A profile die design method for a rubber extrudate using an analogy

Profile die design for extruding rubbers has evolved to the point that three-dimensional finite element analysis of the fluid dynamics is possible, including inlet flow and extrudate swell. These computations are complicated and can involve trial and error when considering extrudate swell. A new method of profile (thin plate) die design is presented which involves a simple finite element computation to predict the die profile to produce an extrudate of prescribed shape: the inverse extrudate process. The method is referenced to an anology between plate deflection and low-Reynolds-number fluid flow. A reference extrudate swell is used to take care of the characteristics of the extruder, operating conditions, extrudate properties, and anology similarity parameters. Analysis for a power-law rubber is presented which predicts the die profile to produce a square extrudate, and a die profile for a tyre extrudate. Comparison of these cases with three-dimensional theory and actual experimental data for the tyre is good.