Gas forge for multiple piece production forging

[hornguy]

Hello all.

I’m in the process of re-jigging my day to day forge.

A little background:
I have been operating a wrought iron business for the last 28 years.

For the last 15 years I’ve been using a thrown together two burner gas forge that was a real gas hog.

when times are good and the work is constant, this isn’t a big issue.

But it’s been a little slower of late and I feel the need to cut costs where I can and be a little more practical about things.

I have been playing around with a blown ribbon burner forge for different projects recently and it has worked out extremely well.

But I prefer a Venturi burner forge for its basic on off easiness and perceived safety (no concerns with blowers failing etc).

My old Venturi forge was oversized and 80% castable refractory with just a little Superwool (lower temp non hazardous wool).

However it was bulletproof and took a lot of abuse.

In the last couple of weeks I have decided to cut it down in size (from approximately 600mm wide to around 450mm.

Also I have removed all of the refractory apart from the floor and replaced it with 2x25mm of isowool 1600 and a 12-15mm coating of 1600 rating castable.

I just used the old basic Venturi burners I made for it in the past.

Whilst they worked, they were now just overly powerful for what is a smaller forge.

A change in mig tip sizes has helped with this for the time being, but I’m planning on replacing the burners soon.

(a job came up and I need the forge urgently to get it done).

Issue is the best plan of attack in regard to heating but not overheating this forge.

It is a wide yet not too deep forge with a slot opening in the front of about 50mm height x 350mm wide.

Also has sliding cast doors on either side of around 120mm x 100mm.

Most work is multiple pieces of flats, rounds or square bar with a heat of about 100-150mm length.

 A bright orange heat is all that is normally required (no forge welding in this one).

My thoughts are to still use a two burner configuration but if a smaller diameter (1/2” rather than the 3/4” I currently have).

Having said that, I don’t want to be too under gunned here as I like it to get up to temp in a reasonable time also.

Here is a short video of it after being shortened and ready-lined, but still using original burners.

[Frosty]

The biggest problem you have is waiting until you're in an urgent rush to change it.

The width, depth, etc. is nice but what I need to know is the volume, I can convert to inches from cubic centimeters or millimeters, no problem. Without knowing the volume I can't say if a particular burner size will do it. 

The easy answer is to use 3 each, 1/2" T burners. You're in a hurry so making a better performing burner is likely to be a trainwreck and I can help with the Ts. In case you haven't read the T burner build instructions this fact will be what determines success or failure for your plan. A properly tuned 1/2" propane burner deliver HALF the output a properly tuned 3/4" propane burner does.

As stated your above plan will cut the burner capacity in half. The temp will drop from maybe yellow to low orange +/-. Tht's just a guess, there are other factors but the burner size is the big one.

Can't you turn down the psi to the burners enough? 

And please post still pics, movies don't show me as much detailed info as stills. I don't even look at burner videos anymore.

Frosty The Lucky.

[hornguy]

Thanks for the reply.

I’m not actually in a hurry as such, but I was at a critical time only due to an unexpected job.

More than happy to take the time to find a solution generally, only this urgent job came up and I needed to deal with it or loose it.

My thoughts were similar in having an extra burner to spread the heat without adding heat ( if that makes sense?).

Am I right in assuming that the two 3/4” burners are more aggressive than three 1/2” burners?

It may sound strange but I’d prefer to just be able to light it up and go about business rather than worry too much about it’s heat output aside from whether it gives me a bright orange without waiting too long.

Also of importance is not having to worry about it overheating and having to crank up the gas to keep a flame that isn’t spluttering etc.

I guess a more efficient set up without a need to constantly monitor.

 

 

[Frosty]

I hear you about the surprise job. I'll take your questions or points in order. 

Yes, more smaller burners spread over a larger area to even the forge temperature out without making it hotter makes perfect sense. A lot of people and processes benefit from even temp over the entire forge. 

The factoid again. One each 3/4" burner has TWICE the output of a single 1/2" burner. In your case it means three 1/2" burners will have 75% the output and use 75% the fuel for that heat as the two 3/4" burners you're using now.

You don't need to think about design or settings once you get it where you want it. I find doing all the brain work up front saves time and effort using it until  the situation and needs change. Once you know how many psi. makes the forge the right temp there's nothing to do but open the tank valve, set the regulator and light it. You can go do something else while it warms up. 

Being able to repeat a specific temperature in the forge is my main reason for having a gauge on the regulator. Some operations work best at specific temps and knowing how many psi delivers THAT temp is handy. A little work up front saves repeated work down the road. Yes?

Sputtering flames can have different causes besides a burner problem. Probably the most common is having exhaust gasses rise or blow into the burner's intake air. Breezes can cause problems too. That's something else to consider and correct after you  decide on the size and number of burners you want/need.

If you never need anything but the orange heat you describe then a ribbon might be THE thing. Two of them using the burners you have now as the inducers will give you good turn down. You should be able to just turn the psi down and get the desired temp in the forge. AND distribute it evenly. 

Putting the burner air intake ports out of the line of the forge exhaust becomes easier as well.

Set it and forget it.

Frosty The Lucky.

[hornguy]

Thanks.

I have considered a ribbon burner for this, but never thought of having two.

I take it you’re speaking of the naturally aspirated ribbon burners?

I’ll need to do more research on those as from what I have read, they are less forgiving of poor design than the blown type.

Hot spots from multiple burners is also not a big problem in this particular forge as the pieces are generally in there for some time soaking up heat whilst I work on another.

Here is a photo of it after being on for only 5 minutes at around 5 PSI (at the tank).

Plenty hot enough, but far from efficient.

 

[Frosty]

Yes, the gun type ribbon burners built to the plans published on blacksmithing sites for so many years has some serious problems. The diffuser is blocking the intake to the plenum so badly it requires dang high partial pressure from the blower. This is why you see forges using them blowing dragon's breath sometimes 4' out the openings. 

That's why I made NARB, all I did was balance back pressure against flame velocity. Too high back pressure is a deal breaker for NA burners and too low flame velocity causes back fires in the plenum another deal killer.

What I did was determine how many crayon size nozzles it took to minimize pressure while maintaining velocity. I used wood mock ups of the burner blocks to test. After about 5 seconds the wood started burning and after 10-15 the flame was unreadable. But that was enough time to bracket then close in on a number of nozzlettes that I could tune a T to work on.

I was stunned and delighted to discover close was good enough. Now all I have to do is get a T close to tuned neutral and the ribbon block and plenum is happy. The NARB produces a stable neutral flame from stop to stop on my 0-20psi regulator, I can literally screw the adjustment out till it's not touching the diaphragm or all the way in and the flames are tuned and stable.

Naturally Aspirated Multiple outlet burners have been around in common use for centuries. The only credit I claim is I tinkered with it and discovered how easily it can be adapted to plumbing parts for the inducer (mixer).

I don't know what it'd take to adapt the commercial burners you're using for NARBs I don't like taking a proven good performer and welding it to something to modify it. 

How old is that forge? I've seen them before and like the burners but have always shaken my head at the forge itself. I might have something backwards though I don't think so. The second picture shows the flame path impinging on the right and flowing around in a clockwise motion, as oriented in the view. yes?

The wide opening is on the right in the end view yes?

If I'm right the burners are oriented so the flame impinges on the floor directly in front of the large doorway and when open blows a lot of flame straight out. 

Were I building a forge like this I'd want the flames impinging so the flow carried the flame away from the opening to stay inside the forge as long as possible. Basically switch them around so the flame hit the other wall first. 

The people who designed it weren't dummies and I've seen the same thing in other make farrier forges. Is it desirable for the burner flame to heat things in front of the doorway?

I don't know enough about your forge, not really but if you could close it down more and the flame wasn't directed straight out the wide door, a single 3/4" NA burner would probably bring it to mid orange.

 That's not a final opinion, and virtually everything else I just said above is speculation based on not much. I expect I'll change my mind as I learn more.

Frosty The Lucky.

[hornguy]

 

The forge is around 15 or so years old.

But it’s not a commercially available forge, it’s one I built myself, so are the burners.

The burners are very basic build venturi using a reducer welded to a 90deg elbow with a mig tip aimed down the center.

These ones cannot be tuned via an air choke, only by adjusting mig tip length.

You are correct about the long slot opening being on the right in the second picture.

The burners are positioned along the centre line of the forge point straight down toward floor.

I do like the idea of two naturally aspirated ribbon burners to replace these.

Do you think it would work to have one 12” ribbon burner with 38 nozzlets fed by two T-Burners or is this not wise for safety reasons?
I could have a plate welded inside the plenum to seperate them.

Two seperate burners would allow more adjustment I guess, and might be easier to cast than one long one.

Should be an interesting project either way.

 

 

[Frosty]

Hmm, they look very  much like a commercial burner that's been around a long darn time. If it's possible maybe lift the intake ends so the flame hits the floor but aimed away from the long door. It would increase the hang time of the flame.

A while back someone was talking about building a long ribbon powered by two NA inducers but I haven't heard anything so I don't know how that'd work.

You could make the 12" ribbon and power it with a 1" T inducer, that's 2x the output of a 3/4" T and in a ribbon burner they have an amazing adjustment range just via the regulator.

I think I'd rather do that than make two ribbons and Ts.

Frosty The Lucky.

[hornguy]

Thanks Frosty.

A 12” burner with a 1” T-inducer sounds like it would work well.

I may position it so that it’s slightly forward of centre aiming into the forge rather than directly on top aiming down.

However in doing this it then puts the plenum closer to forge opening and it may cause it to get hotter quicker.

I suppose a barrier of some sort could be put in between to alleviate this to some degree.

now I just need to look up the plans for a 1” T burner so I can get started.

I’ve added another photo of the current burners from a different angle below.

 

[Frosty]

I think that alignment of a ribbon would work well for improving hang time. What I've found is an overheating burner block is a problem, The plenum would have to approach red heat to cause it to back fire. When I was messing with them in brick pile forges I tried heating the plenum deliberately thinking it'd improve the burn. 

There is another way to angle the nozzlets without tilting the whole burner. Tilt the crayons in the mold. This is another thing I haven't experimented with but the thought has been there. I've always wondered what kind of heat a round forge with a ring burner with nozzlets tilted inward and say clockwise to force a vortex. I've considered fanning the nozzlets to spread heat more evenly still. Or orienting them towards a central spot to concentrate it though I would've made that one a button. 

If you have a gas range you have a multi outlet ring burner.

The build ratios are the same for any size T burner as laid out in the instructions on IFI. The jets follow the same basic rule as burner output. For example a 1/2" mixing tube has half the output of a 3/4" mixing tube. Calculate the area of the tube's cross section and a 1/2" tube is half the area of the 3/4". The mig tip follows the same ratio closely enough to be within easy tuning range. I haven't built a 1" burner since my second successful burner when I discovered it was WAY more than I needed in that forge. I don't recall but I THINK I used either a 0.045 mig tip or a 0.050 mig tip.

That's the best I can recall from when I started messing with the things about the time the internet went public. What mid 80s? It's a long story I'll spare everybody AGAIN. I got a bunch of sales brochures pitching various types of inducers from linear and jet ejectors to "amplifiers" Dyson's fanless products are based on amplifiers. Anyway I started messing with ejectors because you have to detune them considerably to get a flammable ratio. It's much easier to make a poorer performing device than trying to make high performance.

Cool, I managed to shorten it considerably.  

So, my last estimate of jet size for a 1" T burner is relying on a 35 yro memory in a dented brain but it should be in the ball park. Well maybe 0.040 would work, I just don't recall.

Frosty The Lucky.

 

[Mikey98118]

On 11/7/2021 at 1:33 AM, hornguy said:

Am I right in assuming that the two 3/4” burners are more aggressive than three 1/2” burners?

So, a successful scheme for using the plenum chamber for heat regeneration is likely to be the next major breakthrough in ribbon burner design

Who can we trick; er, I mean lead, into slamming his head over and over into that bricl wall?

[Frosty]

1 hour ago, Mikey98118 said:

Who can we trick; er, I mean lead, into slamming his head over and over into that brick wall?

I get too frustrated so I try not to talk to them anymore. 

If YOU'D like to winkle better performance from propane burners try pre-heating the propane just prior to injection. You have to keep in under about 1,000f or it'll spontaneously ignite but closer is better. Say 800f for the amateur home build and it mixes very thoroughly, nearly instantly and as it chills the pressure drops further improving both mixing and induction.

Hmmm?

Frosty The Lucky.

[Mikey98118]

It seems to be a Gordian knot. And the answer will probably be just as frustrating to those of us who only stand and wait, as Alexander's was supposed to have been

[hornguy]

I jumped right in and cast up a 11” x 2” burner head today, (12” was going to be a little too tight a fit.

Letting it cure for a few days and hopefully will get started on the inducer shortly.

I’m struggling to understand the arithmetic in sizing the air intake. I thought I read it as AI=2xD, but it doesn’t seem to work in my mathematically challenged brain.

I’m hoping that with one inducer the mix still reaches the extreme ports well enough.

Some more work has come up (which is great) but it may slow down my progress a little as I will be needing the forge for a lot of it.

I really appreciate your help with this.

 

[Frosty]

Yeah, I'm mathematically challenged but if you're making a T burner a 1" x 1" T would have intake ports 2x the tube dia. Soooo I wing it, try 1" x 1 1/4" T, it should be in the ball park. The again a 1" x 1 1/2" T should work though that's quite a bit more intake area. 

Bear in mind I got NARB working by approximating and bracketing the target until I got there. Outside of a couple basic ratios I've never gotten math to work for me in a usable way.

Frosty The Lucky.

[hornguy]

Thanks, good to know I’m not alone.

I think I’ll go the 1” and 1 1/2” T and I can always choke it a little if needed.

I de-moulded my cast burner this afternoon (got a bit impatient) but it came out fine. The wax coated straws worked well and were super easy to drill out.

I’ll try and source some parts tomorrow so I can get it all happening early next week before I have to start on my next job.

I will report back when I have it up and running and include some photos.

I’m fairly confident it will work out.

 

[Frosty]

If the new burner burns lean rather than choking it try enlarging the mig tip with torch tip files a LITTLE at a time. The more fuel you can get burning in the forge the better and getting enough combustion air is harder than enough fuel. 

Once a T is powering a ribbon you have all the turn down you could want.

Frosty The Lucky.

[hornguy]

Well I managed to get a nice changeover from the two old 3/4 burners to the new Naturally Aspirated  Ribbon or multi port burner.

I used your T burner design with a 1” tube and 1mm or .040 mig tip.

Outside of the forge I couldn’t get it to fire well at all unless I choked off most of the air, and even then it was more like a stovetop burner than anything else.

However I decided to chance it and removed the old burners and made a big cutout for the new one.

I angled the burner diagonally from the top front of the forge toward the back to get a vortex happening.

I threw in a piece of lit paper, open up the gas and it fired up nicely.

As you indicated, it can be run on minimal or maximum PSI without a need to choke the air or adjust in any way.

I ran it at a measly 20 KPA (3Psi) and it brings steel to a nice forging heat in not time.

And it just stays there at that temp unless it’s cranked up.

Perfect for my needs in this (my everyday forge).where I generally bring 20+Pieces of steel to forging heat and continually add more as I have finished with one.

So this forge can sometimes be running for several hours simply bringing 4-5 inch sections of steel to forging heat.

I only ran it for a short while today (maybe 45mins) but will be firing it up for some paying work in the next day or so to put it through its paces.

I don’t see there being too many issues judging by how it performed today.

Below are a couple of photos and a short video of it running.

Photos taken through side doors (which are normally closed while in operation).

[Frosty]

Glad to hear you got it burning properly and it's dong what you want. The flame in the pic looks a LITTLE bit rich but pretty close to neutral. You've been using propane forges in your shop long enough I assume you have good ventilation. I look forward to seeing pics of things after the temp is maxed for your purposes. I'd also like to know how much propane you burn in a day or how long  you get from a tank. 

Your burner put a smile on my face. 

Frosty The Lucky.

[hornguy]

Thanks Frosty 

the flame is lifting of ever so slightly which I would associate with an excess of air.

But choking it doesn’t seem to make a big difference.

Do you think I need more air?

To achieve this would I be better with a smaller jet orifice. 

Edited November 17, 2021 by Mod30
Remove excessive quote.

[Frosty]

Certainly not, it's really close, changing jets is a BIG adjustment. I'd maybe give it a couple gentle swipes with sandpaper and clear the bur. It's really close, we're talking taking a hundredth or two at a time, fine tuning.

Frosty The Lucky.

[hornguy]

Thanks 

I will give it a few strokes and see how it works.

it does seem just a little more stable each time I light it up. Especially once it’s warmed up a bit.

I haven’t had it running for any great length of time yet but I’m thinking it may be worthwhile to have a baffle of some sort between the front slot opening and the burner to direct the hot air up and away from the air intakes. There seems to be a lot of hot air in the vicinity of the air intakes and I don’t know how this may affect its performance.

 

[ThomasPowers]

Re-running exhaust certainly increases the Carbon Monoxide production of a burner!

[hornguy]

Thanks, that’s good to know.

Will definitely make up a baffle to redirect the hot air away. Don’t need any more carbon monoxide in the air.