Principle and structure
The core function of the Wally beater is to process pulp fibers through mechanical action to change the morphology and physical properties of the fibers. The equipment is usually composed of parts such as beating rollers, beating knives, pulp grooves and power systems. During the beating process, the fibers are sheared, squeezed and rubbed between the beating roller and the base knife, resulting in fine fiberization, swelling and cutting off of the fibers, which affects the strength, air permeability and optical properties of the final paper.
The beating effect is usually quantified by beating degree (°SR) or Canadian standard freeness (CSF), and its changes are closely related to parameters such as beating time, specific pressure beating, and slurry concentration. The degree of beating can be approximately estimated by the following empirical formula:
ΔS = k · P · t / C
Among them, ΔS represents the change value of beating degree, k is the coefficient related to fiber raw materials, P is the specific pressure of beating, t is the beating time, and C is the concentration of slurry. This formula helps to predict pulping trends at the beginning of the experiment, but the actual process needs to be adjusted according to the characteristics of the specific fiber raw materials.
Operation process
In pulp laboratories, the use of WALLI pulpers requires a standardized operating procedure to ensure repeatability and comparability of experimental results. First, a certain quality of absolutely dry slurry needs to be soaked and loosened to a homogeneous state, and then transferred to the pulp tank of the Wally beater to adjust the slurry concentration to the specified range (usually 1.5% to 3.0%). After starting the equipment, the beating intensity is controlled by adjusting the gap and pressure between the beating roller and the bottom cutter, and the beating degree is measured at different time points until the target value is reached.
Key operating parameters include pulping specific pressure, slurry concentration, beating time and temperature. These parameters need to be optimized for the type of pulp (e.g., softwood, hardwood, or non-softwood) and the target paper performance. For example, high specific pressure can promote fiber breakage for a short time, while low specific pressure for a long time is conducive to fiber fibrosis. Laboratories usually refer to standard methods such as TAPPI T200 and ISO 5264-1.
Wally pulping machine treatment can significantly change the morphology and properties of pulp fibers, which in turn affects the physical index of paper formation. In the early stage of pulping, the fibers mainly undergo swelling and external fine fibrosis, which leads to an increase in the specific surface area of the fibers, improving the bonding between fibers, thereby improving the tensile strength and breaking resistance of the paper. As pulping progresses, fiber length may decrease due to cutting, affecting the tear and breathability of the paper.
The changing trend of paper performance under different pulping levels can be summarized in the following table:
| Pulping stage | Fiber change characteristics |
| Early days | The fibers swell, and the surface is finely fibrotic |
| Medium term | Fine fibrosis inside, some fibers are cut off |
| Later | The fiber length decreases significantly, and the fine fibers are fully depleted |
| Paper-based performance correlation | The tensile strength increases, the tear first rises and then decreases, and the air permeability decreases |
Therefore, the laboratory can systematically study the relationship between the beating process and paper performance through the Wali beater, and provide data support for industrial production.
Different pulp types
The Wally pulping machine is suitable for pulping research on a variety of pulp types, including chemical pulp, mechanical pulp and recycled pulp. For chemical wood pulp, pulping is mainly aimed at improving fiber bonding, so medium and low intensity beating is often used to preserve fiber length. For mechanical pulp, because the fiber is short and rigid, the pulping effect is weak, it is mostly used to slightly improve the flexibility of the fiber. For non-wood pulp (such as bamboo pulp, grass pulp) or recycled pulp, due to the complex shape of the fiber, it is necessary to optimize the conditions through beating experiments to balance the properties.
It should be noted that the pulping response of different slurries varies greatly, and laboratories need to conduct exploratory experiments in advance to determine the appropriate beating curve. At the same time, energy consumption and temperature control during the beating process also need to be paid attention to to avoid fiber degradation or equipment overload.
Notes:
To ensure long-term stable operation and data accuracy of the Wally beater, regular maintenance and calibration are essential. In terms of maintenance, the wear of the beating blade should be checked and replaced in time to ensure the consistency of the beating effect. The slurry groove and roller body should be kept clean to prevent slurry residue from affecting subsequent experiments; The power transmission components need to be lubricated and maintained. In terms of calibration, the gap and pressure display device of the beating roller should be checked regularly, and the standard slurry sample should be used for comparative testing of the beating degree to ensure that the equipment status meets the requirements of the standard method. Laboratories typically establish internal calibration protocols and keep maintenance logs to ensure the reliability of experiments.
Epilogue
As the basic equipment of the pulp laboratory, the Wali pulping machine has practical value in the research of the beating process and the prediction of paper performance. Through standardized operation, parameter optimization, and equipment maintenance, the laboratory can effectively simulate the industrial pulping process and provide technical support for the paper industry. In the future, with the advancement of fiber analysis technology, the Wali beating machine may be combined with online monitoring methods to further improve the accuracy and efficiency of beating control.
References
1. TAPPI T200: Laboratory beating of pulp (Valley beater method).
2. ISO 5264-1: Pulps — Laboratory beating — Part 1: Valley beater method.
3. Analysis and Detection of Pulp and Papermaking, China Light Industry Press.
4. Papermaking Science and Technology series, Fapet Oy.