Power consumption is the energy source of the impact on fibers or pulp during low-consistency (LC) pulp refining, and the strength of refining affects refining quality and efficiency. The pulp properties, operating parameters, and bar parameters of the refiner plates are important parameters affecting refining efficiency, which can be defined as the ratio of net to total refining power. In this study, LC refining trials for pulps with different consistencies and fiber lengths were conducted using five isometric straight-bar plates with different bar angles to explore the influences of the plate bar angle and pulp properties on the no-load power, impact capacity on fibers and refining efficiency. It was found that the no-load power of the LC refining process decreased with an increase in the plate bar angle while increased when pulp with higher consistency was refined under the same refining conditions. However, the effect of pulp consistency on the no-load power can be neglected when refining is conducted using plates with larger bar angles. Meanwhile, a critical bar angle for straight-bar plates in LC refining may exist, which has the strongest impact on the pulp and highest refining efficiency under the same refining conditions. In addition, the impact capacity of the plate on the pulp and refining efficiency in LC refining can be enhanced by appropriately increasing the pulp consistency and average fiber length when the bar angle of the refiner plate with a sector angle of 40° is less than 30°. Therefore, the efficiency and power consumption of the LC refining process can be adjusted by optimizing the pulp consistency and bar parameters of the refining plates.

Straight- and curved-bar refining plates are two important types of plates commonly used in disc refiners in the papermaking industry. Theoretically, the curved-bar refining plate has a relatively uniform bar interaction angle, which indicates uniform refining effects. The bar angle of the curved bar was proposed and two typical curved-bar plates, the three-stage radial curved-bar plate and isometric curved-bar plate, were designed in this paper. The arc equations of the curved-bar center line and curved-bar edges were established and finally, the specific edge load (SEL) of the curved-bar plate was derived. The determination of bar parameters was discussed, which provides a theoretical basis for the design of curved-bar plates.