Definition
The pulping meter is a key laboratory instrument used in the paper industry and pulp research field to quantitatively determine the water filtration performance of pulp suspension. The measurement is usually expressed as a "beating degree" or "freeness value" in °SR (Schaubert-Regula degree) or CSF (Canadian Standard Freeness). This value is an important index to evaluate the change of fiber morphology and subsequent physical properties of pulp fibers after pulping or pulp treatment.
Principle
The core working principle of the instrument is based on filtration theory in fluid mechanics. It indirectly characterizes the water filtration resistance of pulp by measuring the filtration speed or amount of water filtered out by a specific volume and concentration of pulp suspension through a standard screen under standard conditions. The water filtration resistance mainly comes from the friction and interweaving between fibers and the degree of swelling and fine fibrosis of the fibers themselves. The pulping or pulping process will cause the fibers to split and swell, thereby increasing the specific surface area and binding potential of the fibers, but also significantly increasing the water filtration resistance of the suspension. The pulping meter translates this resistance change into a volume or time parameter that can be accurately measured.
Taking the common Schober Reegler method as an example, the principle formula can be expressed as follows: Measure the amount of water flowing out of the side flow pipe from the start of the water filtration to the cessation of dripping at a port under a specific conical funnel. There is a negative correlation between the water volume and the pulping degree value, that is, the less the amount of water filtered, the greater the water filtration resistance, and the higher the pulping degree value. The relationship is usually determined by instrument design and standard calibration.
Measurement method
The standard measurement process strictly follows the corresponding national or international standards, such as GB/T 3332 (Schauber-Reegler method) or ISO 5267-2. The main steps include: First, prepare a representative and accurately concentrated pulp sample suspension. Once the sample is well dispersed, it is quickly poured into the measuring chamber of the instrument. Under the action of the standard pressure difference, the water is filtered out through the bottom screen, and part of the water enters the side flow pipe. Operators accurately measure the volume of filtrate collected from the side flow pipe or observe the time it takes to filter out a specific volume. Finally, the measured values are converted to standard beating values according to the standard conversion table or the calibration curve built into the instrument.
The entire measurement process has high requirements for ambient temperature, water quality, instrument cleanliness and operational specification to ensure the repeatability and comparability of the results.
Influencing factors
The accuracy of the measurement results is influenced by several factors. The properties of the pulp itself are fundamental factors, including the type of fiber raw material, pulping degree, fiber length distribution, fine fiber degree and slurry concentration. Instrument condition and operating conditions are also critical, such as screen cleanliness and wear, seal integrity, temperature of the measuring chamber and funnel, and uniformity and speed of slurry injection. In addition, environmental conditions such as water temperature and ambient temperature will also affect the viscosity of water, which in turn affects the water filtration rate. Therefore, laboratories need to carry out strict process control and regular calibration of instruments.
Application
The application of pulping meter runs through multiple links of pulp and papermaking. In the beating section, it is the core tool for monitoring and optimizing the beating process, guiding the beating energy consumption control and quality adjustment by continuously detecting changes in the beating degree. In the process of pulping, it is used to predict the overall water filtration performance after different slurry ratios. Before paper production, the pulp degree value is a key reference index for predicting the physical properties of paper strength, tightness, air permeability, opacity, etc. In addition, the instrument is also widely used in fiber scientific research and new paper product development in scientific research institutions and colleges and universities to evaluate the impact of different treatment processes on fiber properties.
Selection
When choosing a pulping meter, it is necessary to consider many aspects. First of all, the measurement standard system that needs to be followed should be clarified, and the instrument design, measurement range and scale corresponding to different standards are different. The degree of automation of the instrument is a trade-off, fully automatic instruments can reduce human error and improve efficiency, but manual or semi-automatic instruments still have their value in basic research and teaching. The material structure of the instrument should be corrosion-resistant and easy to clean, and key components such as screens and sealing rings should be easy to replace. Calibration services, technical support, and accessory supply capabilities provided by manufacturers are also important guarantees to ensure the long-term stable operation of the instrument. Ultimately, users should make the right choice based on their test throughput, budget, and specific requirements for data accuracy and repeatability.