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 16 hours ago 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 16 hours ago 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]

3 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 doubt you ever saw them. But, I had made 3" hummers in the past. From the 3" (2.5") commercially available BS cores. Shot from the 3" mortars racks. 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 would not be pretty.

Edited 2 hours ago by Carbon796