71 replies to this topic

[AdmiralDonSnider]

Your cake is very nice. The problem once again is that I wanna focus on breaks of stars. Any experiences there?

[pyromaniac303]

I made a small cake (12 shots) a while back using sodium benzoate / potassium perchlorate 70:30 burst (0.5g) and 30 mesh BP (0.5g), the dimensions of the inserts were 5/8" inner, 3/4" outer x 2" long. I found the break was quite poor and tended to pop the end caps rather than break the casing. If I get time this year though I may build a cake over summer.

[Mumbles]

That is correct. The stars held up to the pressure of pressing in a clay plug. He did say that he can't put unlimited pressure on it, but it does adequately compact. An arbor press was used.

On page 31 of Pyrotechnica XI, the process is detailed. It's a scary composition. I may try to replace the chlorate with perchlorate some day. It's a flash powder that is granulated like pulverone using wheat paste. It provides it's own burst. It explodes somewhat like a salute. However the granulated consistency causes the particles to burn for a little bit after being expelled from the shell. This makes a bushy cloud of sparks kind of like a titanium salute. I had thought that a similar thing could be done with colored flashes. Instead of being white, you could make red, green, whatever color you wanted. The colored flashes I've made don't burn as fast as normal flash. This could potentially result in a splash of color without the need for a separate burst. I haven't tried it, but I've heard of a commercial manufacturer working on this in the past.

I don't personally know anyone who works in extremely small shells. I go as small as 1" ID for insert shells. They get fired from a 1 3/8" ID mortar for testing. I've thought about making some smaller ones to make some impressive smaller shells. If I were going to go about this, I'd revisit Karlfoxmann's beraq tutorial, and do it similarly. A few turns of kraft. Fill it with microstars and granulated whistle or a mix of BP and flash. Spike it with thin string, verticals only. In shells, the BP slurry priming would work, but visco should work too. They're probably too small to paste traditionally. I'd look into dipping the shells in epoxy, glue, etc to fireproof and increase burst strength.

[Pretty green flames]

Your cake is very nice. The problem once again is that I wanna focus on breaks of stars. Any experiences there?

I think the only factor here is not the formula, it's pure mass of flash powder. Experiment with different ammounts of flash powder in your bombettes, to be honest I would use something between 2 and 3 grams of 70/30 made with -325mesh flake Alu (greasy). One gram, in my opinion, is really not enough to break a bombette hard. Use more flash is my advice. Experimenting with different formulas is just a waste of aluminium, might as well use more of a tried and true formula.

[AdmiralDonSnider]

This might be true, but I fear turning the whole thing into a salute (been using greasy Al). Will give it a try though.

According to my findings there was no unit using more than about 1,2 grams of loose comp for break - although I do not know the chemical details of course. A very useful approach could be using a part of flash for priming the stars - maybe this is how it´s done commercially and contributes a lot of force to the charge.


By the way: I saw you are from Slovenia - do you know Zmuro? This guy makes great round shells. I tried to motivate him to give some tutorials but seems he needs some more motivation...

Edited by AdmiralDonSnider, 17 January 2009 - 11:40 AM.

[Pretty green flames]

This might be true, but I fear turning the whole thing into a salute (been using greasy Al). Will give it a try though.

According to my findings there was no unit using more than about 1,2 grams of loose comp for break - although I do not know the chemical details of course. A very useful approach could be using a part of flash for priming the stars - maybe this is how it´s done commercially and contributes a lot of force to the charge.


By the way: I saw you are from Slovenia - do you know Zmuro? This guy makes great round shells. I tried to motivate him to give some tutorials but seems he needs some more motivation...

I honestly doubt that 2g (3grams might be pushing it, but in a 1" bombette, but i think you'd still be fine) will turn the bombette into a salute, stars are not that easy to shatter when properly made, small ones are especially hard.

Yes, I know Zmuro, I don't think he'll write any tutorials, no matter how many people ask him.

[AdmiralDonSnider]

Your point. I will give that a try next time I make some units.
In the meantime I got into contact with a chinese selling cake products made by his factory and asked for some information about the burst charges of bombettes (there are some videos at youtube showing cakes made by them - quite impressive breaks).

The guy revealed that they are using MgAl based flash along with some BP to make a larger burst. I will probe again and maybe be rewarded with some nice info.


Concerning Zmuro it´s a pity that he doesn´t share his findings. Does he have a special reason for ignoring these requests? However, I assume everything you ought to know about his construction techniques is already out there in Shimizu et. al. and he just succeeds in sticking to these principles.

Edited by AdmiralDonSnider, 17 January 2009 - 04:13 PM.

[Pretty green flames]

Concerning Zmuro it´s a pity that he doesn´t share his findings. Does he have a special reason for ignoring these requests? However, I assume everything you ought to know about his construction techniques is already out there in Shimizu et. al. and he just succeeds in sticking to these principles.

To be honest, as far as I can tell, there's nothing special on his shells, construction wise, I think he uses KP to break most his shells (the newer ones atleast). But construction wise there's nothing really special.

[Mumbles]

You say there is 1 or 2 (maybe 1.2)g of flash loose in the shells. I wonder how much flash is stuck to the stars, as you've suggested. The best way to get the hardest break would be to turn them into salutes, and back it off just a little. Thats how most people I know make rockets. They make them blow up, and back it off just enough to have them constantly on the verge. I've heard of a something to the effect of 0.5mm shrinkage on the nozzle diameter causing the rockets to blow up.

[Pretty green flames]

The guy revealed that they are using MgAl based flash along with some BP to make a larger burst. I will probe again and maybe be rewarded with some nice info.

Overlooked this in my previous reply, this would certainly be plausible, most of the cakes from Brothers pyrotechnics have a really strong break and the flash is really intense which may suggest a Magnalium based flash as these are known to be very bright (can be annoying with some cakes ), I think the ratio is 50:50 with K-perch but not sure on that one.

[AdmiralDonSnider]

I just wonder what he means by saying they use the flash along with gunpowder?! Wonder if that is to contribute gases...

Anyone ever heard about such a "blending" practice...?

[Mumbles]

They probably mean grain gun powder, with flash mixed in. It does in fact produce more gas. It's how I break all my shells, both insert and full break. The full break uses a traditional canule with flash coated over the BP grains to make them pop a little harder. The inserts I fill them about 3/4 way full with stars and add hot granulated black powder powder(-12+30 mesh) to fill in the spaces between stars. Depending on the insert and break desired I add flash to make it break harder. I think the BP in there helps it with ignition too. The timed inserts in the following shell are built like this.

http://www.apcforum....imed spider.wmv

I should probably have measured the amount of flash I put into each one. I just eyeballed it, probably why the last one bursts a little weaker.

[cooperman435]

Indeed I too use granulated BP in my salutes to add bass to the report rather than a crack it produces a much nicer boom instead.

[Arthur Brown]

In Science it's publish OR die! If you have nothing to publish then the work is wasted, In Business it's publish AND die. No-one gives out all the details of their commercial successes, so that they maintain a commercial edge, and hopefully stay in business.
Zmuro may be of the commercial mindset. In pyro there is much dependance on the formulae which are often published BUT the technical method of manufacture often governs the performance of a product. --Even if you know the formula you may not be able to replicate a device.

[AdmiralDonSnider]

I managed to get a little more information about the chinese practice (although the guy I was talking to said he was no technician). I would also wonder, if he revealed all of the details and am indeed aware of that the construction and physical properties are the harder part of the deal, like Arthur stated.


It´s this cake that got my attention, it has superb brakes for its size (30mm inserts), but it´s just an example:

He said they they are using BP along with some (the guy said "2-3g") MgAl based flash to give it a wider break. So I assume:

a.) BP means corned 3FA/4FA mixed into the stars, just like Mumbles described. Meal would make no sence.
b.) MgAl flash means 50/50 MgAl/perc flash, as I don´t know other magnalium flashes. (the chinese seem to use MgAl really excessively in everything they make, stars, burst etc.)
c.) for the 30mm size 2-3g of flash seems a bit too much, but I could be wrong on this one.
d.) in this case the BP is the main break charge and the flash just boosts?!

The load seemingly is quite similar to the one Fulcanelli proposes for small shell inserts (although the case is made differently and in general there is no flash) as far as I know.
Just a pity that it will consume a lot of good grain gunpowder, won´t it?