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A model for simulation of flow in an intermeshing kneading disc region of corotating twin screw extruder is presented. This is based on hydrodynamic lubrication theory for a Newtonian fluid. Numerical procedures are used to compute the pressure distribution and flow field in the kneading disc region. The influence of staggering angle, nip clearance, screw speed and throughput rate are investigated.

The flow of a rubber compound through a die is an essential step of a rubber extrusion operation. The die forms the compound into the desired shape. In many cases, the output of the extruder is limited by the resistance of flow in the die. Too high pressure losses in the die may additionally result in an excessive increase of the temperature, and unwanted crosslinking of the rubber compound may occur. Various possibilities are available to reduce the resistance of flow in the die. The simplest one is elevation of the processing temperature, which leads to reduction of viscosity. This can be done, however, only within some limit. Reduction of the pressure losses in the die may also be achieved by decreasing the die length, but this option produces larger swelling. Other more innovative procedures may be suggested. Evidence exists that the pressure losses in the die can be reduced by introducing sound or ultrasonic waves of high intensity into the die zone. In this paper, we present what we believe is a new idea, another option of decreasing a resistance of flow of the rubber compound in the die. This is achieved by injecting air between the rubber compound and the wall of the die. This paper continues the experimental studies of the authors on the flow of rubber compounds in dies and screw extruders.

A cold feed rubber extruder has been rebuilt into a pin barrel extruder with two rows of pins. A comparative experimental study has been made of the initial cold feed extruder, the extruder with a screw with slices in two flights, and the extruder with pins as well as Slight slices. An experimental study of pumping characteristics (Q – Δp screw curves) and of flow patterns obtained from feeding black and white compound with curatives to the extruder with subsequent vulcanization after steady state is achieved. Longitudinal and transverse sections of the rubber compound cured in the flights are studied. It is shown that introducing slices into screw flights reduces pumping capability. The subsequent introduction of pins has little effect on pumping. The flow marker studies show that introduction of slices into screw flights significantly enhances mixing. Both the improved mixing and poorer pumping is due to backflow through the slices. The introduction of pins is shown to again greatly increase mixing. The results of this study are used to discuss the performance and design of commercial pin barrel extruders for the rubber industry.

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