FRICTION IN THE FEED-SECTION OF SINGLE-SCREW-EXTRUDERS DEPENDENT ON PELLET SHAPE, FILLERS AND ADDITIVES

The friction of different polypropylene (PP) pellets and the subsequent feeding behavior in smooth barrel single-screwextruders have been investigated in this project. A polypropylene homopolymer has been compounded with different pigment concentrates, variable weight content of calcium carbonate, talc and a polyethylene wax plasticiser. Furthermore the length and the diameter of the cylindrical pellets have been changed in a wide range. The friction between the pellets and a metal surface has been measured dependent on velocity, temperature, and pressure with a test device developed at IKV. Significant differences occurred. The software tool BILAN, which was developed at IKV, has been used to simulate the feeding behavior. BILAN calculates the pressure course and the temperature distribution based on the friction measurements. It was shown that the used pigment concentrates do not have a great effect on the feeding behavior, whereas additives and the pellet shape do sometimes affect the friction behavior. A law which is transferable to other polymers has not yet been found. Thus each pellet has to be measured separately to describe the feeding behavior.