Transient Compressible Flow in Injection Molding Runner**

Abstract

Abstract The transient flow of a compressible polymer melt in an injection system consisting of a ram, a runner, and a shutoff valve is studied. Experimentally, the exit flow rate is found to have an initial value determined mainly by the precompression level and a steady state determined mainly by the ram speed. This flow rate can fall before it rises again, or it can overshoot its steady state. Such complex behavior is predicted qualitatively by a simplified mathematical model, which neglects elasticity but accounts for the finite compressibility and bulk viscosity. Four dimensionless parameters governing system dynamics are identified and their effects investigated by computation.