Check for beating in papermaking process



Beater quality check

In order to master the change of pulp in the beating process and control the beating quality, it is necessary to check the beating quality, the main check items are beating degree, wet weight and slurry concentration, and the factory check hydration degree and water retention value.

In order to further the experimental study, the fiber length, screening, fiber external specific surface area, fiber binding area, coarser and so on are also analyzed.

1, beating degree

The degree of beating is commonly known as the percussion degree (0SR) of the production enterprise.

The degree of beating is an index that reflects the degree of water filtration of the pulp.

Generally speaking, the greater the degree of beating, the slower the water filtration.

With 2 grams of absolute dry pulp, diluted to 1000 ml, at a certain temperature (30℃) under the condition of 80 mesh mesh, the water discharged from the side pipe of Schober beater degree meter is the determination result.

Canadian standard freeness (CSF), another representation of the water filtration performance of pulp, as opposed to beating degree, the greater the freeness, the faster the water filtration.

The measuring instrument is similar to the beater degree instrument, and there are certain differences in the measuring method. When measuring, the absolute dry fiber content is 3 grams. The free degree and beating degree can be converted by referring to the table.

There are many factors affecting the dehydration of slurry, and the influence of these factors on the properties of paper is not consistent.

For example, the fine fibrosis of the fiber will affect the dewatering of the slurry, which is conducive to improving the strength of the paper. The cutting of the fiber will also affect the dewatering of the paste, but will reduce the strength of the paper.

It can be seen that the use of fiber cutting or fine fibrosis two different beating methods can improve the beating degree. However, the properties and strength of the pulp are completely different, and the determination of the beating degree can not distinguish them.

Therefore, although the beating degree can comprehensively represent the beating effect and effect of the fiber being cut, split, moistening and hydration, the beating degree can not simply fully represent the nature of the slurry, but also through other ways to detect together, so as to identify the real situation of the beating effect on the fiber.

2. Fiber length

Fiber length is an important index to measure the quality of slurry. The commonly used measurement methods are microscope method and fiber wet weight method.

Microscope method: The fibers are dyed, and the average length and width of 100 fibers are measured with a microscope under a micrometer, and the shape and composition of the fibers are directly observed. This method can identify the quality of the slurry comprehensively, but it takes a long time and is not suitable for production. Now there is a fiber analyzer to determine the length of fiber in common use, the determination time is short, the result is accurate, mainly used in scientific research.

Wet weight method: It is a fast method for determining the length of fiber suitable for production. The average length of the fiber is expressed indirectly by the wet weight, and the wet weight is measured by the frame method at the same time as the beater degree.

For example, the larger the average fiber length, the more fibers are hung on the frame, the greater the wet weight.

Because there are many factors affecting the amount of fiber hanging pulp, the fiber length measured by wet-weight method is not accurate enough.

However, due to the fast, the same stable production conditions, through the comparison method, it can reflect the situation of beating and the change of the nature of the slurry, and can also guide the production.

Screening analysis: For pulp fibers, in addition to measuring the average length of the fiber, the fiber length can also be graded through screening analysis to measure the content of long fibers, small fibers and miscellaneous cells.

Screen analysis is a good analytical method to identify slurry properties, which plays an important role in the study of slurry properties and paper forming properties, but its determination is time-consuming and not suitable for production site.

3. Water retention value

In the standard state, the free water in the slurry is thrown out by high-speed centrifuge, and the amount of water retained in the slurry is quantitatively measured to obtain the water retention value of the slurry.

The water retention value can indicate the degree of swelling of the fiber, thus reflecting the degree of fine fibrosis.

The increase of water retention value of pulp has a good correlation with the increase of beating degree, the increase of fine matter content and the decrease of average fiber degree.

The above properties of the pulp will directly affect the running performance of the paper machine, so the water retention value of the pulp can comprehensively reflect and predict the manufacturing performance of the paper.

4. Hydration degree

A method of expressing the total amount of bound water absorbed by a fiber during the beating process.

The determination method is to heat and boil the slurry for 1 hour, use the heating method to remove the binding water of the fiber, and then determine the beating degree according to the ordinary method; The degree of hydration of the fiber of the slurry is expressed by the difference of beating degree measured by unheated slurry and heated boiled slurry respectively.

At the beginning of beating, the hydration degree decreased with the increase of beating degree value. The hydration degree could not explain the phenomenon that the fiber continued to swell in the late beater, indicating that the hydration degree could not completely represent the swelling value of the fiber.