Design and Fabrication of Wood Chopping Machine

Abstract

In both the chemical and mechanical pulping process, the logs are cut into wood chips by a cone shaped tool before fiber separation. To make the wood chopping process more efficient, one have to investigate in detail the coupling between process parameters and the quality of the chips. One objective of thesis was to obtain an understanding of the fundamental mechanisms behind the creation of wood chips. Another objective with the thesis was to investigate whether it was possible to, in a way tailor the chopping process so as to reduce the energy consumption in a following mechanical refining process. Both experimental & analytical/numerical approaches have been taken in this work. The first part of the experimental investigations, were performed with developed chopping tool. The results from the experimental investigation showed that the friction between log and chopping tool is probably one crucial factor for the chip formation. Further more it was found that indentation process is approximately self-similar, and that the stress field over the entire crack-plane is critical for cutting the chop wood. The developed analytical model products the normal and shear strain distribution and to be more specific, the model can predict the compressive stresses parallel to the fiber direction for an assumed linear elastic & Orthotropic material.