Questions about a star formula

[ExplosiveCoek]

Hm, interesting theory. But I almost never use just a fast bp prime, everything is step primed. Even tiger tail or willow based comps, so this should get them going quite fast and then let them stay lit?

 

There are MCRH in there, 5:1 coated nice and uniform. Not more flash was used then recommended in for instance your plastic 4'' ball shell tutorial. Mostly glitters ignite better than the purely charcoal streamers, probably due to the drossy surface of the glitters after ignition.

 

For instance: 4'' inch sferical shell, MCRH break supported with Apertura flash (5 g), blew stuff blind already. I've seen shell's with 8 gram hotflash still function properly. Even made by myself, but the stars varie . And probably the prime too. Well, I'll try giving them an additional coating with some rough prime and see if that will do something on the ignition of the stars.

 

 

A fast BP prime can actually work against you.

 

First -- it insulates the star material from the heat of the burst charge; so any ignition during the explosion will be ONLY to the prime layer.

Second -- it burns off so quickly that the stars are immediately exposed to cool outside air at too-high velocities to remain lit.

 

Don't mistake the speed of burning of 200-mesh rough powder. It's fast enough, just not AS fast as mill dust.

 

If plain willow and glitters are blowing blind (even without any prime), then I suspect either you're breaking the shells WAY too hard, or you're trying to break them only with a flash bag, and without black powder filler (polverone or grained powder) among the stars.

 

Only extremely fast-burning stars will survive a 'pure flash' burst. With a BP filler, the amount and force of the flash powder may be greatly reduced. It's purpose then is simply to get all the filler involved before the shell opens. The filler commutes its combustion heat to the stars, and also forms a fairly large globe of hot gasses through which the stars must travel before reaching cool air. This aids in igniting them.

 

LLoyd

Edited January 27, 2016 by ExplosiveCoek

[Chunn7704]

what exactly is step-prime? please explain.

[frederick]

Step priming is, in a nutshell, mixing the comp with the prime in incremental layers transitioning from prime to comp.

 

As an example... For a hard to light formula like say silver flitter you could mix 75% flitter comp with 25% BP and apply, the next layer (step) would be 50% flitter and 50% BP, the next step 25/75, and the final step 100% BP.

Edited January 28, 2016 by frederick

[braddsn]

I will add this about primes: and this is personal experience... I think depending on how hard you break shells, there is a place for ball milled bp for prime. I prime 'most' of my stars the same, with a .5mm layer of monocapa, followed by 1mm of ball milled prime. The final layer of bp prime also contains 5% silicon, and 5% diatomaceous earth. I choose to use the ball milled bp for 2 primary reasons: 1) My KNO3 comes to me in granular form, and my charcoal is homemade and not airfloat as I have it stored.. so as opposed to ball milling KNO3 and charcoal separately and screen mixing bp, I just throw it all in and make ball milled bp. 2) A theory that an experienced shell builder gave me for using ball milled bp, is that when breaking shells SUPER hard, the high performance of the ball milled bp can actually be beneficial... it burns for a shorter amount of time, but produces the same amount of energy in a shorter time (thus burns hotter). It ignites the monocapa with no problem after surviving super-high speed, and I get 100% ignition this way. Some comps that are super hard to light (white flitter for example) I will step-prime. Good luck, hope this helps!

[Chunn7704]

very good info thank you again Mr. Braddsn. This will deff helpout.

[ExplosiveCoek]

I think you have a point too brad. The fast uniform ignition of the BP will result in uniform star ignition, whilst the glitter like compo of the monocapa burns hot and sticks to the surface, thereby enabling good ignition. However this priming technique shouldn't be required for firing regular charcoal based streamers.

 

I will make some acetone bound color stars now, this way I know for sure they are completely water free and dry. One more parameter that can be removed from the non ignition list.

[Mixer]

Sometimes the prime can be blamed for blind stars when in fact it could well be that a shell is broken too hard. Critical wind velocities can be different between various types of stars.

Long ago, when I was testing for the desired number of shell paper layers, and an optimum burst was achieved - adding just 2 layers more to the identical shells resulted in 75% of the stars blowing blind. Just something to think on.