Standard Method for Determining the Beating Degree of Pulp Using a PFI Mill

Introduction

Pulp pulping degree is a key parameter to evaluate the degree of pulp fiber treatment, which directly affects the physical properties and production quality of paper. In the laboratory environment, PFI grinding and beating machines are widely used as standardized equipment to simulate industrial beating processes and determine beating degrees. This paper aims to describe the standard method for determining pulp pulp degree using PFI grinding machine, covering the principles, equipment, steps and data processing, in order to provide a standardized reference for related testing work.

Equipment & Materials

The main equipment required is a PFI grinding machine that meets the standard specifications, including a grinding chamber, a rotating fly knife roller and a fixed base cutter. Auxiliary equipment includes a pulping meter (such as a Schober beating meter), a balance (with an accuracy of 0.01 grams), a graduated cylinder, a thermometer and a timer. The material is a pulp sample to be tested and needs to be pre-balanced to standard temperature and humidity conditions (usually 23 degrees Celsius and 50% relative humidity). All equipment should be calibrated before use to ensure measurement accuracy.

Method principle

PFI grinding and beating machine simulates pulping treatment by controlling the gap between the flying cutter roller and the number of rotations between the bottom knife and applying shear and friction to the pulp fibers. During the pulping process, the fibers gradually split into filaments, resulting in changes in the water filtration performance of the slurry. The degree of beating is expressed in Schober degree (°SR), which is defined as the water filtration time for a specific volume of slurry through a standard screen, and its value increases with the degree of beating. The degree of beating R can be calculated by the following formula:

R = k × t

where t is the water filtration time (seconds) and k is the instrument constant. In practical applications, specific parameters need to be determined based on standard curves or calibration results.

Procedure:

First, a standard slurry sample equivalent to absolute dry mass (usually 24 grams) is weighed and diluted with water to a concentration of about 1.57%. The slurry is injected into the grinding chamber of the PFI grinding machine to ensure that the temperature is stable at 20 degrees Celsius. Set the number of beating revolutions (such as 1000 to 5000 revolutions, adjusted according to the pulp type), start the equipment to beat. After beating, remove the slurry and mix well. Take part of the slurry sample and use a beating meter to measure the water filtration time, and repeat three times to take the average. The number of beating revolutions and the corresponding beating degree value are recorded, and the beating curve is drawn to evaluate the beating behavior.

Data Logging and Processing

It is recommended to record the number of beating revolutions, water filtration time and calculate the pulping degree in the form of a table to ensure that the data is clear and traceable. Examples include:

The pulping degree-revolution curve is drawn according to the data, and the beating rate and end point can be analyzed. Note that each experiment should be measured in parallel, and the deviation should be controlled within the standard allowable range (such as Schober degree deviation less than 2%).

Notes:

Before operation, the wear of the PFI grinding blades should be checked and regularly maintained to avoid deviations in the results. The slurry concentration and temperature need to be strictly controlled, and small changes may affect the pulping degree. For different pulp types (such as chemical pulp and mechanical pulp), the appropriate pulping speed range should be explored in advance to avoid fiber degradation caused by excessive pulping. The experimental environment should maintain standard temperature and humidity to reduce external interference.

Conclusion

Determining pulp beating with PFI mills is a standardized, repeatable method that effectively simulates industrial pulping processes and provides guidance for paper production. Through standardized operation and data processing, reliable pulp degree data can be obtained, which can help evaluate the quality of the pulp and optimize the process. It is recommended to combine other fiber analysis indicators (such as fiber length and water retention value) for comprehensive judgment to comprehensively characterize the slurry performance.

References

ISO 5264-2:2011, Pulps — Laboratory beating — Part 2: PFI mill method.

TAPPI T 248 sp-15, Laboratory beating of pulp (PFI mill method).

GB/T 3332-2004, Determination of pulp beating degree (Schober method).