FORCES ON FIBERS IN LOW-CONSISTENCY REFINING - NORMAL FORCE

An expression has been derived to predict the force acting on an ideal floc undergoing compression between passing bars of a refiner. The mo del equations are based upon three assumptions about flocs: they are s pherical in shape with fibres evenly spaced in any cross-section; they cannot support significant normal load until the majority of fibres a re in contact; and they display linear elastic behaviour under compres sion. The validity of the expression was tested in a single-bar refine r operating at 1 rpm, using model nylon flocs. Good agreement was foun d between the experimental measurements and the derived expression. Th e results indicate that the force increased sharply over the first 2-3 mm of the bar, and then remained essentially constant over the remain ing width of:the bar.