Pump-assisted plasticating extrusion*

Within the past several years considerable interest has developed in the practice of retrofitting of plasticating extruders with gear pumps. The primary motivation for this is to reduce surges and fluctuations in the extrusion rate, thereby improving product quality and reducing waste. It is shown that the effectiveness of a gear pump for this purpose is directly related to its volumetric efficiency. The volumetric efficiency depends upon the pump dimensions, the flow behavior of the polymer, and the operating variables of temperature, pressure, and pump speed. Experimental data on a variety of thermoplastic materials has been obtained using a pump with gear wheels of 3.6 cm diameter. These data have been correlated with an empirical equation. Some tentative conclusions are drawn concerning the sizing of gear pumps for specific applications.