39 replies to this topic

[digger]

You misunderstand my friend.

It doesn't increase the burn rate of a given powder but increases the burn rate of a MASS of that given powder. The actual speed of powder burn is not increased.

And Digger yes you are correct as ever. Through my poor explanation I mean that the thin walled spheres increased the surface area (I believe in maybe similar proportions to smaller grains?) as there is no BP contained within.

Is that better?

Sounds good to me.

As you say the linear burning velocity is constant (neglecting pressure effects on burn rate as the pressure increases would be applied to whatever size of particle you choose) therefore for example if you have a 1cm cube and the burn rate is 1cm per second and you light all sides at once then it would take 1/2 second to completely burn the mass. However if you cut that cube into 8 0.5cm cubes and light all the surfaces at once then the mass would burn in 1/4 of a second.

Hence with a coating on rice crispies or whatever you choose then the coating is very thin so it will consequently be consumed quickly even though the linear burning velocity has not changed.

Edited by digger, 06 November 2008 - 10:13 PM.

[cooperman435]

What he said YEP!

Much better explination

[wjames]

agreed.....when i said it increased the burn rate....I meant the same as you did....just i didnt explain it as well.


Well done to digger for a decent explaination !!!!


there is a million and one things you could use.......i bet some of them havent even been tried.. ( he says, whilst looking at that 4 year old box of cous cous....)

[cooperman435]

The trick here is to use something very low mass.

heavy carriers will both ad weight to the shell and mean the ratio of BP to carrier (I have used 2.5 crispies to 1 BP by weight previously) will have to be altered as its the layre of BP you want to maintain as thin as possible and a heavier carrier and the same ratio would result in a thicker layer.

I did try polystyrene balls but they were a nightmare to roll in my star roller but the resulting burst was excelent,

Ive tried to secure a supply of rice hulls and sunflower sees hulls but so far no luck. If anyone has a source or suggestion for another low cost equivelent Id be interested and everyone will benifit from having them available.

[digger]

The trick here is to use something very low mass.

heavy carriers will both ad weight to the shell and mean the ratio of BP to carrier (I have used 2.5 crispies to 1 BP by weight previously) will have to be altered as its the layre of BP you want to maintain as thin as possible and a heavier carrier and the same ratio would result in a thicker layer.

I did try polystyrene balls but they were a nightmare to roll in my star roller but the resulting burst was excelent,

Ive tried to secure a supply of rice hulls and sunflower sees hulls but so far no luck. If anyone has a source or suggestion for another low cost equivelent Id be interested and everyone will benifit from having them available.

I tend to use rice crispies too, however at a 4:1 ratio for BP on larger shells and 6:1 KP on smaller shells.

One thing that may be worth trying is perlite as it is heavy when wet and weighs naff all when dry so it would make it easy to coat in a star roller after a pre soak and drain. It does not de laminate or expand when wet like vermiculite, it should be easy to screen out any dust before use and it is only a few quid for a big bag.

Edited by digger, 07 November 2008 - 10:08 AM.

[Mortartube]

I have never tried it but I reckon Tapioca should work. I use it for star cores anyway. Only problem is, is that I am short on chems at the mo, so won't be trying it soon, so if anyone else wants to give it a bash. Be my guest.

[crystal palace fireworks]

I ve been in touch with various companies/associations etc in the UK about rice hulls, but no luck as yet for a supplier!

But you can buy them from the USA at pyrodirect.com (Kevin) for; 3 llb = $5.50 or 50 llb = $49.75 plus postage/delivery costs, but i don`t know if its worth it!

[digger]

I wouldn't get too hung up on rice hulls, the Chinese use them because they are cheap and available in their location. They are just a carrier after all, it is best to find something light, cheap and locally available.

It has to be said that rice hulls are not necessarily the best carrier in respect to flame propagation through the burst charge due to their interlocking nature.

If you want something similar to rice hulls why not try oat husks?

OAT HUSKS CLICK ME

Edited by digger, 07 November 2008 - 11:37 AM.

[crystal palace fireworks]

Oat Husks looks a equally good carrier,.....and its produced in the UK, thanks digger!

[pyromaniac303]

I have never tried it but I reckon Tapioca should work. I use it for star cores anyway. Only problem is, is that I am short on chems at the mo, so won't be trying it soon, so if anyone else wants to give it a bash. Be my guest.

I use tapioca for stars too, and it seems quite small and heavy compared to stuff like rice crispies that other people are using. It may be useful for small shells though where you need a high powder density as you cant fit that many rice crispies in a 2" shell!

[spanner]

Rice krispies seem fairly sticky when lightly dampened. Does an additional binder need to be used, or will a light spritzing of water on them provide enough "stick"? I realize two or more coats would still need a binder.

[cooperman435]

Pyromaniac303 - Tapioca is not as good as crispies, due to that very reason. It's small, so therefore thicker layer of bp resulting in a slower burn and less power.

A 6" shell technically only needs 50-70g of bp to burst it, so this much spread over all the carrier contained within is the best scenario.

Spanner - I personally add +2% dextrin to all my bp so I can granulate it and coat crispies, whichever I need at the time.

[ener]

Here they sell ricehulls: LINK

[Bonny]

One place to look for rice hulls is brew shops (for making beer etc..), not sure about UK, but I know they can be found in Canada for that use.
I've never tried rice hulls, only BP coated vermiculite. I usually coat either 4:1 or 5:1, with 5% dextrin in the first 3 (or 4 coatings) ONLY, then straight BP for the last coating.

[E-tech]

When I worked at a homebrewing supply store, we sold oat hulls as a lautering aid for people making beer with a lot of sticky grains in the mash. Perhaps a homebrew supply place would be a good source?