Andrew Tang, Hilary Chen and Andy Tang
Abstract: In the fireworks or pyrotechnics industry, black powder (nitrate–sulphur–charcoal) is a traditional and commonly used base for creating other chemical compositions. Due to the large variety of pyrotechnic effects, the creation of such different compositions that meet so many needs has led to many different formulations. The energetic status of such formulations can easily be confused, for instance the break charge used in a breaking aerial shell can produce a tremendous audible sound like flash powder. Nowadays manufacturers may also develop their own chemical compositions by replacing and/or adding different chemical substances in order to give a “perfect” function such as large break. It is always the breaking energy that dominates the display color effect and it may generate unnecessary pressure causing danger to the operators or the audience. European standard UN default classification controls the use of metal alloys in black powder formulations, i.e. flash powder. The time/pressure test is very tedious. In the United States, the usage of flash powder is limited to 50 milligrams for ground items or 130 milligrams for aerial items for consumer fireworks. Sometimes manufacturers add non-metallic chemicals such as perchlorate and benzoate to create a formulation that can still create unnecessary pressure and cause danger. It is necessary to develop a fast and simple test method to evaluate the powder energy no matter what the chemical formulation is. Such a method can be used by manufacturing industry quality control personnel on-the-spot to evaluate the powder energy.
The method uses a simple test fixture which is composed of a steel tube acting as mortar and a standard “weight” steel ball. The powder energy is “evaluated” by the height to which the steel ball is ejected by the explosion of the powder confined in a standard plastic vial sitting inside the mortar. By plotting a graph of steel ball height vs amount of powder used, the graph shows a straight line with a gradient called Energy Return On Powder (EROP value). A market survey reviews powders of different chemical compositions with different EROP values.
Keywords: powder energy, black powder, flash powder, EROP value, mesh size, mortar height
Ref: JPyro, Issue 28, 2009, pp37-50
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