Oh no, not another flash thread!

Is what I hear you cry. But this is a little different to whats been said so far.

Has anyone tried using inert fillers in their flash powders? Supposedly, adding a lightweight 'airy' compound (rice hills, bran, sawdust etc) increases the speed of flame propagation. I think you add something like 10% by volume to the flash. Its supposed to give more 'back per buck' and allows charges to be completely filled with flash. I also believe that it tends to work best in larger charges.

I did attempt this by adding dry sawdust to some of my crappy Nitrate based flash. The burn rate was enhanced by a good deal just in an open air test.

Has anyone tried this in a salute?

I've used Cab-O-Sil as a burn rate enhancer, only because some was mistakenly shipped with my order. It works well. I would estimate it burns 1.3-1.5 times as fast as straight 70/30. I didn't weigh the Cab-O-Sil because it's all lightweight, I added about 10% by volume.

Arm,

yes by accident a few years ago, it was an attempt at a napalm salute.
we used polystyrene balls, coated in flash with a little flash in excess, it made a lousey salute, but a well interesting effect. needless to say it would be ok as a garden firework, but failed misserably at being either a napalm type device or making a louder bang.
the above is an idea of what not to try :)

I personally dont use it, mainly becuase the air takes up too much space, and takes away room for flash powder, so a salute filled all the way full with a fluffy flash powder will only have about 2/3 the weight of a regular flash powder salute the same size, but only filled 3/4 the way up. Most aluminum/perchlorate flash powders burns so fast anyways that it wouldnt need something like cab o sil, since it works well by itself, but you could mix it in with other slower burning comps.

The good thing is that it takes up more room, so with 100 grams of fluffy flash powder you will make a few more salutes than you could with a 100 grams of regular flash powder. So unless you plan on selling your salutes (which I highly reccommend you NOT do), there isnt much reason in my opinion to add lightweight powder to your flash powders.

NickSG

You actually want about 1/4 of the volume of your casing to be empty. It's really a mater of surface area affecting the burn rate. If you fill the casing completely, the casing will burst before all of the power burns. The pressure wave propagating through the mixture will cause the powder on the ends to become pressed against the endcaps and basically become part of the casing for a split second as the paper fails. You may get a bigger flash, as the powder that was unburnt lights in the air, but you will not get any more "bang for your buck." This issue has been discussed many times in rec.pyrotechnics.

If you want nice salutes, mix 1% cab-o-sil or micro spheres with your 70:30 flash mix. This gives tiny voids in the mixture which will allow fast flame propagation. Also, with that 1/4 of empty volume in your casing, it will work even better.

The article about flash powder and Bullseye SP in the September 2002 Skylighter bulletin may also be of interest: http://www.skylighter.com/skylighter_info_pages/article.asp?Item=39

With 7/3 flash powder, you should fill it up 3/4 the way up, but you can fill it up a little more if the case and the plugs are thick (but make sure to leave room for the plugs). If you fill a case 1/2 way with regular 7/3, and another 3/4 full with regular 7/3, you would notice that they are about equal in sound, but the salute filled 3/4 full will be more powerful. Filling 1/2 full sounds the same, but uses less powder so you get "more bang for your buck". With cab o sil, filling a casing full with flash powder (with cab o sil) uses the same amount (in weight) of flash powder as another casing filled about 1/2 way with regular flash, but with cab o sil it takes up more room, and might burn a LITTLE faster. I would just save my money and fill the cases 1/2 way full if I wanted more bang for my buck.

With cab o sil, or other light powders, you can just go ahead and fill it all the way (with room for plugs) since it burns so much faster, it will not make a difference.

From the Skylighter Catalogue:

Cab-O-Sil ™

Fumed silica, colloidal silica. [SiO2] Fluffy white powder, Cabot M-5

Used as an anti-caking agent to retard water absorbtion by hygroscopic chemicals and to make chemicals flow more freely. Sometimes used in flash powders. Four ounces in weight, approximately one-half gallon volume. Shipping wt. 1 lb.

So why does it enhance the burn rate?

I've never heard of Cab-O-Sil being used in this way.

Another product that i know works is powdered Vermiculite made from the mineral mica. Its used for insulation and is basically all air. Trouble is, it comes in f'ing enormous bags.

Originally posted by Arkangel
From the Skylighter Catalogue:

So why does it enhance the burn rate?

Im pretty sure the burn rate is increased becuase the little air space allow the flames from the burning explosive to vent through, and ignite other parts a lot faster. Im pretty sure this is the reason, but if I am wrong please correct me.

This would be very useful for any LE (with a fairly fast burn rate of course).

I have access to lots of vermiculite, (big garden centre a few minutes walk away) and I was wondering what I could do with it. I went and had a look, but it seems quite large, as in 5mm across for most of the pieces. I assume that's a bit too large.

So, can it be crushed ? I mean, to reduce the particle size ? I assume that would also crush the air pockets that make it so useful... so I would be wasting my time. I will go and grab a handful (no one will notice all the spilt bits heading towards my pocket) and see if I have time. Will I be wasting my time ?

I would only use it to "bulk out" my mixes, to make it go a little further. A burn rate enhancement would be a nice bonus of course.

A final question, is it compatible with most mixes ? I mean, as an agricultural product, there's a lot of stuff that could be considered contmainants. I don't want things going off unexpectedly.

Well, personally I've only read about Vermiculite, so I could'nt vouch personally for its effectiveness.

I think it could be crushed without destroying all the air pockets, its strange old stuff, kind of brittle in a way. Have you got a ball mill Gibbo?

For all the shell makers out there, fillers can also be used in shells to save having to use lots of Meal Powder to fill around the stars. The filler (it can be courser here) in this case is dipped in water or an adhesive and then rolled in Meal Powder. This bulky material can then be used in shells to greatly reduce the amount of Meal needed.

Here's another idea that might help, again from Skylighter:

Rice Hulls


When coated with burst-powder, rice hulls are used to break shells. We pack them (the hulls, without the burst powder) in 4 pound bags (about 5 gallons volume).


Basically, you have your shell, into which you carefully put your stars and comp. The rice hulls, (rice crispies) having been thoroughly dusted with burst comp, are then used to fill the shell, and keep the stars in place. This helps in all sorts of ways, and allows you to build some very interesting break patterns within the shell.

Maybe you could add rice crispies to your flash, to take up volume and enhance the burn rate?:p

Unfortunately, no, I don't have a ball mil, but it's on my to-do list. :)

I doubt it would be necessary anyway, it's so light I would be able to crush it with the back of a spoon or something.

I suppose I will ahve to find out. When I get some more chems and tools, (just moved out) I'll be able to continue my 'hobby'. I can't do anything till I get a workbench set up here. But at least my mum isn't getting bitchy any more. :D

I might try a prcedure similar to the rice hulls method of coating it in blackpowder, I've seen it detailed in another thread. I have no rice hulls, but vermiculite may just do. Only problem is, I don't think it absorbs water. That would mean that the powder won't really stick to it.

I may find a way round it. Maybe just some dextrin in the water.