canulle diameters

[MadMat]

I have recently upped the size of my can shells from 2" to 3". All the tables/info ect. I have read gives a range of 3/4-1" for the canulle size for 3" shells. So far, I have only used a 3/4" canulle and have gotten decent results. The few 3" shells I have made so far are simple single color shells. I am wondering what the range is for. Is it for variations in burst charge strength, or for different effect shells or different size stars or ?? Just wondering.

[lloyd]

As your figures gave you originally -- about 25% to 33% of the I.D. of the shell is often relegated to space for the cannule.

 

It +really+ depends on what you're making. Some shells require no cannule at all.

 

LLoyd

[OldMarine]

Lloyd, as you probably know I'm planning my first shell for a rocket.

Wouldn't a cannule be necessary for all but a jumbled star/polverone mix?

Serious question. Please snap the rubber band on your wrist before answering.

[lloyd]

Patrick,

In the case of Italian-style shells, MANY of them are just "jumbled star/polverone mix" (although often the polverone is grained powder, for more burst force).

 

Just as is the case with ball shells, you only need (or even desire) any order in the filling when attempting a particular burst pattern.

 

We used to make production canister shells for the theme parks -- hundreds a week. In many cases, they weren't even what you'd call a proper 'mix'. We'd scoop them full of stars, dump on grained powder until the interstices were filled, then seal 'em up.

 

(last one was Saturday night after the 4-seasons Demo)

 

Lloyd

[OldMarine]

Thanks Lloyd, the video tutorials I've watched were on building particular types of shells that required stacking stars,a cannule and polverone in between. I've got more reading to do!

[MadMat]

I am still using only corned BP for my burst in the 3" shells. Would MCRH be a better option at this size? I was under the impression that even 3" was too small to worry about that.

[lloyd]

Mat,

No, I think corned powder is fine for that application.

 

The issue with cylinder shells is that their volumes are not dependent only on their diameters, but also their lengths.

 

A two-foot-long 3" shell might work just fine with weak polverone or MCRH, where a 2" high 3" dia. 'pancake' shell might not burst well without 7FA commercial powder at its core.

 

You'll have to experiment with YOUR geometries, and with the designs others have offered.

 

LLoyd

[MadMat]

Well I've only fired three of my 3" so far (at new years). All I've done with the rest of the winter is fill up my stock of BP, stars and ect.

The three I fired off on new years were approx. 3-1/4" long. I got a pretty decent burst pattern from them, but there's room for improvement. I plan to experiment with lengths ranging from 3-4" and see what works out the best. Who knows, if things get better as I go longer, maybe I will go longer than 4".

[Bangkokpyro]

Mat as a general rule the height of the casing for a cylinder shell should not exceed the diameter or your burst pattern will suffer, an exception would be a shell containing inserts.

I go with 2 1/2 for a 3 inch 3 1/4 to 3/1/2 on a 4 inch. Both 3 and 4 inch shells have space for a canulle. I would use a 3/4 inch on a 3 and an inch or inch and a quarter for a 4.

Burst for small cylinders like these it's best to use 3 FA rather than the traditional 2FA. Filling the spaces with Polverone is done as with all cylinder shells to pack the content well.

Edited May 21, 2016 by Bangkokpyro