Investigation of the Manufacturing Variables of Cast Double-base Propellant

Abstract

The casting of double-base propellant involves the filling with liquid of a mould packed with solid particles. Simultaneous mass transfer between the phases, known as gelation, retards the flow, hindering the prediction of casting time. A mathematical model to predict casting times is developed via an analytical equation previously used to describe water percolation in soils. The complicating effect of gelation is dealt with by the inclusion of an empirically verified submodel, which is based on the valuable concept of resistance/conductance variation. The effect of temperature on liquid viscosity and gelation is also included. A photomicrographic test to determine the value of a dummy system as an experimental analogue of the hazardous live system demonstrated that this was inadequate and work to verify the mathematical model was then concentrated on the live system. The test is also useful in characterising the behaviour of various powder liquid systems on a microscale. Live casting experiments provided evidence in support of the proposed mathematical model and the empirical constants for a typical system are reported. In these experiments, the temperature effect on liquid viscosity was found to exert a greater influence on casting time than the gelation effect. Casting times predicted by the mathematical model are shown to compare well with industrial experience. In a separate section, the development and testing of a technique to measure the shape of a descending liquid front is presented. Non-planar fronts are shown to exist and these could induce gas entrainment, which is undesirable in the final product.