Forge burner troubleshooting

[Pete Resseguie-Snyder]

Greetings!

I wanted to see if the experts on this forum might catch any red flags that may be causing combustion issues with my forge. I shot a quick video demonstrating the issue. The problem starts 3 mins, 10 secs in:

I built this based mostly on the David Hammer Super C Forge and burner design (minus the side access slot). It has been running stable for months, but now after running for around 30 mins, the point of combustion shifts from the interior of the forge, to the end of the flair (about 1 inch inside the refractory). I get less time if I run it hotter. The burner port leaves about 1/4 inch of space around burner flair. Before shooting the video, I has run for a little over 30 mins. I let it cool for about 15 mins to capture the transition. Don't know if I need to tune the burner, if there are issues with my refractory, or something else that I might not have considered. I've been doing this for around 6-7 months so my knowlege is pretty limited.

 Any thoughts on where I might be going wrong here? Thank you for any input you might have.

Edited December 9, 2018 by Pete Resseguie-Snyder
Added more details.

[Frosty]

Welcome aboard Pete, glad to have you. Did you watch the video before posting it here? Seriously it's so back lit so we can't tell what the burner's doing till it reaches about medium orange and not much then, seriously I have a better view of the trees through the forge than the flame. If the problem doesn't occur till 3:10 into the video why make us download and sit through 3 minutes of video for no discernible reason? 

Then you get to the 10 seconds that count and you start moving the camera around wildly so we can't see what's happening. 

Please, videos are a LOT of bandwidth and some of Iforge's members are still on dial up connections in more remote parts of the world and it costs them money. Please make videos worth the time and yes, money. Look at them before sending and maybe make another video say in a dimly lit space or outdoors in the evening against a dark backdrop. You don't read by putting the light on the far side do you? 

The best I can do at this point is guess judging by the sound. Try cleaning the jet of any waxy residue from the propane, it SOUNDS like it's running a little rich due to low jet velocity. Bear in mind that's JUST a guess.

What was the purpose of closing and opening the choke?

Have you asked Dave?

Frosty The Lucky.

[Pete Resseguie-Snyder]

Thanks for the welcome, the feedback and thanks for giving it a go with my crap video. I do sincerely appreciate it. Not having enough experience to know what info's valuable and not, I just posted what I shot, hoping maybe the before/after with the sound would be telling. I'll be sure to close the garage door if I ever decide to troubleshoot in the future. And maybe consider applying a bit more production value. I did watch before and after and it seemed pretty visible on my tablet, but I'm a total noob when it comes to making and editing video content. Another thing for the to do list.

You may be onto something with jet velocity and cleaning. I did a complete teardown of my burner, cleaned everything and retuned it, moving the flair tube forward a little more than 1/4 inch further than before. I also aimed the burner a little more towards the floor of the forge in case it was catching the refractory lining the burner port. Ran for about 3 hours solid without any hiccups!

Not sure what changed over time since the forge remains fairly immobile. I've read quite a bit about forge assembly, but might need to read more about forge maintenance.

Regarding the choke, honestly did not initially have/use a choke until these problems started. Don't know if it tells a story, but cutting off the oxygen then cranking it back on kind of "reset" proper combustion, at least some of the time until the forge got really hot.

Anyway, thanks again for the assistance! I'm back in business for now. Even with the occasional problems, I'm having blast learning this craft. This forum is an invaluable well of knowledge. Hopefully over time I'll be able to contribute a thing or two.

[Irondragon Forge ClayWorks]

You might have received more suggestions/views, if this was posted in the gas forges section.

[Pete Resseguie-Snyder]

Ah, thanks for the tip. I've browsed parts of the forum via google search results (mostly on forge construction, and trying to comprehend the basics of combustion) but I have not really done a deep dive yet. Been spending my few spare hours after work trying to figure out technique but I'll be soaking in some time getting to know the forums. Looks like an amazing concentration of knowledge here.

[Latticino]

Pete,

If you don't know about them already, you have some additional other great resources here in Rochester:  the NYSDB group (http://www.nysdb.org/) and Arc and Flame (https://www.rocafc.com/pages/blacksmithing).

[timgunn1962]

It's not that easy to tell with the camera moving about and stuff, but what I think is happening is this:

You start with a cold forge and a certain mixture speed through the burner tube. All is fine because the mixture is moving along the tube faster than the flamefront can burn through the mixture towards the burner. As things get hotter, the speed that the flamefront burns through the mixture becomes faster. At about 3 min 10 sec, the flame speed became faster than the mixture speed and the flame travelled back into the burner tube. Once in the tube, the tube heats up and the flame speed gets even higher.

Closing the choke starves the flame of Oxygen and the flame goes out. Opening the choke re-establishes a fuel/air mixture and this reaches the hot chamber where it ignites and the flamefront travels back into the burner tube. 

Turning up the gas pressure once the forge starts heating up will increase the mixture speed down the burner tube and (hopefully) will keep it above the flamefront speed with a hot forge. 

Adjusting the mixture (by moving the choke) can reduce the flame speed (both the flame temperature and the flame speed are highest at, or close to, the stoichiometric mixture), but this will also reduce the flame temperature.

There is actually a lot more going on in a gas forge than most smiths realize.

I'd try to eliminate any gaps between the burner and the forge as far as possible: any air getting in there (secondary air) is air you have no control over. The choke gives you control over the primary air and it's usually best to have all primary air to give maximum control.

[Pete Resseguie-Snyder]

Yeah, Arc and Flame is a priceless resource. Did a sculpture/welding class there a few years before the center was officially established, then took a rustic folders class that my wife got me as a gift a little over a year ago. That last class was the catalyst into blacksmithing. Great instructors all around there. Not familiar with NYSDB just yet. Will research, thank you.

Thank you Tim for that excellent summary. It's working great (as far as I can tell) now after some adjustments. I did plug the burner port more effectively than before. Used some kaowool for that which I'm a little concerned with; I know it shouldn't get hot enough there to breakdown, but still... Maybe some rigidizer wouldn't hurt?

I've figured out the how for constructing the forge and burner. Excited to learn more about why it works (or occasionally doesn't). Thanks again for sharing more detail.

[Mikey98118]

Take a look at the latest page in Burners 101 to find a warning against using ceramic fiber to completely stop secondary air induction in some burners that need some of it to burn completely. Nothing stops use from using some fiber part way around the burner to reducer excess secondary air induction, but don't over do it. Watch the flame as you add fiber, to be sure you don't go too far.