Rotordynamical modelling of a fibre refiner during production

A key component in panel board production is the fibre refiner, whose task is to break cellulose wood chips into slender fibres. This refining process takes place between a rotor and a stator, where a gap of around 0.5 mm is found. In the development of these refiners predicting the dynamics is important; hence, mathematical models are needed. For refiners and other applications like brakes, turbines, and compressors, the interaction between the rotor and the surrounding medium can in many situations be significant. In addition to external load, this interaction can also change the characteristics of the system, which should be considered in the design process. Today, there exists no validated load model for fibre refiner process. Hence, the aim of this paper is to suggest one. ed axial force data were divided into a constant part and a superimposed oscillating part with different frequencies. For both parts a linear dependence on the gap between the stator and the rotor was assumed. Finally, a four degrees of freedom (dof) model was used to fit a pressure distribution to the axial force model. rocess load model led to stiffness and external loads that can be both time dependant. If the pressure distribution only shows a radial variation along the refining zone, all the external loads except the axial one will vanish. The number of functions describing the stiffness parameters also decrease from eight to four. In one case, four stiffness coefficients vanish, whereas the remaining coefficients become constant. This occurs if the process load does not follow the angular vibrations and there is no gap dependence on the oscillating parts of the process load. Numerical simulations showed that by applying a specific process load model, the vibration orbit changed from the unbalance response by means of shape and vibration origin. The unstable domain was further increased when the process load model was applied. ements are necessary to select a realistic process model for a specific application. The derived model can be used in product development to choose suitable system parameters and thus to avoid dynamical problems.