The effect of a vibration force field on the melting process of an extruder is studied. It is shown that the mechanism for melting differs from conventional theory. Experimental studies of melting of low-density polyethylene (LDPE) pellets in a vibration-induced single-screw (VISS) extruder show that melting is initiated on the inside of the barrel and the surface of screw. Models were developed that explain the melting mechanism in those regions. The melting at the surface of the screw is mainly initiated by frictional work on the pellets by the vibration and rotation of the screw. The melting action at the barrel is induced by a barrel temperature higher than the melting point and propagated by viscous dissipation heating of the melt film produced. The theory is supplemented by a calculation sample, which shows good agreement with experimental data obtained on a transparent barrel VISS (T-VISS) extruder and a half-open barrel VISS (H-VISS) extruder with LDPE. The results of the experiment and calculation sample indicate that the introduction of vibration-induced field can improve the melting capacity of extruder to a great extent. The present model enables the prediction of processing parameters for VISS extruders, from which the optimum operating conditions can be obtained. (c) 2007 Wiley Periodicals, Inc.