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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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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