Ermittlung der Reibungsdaten von Kunststoffschüttgütern zur Simulation des Förderverhaltens von Einschneckenplastifiziereinheiten

The external coefficients of friction (ECOF) of the polymer pellets at the inner barrel surface, as well as at the screw surface are decisive factors for solids conveying in single screw plasticizing units. Besides other parameters, such as screw geometry and processing conditions, they affect the pressure build up behaviour and the temperature development in the solid plug. Screw surface treatments, such as plasma-nitriding, CrN, TiN and TiAlN coatings, additionally affect the frictional conditions between the screw surface and the polymer pellets. A new apparatus for analyzing the frictional behaviour of polymer pellets at the screw surface was presented formerly. The newest results of measurements of the ECOF at room temperature are presented in this paper. Three different, polished shafts, one without surface treatment, one with a plasma- nitrided surface and one with a DLC coating were investigated in combination with three types of bulk polymers. The effect of the ECOF at the conveying characteristic of single screw plasticising units is calculated.