3D printing APCP?

Discussion in 'Propulsion' started by Andrew_ASC, Oct 10, 2018.

  1. Oct 10, 2018 #1

    Andrew_ASC

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    With my professor getting an L-2 this weekend, there is another design team at UTC of senior engineering students trying to 3D print solid rocket fuels. They’ve already done hybrid rocket fuel grains but those went NDA. I dug around on google and urged them to be extremely careful with that Wimpy Red variant from some Ex forums. I’m not going to post the composition here. Do you think they can get a fuel to simply burn? We all have our doubts. We were even wondering if the crazy jim boron pellets could be printed. These compounds might wind up with a lot of plastic in them.

    Opinions? Has the prof given them the impossible task? Glad I was on a rocket team using certified motors. Just another wacky university project that might not work at all. Lol.
     
    Last edited: Oct 10, 2018
  2. Oct 10, 2018 #2

    Ben Martin

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    I saw a video of a Canadian rocketry team fully 3D printing their fuel grain using a custom 3D printer that one of the students made. It seemed to work really well.

    Link to video:
     
  3. Oct 10, 2018 #3

    Nytrunner

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    I have less qualms over a 3d printed fuel grain than I do over 3d printed solid propellant

    Their fuel grain is for a hybrid and still requires a concentrated oxygen source from a liquid oxidizer in order to ignite/combust properly.

    Solid propellant has its oxidizer bound up within its compound and has a higher chance of.....issues...... if it gets too warm.
     
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  4. Oct 10, 2018 #4

    Andrew_ASC

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    I’ve made rocket candy as a kid on a griddle outside. It was malleable at low warm temp. No experience with APCP in that regard. I’m not doing any of the mixing on that printed solid fuel project. Just gathered some info from being active in hobby and told them be careful. How warm ballPark before lab legit melts down with APCP? Some RCS website had 170F and you could drill into at 500rpm.
     
  5. Oct 10, 2018 #5

    MClark

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    For propellant they may have issues with porosity.
    They need to develop a formula with thermo plastic binders. Melt temperature could be a problem.
    The whole printing system should be explosion proof and bunkered and located where it would be acceptable to have explosions.
    They really need someone as a mentor that has made propellants in a commercial situation, not just some guy at the launch who got his training forth hand.

    M
     
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  6. Oct 10, 2018 #6

    Andrew_ASC

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    The have a few professors with relevant aerospace commercial/government industry experience. One was involved in a lot of LFRE testing at NASA. They might want to think about the explosion proofing safety concerns though.
     
  7. Oct 10, 2018 #7

    boatgeek

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    I don't want to pee in anyone's oatmeal here, but they need to do waaay more than think about bunkers and explosion proof-ness. All of the major motor manufacturers have had fires, some catastrophic, and I don't think that any of them were deliberately heating the fuels beyond what you would need for mixing the fuel.

    I don't know my butt from a hole in the ground on research motors, so this may be a stupid question. Is the uncured fuel liquid enough that you could do something like a concrete pump and use an automated extruder to push the fuel into the grain molds? It would have to flow well enough that you could suck out bubbles in a vacuum. I'm not sure what the advantage is over standard pouring techniques, except possibly that nobody needs to be in the room while the extruder is doing its thing. You'd fill up the hopper and let it go.
     
  8. Oct 10, 2018 #8

    Andrew_ASC

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    I’m not even on the project and I think the idea itself is not that safe and is dangerous. You can already safely cast APCP and basically some geeky profs living in theory land want it printed likely for grant. They are trying it anyways. I think its performance will not be as good as solid fuel casted APCP for one if it even works.
     
  9. Oct 10, 2018 #9

    Andrew_ASC

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    The only real advantage I see is you could print a core in a complex shape that is impossible to cast. This would allow for new core geometries for APCP motors. I don’t think the compromise in performance loss to make it 3D printable will offset performance of new core technology. Just rambling. My lone prediction is a makerbot goes pyro mode and burns in a lab. And the fuel won’t work as well as what we have already by end of semester. But I’ll leave it at imagine something like a dual thrust burn then regressive or whatever you could dream of thrust curve wise. You wouldn’t be limited to one thrust curve. The shapes of the curves could become new kinds of thrust curves.
     
  10. Oct 10, 2018 #10

    boatgeek

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    A far safer alternative would be to 3-D print a core mandrel in a material with an appropriately-low melting point and use that to cast the grains, along the lines of a lost-wax mold. My first thought was coconut oil since that is solid at 70F but melts below 95F. Plus it would make your motors smell like umbrella drinks. :) Paraffin might work, but the melting point may be too high to safely melt it out. I'm sure there's an appropriate wax somewhere between. You would also have to sort out ignition given a thin layer of wax over the inside of the core. Paging Crazy Jim and the magic boron!
     
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  11. Oct 10, 2018 #11

    Andrew_ASC

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    This is like the complete logical reasonable safer answer. And the prof just said pretty sure that’s been done before. University is just pushing for 3D printed APCP makerbot meltdowns be damned to claim a new technology for unknown reasons. University egos... Need that additive manufacturing grant of something looooooooool.
     
  12. Oct 11, 2018 #12

    G_T

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    I think the people having thoughts about 3D printing propellant should perhaps study carefully some of the history of propellant manufacture. Not much of a stretch to use some old methods converted over to 3D. Except, going wrong a little results in rather bad things happening.

    The current practices for propellant manufacturing have been developed through the backwards looking lens of experience. Experience is something burns down, something blows up, something very poisonous happens, someone dies.

    If someone (preferrably far more than one) person on the team is not already experienced (not just exposed) to experimental composite propellants (design manufacture and testing plus chemistry), or equivalent in explosives manufacture, they should steer well clear of this. They are not likely to have a clue how much they don't know about the subject. They would be leaving the known methods of relatively safe manufacturing and venturing into the unknowns.

    For one thing, propellants should fairly well meet the requirements for insensitive munitions. If you are not already well aware of what that means, then better to exit the project and do a lot more learning first, IMHO.

    For another, it is considered best that electrical devices such as motors and switches not be in the immediate region of manufacture. Friction is to be avoided. Etc. Making that 3D printer be safe for this sort of work is a project by itself, regardless of what it is extruding. Remember that propellant is solid stuff that is designed to be as energetic as reasonably possible without quite being an explosive.

    Lots of etceteras, but I've said enough.

    Gerald
     
  13. Oct 11, 2018 #13

    Andrew_ASC

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    Gerald, I sent your note to the prof to dwell on. Maybe the university won’t cram this project down some undergrads throats. I have a feeling a default makerbot is gonna explode or burn up before the semester ends. That’s their assignment right now to print a solid fuel propellant. Not my call and I really don’t like how it says no friction. There’s going to be friction and heat through that extruder. And motors and switches.
     
  14. Oct 11, 2018 #14

    dr wogz

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  15. Oct 11, 2018 #15

    Andrew_ASC

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    It’s not my assignment dude. The problem is the professors are convinced it will limit the core geometry to print a mandrel. They are sticking to the assignment lack of student experience be damned. Ohhhhh this will be epic fail. Pray that no one legit dies or lab blows up literally. I tried to halt stupidity. None of these profs have energetic material experience. They do have industry rocketry experience. They are overconfident IMO. These other kids never seen a HPR rocket or APCP. Yup it’s gonna end well yeah right.... I need to step away from keyboard and take a deep breath.
     
  16. Oct 11, 2018 #16

    Andrew_ASC

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  17. Oct 11, 2018 #17

    Andrew_ASC

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    Prof likes the intestine device and is reaching out to contacts at JAXA. Well there’s a small step in the right direction.
     
  18. Oct 11, 2018 #18

    Landru

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    I am 100% certain it is possible to extrude APCP through a nozzle into a grain geometry. There will be a huge challenge figuring out how to get the right viscosity so as not to collapse the grain while printing, but I feel it is possible.

    The problem is porosity.

    It is extremely difficult to even get 98% density using low viscosity extruded plastic (FDM) and the big issue is the last 2% aren't bubbles, as in cast propellant. The gaps are long paths parallel the extrusion. Add high pressure and each of these paths is a massive, unpredictable increase in surface area inside the grain. There would be thousands of such gaps in even a modest size H motor. It may be possible to solve this with a high vacuum environment, but that adds an awful lot of problems for a CNC machine which requires cooling to motors and electronics.

    If I was going to try and make propellant in some form of additive manner, I would investigate an SLA process, possibly using a mix of resin and ultrafine AP. The hard part is getting a high enough ratio of AP to resin, and still having the mix able to be spread and cured by a laser. You would probably need a system like the large 3d Sysytems machines where the part is in the vat of resin and a spreader coats the top and a laser cures from above.

    As a practical answer, I don't see any benefit which couldn't be obtained more easily through other, cheaper, safer methods.
     
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  19. Oct 11, 2018 #19

    G_T

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    The typical print head for current cheap 3D printers is about 100C less than the auto-igniton temperature of pure AP. Add ready fuel in intimate contact in a fluid form and that auto ignition temperature is going to decrease quite a bit. Boom.

    3D printed mandrels, sure. Fuel? Sure. Propellant? H#@@ no. Not with the usual methods.

    I think my input has gone about as far as it can outside the research forum. I could suggest ways it may be possible to do it, but not with any existing equipment. Plus I don't see the benefit vs the extensive development and equipment costs, plus the MUCH slower manufacturing which means cost per pound of cast propellant would go up tremendously. And how is case bonding going to be achieved? There isn't a practical application here.

    The stomach approach and other continuous mix on the fly methods are potentially much more practical. But I think the stomach method is an expensive solution to a fairly simple problem that has already been solved in other areas of materials industry. It is cool though! But if it doesn't make propellant at least as good as current methods than IMHO it doesn't fly either.

    Gerald
     
  20. Oct 11, 2018 #20

    MClark

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    We made grains with a compounder extruded for auto airbags from pvc and potassium perchlorate.
    Extrusions had 4 or 7 holes and just needed to be cut length. Made tons of it for TRW.
    Only leveled the building twice.

    M
     
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  21. Oct 11, 2018 #21

    OverTheTop

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    :eek:
     
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  22. Oct 11, 2018 #22

    Andrew_ASC

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    Well I showed one of the guys on the 3D print team an APCP fuel grain from a CTI reload. I let him handle it under supervision for a few minutes. Talked of the CTI fire too and how they even had issues in industry manufacturing it safely over decades when dealing with large amounts. Told them Mclark’s comments of the airbag industry error. They said they are going to try the sugar fuels first based on you all’s experience feedback that sugar fuel might be less violatile. Later in the semester they are looking to try APCP or some kind of AP based blend. The professors are hell bent on getting that exotic core geometry even if all they can print is sugar fuel at first.
     
  23. Oct 11, 2018 #23

    grouch

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    Just work in trying to print common sense. This 3D printer stuff is getting out of hand.
     
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  24. Oct 11, 2018 #24

    G_T

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    Sugar melts and is both the fuel and the binder in normal sugar compositions upon solidification. It does not crystallize or solidify immediately but takes time. The printing rate will have to be extremely slow, or chilled which will cause micro cracks all over the place, or it will slump. It is not a dimensionally stable material. It does not have high structural integrity. It is unsafe to do. It is sounding like these people don't even know how little of a clue they have.

    // A fool and his plan are soon departed //

    Bad plan. It is starting to sound like a rocket launch. When someone pushes the button, SOMETHING is going to happen. When they try this, someone post the video so they can get a Darwin out of it!

    One of the worst case scenarios is if they get some initial success somehow with a very small sample, so then they try to print their grain with a much larger supply of chemicals... This concept won't scale linearly with sugar propellants.

    Show them what a burn pile is like. Talk to them about the toxic and corrosive nature of the exhaust products. Show them the high heat output, and that it cannot be extinguished by any reasonably feasible method. Let them know that usual things used to put out fires can even become fuel for such a fire. Water is a fuel for metals for instance. ALICE rocket propellant is an example. Metal is a fuel for oxidizer and burns hotter than the sugar will. Let them know that when a fluid version of propellant gets burning it might just blow burning globules around. Let them know that the burn rate is exponential vs pressure. Therefore if any of it gets confined and burning it will CATO. A CATO next to burning liquid propellant might get extremely interesting over a rather small time frame.

    With liquids, if it goes first order, you won't find your test stand. Or in this case, the printer.

    I wonder if their exotic core geometry is even anything sensible to be putting in a rocket motor. I wonder if they have even done the analysis on that part of the problem. Given how little knowledge they seem to be showing I am doubtful.

    Sorry if I am sounding very pessimistic. I cannot convey how pessimistic I am.

    IF they really intend to do this, the first thing they need to build is a remote robotic controlled bunker with a soft roof. So it blows up rather than out, and then burns out safely away from anyone or anything. And they should budget for multiple bunker rebuilds.

    I wouldn't place their odds of success any better than that of a chain smoking blind drunk mixing black powder dry in the desert with the wind blowing.

    Gerald
     
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  25. Oct 11, 2018 #25

    Andrew_ASC

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    I don’t blame you one bit Gerald. I don’t even agree with it and I helped found the rocket team at UTC. I’m like there were hobbyists killed doing it the safe proven way of mixing motors. We had zero loss of life or injuries so far with my teams and mentoring other teams using certified motors for launching HPR rockets over four launches by now and that part is expanding to SLI. I graduate soon. But profs are reaching out to JAXA for help.
     
    Last edited: Oct 12, 2018
  26. Oct 12, 2018 #26

    Andrew_ASC

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    After much texting they are dropping APCP from the print list until program advances in safety capabilities. They will attempt sugar fuel first.
     
  27. Oct 12, 2018 #27

    watheyak

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    deeee leeted.
     
    Last edited: Oct 12, 2018
  28. Oct 12, 2018 #28

    jderimig

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    Although I fail to see what problem get solved by this solution a better technology would be SLA with UV curable urethane as the AP binder.
     
  29. Oct 12, 2018 #29

    Andrew_ASC

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    And I’d like it if the chem lab doesn’t explode since it’s next to like nine other classrooms full of people. You can avoid conflict and let bad sh*t happen or you can crash through a brick wall like kool aid guy with arrogance on the internet. At least they aren’t doing APCP anymore. Jesus Christ. I can finally sleep after a day of unrest.
     
  30. Oct 12, 2018 #30

    grouch

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    Andrew saves the day.
     
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