71 replies to this topic

[AdmiralDonSnider]

Detailed specs are given in the first link (pyroguide) of my first post: I was talking about the last example with nine pumped stars. So the wall thickness is 2mm, with an 22mm ID shot from a 29mm mortar....see link.

I replaced the unknown 1,1grams of loose comp with 1g of 70/30 flash using coated bright Al (bronze): the break was rather a salute than a burst of stars (although some stars/fragments of them?? did ignite.) It was an unsightly effect. So one will need much less than 1g, probably half of it. I guess the chinese flash is slower than mine - with good reason.The stars used in bombettes are always rather fiercely burning.

Edited by AdmiralDonSnider, 05 September 2008 - 11:22 AM.

[Pretty green flames]

Snider, what kind of a report do these bombettes have (commercial ones)? From my experience, a low pitched report may be a sign of a perchlorate based flash, while a high pitched report may indicate a nitrate based flash composition. Note that this is based entierly on my own observations from small ground salutes made from different report compositions.

[MDH]

There is a great possibility that this flash is being slowed down with another fuel and anticaking agent such as fine wood dust or a small amount of dextrin. This would slow down the composition and create the flame envelope.

EDIT: pretty green flames I think you may have the nitrate/perchlorate comparison switched around - nitrate (standard 50/25/25 or 50/40/10 or 60/30/10) is typically deep sounding, while perchlorates are very high pitched due to the greater speed.

Edited by MDH, 07 September 2008 - 04:40 AM.

[Arthur Brown]

If the flash is to be slower then a different Al powder size distribution will assist in rate control . Say 50% of the Al being 400 - 600 mesh and 50% being 200 - 400 mesh. A mix like this would stil analyse as Al and Perc but have different properties from an all 400 mesh product.

[AdmiralDonSnider]

I was off for quite a long period of time. However I took some time to do further investigations and tests on these units and had a good degree of success. The breaks still are improvable. Maybe my design could act as a starting point for further discussion. As I said there is no literature about bombettes (except reports) and who wants to make colour breaks is contingent on cooperation.

I focussed on the following:

a.) Break charge: I realized that bombettes are broken using a kind of dirty flash employing flake Al (nominal mesh size smaller than 200) with or without grease, probably using the 70/30 formula. There was no commercial item that contained dark Al for flash. The weight range of the flash charges showed some continuities.

b.) Container: I couldn´t find any commercial item made from virgin kraft paper. Bombettes use inferior kinds of paper - kraft partially made from waste paper or plain recycled paper (as used to protect the floor from scratches). While this practice reduces the production costs, it may also have some practical background: Containers from virgin kraft are a lot stronger and thus harder to break.

c.) Plugging the tubes: Most commercial items are either plugged with clay on both sides, or with clay on one side and paper plugs on the other. A third variety uses clay on one side and clay forced between two disks on the other. I´m not sure how the first version is constructed (you can´t plug the filled tube pressing in some clay). Generally it´s very hard to sufficiently plug both side to allow pressure to be equally built up inside. The units fail if one side blows out easily. However some of you may argue that the properties of the plugging and the container won´t do much difference in a flash-broken unit cause flash will break anything you give it - I leave this point open.

d.) Stars: Most bombettes come from china where MgAl/metal-fuelled stars are the standard choice. The stars burn bright and are heavily primed.

e.) Clay: the clay seems to be an important factor; most items seem to use red fireclay mixed with grog.



So far I managed to develope the following manufacturing method (note that I was using untreated bentonite because I had no other clay at home), which may serve as a starting point for improvement.

My own units were:
50mm long, 25mm I.D. with 1mm wall (27mm O.D.) shot from 30mm cakes (using about 2,5 grams of mediocre 3FA/4FA)

container wet rolled using diluted white glue, made from a thick caliper of plain waste paper as used by workers to protect floors, rolled against grain

lower plug: 15mm of bentonite pressed in with a hydraulic press, pressed until container slightly deforms (note that plain bentonite is easily affected by moisture-->so I omitted priming the units or adding tails, but they all lit)

clay drilled with 2,5mm drill

inserted 20mm of 2,5mm visco (1cm/sec), fuse stands out about 3mm, split-tied blackmatch (being impossible to use damp primes)

loaded units with 10-12 8mm primed pumped stars and 0,8 grams of 70/30 flash (perc/bright Al coated with 1% stearine)

inserted a disk

stripped the remaining paper using a sharp knife, then applied a little hot melt glue to the disk and closed the units in maltese style (uncommon method, but I gave it a try to find out if it allows more pressure to be built up, it worked-->method improvable)


I shot about 25 of these on new years eve and they all succeeded. Although quite sightly the break could be harder (larger flower) and more symmetrical. I will try using 1g of flash next time. However, so far I was quite happy with what I´ve got.
Feel free to criticize and improve this attempt.

Edited by AdmiralDonSnider, 14 January 2009 - 03:28 PM.

[Mortartube]

This sounds very positive. Keep up the good work.

You may have some success using newspaper to make the bombette cases as it has no real grain compared to kraft and many other papers, so a good break may be easier with it.

[Potassium chlorate]

That must be some kind of flash; we had a commercial cake for New Years Eve, probably about a kilo powder in it. 50 shots, which would mean 20 grams of powder in every bombette. They were 1" or even 3/4", but the bangs were pretty loud.

[pyrotrev]

I wonder whether the Chinese use a flash containg sulphur (or other non-metallic fuel) to break bombettes... It strikes me that something producing more in the way of gaseous combustion products would likely both decrease the risk of stars being blown blind (slower explosion) and give a bigger burst due to increased expansion. Anyone ever tried granulated whistle in bombettes?.

[AdmiralDonSnider]

I wonder whether the Chinese use a flash containg sulphur (or other non-metallic fuel) to break bombettes... It strikes me that something producing more in the way of gaseous combustion products would likely both decrease the risk of stars being blown blind (slower explosion) and give a bigger burst due to increased expansion. Anyone ever tried granulated whistle in bombettes?.

This could be a good point. Does whistle produce more gas than flash - I never used it...?

[Potassium chlorate]

This could be a good point. Does whistle produce more gas than flash - I never used it...?

Flash actually produces very little gas. It produces smoke in form of particles, though. MgO and/or or Al2O3 and KCl for perchlorate based flash.

[AdmiralDonSnider]

Concerning more "gaseous" break charges I found something called "Chinese No.3 flash powder" in the web, although I don´t know the original source.

It´s
KNO3 5parts
S 3parts
Al 2parts
KClO4 1part

Worth a try?

Edited by AdmiralDonSnider, 14 January 2009 - 07:34 PM.

[Potassium chlorate]

Yes. The KNO3 and S will probably make some more gas, especially SO2.

[Mumbles]

This goes along with the last few posts, but have you considered using a non-standard flash ratio? Increasing the aluminum will slow the burn somewhat, and increase ignition. 60:40 still would pack a decent punch.

BTW, you most certainly can press clay directly over stars and burst. I never considered it until I saw it done. The guy got the idea by disecting excalibur class C shells. According to him, that is how they do it. He adds stars, grain BP, and flash. Compacts it all together, and presses the top clay plug over the top. I don't remember a paper disk being in there, but I personally would to avoid mixing. He uses pretty thick walls too. This plug obviously has to be pressed more lightly, but apparantly you can adequately compact it with a press. I pound the stars in my canister shells to settle and compact them. No problems, no crushed stars.

Not the best example of the technique, but they're in the 2nd candle:
http://www.secac.com...man-candle.html

Your description makes it sound like there are stars and some loose powder, not filled solidly. Pressing in clay may not work in this case.

Most of the bombette stuff I've heard of utilize a rosette type of thing. It's in the fulcanelli papers. Basically the stars are a bound flash and they provide the burst. Perhaps the additional flash is to give it a bit of boost.

Edited by Mumbles, 15 January 2009 - 02:57 AM.

[AdmiralDonSnider]

This goes along with the last few posts, but have you considered using a non-standard flash ratio? Increasing the aluminum will slow the burn somewhat, and increase ignition. 60:40 still would pack a decent punch.

BTW, you most certainly can press clay directly over stars and burst. I never considered it until I saw it done. The guy got the idea by disecting excalibur class C shells. According to him, that is how they do it. He adds stars, grain BP, and flash. Compacts it all together, and presses the top clay plug over the top. I don't remember a paper disk being in there, but I personally would to avoid mixing. He uses pretty thick walls too. This plug obviously has to be pressed more lightly, but apparantly you can adequately compact it with a press. I pound the stars in my canister shells to settle and compact them. No problems, no crushed stars.

Not the best example of the technique, but they're in the 2nd candle:
http://www.secac.com...man-candle.html

Your description makes it sound like there are stars and some loose powder, not filled solidly. Pressing in clay may not work in this case.

Most of the bombette stuff I've heard of utilize a rosette type of thing. It's in the fulcanelli papers. Basically the stars are a bound flash and they provide the burst. Perhaps the additional flash is to give it a bit of boost.

I never tried altering the 70/30 ratios. The main thing is that I highly doubt that it is this comp that breaks commercial units. Without a scientific instrumentary I can only visually judge that it´s some kinda flash making use of bright Al.

Concerning pressing you mean that the pressure necessary to make the plugs is not sufficiently high to break the stars into pieces, right? All units I dismantled where quite solidly filled, but always showed free space between the stars (means that the units were not completely filled with powder and stars).

Can you give more information about the last statement with the rosettes. I will read the text in Fulcanelli and Hardt, but I don´t know what you mean by saying "the stars are a bound flash and they provide burst". Do you mean the stars are primed with flash? Maybe your statements make some radical improvement possible...

By the way...is there any serious pyro you know who is specialized in cake items or knows about the industrial methods who could give some valuable information to avoid a long trial and error process. Bombettes are the "main" small scale fireworks nowadays and I doubt there is no serious source for this topic

[portfire]

AdmiralDonSnider you could try my Cake thread, should be some useful info for you, look for the tutorial.

http://www.pyrosocie.......43&hl=Cakes