Another NARB Experiment (Pic heavy)

[Buzzkill]

I've been on lifting restrictions due to surgery recovery the last couple months, so I decided to rebuild my forge and I worked on a new NARB design as well.

The last NARB I made used a portion of an IFB with lots of 1/8" holes drilled in it.  It worked well for a while, but lately I was having to turn the pressure up significantly to keep it from burning back into the plenum.  I dislike casting burners, so I'm always trying to think of designs that will function well and allow me to replace the burner head without casting a new one.

Here's what I came up with (with some consultation with Frosty in PMs):

I used a piece of fiber board rated for 2600 degrees F for an "insert" into a cast refractory "box" that is cast directly onto a steel plenum made from folding sheet metal (around 1/16" thick) into a box with an open end.  The refractory box has a lip about 1/8" placed so that the fiber board insert rests on it and is flush with the edge of the refractory box on the flame side.  I didn't start taking pictures until after I had already cast the refractory box onto the plenum and tested a fiber board insert or two.  I'll share what pictures I have though.

This pic shows the burner after testing and another insert sitting on the burner face for reference.  That one had 75 "nozzlettes" with inner diameter of 2 mm.  It wasn't enough throughput, so I moved to bigger holes.

 

I ended up using stainless steel sleeves in the holes in hopes that this will prevent/reduce degradation of the fiber board in use.  I had wanted to try this before with cast burner heads, but was concerned that the difference in thermal expansion would cause problems.  Fiber board has enough "give" to it that this should not be a problem.  The sleeves I used have this description "T316 Stainless Steel Protective Protector Sleeves for 1/8" 5/32" 3/16" Deck Cable Railing Kit."

Here's what an insert looks like from the plenum side after all the sleeves have been installed and cemented in place:

 

This gives me 44 holes on slightly larger than 2" x 6" fiber board insert.  The ID of these sleeves is 13/64", and the length of them is such that they don't quite reach the opposite side of the fiber board I used on the flame side - which is what I wanted.  The fiber board was listed as .8 inches thick btw.

The next pic shows the burner after cementing the fiber board in place, test firing, and then coating the flame face with a kiln wash that is supposed to be good up to 3000 degrees F.

Here's a pic of the cement I used to keep the sleeves in place and to glue the fiber board to the cast refractory box.  It's only rated for 2000 degrees F, so I don't know how it will hold up long term.

The next pic shows the burner functioning with no visible pressure showing on the gauge, so less than 1 psi.

This is what it looks like from the outside of the forge.

I tried a number of different combinations of 1/2" and 3/4" T burner modifications.  In the end I believe my best results were with a standard 3/4" T burner setup using a .030 mig tip that was trimmed back a little over halfway compared to the opening when viewing from the side.  That took me from cold forge to "forging orange" in about 10 minutes.  It took me a total of 20  to 25 minutes to reach what I'll call "butter stick yellow" heat where I'm comfortable forge welding high carbon steel.

After running at forge welding heat for 20 minutes or so I turned it back down to less than 1 psi without it burning back into the plenum.

There are some issues though.  First off, I can't keep it lit outside the forge even with very low pressure.  It blows the flames off the burner face.  Inside the forge it stays lit, but there is some flame lift away from the burner face until the forge gets hot.  If I did my calculations right this burner has about 80% of the throughput capacity of a 19 crayon hole burner.  However, with the shorter nozzlettes and the different material the friction is certainly different.  I'm not educated/smart enough to try to figure out a direct comparison between the two.

Secondly, in my forge at least, this design suffered from what I'll call "harmonic howling."  This is a sound similar to, but more intense than, blowing across the top of an empty glass bottle.  It is affected by a combination of back pressure and temperature - and maybe other things as well.  Once it starts it can be stopped by covering the air intakes to reduce the flow or by turning the regulator down.  Over time as the forge heats up greater pressure can be used without the phenomenon occurring, but it really can be annoying when it's happening.  I did a little online research and found that model steam engine propane burners sometimes have the same issue, for whatever that's worth.

I've only had this in use for a handful of hours, so I have no clue as to the longevity.  My goal was to create something that functions well and that I could quickly refurbish without having to do more casting.  Hopefully when/if it fails I can just remove the old fiber board insert, cement in another one and get back to business.  However, it won't surprise me too much if my cast refractory box fails before or when the fiber board does.   I used sifted Kastolite 30 for the box because that's what I had on hand, but I believe there are better options out there.

I didn't need to make the steel portion of the plenum quite so long.  That could have been about 1.5 inches shorter, and I don't think it would have negatively affected anything.  Since the plenum is so large I get a pretty good pop when I shut the gas off and the FAM inside the plenum ignites.

I still need to get the forge interior coated with Plistex, but it is functional as it is and so far the burner seems to be performing in line with my expectations.

[JHCC]

Interesting!

[Frosty]

Good write up Steven. Good looking flame and so little dragon's breath as to not be there at all. SWEET.

I'm especially impressed with the cable sleeve nozzlettes and I've been noodling ways of casting the block around them without different COEs breaking the cast block. 

Hopefully it'll get more folks interested in building ribbon burners.

Frosty The Lucky.