The goal of this master thesis is the determination of the external coefficient of friction of various polymer pellets with the academic program materials and processing technology developed tribometer. The fundamental influence of surface roughness of the steel shaft, the pellet shape and size and the molecular weight distribution on the external coefficient of friction of polymer pellets in the solids conveying zone is investigated. In order to determine the influence of surface roughness, the external coefficient of friction of various polymer pellets was measured on three steel shafts with difference surface roughness. The tested polymer pellets are HDPE (High Density Polyethylene), PP (Polypropylene), PC (Polycarbonate) and PMMA (Polymethylmethacrylate). An increase as well as a decrease in the external coefficient of friction with higher surface roughness can be deserved depending on the polarity of the investigated polymeric material. In order to investigate the influence of the pellet shape and size on the external coefficient of friction, a virgin-PP and two compounded PP pellet types (short and long cylindrical shapes) were examined in dependence on velocity and pressure. The external coefficient of friction of the long cylindrical PP-pellets is always higher compared to the short cylindrical and the virgin PP-pellets. Using a contact mechanics model explains that a higher calculated contact area leads to an increase in the external coefficient of friction at a constant normal force and velocity. Three PP types with different molecular weight were measured to determine the influence of the molecular weight distribution. There is a decrease in the external coefficient of friction with a higher averaged molecular weight or a lower polydispersity. Furthermore a decrease in the external coefficient of friction of all three PP types with a higher pressure or a lower velocity can be observed.
|Translated title of the contribution||Influence of surface roughness, pellet shape and size and molecular weight on the external coefficient of friction of polymer pellets|
|Publication status||Published - 2011|