One more newb NARB.

[Daren.McIntosh]

After reading all 42 pages of Frosty’s 2016 thread, I decided to try to cast a NARB with a WHOLE BUNCH of 1/8” holes. Something like 135. 
 

I found a chunk of perforated plate in the scrap bin at the metal supplier. I used that as a jig to hold greased up 1/8 filler rod for the sprues. 
 

The refractory is Greenpatch 421. No idea how that’s going to go. 
 

I’ve been dragging my feet on this project forever, but I’ve finally got the thing together and shooting flames. 
I don’t have my forge finished yet, so I can’t judge it in its natural environment, but I am pretty happy with what I’m seeing and hearing so far. 

I’ll post updates as I go. Feedback is appreciated, by all means, if you see something, say something. 

[Candidquality]

Burner?  Jet size?  Pressure?  

Curious how this is working for you.  

What are you going to put this in?  So many questions.  

Congrats on jumping off the cliff finally. Be safe.  

 

As for feedback, i'll leave that up to the experts.  Have a feeling it is warmer than a bic lighter, so should heat up something.  Thinking smores right now....

[Frosty]

Welcome aboard Darin glad to have you. 

She's running mighty rich there partner, she needs a little tuning. Ribbon burners don't really need to be in the forge to tune them, they're a lot less sensitive to back pressure than single outlet burners.

Other members have made ribbon burners with small orifices Laticino for one.

I'm sure they'll chime in when they see the title of your post.

Frosty The Lucky.

[Latticino]

Actually Frosty, my multi-port burners have all been made for forced air burners, not naturally aspirated.  I think you must be remembering someone else.  I recall that someone was trying one of those "shower head" style burner outlets with countless small outlets, and it worked fairly well, but haven't heard anything regarding it recently.  

As Frosty says, it does look a bit rich.  Might still be volatiles burning off from the refractory, sometimes that takes a while.  If not, you may have to go through the experimentation stage to properly tune your burner to the multiport outlet.  I can't be too much help there as most of my design experience is with forced air burners (though I certainly have used plenty of the latter type).

[Daren.McIntosh]

Thanks for the questions and feedback.

It’s good to know that the bright yellow flames are more likely running rich than just a product of burning without back pressure. At this point, I’m just pleased that I didn’t blow up or break anything.
 

The burner is a standard 3/4” Frosty T design that I built 3 years ago, and never tuned. 
I can’t remember what tip is in there, most likely whatever is recommended in the build instructions, but never trimmed or adjusted in any way. 
The photo with less flame is 2psi, more flame is 10 psi. 
 

The plan is to side mount this in a table style forge with the top being half a party balloon tank. I wanted a “convertible” forge because I am interested in ornamental iron work and art pieces, but I am not currently interested in burning coal, and didn’t want to be restricted to a tiny forge opening. 
I’ll mess with it more when I get home tonight. I had all this figured out enough to start building it years ago, now I have to go back and re-figure out what I was thinking. I can’t remember my intended forge volume. 

 

[Buzzkill]

I did one similar to this.  I'd have to find my notes or pull the burner to do a hole count, but I think it was around 160 holes at 1/8" diameter.  I used bamboo skewers and petroleum jelly for the holes.  I sifted Kastolite 30 and used that for the refractory.  My memory isn't what it used to be, but I think I ended up using a schedule 80 3/4" pipe nipple with a .023 mig tip to get the fuel to air ratio where I wanted it.  I'm still using that setup, so I can check it out and report back if I remember.

I'm pleased with the overall performance of the burner.  Although I sometimes do get some harmonic howling for a few minutes while it heats up, in use it's generally whisper quiet and provides a great even heat in the forge.  The operational range is excellent as well.  I can go from less than 1 psi showing on the gauge to over 20 psi.  If I've been operating at forge welding temps for a while and try to go back down under 1 psi it will experience some burn back into the plenum, but that's not surprising.

I hope yours works out as well.  I'm certainly interested to learn how it performs for you after you get a few hours on it.

I've also built the style forge you refer to.  I couldn't tell if you are planning to do a floor mount burner or mount it in the shell.  Both work well, but I found I prefer the shell mount burner location due to the amount of floor space I had to sacrifice with the floor mounted orientation.

You may find that half a helium tank is a bit small for that burner.  Unless you will only ever need to heat straight pieces you may want a little more diameter to work with.  If I recall correctly I ended up building my latest one with about 9 inches width at the floor and about 4 inches at the apex.  That gives me a little wiggle room for oddly shaped pieces.  Unless you are going to do long twists you can keep the length to 8 or 9 inches to keep the volume down where a single 3/4" fed burner is enough for forge welding.

Just my 2 cents, but it looks like your burner should do well with a little tweaking.  I'd try the next lower size mig tip as a first step if it were me.

[JHCC]

How was the Greenpatch for the casting?

[Frosty]

Who's directions did you follow to make the T burner? Either not mine or you misinterpreted how to calculate the tube length. The mixing tube in your above picture is WAY too long.

The ratio is 1:8 or 1:9 max. This ratio means for every diameter increase the length needs to be 8x. this is calculated by dividing 8 by the diameter 8 x .75" = 6". Or 9 x .75 for 6.75" tube A 3/4" T burner should have a 6" long mixing tube. much longer than 6.75" starts to inhibit combustion air induction. 

Making them much longer increases skin friction to the point it inhibits induction. Changing out your tube will go a long way to leaning out the flame. Do this BEFORE  trying to tune the burner by trimming the jet.

Frosty The Lucky.

[Latticino]

I suspect the multiport openings, abrupt change in direction at the connection to the burner head, and potential baffle inside the burner head will also contribute to friction losses and loss of induction as well.  There should be a bit of turbulence in that head which will help with mixing, so experimenting with a shorter mixing tube might be worth consideration.

[Frosty]

When I developed NARB I eliminated a baffle entirely, placing the intake port at 90 to the orifices evened the flow across the orifices. The way the diffuser is welded across the intake port in the plenum is the main reason some of the build plans call for such high static pressure from the blower and shoot dragon's breath a couple feet out the doorways. Those pics and plans are why I started tinkering with NARB. Commercial multiple orifice burners operate on very low PSI and produce very soft HOT flames. NARB is my awkward attempt to copy a commercial version. 

I discovered a LOT of factors that inhibited flow velocity for one, skin friction increases as a square of the circumference. (If that makes any sense) Basically the area is the square of the radius. so the smaller the orifice's diameter the greater the ratio of circumference and friction. EG a 1/8" orifice will have one quarter the carrying capacity of a 1/4" orifice and 2x the circumference/friction. 

That's why you need to increase the number of outlets from say 20 for 1/4" dia. to 80 1/8" dia outlets to equal carrying capacity before factoring in considerably higher skin friction. I don't think 160 orifices is a bad departure point for 1/8" orifices.

I did a LOT of mock up test burns before I got a good enough NARB. 

If I make another I'll cast a much thinner burner block and add bubble silica to the Kastolite-30 AFTER I sift it on a 40 sieve. Dang, now I'm starting to relive the thoughts and ideas I had earlier. One thing I will do when I reline my current NARB forge is mix Zircopax with the Plistex for a final kiln wash. Somewhere I have pages of sketches for a reasonably practical way of casting the flame face side of the burner block with about 1/4"+ zircopax, bubble alumina, Plistex blend as a heat shield. 

And THAT is why I haven't actually made another. 

Frosty The Lucky.

[Daren.McIntosh]

The tube was 8” long for some reason, thanks! I grabbed a 6” nipple on the way home from work today. I’ll try to make time to fire it up tomorrow. 

There is no diffuser in this burner, I figured splashing off of the other side of the plenum would be sufficient. 
 

As for the forge, I really liked the idea of Eric Fleming’s ribbon burner table forge. But, like Buzzkill, I was not a fan of the floor space lost to the burner. My plan is to mount the burner on the side. 
The forge body has a 7” diameter chamber. With the flat bottom, the height is 6”. 
According to this Partial Cylinder Calculator, the volume should be 350ci. The plan is to allow for different forge bodies in the future without completely tearing apart the forge. 
The floor will be cast and the front/rear “porch” areas will be replaceable firebrick.

The green patch says it is good for up to 3” depth, but if I were to do it again, I would likely cast it in layers as I did get some warping/shrinkage. If I do that in the future Frosty, I may do as you say and make the first layer as a heat shield. 

 

 

[Frosty]

Making the tube 8" long no matter what the diameter is is a common mistake. I don't think ratios are taught in school anymore so I started explaining the 1:8 as clearly as I could. Even then. <sigh>

You don't need even 1/2" of Greencast for the floor, I actually have about half a sack left from before I discovered Kastolite. Just rigidize and heat set ceramic blanket under the floor before applying the hard refractory flame face. K-26 IFBs under the floor work nicely too, they'll support anything a person is likely to try heating and the Greencast makes fine armor.

From this angle your jet looks a little too deep. When making a new size I use 1/2 way across the air intake port as the departure position for the end of the mig tip. That's a little deeper than I prefer so it leaves me room to fine tune. I have a drill gage I marked to gage mig tips for 3/4" burners. Hold the mig tip's step where the threads begin against the 90* edge of the gage and there is a mark filed in the drill gage where the proper departure length for a 3/4" burner. Hold the mig tip in the gage and scribe the cut mark and cut it. I cut them by chucking them in a reversible hand drill and make the cut with a dremel cut off wheel. Makes nice clean cuts a touch with sand paper cleans right up. A pass with a torch file and it's ready to install and tune.

Of course that only makes sense if you're making lots of burners. OR had a machinist Father who taught me from farther back than I can remember to ALWAYS make marking jigs. Can''t get the machinist influence out of your blood and bones you know. Everything on this house was measured within a 1/32" AFTER I weaned myself off measuring to 1/64".

Frosty The Lucky.

[JHCC]

1 hour ago, Frosty said:

I started explaining the 1:8 as clearly as I could.

That was a proportional response.

[Buzzkill]

15 hours ago, Daren.McIntosh said:

My plan is to mount the burner on the side. 
The forge body has a 7” diameter chamber. With the flat bottom, the height is 6”. 

This is where it can get a little bit challenging.  You really don't want the flames entering the forge chamber from the side at floor level where they will hit your stock before combustion is complete. You, in my opinion at least, want to install the burner so that the flames enter the forge near the apex of the forge chamber and have a little room for combustion to complete before impinging on the lining. Based on your pictures I'm guesstimating you have about 2.5" from the mixing tube to the business edge of the burner head.  Unfortunately this means the preferred mounting spot is such that your mixing tube will hit the side of the shell before the burner head gets as deep into the forge body as would be ideal.  Of course you can flip the burner 180 degrees so that the T is sticking up above the forge, but then you need to build some support for the mixing tube to help hold the burner in place, and it also increases the likelihood of recycling exhaust gases.  I prefer the side mount near the top to encourage swirling of gases in the forge, but I think this issue is why some people mount ribbon burners in the top of the forge body and point the flames straight down.

As with most things, there are advantages and disadvantages to the various options here.

[Frosty]

1 hour ago, JHCC said:

That was a proportional response.

What are the odds of that?

Frosty The Lucky.

[JHCC]

Even odds.

[Daren.McIntosh]

Thanks for all of the feedback. 

I installed the shorter pipe to great success. (Second pic.)

Then I shortened the mig tip to 1/2 way. (First pic.)

 

Buzzkill, I had planned on mounting the burner along the floor, not thinking that direct contact would be much of an issue given that these flames are not quite as intense as a single orifice burner. If that setup would be particularly detrimental to the steel, I can mount it higher and deal with the burner tube being angled. 
 

The plan was to use ceramic wool under the floor with a decent layer of refractory on top to protect it. 

[Frosty]

That's looking much better, how about a closer shot of the primary flames, it might want a BIT more fiddling.

Having the flame impinge directly on the work is less effective, even detrimental in the type "forge" we build. What we use are reverberatory furnaces which means the flame heats the furnace liner and the refractory liner stores the energy radiating it back into the chamber as intense IR radiation. The IR radiation is what heats our work. The burner flame is actually cooler than the superheated refractory forge lining.

Absorbing and storing energy is why some materials work better than others  for the fame face, Plistex conducts thermal energy more slowly than Kastolite or other hard refractories so it becomes hotter and the surface racing the forge chamber is the path of least resistance for it to shed heat as IR radiation. Zirconium is a worse conductor and so stores and radiates more intense IR. 

It's counter intuitive but the refractory is absorbing and concentrating energy from the flame, the concentrating is what makes the liner hotter than the flame itself. Kind of weird but it works.

Sooo, having the flame blow directly on your work actually inhibits an effective transfer of heat. first it isn't finished burning so isn't as hot as it will be. Second it makes a flame shadow behind the work and the energy doesn't transfer to the refractory liner well.

If however the burner block is far enough away the flame has finished with combustion it isn't so bad. The darker more transparent flames are the outer flame envelope and have nearly completed combustion and will fill the chamber regardless so blowing directly on the work isn't as bad. Not great but not too bad.

Frosty The Lucky.

[Daren.McIntosh]

Makes sense. Thanks Frosty. 
 

Here are some closer shots of the flame. 
most of these are at 1-2psi. The longer flames are 4-5. I’m digging how quiet this thing is. 

Hopefully I’ll get time to start rigidizing and coating wool this weekend. 

[Frosty]

Nice even flames, looks a little rich from here. I love how quiet my NARBs are but be aware they aren't quite as hot as a single outlet burner.

Frosty The Lucky.

[Daren.McIntosh]

Lucky, have you been able to weld with a NARB forge?

I’m not planning to weld up huge stacks of Damascus regularly, but I was hoping to stick a few pieces together for some upcoming projects. 

[Frosty]

Yes. You have to be more careful with the prep but it welds well.

Frosty The Lucky.

[Buzzkill]

On 7/29/2023 at 6:37 PM, Daren.McIntosh said:

have you been able to weld with a NARB forge?

High carbon billets weld well with my NARB powered forge. As Frosty indicated, prep is key. Every mating surface has a fresh shiny grind, and the layers have uniform dimensions. I don't use flux - just a dip in oil before heating.  I haven't tried to forge weld low carbon or irregularly shaped stock, but I'm pretty sure I could do it - especially if I used flux.

[Daren.McIntosh]

It’s been slow going, but I’ve got the refractory pretty well cured and coated with Plistix. 
Doing short test fires now. 
 

[Frosty]

It's still running pretty rich but that's just an adjustment. 

Frosty The Lucky.