14 replies to this topic

[butch24]

I have seen differant answers to this question. I have seen 3-1 meaning say if you had 100 grams of rice hulls you would use 300 grams of black meal powder is this right?

Edited by butch24, 31 July 2011 - 12:12 AM.

[Arthur Brown]

There is no "right" answer! This is a design standard for your style. I've heard of people using that sort of number. Shimizu's book will likely give you some guidance for using rice hulls.

[dan100]

I have seen differant answer to this question. I have seen 3-1 meaning say if you had 100 grams of rice hulls you would use 300 grams of black meal powder is this right?

it is just a ratio and can go higher ive seen 7-1 depending on what you want to fill.
personally 1-1 or 50-50 is enough to break 3" cans and balls smaller shells use no filler bigger shells use more burst coated on the media.

dan.

[Peret]

A lot depends on the quality of the meal powder you use. If it's a slow powder, you'll get a slow break and probably need to use more. I make my own powder with willow charcoal and use 4:1, which gives a fairly hard break with a satisfactory bang with 3 inch shells. 4:1 is not a very heavy coat, it still leaves some brown hulls showing at the edges.

[Mumbles]

I've always used 5:1. It's always seemed to be the "standard" that I've saw around when I was first starting out. It's also about the average that is given for various compositions in Shimizu's FAST on page 214. That being said I've seen ratios as high as 10:1 so clearly there is wiggle room.

I unfortunately happen to completely disagree with what Dan100 just said. Smaller shell use a higher ratio of BP to carrier. Larger shells will not handle the same burst power of a 3" shell, so they typically use a lower ratio of burst to media. Shimizu's book clearly shows this for the cotton seed example, but oddly enough has the opposite (but small) trend with cork. I've had it described to me that you can burst a 12" shell with rice hulls just dusted with BP until they are black, even though that seems a bit low if you ask me for a good petal.

Edited by Mumbles, 04 August 2011 - 06:04 PM.

[dan100]

personally 1-1 or 50-50 is enough to break 3" cans and balls smaller shells use no filler bigger shells use more burst coated on the media.


for shells under 3" i think stronger break is needed so no filler is used just polverone or corned bp,coating a carrier with 5-1 or more would be no saving unless mass production is a concern.
for bigger shells ive seen higher ratios of bp on media used ie 3 inch plus 4-1 and over.
if 1-1 is good for 3" larger shells with 4-1 do have more burst on the media.

i also understand that 12" shells and up wont handle heavy break hence why inert fillers are sometimes used, fast violent burst would likely break the shell before it was consumed ruining the break and may blow the contents blind.
contradicting that ive seen multiple petal shells with no filler.

there are very few people here that have,do or will make a 12" shell, when i say big i dont mean that big.

dan.

[Mumbles]

I guess I should have specified one point. I have some doubts as to the true effectiveness of 1:1 BP:rice hulls. If it works to a satisfying level for you, that is all that matters though. I just don't think it would give me the breaks I desire. 4:1 on puffed rice was pretty decent in a 3" ball shell for me. I have a hard time believing something containing 1/4 the burst would get it there.

For what it's worth I have made 8" and 10" shells which were mostly burst with 5:1 BP on hulls, which went quite well. It's a pretty ubiquitous burst.

Edited by Mumbles, 08 August 2011 - 12:48 AM.

[cooperman435]

well to add my part to this discussion I've used nothing but 2.5:1 rice crispies with results that satisfy all my shell sizes, for larger shells Id reduce this to 1.5 or even 1 to 1.

When a shell bursts only a tiny proportion of the burst actually "bursts" the shell, the moment the casing is ruptured any combustion of un-burnt BP afterwards is essentially wasted (as far as bursting goes anyway, it does assist in ignition of the stars still), so I see flame propagation as a far more important issue than BP content. I simply want more of it to burn as fast as possible before the shell case is broken, therefore loose grains of coated crispies with plenty of air gaps to allow a flame to spread "like wildfire" (scuse the pun) is in my opinion far more useful.

Even at 1:1 theres a noticable flame after the burst so I believe I could go down to that for most sizes anyway.

[Vic]

It looks like my seven to one is over kill then, but it works for me.
But how many of us are using boosters as well?

[Mumbles]

There is always going to be visible fire coming out of a burst. It's not like it's completely consumed inside the shell.

In my mind, I want the most BP to be burning at once inside a shell. I imagine a shell a lot like a pipe or a hose. There is a burst pressure where while pressurizing it, it will eventually fail. Then there is another burst pressure, which is higher, which it will fail at from a sudden spike in pressure. I want to get to the second one with a shell. 5:1 may not be 5x better than 1:1, but it seems like it would be some level better. BP is too cheap to worry about economics. I guess I'll have to try it sometime.

[cooperman435]

I agree MUMBLES but when you think about it logically as its the volume of BP burning to be high you want a high surface area not necceserally a high content of BP, I believe that even at 1:1 that any BP that WILL burn before the shell bursts will be burning but still excess remains to be consumed after the burst so any more is a waste.

[Mumbles]

BP has a pressure gradient toward burning much the same as smokeless powders or KP type mixes. It would make sense that the "optimal" amount of BP would be a uniform covering of each hull to a depth where the BP was fully consumed upon rupture of the shell wall. There is a surface area imposed limit to how much BP can be burning at once, but the rate will be exponential based upon pressure. I used to add BP in 5 increments to my hulls, and they wouldn't be close to fully covered until at least 3:1 or so IIRC. Then again I got the hulls pretty wet as I was adding a good amount of powder, so there was probably clumping.

[megabusa]

Do you use the dust straight from the mill to coat the rice crispies, or do you granulate it first ??

I've never used it as I only make 2" & 3" shells, but I am considering using it for the 3"s to reduce the amount of BP it uses.


Cheers,

[Vic]

Do you use the dust straight from the mill to coat the rice crispies, or do you granulate it first ??I've never used it as I only make 2" & 3" shells, but I am considering using it for the 3"s to reduce the amount of BP it uses.Cheers,

Use milled BP dust made with spruce or willow or you could go exotic and use grape vine but there is no need. Granulated or pulverone BP are kept for Maltese/Italian canister shells, that do not need the compressive strength that you can get from coated rice hulls or crispies.

[dan100]

Do you use the dust straight from the mill to coat the rice crispies, or do you granulate it first ??

I've never used it as I only make 2" & 3" shells, but I am considering using it for the 3"s to reduce the amount of BP it uses.


Cheers,

straight from the mill with as much dextrin as you desire [under 5%] soak the filler [spray if its crispies] drain it well [ i spin it in a sock around the head ] add it in a star roller for higher ratios, tupperware tubs are fine for 1-1 or let dry and re apply another part.

i should also say that the grass seeds i use differ from rice hulls in size and surface 1-1 on hulls woudnt give much cover and may have a higher percentage of filler to bp.

dan.