Appl. Sci. 2025 , 15 , 9160
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The disk refiner, particularly when fitted with ultra-fine bar patterns, applies highly controlled and intense mechanical action to the pulp fibers. Its consistent bar and groove dimensions, along with uniform gap clearance, enhance the frequency and effectiveness of fiber-bar interactions [24], as illustrated in Figure 6. This design, characterized by uniform bar dimensions, enhances refining efficiency by maximizing the contact surface area and increasing the frequency of bar impacts against fiber bundles captured by the bar edges [25,27]. Consequently, this leads to more effective fiber modification, including both internal and external fibrillation, which is crucial for rapidly developing fiber properties. These factors contributed to the refiner’s ability to reach the desired freeness level more quickly than the beater. In contrast, the Valley beater operates with wider flybars and larger grooves, resulting in less precise mechanical action at lower rotational speeds. The beater relies on repeated compression and shearing to gradually increase fiber flexibility and surface area through fibrillation. However, as illustrated in Figure 7, the less controlled geometry means that some fiber bundles may pass through the beater without adequate modification, neces- sitating longer processing times to achieve similar freeness levels [28,29]. Additionally, fibers that become trapped in the grooves between flybars are not efficiently beaten, further reducing the overall efficiency of the process [28].
Figure7. Schematic diagram of the beating mechanism using a Valley beater.
These findings are consistent with prior studies, which have shown that disk refin- ers are generally more effective than beaters in rapidly developing fiber properties and achieving targeted freeness levels [25,27]. The superior performance of the refiner in this study can thus be attributed to its ability to deliver more uniform and intense mechanical treatment, resulting in faster and more efficient freeness reduction. In summary, while both refining and beating are capable of modifying fiber properties, the disk refiner with an ultra-fine bar plate offers significant advantages in process efficiency and control. 3.2. Fiber Length Figure 8 illustrates the comparative effects of a beater and a refiner on the length- weighted mean fiber length of SwBKP and HwBKP. The results show that both SwBKP and HwBKP experience a faster reduction in fiber length when processed with the refiner compared to the beater; however, at equivalent freeness levels, the refiner consistently preserves longer fiber lengths.
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