Mechanical pulping, both grinding and refining, involves energy consuming rapid wood compression. To improve the energy efficiency, one needs to deeper the understanding of the mechanical response of wood. Standard measurements at room temperature do not give relevant information since the conditions during pulp production are to a great extent different. Therefore we studied repeated rapid wood deformation in a hot steam environment at high strain rates. Samples of Norway spruce were studied prior to, during, and after cyclic compressions. The consequences of up to 24000 unipolar (constrained compression and free relaxation) compressions with a 0.75 mm peak-to-peak amplitude applied at 500 Hz frequency were quantified by ultrasound combined with tests in an were quantified by ultrasound combined with tests in an split Hopkinson device. The treatment caused plastic changes in the wood material, as indicated by decreased stiffness (elastic modulus) of the samples. Measurements revealed the presence of a fatigued layer (localized change) near the impacted surface. These findings support a hypothesis about the material behavior, which was utilized in development of the energy efficient surface. In this paper, we analyze the measurements previously introduced in Salmi 20111 from a mechanical pulping point-of-view.
Ultrasound Fatigue Localization Mechanical pulping Energy consumption
Ari Salmi Lauri I. Salminen Risto Montonen Birgitta A. Engberg Tomas Bj(o)kqvist Edward H(ae)ggstr(o)m Mikael Lucander
VTT Technical Research Center Finland,P.O.B. 1000 FIN-02044 VTT,Finland;University of Helsinki,Divis VTT Technical Research CenterFinland,P.O.B.1000FIN-02044VTT,Finland University of Helsinki,Division of Materials Physics,Electronics Research Laboratory,P.O.B.64,FIN-00 FSCN, Department of Natural Sciences,Engineering and Mathematics, Mid Sweden University,SWE-85170 Su Department of Automation Science and Engineering,Tampere University of Technology,P.O.B. 692FIN-3310 University of Helsinki,Division of Materials Physics,Electronics Research Laboratory,P.O.B.64,FIN-00 VTT Technical Research Center Finland,P.O.B.1000FIN-02044VTT,Finland