DETERMINATION OF THE DEGREE OF FILL IN A COUNTER-ROTATING TWIN-SCREW EXTRUDER

Current residence time distribution models for counter-rotating extrud ers are mainly developed for fully filled machines. However, in practi cal situations, these extruders operate under starved conditions. To o vercome this missing link in the current models, this paper describes the average degree of fill in the situation of starvation. This degree of fill is determined by the length over which the extruder is fully filled and the degree of fill in the partially filled zone. The compar ison of the experiments with the theory shows that the existing theory underestimates the length of the fully filled zone by about 30%. The degree of fill in the partially filled zone is well predicted by takin g into account all non-pressure driven leakage flows.