel flames fluctuate more than oxy-fuel flames, so the "perfect" flame is likely to be slightly oxidizing part of the time. Since a wisp of secondary flame will burn up completely in your forge or furnace, it is better than scale added on work pieces during heating, or oxidative damage to super-heated crucibles. It should go without saying that tertiary flames indicate poor burner construction, or a very bad job of tuning.

    So, what is the practical upper limit for secondary flame? Is there flame coming out of the exhaust opening? Then your burner is either tuned too rich, or its gas pressure is turned up far too high.

    Even with the best possible flame (which you can visually detect), there may be some excess superheated oxygen molecules, escaping the primary flame envelope (due to excess air induction). But any such oxygen molecules, which impinge on super-heated metal, will combine with it, to rapidly create scale, and to burn away some carbon content in ferrous metals. What this means is that every extra inch of distance between the flame’s tip and your work pieces (or crucible wall) is highly desirable. Hot crucibles are inclined to suffer damage in the presence of superheated oxygen, leading to spalling, cracking, and early crucible failure.

    It is an advantage to building a tunnel, oval, or “D” forge with the flame angled away from heating stocks (or aimed between the crucible and equipment wall, in casting furnaces); or with the ceiling at least far enough from the work (in box shaped equipment), to keep a vertical flame from impinging on heating stock; increased room for the flame is one of the reasons for including a plinth in your casting furnace. Since different burner designs create different flame lengths, and since they also vary by how far the burner is turned up, there can be no pat answer on the height of a box forge or plinth height in your casting furnace; these are judgement calls on the builder's part.

    Most people find little reason to turn a burner up full blast, so the flame can be measured for length at a maximum of 20 PSI, and that can be used for a good distance measurement. You want at least two-inches beyond flame tip, and any surface it impinges on; the longer that length the better. No practical forge can include further length for tertiary flames, so construct and tune your burner well enough to avoid making them. Crucibles are tapered at their bottoms and should be raised on plinths to help keep the flame from impinging on their bottoms, since most casting furnaces are cylindrical, with a burner placed low on its vertical wall, and aimed horizontally at a tangent between furnace wall and crucible wall.

    However, flame length is most important if your burners are top mounted and facing toward a forge’s floor. Some people mount their burners high up on a sidewall, and facing horizontally across a box forge or furnace, to get around early flame impingement on work surfaces; this helps prevents scaling on heating stock, and also lowers thermal damage on walls (which can be further away from the flame tip, for the same cubic inches when ceilings are lowered; a win-win use of space).

    Is an exhaust flame just the tail end of the burner's flame? It can be just that in equipment that is loafing along, with interior surfaces that are only at red or orange heat. But in a forge or furnace that is turned up into yellow or white heat ranges—no. In fact, the goal is zero output flame; just clear super-heated exhaust gases. When your forge or furnace is capable of radiant-oven performance, everything about the exhaust discharge changes.

    With the average forge or furnace, a small amount of blue exhaust flame has been considered normal—in the past. But in proper equipment, should you keep turning up the input flame beyond its ability to completely burn internally, you still won't get blue exhaust flames; some of the yellow-white “atmosphere” will overflow out of the exhaust, and complete combustion within a few short inches, but without a trace of blue or purple flame (which indicates a probable buildup of carbon monoxide in your shop).

    What is different? The forge or furnace itself is changing the combustion equation by super-heating any byproducts of the primary combustion envelope. How is this possible, since immediately after combustion, exhaust gas temperatures naturally decline? Intense radiant energy from incandescent surfaces is being bounced back and forth through those gases. The whole forge interior becomes an ignition point; not just refractory surfaces. Thus, secondary combustion is exponentially increased; ensuring that any leftover fuel from the primary flame envelope has plenty of time to completely burn off.

    If the equipment interior is red-hot, you should consider heat losses in combustion byproducts to be accumulate faster than radiant energy is being added. In yellow to white-hot forges, combustion losses are no longer faster than radiant energy gains. It is not possible to understand internal combustion processes in a modern forge or furnace as just a chemical process, because of added heat gain from highly radiating surfaces; such equipment is as much radiant oven as gas appliance.

     While exhaust flames from your forge can simply be the result of fuel that has not combusted because of fuel gas pressure being turned up too high, the more common cause of yellow exhaust flames is a large secondary flame (from a poorly designed, constructed, or tuned burner).

    I have noticed that fairly opaque yellow to orange flame can be created from some kinds refractory that are "cooking off" calcium from their binding agent; these flames will not abate until the process is complete. As the flame turns from yellow to orange, it becomes more transparent, and may even seem to sparkle in a manner reminiscent of fireworks, if the forge is running hot enough at the time.

    This does not preclude other colored flames, such as purple and blue from being present in the orange exhaust, but they are an indication of poor combustion, and must be ignored until the refractory finishes out-gassing. It is best to address one symptom at a time.

 

Caution: Blue exhaust flames are a sign of a reducing forge atmosphere, which even a perfect burner will give off, if its air intakes are choked enough. Be aware that blue exhaust flames will be accompanied by carbon monoxide production. Carbon monoxide monitors are cheap and effective health insurance.

 

 

Burner placement: The first question asked about burner positioning should be why; not where. Burner positions are always dependent, but not primarily on best circulation of hot gases; that is a tertiary concern. Flame impingement should be your first concern. The point where a burner's flame is aimed must be physically tough, up to thermal stress, and as far from the flame tip as you can manage.

    If your insulation is only protected by rigidizer and a thin seal coat, the flame needs to impinge on a high alumina kiln shelf or an exceptionally tough high alumina cast refractory floor (ex. Kast-O-lite 30). On the other hand, if the equipment’s interiors have a 1/2" or so thick layer of such a refractory, and is finished with a heat reflecting coating (such as Plistix 900), wall impingement is no longer a big issue; it's just one more factor, to be balanced against others of equal concern.

    You also want it to avoid flame impingement on workpieces or crucibles. If top mounted in a tunnel or “D” shaped forge, you would want the flame to strike as far from the first surface it will impinge on as possible. In that case, I now prefer to aim the flame diagonally downward at the far edge of the floor, so that it continues up the opposite wall, away from heating stock. The burner should be mounted at about three o’clock position. If you intend to employ crucibles in such a forge, use two smaller burners, with the crucible positioned between their flame paths. But why would you use top mounted burners in a forge these days? Only if you have a thin finish coating over ceramic wool insulation, instead of a 1/2” thick hard refractory flame layer over the insulation, which is also coated with a heat reflecting  coating, like Plistix 900.

    In most box forges, the burner was previously placed at the top. And the flame was aimed at the floor; the point of this was for the flame to impinge on the toughest surface that could be provided, so that weaker wall surfaces might be spared the ravages of flame impingement. High (purity) alumina kiln shelves, or high alumina-based refractories are one the most effective choices to employ as an equipment floor; this was the limitation for decades, but with better wall materials available at reasonable prices, this limit is fading; allowing burners placed high up on side walls, facing across the interior at the opposite wall, and passing over the work.

    The latest development in burner positioning is placing them low on the wall, or even in the floor, and aimed up and inward in “D” forges, and aiming across the top of oval forges; this requires cast refractory flame surfaces (with heat reflecting finish coats) in floor, walls, and ceiling.

     Circulation is also a concern; fortunately, this takes nowhere near as much encouragement as is commonly supposed. With today’s stronger burners, there is a natural tendency for hot gases to circulate within most forge and furnace shapes; including box forges. In fact, the only burner position that would greatly interfere with sufficient circulation of hot gases, would be with the flame aimed directly toward the exhaust opening!

Note: Positioning burners near the exhaust opening provides a close second to the previous example of exceptionally bad planning.

Mounting burner ports: Typically, a burner port (entrance structure) consists of a short steel tube or pipe with about 1/4” larger inside diameter than the burner flame retention nozzle’s outside diameter. This allows enough space to aim the burner somewhat within the portal.

    The burner is held in position and aimed, with two rows of thumbscrews; each row has three equidistant screws. One of the advantages of these screws is that they can hold a length of pipe or tube in place within the portal, and resting exactly where the flame is intended to impinge, while the portal opening is being ground into an oblong shape (to allow the tube to be aimed at a desired angle). This method ends up with a very close fit between tube and shell opening, to promote easy silver brazing of the port’s tube to the equipment shell. You are building a burner, so  employ it to help construct its forge. Why use six screws to hold the burner? After all, commercial forges mostly use only three screws to hold their burners; some have only a single screw. You are not trying to maximize profit on a product, but to build the best forge you can. Six screws allow flame impingement to be moved a little way, if your construction is less than perfect.

    Alternatively, you can drill and mount a burner port in the shell with three bent flat bars and some pop rivets, or screws. Bracketing parts together can end up looking tacky if you do not manage to keep the shell opening tolerances close. Employing screwed brackets can also be a be a minor pain, if the burner’s port tube is positioned at an angle.

    Welding equipment parts, such as burner ports unto a thin steel shell, takes a wire feed welding machine and a learning curve. Some people are reworded with distortion in the shell, because of welding contraction; it only takes a little time to learn to run a wire feed welder, and somewhat more to learn to bridge gaps with one; but it takes a lot more time to learn where and how much to weld without creating distortion. Neither hard brazing (braze welding), nor silver brazing creates that problem.

    Hard brazing requires an oxy/fuel torch and some skill, or an air/fuel torch with propylene fuel, and considerable skill. Silver brazing can be done with an air/fuel torch, propane, and close attention to setup as the only skill. But most silver brazing alloys will not bridge gaps wider than 0.005”. However, some aluminum/zinc-based flux core soldering alloys, like BLUEFIRE Low Temperature Aluminum Zinc Alloy Brazing Rods, do bridge small gaps, melt at 728 °F (387°C), and can be used to bond aluminum alloys, stainless and mild steels, iron, bronze, nickel, titanium, zinc, copper, and brass. It works best when their Silver Copper Brazing Flux Powder is employed along with the filler rods (good on mild and stainless steels, silver and copper alloys, and other metals).

    Silver brazing by hand torch benefits from a lower temperature filler with broad melting ranges, such as Ufhauser silver braze filler A-54N (54% silver/ ), which has a broad elastic range (250 °F), and bridges minor gaps (up to 0.012”); it can be considered something of a capping alloy (capable of forming a weld bead), but if heated too slowly it may suffer from liquation (where the alloy separates into solid and liquid zones); it can only be  remelted well above its normal brazing temperatures, afterward. For this reason, alloy A-54N should be heated rapidly through its melting range; it has a melting range between 1325 °F (dark red) and 1575 °F (bright red). If you are joining a thin shell from a tin can to a thicker tube, keep the flame mostly on the tube.

    This filler alloy has a good color match to steel. Reasonable care with a sanding drum or grinding stone in a die grinder or electric rotary tool, will easily produce a sufficiently close-fit in the joint between a burner portal tube and the forge shell’s opening. If you are silver brazing on stainless steel, I recommend polypropylene fuel gas (if you employ an air/fuel torch), and black brazing flux.

     Old car mufflers are zinc coated, and new mufflers are coated with an aluminum-zinc alloy. Silver brazing parts to this kind of forge shell will ensure lots of damage to the plating. Stay Brite silver solder may be employed afterward, if you don’t want to paint the forge shell. Some zinc-based soldering alloys are zinc-tin-lead (avoid these), zinc-tin-copper (excellent), or zinc-cadmium (use fume rated respirator with these and follow all safety guidelines to the letter).

Note: The main ingredient in zinc flux is zinc chloride (follow safety guidelines listed on its container); it is the only ingredient in many of them; it tends to “tin” the surface of steel, rather than just cleaning it. If steel is freshly cleaned and power buffed with stainless steel wire wheels, it can be zinc soldered without flux, but why do things the hard way? Zinc’s melting point is 787 °F; comfortably below its boiling point of1665 °F. Zinc fumes are easily seen and smelled; avoid them. Unlike lead fumes, it takes a much heavier dose of zinc vapors to cause fume fever. Unlike lead, the body can tolerate a little zinc, but keep your dose tiny; none is best. No metal fumes are good for your lungs.

Caution: All metals give off toxic fumes upon reaching their boiling points, and all are toxic; some are simply more toxic than others. Using zinc coated sheet metal or parts (such as old car mufflers) is okay, if you are careful about doing it. The boiling temperature of zinc (the point at which it makes fumes) is 1665 °F (bright red heat). Your forge shell should not get higher than one-fourth that temperature, during heating cycles. But you do need to be careful to keep the shell well away from the edge of the exhaust openings, by not cutting the openings in ceramic fiber, kiln shelf, or cast refractory next to the shell; see to it that there is at least ½” of distance between them. But zinc coated flame retention nozzles or mixing tubes need to be stripped of their coatings. There is no need to avoid zinc coated reducer fittings on a burner’s air openings. In other words, keep zinc away from part surfaces that may become incandescent.

Note: Preheat temperatures should be kept down to 600 °F (315 °C on zinc coated surfaces, such as old car mufflers, to avoid damage to the existing coating on their surfaces, and to keep scale formation down on the steel; “tinning” the bare steel with a zinc chloride-based flux will help with this. Remove all residual flux with hot water and a clean rag after silver soldering.

    Larry Zoeller (of Larry Zoeller Forge) is credited for first mounting schedule #40 pipe to a forge shell with conduit locking rings; he calls it a “burner holder assembly.” If you are looking for fast and easy, he sells them for $25 and shipping from his website. Their main limitation is that they can only position burners at right angles.

    Ideally, the burner port’s tube should be completely external to the forge shell; in any case, it should not extend inside the forge further than is needed to secure a locking ring.

    A washer should be provided to slide back and forth on the burner’s mixing tube near the outside of the portal, so that it can limit how much secondary air the burner flame can induce through the gap between the burner’s mixing tube and the portal wall. A nut can be silver brazed onto the washer, so that a thumbscrew can keep it positioned at the right distance away from the portal edge; limiting secondary air into the forge to only what is needed for complete combustion, without lowering internal temperatures needlessly. Considering air introduced from the burner opening as no different than air from other openings is a sad mistake, since those other openings do not have fast flames to induce air into the equipment.

Burner ports for brick forges may simply sit on the top of brick ceilings, for down facing burners; or be attached to a structure made of steel angle, and threaded rod, for side facing burners mounted high up on one of a brick forge’s side walls. Side mounted burners take a little more work, but pay it back in increased heat management.

Exhaust opening size: The last aspect of flame management, is the internal atmosphere’s exit point. One thing backyard casters and blacksmiths both worry about is how large to make exhaust openings on their equipment. Too small and you have high back pressure killing burner performance; too large and you cannot retain enough heat to do your work. Of course, the closer to the "right" opening size your equipment is the stronger the forge or furnace can be built. Just don't confuse the right size for a “perfect” size. With burner output that can by varied (turn-down range), there cannot be any such thing as a perfect opening size. The right size is what is needed to accommodate the burner's highest output (the highest you are willing to take it to), without creating a buildup of backpressure in the equipment.

    Variable is the optimal opening size; all other dimensions can be outright wrong, but are seldom just right, with a variable burner flame; this is one of the many reasons for controlling exhaust flow with an external baffle wall, positioned beyond an oversized exhaust opening; thus, permitting the least heat loss through radiation, while maintaining optimal pressure of circulating gases in the forge.

Note: It is smart to include a ring of hard cast refractory around the exhaust opening, which protrudes beyond the shell a little bit; diverting hot exhaust gasses away from the shell, where it would super-heat the metal.

    If you place a movable brick baffle wall in front of the forge, keep the bricks at a small distance from the exhaust opening (start with 1” of distance, and move farther or closer, to optimize internal pressure); this allows hot gases to move up and out, between the exhaust opening and brick wall, while generating heat from a re-emission coating on the near side of the bricks, and radiating it back into your forge. Keep the stock opening in the brick only as large as is needed to move parts through.

    This arrangement helps to slow the flow of expended gas in the forge interior to what is needed, and no more; as it gets close to the exhaust exit, the gas speeds up and through the opening; another desirable trade off. So, you are gaining hang time for the heated gas in the forge, and recuperative savings from emission of radiant energy; a win-win situation. A baffle wall also minimizes the impact of infrared and intense white light on your eyes and face, improving your health and comfort.

Doors: While a movable brick baffle wall is simpler to construct, maximum part clearance will be provided with a hinged and latched forge door (stainless-steel toggle latches make a good choice). The door structure should contain built-in interchangeable baffle plates (cut from high alumina kiln shelves), trapped in a steel angle frame. A door also makes building the refractory structures inside of equipment much easier, and permits larger parts to be heated than would pass through a smaller exhaust opening. Best of all, it allows closely contoured movable internal baffles to be employed, which would not pass through an exhaust opening; this promotes the use of a single burner to heat small parts, saving money in tunnel, oval, and “D” forges, which are run by two or more burners; on these forge shapes, the door is a step up from an exterior brick baffle wall; it should include  parts entrances (plates) with varied openings; for instance, with several plates cut from kiln shelves, which have different openings drilled and cut into them (for passing stock through); these can be exchanged, and held within a pocket structure on the door. These improvements do not all need to be seen to at once, so long as a hinged and latched door is bult onto the forge shell. On forge/furnaces, the door can be left as is, or can be attached to a single pin hinge, and revolved out of the way.

Sliding doors: Some people prefer vertical or horizontal sliding doors, instead of hinges. People usually employ the new tougher insulating bricks as sliding doors. High alumina kiln shelves are seven times more insulating than clay fire brick, but not as insulating as the new insulating fire bricks, now being used as linings for pizza ovens and home fireplaces; but high-alumina kiln shelves are tougher at incandescent temperatures than the new bricks; this is a consideration for something you will end up shoving parts back and forth through. Exchangeable kiln shelves, with different part openings drilled and cut into them are fine, but building an elaborate system of exchangeable kiln shelf parts, to ape the ability of bricks to infinitely vary their openings, comes under the heading of "gilding the Lilly." The additional energy savings it provides, probably is not worth the effort. Make up additional openings in kiln shelve baffle plates sparingly.

    Diamond or carbide coated rotary burrs (and diamond or carbide coated hole saws) are the preferred way to drill holes in kiln shelves. Friction cutoff blades (safest) and diamond coated blades (only of small diameter) are the best ways to cut out straight lines between those holes.

    A hinged and latched door, can also work on a box forge. Yet, movable bricks, trapped in an angle iron, or structural channel frame, will be more convenient than a hinged door, for most box forges. Furthermore, steel channel frames work best, for sliding those doors up and down on woven wire, while, running pulleys, and counter balanced with lead weights.

    You want to coat the hot-face side of either kind of door with one of the re-emission coatings. You can use a formula of 95% zirconia silicate powder (crushed zircon) and 5% Veegum (or 5% bentonite clay as an alternative); this mixture makes a tough heat reflective coating. The ingredients should be available in ceramic supply stores. Zirconium silicate can also be mixed with fumed silica to make a tuff and heat reflective coating on hard refractories, or on ceramic fiber products. There are other choices, Like Plistix 900F, but none of them are easily purchased in other countries. Zirconium silicate and bentonite clay should be readily available in pottery supply stores, all over the world.

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

Forge Floors: If you do not plan to do much forge welding, laying down a Kast-O-lite 30 floor over ceramic fiber insulation (or Morgan’s K26 insulating bricks) will provide a floor that is tough enough, and more insulating than kiln shelves. For occasional welding, some people use a stainless steel baking pan, filled with the kind of kitty litter that is made from pure bentonite clay bits to shield the forge floor from welding flux, But frequent welding is certain to slop flux onto a forge floor. A kiln shelf, that is trapped in slightly oversized slots in the forge shell, will pay for itself with the ability to be easily slid out and resurfaced, once its top is fouled with flux. Once the flux cools into a hardened glassy layer, a flap disc can remove it with little effort, before the widening puddle slops over the shelf’s edge. Do not forget to where safety glasses, and a dust mask, while grinding away the flux. If you are also going to use a tunnel forge as a casting furnace, the kiln shelf can simply lay on the round forge wall, when your forge/furnace is in the horizontal position.

Forge Shells: Variable shaped brick-pile forges can be mounted on a suitable (fireproof) surface, with nothing more than metal angles, and threaded round bar, to hold them together. “D” shaped, tunnel, and oval forges are best contained in Sheet metal shells. If the forge has sufficient insulation to keep its outer surface below 400 degrees Fahrenheit, aluminum can be used for its shell; otherwise, steel or stainless-steel is a better choice, because all aluminum alloys lose their temper at 400 degrees, becoming soft. Hex shaped forges (i.e., Modified tunnel and oval shapes) can employ noncombustible fireplace backer board as their shells. If you live in an area where sheet metal has become ridiculously overpriced, old appliances are another source of sheet metal. Coffee cans, car mufflers, propane cylinders, non-refillable Freon, or helium cylinders, and paint cans, all make satisfactory forge shells. Smaller “D” shaped forges were once made from mailboxes, but I do not think they are a worthwhile effort.

Insulation: Layers of ceramic fiber insulation 2” thick (in two 1” layers) can be pushed into shape inside of steel containers, and stiffened with colloidal silica rigidizer. After firing, the stiffened insulation will adequately support up to a ½” layer of hard refractory, in the bottom third of a cylindrical wall while it dries. The next hour, the cylinder can be rotated, and a further third can be covered, and the final third can be covered in the third hour. Remember to thoroughly wet down the older refractory area, where the freshly spread refractory will blend to it, to ensure complete adhesion between the old and new layers.

A double layer of insulation is usually used as the subfloor below forge floors.

Note: fumed silica in water is also known as colloidal silica. Silica (silicon oxide) is the main ingredient in common glass. However, glass has a much lower melting temperature than pure silica, because lime and potash are mixed into it, for the express purpose of lowering melting temperatures (the lime), and promoting the process of melting (the potash). Fumed silica easily melts initially, because the powder’s particles are so small that it has a tremendous amount of surface area, to promote the melting process. After the initial firing, this silica becomes pure quartz glass, and remelting it would take far higher temperature (3,133 °F; 1,723 °C). This is why fumed silica easily melts (once) on the surface of ceramic fibers, to rigidize fiber insulation. And why it also works as one of the binders in some high alumina refractories.

 

Working with castable refractory: There are several hard castable refractories used as flame faces in forges, and casting furnaces. So far, I think Kast-O-lite 30 serves best in both kinds of equipment.  You can carefully drill, grind, and scrape it, as the refractory is still setting up; this goes well enough, during the first hour, but far less easily after the refractory completely sets. During the week of curing, the refractory continues to harden, very like concrete.” In fact, castable refractory is a form of concrete; what sets it apart is that the chemically locked water that remains after curing can be—CAREFULLY—steamed out of the finished form by firing. Concrete cannot be fired; it simply explodes when heated; this difference is due to what is used as the binder in concrete; Portland cement. Aside from firing, the more familiar you are at working with concrete the more you already know about working with castable refractory.

    The other difference is that refractory has no rocks used as filler material; instead, refractory has ground up chunks of alumina rubble (aggregates), which help to stabilize the refractory against thermal shock. Insulating refractories, such as Kast-O-lite 30, also contains silica (or alumina) spheres, to create insulating voids, which are also crack interrupters, along with calcium aluminate cement for a binder.

    It was Kast-O-lite 30’s resistance to thermal cracking that first made it popular among home casting enthusiasts twenty-five years back. We were already using Perlite to make our own semi-insulating hard refractory. Kast-O-lite 30’s resistance to cracking during thermal cycling could not be matched by other refractories.

    Mixing and drying instructions for refractory mixtures will be found on the 55-pound bag it originally comes in; but mixing and curing instructions are less likely to be included with smaller amounts purchased from resellers online. The most used refractory in heating equipment is Kast-O-lite 30, because it is use-rated to 3000 degrees Fahrenheit, not inclined to thermal cracking, lighter weight, and is semi insulating. Kast-O-lite 30 is known as a gunning refractory, which means that it can be flung on walls of large industrial equipment through special nozzles, rather than only being cast in place; the qualities that makes it good for gunning, also make it useful for spreading in layers as thin as ¼” by hand troweling, onto the inside of curved internal surfaces.

Kast-O-lite has up to one year expected shelf life, if stored in a dry container at moderate room temperatures (50-70F); it should be mixed with no more than 20 percent water, and mixed for three minutes, then poured within ten minutes, into stout water tight forms for best results as cast forms. A small amount of vibration will improve the casting’s finish surfaces. Keep the casting covered with a damp towel during air curing, which takes between sixteen and twenty-four hours, and keep the casting above sixty degrees Fahrenheit while it is air drying, for a week, with the help of a small incandescent light bulb.

    The first thirty minutes of set up time is the most important, as the mix is changing from thick mud, into a solid. If you have cast horizontal mating surfaces for the upper and lower halves of a clam-shell forge, or vertical mating surfaces for the forge shell and door in a horizontal forge, you want to use the edge of a steel carpenter’s square, etc., to flatten the mating surfaces by scraping. If you did a good job of cutting and grinding forge shell’s edges for close tolerance, this is where it pays off.

    What if you did not? It isn’t too late to fix your mistake. Low places, which don’t meet up with mating surfaces can be filled in with Plistix 900F. Thoroughly clean, and then wet the surfaces where you lay the finish coat. Place wax paper over the top of the new layer, and then close the mating surface against it during drying and curing. The wax paper should come away from the dried surface easily; if not, just let it burn away during firing. High spots must be ground away. If you grind too far, just use the refractory coating to correct that mistake, too. Do not try to do the whole repair job at one time. Correct your mistakes one at a time.

    How much firing? Once the chemically locked water is driven out, is firing finished? No; most people consider this to be good enough, but without frequent firing during wet weather, the refractory can still slowly regain some water content from ambient air; necessitating the same careful fire drying routine you used during the initial firing, to keep the accumulated water content from cracking the refractory from internal accumulation of steam pressure; unless you take firing to the next step, which is called calcining. Basically, you heat the fired refractory up to yellow incandescence all the way through the form. It will begin on the inside surfaces (flame faces) and slowly soak through the refractory until it reaches its exterior surfaces (“cold” faces).

    Technically, calcining is the process of removing, by very high temperature (but below melting points), any volatile particulates, and finishing the oxidization of anything that can be oxidized, in a substance. Many of the constituents of a refractory mixture are separately calcined long before being included in the blend. But the cast refractory article may also be “calcined” at the melting point of glass to improve strength and durability, while making the refractory far less porous. One example of calcining would be fine porcelain, which is fired at higher temperatures for extended periods versus a ceramic coffee mug, which is minimally fired at much lower temperatures. One of the binding agents in most refractories is silicon. Some of the other constituents in many refractories are materials that contain silicon (like clay, which is likely to contain up to 40% silicon). When a fired refractory product is kept at high temperatures for an extended period, the silicon content begins to liquefy, gluing the other ingredients together more thoroughly, and filling in any micro gaps between refractory particles; effectively toughening and waterproofing the refractory.

    So, “calcining” is a word with a double meaning; its proper use is one thing, and the second use is closer to industrial slang. Despite all the good and honorable intentions of English teachers everywhere, industrial slang follows an extension of the ‘golden rule (“them what has the gold makes the rules”). In this case, “them what has the power makes the rules”). In other words, OEM sales departments choose what they consider proper industrial terms for their products. And, as with so many other lessons from the school of hard knocks, we can like it or lump it, but we are not going to change it.        

One correction Mike. Kastolite castable refractories do NOT DRY. This is a common mis-impression. The binder crystalizes into a solid by molecular bond between the water molecules and calcite molecules. It sets from as mixed to a semi solid quickly in approximately 15-20 minutes (IIR) depending on water added.

Once set it requires to be kept at 100% humidity to supply sufficient moisture for the calcites to crystalize adequately. Like Portland cement concrete, the calcites NEVER stops absorbing moisture and crystalizing.

As far as practical uses for our needs, the full strength cure time is 7 days at 100% humidity. Unlike Portland cement calcite binders those in Kastolite refractories will not become unbonded with the moisture at the rated temperature. The calcites in Portland cement are burnt lime or "Quick Lye" and so are not one type of calcite, the big horizontal drum in concrete batch plants is the roaster (whatever it's called) The plants receive lime stone gravel and it's roasted on site. Burnt lime is too unstable to ship as is inexpensively. So it's usually burnt, mixed and bagged for sale locally.

Anyway, Kastolite 30 does NOT dry it cures. If you treat it like it dries you WILL degrade it's performance, strength and max temp tolerance.

Yeah, I got sucked into this rabbit hole, partly because I had to study how Portland cement and other similar binding compounds work when I worked in the State materials lab.

Frosty The Lucky.

 

So, the practical difference would be that what is going on in the product is not calcining at all, but simply the silicon content partially melting in the voids?

Because I have deliberately taken Kast-O-lite 30 up high enough to make the change. And have also taken the product up just long enough to only change the inner part of a casting furnace's wall; when it cooled off, you could see the difference between the inner and outer thickness; they not only had different hues, but their was a line between the inner and outer portions of cast refractory.