Numerical Analysis of Wood Chipping

Abstract

Normally, in pulp wood chipping, the chips desired are thinner and have less fiber damage than those currently being produced. However, experiments to develop chippers are rather laborious, so there is a need for a mathematical model to complement the experiments. A two-dimensional finite element model was developed in order to be able to predict chip thickness and chip damage, the model incorporated a fictitious crack model and elasto-plastic material properties. The sensitivity of the 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 cutting knife and of the friction between knife and wood were calculated. The general impression of the modelled chip formation was that the results of the finite element model were in reasonable agreement with experimental observations and that the model yields qualitative results that are trustworthy. The calculations indicate that there is a strong interaction - which greatly influences chip formation - between the knife angle and the coefficient of friction between the knife and the wood. 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.