This standard specifies the method for evaluating the fiber properties of pulp using the Bauer Mc Nett fiber sieving method. This standard is applicable to all kinds of pulp for papermaking. GB/T 2678.1-1993 Pulp sieving method GB/T2678.1-1993 Standard download decompression password: www.bzxz.net

National Standard of the People's Republic of China
Pulps-Determination of screened components
Pulps-Determination of screened components Subject content and scope of application
GB/T 2678.1-93
This standard specifies the method for evaluating the fiber characteristics of pulp using the Bauer McNett fiber screener. This standard is applicable to all kinds of pulp for papermaking. 2 Reference standards
GB740 Collection of pulp samples
GB741 Determination of moisture content of pulp analysis samples GB/T1462 Wet dissociation of pulp in laboratory
GB10336 Determination of fiber length in papermaking
3 Principle
Pour the pulp suspension into the sifter, and each sifting container is equipped with a sieve. The containers are stepped. When the pulp suspension flows from one container to another, pulp with different fiber lengths is retained on different sieves. The fiber length of the retained pulp is consistent with the mesh size of the sieve plate. At a certain water flow rate, after sifting for a certain period of time, collect the fibers on each sieve plate, dry them, and after constant weight, report the results according to the mass percentage of the sample input according to the amount of fibers retained on each mesh. 4 Instruments and equipment
4.1 Sifter
Sifter of different types from different manufacturers has poor comparability of measurement results. This method specifies the use of a Ball fiber sieving instrument for papermaking 1. Note: 1) The Ball fiber sieving instrument for papermaking produced by Chengdu Aviation Instrument Company is available for selection. The instrument consists of five stepped elliptical containers, and the following main components are also connected to the containers, as shown in Figure 1. Constant pressure water tank: At the water inlet of the instrument, it is used to maintain a certain working water level, and the excess is discharged from the overflow pipe. Agitator: Installed inside the screening container, driven by five motors, with a speed of 580±40r/min, used to fully disperse the fibers in the water and make directional movements, so that most of the fibers can move parallel to the screen, so as to facilitate the screening of fibers by length. Partition: Installed in front of the screen plate and the grid plate, used to prevent water and fibers from rushing vertically to the screen. Screen plate: Used to classify fibers, the screen plate mesh can be selected according to the different properties of the slurry. The screen is made of stainless steel. Approved by the State Administration of Technical Supervision on August 7, 1993 224
Implemented on March 1, 1994
GB/T2678.1-93
Figure 1 Pulp sieving instrument
1. Overflow water tank; 2-Electric timer; 3-Sealed pipe joint assembly; 4-Frame; 5-Elbow water nozzle; 6-Agitator; 7 Screen plate; 8-Baffle; 9-Grid plate; 10-Motor; 11-Cable pipe; 12---Water tank; 13-Water tank body; 14·Vacuum suction cup assembly 225
GB/T 2678.1-93
Grid plate: Installed on the screen plate close to the screen, the pulp suspension flows to the drain through the grid plate, and the front and back sides should not be reversed. Sealing pipe: Used to seal the connection between the screen plate and the container to prevent fibers from leaking from the connection. The sealing tube is a rubber tube specially configured by the manufacturer. When used, compressed air of appropriate pressure is injected to swell the tube body, so as to achieve a better sealing effect. Filtering and drainage device: used to filter the fibers in each screening container. The drainage method of vacuum suction cup or bag filtration can be used at will. The vacuum suction cup is connected to the vacuum pump to improve the drainage efficiency. The filter paper used on the vacuum suction cup is a quantitative analysis filter paper with a diameter of 16 cm. The bag can be made of high-quality bleached or unbleached fine cloth. In order to facilitate the collection of fibers, the bag is made into a triangle with an arc bottom. The selected cloth cannot contain any filler or rubber.
4.2 Standard fiber separator 1 (see Figure 2). Figure 2 Standard fiber separator
1-body; 2 container; 3-mixer; 4-electronic control device Note: 1) GBJ-A standard fiber separator produced by Changchun Small Test Machine Factory is available for selection. 4.3 Oven: can control the temperature to adjust 105±2C. 4.4: Balance: one with sensitivity of 0.0001g and one with sensitivity of 0.001g. 4.5 Weighing box: aluminum box with diameter of 50~~70mm. 4.6 Others: common equipment such as beaker, measuring cylinder, plastic cup, etc. 5 Sample preparation
The sample shall be collected in accordance with the provisions of GB740. 5.1 Determination of sample moisture: in accordance with the determination method of sample moisture of pulp analysis in GB741. 5.2 Sample dissociation: weigh 10±0.05g (with known moisture) of absolute dry pulp sample, and weigh to 0.001g. If the sample is dry pulp (moisture content is less than 30%), soak it in water for 4h for wood pulp and 6h for straw pulp. During the soaking process, squeeze the pulp sample by hand from time to time to promote water penetration, and then dissociate it in the fiber standard dissociator, 75,000 revolutions (or 25min) for wood pulp and 45,000 revolutions (or 15min) for straw pulp. If the slurry is wet or paste-like, dissociate at 15,000 revolutions (or 5 minutes). If the sample is mechanical pulp, it is necessary to perform necessary delatency treatment according to the specific situation before screening. Generally, it can be soaked in 85C water for about 20 minutes before dissociation. The total volume of slurry and water during dissociation is 2000mL. 226
GB/T 2678.1--93
When dispersing slurry, it is not suitable to use a high-speed electric stirrer because it has a significant cutting effect on the fiber. In order to save time, the moisture content of the solid slurry sample can be estimated empirically. Take about 10g of the absolute dry slurry sample and take another sample for moisture determination at the same time. The result is used to calibrate the accurate amount of the sample added to the sifter. If the mass is within 10% of the required amount, it will have no significant effect on the mass percentage of each component. 6 Screening test
6.1 Mesh selection: In order to meet the test requirements of different pulp types, the mesh of the selected sieve plate is different. This standard stipulates the use of the following meshes when evaluating fiber quality by screening:
Medium fiber 14, 28, 48, 100.
Long fiber 10, 14, 28, 48, 100.
Short fiber 14, 28, 48, 100, 200. The use of the above series of screens is convenient for uniformly evaluating the fiber length and pulp filtration performance through the fiber quality retained in each screening container. Usually, long fiber pulp refers to pulp with an average fiber length of about 4 to 5 mm, such as high-quality coniferous wood pulp and some cotton, linen and artificial fiber pulp that has been cut. If the average length is greater than 5 mm, the mesh needs to be adjusted separately. Short fiber pulp refers to pulp with an average length of less than 1 mm and about 1 mm. Such as general stone-ground wood pulp and some straw pulp. These pulps contain a large number of fine fibers and miscellaneous cells. Some can be retained within 200 mesh, and some pass 200 mesh. These two parts of fiber have different effects on pulp quality, so it is necessary to add a 200-mesh screen plate for this type of pulp. If the fiber is too short, the 14-mesh screen plate can be omitted as appropriate. For screening tests with special requirements, screen plates with different mesh numbers can be selected according to specific requirements. 6.2 Start the machine
6.2.1 Thoroughly clean the containers and screen plates of the sieving instrument to ensure that there are no fibers or attachments on the wall and the screen. 6.2.2 Install the screen: Install the coarsest screen plate into the top screening container, and then decrease it. When installing the screen plate, place the sealing tube in the sealing groove of the screen plate and install it together with the screen plate. Be careful not to let the sealing strip be subjected to excessive tension to avoid leakage of pulp in the thin parts. 6.2.3 Turn on the water: Turn on the water pipe and adjust the flow so that the constant-level water tank just overflows, and the overflow water diameter is about 6 to 8 mm. Make the water flow rate supplied to the screening water tank 11 ± 0.5L/min. After the water flow is stable, start the motor to prepare for screening. 6.2.4 Disperse 10g of dissociated fiber sample evenly in 2L of water, and inject it into the first screening water tank within 15-18s. Start the timer at the same time, and screen accurately for 20min±10s. Stop the machine and stop the water supply immediately after screening. 6.2.5 Collect the slurry in each screening container. You can use a vacuum suction cup assembly or a cloth bag. During the screening process, you can install the filter paper with constant weight on the vacuum suction cup, or install the cloth bag on the receiving plate. After the screening is completed, remove the plug of the sieve slot, let the slurry flow into the receiver, and start the vacuum pump to speed up the filtration speed. If necessary, the slurry that passes through the 200-mesh screen can also be collected with a cloth bag. 6.2.6 Use a thin water pipe to carefully rinse the sieve slot and all parts of the sieve plate, and the washing liquid also flows into the receiver. 6.2.7 Remove the filter pad, use your fingers to remove the pulp attached to the wall of the device, fold the filter pad into a semicircle, squeeze the filter disc in your hand, remove as much water as possible, mark it for easy identification, and then dry it to constant weight. You can also separate the filter paper and the fiber pad, and use a weighing bottle to dry the fiber to constant weight.
If a cloth bag is used for collection, squeeze the collected fibers in the bag and then transfer them to a weighing box of known weight. The fibers must be transferred cleanly without loss.
6.2.8 Dry the sieved pulp to constant weight in an oven at 105±2℃, and weigh it to 0.001g. 7 Calculation
7.1 The test results are generally directly expressed as the percentage of the weight of the fiber retained on different meshes to the weight of the test sample, and the calculation formula is as follows. X, = 100:W
X,= 100.0 (X, + X2+ Xs+ X)
Wherein: i--component number;
(1)
GB/T 2678. 1-93
W. The fiber dry weight of each component on each sieve, g; W--sample weight (absolute dry), g;bzxZ.net
X,-i sieve component percentage;
--the percentage of fine fibers passing through the last sieve. 7.2 Calculation of weight average fiber length: One method is to measure the fiber length and then calculate based on the measurement results. Another method is to determine the fiber weight of each sieve component and the average fiber length of each component through a sieving test and then calculate. The calculation formula is as follows.
Wili +Wet? ​​+Wsts +.. + Whin
Where: Lw—
weight average fiber length of the sample, mm; W—weight of the sample (absolute dry), g,
W, fiber weight of each screening component (absolute dry), g; l—average fiber length of each screening component, mm. (2)
For the same type of pulp, the average fiber length of each screening component does not change much when the sample changes, that is, l1 and l2 can be regarded as known, and the measured data can be used. If the fiber length of the screening component is unknown, take a small amount of undried sample from the filtered sample for measurement according to the GB10336 method.
7.3L, S factor: L factor is defined as the weight percentage of fiber retained in the 48 mesh screen of the Ball sieve. If other sieves are used before the 48-mesh sieve during screening, this weight percentage is the sum of the weights of the fibers retained on each sieve before 48 (absolutely dry, g) as a percentage of the weight of the sample input. For mechanical pulp, this value is linearly related to the weight average fiber length of the sample and is called the L factor. The S factor, also known as the morphological factor, is defined as the specific surface area of ​​the fibers that pass through the 48-mesh and remain on the 100-mesh net. It can also be expressed as Canadian freeness. This value is directly related to the fiber fineness of the sample. The L and S factors are often used to evaluate the quality of mechanical pulp. 8 Reporting results
Prepare a table, mark the mesh number of the sieve used, and report the results as a percentage of the fiber retention on each sieve to the sample input, as shown in the following table.
Mesh number
Use the average of two measurements and report the results to one decimal place. If the relative error of the two tests is greater than 5%, samples need to be taken and re-measured. If necessary, supplement the report on the weight average fiber length of the sample and the L and S factors. The weight average fiber length is accurate to 0.05mm.
Additional Notes:
This standard is proposed by the Ministry of Light Industry of the People's Republic of China. This standard is under the jurisdiction of the National Technical Committee for Paper Industry Standardization. This standard was drafted by the Paper Industry Scientific Research Institute of the Ministry of Light Industry. The main drafters of this standard are Wang Juhua, Zou Wenxiu, Xue Chongyun, Meng Wenyou, and Wang Rui. This standard refers to the American TAPPIT233cm-82 "Determination of fiber length of pulp by grouping method". 228
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