Moonburner malady

blackjack2564 said:

Every procedure has it's own unwritten little tricks, now you know a couple of them...lol

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My unwritten trick on bates grain motors is to pre-glue the o-rings to the tops of the grains. Then, each grain can be pushed to the end of the tube instead of trying to push all six grains when inserting the final grain. This makes the whole process a piece of cake.

Jim

mikec said:

People are just speculating about that, I have no idea what the CTI adhesive is -- CTI doesn't use HTPB in their propellant AFAIK (it's thermoplastic) so I don't know why they would use it for adhesive. As I've said, AT just tells you to use hobby epoxy on their moonburners; if you use 30-minute you have more time. Further, they don't tell you to glue the grains to the liner, so you can assemble them outside the liner or at least not worry about having them seize.

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Cti absolutely uses htpb in the propellant...I've seen the drums at the plant in canada.

tbonerocketeer said:

Cti absolutely uses htpb in the propellant...I've seen the drums at the plant in canada.

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You got to go to the plant?!? Niiiiice!

jrkennnedy2 said:

You got to go to the plant?!? Niiiiice!

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I've actually been 2 times now. It's a neat place. Been to aerotech as well...guess it's perks of being a dealer.

well oh crapola.... this thread just saved me a CATO... mucho thank you
I cannot 100% remember if i glued the grain faces on my M840... expensive mistake, but better burn barrel than exploding in mid air. Ho hum..

informative thread... again THANK YOU...

sorry about the OP's prob, but, this may save a few more of us from making BOOMSTICKS instead of motors..

Salvage-1 said:

well oh crapola.... this thread just saved me a CATO... mucho thank you
I cannot 100% remember if i glued the grain faces on my M840... expensive mistake, but better burn barrel than exploding in mid air. Ho hum..

informative thread... again THANK YOU...

sorry about the OP's prob, but, this may save a few more of us from making BOOMSTICKS instead of motors..

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Dont burn barrel the motor . If you cannot remember for sure , cut the liner off the grains . You can purchase a new one . peel a layer of glassin off the casting tube and re epoxy it .

Eric

3stoogesrocketry said:

Dont burn barrel the motor . If you cannot remember for sure , cut the liner off the grains . You can purchase a new one . peel a layer of glassin off the casting tube and re epoxy it .

Eric

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Well.. yes, tis something to try.. especially since the 840 is 'rare' at the moment

3stoogesrocketry said:

Dont burn barrel the motor . If you cannot remember for sure , cut the liner off the grains . You can purchase a new one . peel a layer of glassin off the casting tube and re epoxy it .

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As I mentioned earlier in this thread, epoxy is not a good inhibitor. The flame front will get between the epoxy and propellant. Also, peeling the casting tube after previously gluing could give a paper spiral layer that is too thin. If you want to try recovering the grains, use a 1:1 EW ratio of HTPB:curative as the adhesive/inhibitor. If it's too thick to handle, add 10% DOA(plasticizer) There are no compatible solvents to thin HTPB and still have it cure correctly

Consider the cost of the rocket and the motor hardware, and possibly the onboard electronics, before trying to save money on a questionable reload.

jsdemar said:

As I mentioned earlier in this thread, epoxy is not a good inhibitor. The flame front will get between the epoxy and propellant. Also, peeling the casting tube after previously gluing could give a paper spiral layer that is too thin. If you want to try recovering the grains, use a 1:1 EW ratio of HTPB:curative as the adhesive/inhibitor. If it's too thick to handle, add 10% DOA(plasticizer) There are no compatible solvents to thin HTPB and still have it cure correctly

Consider the cost of the rocket and the motor hardware, and possibly the onboard electronics, before trying to save money on a questionable reload.

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I had the problem of the grains being too small on an O-3400 a while back. After discussions with CTI, we elected to build up the diameter of the grains using HTLO and Papi 901 with microballoons. The process was successful and the motor worked fine (some might argue too fine). The process I used was documented here:

https://www.rocketryforum.com/showt...e-stager&p=1617436&highlight=3400#post1617436

Jim

jsdemar said:

As I mentioned earlier in this thread, epoxy is not a good inhibitor. The flame front will get between the epoxy and propellant. Also, peeling the casting tube after previously gluing could give a paper spiral layer that is too thin. If you want to try recovering the grains, use a 1:1 EW ratio of HTPB:curative as the adhesive/inhibitor. If it's too thick to handle, add 10% DOA(plasticizer) There are no compatible solvents to thin HTPB and still have it cure correctly

Consider the cost of the rocket and the motor hardware, and possibly the onboard electronics, before trying to save money on a questionable reload.

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John,
Would epoxy with an opacifier be a better inhibitor, or is that not the problem? If I made motors I’d probably want to have HTPB but I don’t know that I would want to keep it stored just for the occasional commercial moonburner. However, I always have bunches of epoxy.

Steve Shannon said:

John,
Would epoxy with an opacifier be a better inhibitor, or is that not the problem? If I made motors I’d probably want to have HTPB but I don’t know that I would want to keep it stored just for the occasional commercial moonburner. However, I always have bunches of epoxy.

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An opacifier helps, but it's the melt characteristic of the epoxy, inability to bond to the propellant, and its stiffness.

There are small-quantity consumer-accessible polyurethane+MDI 2-part adhesives (say that 3 times fast!). Some have 10 min cure times, some longer, some have various fillers. The one-part polyurethane adhesives (for construction and cement) are typically moisture cured over 24 hours (not convenient). In general, they are much better than epoxies or silicone adhesive for inhibitors or bonding grains together. I'm not going to recommend a specific product until I have more experience with them. But, they are available from 3M, Loctite, Sika, etc.

jsdemar said:

An opacifier helps, but it's the melt characteristic of the epoxy, inability to bond to the propellant, and its stiffness.

There are small-quantity consumer-accessible polyurethane+MDI 2-part adhesives (say that 3 times fast!). Some have 10 min cure times, some longer, some have various fillers. The one-part polyurethane adhesives (for construction and cement) are typically moisture cured over 24 hours (not convenient). In general, they are much better than epoxies or silicone adhesive for inhibitors or bonding grains together. I'm not going to recommend a specific product until I have more experience with them. But, they are available from 3M, Loctite, Sika, etc.

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Thanks!

jsdemar said:

As I mentioned earlier in this thread, epoxy is not a good inhibitor. The flame front will get between the epoxy and propellant. Also, peeling the casting tube after previously gluing could give a paper spiral layer that is too thin. If you want to try recovering the grains, use a 1:1 EW ratio of HTPB:curative as the adhesive/inhibitor. If it's too thick to handle, add 10% DOA(plasticizer) There are no compatible solvents to thin HTPB and still have it cure correctly

Consider the cost of the rocket and the motor hardware, and possibly the onboard electronics, before trying to save money on a questionable reload.

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Yea, nothing like what you Big Dogs deal with but, I nuked a 4" Mania, 2 RRC2+es with mounts batts etc, A Eggfinder GPS, a Mobius camera on one of those cool internal mounts (munching both parts), an Aero Pac retainer ring, and 6gr 75mm CTI case. Somehow the Lrg LOC Angle parachute came out unscathed (and unsinged). These grains were recovered from a prior M840 "stuck grain" build (my fault), the adhesive sanded off and re-inserted into a new liner using Gorilla Glue (GG) as the adhesive (yet another bad move on my part) resulting in my starting this thread. I tell you what, this thread has become more informative than I could have imagined and well, maybe even if it costs me quite a few $$$ to try again, I'll learn and remember something. In that case IT WAS WORTH IT!!!!

Much much THANKS!!!!

I am feeling quite lucky, after spending a couple of hours and some attention, I managed to get the grains out, and i believe that they are reusable.
Two things worked in my favor
1) I mistakingly put the supplied O rings between each grain, and i didnt put glue on each face
2) The provided CTi adhesive never set, not even a little bit. There was still liquid that could be wiped off the outside of the casting tube. Yes, i did keep the rest of the adhesive from building this, and that set hard within an hour or so.

1:1 EW Ratio HTPB:Curative will be the next step in building this