LiamPyro Posted June 18 Posted June 18 Quick question about priming strobe stars. I made up a test batch of Hardt's white strobe (51% Ba(NO3)2, 8% KNO3, 13% 200-325 mesh MgAl, 23% sulfur, 5% dextrin) and cut them into ~1/8" cubes, dried, and primed with +20% w/w Monocapa prime, +30% w/w Fencepost prime (basically just a BP+Si intermediate layer for delay), and finished with around +20% w/w granulated BP. Weights for prime are with respect to the unprimed star mass. Plenty of prime it would seem... but no, they blew blind when used as the inner petal on a test shell. They strobe fine on the ground. Video playback shows the prime lighting up nicely, then burning away as the petal expands, leaving unlit stars. Monocapa prime is similar in composition to some strobe igniter primes I've seen, so I thought it would be sufficiently hot, but maybe not? How bad is the critical wind velocity on strobes? Do I need to incorporate an additional delay prime to allow them to slow down more (I assume that this is one reason why they're often used as cores in larger stars)? Trying to get this sorted before the 4th so I can have some Nishiki Kamuro shells with strobe inner petals!
Zumber Posted June 19 Posted June 19 First of all your strobe star has dried pretty well? I have no idea about weather in your area. Where is the video playback? It sounds you have forgotten to attach it.
LiamPyro Posted June 19 Author Posted June 19 Yes, the stars were completely dry. I've attached the video, though the camera conveniently unfocused just before shell burst so it's hard to see what's happening. The outer petal stars were nice, and you can see one or two strobes flashing, but the rest were blind. It was supposed to be a full strobe inner petal. IMG_2310.MOV
Carbon796 Posted June 20 Posted June 20 (edited) That seems pretty odd. That's a ton of prime. On average my total prime layers, would all add up to 25-30ish percent. Your video won't play for me. Was it a hard break. Do you think they possibly could have blown blind ? Granular BP is probably not the best choice for fast moving stars. Honestly I wouldn't even use it to finish stars with. If the star just failed to light. With all of that prime, it should be easy to see. You say that pinball is just BP + SI. But, I would bet that it is, or should be more similar to, scratch mix + SI. I only make that distinction because, they ( BP/scratch mix ) are not really interchangeable in use. Edited June 20 by Carbon796
Almostparadise Posted June 20 Posted June 20 56 minutes ago, Carbon796 said: That seems pretty odd. That's a ton of prime. On average my total prime layers, would all add up to 25-30ish percent. Your video won't play for me. Was it a hard break. Do you think they possibly could have blown blind ? Granular BP is probably not the best choice for fast moving stars. Honestly I wouldn't even use it to finish stars with. If the star just failed to light. With all of that prime, it should be easy to see. You say that pinball is just BP + SI. But, I would bet that it is, or should be more similar to, scratch mix + SI. I only make that distinction because, they ( BP/scratch mix ) are not really interchangeable in use. I figured a fine granulated bp top coat would easily light up the primed underlayer, but your saying maybe not the best choice for fast moving stars. Could you elaborate? I often learn things from your input as well as op's posts, so I'll say thanks!
Carbon796 Posted June 20 Posted June 20 (edited) A fine grained BP may/will/can burn off too fast and clean. Before, its able to transfer any appreciable heat, into the star. Especially if its moving fast. Where as a scratch mix will burn slower and more slaggie/slaggy ( SP ? ) it transfers more heat into the star. Similar to why SI is used/added. I would have thought, he had more than enough prime. ( and the right ones ) On that star to get it lit. ( The only thing that sounds off about it to me, is the BP finish prime ) He's going to need to determine, if they blew blind. Or if the prime lit, but failed to light the star. Which should be easy to detect, if the video isn't too poor. Edited June 20 by Carbon796
Almostparadise Posted June 20 Posted June 20 So pulverone may be better suited as a granulated top layer since it would be slower burning?
LiamPyro Posted June 21 Author Posted June 21 Yes, the prime lit. I can see the inner petal prime burning off, leaving unlit strobes. The break wasn’t all that hard - the outer petal stars drooped considerably before burning out. I chose -50 mesh granular BP (cedar charcoal) as a final coat, since my stars seem to blow blind without it. I’ve had enough of blind stars! I did a comparative “study” (which I should post…) of different primes in an “extreme case” of hard-broken flash bombettes, and found that finely granulated BP had the best ignition. Dusty meal and screen mix were both worse (esp screen mix), and the “control group” of air float meal prime with a smooth (not dusty) final surface was atrocious, only one test star lit. The outer coat is intended to just catch the fire, before transferring ignition to fencepost prime and then either to the star surface or to a tertiary hot prime. I’ve found that keeping stars lit is usually pretty easy as long as there is sufficient prime of the correct composition, it’s the getting them to catch fire from the break (esp rolled stars) that’s difficult. 1
Carbon796 Posted June 21 Posted June 21 (edited) I'm pretty sure I've either made that formula before, or the similar Bleser equivalent ( iirc ). As 1/4" cut stars, had no problem lighting them. But, they didn't really strobe reliably for me. Edited June 21 by Carbon796
Pyroboy Posted July 28 Posted July 28 To light Strobestars when using a decent burst charge can bee a pain in the ass. If the storbe stars travel to fast they will bee blown blind! I would try your stars in a waterfall shell or rocket. No burst, just some soft push out of the header / shell. then you should check, if the stars burn, whenn just falling to the ground. If that speed is to high for the stars to burn properly you won´t have any success with that comp. If they work I would recommend to give them a delay on top of your priming, so that they can slwo down before the prime lights them. If you check commercial fireworks that use nitrate based strobes you will always see a long delay before the stars light. Like in this video: Zink 915 Rocket
LiamPyro Posted July 31 Author Posted July 31 I think you're right, Pyroboy. Interesting video... when played frame by frame you can see the prime burning, then what appears to be some kind of dark relay before the strobe lights up. I'll test the stars again, but with a very soft break. Simple enough diagnostic test. Maybe this strobe comp is best used for a core in round stars, and not as a microstar. Anyone have any comps they recommend that have decent critical wind velocity?
Pyroboy Posted July 31 Posted July 31 (edited) I could not really solve this problem yet. But what I found is that binding strobe stars with NC gives a more stable strobe, even if the velocity is higher. But it does not solve the problem entierely. I even never used a lot high sulfur strobe mixtures. I started with Jopetes white strobestar (see pdf in this forum) and then quickly changed to comps without sulfur. I had the chance to semiquantify the ingredients of ZINK white strobe stars. The forumaltion is quite near what I posted here: Strobe Microstars without AP You just have to scip the parlon, CPVC, saran in the green formulation and get basically what I found in the analysis. Regarding on the MgAl you have to adjust KClO4 and catalyst. I found this comps better, because they were a lot brighter. So I have done most of my tests with this kind of comp. Good luck and share, what results you get :)! Edited July 31 by Pyroboy
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