Tried this particular formula and formed cut star, primed by "step prime" method.
1 layer 1mm 50 hot BP + 50 color comp
2 layer 1mm 75 BP+5%mgal + 25 color comp
3 layer 1mm 90%green BP + 10% mgal
I have used 4% dextrin for all layers.
Color on the sky is not bright enough. Its look like color changing star on sky (orange to red) orange due to BP and color comp mix. Tested in 3 inch shell. Stars were burning till it hit the ground.
Overall not upto the expectations.
P.S missed to record the video.
Changed the above composition little bit by adding dark aluminium and output is decent.. fast buring mix on ground. Color is vibrant. Yet to test the star
Strontium nitrate -55
Sulphur - 5
Mgal 200 mesh - 10
Dark Al- 10
Dextrin - 5
PVC - 15
This time swapping the step prime with hot prime (BP+Si).
Any suggestions on prime ?. 2mm prime is enough to ignite the star ?.
Anyone tried similar formula?
That's the first time I've heard of tri-layer priming. Your revised approach should work ok. Too thick of priming and you're going to have that orange effect interfering with your red as the colored core starts up while there's still a lot of charcoal-based prime burning off.
Stars burning until they hit the ground is of course not desirable. Are you positive your strontium nitrate is dry? I religiously oven dry my strontium nitrate (after a run of crystals through the coffee grinder) and keep it with desiccant in storage. I also never dextrin-bind strontium nitrate comps because...water.
Strontium nitrate is hygroscopic enough already that you need to worry about atmospheric water vapor absorption. But when you purposefully add water to get it damp, it simply will not give back all of that water. Your cores will be damp. Maybe you would be able to "cook off" the water from the cores in a drying box, but if you then moisten the surfaces with water to prime, you are probably going to add back more water for the thirsty nitrate core to absorb during priming. Damp stars are slow burning/cold burning stars.
You already have PVC in that mix. Why not use an organic solvent so that the PVC can form a water-resistant protective shell and still be available to donate chlorine?
I pretty much only use dextrin as a binder for charcoal-based stars (and expect long drying times with large ones/comets) & their primes, lift/burst BP, and blackmatch.
I'm a big fan of fast & simple rubber stars for brilliant reds. My inner prime for red rubber contains a little less Si (3% I find sufficient) and a little more MgAl (perhaps 7-10%) to get the Si hot enough (quickly) to actually oxidize, melt, and do it's molten glass slaggy heat-transfer action. If you don't get Si hot enough, then it's just going along for the ride as an inert freeloader. Si's melting temp is about 2600F. That's hot. BP burns at 2500+ F, but takes a moment to get there. So the metal is important to get up to temp fast (MgAl 50:50, starts melting at around 850F; http://docs.lib.purd...dissertations).And MgAl burns hot super hot, >3000F, so they Si and MgAl work together nicely.
Looking forward to the results of your star revisions.
Edited by SharkWhisperer, 19 June 2021 - 11:58 PM.