Discussion of Process Effects on EX-99 Propellant Characteristics and Continuous Extrusion Behavior

摘要

This report documents the process study for the production of EX-99, in a twin-screw extruder. Using powder supplied by Bofors AB, this was the first effort in the United States to produce this formulation in a continuous process. For reasons of quality and efficiency, a factorial experiment strategy was employed to quantify the effects of screw design, solvent content, extruder speed, and process temperature. This study was unique in that samples from each of the 12 treatment conditions were submitted for test and evaluation. Using regression analysis, a number of predictive models were presented for characteristics such as, dry grain diameter, perforation diameters, web thickness, occurrence of white patches, die pressure, and extruder torque. The importance of the experimental approach is illustrated not by the knowledge of which factors are important to which measurements, but by the power to predict results at untested process conditions. Two parameters, inner and outer web diameter, were jointly solved to find the process conditions that minimized the difference between the two dimensions. Incorporating the lead engineer's input as a basis for process conditions, an optimal setting was calculated. This new setting was the basis for a 600-pound production run with good results.