Another FrankenBurner

3D printed plastic burner experiments (photo heavy)

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On ‎1‎/‎9‎/‎2019 at 3:05 PM, John in Oly, WA said:

On your molds cracking during cool down after burnout. How cool are you letting them get?

I was cooling them to room temperature.  We just barely started on the casting phase and we had not done the homework.  The investment used has been plaster of paris.  I have done a bit of homework since your post to learn what you are talking about.  I will be building a vacuum platform and using flasks on future molds.  Thank you for all of the information and making me do my homework.  I may eventually shift over to the wax filament but I have the Bowden system and read that direct is the only way to go for the wax.  I'm sure I will come up with some questions.

Controllable pitch ribs sounds like a fun experiment.  I will have to create a different model to play with that.

 

23 hours ago, Mikey98118 said:

which one of the three flame photos at different exposures most closely matched what your eyes saw?

I was demonstrating the difference in exposure.  I was able to take a picture of a purple oxidizing flame which would have been determined rich based on photo alone.  I always judge the flame based on what I witness.  What I witnessed was the nozzle temperature of the left image and the flame of the right image.

Thank you for posting all of your flame reads throughout the forums, so that I could learn to interpret the flames.  Without that, all of these experiments would not add up to much. 

 

8 hours ago, Frosty said:

Have you considered making the intake structure larger in diameter?

I sure have considered it and intended on doing so.  I am pretty sure, the more we strive for lower velocities, the more the burner is going to look like a wasp waist burner.  As to the length, are you talking about the length of the trumpet shape or the length of the ribs? 

At first things moved fast with a few different big picture tests.   Now I am getting into the nitty gritty.

I am going to start changing one thing at a time with each print to determine what changes.  I still need to play with the practicality of the helix on the ribs, the shape of the airfoil, the angle of the ribs, the diameter and curves of the trumpet shape, and the ratio of air inlet to rib surface area.

8 hours ago, Frosty said:

Just a thought, my brain won't stop thinking things you know.

That is a great thing.  Keep them coming.  Anything that you want to test, I am willing to test.  

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I used plaster of paris when I started out. Read somewhere that adding sand to it made it durable enough for casting. It doesn't. Had one plaster of paris mold crack apart while pouring the metal. Good thing I had it all in a large tray of sand, otherwise it would've been hard to contain the disaster. After that, I did my homework and switched to real casting investment.

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Did you happen to be using a flask for this failure?

What investment are you using?  

I've heard the sand/plaster mix for foundry/forge formation.  It works equally bad for that from what I've read.  

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Agree with John.  Plaster of Paris degrades at a very low temperature.  You need to use an investment for casting.  Do a search for "molding investment" on amazon.  I've done more shell casting, but did some investment casting years ago and that's the type you should get. 

For DIY investment, as I recall it was equal mix of 1/3 casting plaster, 1/3 sand, 1/3  grog (I read that powdered clay available at pottery supplies would work, I think powdered old soft firebrick would probably work too).  The Plaster is a binder, the sand is a refractory, and they powdered clay/grog is a modifier and strengthen the mix.  Give that a try, it will work better then then plaster of paris alone.

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On ‎1‎/‎8‎/‎2019 at 8:17 AM, Another FrankenBurner said:

Frosty, I had another thought.  It would probably disrupt the FAM stream but if the entire mix tube were aluminum, fins of some kind could be printed inside the outlet end of the mix tube.  This would act as a heat exchanger to both cool the mix tube and preheat the FAM.  It would have to be balanced to prevent suck back and also melt down.  High output burner melt down sounds like no fun.  I have 2 shutdown ball valves(one at each end), the idle valve assembly, and the final needle valve.  I like safety nets.

I would suggest incorporation a short (4" long) stainless or mild steel section of mix tube onto the end of any cast aluminum mixing tube, for safety's sake; it is generally the last three or for inches of mix tube that really heats up.

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We are relying on that for safety net, especially since the prototypes are run in plastic.  For a few experiments we have used shorter steel mix tubes but most of them are 5 inches or so.  As we obtain higher nozzle temperatures, the mix tube transfers that heat.  

Once the burner is aluminum and mounted in a forge, we will be making your secondary air choke to control secondary air and block radiant heat out.

I am now playing with larger diameters which will have some hollow space at the mix tube end of the cast.  I am going to experiment with cooling fins, like air cooled engine cylinders, on the outside of the cast.

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On ‎1‎/‎12‎/‎2019 at 10:01 PM, D.Rotblatt said:

Do a search for "molding investment" on amazon.

For DIY investment, as I recall it was equal mix of 1/3 casting plaster, 1/3 sand, 1/3  grog

I will do both.  Thank you for the recipe.  I have found a few recipes which are all similar.  Usually 1/3 plaster, 1/3 silica sand, and 1/3 something else. (clay, grog, hydrocal, etc.)  One recommendation to paint the item in a good investment (he recommended Kerr products) for detail and then use the diy recipe for the remainder of the mold.  I will experiment with all of the above.  My casts do not need the intricate detail that jewelry requires.

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On ‎1‎/‎11‎/‎2019 at 7:31 PM, Another FrankenBurner said:

What investment are you using?

I have some Kerr Satincast. I understand they are out of business now. And I have some Certus Prestige Optima, which is supposed to be designed for 3D printed resins (SLA), wax based polymers and wax/plastic hybrids.

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On ‎1‎/‎10‎/‎2019 at 12:04 PM, Frosty said:

Have you considered making the intake structure larger in diameter? It wouldn't need to be so long as these proto types but the larger intake flare would induce a stronger vortex with a stronger low pressure zone in the center.

Version 2.7.2 next to version 2.7.1:

burners.jpg.e3f6ed8fa89b31718fead866bdde9ea8.jpg

It is 1/2 inch larger diameter.  I stretched the airfoil so the air inlets are still 50/50 with the ribs.  I am going to print another with smaller ribs.  I started to tinker with it but ran out of fuel.  It seems happy with the 0.032 drilled mig tip and accepts lower pressures then it's smaller counterpart. .  

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I don't think smaller ribs will improve the design. Maximum spin will always improve the burner. Excess air space won't in my opinion; of course, I can always be wrong :rolleyes:

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I was able to do some tinkering today.  I had previous CAD and printed several iterations of the larger diameter burner with changes to the ribs only.  The intent was to determine if the helix ribs are beneficial or harmful to burner function.  Below are the burners tested against each other today.  

1046576145_EvolutionofBurners.thumb.jpg.ad750589f5aec37ce5d90fdeedc1f22e.jpg

These are all 1/2 inch burners.

Diameter comparison:  Going to the larger diameter is an improvement.  Version 2.7.1 always has a small secondary flame, version 2.7.2 eliminates it for the most part.  Version 2.7.1 can be turned down to 6 psi before it starts to stall and it is burning very poorly by then.  It is happy above 8 psi.  Version 2.7.2 will run below 1 psi but it begins to produce a secondary flame if under 2.5 psi.  It is happy at 3 psi and above.  Both are happy to run above 20 psi.

2.7.2: So far this guy is the winner.  The helix ribs reduce some of the air induced but it is because it is using the energy to add extra spin down the mix tube.  This makes a flame which appears stable and constant.  It induces enough air so it doesn't create a problem.  It is happy with a larger range of pressures without having secondary flame show up.  It is much less susceptible to drafts then the other designs.  

2.7.3: Ribs are straight with the same airfoil shape as 2.7.2.  This design induced less air and produces a secondary flame unless at higher pressures.  It was not tested long as it was a poor performer.

2.7.4: Ribs are straight, rounded.  This design induces more air then 2.7.2.  The flame is more turbulent and less stable.  It has obvious signs of spin down the mix tube when looking at the secondary flame.  The spin almost seems to oscillate or collapse which is what causes the stability issues.  It has a fluctuating roar.

2.7.5: To see what would happen with maximum air opening.  Going to the linear burner.  It induces the most air of the bunch, at the lowest pressures.  It has a secondary flame at most pressures.  I guess it is poor at mixing.  

 

Here are some images of 2.7.2 flames at different pressures.  I like it's wide accommodating range.  Above 5 psi, it needs a bigger mig tip as it induces too much air.  They were all taken shortly after startup to prevent orange in the flame from the nozzle.

Low flame, <1 psi, without a nozzle:

1564987522_microflame.jpg.ae87d582bdb259d3352951cf842c6e56.jpg

I had a burner flare from Larry Zoeller meant for a 3/4 inch burner.  I made a step out of 3/4 pipe to the 1 inch stainless flare.  This gives me a stepped nozzle which is also flared. 

Here is a small flame at 3 psi:

1311113912_smallflame.thumb.jpg.d1c8a04f5cc798029a829ae8bfce7b2c.jpg

Here is a flame at 5 psi:

1814208991_MedFlame.thumb.jpg.bf1e5aa49037ef263a0eaa8d8b3ae354.jpg

Here is one at 10 psi:

1280047932_HighFlame.thumb.jpg.77193d12f5a34b52b62fa9c4f22bf455.jpg

 

Now I am going to play with the length of the ribs as they are much longer then needed.  I have 1 inch long air openings and based on playing with two chokes, I suspect it will be happy with 3/8 - 1/2 inch.

As always, any conversation, criticism, suggestion, idea, or education is welcome and wanted. 

Bigger diameter is better, thank you Frosty, you were right.  More spin down the mix tube is better, thank you Mikey, you were right.

 

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So far 2.7.2 has my vote. Beautiful looking flames.

From the orientation of looking down the tube intake to nozzle which way is it rotating, counter clockwise?  

Frosty The Lucky.

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It is rotating clockwise currently.  That could be easily changed if you think we should try it.  I printed a previous version in both directions and did not notice a difference in the flame aside from the direction it was rotating.  

I plan on playing with diameter to determine the optimal diameter.  Like with the experiments with the ribs, I will change nothing but the diameter for a few version to see how diameter changes affect the flame and what the maximum size is before it becomes a hindrance to performance.  The only complication is the shape of the trumpet.  To maintain the curve of the trumpet on larger diameters, that section will be longer.  If it is not lengthened, the trumpet gets sharper which makes it more of a conical funnel.

The current trumpet is approx. 1.7 inch  diameter, 1/2 inch long, and necks down to 0.622 inch throat diameter (1/2 inch pipe ID):

outlet.jpg.7e4745c996858280fde0e511ece4421b.jpg

Originally my focus was on inducing enough air as this has been such a problem in the past with burner designs.  The burner being printed with proper shapes makes it easy to induce too much air so it is no longer the focus.  Now the focus is the cleanest burning flame over the largest range of pressures which is still stable.  A few of the burners had a perfect flame at an exact pressure and were very picky about tuning.  I had one burner which produced a purple flame but also had a large secondary flame which I took to mean improper mixing.

I am pretty happy with 2.7.2 so we will be working on casting him in aluminum for some actual forge testing. 

We are also in the process of making another forge for these burners.  This time using a cnc foam cutter to cut the inner profile for a mold for the kast o lite.  I am attempting an oval split forge with burners angled upward from the bottom half.  I am shooting for 350 cu. in. with more floor space.  I took a 4.5 inch diameter circle, cut him in half, and split the halves by 3 inches.  The forge is 12 inches long, my math came out to 352.8 cu. in.

When I am done tinkering with the induction portion of the burner, I will be 3D printing forms for a NARB to match the burner.

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I tested another version today.  Major changes to the flame.  I took the trumpet restriction and doubled it's length.  

498053401_2.7.8-9.jpg.ff47fbe1e3cb66d3a6b56f4ccc9563f1.jpg

This change increased air induction by a magnitude.  With the 0.023 mig tip it is producing an oxidizing flame with the pressure needle resting on the minimum peg.  I ran it with another tip, an 0.025 which has been drilled to 0.032 actual.  It also produces an oxidizing flame.  It's low pressure range is the best I have produced.  

I am going to use torch tip cleaners to enlarge the jet.  I also ordered some 0.030 mig tips to see if it can support that large.

 

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I don't think the direction of rotation makes a difference, should say I don't know if it does. I was curious so I could get a better mental picture of how the ribs were acting. 

I'd be tempted to bracket the jet dia. rather than creep up on it. 

You have some REALLY cool toyls.

Frosty The Lucky.

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Well, since we're on the topic of jets, has anyone attempted using a 3D printer nozzle as an orifice?  The common sizes range from .2mm up to 1.0mm in 0.1-0.2mm increments.  They don't have a long diametral transition, so the flow out the tip is likely to be turbulent, but dang if they're not cheap (and get to *really* small sizes!).

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Frosty: Here is a shot from the top to hopefully explain the ribs.  I mostly have no clue what I am doing so at one point I looked into airfoil design in an attempt to streamline.  

top.jpg.59407c489934792e29ac2af8a920c805.jpg

I have ordered 0.030, 0.035, and 0.045 mig tips.  I will take your advice and not get out the tip cleaners until I have an upper bracket.  I am expecting the 0.030 to be over sized.  It would be nice if I am wrong.   

HojPoj: That is a fun idea.  Bigger selection in sizing, super cheap, and listed by their actual diameter.  Wouldn't that be nice.  Like you, I suspect the turbulence/spread makes them poor performers.  I have seen a few posts in which people had drilled out their own jet, left the length short, and it didn't work well.  Cheap enough to play around with anyway.

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Your changes are dead on so far. you will probably need a .030" MIG tip to keep current with the increased air induction.

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I'd sure like to see a stream of smoke induced into the system. Be interesting to see the motion of the air. 

I'm thinking 0.030 is conservative.

Frosty The Lucky.

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I will do some smoke tests since I am waiting for mig tips at this point.  Also since I am waiting, I scaled and printed a 3/8 version of 2.7.9 to see if it could induce enough air with an 0.023 mig tip but I have to make mix tubes and proper nozzles.  I stuffed a 3/8 nipple into it and faked some nozzles and it runs rich.  I haven't given it much of an attempt yet. 

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That is unlikely to work out. A .023" MIG tip runs a little too rich for a 1/2", si even your improved air chamber design isn't likely to be enough to run one in a 3/8"; not that I wouldn't be delighted to be wrong about this :)

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I suspected that would be the case when I printed the 3/8 burner.  As I am waiting for larger mig tips to try in the 1/2 inch burner, I figured why not give it a shot.  I was hoping that since I might be able to upsize the mig tip in the 1/2 inch, just maybe I could pull off a mig tip with a 3/8.  I am toying with increasing the diameter and length of the reduction in an attempt to induce even more air.  Mostly to learn about the limits.  Fun experiment and challenge.  I imagine even if I did pull off inducing enough air, the volume would be great enough, the FAM velocity down the mix tube would be very high.  

As is, with the 1/2" burner, I am anxiously awaiting the mig tips.  I am curious what the change did to the induction curve.  I would rather have better range without fiddling with a choke then absolute maximums.  Though, I want to find the maximums I can achieve so that I can understand the hows (and maybe the whys) and detune from there if needed.

With the turn down range of the 1/2" burner, I suspect it will work well in a small forge.  After seeing AngryDaddyBird's first forge, I am building a coffee can forge to test.

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4 hours ago, Another FrankenBurner said:

I imagine even if I did pull off inducing enough air, the volume would be great enough, the FAM velocity down the mix tube would be very high

Too high flow speed and too rapid spin can be equaled out with a longer mixing tube, or a larger stepped nozzle diameter.

With larger burner sizes, a longer mixing tube can get akward. Hower, in smaller burner sizes, extra length in the burner tube can be an advantage.

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I suppose it is all a balance choice.  For practicality, a longer mix tube and/or larger stepped nozzle would be comparable to moving up to the next ID mix tube with the same jet.  So long as the low end range of the next size is low enough, it's easier to build.  I still see the practicality of the 3/8 burner but see why you state that it requires moving on to needle stock or capillary tubes.  

I have been thinking about the dynamics of each piece with my experiments.  Trying to learn what they all do.

With the trumpet length, if the diameter is unchanged, I suspect that shortening the trumpet induces more spin and less air and vice versa when lengthening it.  I suspect that increasing the diameter increases both, spin and air induction.

I am starting to understand the relationship between mix tube diameter, jet diameter, and output desired.  It has more to do with mix tube velocity vs btu's and less to do with induction than I originally thought. 

I'm still not entirely sure how mix tube length works.  I feel it is the balance measurement I know the least about.  Longer mixes better, lowers velocity, and reduces air induction.  Right now I trial and error with a range of lengths but the best balance usually falls close to the 8-9 rule of thumb.  

I will continue playing with a smaller throat with a taper out like in version 3.3.  It makes the heads longer but I am curious if there are any benefits.  

After learning what all this stuff does, finding a balance between inducing enough air, adding good spin, mixing properly, and not being overly large while being stable over a good range, will be the next step.  This balance can be shifted depending on application requirements.  

With all the fun talk over in the NARB thread, I am wanting to jump on that bandwagon as well.  So many exciting projects.  I better finish the inducer learning first.

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