The Control of Power for Efficient Batch Mixing

In the batch mixing of composite solid propellants, small variations in the mixing process can lead to unacceptable variability in the properties and performance of the propellant grain. A new closed‐loop mixing strategy is proposed to improve the robustness of the mixing process with respect to these small variations, and thereby to reduce the variability of the finished grain from batch to batch. The new mixing strategy is based on the hypothesis that repeatability of mixing results can be improved by doing the same amount of work on each batch and that mixing efficiency can be improved by continuously controlling power. Justification of the hypothesis is given. The effectiveness of the new mixing strategy is demonstrated through simulations, using a process model based on measurements and analysis of an existing process for the batch mixing of an ammonium nitrate composite solid propellant. Results indicate that the new strategy improves the repeatability of the mixing process by reducing mixing power fluctuations and by eliminating variations in work done on the mixture from batch to batch. The new mixing strategy is shown to be feasible. Because the new mixing strategy is successful with wide robustness margins for this specific difficult mixing process, the strategy should be effective in the batch mixing of a wide range of composite solid propellants.