Cylinder shell burst column

[All10Fingers]

This may be a silly question but, when one is assembling a cylinder shell, the burst is contained within the center of the shell via some sort of tube structure.(At least mine are). My question is, is the column in the center only there to keep the burst charge where we want it?  Or should I make a stronger walled center tube to provide extra confinement of the burst within the larger shell.

So is a simple rolled piece of paper sufficient or should I use a heavier paper rolled thicker with some glue?

[Zumber]

11 minutes ago, All10Fingers said:

This may be a silly question but, when one is assembling a cylinder shell, the burst is contained within the center of the shell via some sort of tube structure.(At least mine are). My question is, is the column in the center only there to keep the burst charge where we want it?  Or should I make a stronger walled center tube to provide extra confinement of the burst within the larger shell.

So is a simple rolled piece of paper sufficient or should I use a heavier paper rolled thicker with some glue?

 

The sort of tube structure you are talking about is called "Cannule" this term may help you later for study. The burst charge usually coarse Granulated bp is poured through this Cannule at the center of shell and it is later removed, so you have nothing to do with its thickness.

Outer shell casing as I can see in your image is heavy walled generally it consists of few turns of Kraft and later it is spiked to reinforce it and pasted with few turns of kraft paper.

This link may help you in understanding function of Cannule.

 

[Carbon796]

 

Typically a brass or copper thin walled tube, is used for the canulle " former". Its important for it to be perfectly centered in the shell, during filling/consolidation. I have in the past made custom sized ones as needed. From plastic soda bottles. You can not consolidate the shells as firmly, with them. As the metal ones, because the shell contents will bite into them.

A few turns of paper . . . Is a minimum of 1 turn of 70# virgin kraft.  Per inch of nominal diameter. Dry for the case and an equal amount/weight of pasted/broken virgin kraft for the paste wrap. Assuming your building pasted American/Italian styled cylinder shells.

With that machine wound core you're better off building a salute or a sky mine.

Edited February 25 by Carbon796

[All10Fingers]

"Cannule" neat thank you Z. Thank you both actually. That answers my question and comes with some bonus wisdom directly from the experience of some very accomplished pyros.  My "cannules" for this size have typically been a plain toilet paper roll. Except I would glue them in place and use it for additional support to keep the bottom from getting blown thru at launch.

I know the casing is thicker than is necessary, but I have dozens of these tubes in 3 and 5 ft lengths and I'm continuing to accumulate more from a couple businesses in town.

So my thinking was to buy an appropriate sized mortar, make myself a hug for forming end plugs and experiment from there. I actually make 2, 3, and 4 inch cylinders and they all always start from a pre-made cardboard tube leftover from some other application.

Its pretty straightforward. Plug it, fill it,wrap it in paper, then wrap with string, and again with paper. (For some reason my 4 inch diam, 2.5 lb, bottom fused cans seem to be more reliable and controlled than my 1.91 inch diameter 80 gram shells. But you are correct mr carbon in That I often end up with a "sky mine" where just the ends blow off... I'm still new enough that I consider that a success.

On this particular shell, I've made the end extra thick and plan to add a few grams of flash to my usual BP burst.  And I'm trying a new stronger string so hopefully this one will have enough juice to make confetti out of all that cardboard and paper. I guess we'll found out this weekend...hopefully

[Carbon796]

If the ends are blowing though, the contents are not consolidated well enough. Spiked hard enough. Although you're using the term plug. The "shell" should have end disks that sit on top of the machine wound cores walls. I would probably use a minimum of double inners and a single outer. 2 strands of 8ply cotton twine is typical for 3-6" shells. Although above 5" I preferred 1mil hemp twine.

If your interest is just a sky mine type effect. You do not even need to use a canulle. Fill the fused end of the shell with a layer of BP. Jumble fill/consolidate the rest of the shell with your stars/polverone. Usually the ends of the shells are slightly biased. Fused side stronger, star end weaker. Horsetail shells are made similarly, broken slightly early.

As a side note. Don't forget that a "proper" cylinder shell, is meant to break/pattern radially. Which is going to be very difficult to achieve. Using heavy walled cores.

Edited February 25 by Carbon796

[Mumbles]

Those tubes are probably better suited to salutes/lampares, bottom shots, or even as mortars themselves. I don't love the idea of a tube like that becoming fallout from the sky if it were to turn into a sky mine. 

Normally constructed shells made from rolled paper casings and string may not always fully disintegrate, but at worst they tend to flutter down.  

I've used a lot of things to act as the former for the cannula. As Carbon alluded to, metal is the best choice if available. Off-cuts of copper pipe tend to make pretty convenient sources up to a certain size. Proper metal tubes for larger shells can be somewhat more difficult to happen upon. I've used PVC or other plastic pipe in a pinch before. I generally put at least 1 turn of thin kraft paper over it, or a few turns of tissue paper. Neither will stand up to the fire spreading inside the shell, and help to prevent stars and polverone from biting into the softer material. I've ruined the packing and settling on my fair share of shells before learning that lesson.  One tip if you do use something like plastic or metal that has a thicker wall, make sure to pipe sticks out of the shell a couple extra inches and overfill from what looks like level with the contents. You have to fill the void left from the wall of the pipe. A little too much isn't a big deal. It just spreads out and becomes part of the polverone I typically use to level off the tops of shells.

[Carbon796]

11 hours ago, Mumbles said:

Those tubes are probably better suited to salutes/lampares, bottom shots, or even as mortars themselves. I don't love the idea of a tube like that becoming fallout from the sky if it were to turn into a sky mine. 

Normally constructed shells made from rolled paper casings and string may not always fully disintegrate, but at worst they tend to flutter down.  

I've made 3" hummers in the past. From the 3" (2.5") commercially available BS cores. Shot from 3" mortars. They had rammed clay end plugs. They would spin up really fast. ( dual tangential nozzles ) And with the added inertia of the heavy core and clay plugs. They would still be whistling/buzzing on the way down. Long after the fuel was burnt. 

But, as you've pointed out above. They hit the ground with an authoritative impact. You didn't want anything to be under them when they came down. I always wanted to put a few rows of those in an 8 or 12. But the fallout from them, probably wouldn't be pretty. If they hit anything.

Edited February 26 by Carbon796

[All10Fingers]

update for those interested.the plugs I'm using are just alternating later of Kraft paper, ram board, and a box of crackers. Then paper then ram board.and so on. Until the plugs are roughly as thick as the cylinder walls. I also added flat discs on the ends. Here you see it as it is before I string it.  I also gave it a relatively hard break charge in that instead of BP coated cereal. I skipped the rice crispies and used BP with about 8 grams of 70/30. Hopefully that will be enough to at least split the case. Stars are pyro science blue and C6 and a added a little titanium to the spolet mix so it should track pretty good.

And if it puts any minds at ease...I live in the middle of nowhere. Where I shoot there are no people, buildings or vehicles anywhere near the site.

I'll take more pics as I go for your reviewing. I may sound defensive when I reply to post but I truly do appreciate everyones criticism and advice 

[Zumber]

I still think you should change cylinder casing and save these casings for other purposes, it is too much thick and strong & it might turn it into sky mine than a better break. If you have dozens of such you may use it for another purpose as stated earlier like salute casing,mortor tube, fountain etc. 

[All10Fingers]

I probably will now that I've got some better material than before. This way is nice and convenient but they weigh a ton and that thick does interfere with  the break sometimes...still gunna finish this one tho

I do kinda wanna try one of those buzzy spin things. That sounds like something my dog would chase...here's my uninspiring string'ing

[All10Fingers]

here she finished and ready. Everything is solid, no loose paper, perfect fit in the mortar. Doesn't make any noise if I shake it. And aside from the ugly crease on top, this might be the most aesthetically pleasing unit I've made yet (which isn't saying much). Now I just hope I have enough  BP left to launch it...the weather hasn't allowed me to run my mill since November and I'm down to my last half a jar

[Mumbles]

One other suggestion I would have is to work on your pasting. With the discs you showed and thickness of the tubes, I don't think you'll have any problems, but if you were to swap to hand rolled casings pasting like that would be a recipe for flower pots. Ideally, you want to extend the spolette length so that it sticks at least an inch if not a couple of inches out the top of the shell. Then paste the paper down layer by layer so that it sits up against and starts to rise up the spolette tube somewhat. If you read Fulcanelli or other more traditional manufacturing literature you will see a "crown" mentioned many times. This paper building up against the spolette is what forms the crown. The paper also doesn't look particularly broken in. Normally you can see the spiking sticking out like ribs on a skinny girl after it shrinks down after drying.

[Carbon796]

" Proper " Pasted crown. The paper should make a smooth, seamless and bonded transition.

 

Edited March 5 by Carbon796

[All10Fingers]

 

If you listen close, you can hear my drunk parents in the background lol. Happy Birthday mom

[Carbon796]

Looks like it needs less break and better star saturation.

 

 

Edited March 5 by Carbon796

[All10Fingers]

I 100% agree. That's what I get for choosing blue for the primary color. I know a couple greens that haven't let me down, and I'm pretty good at red and pink...but the moment Copper gets Involved I fail cause blue and purple are always trouble.

Maybe May Copper is bad...I know my prime could of been better but they tested well. I was expecting at least a few lights.

[Almostparadise]

Looks like maybe a bit too much booster in that shell. It may be tough to obliterate a heavy casing like that w out obliterating your stars.

[All10Fingers]

It was about 7 grams. But ya, the booster in combination with the heavier stoppers in the ends and doing something new with the string. It seems i over shot my target pressure

[Carbon796]

It's easy to have a love/hate relationship with blues.

Edited March 5 by Carbon796

[All10Fingers]

I don't have any AP. I once made a similar blue but but with hexamine and pine resin...it looked really cool with tiger tail. Which was kinda the effect I was going for.

But i still think it's my priming. That's one step in the process I haven't developed a system for. I might have to track down some silicon or something similar. I've been adding a little aluminum to some BP and sprinkling it over top like sugar. But I know I could do better

[Carbon796]

Sprinkling over the top like sugar. Doesn't sound like you're actually really priming anything.

Edited March 5 by Carbon796

[All10Fingers]

On 3/2/2025 at 12:20 AM, Almostparadise said:

Looks like maybe a bit too much booster in that shell. It may be tough to obliterate a heavy casing like that w out obliterating your stars.

I just wanna take a moment to recognize and acknowledge Paradise here. Maybe I'm geek but it's rather refreshing to see the correct usage of too and to in a conversation. I bite my lip everyday to stop myself from correcting people on this completely inconsequential detail. 

[Almostparadise]

I can't take all the credit here. The one or two grade school teachers I no doubt ruined are the real heroes. Thanks just the same 😉