Measurement and interpretation of spatially registered bar-forces in LC refining

A high resolution rotary encoder and a piezo electric force sensor are implemented in a 16-inch laboratory-scale low consistency refiner to explore the effect of plate gaps on bar-force profiles. The sensor replaces a short length of a stator bar and measures normal and shear forces applied during the passage of each rotor bar. The rotary encoder data is used to locate the rotor bars relative to the stator bar in which the sensor is located. Previous work with this type of force sensor focuses primarily on the distribution of the maximum force measured during the passage of each rotor bar over the sensor or bar passing event, BPE. In this work, force profiles for bar passing events are registered to the position of rotor bars relative to the stator bar in which the sensor is located. These registered force profiles are measured for a range of plate gaps and two different pulp furnishes. The angular reference provided by the encoder makes it possible to generate mean force profiles. As force data for individual BPEs is highly variable, these mean force profiles have potential to shed light on the fundamental mechanisms of mechanical refining. For large gaps, there is a late peak in the force profiles that occurs toward the end of the bar passing event. For gaps that are less than the critical gap, below which fiber cutting occurs, there is an early peak in the force profiles that occurs at the start of the bar passing event. It is hypothesized that the early peak represents the corner force and, therefore, that corner force is causal in the onset of fiber cutting. To explore this hypothesis, a model is presented connecting corner force and friction force to the progression geometric variables during the bar passing event such as the bar edge length engaged at any point in the bar passing event and the area covered by the rotor bar on the force sensor at any point in the bar passing event.