GB/T 2678.1-2026Pulps - Determination of screened components (English PDF)

Foreword

This document complies with the provisions of GB/T 1.1-2020 "Standardization Work Guidelines Part

1.Structure and Drafting Rules of Standardization Documents". Drafting. This document is Part 1 of GB/T 2678.GB/T 2678 has the following parts published.

---Pulp sieve analysis method (GB/T 2678.1);

---Determination of water-soluble chlorides in paper, paperboard and pulp (GB/T 2678.2);

---Determination of chlorine consumption (delignification degree) in pulp (GB/T 2678.3);

---Determination of water-soluble sulfates in paper, paperboard and pulp (GB/T 2678.6). This document supersedes GB/T 2678.1-1993, "Method for Determination of Pulp Sieve Components". Compared with GB/T 2678.1-1993, the only changes are structural adjustments. Aside from editorial changes, the main technical changes are as follows:

a) The scope has been changed (see Chapter 1, Chapter 1 of the.1993 edition);

b) Added terms and definitions for weight-average fiber length and L-factor (see

c) The description of the number of screening containers in the equipment has been changed (see 5.1,

4.1 of the.1993 edition);

d) The sample taking and preparation methods were changed (see Chapter 6, Chapter 5 of the.1993 edition);

e) The descriptions of the water inlet and sample addition procedures in the test protocol have been revised (see

7.4 and 7.5, and

6.2.4 in the.1993 edition);

5 Instruments and Equipment

5.1 Sieving Instrument A Pall fiber sieve for papermaking consists of a four- or five-stage stepped elliptical sieve container, connected to which are the following main components. part.

a) Agitator. Installed inside the screening container, driven by a motor at a speed of (580±40) r/min, to ensure thorough dispersion of fibers in water. They also move in a directional manner, with most fibers moving parallel to the sieve plate, so that the fibers can be sieved according to length;

b) Baffle. Installed in front of the screen plate to prevent water and fibers from rushing vertically towards the screen plate;

c) Sieve plate. Made of stainless steel, used for grading fibers. The mesh size of the sieve plate can be selected according to the different properties of the pulp.

d) Screen plate. Installed close to the screen mesh on the screen plate, the pulp suspension flows through the screen plate to the drain outlet;

e) Sealing tube. used for sealing the connection between the sieve plate and the container;

f) Filtration and drainage device. used to filter fibers from each screening container, and can employ vacuum suction cups or bag filters for drainage. The suction cup connects to the vacuum pump, improving drainage efficiency. The cloth bag can be made of high-quality bleached or unbleached fine cloth. For easy fiber collection, the cloth... The bag can be made in a triangular shape, preferably with a curved bottom. The fabric used should not contain any filler or adhesive.

Note. Different types of sieve analyzers from different manufacturers have poor reproducibility of test results.

5.2 Dissociator The standard dissociator shall comply with the requirements of GB/T 24327, and the circulating dissociator shall comply with the requirements of Appendix D of GB/T 29285-2012.

5.3 Oven It can maintain a temperature of (105±2)°C.

5.4 Electronic Balance The graduation values were

0.1 mg and 1 mg, respectively.

5.5 Weighing Box Aluminum boxes with a diameter of 50mm to 70mm.

5.6 Filter paper The filtration time meets the requirements of type 101 or type.201 in GB/T 1914-2017.

6 Sample collection and preparation

6.1 If evaluating a batch of pulp samples, sampling should be performed according to GB/T 740.If the test is used to evaluate other types of samples, it should be ensured that... The samples taken are representative.

6.2 Determine the moisture content of the sample according to GB/T 462.

6.3 Chemical pulps shall be dissociated according to GB/T 24327; mechanical pulps shall be dissociated according to GB/T 29285.After dissociation, the pulp shall be diluted with water. The concentration of the diluted slurry shall be determined according to the provisions of GB/T 5399, up to approximately 0.3%.

6.4 For chemical pulp, (10.000±0.050) g of oven-dried pulp sample may also be weighed and dissociated according to GB/T 24327.The total dissociated volume is... (2000±25) mL. Wood pulp and bamboo pulp dissociate at 75000 rpm, straw pulp dissociates at 45000 rpm. If the pulp is wet or liquid, dissociation... 15000r.

Note. Generally, the sieving results of each fraction are expressed as a percentage; therefore, the sample addition amount does not need to be accurate to 10g. For air-dried slurry samples, estimate the amount first. To determine the moisture content, weigh approximately 10g of oven-dried pulp sample. Simultaneously, measure the moisture content of another sample; the result will be used to calculate the accuracy of the sample added to the sieve analyzer. Oven-dried mass. If the oven-dried mass is between 9g and 11g, the sample mass has no significant effect on the mass fraction of each fraction.

7 Experimental Procedure

7.1 Select the appropriate series of screen plates with different mesh sizes based on the pulp fiber length. For long fiber pulp, select 10-mesh, 14-mesh, 28-mesh, or 48-mesh screen plates. For medium fiber pulp, choose 14-mesh, 28-mesh, 48-mesh, or 100-mesh sieves; for short fiber pulp, choose 28-mesh, 48-mesh, 100-mesh, or 150-mesh sieves. 200-mesh series sieve plates. See Table 1 for a comparison table of basic sieve plate mesh and aperture dimensions.

7.2 Thoroughly clean all containers and sieve plates of the sieve separator (5.1) to ensure that there are no fibers or attachments on the inner walls of the containers, the agitator and the sieve plates.

7.3 Load each level of sieve plate into the sieving container one by one, and then install the partition plate.

7.4 Open the water inlet and adjust the flow rate so that the constant-level water tank just overflows, or adjust the inlet flow rate to (11.0±0.5) L/min. Wait for each stage... After filling all the screening containers with water, start the motor.

8 Calculation

8.1 The mass fraction of fibers (fractions) remaining on different mesh screens is calculated according to formula (1), and the mass fraction of fibers flowing through the final screen is calculated according to... Calculate using formula (2).

8.2 Calculation of Weight Average Fiber Length (LW). The weight of each grade was determined by sieving test, and then the weight of each grade was measured separately using a fiber length analyzer. The average fiber length (l) of each segment is calculated using formula (3).

8.3 Calculation of L factor (Lf). The L factor is calculated according to formula (4), and the result is expressed as a percentage.

9.Results indicate The results are reported using quality scores at each level. Example. Medium fiber. R14, P14/R28, P28/R48, P48/R100, P100, where R represents the mass fraction of the fraction remaining on a certain mesh screen, P represents... This indicates the mass fraction of the particles passing through a sieve with a specific mesh size. The arithmetic mean of the two measurements was taken as the experimental result, rounded to 0.1%. The absolute difference between any first-order fraction in the two experiments... If the value is greater than 5%, resampling and testing are required. If necessary, indicate the weight-average fiber length and L-factor of the sample in the report. The weight-average fiber length should be accurate to

0.05 mm.

10 Test Report The test report should include the following information.

a) This document number;

b) Date and location of the test;

c) All the information needed to identify the sample;

d) The number of sieves used and their mesh size;

e) Test results;

f) Any deviation from this document or other circumstances that may affect the measurement results.