Simulation of extrusion coating by tape drawing

Abstract

AbstractNeck‐in and maximum stress were studied in a tape‐drawing experiment using a 3.5 MI low density polyethylene at 300°C. The conditions of the experiment were designed to reproduce closely those found in extrusion coating lines. The maximum stress was found to increase roughly with the 1.6 power of the drawdown ratio and the 1.0 power of the extrusion speed over a stress range of 4 × 103 to 5 × 105 Pa produced by drawdown ratios ranging from 2 to 22 and extrusion speeds of 2.3 to 6.1 cm s−1. The neck‐in decreased weakly with drawdown ratio at low extrusion speed and with extrusion speed at constant drawdown ratio. After carefully characterizing the test resin in shear and extension, the similarities between predicted pure‐shear (planar extension) transients and the tape experiments were studied. It was found that the trends, but not the magnitude of the experimental maximum stress were quite similar to the calculated longitudinal stress in pure shear. The behavior of the transverse to longitudinal stress ratio in pure shear was similar in behavior to the neck‐in results, but considerable improvement was achieved by adding in a decayed stress from a simple‐shear transient to simulate the conditions produced by the extrusion die. The philosophy of purposefully studying similarities between transient, pure or simple deformations and steady, complex processes is discussed.