Comparison of Screw Extrusion of Rubber Compounds with Different Extruder/Screw Combinations

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Abstract
The extrusion of rubber compounds has long been an area of industrial importance. There have, however, been few basic studies on the flow characteristics of rubber compounds. Considerably more extensive investigations have been reported on the mechanisms of screw extruders for thermoplastics. The latter researches are summarized in the monograph by Tadmor and Klein and the textbook of Tadmor and Gogos. Maddock, and others carried out experimental studies which led to basic flow mechanisms of thermoplastics in screw extruders. Maddock fed pigmented pellets to screw extruders and pulled screws from the barrel with the plastic stips in it, which were then unwound and cross-sectioned. Few screw-pulling investigations have been published for rubber compounds. We are only familiar with the work of Menges and Lehnen and our own recent studies. In the present paper, we describe a fundamental study of flow mechanisms in screw extruders for rubber compounds. We expand our studies based on the Maddock screw-pulling procedure, with rubber strips containing markers in a comparison of three different screw extruders. The placement of the rubber is recorded and the rubber sections examined for their flow patterns. This work also extends our earlier market experiments on flow of rubber compounds through dies. Our results on screw extruders exhibited both transverse flow patterns and sometimes showed a starved, partially filled screw. Our efforts in the present paper seek to generalize these results. We also describe a theoretical model for the flow of rubber compounds in a screw extruder and compare it to our experiments.

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