NUMERICAL-ANALYSIS OF WOOD CHIPPING

Normally, in pulp wood chipping, the chips desired are thinner and hav e less fiber damage than those currently being produced. However, expe riments to develop chippers are rather laborious, so there is a need f or a mathematical model to complement the experiments. A two-dimension al finite element model was developed in order to be able to predict c hip thickness and chip damage, the model incorporated a fictitious cra ck model and elasto-plastic material properties. The sensitivity of th e model to changes in material data was controlled, and the results of the calculations were compared to experimental observations reported in the literature. Finally, the influences of the geometry of the cutt ing knife and of the friction between knife and wood were calculated. The general impression of the modelled chip formation was that the res ults of the finite element model were in reasonable agreement with exp erimental observations and that the model yields qualitative results t hat are trustworthy. The calculations indicate that there is a strong interaction - which greatly influences chip formation - between the kn ife angle and the coefficient of friction between the knife and the wo od. The results suggest that a chipper knife should have a small knife angle complemented with a bevel, and should have a small coefficient of friction to wood.