Venting shells?

[Richtee]

Am building some effects stuff for some 3" display shells. Go-getters and rolling some stars with Dragon Eggs for cores.

 

I am concerned about ignition of the components in the shell.

 

Considering: A "flash bag" type thing, with a short fuse, with maybe a couple grams ball milled BP to get a nice conflageration going before the break actually happens- by venting the shell. I have about 2G 70-30 perc-dark I will nestle in the center, with maybe a .25 second fuse.

 

Obviously the bag is plenty to bust the plastic hemi, but the "ball of fire" INSIDE the shell before break intrigues me.

 

Any input/experience with this? Thanks!

 

On edit: Perhaps even less break? 1g should be sufficient, and perhaps avoid shattering the innards?

[justanotherpyro]

I'm not sure what your question is exactly. Is it something along the lines of whether or not the break charge (flash bag) creates enough pressure to break the shell before the stars have a chance to light? If so, then here is a break down.

 

The pressure that breaks the shell is the very hot gas from the burst. If flash is used it is creating some very serious heat before the shell does break. The pressure must also be exerted on the interior surface of the shell to break it(obviously). That being said, the components of the shell are definitely exposed to some very hot gases and thus are ignited. If a lot of flash or whistle is used then the stars still have their chance to light, but they may " blow blind " because even though the lit in the initial burst they have too high of a velocity to stay lit.

 

You have to get a feel for how hard of a break certain stars can take, and the effect you want. For the most part if you prime stars correctly and they are rock hard you can load them in a shell and break it pretty hard. I have used upwards of 5g flash to break 3" shells. Test your finished stars or inserts in a star gun and try shooting them at different speeds. If they survive a really hard shot then you know you're probably good to load them into a hard breaking shell.

[Richtee]

Sorry, I was not very clear I guess.

What I propose is to vent the shell to allow a ball milled charge of a gram or so of BP create a "little Hell" inside the shell WITHOUT breaking. THEN the flash bag AND everything else will surely be ignited.

 

The vent is in there to prevent a break... allowing time for assured ignition on everything.

 

I have built the shell. Put a .25 inch hole in the top and covered with duct tape. Should blow out easy, allowing about .25 seconds for ignition of everything before the smaller...went with 1.5G flash bag goes.

[Pretty green flame]

Dude, what you want to do is paste the shells with more layers of paper, the stronger the shell casing the more pressure is needed to burst it. And the time for the pressure to rise to the breaking point of the shell will be longer with a stronger case. Thus the stars will be exposed to the heat for a bit longer than a weak casing.

 

Although you should worry, with a flash break, the metallic fuel creates such hot gasses the stars are with no doubt experiencing a small hell in there.

 

You could hoewever use a dirty flash formula, it's formulated so that it has a lot of hot molten slag that is thrown around which will surely ignite your stars.

[Richtee]

You could hoewever use a dirty flash formula, it's formulated so that it has a lot of hot molten slag that is thrown around which will surely ignite your stars.

AhhhHA! Dirty flash... add some nitrate? Extra Al?

 

That sounds like EXACTLY what I want.

 

I have not used pasting yet. Have been using fiberglass tape with a wrap of aluminum tape toprotect the shell from the hot lift gasses.

 

Will pasting gain me that much in a 3" to justify it?

 

I usually use benzolift as a break- works well, but I suspect some are coming out blind. Maybe I need a better prime as well.

[Pretty green flame]

This is Ofca Bursting charge, often reffered to as Dirty flash

 

Potassium perchlorate 23

Potassium nitrate 22

Barium nitrate 11

Sulfur 11

Antimony trisulfide 11

Aluminum, flake, 325 mesh 22

 

Now, you could also go simpler by using a slow flash formula, basic 70/30 but with coarser aluminium, 325mesh bright Aluminium for example. I'm going to stop discussing flash here as it's a rather delicate subject.

[Richtee]

I'm going to stop discussing flash here as it's a rather delicate subject.

Thank you, and yes, we don't wanna raise the ire of the powers that be. Altho... after first asking for HE access, I recanted... because I have no interest in most of the stuff. But the "F" word has uses for me. Shame it has to be there.

 

Tis what it is.

 

Looks like I gotta order some stuff. No B nitrate or Antimony.

[justanotherpyro]

I think its easier to just heavily prime stars. I have recently started using Si in my BP prime and this gives the molten glass slag which greatly aids in ignition of stars.

[TheSidewinder]

We're working on a solution to the whole "F" word issue.

 

In the meantime, careful discussion of such is allowed, as long as it's done in a responsible and mature manner.

 

Also, our PM system works very well.

[Richtee]

An update:

 

In celebration of the Wings hard fought victory last night...

 

The vented shell worked flawlessly. I don't know if the venting helped or not, but I DID carefully watch the flight.. and there WAS a little "rocket" of flame out of the shell before the burst. And it looked like everything lit.

 

Worth it? prolly not, considering the info posted previously.

[psyco_1322]

Got a video?

[Richtee]

Got a video?

Sorry...I have yet to video anything. Should have thought of it as I was out at a bud's to watch the game and he has all sorts of cool cams. And a 62" Hi-Def Toshiba. Man..almost like having front row tickets!

[bogey1]

on the dirty flash, wouldn't a little more alum work to?