Inter-Batch Variation and the Effect of Casting Vacuum on Ballistic and Mechanical Properties of a High Performing Cast Composite Ricket Propellant

A study was conducted to measure the variation in propellant properties for three consecutive batches of an identical formulation. A secondary study was performed to assess the effect of casting vacuum on propellant density, hardness, mechanical properties and burn rate. Only small differences in properties between batches were evident and most were assessed as being within the uncertainty of the measurement techniques. Batch to batch variation, as measured by percentage coefficient of variation, were below industry variances with the exception of elongation at maximum stress which was significantly higher. Casting vacuum did not significantly affect propellant hardness, density or mechanical properties. Burn rate of propellant cast without vacuum had a slightly higher burn rate and lower burn rate exponent (n). A reason for this may be that the application of casting vacuum in combination with vibration results in enhanced settling of solids including ammonium perchlorate (oxidiser) and iron oxide (ballistic modifier). A higher fraction of both solid ingredients results in a lower overall burn rate and smaller n. While casting vacuum did not adversely impact propellant properties for small plain moulds typically poured for research purposes at DSTO, casting vacuum is likely to be more important for large rocket motors with intricate grain designs. The application of casting vacuum also produced more consistent results for some properties and is recommended where possible. Approved for public release RELEASE LIMITATION