Hi all.

 

In addition to my other post about my new coal forge, I'm using the January slow period to rebuild my gas forge as well. I have a double burner (venturi) built from an old 13kg butane bottle and soft firebrick. The burners are from a cheap Vevor forge I bought a couple of years ago. I made a mistake in building the forge in putting hard brick in as a non-removable floor and it just sucked all the heat out of everything. Took an age to heat up. Since then I'm layering half cut soft bricks on top but they are disintegrating and take up half of my forge volume. The problem I'm having with my burners is that the flame keeps puttering out, which is usually a sign of running out of gas, but it's a new bottle. It will only stay lit for less than a minute some times, and im getting about 1 heat before having to relight it.

 

So, I'm going to build a new forge. I'm doing another gas bottle design (it makes a great container). I want to make the best forge I can, so It will do me for several years. I have a good blower so I'm thinking that a forged air ribbon burner might be the best option, but I dont know anyone with a ribbon burner so I've never been able to compare. My main focus is on gas efficiency. My current forge runs on next to nothing (a 47kg propane bottle lasts me 3 months as a fulltime smith). So would a forced air ribbon be the most gas efficient way to go? (understanding that it takes a lot more effort to build) (I'm also not sure how a naturally aspirated ribbon works tbh). Also, would forcing the gas and air into the forge at a constant pressure rather than relying on air being drawn in by the gas flow also fix the issue of the forge going out and puttering?

 

I think if I want to make the most effective forge I can, I probably also need to move away from soft firebrick and towards ceramic wool. oh dear.

 

As always, love ya feedback. Thanks

I’ve only built naturally aspirated ribbon burners myself, but I’ve also used a forced air one in Latticino’s shop. I like both, but the NARB has the advantages of being a bit quieter than the FARB (although this depends on the motor one chooses) and not needing an external power source. This latter is relevant if you’re likely to lose power or (as in my case) you need the one extension cord in the shop for something else.

I'm not too bothered with the noise to be honest, ill be using the same blower as I hook up to my coal forge (bounce house blower). The gas forge I've got at the moment is loud as all hell. And I have very stable electricity. My main focus and concern is: gas efficiency as much as possible and a stable burner. The problem I have at the moment with my venturi burners lighting and burning for a while and then going out and spluttering. I'm wondering if a forced airflow would stop this happening?

23 minutes ago, Drunken Dwarf Iron said:

And I have very stable electricity.

Don't count on this, being wrong could cost you and others their lives.  If building a ribbon burner forge, make sure you install an NC (normally closed) valve in the propane line.  This valve only opens when there is power and will close when power is lost.  

thats a good shout tbh, but easily included

Edited December 14, 2025Dec 14 by Mod34
Removed unnecessary quote.

actually, yeah. Now I think about it, would wire a NC valve into the on switch for the blower. So gas would only be allowed in when the blower is recieving power

A couple points though I'm sure more will occur as I write. First, efficient is simply a matter of adjusting the fuel air ratio for a neutral flame. Period. What you actually want is an effective forge, one that performs as desired with minimal waste. It is up to the operator when to light it and shut it down. 

I'm not picking semantic nits, it can make real world difference placing and filling orders.

Whether a burner is Naturally Aspirated (NA) or blown (Gun) only determines how the fuel and air is supplied to the furnace. Both have advantages and disadvantages.

Blowers are actually louder than NA devices but are easily muffled by placing them in an enclosure to isolate the fan from the shop floor. Often the noise can be reduced enough to live with by simply aiming the intake side away from the room towards something that doesn't reflect sound like a concrete wall or resonates like an uninsulated plywood wall. 

One of the main issues is the volume of your proposed forge, it's awfully small for a gun burner though small blowers are common enough. Making a multiple outlet burner to make the forge atmosphere (thermal) you need is just plumbing.

Building gun burners is easy but you must adjust them every time you want to change the temperature in the forge.

Making a NA burner requires more precision and basic tools but once adjusted changing temperature is just a matter of increasing or decreasing butane pressure, the velocity of the fuel gas determines the volume of combustion air induced into the mixing tube. 

Either type burner has it's advantages and disadvantages but either will do the job. 

There are safety devices that can close the fuel line automatically if the fire goes out. Some look for a flame, heat, raw gas, lack of combustion byproducts and I'm sure ones I don't know about. These devices are something to discuss with a furnace supply / repair business. 

And ABSOLUTELY have CO (Carbon Monoxide) monitor alarms mounted about head high in the building!

Cylindrical gas forge discussions and plans are covered in great depth in the Forges 101 section of the Iforge forum. 

The basic build is simple. Two layers of 1" 8lb. ceramic refractory blanket. cut a LITTLE larger than necessary to cover the inside of the forge so it holds itself in place by compression. Please don't make me tell you the inner layer needs to fit the ID of the outer layer. Yes?

Once the outer layer is in place and the burner port holes are drilled you want to "rigidize" it. We've found that simply mixing fumed (colloidal) silica powder and clean fresh water with a couple drops of food coloring so you can see the coverage. works nicely. Don't mix it thick, if some won't go into suspension it's saturated and will NOT hold more.

Spritz the blanket with water so the rigidizer solution can flow along the fibers collect at intersections, bond and actually work as necessary. This is called buttering, the exact same process and reason you see masons dipping bricks in and brushing the previous course with water before setting them in the mortar.

Butter the blanket and spray on the rigidizer solution, the food coloring indicates how heavy the solution is in any given location, even and well dosed is good. You can't really apply too much rigidizer but the point of diminishing returns is pretty low so don't get silly. Same for buttering, you should however drill a couple drain holes in the bottom of the shell so any moisture can escape when you light a fire. Water vapor is a byproduct of combustion and WILL infiltrate the refractory collecting against the shell because it's cooler. You REALLY want a way for steam to escape non-energetically!

Anyway, after applying the rigidizer, light the burners and heat the refractory to red, more is unnecessary. Red heat vitrifies the near microscopic particles of silica and locks the refractory fibers together at intersections. This does two things, the most important it prevents particles that break from floating around in your breathable air. Enough exposure can cause a silicosis like condition that is best to avoid. The second thing it does is make the blanket stiffer and considerably more durable. The hard flame face refractory layer if applied on a soft resilient subsurface will break up when pressed on. Think sheet of window glass on a foam pad. 

Once the outer layer is installed and rigidized fit the inner layer and rigidize as before. 

The last step is applying the "water setting high alumina refractory flame face layer." It's a mouthful I know but it's important. Water setting means you mix the dry product with JUST ENOUGH water you can trowel in onto the blanket in a thin 1/4" - 3/8" thick layer. AFTER you butter the blanket!! Yes?

Clear and apply 2 layers to the burner ports, just like you rigidized and cured. Applying two 1/4" layers to the ports will decrease their diameter by an inch so drill or cut the holes large enough the ports are larger than the ID of the burners. Who forgot to mention that before?

The reason to apply multiple thin layers instead of one thick one is durability. The hard refractory WILL crack and spall, thin layers flake off thin flakes which are easy to patch. Thick layers tend to flake and spall all the way to the blanket requiring you remove the liner and replace it. It also takes much less than half the time to apply multiple thin layers than single thick layers and shrink checking (cracking as it sets just like concrete) is less and does not penetrate the entire hard layer. 

If you watch how to videos made by companies selling low end gas forges like Vevor, they paint their refractory on with a brush at a consistency like latex house paint. Their liners do NOT last worth spit and can't be patched. 

The water setting high alumina refractory that seems to be the current standard this side of the pond is "Kastolite 30 li. It's a "bubble" refractory, part of the aggregate is evacuated silica spherules which do two good things, commercially they're used to make the refractory physically lighter and withstand the expansion and contraction of thermal cycling better. A third and lesser effect is insulation. 

The refractory is marked world wide under different names and made by different manufacturers. HWI makes and sells it here, I don't know about the UK though.

The alumina binder in the refractory makes it borax base forge welding flux resistant and also give it a higher max working temp. 

A flat floor in the forge can be made easily enough by laying a narrow layer of refractory blanket on the bottom with the edges feathered for a smooth transition from flat floor to curved walls. An easy visual is to draw a circle with a straight horizontal line across the bottom. The space between horizontal line and circle represents a cross section of the refractory layer for the floor. It gets rigidized and a hard refractory layer at the same time as the rest of the forge. 

I do NOT recommend a firebrick of any kind as a floor in a forge. They don't really serve a good purpose in a well build forge made with kiln washed modern refractories.

The last step is applying a high alumina kiln wash, this is a last layer of armor for the forge and available from kiln suppliers. It is used to prevent pottery and glaze from firing to kiln furniture and is an excellent finish in gas forges. It fires hard and slick like a glazed cup and if it contains alumina is very resistant to welding fluxes.

Orienting the burner(s) is important to heat the refractory liner evenly. The burner flame isn't what heats the stock, it heats the liner to incandescent yellow and the re-radiated IR is what heats the stock.

Old thinking is to aim the burner straight down at the floor. It works, the random turbulence as the flame disperses 2 dimensionally on the floor then up the walls heats the liner but also blows more flame out the doorways. 

Current thought is to orient the burner(s) so the flame induces a swirl in the chamber, heating it more quickly and thoroughly while less flame is aimed directly out the doors. Of course the doors are the only path for exhaust to escape but there's no good reason to aim it out. Some folk like to orient the flame along the top of the forge so it flows down the far wall and around. The other method is to orient the flames to impinge on the floor less than halfway across directing them up the far side and around. 

Both have pros and cons we can get into later, my fingers are wanting a break and I've probably exceeded my ramble on limit for a while. I've also said more than enough to give you plenty to think about for a while.

I check in regularly and am happy to help so give a shout I'll get back.

Frosty The Lucky.

 

 

Hi Frosty, always a pleasure. And a REALLY helpful post. I was absolutely going to go through the gas forge 101 section with the actual building technique, but that was a really useful description to go through. Thanks.

So my current forge I have my burners coming in at approximately a 45degree angle to create a bit of a flow round the forge volume rather than pointing straight down onto the piece, however it is still pointed at the middle of the forge floor. And I agree, there isn't place for fire bricks in the floor, I was aware I'd made a mistake there the moment I'd finished the build

I've never actually heard them described as "Gun Burners", that's an interesting new bit of lingo. Yes, there is a difference between effective and efficient, I guess what I am looking for is a forge that allows me to do the amount of forging I do now without getting through any more gas. But most importantly without fuss. At the moment, my forge is out of action for a few days while I tinker with whatever is wrong with my burners. I think what I was expecting from forced air burners is less of a pain with tuning and getting it to run consistently as you're not relying on the exact pressure of propane drawing in the right amount of air, you're forcing it in. Also I was under the impression that the main efficiency gain with ribbon burners is that with many small flames rather than one big one, theyre providing a more spread and even heat, and more of the combustion is being completed before it leaves the forge.

I just get really frustrated getting this stuff wrong, y'know. There's enough imposter syndrome trying to do this for a living as it is

2 hours ago, Drunken Dwarf Iron said:

Also I was under the impression that the main efficiency gain with ribbon burners is that with many small flames rather than one big one, they're providing a more spread and even heat, and more of the combustion is being completed before it leaves the forge.

Than your impression majors on the minors. Using many small flames, spread apart will tend to more evenly distribute heat. I say tend to, not because they will not, but because it is only one path to that goal. 

I say majoring on the minors because, NO, that is not the main advantage of multi-flame burner heads or burner nozzles. To get the hottest flame from any given fuel, the flame takes a fair amount of acceleration. Without starting some endless debate about how much acceleration serves a burner best, I will simply move on to a faster flame's downside; rapid venting out of the exhaust opening. 

Here is the crux of the matter: The larger the flame the longer the distance required for it to slow down before being vented. So a bunch of fast hot little flames will slow down to minimum speed sooner before being vented; this means that atmospheric exchange happens slower; slowing vent speed (which sets minimum speed) even more. This is a win win situation for forge efficiency 

My old way too large shop forge still has split hard firebrick floors, replacing them was cheaper and way faster than replacing the 20" x 20" one piece cast in place refractory floor I built in originally. I actually cast it into the angle iron frame with 1/4" round welded across side to side and corner to corner like I was laying rebar in a concrete form. talk about clueless.

Your burner is aimed just fine.

I heard the term gun burner from the guy repairing our furnace. He corrected me as soon as I said blown burner. I'd started pumping him about burners and learned a lot of general information. I've seen them called other things, one IIRC was someone in the UK but that was a long time ago.

It's hard to tell what might be the problem with your burners but them shutting down after they've been burning a while probably means a bad design. If you post some pictures of them we might have some ideas.

Something Mike never seems to say about the benefits of multiple outlet burners is the slower over all flame speed. sure the small flames are moving faster but not for very far. This means that the flame stays in the forge longer so it will shed more energy to the liner to be reradiated as IR to heat your work.

Frosty The Lucky.

Drunken Iron Dwarf (DID), as you are based in Blighty, you have access to the UK-made AMAL propane injectors, without having to pay for exorbitant shipping across the Pond.

I used a 3/4" AMAL injector with about 9" of malleable iron pipe, threaded at the ends (usually referred to as "Nipple") and have used it successfully as a single-port burner, and as the feed into a multi-port burner (NARB - Normally Aspirated Ribbon Burner) that I made out of a soft firebrick.  I found the NARB was much quieter, and required much less gas for the same amount of Yellow heat in my forge, due to it almost eliminating the "Dragon's Breath" (wasted heat) I was getting with the high-velocity single-port burner. Having used a NARB I'm never going back to single-port burner.

I started my NARB development journey half-way down Page19 of the "Naturally Aspirated Ribbon Burner. Photo heavy" thread, if you are interested.
Also I've been using alternative solutions to refractory coatings for my forges, as it is a pain to get Kastolite30 high-alumina insulating refractory, this side of the Pond.

Good luck with your build.
Tink!

Good to see you Tink! Nothing beats local knowledge for this sort of thing.

Frosty The Lucky.

sorry for going AWOL from the conversation, was driving across the country most of the day after spending the weekend with the in-laws. This is awesome advice and information, as usual. Thanks for chiming in Tinker Tim, it is really useful having the experience of someone who has access to the same stuff as I do. 

I'm going to dig into the NARB thread, and tomorrow when I get into the workshop I will take photos/video of my burners failing at their one job. My concern has been that if I'm going to rebuild, I want to build the best option I am able to, and if thats a NARB then that's that. Also, something that I know is not going to be as unreliable as my current burners. What may help with that is a more solid understanding of why they are failing, so taking some pics/video of them may help in that regard.

(AWOL) Absconded With Old Lorry?

There's no time clock here and the holiday season is really getting going so folks are haring off all the time. I hope you had a good visit.

While I've never used one I've heard plenty. If you switch to AMAL injectors you'll be golden. They're good strong stable burners. 

Next step is building a forge to put them in. 

Frosty The Lucky.

Good Morning, 

I have had an AMAL 3/4" injector/Burner in one of the Blacksmith Association (VIBA) Forges for a few years. The people who use that Forge, don't have to make any adjustments, other than adjusting the pressure up to get it going, then backing it down. It takes a Lickin' an comes back Kickin'. I bought a spare and I haven't had to use it.

Neil

I know nothing about AMAL burners; what I do know is that underestimating any UK made propane equipment is not a smart move. Back in 2006 I purchased a high end UK manufactured propane torch, because it was England that first designed air-fuel brazing equipment, and perfected it. So I figured they probably still had plenty of tricks to show me about manipulating gas flames. I wasn't disappointed. However, the buyer needs to be sure that the equipment is UK built; not just repackaged Chinese stuff.

Been a while since you studied the martial arts Mike?

A first principle is, "never underestimate anybody." It delves into the tactics of mistake after that. 

Sorry for the sidetrack but it happens to me all the time. Unless I'm mistaken old Blighty was using various gas injectors before America was a colony. Though CO isn't my favorite lamp of stove fuel.

Frosty The Lucky.

Could you document the build of the forge including the burner(s)?

I'm running against the limits of my current forge. And looking for inspiration

So, I've had a better look at the AMAL injectors and they look fabulous. Definitely better than something I could put together. Not as expensive as I expected either tbh. I've attached photos of my current terrible burners.

I think my next job is going to be to load the forum on my tablet, get a large mug of tea and read through the whole NARB thread. I have questions about yours TinkerTim, I see you'd mounted the pipe onto the side of your burner and I have questions about orientation etc, but I'll read the thread first. Most questions I may have have probably already been answered. I like the idea of being able to use a soft firebrick as the ribbon insert as yeah, some of the common american refractories seem to be a nightmare to get hold of.

I will be back in, however long it takes me to read a monster thread

4 hours ago, Drunken Dwarf Iron said:

I like the idea of being able to use a soft firebrick as the ribbon insert as yeah, some of the common American refractories seem to be a nightmare to get hold of.

Well, to begin with the most famous "American" refractory series; Kast-O-lite, which we use to make ribbon burners, is a Morgan product; this is an international company that makes their products in several countries for convenience sake. You should know that they started in England and probably still manufacture lots of their stuff there. Your confusion comes from the brand names that their subsidiaries slap on the parent company's products. I would suggest that you look up the Kast-O-lite refractory line, and study its composition and characteristics. Then look for a matching or similar local refractory. Once you have mastered this hurdle, please inform your countrymen, to save them this hassle.

  Finally, you should know that Kast-O-lite 30 is simply a standard high alumina refractory (about 67% alumina to clay content and a binder) with tiny glass bubbles added to do all the 'magic' in this product. You should be able to buy bubble alumina, or its cheaper glass alternative at a concrete supply house.

  Before Kast-O-lite 30 started being marketed, hobby casters used Perlite to do the same jobs as glass bubble alumina; it worked just fine, but why bother when we could buy  Kast-O-lite 30 for the same price as the commercial refractories that others were using to mix with Perlite? The homemade product came with minor risks and the Kast-O-lite was risk free.

Well, what minor risks? People would go overboard with the Perlite, to get more insulation value from their refractory. The limit should be one-third Perlite by valume, but people will do what they do 

  Before we they got clued in to Perlite, home casters used sawdust, which would burn out during firing, leaving insulating voids in the refractory body. However they made no improvement over other refractories when it came to crack resistance; Perlite did, and so does any refractory that includes bubble alumina or glass bubbles. Crack resistance is what made Kast-O-lite refractories famous. 

19 hours ago, Drunken Dwarf Iron said:

I've had a better look at the AMAL injectors and they look fabulous.

They’re all the same. If you’ve seen one, you’ve seen AMAL. 

I'm up to page 14 of the NARB thread, getting through it

Looks like it's definately the way to go, with an AMAL injector.

JHCC, did you find that mounting gas pipe pointing up rather than horizontal or down introduced any issues? I like the way my burners are currently directed (45degree angle from the top) but the way I would like to ideally lay that out would be an upwards facing pipe and an additional 45 degree elbow, and I dont know what that would do to air velocity

Short answer: no.

Longer answer: nnnnnnnnnnnnnnnnnnnnnnoooooooooooooooooooooooooooooo.

Actual longer answer: The NARB is essentially unaffected by gravity, so whether it points up, down, sideways, or 'round the mulberry bush* doesn't really make much difference. The most important thing is to position it so that it isn't affected by the exhaust gasses from the forge.

 

 

*Or prickly pear, if you're thinking more T. S. Eliot than Mother Goose.

hah. Good to know. So direction against gravity is unimportant, what about additional bends in the path? like this?

I'd personally recommend having the ribbon mounted so that it blows horizontally, with the flame coiling around the inside of the forge, rather than at the angle shown, with the flame directed at the floor.