Forges 101

[Mikey98118]

5 hours ago, localsmith said:

I acknowledge that you and frosty are experts in the field and I have learned a TON from both of you and am very thankful for the educational content you both have provided on here. I thought that most heat loss was from the size stock you put in the forge?

I should not have led with my expert status; I  apologize  for that. All that matters are facts.

[Frosty]

There are a lot of different criteria to observe or chase building anything. A criterion Ron Reil chased was low psi to the burner. Is it important? If lowest possible psi is your goal. Does it make a better burner? Only if it performs as needed. . . maybe.

You seem to be interested in fuel economy. How are you measuring it and why?  Your "why" may be entirely different than a fellow working in close quarters who needs to limit CO production because of limited ventilation. And so on.

I'm not interested in efficiency EXCEPT as a meter to help judge effectiveness. 

Your above question is easing YOU into the question of "most desirable." You keep saying fuel efficiency but when you start asking about minimum forge chamber size VS. work size you are square in the effectiveness zone. 

Of course there's a point of diminishing returns, it can be super efficient but if it takes a couple hours to heat the work what's the use? 

An efficient burner is EZ. PZ. Mike's are more efficient that a T because you can adjust the fuel air ratio in real time. An EFFICIENT burner is one that produces a NEUTRAL FLAME. PERIOD. It's also the most economical, it's squeezing all the energy from the fuel it has. 

Effectiveness comes with how you use it.

I'm in danger of blathering so I'll drop that for now.

You were asking about forge volume VS. work size. Once again there are variables lodged between a few physical limitations. These start with burner performance.

If you choose a gun then a number of variables go away as the blower simply forces the flame along the path requiring smaller exhaust, back pressure isn't as much of an issue.

If on the other hand you choose a Naturally Aspirated burner then Back Pressure is king. There MUST be sufficient path capacity to allow the flame and exhaust gasses to escape or the pressure build up will inhibit or kill the burner. Pffft. 

Whatever billet size you're planning on it MUST have enough annulus (space between the work and forge flame face) to allow for free flow. If for example you made a 4" x 4" chamber for a 3" x 3" billet there MIGHT  be enough space around it to allow flow without inhibiting the burner. 

I say MIGHT because I do NOT know, I'd have to experiment and see and I'm not going to. What I can surmise with some accuracy is the flame velocity will be high. 

I see 7x for the expansion ratio of the flame from the combustion air and propane. I don't know if that's accurate but for the purposes of discussion we can use it. 

For an annulus only 1" wide you'll have to align the burner nearly tangential to the forge liner and if it's square you'll be doing that to a flat face aimed at a perpendicular corner. Doable but not ideal.

So, let's assume there is enough annulus for the flame to expand and flow freely. How fast is it flowing? The faster the flame the less time it has in the forge to transfer energy to the forge liner to radiate back into your billet and work for you. 

Last I checked Ron's "small" forge followed the one each 3/4" burner per 300 cu/in chamber volume. The same ratio holds for any sized burner eg. a 1/2" mixing tube is 1/3 the diameter of a 3/4" tube and has an area of cross section 1/2 that of a 3/4" tube. The burner output is a function of the area of cross section of the mixing tube. I don't know if that's mathematically of fluid dynamically correct but it works as a rule of thumb for home built burners.

An almost too large burner for the forge volume will pump a LOT of energy per second into the liner and seeing as Ron was on a quest for the minimum possible propane psi. his burners had decently low nozzle velocity so the flame had decent hang time in a smaller forge chamber.

Hopefully that ramble is enough for you to figure out how much chamber you need for the burner you use to operate around the stock you wish to heat.

Another criteria you need to consider is what you are doing. If you are working on ONE thing at a time, say your hammer head. It's going to take time to bring to heat and soak through so a relatively thin hard refractory layer in the liner will do. You don't need recovery speed, if you work the piece until it's too cool to work a thick refractory liner still isn't going to have enough thermal mass to reheat your work quickly. You'll have some time to think, go to the head, sweep the floor, etc. it'll be a while.

On the other hand if you're do lots of tent stakes from RR spikes you'll be doing a couple few heats per spike and don't want to stand around waiting. You'll want to have several spikes in the forge at a time so you can cycle them through, work on one while the others are heating up. In this case having a liner with lots of thermal mass will provide a rapid recovery time. The flame heats the liner and the liner radiates IR heating your work. Soooo, a thin liner will lose heat quickly but a thick one will have collected much more energy and won't cool as far or quickly. The flame will be better able to keep the liner HOT enough for the rapid cycling of the work.

Efficiency is easy, a little experimentation will tell you how much burner will do what you need/want. Asking a bunch of guys on the internet can NOT tell you what YOU need. Sure lots will tell you but how can anybody but YOU actually know?

Fuel economy is WAY down the list of criteria for all practical intents and purposes. It's not like you're setting up a blacksmith shop with several employees working out of different forges. A 1/2" burner will use about 1/2 the fuel per hour as a 3/4" burner, not counting how hard you're pushing it. PERIOD.

By asking these questions you're demonstrating you don't have enough experience to know how fast you can work or what kind of work you'll end up doing a couple months or a year from now.

Designing an economy forge as your first one just isn't practical, you can't know what YOU will need or want. Heck, you can forge your hammer with a JABOD and a couple sacks of charcoal. 

Just build a basic propane forge knowing it's just the first. You'll be building more as you learn the craft. 

Not knowing what you want or need is why I encourage brick pile forges to beginners. They aren't labor intensive and don't lock you into making do with what you cast in concrete. Don't like the shape or size? Change it, move the burner, add another, make it big, small, in between.

I've been building propane forges going on 35 years and I bought a case of Morgan Ceramics, K-26 insulating fire brick because I always experiment with my next forge build with a brick pile. They're great for public demos, spectators may want to give smithing a try but building a propane forge can be intimidating enough they try something else. A pile of bricks and some plumbing fittings though? OH BABY YES that's something anybody can grasp and do.

Frosty The Lucky.

There are a lot of different criteria to observe or chase building anything. A criterion Ron Reil chased was low psi to the burner. Is it important? If lowest possible psi is your goal. Does it make a better burner? Only if it performs as needed. . . maybe.

You seem to be interested in fuel economy. How are you measuring it and why?  Your "why" may be entirely different than a fellow working in close quarters who needs to limit CO production because of limited ventilation. And so on.

I'm not interested in efficiency EXCEPT as a meter to help judge effectiveness. 

Your above question is easing YOU into the question of "most desirable." You keep saying fuel efficiency but when you start asking about minimum forge chamber size VS. work size you are square in the effectiveness zone. 

Of course there's a point of diminishing returns, it can be super efficient but if it takes a couple hours to heat the work what's the use? 

An efficient burner is EZ. PZ. Mike's are more efficient that a T because you can adjust the fuel air ratio in real time. An EFFICIENT burner is one that produces a NEUTRAL FLAME. PERIOD. It's also the most economical, it's squeezing all the energy from the fuel it has. 

Effectiveness comes with how you use it.

I'm in danger of blathering so I'll drop that for now.

You were asking about forge volume VS. work size. Once again there are variables lodged between a few physical limitations. These start with burner performance.

If you choose a gun then a number of variables go away as the blower simply forces the flame along the path requiring smaller exhaust, back pressure isn't as much of an issue.

If on the other hand you choose a Naturally Aspirated burner then Back Pressure is king. There MUST be sufficient path capacity to allow the flame and exhaust gasses to escape or the pressure build up will inhibit or kill the burner. Pffft. 

Whatever billet size you're planning on it MUST have enough annulus (space between the work and forge flame face) to allow for free flow. If for example you made a 4" x 4" chamber for a 3" x 3" billet there MIGHT  be enough space around it to allow flow without inhibiting the burner. 

I say MIGHT because I do NOT know, I'd have to experiment and see and I'm not going to. What I can surmise with some accuracy is the flame velocity will be high. 

I see 7x for the expansion ratio of the flame from the combustion air and propane. I don't know if that's accurate but for the purposes of discussion we can use it. 

For an annulus only 1" wide you'll have to align the burner nearly tangential to the forge liner and if it's square you'll be doing that to a flat face aimed at a perpendicular corner. Doable but not ideal.

So, let's assume there is enough annulus for the flame to expand and flow freely. How fast is it flowing? The faster the flame the less time it has in the forge to transfer energy to the forge liner to radiate back into your billet and work for you. 

Last I checked Ron's "small" forge followed the one each 3/4" burner per 300 cu/in chamber volume. The same ratio holds for any sized burner eg. a 1/2" mixing tube is 1/3 the diameter of a 3/4" tube and has an area of cross section 1/2 that of a 3/4" tube. The burner output is a function of the area of cross section of the mixing tube. I don't know if that's mathematically of fluid dynamically correct but it works as a rule of thumb for home built burners.

An almost too large burner for the forge volume will pump a LOT of energy per second into the liner and seeing as Ron was on a quest for the minimum possible propane psi. his burners had decently low nozzle velocity so the flame had decent hang time in a smaller forge chamber.

Hopefully that ramble is enough for you to figure out how much chamber you need for the burner you use to operate around the stock you wish to heat.

Another criteria you need to consider is what you are doing. If you are working on ONE thing at a time, say your hammer head. It's going to take time to bring to heat and soak through so a relatively thin hard refractory layer in the liner will do. You don't need recovery speed, if you work the piece until it's too cool to work a thick refractory liner still isn't going to have enough thermal mass to reheat your work quickly. You'll have some time to think, go to the head, sweep the floor, etc. it'll be a while.

On the other hand if you're do lots of tent stakes from RR spikes you'll be doing a couple few heats per spike and don't want to stand around waiting. You'll want to have several spikes in the forge at a time so you can cycle them through, work on one while the others are heating up. In this case having a liner with lots of thermal mass will provide a rapid recovery time. The flame heats the liner and the liner radiates IR heating your work. Soooo, a thin liner will lose heat quickly but a thick one will have collected much more energy and won't cool as far or quickly. The flame will be better able to keep the liner HOT enough for the rapid cycling of the work.

Efficiency is easy, a little experimentation will tell you how much burner will do what you need/want. Asking a bunch of guys on the internet can NOT tell you what YOU need. Sure lots will tell you but how can anybody but YOU actually know?

Fuel economy is WAY down the list of criteria for all practical intents and purposes. It's not like you're setting up a blacksmith shop with several employees working out of different forges. A 1/2" burner will use about 1/2 the fuel per hour as a 3/4" burner, not counting how hard you're pushing it. PERIOD.

By asking these questions you're demonstrating you don't have enough experience to know how fast you can work or what kind of work you'll end up doing a couple months or a year from now.

Designing an economy forge as your first one just isn't practical, you can't know what YOU will need or want. Heck, you can forge your hammer with a JABOD and a couple sacks of charcoal. 

Just build a basic propane forge knowing it's just the first. You'll be building more as you learn the craft. 

Not knowing what you want or need is why I encourage brick pile forges to beginners. They aren't labor intensive and don't lock you into making do with what you cast in concrete. Don't like the shape or size? Change it, move the burner, add another, make it big, small, in between.

I've been building propane forges going on 35 years and I bought a case of Morgan Ceramics, K-26 insulating fire brick because I always experiment with my next forge build with a brick pile. They're great for public demos, spectators may want to give smithing a try but building a propane forge can be intimidating enough they try something else. A pile of bricks and some plumbing fittings though? OH BABY YES that's something anybody can grasp and do.

Frosty The Lucky.

[Another FrankenBurner]

Ron Reil's main forge is massive.  I have spent many hours in front of it and never needed its full potential.  I believe it is 8 inch internal diameter, 24 inches long for ~1200 in³.  It has four 3/4" burners.  Though usually only the first one or two are used.  It was designed with minimal mass so that it would heat up to high temperatures quickly so not much in terms of "storing" heat.  He no longer employs the sliding back wall.  If you are after fuel savings, it is not the direction I recommend.

I have built many forges and quickly learned that I like the smallest forge that will do the job.  My go to forge is 43 in³.  It stretches the propane.  I have forged a 2.5 lb hammer with it, mostly just to do it.  I fought heat distribution a bit, having to turn the stock often, as the internal height and stock height were close.  For most other day to day things, it does exactly what I need it to.  When it doesn't, I fire up whichever forge does.

I would not forge weld with poor heat distribution.  Though, most things I forge weld are not very large and the little forge does great with that.  The biggest things I have found with forge welding are hitting the minimum temperature and not being oxidizing.  A smaller forge will hit that temperature with less fuel than a larger forge.  

As to forge volume and fuel consumption being linear, nope.  As Frosty has pointed out, even forge dimensions can drastically change fuel requirements.  More length, more friction.  Even if a forge was dimensionally scaled, it would have more or less surface area for loss.

My first forge was a freon cylinder forge.  About 3.5" ID by 12" length for ~115 in³.  It originally ran with a 3/4" modified sidearm burner.  I eventually replaced the burner with a 1/2" burner which used less fuel and the forge was able to obtain a higher temperature.  When the large burner was turned up beyond a certain point, the flames coming out the doors got bigger, but the forge didn't get much hotter.  This forge always had a large temperature gradient from the hot spot out.  Its length versus its other dimension was too different.  

 

[Mikey98118]

Good stuff, guys. But, what about external racks to keep large work off of the floor, so that the internal atmosphere can circulate around it? I mean, you presented him with an excellent brier patch, but lots not forget any thorny issues

Another FrankenBurner,

Have you tried two 3/8" burners in your Freon cylinder forge, instead of a single 1/2" burner? What, you thought you were already in the deep end of the pool? Mikey will glandly help you to find exiting new adventures

 

[Frosty]

Allowing flame to circulate all the way around the work is ideal. A person can texture a hard refractory floor in the direction of the flame flow. A modified tile trowel comes to mind. 

A short term spacer I've used is round soap stone marking "chalk." It'd work better if the soap stones were larger diameter and laying rectangular soap stones on edge is kind of unstable. But works okay, sort of.

Pieces of broken hard fire brick make decent spacers as well.

Frosty The Lucky.

[localsmith]

Frosty I really appreciate your post along with Mikeys. I have learned a TON from both of you and both of your recent posts have made me think more about what I'm looking for in a forge and why. 

In regards to why low fuel consumption is important to me, my first forge was a gas hog and I didn't know it until I designed a better burner. It required a psi of 12 just to reach forge welding heat on 1/2" X 1" flat stock. My current burner allows me to hit forge welding heat at 8psi which is a big improvement using the same sized orifice with the same sized stock.

For me fuel consumption and efficiency is extremely important because gas can be expensive and its in my experience that a forge that is more efficient burns hotter. If I can get a tank of propane to last 3X longer due to engineering improvements I'm all for it.

I've had burners that were so inefficient that they used 3X as much fuel as my current burner yet did not produce as hot of a forge interior. 

I considered designing a forge that was based off of the reverbative design that's out there but I don't like the fact that the front and back have to be closed up most of the time. I feel like the more I learn about burner design and forge design the hotter and more efficient I can make a forge. 

I'm always learning new things as I did not know that friction within the forge was a big deal. I figured that a smaller forge might reach the point of diminishing returns because I theorized that the smaller/shorter forge could possibly lose heat to the environment quicker since there is less total heat within the forge at any given moment which means there could potentially be more heat loss per minute compared to a larger forge. 

As an anecdote I read about your idea of using a polished stainless steel forge interior to potentially increase the IR heat being reflected within the forge and thought it was an interesting idea. 

[Mikey98118]

Frosty,

What you brought up about efficiency is not the same as effectiveness was good; most of us tend to lump these two issues together. Not consciously, but it's good to pay deliberate attention

Localsmith,

An exterior bar to hold the work pieces above the forge floor does the most good with large pieces. Efficiency, and effectiveness go hand in hand in burner design. But effectiveness is gained or loss with every detail in forge design.

A great burner that is poorly positioned on the forge shell, or pointed in the wrong direction, won't do well.

 The shape of the forge interior is as important as its volume. Several burners added to a long narrow forge is a recipe for back-pressure issues. But a long narrow forge could be adequately served with the right ribbon burner design.

There are only a few decisions that must be made correctly when designing the forge (burner openings, ceramic materials, and what kind of floor, etc.). Must decisions can fall into the category of add-ons; like a parts rack/bar/rest. Even a hinged and latched door on one or both ends can be carefully cut and remounted on a completed forge.

But, Frosty is right that most beginners would probably be happiest with a changeable brick-pile forge. Once they have made up their minds about what they most need, all those parts and materials can be recycled, if they are willing to give up that forge by then.

 

[Mikey98118]

I believe that, at present, Chile Forge is the top-of-the-line commercial forge for commercial work  (for a slower pace, I would go with a single burner Diamondback). Do I think there is a better forge for doing commercial work than the largest Chile forge? Yup; a properly built ribbon burner forge will get almost as hot with a smaller fuel bill, and should cost about one-six the money, plus sweat equity, to build. Do I believe this is true across the board, size wise? Nope; ribbon burners will always be most efficient in larger equipment.

    A gas forge made from a five-gallon propane cylinder is probably the smallest size I would heat with a ribbon burner, so it makes a good example to use, if we want to test the limits of ribbon burner superiority. Using two ½” high-speed tube burners, instead of a single ¾” burner, and a movable internal baffle wall, will allow this forge to equal the ribbon burner’s efficiency on small work, and that is as good as you can do; this isn’t a win against ribbon burners, but cuts your losses enough to extend how far single flame burners can compete with multi-flame burners. With smaller forge sizes, single flame burners, if well built, will hold their own.

    Every forge shape discussed below can also serve as an adequate casting furnace, with minor modifications. Tunnel forges mostly need extra legs to allow them to be placed in vertical and well as horizontal positions. Other shapes require internal movable/removable walls and a hinged and latched door.     I like oval forges because they are a strong shape, and therefore more portable, than a “D” shape forge, which should be mounted on a table. There is no denying that the “D” shape is a much easier and cheaper forge to build; its floor is completely flat, making it natural to employ Thermal Ceramic’s (a Morgan company) K26 tough and highly insulating firebrick to make it. The top and sides can be shaped by bending sheet metal over a propane cylinder. Rigidized ceramic wool will stay in place under the arched portion of its shell.

Size: Bigger is usually not better. Once a forge is outmatched by the workload it becomes a part-time tool. But an outsize forge quickly becomes an embarrassment collecting dust in a corner; the reason why is excessive fuel consumption. Even if you don’t mind the expense, the heat buildup in your shop won’t be welcome.

Shape is mostly a question of personal preference. You can always tell how personal by how loudly this view is denied. There are a few special duty designs, such and “clam shell” forges for wrought iron scrolls, and armor. At the other extreme are brick pile forges that can be reconfigured for special jobs; these are more likely to become popular since Thermal Ceramics started marketing Morgan K26 highly insulating firebricks. Long narrow shapes aren’t useful for much outside of picket twisting, or twisting ornamental “rope” for later use in baskets, etc.; it will take a ribbon burner to avoid back-pressure problems.

Box forges don’t necessarily need a solid shell; steel angle and thread stock will do just fine with insulating brick in their construction; this kind is also known as a brick-pile forge. Many people prefer sheet metal; in that case, it is important to remember not to attempt welding them completely. You need to have some movement possible in every direction, by placing in oversize holes or short slots at its top and bottom, to keep the form from being distorted during thermal cycling.

Farrier forges should be lightweight and physically hardy. Since farriers usually travel to ranch sites, their forges must withstand a lot of shocks; this must be taken into account in everything from your choice of refractory, to the construction of the legs (spring loaded are best). A wide box forge with minimum height is useful. Multiple small burners, placed high up on one side wall, aimed across the forge to the other side wall, serves well. One small high heat commercial clam shell shaped forge (its shell’s top doesn’t move) claims to be good for farrier work. Farrier forges are the only kind that won’t serve for casting.

Tunnel forges and furnaces are the most common shape because there are is a variety of steel containers that can be recycled for their use; they are the easiest shape to swirl heated internal atmospheres in. Cylinders also provide strong light shells, with good heat dissipation from ambient air currents.

Oval versus tunnel forges: I prefer oval forges because they are a strong shape, with most of the advantages of tunnel forges, except for ready made shells; in exchange for added construction work, their wider interiors accommodate more parts, or plate. However, their burners should be place at the side, and aimed slightly upward and toward the opposite wall, so that the flame passes over your work pieces, and down the far side, before touching steel. Furthermore, the flame face and floor should be made of high alumina castable refractory that is also oval shaped. So why do commercial oval forges use ceramic board for a flame face? Because these products have to survive shipment to the customer. I’m sure that you will be far more careful, when moving your own forge, than any shipping company would.

“D” forges: Are less portable than tunnel or oval forges; they should be mounted on a table. Both tunnel and oval forges do a better job of cooling down their shells. There is no denying that the “D” shape is a much easier and cheaper forge to build than an oval; its floor is completely flat, making it natural to employ Thermal Ceramic’s (a Morgan company) K26 tough and highly insulating firebrick in their floors. The top and sides of the shell can be shaped by bending sheet metal over a propane cylinder. Rigidized ceramic wool will stay in place under the arched portion of its shell. Smaller “D” shaped forges are usually built-in post boxes.

Clam-shell forges are most useful for large scroll work, bowls, and small round shields. But since top parts of this equipment are meant to be raised above their bottoms, so that their internal volume can be increased for parts like helmets, and reduced to keep fuel use down on flat work, they are easily employed in casting. Instead of solid walls insulating bricks are stacked between bottom and top.

[SinDoc]

Mikey, as you are effectively the God Father of burners *insert cheesy movie pun here*, I always enjoy reading your stuff as it is super informative (even if I dont understand all of it).

You say outside of Chile Forges, you would recommend Diamondback. Without straying too far from the main topic, why? I have been looking at picking up another forge to work with other than my Majestic. While I like my Majestic, it does seem to be a bit of a gas hog.

[Mikey98118]

5 hours ago, SinDoc said:

You say outside of Chile Forges, you would recommend Diamondback. Without straying too far from the main topic, why? I have been looking at picking up another forge to work with other than my Majestic. While I like my Majestic, it does seem to be a bit of a gas hog.

No; not outside of Chile, but right along side of it; Chile forges are outstanding; I'm really glad someone builds them; but they are kind of like a Roles Royce. If we only had a choice of Roles or nothing, poor boys would walk. Given a Choicd of Chile or nothing, beginners would walk.

So, what is good about Diamondback? Its price is relatively low; "it takes a whipping and keeps on ticking." It works well enough not to be a gas hog, and lasts as long as you like. Of course, I've only paid attention to their single burner forge; about the larger models, I haven't a clue.

We really need to coax more owners to discuss their forges; good, bad, or indifferent.

 

It might be closer to call me the Godfather of PICKY burners, and Frosty is the Godfather of practical burners.

5 hours ago, SinDoc said:

our stuff as it is super informative (even if I dont understand all of it)

You should speak right up, if you don't follow what I write. You may catch me out

[Frosty]

Oh Puuh LEEZE Mike! God father me no . . . things. I just adapted an existing device by detuning so it barely works and is easy to build. 

Localsmith: Where are you? There are probably a number of forum members living within visiting distance that would help you figure this stuff out. 

What's wrong with running 12psi? I run NARBs between 8-12psi and I get close to 15 hrs from a 40lb tank of propane. That comes to about $3/hr for a too large 2 burner forge. That's pretty economical for what it is. Just FYI, the NARBs have a stable usable flame from stop to stop on my 0-30psi regulator, zero to 35psi on the gauge. 

Were economy my main criterion I'd run a much smaller forge and only break out the large one when it was necessary. 

You need to stop watching online videos until you have a handle on how these things work, lots of the things you say just ain't true.

For example. Do you know what a "reverberatory" forge is? Whoever said you have to close all the openings sure doesn't. You can look these things up if you stick to the base terms. First is to remember what WE call "forges" are in reality, "furnaces." Special use furnaces but furnaces none the less. So, If you search "reverberatory forge," you'll get a load of hits written by guys who don't really know what's what. 

If on the other hand you use the terms, "reverberatory furnace," you get hits written by folk who know what they're talking about. Not all of them of course but the signal to noise ratio is MUCH better. 

Don't worry, I'll explain what reverberatory furnace means and how it works in a bit but I'm trying to work a couple things in I think will really help you figure things out faster and more reliably.

AND "noise to signal" ratio is an old radio operator's term meaning good signal, be it morse code, understandable voices or music compared to noise, static and such. Signal (good stuff) noise (Bad stuff) Yes? Places like Youtube and Facebook are 90%+ noise to signal and it's really hard to tell the difference until you have enough good knowledge to sort it out.

Back to reverberatory forges. That is EXACTLY what we're talking about making. I don't know how the word reverberatory applies but in this use it's a furnace that burns fuel to heat the furnace walls. The furnace walls radiate intense infra red radiation which is what heats the work inside. The burning fuel doesn't really heat the work directly, it heats the furnace and it's the furnace that heats the work. Make sense?

You need to start cooperating us here. We don't need to have know what YOU think efficient means, all you're doing is muddying the waters. You even got Mike using efficient when he meant to write EFFECTIVE.

Another unintended consequence being it reinforces YOUR mistaken understanding of the things and confuses other folks just learning how these things work. 

Telling us what you were thinking of trying is just noise. The unrealistic things you'd make IF they existed is noise. For example a burner that's 3x as efficient as yours. Just doing it right may be 3x better but we can't tell because you haven't told us what you DID.

What you DID and what happened is SIGNAL, we can evaluate that, ask intelligent questions and make suggestions. Can't do a thing with what you thought about if it were 3x better.

Repeatedly explaining what YOU mean is bordering on arguing with us. You asked us for help, how about you learn what WE mean instead?

You described your two forges and their performances well and we were able to evaluate them and explain the problems getting the performance you were hoping for. That's a good example of what we can do with SIGNAL. 

I'm not trying to give you a hard time but I'm doing WAY too much writing for nothing having to wade through the noise hunting for some signal. 

I don't want to chase you off. What I sincerely wish to do is help you build a good working forge or probably a couple.

BUT and this is fair warning, I'm not going to spend a bunch of time writing just to have it drowned in noise. 

Frosty The Lucky.

 

[Mikey98118]

The only fuels you should be concerned with are propane and propylene; both are LPG fuels (liquid petroleum gas); both are heavier than air. Adiabatic temperatures are the mathematically derived greatest possible combustion temperature of a given fuel; that of propane and propylene burning in air are about equal. The actual flame temperatures of air/propylene flames are a lot hotter than that of propane. Why? Because in the real world, how hot a flame burns depends on how well the burner’s design can combust the fuel; most hydrocarbon fuels will burn at about the same heat in a jet engine; the richer hydrocarbons will simply require less fuel. how hot they burn in a torch or burner varies widely.

    The so-called MAP gas, sold in 16 oz. yellow canisters at hardware stores is actually propylene; “MAP” is an advertising gimmick, that was probably meant to be confused with MAPP gas, which hasn’t been produced since 2008. MAPP flames were only rated fifty degrees hotter than propylene anyway.

    Propylene costs about twice the price of propane in canisters, but only about one-third more than propane in refillable cylinders down at your local welding supplies store. Since it provides about one-third more heat, this fuel might seem to produce no major advantage in heating equipment; but, no matter how cleverly you design a forge, to reduce exhaust speed, the gases lower limit depends on how much fuel must be combusted to attain desired internal temperatures. So, flame temperature, sets an unexpected limit on efficiency.

[Mikey98118]

Well, that was poorly put. The lower limit that depends on the heat of burner flames is the rate of gases being expelled.  Slowing the rate of flow out of the exhaust opening is a pretty big deal, since those gases are all through doing anything positive at that point.

Multi-fame burner heads, like ribbon burners, do a fine job of putting the breaks on exhaust speed.

Both careful positioning, and aiming of burners can lengthen the path of exhaust gases nicely.

But, the lower flame temperature is the greater the amount of fuel and air that must be combusted in obtaining desired temperatures.and so flame temperatures set the limits on how much good clever deigning can do.

[Mikey98118]

Two smaller equals one larger burner

Heat management is about more than how hot fuel burns. The reason flames 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 its hang time; depositing more combustion energy on internal surfaces. What isn't so clear is that the heat gained isn't added by hot gases blowing an extra foot or two at high speed; it’s due to a continuing drop in velocity over that added distance.

    Combustion gases begin to slow as soon as they leave the flame envelope, but small flames decelerate quicker than large flames. The flames of two 1/2" burners will use the same amount of fuel to produce an equal level of heat as a single 3/4” burner; but will drop velocity much faster in a five-gallon propane cylinder forge or, increasing efficiency; because they can burn faster/hotter without creating a wasteful tongue of fire out the exhaust opening. "Two is better than one" can be scaled down or up depending on forge size. Two 1/2" burners equal one 3/4" burner; two 3/8" to one 1/2; or two 3/4" equals one 1" burner.

[Frosty]

Going to tell them whether flame velocity or energy transfer is the cause or effect?

Frosty The Lucky.

[Mikey98118]

For the purpose of this discussion only...

Energy transfer is the desired effect that we want to effect

Flame velocity is a cause that is no longer desired 'cause it will adversely effect the desired effect--at this stage

Cheesy puns, but plain answers.

[Mikey98118]

If we are discussing flame faces, energy transfer onto them is a highly desired effect, but, even a few thousandths of an inch beyond that surface, we are faithfully trying to stop this effect from proceeding any further.

Exhaust flow is a necessary effect, that can become the cause of problems, if it isn't nicely controlled.

So, the what of things depends on when and where

[Mikey98118]

So, if our main goal is to raise surface temperature only on internal surfaces, with minimum penetration into the refractory beyond them, we come to the how and why of things. The answer to both questions is...re-radiation; commonly described as "heat reflection."

Thus, the last thing newbies are concerned with, becomes the first opportunity to get the most out of their equipment.

Is it time to discuss finish coats again?

[Mikey98118]

Sealing and high-emissive coatings for ceramic fibers and other inner surfaces

 

Rigidized ceramic fiber products still need to be sealed for safety. Furthermore the various coatings used for sealing tend to create a tough surface layer that holds high-emissive coatings from peeling away from the fiber’s surface; an irritating tendency that results from spreading high-emissive coatings directly on fiber products (those that aren’t rigidized first). Just as not all sealants are rated as high-emissive, not all high-emissive coatings are effective sealants, so we need to review the better-known products:

 

ITC-100 is strictly a high-emissive coating; Twenty years ago, I found that deliberately separating it by adding more water caused the non-colloidal particles to separate out, refining the coating, and greatly increasing its emission of radiant energy.

    I’m not sure it is the same formula today. But. you can make a better formula, for less money than this product now costs. 100% colloidal zirconium flour can be purchased from various labs and mixed with phosphoric acid to make a high-emissive coating rated above 90% “reflective” of radiant heat. 

    Some hobbyists concoct a tough sealant coating that is also a high-emissive product; they purchase zirconium silicate flour from a pottery supplies store, and mix it down with clay powder.  Zirconium silicate, while very tough is only rated at about 70% heat reflective, but I think this figure is misleading; since the other part of its structure is clear natural crystal, which will pass light rays with very little interference, and since the actual mechanism for its “heat reflection” is re-radiance, I believe its overall performance in thicker layers will prove to be considerably higher than 70%; it is also very resistant to borax, and an economical choice.

Others make a slurry of Zircopax to colloidal silica.

 

Plistix 900 is rated at 70% heat reflection, and makes a tough smooth sealing coat rated for use at 3400°F.

 

Matrikote 90 AC Ceramic Coating (one of the product line from Allied Minerals) is a very tough hard 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 especially 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 for use 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.

 

[Frosty]

On 12/30/2021 at 11:11 AM, Mikey98118 said:

For the purpose of this discussion only...

Energy transfer is the desired effect that we want to effect

Flame velocity is a cause that is no longer desired 'cause it will adversely effect the desired effect--at this stage

Cheesy puns, but plain answers.

 Sorry to be slow but I've been under the weather.

I see you've never really thought about it have you? 

There are only two ways to lower the velocity of a HOT flame, disperse it across a large nozzle or leach the energy. 

Keeping the flame in the furnace chamber longer means it must transfer energy to the cooler liner, lowering it's velocity. If nothing else cooling causes it to shrink, less volume passing through an orifice travels more slowly.

The lowering velocity does not heat the liner, heating the liner lowers the velocity.  Lower velocity is the effect of transferring energy to the liner.

In the real world of making an effective burner forge device the above tidbit has no effect. It's just a factoid and I tossed it at Mikey to rattle his cage a bit. 

Not being able to  respond to his reply in a timely manner would make it trollish but I wasn't trolling. Honest.  

Frosty The Lucky.

[Mikey98118]

Alas, our arguments are reduced to nuances, but if you say a dozen and I say twelve, people listening can only benefit From different viewpoints. Heard any good jokes?

 

[Frosty]

Yeah, it's true. What does it say about me that I still have to finish  thought a week or two after it's past it's "interesting" date?

There were some pretty good puns about Deb's upcoming knee replacement rolling in. Other than that if I've heard any jokes I don't remember. <sigh>

You?

Frosty The Lucky.

[Irondragon Forge ClayWorks]

The only joke I have heard lately would get me banned.

[Mikey98118]

I do like it when humor breaks out around here. It's like a reality break

[Mikey98118]

On 1/8/2022 at 6:46 PM, Frosty said:

There were some pretty good puns about Deb's upcoming knee replacement rolling in.

Sorry to hear that. Kathy has been putting it off for over two decades. I think she is hoping they'll outlast her. And youngsters think old age is boring...it's more like a wild ride. Of course a heart attack and two strokes did wonders for my never-satisfied attitude. Just getting back up off the floor is quite the adventure these days