15 replies to this topic

[Dalle]

If I'm going to make a 3" or 4" ball shell.

what kind of burst chagre should I have in it?

seems like some have only BP and some (coted rise hulls) what is the difference and why.

[Arthur]

There is no simple answer! Too much break charge and the shells spread far and wide and look underfilled. Too little burst and the burst looks small in the sky. A burst charge for a big shell could be 2 : 1 powder to hulls ratio but a small shell may need 7:1 powder to hulls. 

 

Remember that the burst charge must hold everything in place before it actually breaks the shell so you still need enough volume of carrier to fill the shell.

[cmjlab]

Fireworks the Art, Science, and Technique (F.A.S.T.) by Takeo Shimizu discusses construction of ball shells and is a interesting read (even if it is just the chapter in ball shell construction) - if ball shells are your preferred style, then you should invest in a copy..... Well worth it IMO.

A 5:1 B.P. to Rice Hills is a common means of making B.P. Coated Rice Hills for a 3-4" shell.

A 3" shell may be even better filled with just plain B.P. (ballmilled and screen granulated, usually with a 50:50 Isopropyl Alcohol to water solvent OR milled with a small amount of dextrin and granulated with water)

A 4" shell is probably filled with B.P. coated rice gulls, more often than not.

Granulated b.p. is less dense with plenty of surface area to burn fast.

Rice Hulls are a filler (cheaper) & carrier for B.P. on which the goal is to use enough B.P. to get a satisfying break - but not overpower the break and blow your stars blind.

Then there is corned B.P. which is pressed to a certain compaction level, dried, then broken into pieces and screen sorted to the desired mesh sizes. You get a denser B.P., so therefore you get more B.P. in a space than you would from the other two methods.

There is no perfect solution, you have to do some trial and error to see what works best with what you have for materials and B.P.

What is your experience, tell us a little about yourself, pyro experience/endeavors, and what you are trying to make (end product) and maybe we can help a little more.

[Mumbles]

There's going to be some trial and error to find what works for you.  

 

BP coated hulls are used frequently to make more economic use of BP.  There's a comparatively large volume of space in ball shells to be taken up by the burst.  Using granulated or corned BP would make shells get heavy pretty fast, and not be the most economical use of it.  3 and 4" shells can be made to work just fine with BP coated rice hulls (or another carrier).  Some may prefer a harder break, and will tend towards adding a booster like slower flash powder or whistle mix.  Others have better luck with different bursts like H3 or a perchlorate based burst.  

[Arthur]

Remember that the first function of the burst charge is to hold all the other contents in the right place against storage and transit settling and the setback due to the launch. After that, when the shell arrives at the right place in the sky, the power of the burst charge splits the case, ignites and spreads the functional contents (stars, inserts etc). Many builders will use as much carrier (rice hulls etc) as possible to get the cost down and the weight down.

Flash powder even as a booster tends to leave an ultra-bright burst which distracts from the intended effects, Too much powder and the shell bursts very big and the effects are lost in the sky. 

[Dalle]

Thx for all tips and trix,

[MadMat]

The size of your shell is the real determining factor for what you use for a burst charge. Smaller shells usually require "boosting" the BP to get an adequate burst. There are a number of things you can use for boosters such as flash powder, whistle mix or even simply adding some dark aluminum to the BP. Then on the larger end of things BP coated rice hulls are used. Personally, I use simple granulated BP for 3-4 inch shells with good results. I would say 5 inch and larger is where you might want to consider using BP coated rice hulls. One major reason for using BP coated rice hulls is simply to lighten up the weight of the shell. I should add that all my experience is with canister shells not ball shells so you might find differences in what works for a given size. One last thing to consider; the stronger your burst charge, the harder it is to ensure complete ignition of all the stars in the shell. But on the other hand a weak burst charge equals a disappointing effect. Experimenting is the only way you are going to find what works best for you. Personally, experimenting and learning is my favorite part of this hobby!

Edited by MadMat, 29 August 2023 - 01:00 AM.

[kingkama]

Flash powder even as a booster tends to leave an ultra-bright burst which distracts from the intended effects. 

Anyone in professional pyrotecnics use a metal/oxidizer booster for breaks all kind of shells spherics and cylindrical, shells are all filled in BP on a chosen carrier, sure Is not a 70/30 that Is used for this pourpose.

[kingkama]

The size of your shell is the real determining factor for what you use for a burst charge. Smaller shells usually require "boosting" the BP to get an adequate burst. There are a number of things you can use for boosters such as flash powder, whistle mix or even simply adding some dark aluminum to the BP. Then on the larger end of things BP coated rice hulls are used. Personally, I use simple granulated BP for 3-4 inch shells with good results. I would say 5 inch and larger is where you might want to consider using BP coated rice hulls. One major reason for using BP coated rice hulls is simply to lighten up the weight of the shell. I should add that all my experience is with canister shells not ball shells so you might find differences in what works for a given size. One last thing to consider; the stronger your burst charge, the harder it is to ensure complete ignition of all the stars in the shell. But on the other hand a weak burst charge equals a disappointing effect. Experimenting is the only way you are going to find what works best for you. Personally, experimenting and learning is my favorite part of this hobby!

If you don't use a booster Rich in metals and oxidizer you never obtains a evens break and all star ignition also no strong break.

[pyrokid]

Kingkama, how would you explain the improvements to symmetry, ignition, and break strength associated with the use of boosters?

[Dalle]

Soon time to try the first ball shell.

Where can you buy fuse that burns fast? the ones they have when they shoot (ball shell).

The company I trade from only has time fuses 1cm/sec.

[Arthur]

With time fuse 1cm per second is usual, Maybe you could use quickmatch to pipe fire from the fuse to the centre. It's usual to take an over length piece of time fuse and split it to the right length and cross match at the split (with a single strand of black match) so that there is a good chance of the fuse taking fire from the lift.

[Dalle]

Yes i understund that, my questien was vhere to buy quickmatch.

The problem is solved.

[Richtee]

I make my QM. Spiral wound paper tube, 5% dextrin added BP on cotton string. It’s messy, but extremely “quick”. You making your own BP? If so, this is the way to go. Buying QM is difficult even here in the US.

[Dalle]

I make my QM. Spiral wound paper tube, 5% dextrin added BP on cotton string. It’s messy, but extremely “quick”. You making your own BP? If so, this is the way to go. Buying QM is difficult even here in the US.

I notis that, the seller i buy my stuff from in Polen tell me.

(According to current regulations, this type of fuse is not obtainable without special permissions. Furthermore, it falls under shipping class 1.1G, making standard packaging highly risky. We are unable to offer this fuse.)

Yes i make my own BP so thx for tip about cotton string.

[kingkama]

Kingkama, how would you explain the improvements to symmetry, ignition, and break strength associated with the use of boosters?

Much hot and oxigen rich gas, higher charge density. You never would have the same Power usinng BP.