Polymer and Materials Science
Wiley InterScience Backfile Collection 1832-2000
Chemistry and Pharmacology
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
The mechanics of energy conversion in an extruder is extremely complex. Generally speaking, the extrusion process utilizes two sources of energy: (1) mechanical energy which is imparted to the polymer by the rotational motion of the screw, and (2) thermal energy (heat) which flows between the polymer and surfaces of the barrel by conduction and convection.Modern extrusion processes are relatively wasteful of energy because, operating at high speeds, they often dissipate an excess of mechanical energy as heat that has to be transferred (by barrel cooling) from the polymer and discharged into the surroundings as waste energy.Until recently, little attention was paid to this wasted energy. Energy was relatively cheap and the process economics favored was high speed operation despite its associated energy wastage. With the recent introduction of gear pumps for extruders, low pressure extruder operation becomes a possibility. It appears that this type of operation may result in a significant improvement in energy efficiency.This paper attempts to analyze the energy economy of extrusion processes and to understand where and how energy savings can result from the use of gear pumps. It shows that if substantial energy savings are to result from the use of gear pumps, these savings will come about not because of increased pumping efficiencies, but because low pressure operation has made a fundamental change in the energy conversion processes occurring in the screw.
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