Ribbon burner design

[savage_sultin]

Hey folks, im new and this might be discussed before but when I searched I didnt see my question. im making a ribbon burner and for the holes im going to use stainless steel straws cast into the cement. would you think they would be fine? I dont see them being an issue, seen the pine ridge burner and they use a steel metering tubes 

[JHCC]

Welcome to IFI! If you haven't yet, please READ THIS FIRST!!!

I don't have an answer to your question, but it's an interesting one. If the use of SS tubes would work, that would certainly obviate the need to worry about how to remove the casting cores from the multiple ports in the burner block. Not sure how differential rates of expansion and contraction would work, though.

[savage_sultin]

thanks, regarding the "3a. Pro tip #1: When doing your research, don't bother with the Search box up at the top of the page; it's pretty worthless. Go to google and include "site:iforgeiron.com" as one of your search terms." thats pretty much what I used but checking out google now. thank you im navigating through the site now, ive been forging for a while but just switching from Venturi to a ribbon burner

[JHCC]

My work here is done.

<Rides off into the sunset.>

[HojPoj]

While Stainless isn't a stellar heat transfer medium, it's still better than the refractory.  You may run into some issues with pre-ignition in the holes as the forge temperatures slowly creep up the tubes.  I know Frosty has mentioned the problem on more than one occasion with the NARBs, particularly when turned down a little too far.

[savage_sultin]

this is the concept but I would bring the metal straw closer to the end maybe all the way to the edge. I was wondering about pre-ignition as well, but with cool air blowing over it constantly I thought it might not get that hot.

[Paragon]

I'm building a burner as well.  From the information that I have found, Pine ridge uses metering tubes so if there is a leak between the plenum and block, it could only occur where the metering tubes are.  If there is a gap, it wouldn't matter as the air will carry the mid out the block to the forge.  It can't backtrack and snake through between the block and baffle plate out the side.  You have to remember that they are building these things for high out and large forges/kilns/etc and one less failure point is what they were going for.  Their tubes do not extend to the end of the block so the castable still takes all the forge heat.  I have a feeling the blocks are cast separately then attached to the plenum.

If you do use metering tubes, I wouldn't have them go through to the face.  I was contemplating the idea before I understood why they do it and it just was more complicated with unknown gain.  Pineridge has their tubes sized for their burners.  Unknown what they use but it seems that the holes in the castable are 5/16 from what I found.  The internal plenum baffle is also different than what you see as standard here.

I was thinking of necking down the crayons and using those as an integrated metering tube nozzlette system but I am tending to lean toward just using regular. Below is a crayon necked down to 1/4".  This will mean less flow and possible more needed fan pressure.  I don't know if it is going to do anything positive other than possibly increase velocity right there and decrease chance of the flame propagating into the plenum which shouldn't be an issue if the blower is running ok.

[Buzzkill]

1 hour ago, savage_sultin said:

but with cool air blowing over it constantly I thought it might not get that hot.

I can't speak for others, but on my NARB the final 3/8" or so exposed to the forge chamber stays hot enough to glow the same color as the rest of the forge interior when in use.  The plenum gets warm enough that it's uncomfortable to leave my bare hand on it for long.  I do not know if this is because of heat creeping back from the burner head or if it is due to the heat that eventually makes it through insulation and outer forge shell. 

It's a bit of a balancing act I think.  The more air/gas you push through the burner the more it can cool things off, but you're also generating more heat inside the forge at the same time.  My NARB will definitely backfire at a higher pressure (still less than 3 psi) after running full out for a while than it does when I first get going, so there does appear to be an impact on the ignition point due to the temperature at the outlet nozzlettes.  I suspect that the metering tubes you showed in the illustration are deep enough in the refractory so that the difference in thermal expansion between the 2 materials is insignificant.  My guess is if you run the tubes all the way to the ends and then reach incandescent temperatures the difference in thermal expansion will create some issues in fairly short order.

[savage_sultin]

11 minutes ago, Buzzkill said:

I can't speak for others, but on my NARB the final 3/8" or so exposed to the forge chamber stays hot enough to glow the same color as the rest of the forge interior when in use.  The plenum gets warm enough that it's uncomfortable to leave my bare hand on it for long.  I do not know if this is because of heat creeping back from the burner head or if it is due to the heat that eventually makes it through insulation and outer forge shell. 

It's a bit of a balancing act I think.  The more air/gas you push through the burner the more it can cool things off, but you're also generating more heat inside the forge at the same time.  My NARB will definitely backfire at a higher pressure (still less than 3 psi) after running full out for a while than it does when I first get going, so there does appear to be an impact on the ignition point due to the temperature at the outlet nozzlettes.  I suspect that the metering tubes you showed in the illustration are deep enough in the refractory so that the difference in thermal expansion between the 2 materials is insignificant.  My guess is if you run the tubes all the way to the ends and then reach incandescent temperatures the difference in thermal expansion will create some issues in fairly short order.

Ok thanks. I wasn't sure if the cooler air would keep it  cool. I think ill keep them short

[Mikey98118]

The fact that the Pine Ridge burners use these tube successfully is a good indication that they can be made to work; that pretty well trumps all my questions about preignition from heat or gas leaks

[Frosty]

Not necessarily Mike, Pine Ridge has been making these things for how many decades, century(ies)? They just have everything tweaked and are using designs perfected a few hundred years ago. 

Buzz: You're doing it backwards running high psi then backing it off. That preheats the burner block and when you turn the psi down there isn't as much fuel air flowing through it so the heat continues to soak into the block and the fuel air velocity has been reduced. It WILL fall below it's rate of propagation and back fire.

I found I have to keep turning the psi up with time and can spend several hours without backfires. Not a lot, I start at maybe 2-3 psi and turn it up maybe 1 psi./hr. to keep it below flash temps. I haven't made another multi orifice burner in a while but was thinking of making the block about 1/2 as thick and texturing the inside for increased surface area and better cooling.

Frosty The Lucky.

[Buzzkill]

Just now, Frosty said:

Buzz: You're doing it backwards running high psi then backing it off. That preheats the burner block and when you turn the psi down there isn't as much fuel air flowing through it so the heat continues to soak into the block and the fuel air velocity has been reduced. It WILL fall below it's rate of propagation and back fire.

That's not standard procedure for me; it's just something I noticed over time.  If I won't be forging for a little while but I don't want to let the forge completely cool off I'll back the pressure way down to maintain glowing heat.  That's when I find out where it starts to backfire.   When I do start to get backfires I just nudge the pressure up about a half psi and it's all good again.

With the forge cold I can run my NARB under 1 psi without backfires.  I'm still blown away by how effective and comparatively quiet it is, and it's only a little more work than a single port burner.  Thanks again for all your insight and info on making NARB's.

[Frosty]

That makes sense, I obviously wasn't clear about what you were doing. Sounds like we're doing the same basic thing a little differently, works works.

I'm way too new to these things to "know" much of anything I go with what works and your's does.  It's being filed in my "this works" folder. Unfortunately that's in my dented haid.

Frosty The Lucky.