Experimental and Numerical Analysis of Single Screw Extrusion Process for Thermoplastic PBX Based on PVT Properties

Abstract

Much of surplus ammunition stockpile inevitably requires demilitarized processing technology in the explosives industry. For the safe waste treatment and recycle, the thermoplastic polymer bonded explosive (PBX) can effectively reduce the military cost and non-conforming products. In addition, the thermoplastic PBX has excellent application prospect as the future explosive due to the good mechanical properties and insensitivity. However, for high solid content, most of thermoplastic PBXs still maintain a considerable viscosity even in high-temperature melting state, rendering traditional casting process unsuitable. In this study, a measuring method was adopted to accurately obtain the correlation of Pressure-Volume-Temperature (PVT) for the simulative materials of thermoplastic PBX at first. The equations of state for PVT and viscosity model were then created, which are of great significance in single screw extrusion. An experiment system of single screw extrusion was designed to implement the molding process considering the poor liquidity problem of the ther-moplastic materials. Excellent molding stability (1 < 0.5 % variation) was achieved for the extrusion system. Moreover, a numerical investigation was also performed. Good agreements were yielded by comparing the simulation data and experimental results. The effects of operational parameters, i. e., the entrance pressure, barrel temperature and rotation speed on molding process of the thermoplastic materials were investigated in detail. The wall shear stress decreases with the feed inlet well sealed whereas the maximum temperature rise increases a little due to limited thermal diffusion. Either increasing temperature or decreasing rotation speed is beneficial to overall process safety. However, production cycle and attainable molding density also need to be considered at the same time. Furthermore, the process parameters should be optimized on the basis of the PVT and viscosity properties of material in practice. The investigations above can be a better guidance for the development and implementation of thermoplastic PBXs molding process.