EXISTING SCALE-UP RULES FOR SINGLE-SCREW PLASTICATING EXTRUDERS

This paper gives a review of existing scale-up rules for single screw plasticating extruders. It is shown that there were and still are rather varied trends. The main three are: - scale-up rules under the boundary conditions of an invariant shear rate, - scale-up rules including the power law, - scale-up rules including the zones of operation. In Europe, at least, the scale-up rules, which take the power law-flow characteristics into account, seem to have been established in practical terms. For economical reasons conventional extruders are designed in such a way, that the output increases with the square of the diameter. This however, results in the problem that the melting rate does not follow the same scale-up rules as the pumping rate and the solid conveying rate. Thus the discussion continues, to calculate the operating section lengths according to varying scale-up rules. Finally the scale-up problem is discussed once more with respect to the dominant dimensionless numbers, and despite several similarity theoretical difficulties a standardized solution will be attempted to be found.