Rotor selection for a Searle-type device to study the rheology of paper pulp suspensions

The trends in the paper and board industry towards higher production and efficiency, lower costs and improved product quality make it necessary to further optimise each unit of the papermaking processes. This requires detailed knowledge of the rheological behaviour of pulp suspensions. However, pulp suspensions present such complex and unique properties that there are no standard methods for studying fibre network deformation and pulp flow behaviour. This paper presents the design, calibration and validation of a Searle-type rotational device which has been specially adapted to measure the rheological behaviour of pulp suspensions. Three different internal rotors have been compared: cylinder, plates and bars. The torque required to maintain different set speeds of the rotor is measured. The device was calibrated for the three different rotors, with water and glycerol solutions of known viscosities, based on the concept of dynamic similarities of the fluids. The rheological study of a hardwood kraft pulp suspension with a fibre concentration of between 3 and 30 g/L was carried out. Results show the plate torque-based device has the highest resolution and can be used to determine the rheological behaviour of pulp suspensions