Effect of impact velocity on the fracture of wood as related to the mechanical pulping process

The fiber separation step in refining is crucial for energy consumption in subsequent refining where the pulp properties are developed. The size reduc tion of chips during refining is dependent on refining intensity and chip s trength. Factors affecting these two parameters are discussed in a literatu re review. The impact strength of chips and the break down of chips to sepa rate fibers are also discussed. Specifically the effect of impact velocity on the fracture of wood has been studied by use of a failing weight impact tester. Samples were prepared from a freshly cut log of Norway spruce, Pice a abies, and the impact strength was measured using an instrumented falling weight impact tester. An increase in impact velocity from about 2.7 to 4.8 m/s resulted in an increase in impact strength of about 50%.