burst charges

[MadMat]

I am planning on making the jump to 5" cylinder shells. Is it a good idea to start using MCRH at this size? Also I have heard of using puffed rice instead of rice hulls... any suggestions?

[OldMarine]

I'm reading up on this myself and all I've read says that 5" is the point you definitely got to MCRH. 4" shells can use it but sometimes need a booster. I use rice hulls because it's what I can get free but the turd-head who roped me into this hobby used Pop-Eye puffed rice for burst and lift.

[Mumbles]

You make a switch with ball shells, but not necessarily cylinder shells. Cylinders typically use granular BP throughout all sizes. The only real change I make is using a 4FA instead of 2FA in smaller shells like 3". Comparatively speaking, cylinder shells have less room for burst. A 5" ball shell with 1/2" stars is going to have roughly 19 cu. in of burst. A 5" cylinder shell is going to have roughly 9 cu. in. With space at sort of a premium it makes the most sense to stick with the densest burst available.

 

I have used coated rice hulls in cylinders before. They worked fine, but I think I get better burst with granular BP personally. Rice hulls probably burn faster, but the lower density means they probably don't have the same heaving power. The compressibility of rice hulls has always made me question it's use a bit too. Maybe build a couple and see what works for you.

 

There are a couple instances where it might make sense to use a carrier, such as in comet shells. There's a lot of open space in the middle. You can certainly fill it with straight 2FA, and it'll break plenty large. It's probably more typical to cut the 2FA with polverone though to save money and temper the burst a bit. This is an instance where coated hulls might be more suitable. I believe Kyle on passfire does some shells like that.

[OldMarine]

I'm having trouble picturing a sphere having more capacity than a cylinder with the same diameter and height.

I suck at math but I think I read a cylinder has 1.5 times the volume of a sphere. Please correct me if I'm wrong.

Edited May 13, 2017 by OldMarine

[bobd]

Pat:

The volume of a sphere of radius R is V = 4/3 *π*R**3

 

The volume of a cylinder of radius R and height 2R is V = (π*R**2) * 2R = 2π*R**3

So the ratio of the volume of the sphere to that of the cylinder is:

 

(4/3πR**3)/(2πR**3) = 2/3 Or the cylinder to the sphere = 3/2 or the 1.5 times you remembered.

note the **3 means to the 3rd power (or cubed), **2 means squared

Hope this helps,

Bob

[lloyd]

Patrick,

I'm having a little trouble understanding Mumbles's post, too. You're correct that a cylinder has more volume than a sphere (of the same diameter), but if guessing, I'd say he probably was referring to something about the geometry of the filling, not the gross capacity of the shell.

 

Lloyd

[Maserface]

Mumbles said "comparatively less room for burst", not less total volume.

 

To elaborate, cylinders typically are built with a dense central core of burst powder, known as a canulle. For a 5" shell you'd probably use a 1.375" or 1.5" canulle, which depending on the height would give you roughly 9 cu. in, which mumbles mentioned.

 

Ball shells are typically built with the stars lining the wall of the casing, and the rest is filled with burst. Besides the stars, the remaining volume is going to be roughly 19 cu in.

 

It would do you well to study both "fulcanelli" and "FAST", and note the many differences between each style (cylinders and balls).

[OldMarine]

I've read them but as I said I can't picture how it works. I'm starting on ball shells/headers so I guess I'll see it soon enough.

[Maserface]

Maybe I can explain it another way..

 

Which has more volume, a 1.5"x4.5" cylinder or a 3.5" sphere?

[OldMarine]

Maybe I can explain it another way..

 

Which has more volume, a 1.5"x4.5" cylinder or a 3.5" sphere?

Hell if I know! Please see my estimation of my math skills in the above post.

I double my mathematical ability every time I take my shoes off.

Edited May 13, 2017 by OldMarine

[MadMat]

I did the calculations, and if the cylinder has the same height and diameter, a cylinder has more gross internal volume than a ball. But as stated, the internal geometry is vastly different.

Edited May 13, 2017 by MadMat

[Maserface]

Here goes another attempt

 

https://drive.google.com/open?id=0B_nZUzPzTycmd2ZEWDNGbGtOVzA

[lloyd]

"It would do you well to study both "fulcanelli" and "FAST", and note the many differences between each style (cylinders and balls)."

----------------

Really? You'd say that to me? I probably read them both cover-to-cover 30 times before you even knew they existed!

 

And I do this for a living (both cylinder and spherical shells!) GEESH!

 

Anyway... I'm pretty sure he WAS talking about "cross-section", not "total volume".

 

But Mase, you are ENTIRELY incorrect in stating that "most spherical shells are built that way". Perhaps YOU need to read FAST again, and while you're at it, look up a fully-filled chrysanthemum, instead of a hollow-sphered peony. Again, GEESH!

 

Lloyd

[Maserface]

Lloyd, really?! Do you really think that I thought YOU had never read those volumes? REALLY?! And what difference does it make who read them first?! You need to take a chill pill my friend!

 

And so it's off my chest, I never said most, I never said all, I said typically, as in its typical to build spherical shells this way, is that ENTIRELY INCORRECT?

 

YES there are many ways to build spherical shells (and cylinder shells) but for the sake of the amateur (who I am addressing), I'm going with the basic, "build a ball shell seminar" style, round peony.

[lloyd]

Mase,

 

You responded to ME. If you didn't mean ME, then you should have stipulated to whom you were responding.

 

It means a heck of a lot concerning "who read it first" when you're talking about two or three decades more experience actually making them!

 

And, I find your position on shell-making to be both wrong and biased AGAINST beginners who've not done it, yet.

 

Your position doesn't give them a chance to learn how it's really done -- it's "your way or the highway", and that's complete BS. The information you gave them is WRONG. Admit it, or bow out of the conversation.

 

Lloyd

[Maserface]

Honestly Lloyd I have no idea what you are talking about.

[lloyd]

Yeah, I know. More's the pity.

<sigh>

Lloyd

[Maserface]

Oh boy! Well I guess we gonna do this again!!

 

Tho OP asked about BP coated rice hulls, in cylinder shells.

 

Mumbles said that the reduced volume area for BURST in cylinders lends itself better to the use of granular powder, not rice hulls.

 

Others chimed in that they didn't understand that, because a cylinder has a higher volume than a sphere of the same size.

 

I chimed in that mumbles was referring to the area in each shell that contained ONLY the burst charge, not the total gross volume.. Then I offered some literature on the construction of said types, for a better description and illustration of each type.

 

It was still confusing for some, so I clarified the volumes in each type, more specifically, and I added a visual aid for the guys who were asking for help.

 

You came in and said that I was "ENTIRELY incorrect" and then misquoted me.

 

I corrected you, about what you misquoted me, and clarified my stance once again (stating that I agree NOT ALL shells are built the way I described)

 

You said that my position was "WRONG and biased against beginners" and that I was giving them "my way or the highway" and to admit I am wrong and bow out.

 

 

 

you are making a LOT of accusations, and personal attacks, but have yet to show me what I said that was so egregiously wrong, or where I gave anyone "my way or the highway".

 

 

 

*shrug*

[Mumbles]

Didn't mean to cause such a ruckus. I think Mase got to the gist of it though. I was just talking about the volume of burst used in a shell of each respective style. Cylinders have 50% more volume of a ball the same diameter, but cylinder shells use less room for burst. Ball shells in a warimono type configuration, have the walls lined with stars and then the remaining space is filled with a bursting charge. I think in my previous post I estimated a casing with 4.5" OD, and 4.3" ID with 1/2" stars. This leaves an approximately spherical void for burst of approximately 3.3" in diameter, which has a volume of 18.8 cubic inches.

 

A 5" cylinder shell uses a central column of burst called a cannule. This column is 1.5"-1.75" in diameter going off of Fulcanelli specs. I used the average of the two, at 1 5/8" and 4.5" long. This has a volume of 9.3 cubic inches. These values were just to illustrate why cylinders tend to use granular BP while ball shells tend to use a carrier. Note: This is a generalization, and not meant to be inclusive of all shell sizes, styles, or effects.

 

There are multiple ways to build shells for different effects. In my experience if you ask someone with a working knowledge of pyrotechnics to build a ball shell, they're probably going to default to a warimono configuration with a single layer of stars along the wall with the remaining space in the center filled with burst.. Similarly, if you ask that same person to build a cylinder shell, it's probably going to be italo-american with a central cannule and stars filled around this packed in with polverone. I didn't really think I was making a stretch or going off on a limb by assuming this. At least with regard to the question posed by the original post, the ball shell in a peony configuration seemed to be confirmed by the question of when to switch from granular BP to coated rice hulls. The other common type of ball shell, poka shells, are quite soft broken and burst with granular BP in all sizes anyway.

[lloyd]

"...if you ask someone with a working knowledge of pyrotechnics to build a ball shell, they're probably going to default to a warimono configuration with a single layer of stars along the wall with the remaining space in the center filled with burst."

 

---------

Eh... Maybe if you ask an experienced person to build you a "single petal shell" he/she would do that. We make, buy, sell, and display all sorts of multi-petal spherical shells that don't have that configuration, require a TINY central burst (usually of flash... or a 'booster' comp), and do not have more room for burst than a cylinder shell of the same size.

 

I buy the "leaning" toward warimono-style single-petaled shells, but they do not comprise the width and breadth of the style of art of spherical shells.

 

Lloyd