About paper pulping system
December 10, 2020
Beating quality inspection (paper making machinery)
In order to grasp the changes of pulp during the beating process and control the quality of beating, the quality of beating must be inspected. The main inspection items are beating degree, wet weight and slurry concentration, as well as factory inspection of hydration degree and water retention value.
For further experimental research, microscopic analysis of fiber length, sieving, fiber external specific surface area, fiber bonding area, thickness, etc. is also required.
1. Beating degree
The degree of beating is the degree of percussion (0SR) commonly known by the manufacturer.
The degree of beating is an index that reflects the degree of difficulty in the drainage of the pulp.
Generally speaking, the greater the beating degree, the slower the water filtration.
Dilute 2 g of absolutely dry pulp to 1000 ml, and pass through an 80-mesh net at a certain temperature (30°C by our company). The amount of water discharged from the side pipe of the Schober Beater is the measurement result.
Canadian Standard Freeness (CSF), another expression of the drainage performance of pulp, is opposite to the beating degree, the greater the freeness, the faster the drainage.
The measuring instrument is similar to the freeness meter, and there is a certain difference in the measuring method. When measuring, the absolute dry fiber content is 3 grams. Freeness and beating degree can be converted by looking up the table.
There are many factors that affect the dehydration of pulp, and these factors have inconsistent effects on the properties of the paper.
For example, the fibrillation of fibers will affect the dehydration of the slurry and help improve the strength of the paper; and the cutting of fibers will also affect the dehydration of the slurry, but it will reduce the strength of the paper.
It can be seen that the use of two different beating methods, namely fiber cutting or fibrillation, can improve the beating degree. However, the properties and strength of pulping are completely different, and the determination of the degree of beating cannot distinguish them.
Therefore, although the degree of beating can comprehensively indicate the beating effects and effects of fibers being cut, split, swelled and hydrated, the degree of beating cannot simply and completely represent the properties of the slurry, and it must be tested together by other methods to determine The real situation of the effect of beating on fiber.
2. Fiber length
Fiber length is an important indicator to measure the quality of the slurry. Commonly used measurement methods include microscopy and fiber wet weight method.
Microscope method: dye the fibers into a sheet, measure the average length and width of 100 fibers under a micrometer with a microscope, and directly observe the shape and composition of the fibers. This method can comprehensively identify the quality of the slurry, but it takes a long time and is not suitable for production use. Nowadays, fiber analyzers for measuring fiber length are widely used, with short measuring time and accurate results, which are mainly used in scientific research.
Wet weight method: It is a fast method for measuring fiber length suitable for production. The wet weight indirectly expresses the average fiber length. The wet weight is measured by the frame method, which is performed while measuring the beating degree.
For example, the larger the average fiber length, the more fibers hanging on the frame, and the greater the wet weight.
Due to many factors affecting the amount of fiber hanging, the fiber length measured by wet weight method is not accurate enough.
However, due to the speed and the same stable production conditions, the comparison method can reflect the beating situation and the changes in the slurry properties, and can also guide the production.
Sieve analysis: For pulp fiber, in addition to measuring the average fiber length, sieve analysis can also be used to classify the fiber length and measure the content of long fibers, fine fibers and miscellaneous cells.
Sieve analysis is a better analytical method to identify the properties of the slurry. It plays an important role in studying the properties of the slurry and paper-forming properties, but its measurement takes time and is not suitable for the production site.
3. Water retention value
In the standard state, the free water in the slurry is thrown out with a high-speed centrifuge, and the amount of water retained in the slurry is quantitatively determined to obtain the water retention value of the slurry.
The water retention value can explain the degree of fiber swelling, which reflects the degree of fine fibrillation.
The increase in the water retention value of pulp has a good correlation with the improvement of pulp beating degree, the increase of fine matter content and the decrease of fiber average degree.
The above-mentioned properties of pulp will directly affect the running performance of the paper machine, so the water retention value of pulp can comprehensively reflect and predict the papermaking performance of paper.
4. Degree of hydration
It means a method for the fiber to absorb the total amount of bound water during the beating process.
The measurement method is to heat and boil the slurry for 1 hour, use the heating method to remove the bound water of the fiber, and then measure the beating degree according to the ordinary method; the difference between the beating degree measured by the unheated slurry and the heated boiled slurry is used to indicate the slurry The degree of hydration of the fiber.
At the beginning of beating, the hydration degree decreases with the increase of beating degree. The degree of hydration cannot explain the continued swelling of the fiber in the late stage of beating, indicating that the degree of hydration cannot fully represent the swelling value of the fiber.