Coating rice hulls

From PyroGuide

Burst charges are frequently coated onto inert materials such as rice hulls to allow them to burn efficiently and to lower the loading density. This page shows how to efficiently coat powdered burst charge compositions such as black powder, KP or H3 onto rice hulls to make readily usable burst charges for round shells or other devices.

Good round shells depend on a delicate balance between mainly the strenght of the burst charge and the strenght of the container. To adjust the strenght of the burst charge, two means are: (a) adjusting the burn rate of the (unloaded) charge itself (by using finer raw materials, better mixing etc.) and (b) adjusting the weight of the loaded charge in a shell (note that the strenght can also be adjusted by changing the amount of pasted layers, as the burn speed of all charges is more or less contingent on the ambient pressure). In order to optimize the break (without allowing energy of the break to be wasted) it is also important to optimize the consumption of the charge. This is connected with both (a) and (b).

In the one classic source on round shell making, Shimizus book "Fireworks; the art, science and technique", the author stresses the importance of matching the loading density and the size of the burst charge granules to both the properties of the burst charge and the size of the shell (see pp.207-214). Smaller shells use stronger burst charges (stronger, i.e. a fierce charge on small nuclei) in order to compensate for the smaller amount fitting in these, while larger shells allow more burst charge to be loaded, which consequently has to be less strong(to prevent the stars from being destroyed or blown blind). Adjusting the strenght of a charge is not necessarily done by adjusting its burn rate (a) or altering the weight of the charge (which is difficult by the way, as round shells are loaded by volume, and the volume of a shell is limited), but is most conveniently done by altering either the size (i.e. kind) of the nuclei or the weight ratio of the carrier material (hulls etc.) to the pasted-on burst charge.

With a given kind of nuclei and given properties of the burst charge composition, a ratio pasted composition to hulls of e.g. 5:1 will increase the weight of the active burst charge in a shell compared to 3:1. However, an inappropriate ratio (e.g. too much of the comp pasted onto a single hull) will spoil the balance between charge and container, wasting energy or even destroying the shells appearance. This is why it´s important to match this ratio to the shells design, its size, the burst charge comp, the nuclei etc. Shimizus values may be employed or may serve as good starting points for conscious modifications (e.g. for willow shells etc.)

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