Burst Comps and shell construction

[Dragonflightpyro]

I was wondering if someone could please explain some theory of shell construction to me. I keep reading posts (here and elsewhere) where someone asks about adding flash, slow flash, whistle, or something else to their current burst charge to get better shell bursts. The usual answer is either add whistle at most or more frequently it has something to do with BP or shell construction methods. What I don't understand is why isn't flash used for burst in a higher proportion but smaller amounts leaving the more room in the shell for stars? A related question: why aren't shells just filled with burst charge and stars. I see so many shells where the rice hulls look more like filler than needed composition of the shell with stars only touching the shell casing. I've seen other shells with inserts leaving almost no room for hulls. Thanks.

Alex

[marks265]

Shell construction is not really a theory as you ask. It is rather more like a learned manipulation per individual fireworker based on shell type and size. No matter which type of shell comes to mind, the burst charge is fine tuned to match the effect of the shell and the construction of said shell. The boosters you mention such as flash or whistle do not take a lot of room in regard to "filler". However a small amount in excess can send you from hero to zero. This is something you learn when building with your own manipulations.

 

To further complicate matters, the characteristics of all materials used can change things one way or another. This can be a pretty big umbrella, especially when chasing an unexpected problem.

 

If flash or whistle was used in a high proportion you would have a salute and not a shell with an effect. Just fine tuning black powder (in how it's made or proportion of make up) alone can change the outcome. This of course also varies with shell size. To ball park it, there is a theory where 1 gram of flash should be used per inch of shell, loosely speaking of course. With that in mind you can quickly see why not to fill a color shell with flash.

 

It would be much better for you to ask this type of question for a particular shell of both size and effect. When narrowed down this far it can still drive ya nuts in some instances.

[mikeee]

Dragon,

 

Search for Fulcanelli shell building articles on google and read up on the methods described in these articles and you will have a better understanding of why certain aspects of shells change with the size. Large shells will use BP coated rice hulls, shredded cork, cotton seed etc for multiple reasons. Certain types of stars can handle hard breaks, while other types of stars will not survive a hard break using flash powders. Each type of shell, stars, inserts, etc. require fine tuning of the overall shell construction and the compounds used to break the shell and deliver the desired effect.

 

If you build your own shells and your BP is not breaking your shells to the desired effect, you can always add some whistle or flash to increase the size of the break to achieve your desired goals. Add too much flash and certain stars will blow blind and some stars can shatter during the break. You will need to fine tune your shell construction method and compounds used on every batch of black powder or burst charge made until you have your methods and compounds dialed in to a consistent product.

[Dragonflightpyro]

Thanks for the responses. I didn't know about blowing stars blind. I was never intending to fill the shell with flash, only to have a very small flash core in replacement of BP for burst and didn't understand why that wouldn't work. I have heard of Fulcanelli but was unable to find anything pyro related on Amazon, just life story type of literature. It all sounds a little "DaVinci Code."

 

Is there say a master list, maybe not master list but a list of books recommended for aspiring pyros? This is just a quick question. I will search around and see what I can find, but I'd appreciate if someone could maybe separate the trash from treasures.

[starxplor]

I was wondering if someone could please explain some theory of shell construction to me. I keep reading posts (here and elsewhere) where someone asks about adding flash, slow flash, whistle, or something else to their current burst charge to get better shell bursts. The usual answer is either add whistle at most or more frequently it has something to do with BP or shell construction methods. What I don't understand is why isn't flash used for burst in a higher proportion but smaller amounts leaving the more room in the shell for stars? A related question: why aren't shells just filled with burst charge and stars. I see so many shells where the rice hulls look more like filler than needed composition of the shell with stars only touching the shell casing. I've seen other shells with inserts leaving almost no room for hulls. Thanks.

Alex

 

You are correct in seeing rice hulls as a filler. If you fill a shell with only BP and stars, at some point in size they become so heavy that the lift charge is unreasonable. By coating rice hulls or other physically large but low mass(less weight) items with BP, you can still break open a large shell but use a much much smaller lift charge. I do not know where that limit is but I have read anything from 3" to 5" to start using a spacer like rice hulls.

[Nessalco]

Thanks for the responses. I didn't know about blowing stars blind. I was never intending to fill the shell with flash, only to have a very small flash core in replacement of BP for burst and didn't understand why that wouldn't work. I have heard of Fulcanelli but was unable to find anything pyro related on Amazon, just life story type of literature. It all sounds a little "DaVinci Code."

 

Is there say a master list, maybe not master list but a list of books recommended for aspiring pyros? This is just a quick question. I will search around and see what I can find, but I'd appreciate if someone could maybe separate the trash from treasures.

 

The Fulcanelli articles, as mentioned. Ned has reprints in his store.

 

Hardt: Pyrotechnics

 

Shimizu: Fireworks: The Art, Science, and Technique

 

Beyond that, spend time in the forums, read, ask questions, and think. It will all come together.

 

Kevin

[nater]

One can make certain shells with a small flash break and little else. As said, it depends on the star and shell construction. Traditional spiderweb or sfera shells use hard, easy to light stars. The burst is a small flashbag surrounded by the stars it comets with polverone (a type of weak BP) as a filler.

 

Otherwise, the other posts are all correct. With a flash burst, it is too easy to turn the shell into a salute or blow the stars blind. Then Chinese are able to achieve very strong flash breaks with very good star ignition. We have not figured out their secret yet.

[madchase]

Anyone seen any information on the internal physics of spherical shells? By that I mean, internal p.s.i. to rupture different shell compositions, why specific star shapes maintain under force, ext.

[Bcorso85]

The smaller the shell, the less room for a burst charge. So to get a commercial 2.5inch shell to break 20 feet wide the break charge has to be powerful. Larger shells have lots of volume that needs to be filled because most shells only require stars along the walls of the casing or hemisphere. If the charge is too powerful in any size shell, the stars will blow blind because the reaction was so fast the stars didn't have an opportunity to ignite. Certain effects in shells have layers of burst and stars (Double petal shell for example). Some other shells like a Poka shell (shell of shells) on require a soft break. But if you have for example an 8 inch round shell, there is a massive amount of room for pounds and pounds of bp....combined with being confined tightly....which increases deflagration and power of the weaker powder.

 

As far as burn rates and speed of deflagration.... it's all in Shimizu's book Fireworks: Art, science, and technique. But honestly the actual pyscics aren't necessary. Start with some small shells with some willow or paulonia charcoal. It will be hot powder.

 

Shimizu's books is literally the bible for what we do. Fulcanelli's books are incredible. Even more detailed for canister shells.

 

Some primes, like a pinball prime will help ignite stars in hard breaks.

[madchase]

Thanks Bcor. Ive got Shimizu's books. I have to go back through them. Theres alot of stuff to retain in them and I alway get inspired and sidestracked by the content. My question was somewhat vague unintentionally. I should have asked for formulas. I've found most of the answers to the question in my old school book with the exception of star integrity.

[OblivionFall]

Anyone seen any information on the internal physics of spherical shells? By that I mean, internal p.s.i. to rupture different shell compositions, why specific star shapes maintain under force, ext.

The amount of psi you could assume would be a lot. Would be difficult to test that.

[pyroind]

I was wondering if someone could please explain some theory of shell construction to me. I keep reading posts (here and elsewhere) where someone asks about adding flash, slow flash, whistle, or something else to their current burst charge to get better shell bursts. The usual answer is either add whistle at most or more frequently it has something to do with BP or shell construction methods. What I don't understand is why isn't flash used for burst in a higher proportion but smaller amounts leaving the more room in the shell for stars? A related question: why aren't shells just filled with burst charge and stars. I see so many shells where the rice hulls look more like filler than needed composition of the shell with stars only touching the shell casing. I've seen other shells with inserts leaving almost no room for hulls. Thanks.

Alex

hi Dragonflightpyro,

in india the highest sized commercially available shell you can get is 3 inches spherical and approx 2 inch cylindrical. the spherical shells are made of plasctic balls and the cylindrical shells are made with paper..almost all of them use flash powder burst charge which seems slow compared to to a cracker flash(tested on ground). the stars are always round and vary in size. the branded costly shells use granulated BP for lift.. the cheap shells available even use flash for lift charge. the stars are dumped just like that and the entire shell is filled with flash. i have heard blind stars falling on the tin shed in my backyard and have sometimes collected them. they were blown blind by the force of of the burst. but all around the forum and web all shell builders seem to use BP coated rice hulls or any other stuff but not flash. i think its cheaper and faster to produce them in the factory..otherwise it makes no sense to use flash as burst in shells. I had talked to a small factory owner and he said flash requires less turnaround time and in peak demand season it is easy to just fill the shells so there is no time wasted as to prepare the BP and fill it. also Bp needs corning, coating and drying.hence they follow this process.

if you need i can post some pics of the same of a de constructed shell

[dynomike1]

I hear a lot about corning, an i don't totally agree. I dont corn mine and i can burn some on tissue paper without scorching the paper. After reading some of this, maybe it's the difference whether you are making Peonies or a Poka shell. Canister shells use MCRH, granulated bp, pulverine and a touch of flash. In plastic you would use more flash because you dont do alot of taping like paper shells. Bp is cheaper than flash. It would appear that in the busy season they would have plenty of bp made.

Edited November 13, 2015 by dynomike1

[pyroind]

I hear a lot about corning, an i don't totally agree. I dont corn mine and i can burn some on tissue paper without scorching the paper. After reading some of this, maybe it's the difference whether you are making Peonies or a Poka shell. Canister shells use MCRH, granulated bp, pulverine and a touch of flash. In plastic you would use more flash because you dont do alot of taping like paper shells. Bp is cheaper than flash. It would appear that in the busy season they would have plenty of bp made.

Hi dynomike,

You are right about bp being cheaper than flash but the issue is timing. Most factories here are seasonal and their main workforce are farm workers who start working there from august till dec because all major festivities are around that time. Also the factories are situated in villages and majority of them work in the farm. The factories here employ very few permanent staff. Flash does not require any special process for manufacturing. A 3 inch d1 glitter shell costs rs.90-100 INR. And if purchased in bulk you can get them as low as 60INR. While the highest branded ones go for INR450 for a pair. But the demand is huge and most shops go out of stock a day after diwali. The main issue i think is time saving..also the plastic ball shells have a canvas cloth glued around them as taping but the cylindrical shells have none.

[sora]

Just curious what flash composition they use as lifting charge

[Zumber]

no commercial product uses flash as a lift.....I have only seen some traditional uses flash lift but its very very rarely.........they do uses heavy duty iron pipes as a mortor also if flash is used as a lift 30 percent shell will burst itself in mortor even if it is reinforced with papers or glued cloths over it.

I wont mension formula here but just for your curiosity i will mension only contents

Ba(NO3)2

S

999 Aluminum powder.

[pyroind]

hi swapnilsutar,

i had bought 30 nos of 3 inch ball shells from the biggest market in s24-parganas just a day before diwali of 2014 . all of them had flash as burst charge and lift charge. after igniting 3-4 shells i got curious by their boom and flash being made at the time of launching the shell and decided to keep one of them for dissection. and by the way none of them were dud and all had fired with proper height and at at proper apogee. i was taken back when i found flash inside the shells as lift during dissection ... i think the pyrotechinicans have fine tuned it to such an extent that none of the shells burst itself in the mortar. they were locally produced and were priced at rs.90/-INR. i still have the shell casing,spollettee and the ball casing with me . the stars were all glitter. you can easily identify a lift charge by the sound and flash they make.

[dynomike1]

Hi dynomike,

You are right about bp being cheaper than flash but the issue is timing. Most factories here are seasonal and their main workforce are farm workers who start working there from august till dec because all major festivities are around that time. Also the factories are situated in villages and majority of them work in the farm. The factories here employ very few permanent staff. Flash does not require any special process for manufacturing. A 3 inch d1 glitter shell costs rs.90-100 INR. And if purchased in bulk you can get them as low as 60INR. While the highest branded ones go for INR450 for a pair. But the demand is huge and most shops go out of stock a day after diwali. The main issue i think is time saving..also the plastic ball shells have a canvas cloth glued around them as taping but the cylindrical shells have none.

I understand what you are saying. There's a lot of that going on around here.(Temporary help) I wished i could buy shells that cheap, i would have more time to make more specialty shells for the 4th.

[dynomike1]

Here is some of my 3 and 4" stand alones that all i like is the lift powder. These will go up at 5sec. behind my 8" at .5sec. apart to finish the show.http://s704.photobucket.com/user/dynomike2/Fireworks/story

Edited December 29, 2015 by dynomike1

[MadMat]

I talked to Harry at Skylighter about burst charges a while back, and he was pretty helpful and said some things that made a lot of sense. For one thing, flash alone as a burst charge isn't good. As was said earlier, too hard of a break and you have a number of problems. Another thing is that the bright flash will actually take away from the effect of the stars. Keep in mind that you are more than likely shooting off your shells at night, your audience will have their eyes "dark adjusted". You shoot off a shell with a real bright flash and it will take a while for "dark adjusted" eyes to recover and there goes the effect of your beautifully colored stars. Personally, I used 65% fine granulated BP and 35% flash (70/30 perc/no sulfur). This has worked great for my 2" and 3" can shells. Because my shells are small, I don't use coated rice hulls. I also usually dust polverone in with the stars as a filler. Besides added more hot gasses to the burst, the polverone solidifies the shell a bit and just maybe helps with the ignition of the stars.

[lloyd]

Sigh... if that's all Harry told you about flash as burst, then I'm going to have to knock him around some at our next meeting!

 

There's also this 'little thing' about flash's being a negative explosive with no net gas output.

 

Since Harry knows that, I'm betting you just left that part out; huh?

 

Lloyd

[MadMat]

Uhh... actually he never mentioned that.

 

Also, Am I correct in assuming that the 35% flash in my burst mix basically only speeds up the burn rate and increases the temperature?

Edited December 30, 2015 by MadMat

[dusty56]

Lloyd. Please explain about flash being negative with no gas output. I don't understand. When the fuel burns it produces heat and enough force to to do damage to me. And I thought it was used to increase the burst radius of a shell. I use a whistle mix with my 3,4, and 5 " round shells and am pleased. I am working with 1 1/2" shells to be used in a shells in shell device. I shot one tonight and was not pleased with the break and was going to start experimenting with flash for the burst.

[PIL]

Lloyd. Please explain about flash being negative with no gas output. I don't understand. When the fuel burns it produces heat and enough force to to do damage to me. And I thought it was used to increase the burst radius of a shell. I use a whistle mix with my 3,4, and 5 " round shells and am pleased. I am working with 1 1/2" shells to be used in a shells in shell device. I shot one tonight and was not pleased with the break and was going to start experimenting with flash for the burst.

Flash powder seems to have no gas output,just solid KCl and Al2O3 at room temperature .However the heat which is generated by aluminum combustion is way enough to turn KCl into vapor.

In China,most small shells(1 inch small cylinders) are burst with pure flash.Those export cakes that use whistle mix break equally hard . You may try using just granulated whistle or a mixture of flash and BP,depending on your priming techniques.

[lloyd]

PIL is correct ... 7:3 flash powder has no net gaseous combustion products.

 

Although very small shells can be broken with flash, alone, it's greatest value is in accelerating the ignition and combustion of a gaseous burst filler.

 

I'm partial to using a small flash-loaded coupette surrounded by grained powder or coated hulls, rather than distributing the flash in the BP burst. Done that way, and 'balanced' well, you see no bright flash when the shell opens, because the BP will have absorbed and cooled the flash below incandescence before the shell opens.

 

When one mixes flash with the burst, there almost always results an unpleasant bright flash of light upon the shell's opening.

 

LLoyd