Forge Build: Ribbon Burner

[RockLobster]

I’m in the process of building a forge and plan to use this thread as a place to document this build.  Please feel free to use any of this information or provide helpful comments.

A little about me and my thoughts for this build:  I’m relatively new to smiting.  I’ve taken a number of classes on blade making and blacksmithing but now the time has come to set up my own shop.  This is a hobby for me but I take pride in having a quality setup.  Initially I planned to buy a middle tier propane forge but I enjoy fabrication and thought I would enjoy building my own forge to my standards.  After some research on various forge styles I settled on a ribbon burner propane forge.  The inspiration for the design comes from a forge I used at The Steel Yard in Providence RI, so I have a good idea of the functionality I’m looking for.  It may be slightly more complicated than is necessary but as I said, I enjoy the fabrication process. 

The initial design (REVA):

My initial thoughts for the design are as follows, this is likely to be subject to change as I get deeper into this project.  I have access to CAD (solidworks) so I’m able to fully model this before I get to building.  I also plan to make a full drawing set and post it here for anyone to use, once the design has been proven to work.

The forge body will be formed from 11 GA steel plate.  Two halves welded together to form an octagon shape 18” wide with an overall length of 20”.  Insulation will be 2” of Inswool covered by ¾” Kastolite-30 refractory mortar.  The floor is sized to allow for (QTY:4) half thickness fire bricks to be placed as a sacrificial floor and easily replaceable.  The front door will open vertically on a cable pulley system.  Right now I’ve got a handle mounted to the side to actuate the door but this may change once I see how I like the function.  The rear door is a less complicated peg & hole hanger system and will have a removable handle so it can be moved while hot.

Burner:  The burner body is a 3” x 3” x 1/8” tube, 12” long, with mixing baffle, and 2” NPT pipe union.  It will be cast from Mizzou using the straw method with (QTY: 41) 0.30” holes.  The burner slides into the forge and bolts in place as to be removable for future repairs.      

Forge Stand & Blower:  I also plan to make a steel table for the forge to sit on which will hold the blower.  Design for this to come later.

 

So for I have fabricated the ribbon burner weldment assembly.  

[Latticino]

Couple of comments:

1. Going to be a rather large forge.  Are you planning on doing architectural forgings, or have a power hammer or hydraulic press?
2. Make sure you build in some slop in your front door guides.  As the door heats up it will expand.
3. Consider extending your castable past the metal door openings of the forge proper and past the framing around the doors themselves.  In the current configuration you will get heat transfer to the forge liner and door frame.  These will see scaling and warpage.
4. Might want to add a counterweight to the front door system, or some form of toggle ratchet.  Otherwise what holds it open when you move to do forging?
5. Make sure you include a gap of some sort for venting when the doors are "closed"
6. With that baffle and 4" thick burner block you will need to be sure to select an appropriate high pressure blower.

[RockLobster]

18 hours ago, Latticino said:

Couple of comments:

1.  I want a good sized forge, one with a rather wide mouth.  I plan on making decretive iron railing sections and also want the ability to forge a good sized axe head.  It’s similar in volume to one I’ve used before.  I’m more hoping that I will find the burner is well sized for the volume.  No power hammer but I've already got ideas on making a press as my work does hydraulics. 
    
2. I plan to leave ¼” gap.  I’ll mill down angle iron for make the track.
    
3. Good advice, I was thinking I may need to alter the casting a bit for this reason.  I’m planning to use an interior form while casting the refractory.  The casting will probably need to be done in two parts to get the form out.  I’m hoping that won’t leave a seam between the two cast sections which would be prone to failure.
    
4.  Plan is to tighten the bolt to apply enough friction to hold the door open.  If I don’t like how that feels I can add a counter weight or locking mechanism.
    
5. I will probably never run the rear door fully closed although I show it that way in the model.
    
6. The baffle holes were made to give more open area than the input pipe as to not cause too much restriction.  I could make the burner block a little less thick maybe 3” or 3.5” at a minimum.  My assumption is the 41, 0.30” holes should allow for pretty decent flow.  I will certainly need to play around with air & gas flow.  Hopefully that doesn’t involve finding the point where blow back is possible.  With air & gas mixed in the plenum I’m sure there is a danger here if the flow is too low.  Anyhow the burner is designed to be replaceable if I find this one is simply no good.  

[Frosty]

11ga. is serious overkill for the shell, I find 14 ga is overkill but easy to weld and a net win. You aren't going to be heating hundred lb.+ stock the shell's main use is containing the refractory and providing a good surface to attach components. 

I used to recommend 1/2" Kastolite 30 on the floor but have changed my mind to 3/8" max floor and 1/2" max walls and roof. Kiln wash with a good high alumina product like Plistex or Matrikote as the final layer of armor for the flame face. The benefits are multiple. If you reduce the hard refractory to 3/8" or less you can trowel it in and not worry about forms. If however you wish to cast the hard refractory with forms use "Sonotube" the paper concrete forms, you simply peal or burn the paper form off once the inner liner is set. EZ PZ. If the sonotube isn't quite the right size buy the next size larger and cut strips from the side and close it up with hose clamps to make it smaller. 

Another easy to make form is too use plastic pipe wrapped in a few layers of parchment paper so it'll slip out of the hard liner. Form the outside with a cloth wrap. Roll the refractory between spacers clamped to the table. I use 3/8" square hot rolled steel because I have it on hand. Cover the rolling board with the cloth, an old sheet works nicely. Mix up your refractory and beat it between the spacers, when close use a roller, a rolling pin or piece of plastic pipe, whatever so long as you can put force on it. Once it's rolled to thickness remove the spacers, lay the inner form wrapped in several layers of parchment or waxed paper on the refractory and using the cloth roll it around the form. When the ends of the refractory meet trim them with a knife to match. Use an angled cut and leave a LITTLE extra so you can pound the two together. The cloth will allow the refractory to dry so leave it till dry. However do NOT leave the inner form in, once the refractory sets remove the inner form or the liner will crack as it shrinks!

I eliminated any diffusion structures in my multiple orifice "Ribbon" burners by making the plenum taller, say 2" x 3"+ and mounting the input port horizontally at the top. The fuel air blowing into the plenum disperses nicely against the far side and spreads evenly enough to not matter.

Using too many outlet nozzles (40 in your case) is not a problem if the flow velocity through them falls below the rate of propagation for the mix and it backfires. It won't explode your burner, unless you're using a roots type blower the worst it can do is blow back to the blower fan and you can shut it of. You WILL notice. If burning back is a consistent problem, first turn the blower and fuel up a LITTLE at a time. If that doesn't work, start blocking nozzles one at a time until you arrive at the right number and make the blockages permanent with a little water setting hard refractory. Done deal, ribbon and blower is matched.

Orrr you can do what I did and make wooden test burner blocks that screw to the plenum. Drill holes, test fire, make notes. Wooden blocks will only last seconds before the wood starts burning and you won't be able to tell if the fuel air mix is good but it only takes a few seconds to evaluate a flame. 

Bear in mind you're planning a gun (blown) burner and must adjust fuel to air flow any time you wish to turn the fire up or down so fine adjusting the air fuel ratio will be easy with a little practice.

Also bear in mind that the forge and burner are two parts of one machine and need to be balanced to work well together. If you're following the plans printed in one of the ABANA magazines, or by John Emerling on his website or Wayne Coe, on his. Those plans have a grossly overpowered blower to make up for the crazy tight restriction of the as drawn diffusion plate. To overcome the restriction the mix velocity is crazy high and blows flame (Dragon's Breath) sometimes 2'+ out the forge doorways. 

This bit of overkill is why I developed the NARB (Naturally Aspirated Ribbon Burner) I can forge weld easily with about 2" of Dragon's Breath but my doorways are full length down the side. 

You want sufficient CFM from your blower, buying for high static pressure is a mistake.

Well, that's way more than enough typing for now.

 Frosty The Lucky.

[Latticino]

On 8/9/2023 at 6:24 PM, Latticino said:

appropriate high pressure blower.

Well, by appropriate I meant to avoid the typical "squirrel cage" style blowers and lean towards a centrifugal style with radial impeller like this (Dayton 2C862):

[Frosty]

Ayup, that's the kind, high volume low pressure. 

Frosty The Lucky.

[RockLobster]

17 hours ago, Frosty said:

 

Using too many outlet nozzles (40 in your case) is not a problem. . . . If burning back is a consistent problem, turn the blower and fuel up a LITTLE at a time. If that doesn't work, start blocking nozzles.

I’m starting to wonder if the 40 nozzles is a bit excessive.  I see other people using 32 for a similar size burner.  However you bring up a good point that holes can always be plugged up after the fact.  My thought on the 40 holes is the combined area (cross section) of the nozzles should be similar to slightly less than that of the inlet pipe (2” SCH 40).  At 41 the combined area (2.90 SQIN) is still less than that of the 2” pipe (3.36 SQIN).  I’m certainly not looking for 2 FT of dragon’s breath at the forge door. 

Side note: plenum baffle open area is 3.68 SQIN (5/16” hole X 48)

11 GA is certainly overkill but it’s the material I can easily get from my work.

Thank you for the detailed comments, I certainly appreciate the advice.

[Frosty]

Have you read the "NARB lives" section? I spent quite a bit of time discovering your perfectly good intuitive ideas about intake area and nozzle area ratios doesn't work. A gun burner can brute force past the problems but the result is a giant room heating CO generator.

The outlet nozzles on NARB are 2x the area of the mixing tube. The longer the outlets in the burner block the worse the ratio gets, I believe it's largely due to friction but maybe not.

So, NO I do not thing 40 nozzles are too many to use as a departure point.

Frosty The Lucky.

[Buzzkill]

I have not found a reliable "rule of thumb" for the ratio of the area of mixing tube to the combined area of the nozzlettes.  My conclusion is that there are too many variables to come up with a reliable guesstimate for a starting point.   The diameter and length of the the individual holes will definitely play a part, as will the material of the burner and the relative smoothness of the the interior of the holes.   

I have not found a better way than Frosty's approach.  Use a block of wood if you can and start with more holes than you think you need.  Block off holes until you stop getting burn back into the plenum at low to moderate pressure.    Make another block with that number of holes of the same diameter and test again.  If that one comes back with little to no flame lift off the face and no burn back into the plenum you should be set for casting.   That's for a naturally aspirated burner.  If you are running forced air there is more flexibility to err on the side of too few holes without seriously negatively affecting the performance of the burner.  Having too many holes will limit your turn down range in both cases.  However, holes can be plugged easier than adding new ones.

[RockLobster]

Update: Burner casting, gas nozzle, & burner test fire 

Burner mold:

Making the mold was fairly straight forward, sides are cut from 1/2" plywood.  I used a "laser" (cheap diode laser) to cut 1/8" plywood so the straw layout would be exactly as modeled with CAD.  This saved me hours of drilling.  I then coated all the inside surfaces with axle grease and let it soak into the plywood.  Note that I did reduce the thickness of the Mizzou.  Originally I had it at 4.25" thick and I reduced that to 3.5".

 

 

 

 

 

 

 

 

 

  

 

 

 

 

 

 

 

 

 

 

Casting the burner block:

The casting also went well, I probably mixed a little too much water in the Mizzou but I don't think that was any problem.  I added it in four layers taking time to stir the Mizzou around the straws and vibrating with a drill (bent steel rod in the chuck).  Then set the burner weldment in the mold and waited two days before removing the wood.  The straws worked perfectly pulling right out of the casting, no messy crayons to drill/melt out :).

[RockLobster]

Gas nozzle: 

Next I fabricated the nozzle to inject the propane into the air stream.  The main air pipe is 2", For the gas inlet I used 1/8" pipe.  I drilled a hole in a pipe cap and welded the 1/8" pipe to it.  I used a 90deg 1/8" elbow centered in the 2" tee, also ground it down a bit to try an minimize the flow restriction.

You can also see a picture of the blower I have with a flange to 2" pipe adapter.  I had purchased this blower some time ago and was concerned it might be undersized but figured it's what I had on hand and might as well give it a go. 

   

 

Burner Test Fire: 

At this point the burner had been drying for about five days and I was ready to test fire it.  Note that I used a 2" ball valve to control the air flow and 3/8" ball valve for the gas.  It seemed to work excellent.  I admit I don't have a trained eye for exactly what a proper flame should look like.  I found the blower could supply enough air to achieve flame liftoff and even blow it right out.  After a bit of fiddling I found a gas to air radio that looked good (to my untrained eye).  This is what you can see in the pictures below.  Note the ball valve for the air was about halfway closed, so I'm thinking this little blower might just be enough? 

Anyhow, this is very positive progress and I'm now very eager to get the forge body build! 

I also realize the flame is very hard to see as I wanted to do this outside.  I plan to fire it again at night when I can see the flame better and further experiment with the air to gas ratio.

  

 

 

[Buzzkill]

Looks good to me.  It's not uncommon to put at least one 90 degree elbow in between the point where you introduce the fuel and the burner to help mix the fuel and air. 

The great thing about forced air burners is you can control the forge atmosphere easily by adjusting the amount of air flow or fuel.   It looks like you have plenty of blower power to go with the large fuel orifice, so you shouldn't experience any limitations in that regard.

Looking forward to see what you mount it in.

[RockLobster]

The forge build continued with the fabrication of the forge body shell.  This was made from 11 GA steel plate, 11GA is overkill for sure but it’s the thinnest my work keeps in stock.  I chose the octagon shape so the interior could be cylindrical while giving flat surfaces on the outside for mounting components.  It can also be easily formed in a press brake and I think it looks great.  I formed two halves by making three bends in each side.  Next I milled out a slot in the top for the burner.  I then set a collar into the burner slot extending on both sides.  This will help to encapsulate the Inswool at the burner pass-through and provide a solid mounting point for the ribbon burner.

 

I made two end plates for the forge body using a hand held plasma cutter and wood template to trace the outline.  Then TIG welded all the seams with a continuous bead for an airtight seal.  Next I added 1/2" flat bar in a matching octagon shape, offset 2” from the edge.  This gives an easy and clean looking edge to the cast refractory at the outside face.  Finally I decided to drill 7/16” holes around the edge of the opening.  My thought is this will make for plugs of cast refractory that bond the exterior face to the interior, to help resist cracking and chipping on the exterior refractory.  I’m hoping it won’t do the opposite and cause cracks under thermal cycling.

 

With the forge tub weldment complete it was time to line it with insulation, I used 2” of Inswool, (actually 2X 1” layers).  I coated each side of both Inswool blankets with rigidizer before installing.  When I cut the blankets to size, I slightly oversized each dimension by about 1/2" for a tight fit when installed.  Then it was on to making a mold to cast the refractory.  One thing I would have changed if I did this again was to make the center of the forge a straight cylinder.  I was initially thinking it would be a good idea to have it neck down as to have a lip to help keep heat in the forge.  However this made the mold a real bear to make.  It had to be made in sections that each disassembled to fit inside and then reassemble in place.  It took me nearly as long to fabricate the interior mold as it did to do all the metal fab for the forge body.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

I used Kastolite-30 refractory mortar, about 1/2" thick in the interior cylinder walls and 1" thick at the end walls.  After letting it cure for a few days I removed the interior mold.  This was also difficult and I ended up cutting it into pieces to do so.  The up side of this laborious molding process is that it left a very clean looking casting in exactly the shape I had intended.  I really wanted the opening to have the semi-circle shape with a flat bottom.  My thought is this will give a nice spot to rest work without it rolling to the center.  Finally I applied a thin coating of Plistix 900F to finish the refractory surfaces.

 

With the forge body complete I installed the ribbon burner and was please to find it fit like a glove.  I also fabricated a custom table for the forge to sit on.  This made it easier to mount the blower and provided a protected area.  I plan to make an adjustable work holder on the table at a later time.  At this point I could finally fire the forge!  I’ll admit I don’t have a trained eye for fine tuning the fuel/air ratio but I’m extremely pleased with the function.  It seems like I have a good range of adjustability which is good because it’s quite thirsty on a higher setting.  I fired it for just a short time at first to allow the refractory to cure.  After repeating this a few times, I really let her rip for about an hour.  I have just a K type thermocouple, I’m sure it’s not particularly accurate but I took readings of about 1,700 deg (amazon says it’s good to 1,800 deg F even though most other K types are not rated for that).  Regardless I will need to make the doors for the forge before I really know what kind of temperature it can achieve, I’m just hoping I can do forge welding without a hydraulic press.  I did put a piece of mild steel in there during the test and it achieve a nice light red/yellow color.

 

[Frosty]

Oh MY! That's a beautiful forge! You put a lot of thought and time into it and it shows.

I used sonotube (cardboard, concrete forms) to mold the flame face in my old cylindrical forge and quickly discovered there was NO WAY I was going to peal it out so I burned it out with few charcoal briquettes.

Your burners are running darned rich in the pics. If you tune the flame's shape like you would an oxy acet torch it will get you in the ball park. 

The only thing missing is a porch out front of the opening. 

Check out Mikey's "Thermal Baffles" rather than doors. 

Well done!

Frosty The Lucky.