Sputtering burner

[Naroe]

Hello everyone

The last couple weeks I have been building a little gas forge.

It uses a 1/2" burner I bought here in Australia.

I used 9" round pipe and lined it with two layers of ceramic fiber insulation and hardener. The forge chamber is 4 and 1/2 inches across and 8 long.

When I tune the burner it works perfectly at 1-30psi.

It all looks to be going well when I put the burner in the forge however when I reduce the oxygen with the choke the burner starts sputtering. At lower pressures the huffing sound is longer between huffs. At higher pressure it still does it but much faster.

I'm wondering if my chamber is too small and causing backpressure? Because when the forge gets up to heat there are quite large flames out the front. Maybe 6-8 inches?

Ive been doing heaps of reading through this forum and am struggling to find an answer. I've attached a few pictures which hopefully upload.

Thanks for your time!

[swedefiddle]

Good Morning,

The simple answer, DON'T restrict the Air. You need to hear the Forge roar, when everything is working. Sometimes you have to be patient and wait for the refractory inside the Forge to kick off and complete more combustion. It always works better when it is up to temperature. Listen for the ROAR and adjust to keep it when the inside of the Fire-Box is hot. Running the Burner when it is inside the Forge is WAY different than looking at the flame, clamped in a vice. The Forge gives back pressure.

Neil

[Naroe]

hmm seems simple enough!

The main reason is I had heard that having the forge running a bit richer means less scale forming on a knife blade.

 

Is the flames coming out the front that much pretty normal?

The lowest temperature I can get inside the forge is 1700°F. Which I guess I won't be heat treating in. 

[Frosty]

A LITTLE rich, yellow flames in the dragon's breath is a LOT rich. Tune your burner in the forge, that's where you're going to use it. Once the forge is up to temp put a piece of relatively thin steel in it. If it forms scale IN the forge close the choke a LITTLE, say 1/4 turn and check again with another piece of steel.

Do NOT change more than ONE thing at a time or you'll never know what did whatever happens. Change A thing a LITTLE bit test and note it in your note book.

The burner should roar loud enough you'll have to shout to be understood anywhere near it.

How do you know 1,700f is the lowest temp you can get in your forge, you don't have the burner tuned. Put the instruments away till you get it burning properly and we'll tell you how to turn it down.

Frosty The Lucky.

[Naroe]

Thanks heaps for the replies!

I'll be back after some testing then! One thing at a time in tiny adjustments.

[Mikey98118]

A huffing sound comes from running a forge at low a gas pressure; the flame photos confirm a weak flame. You need to run the flame hard enough from any size of burner to keep it strong. If that gives you do much flame through the exhaust opening, then the answer is to use a smaller burner.

[timgunn1962]

A couple of questions.

Does the huffing seem to be the flame running back down the burner tube from the forge chamber, or the flame running back through the forge chamber from the forge mouth?

Usually, the flame running back down the burner tube is due to too low a gas pressure and it tends to be more likely when the mixture is closer to neutral. It happens when the mixture speed along the burner tube is less than the flame speed through the mixture. The flame aceelerates down the tube until it runs out of mixture and goes out. Then the gas and air mixture reaches the hot forge chamber, ignites and repeats.

At lower pressure, the flow is less and it takes longer for the fresh mixture to reach the hot chamber.

I can sort-of-visualise a similar thing happening in the forge chamber, but I think it would need some pretty specific conditions and does not seem particularly likely. One of the conditions in my mental model is high back-pressure, so a photo of the inside of the forge showing the burner placement would be useful.

Are you getting the forge chamber hot before you try to choke the burner down? Burning at the rich mixtures that give flame temperatures in the Heat-Treat range is getting pretty close to the edge of what is normally considered to be the flammable range, perhaps even beyond it. The text-book vales for Upper-and Lower Explosive Limits seem to be based on room temperature gas/air mixtures. At higher temperatures the range certainly seems to be wider, but I've not seen any rigorous test data either way.

I find I need to start my HT forge with a fairly wide-open choke (probably around the setting used for your first pic, perhaps even a little more air) and get the forge stable at a higher temperature than I want, then take the temperature down by choking the burner in small steps, leaving it to stabilise after each step.

On my forge, there is no chance of starting with the final mixture and getting the flame to stay alight long enough to bring the forge temperature up from cold.

What gas pressure range is your burner intended to operate with? And what gas pressure are you running? I tend to run my burners to 60 PSI/4 bar max for welding and usually run around 20 PSI/1.3 bar for HT.

Forging is done with the burner in a fairly conventional forge, but I transfer the burner to a purpose-designed HT forge for Heat Treating.

With the finely-adjustable air:fuel ratio provided by the commercial Venturi, you have control over the flame temperature in a way that most NA burners do not. Where most people would just think in terms of turning down the pressure to reduce the amount of gas being burned and therby reduce the forge temperature, you can think in terms of reducing the airflow but leaving the gas flow/pressure fairly high and reducing the flame temperature.

https://www.youtube.com/watch?v=1xvWkXBXY6U&feature=youtu.be

It's not my video, but it's one of my HT forges with a burner built on an Amal atmospheric injector.

[Frosty]

Tim: Who are you asking? The OP doesn't know how to tune a burner to start with so asking him for detailed info isn't terribly productive.

You're seeing two things in the above pics. First is a too rich to VERY rich air fuel mixture running at high pressure. The huffing he's experiencing is probably the burner backfiring as the fuel air mix speed drops close to the flame front velocity. A full blown backfire can be pretty scary sounding.

I don't think his forge was getting hot enough for the forge itself to be huffing, that happening would muss your hair.

Commercially the choke plate is to adjust fuel air mix, NOT adjust temperature anymore than the choke on a gas engine is for slowing the engine RPM or stopping it. Are you old enough to remember cars and trucks with a choke knob on the dashboard? Ever see anyone adjusting their speed pulling and pushing it like a throttle?

The throttle on a naturally aspirated forge is either the regulator or a needle valve controlling fuel quantity. Once the air fuel ratio is adjusted the ratio will remain consistent in a fairly flat curve throughout "Primary" fuel pressure settings.

I'm not sure of the point of the video, a small burner in a large volume WILL hold a consistent temperature. No question there. Is it how that particular commercial burner is adjusted? It's not uncommon for commercial devices to have one point of adjustment so the end user can't mess up a pre-adjusted system. The adjustment knob on that burner is in exactly the right position to adjust output with a needle valve at the jet. The gauge apparently doesn't change with the knob settings. The video doesn't show an angle to see what's actually happening when the knob is turned.

I'm aware the world is full of devices and ways of doing things I'm unaware of so all I can comment on is what I know or surmise.

Frosty The Lucky.

[Naroe]

I tested out my forge again today and I made small adjustment as you said Frosty. And I think it seems to be running well I just need to use it more and get used to how it runs.

I was also reading somewhere that the sound of the forge will change at the point where the mix is pretty much neutral. There is a point where it really roars and then slightly past that point it rumbles a bit more. Does that make sense?

A couple more questions. The hole in the insulation for the burner tip is the same size as the outside of the burner or should it be the size of the inside of the flare tip? Or even taper out the closer it gets the the chamber?

There is a tiny gap around the burner flare, about 1/16 of an inch. Would it run better if I stuff something in there?

The burner gets too hot to touch a long way up the burner and is cool about an inch from the gas nozzle. I probably had it running hotter than I would for normal forging this time though.

Sorry about all the questions but I like to do things properly.

Thanks

Nathan

[Frosty]

A 3/4" burner should be loud enough you have to shout to talk to folk even close to it. Yes, different fuel air ratios sound different but until you've listened to your burner in it's different ratios you have no real basis to judge. You can NOT make anything but gross judgements after reading what someone else THINKS.

I could probably listen to yours and tell you how rich it's burning but it'd have to be in person, audio files are not accurate.

How far do you have your nozzle inserted into the liner?

I don't like any gap around the nozzle it allows the fuel air flow to induct outside air and oxy. If your burner requires outside air to burn clean its not adjusted properly.

Too hot to touch a couple inches out of the forge is okay but it sounds like you have ignition in the tube. You're probably still running your propane at too low psi. You do NOT want ANY ignition happening in the burner. 1/2" up into the flare or thread protector is acceptable but not optimum. It would be close enough.

If you're moving enough fuel air it will cool the burner tube by absorbing the conducted heat from the flame up the tube. About 3" from the nozzle my burners are pretty warm but cooler than fresh a cup of coffee. Cooling the burner tube pre-heats the fuel air mix.

You either have your burner too far into the liner or running our propane at too low psi.

Sure, you can form the forge liner into a flare, just don't get carried away or it'll induce turbulence and it will burn back in the liner. You want the flame (HEAT) to occur IN the forge, not the burner, liner, etc.

Ask away, you're asking good questions.

Frosty The Lucky,

[Naroe]

I fired the forge up for an hour and a half just now and the burner flare started to flow red hot by the end. I have it sticking about 1/2 inch into the 2 inches of insulation.

I tried running the forge at slightly lower and higher pressure but the burner pipe is still hot at half way up the 6" length. If anything the higher pressure just made the burner flare hotter. I tried running the forge from 6-10psi. Which is when it's roaring loud.

Here's a picture of the closest I could hold the burner tube to the forge. 

[calala]

Naroe

Why don't you give Corin who is the supplier of these burners a phone call, I am sure he will assist you. He can't reply on I.F.I. because he has been banned.

Cheers John.

[Naroe]

Thanks for the suggestion John. I may just do that but to be honest, ordering this and a couple other things wasn't very smooth sailing so I am reluctant to bother him.

 

[Frosty]

What is the big cylinder it's screwed into? Is there something forming a flare inside it? It looks to be attached to the forge shell by the bolts through the steel ears.

The way it looks the burner tube makes an abrupt diameter change to what 1 1/2" dia.? If so that isn't a flare it's a design flaw. A diameter change that abrupt will induce turbulence that amounts to a stall and make the flame burn IN the larger piece of pipe and not in the forge where it belongs.

The burner itself is commercially made and shouldn't need more than a little adjustment of the choke plate to operate properly at almost any psi. If that cylinder is part of the burner as sold, call the maker and find out what it's doing there and what's wrong.

How about taking the assembly off the forge and taking a pic inside the burner from the forge end. I'm having real trouble imagining what that thing is.

Frosty The Lucky.

[calala]

Frosty you are right in your thinking about the end section. Its a steam pipe connector that is threaded at one end and yes it has been machined further out at the none threaded end. Corin puts these together mainly for use as hand held, a mate has one & they work well in that situation. I have been told that they are also used in forges but I would think that a different end section would be screwed on. Naroe should ring Corin and inquire he will steer him in the correct direction for sure.

Cheers John.

[Naroe]

Interesting to know John.

Corin has them on his knife making website as a forge burner. No mention of handheld. 0. I called them initially for advice before starting my forge build and they offered nothing I already didn't know. But enough of that.

 

Here is a picture of the top it came with. The 1/2" burner tube screws into the smaller end.

Would a connector to a short 3/4" pipe work as a flare? Would a small step like that cause a slow in the flow speed for a flame to sit at the end?

I also have a metal lathe that I could make something up with a taper. 1:12 ratio I've been reading. Not sure on the length though if my burner tube is already 6" long.

I should have just made my own burner haha

 

[calala]

Naroe could you let me know where you live as I might know a smith in your area to help with the burner. Cheers John.

[Frosty]

I don't like that . . . THING at all, it extends the length of the tube needlessly and to the detriment of function, then it just increases in diameter to 1.2" abruptly. Both of these "features" hurt efficiency.

Talk to the folks at the local plumbing supply see if they're still getting pipe with steel "thread protectors" and replace that . . . thing on the end with a thread protector. If they don't have steel thread protectors a 1/2" pipe coupler is good. Thread protectors are cheap even free and work well, heck they're throw aways, cost more to ship back than they're worth. The ID of the treads that screw onto the burner tube is plenty of increase to help induction and stabilize the flame just at the end of the burner outlet. The threads actually reduce friction by creating a barrier of still air against them. Its counter intuitive but it. . . is.

I don't use a "flare" all I've ever used is a thread protector or pipe coupler. The one "flare" I turned on my lathe didn't work enough better to make it worth the effort. If you want to make one, set your angle feed to 12* and don't get carried away. I've found deburring the ends of the burner tube improves performance as much or more than any high tech "improvement" I've seen so far.

The length of that tube is much longer than the basic ratio says it should be. 8-9 x the dia. a 1/2" dia burner tube should be 4"-4 1/2" long. There is leeway in the ratio but 6" pushing it. Then if you add the long section of straight pipe in that fitting the total length of the burner tube is long enough to hurt induction. Uh, I'm in danger of starting to repeat myself, I'll close by saying there is NOTHING, zippo, nada, I like about that fitting. I think a burner would work better without anything on it than that . . . thing. 

Frosty The Lucky.

[Buzzkill]

What Frosty said.  I've experimented a little with something like you show and the flame burns inside it.  The way that is held to your forge means most of the actual flame is burning before it enters your forge and is wasting energy heating that thing up and dumping some of that heat into the open air.  I'm guessing that you can actually see part of that piece glow outside the forge when you get your forge up to temp.  I defer to Mike and Frosty on all things NA burner, but I will share a short story here.  I had trouble with a T burner I built blowing the flame away from the end of the burner tube until I got up to a good temp.  This was to the point that it was annoying.  Finally I took the tube over to the anvil and used the horn and light blows to gently and slightly flare the end of the burner tube that sticks into the forge.  Hopefully I'm not making Frosty or Mike cringe too much here.  The bottom line is that improved my flame stability significantly and I'm able to light the burner and bring the propane up to operating pressure immediately without any flameout after making that modification.  Of course it's highly imprecise compared to other methods of adding flares and possibly decreased maximum performance a little, but for me the gain in flame stability was worth it.  Any time I've tried to use a bell reducer or any other fitting on the end as a flare that has an abrupt change in diameter I've always ended up with the flame burning inside the fitting and experienced a decrease in performance (strangely enough just as Frosty and Mike said I would).

[Frosty]

I've flared the end of the burner tube on the anvil horn but I had better luck putting a cap on the other end, heating the output end and driving it straight into the horn's end, then dress it as Buzz describes. It was a lot of work but worked. The end of the horn on my Soderfors is round, pointed and smooth so using it for a male die is practical.

The increase in diameter makes the air fuel flow fill a larger volume so it has to slow down which helps prevent it from jumping off the burner. It also increases the vacuum drawing air in. Increase the volume too much and the air fuel mix is moving slower than the "rate of propagation" or "Flame front" of the mix so it burns back into the burner tube.

Frosty The Lucky.

[ThomasPowers]

As I understand it: with a taper in the right "zone" at some point the forward speed of the gas mix will equal the burnback speed and so have a stable flame; and being a taper it allows for some adjustment of gas pressure as the stable point can "slide" forward or back inside it.

[Naroe]

Excellent! I'm actually learning heaps more from this than I would have if the burner was perfect from the start. So in that way it's been good.

Thanks for the good replies!

Ive already bought some slightly different lengths of pipe and a coupler or two to try out. I'll do some more testing next week once my engagement party is done and dusted after tonight!

[Frosty]

Remember the ratio for tube length is 8x dia.

Frosty The Lucky.

[Naroe]

I initially tried the 6 inch burner with a coupler on the end but it sputtered too much. So I bought a 4 inch pipe and with the coupler on the end it would be 4 1/2 inches. It works super well!

I had time to fire it up last night (5pm) for half an hour and the burner tube got warm but nowhere near as hot as the old pipe+weird end.

I was only able to use it for half an hour because the neighbour started shouting abuse about the noise. So my next project is deadening my ringing anvil haha I've bought silicone and plan to add layers between the floor and wooden stand and the stand and the anvil. Magnets made a massive difference initially as well.

[Frosty]

A 3/4" tube should be 6" long not counting the coupler or flare. Did you turn up the pressure?

When you change something, experiment with all the settings before you try another change. Changing a physical property of a device often alters the variable settings: psi, choke, etc.

(For instance and do NOT let this example confuse you!! For instance, when I was using a 3/4" TEE I couldn't use a 0.035" mig tip and had to run higher pressure. The intake ports were literally half the area so it took a stronger gas jet to induce combustion air and even then less was available so I had to use a smaller gas jet to achieve the correct ratio. And that's the example I change one thing and two others are altered. Smaller air intakes require a stronger vacuum and still don't allow enough air in so I have to reduce the volume of gas but increase it's velocity.)

You got rid of that thing on the end. Don't start randomly changing everything else! Go to the tuning sequence Fire it off, observe the flame shape, length, dragon's breath, etc. Make notes and compare the to pre-change results for the SAME pressure setting. Tune for the observed results, say there is more dragon's breath and it's more orange. What do you do? It's running richer, maybe open the choke plate a LITTLE BIT, say 1/4 turn. Observe the results and note them.

However if there is more dragon's breath but just a hint of orange turn the pressure down a LITTLE BIT. Observe the results, make notes. compare them to other observations with similar settings.

Have I caused you to lose sight of what you're really interested in yet? The #1 most important initial target you want to see is good working temperature in the forge. So don't forget your goal and also don't forget high temp isn't the only important condition. you can run a burner lean and get really high temperatures but you'll scale you steel to nothing quickly so you need to trade a little hot for carburizing atmosphere in the forge so it doesn't bur your work right up.

Frosty The Lucky.