Some standard content:
JB/T9227—1999
This standard is a revision of ZBJ31009-90 "Bentonite and Cement for Foundry". During the revision, the original standard was edited and the main technical content remained unchanged.
This standard replaces ZBJ31009-90 from the date of implementation. Appendix A of this standard is the appendix of the standard.
This standard is proposed and managed by the National Technical Committee for Foundry Standardization. The drafting unit of this standard: Shenyang Foundry Research Institute. The drafters of this standard: Luo Yuansheng, Shang Shuzhen. 589
1 Scope
Machinery Industry Standard of the People's Republic of China
Bentonite and clay for foundry
Bentonite and caly for foundryJB/T9227:1999
Replaces ZBJ31009-90
This standard specifies the classification, technical requirements, test methods and inspection rules of bentonite and clay for foundry. This standard applies to bentonite for foundry, which is used as a binder and suspending agent for molding sand, core sand and coating in foundry production and whose main component is montmorillonite.
This standard also applies to foundry clay, which is used as a binder for molding sand, core sand and coating in foundry production and whose main component is kaolinite. 2 Referenced standards
The provisions contained in the following standards constitute the provisions of this standard by reference in this standard. When this standard is published, the versions shown are valid. All standards will be revised, and parties using this standard should explore the possibility of using the latest versions of the following standards. GB/T 2684--1981↑
Test methods for raw sand and mixtures for foundry
GB/T7322-1997Test methods for refractories JB/T9224-1999
Standard sand for testing foundry binders
JB/T 9225-1999
3Code
Chemical analysis methods for foundry binders and bentonites 3.1P-foundry bentonites.
3.2N-foundry binders.
4Classification, grading and grades of foundry bentonites and clays 4.1Classification, grading and grades of foundry bentonites 4.1.1Classification and grading of foundry bentonites 4.1.1.1Foundry bentonites can be divided into four categories according to their main exchangeable cations. Different types of bentonite are represented by the bentonite code "P" and the chemical element symbol of the main exchangeable cation, and are called bentonites accordingly. If the amount of a certain exchangeable cation accounts for 50% or more of the cation exchange capacity, it is called the main exchangeable cation. If the amount of any exchangeable cation accounts for less than 50% of the cation exchange capacity, the two exchangeable cations with relatively higher content are the main exchangeable cations.
For example, bentonite with sodium ion as the main exchangeable cation is represented by PNa and is called sodium bentonite. For example, bentonite with calcium ion and sodium ion as the main exchangeable cations is represented by PCaNa and is called calcium sodium bentonite (the symbol of the cation with higher content is in front).
The classification of bentonite for casting is shown in Table 1.
Approved by the State Bureau of Machinery Industry on June 24, 1999 590
Implemented on January 1, 2000
JB/T9227-—1999
Sodium bentonite
Calcium bentonite
Sodium calcium bentonite
Calcium sodium bentonite
4.1.1.2 According to the different pH values, bentonite can be divided into acidic and alkaline types, represented by S and J respectively. 4.1.2 The classification of bentonite for casting shall be in accordance with the provisions of Table 2 according to the wet compressive strength value of the process sample. Table 2
3 The classification of bentonite for casting shall be in accordance with the provisions of Table 3 according to the hot wet tensile strength value of the process sample. 4.1.3
Grade code
Wet compression strength value of process sample
≥70～100
>50~-70
≥30～50
Hot wet tensile strength value of process sample
>2. 0~2. 5
≥1. 5 ~2. 0
4.1.4 The grade of bentonite for casting is expressed by the strength value grade of bentonite mineral characteristics. In the strength value grade, the former is the wet compression strength value grade, and the latter is the hot mixed tensile strength value grade. For example, the acidic calcium expansion t: with a wet compressive strength of 30~~50kPa and a hot wet tensile strength of 0.5~~1.5kPa is graded PCaS-3-5. 4.2 Grading and grades of foundry clay
4.2.1 Foundry clay is divided into two grades according to different refractoriness, see Table 4. Table 4
High refractoriness
Low refractoriness
Foundry clay is divided into three grades according to the wet compressive strength value of the process sample, as specified in Table 5. Table 5
4.2.3 Foundry clay is divided into three grades according to the dry compressive strength value of the process sample, as specified in Table 6. Refractoriness
1350~~1580
Process sample vortex compression strength value
≥30-50
Grade code
JB /T 9227
! 4.2.4 The brand of casting clay is expressed by refractoriness grade and strength grade. In the strength grade, the former is the wet strength grade and the latter is the dry compression grade. For example, the brand of casting clay with high refractoriness, mixed compression strength of 30-50kPa and dry compression strength greater than 500kPa is NG-3-50.
5 Technical requirements
5.1 Technical requirements for bentonite for casting
5.1.1 The wet compressive strength and hot wet tensile strength of various brands of bentonite for casting process samples shall conform to the requirements of Table 2 and Table 3. 5.1.2 The amount of methylene blue adsorbed by various brands of bentonite for casting shall be at least 20g of methylene blue per 100g of bentonite. 5.1.3 The water content of various brands of bentonite for casting shall not be greater than 12.0%, and a water content of no greater than 15.0% is allowed in winter. 5.1.4 More than 95% of the weight of various brands of expanded clay for casting shall pass through the No. 10 casting test sieve with a mesh size of 0.075mm.
5.2 Technical requirements for casting clays
5.2.7 The refractoriness of various brands of casting clays and the wet and dry compressive strength values of process samples shall comply with the provisions of Table 4, Table 5 and Table 6.
5.2.2 The water content of various brands of casting clays shall not exceed 10.0%. 5.2.3 More than 95% of the weight of various brands of casting clays shall pass through the No. 09 casting test sieve with a mesh size of 0.106m.
6 Test methods
6.1 Preparation of test materials
6.1.1 The test materials must indicate the name, origin and sampling period of the test materials. 6.1.2 Except for the samples used to determine the moisture content, the samples used for other tests must be dried at 105-110℃ for 2h (the thickness of the samples should not exceed 15mm), and then the dried samples should be stored in a dryer for testing. 6.1.3 For samples in doubt or for arbitration tests, the remaining samples after the test should be kept for three months for review. 6.1.4 Preparation of mixture for strength test
6.1.4.1 Preparation of mixture for casting clay process sample: Put 2000g standard sand (JB/T9224) and 200g casting clay into SHN sand mixer, dry mix for 2min, then add 100mL water and mix for 8min. 6.1.4.2 Preparation of bentonite process sample mixture for casting: Put 2000g standard sand (JB/T9224) and 100g foundry bentonite into SHN sand mixer, dry mix for 2min, add 40mL water and mix and grind for 8min, and measure the compaction rate according to the provisions of 2.4 of GB/T2684--1981. When the compaction rate is less than 13%, add a small amount of water (the amount of water added can be estimated as 1.5% compaction rate per milliliter of water), mix and grind for 2min, and check the compaction rate. If the compaction rate is greater than 47%, sieve the sample 1~2 times and check the compaction rate again. The compaction rate is within the range of 43%~17%.
6.1.4.3 The mixed test mixture should be stored in a sealed state to prevent water from volatilizing in preparation for the test. The mixture should be placed for 10min before measurement, but it should not be measured after more than 1h. 6.2 Determination of water content
The water content of bentonite and clay for casting shall be determined according to the provisions of 2.1.2 of GB/T2684-1981. 6.3 Determination of particle size
6.3.1 Main instruments and equipment
Balance, sensitivity 0.1g;
Test sieve for casting.
JB/T 9227
6.3.2 Determination of sieve weight Weigh the dried sample 20.0g is placed in a dry casting test sieve, and the sieve is moved horizontally. If the sieving performance is poor, the lower end of the sieve frame can be gently knocked with a wooden block to vibrate the sieve. After sufficient sieving, weigh the residue on the sieve and calculate the sieving amount using formula (1), with the value accurate to the decimal place.
6.4 Determination of pH value
6.4.1 Main instruments:
Acidity meter (glass electrode);
Electromagnetic stirrer;
Balance, sensitivity 0.1g.
6.4.2 Test method
Sieve amount = double sample amount = sieve residue × 100%
Sampling amount
Weigh 5. (g of sample, place it in a beaker with a capacity of 150mL, add 100ml of neutral distilled water, stir it with a stirrer for 5 minutes, and then immediately measure the pH value with an acidometer.
6.5 Determination of wet compressive strength value
6.5.1 Sample preparation shall be in accordance with the provisions of 6.1.4. 6.5.2 Test shall be in accordance with the provisions of 2.6 of GB/T2684-1981. 6.6 Determination of dry compressive strength value
6.6.1 Sample preparation shall be in accordance with the provisions of 6.1.4. 6.6.2 Test shall be in accordance with the provisions of 2.6 of GB/T2684-1981 2.6. 6.6.3 The sample drying specification is: keep the sample at 180℃±5℃ for 1h, and then measure the sample after it cools to room temperature in the dryer. 6.7 Determination of hot and wet tensile strength value
6.7.1 Sample preparation shall be in accordance with 6.1.4. 6.7.2 Main instrument: SQR type molding sand hot and wet tensile strength tester. 6.7.3 Test method: Prepare the sample in the special sample tube of the tester, and place the sample tube on the tester. Place the heating plate that has been heated to 320℃±10C close to the sample for 20s, and then load until the sample breaks. Read the test data from the recorder. Use the same mixture to measure three samples, and take the arithmetic mean as the hot and wet tensile strength value. If any of the values is different from the average When the values differ by more than 10%, the test shall be repeated. 6.8 Determination of refractoriness
The determination of refractoriness of foundry clay shall be in accordance with the provisions of GB/T7322. 6.9 Determination of cation exchange capacity and exchangeable cation content The determination of cation exchange capacity and exchangeable cation content of foundry bentonite shall be in accordance with the provisions of Chapter 12 of JB/T9225-1999. 6.10 Determination of methylene blue adsorption
The determination of methylene blue adsorption of foundry bentonite shall be in accordance with the provisions of Appendix A (Appendix to the standard). 7 Inspection rules
7.1 Batch
Intermediate grades of bentonite or clay delivered at the same time are considered a batch. 7.2 Selection of inspection samples
7.2.1 Each The sampling of batch products shall be carried out by random sampling method, and the number of samples shall not be less than Vn/2. n is the number of bags of delivered products, and the number of samples for each batch shall not be less than 2 samples.
JB/T9227—1999
7.2.2 The test materials shall be obtained from the selected samples by the "four-point method", and their weight may be determined by the test item!I, but shall not be less than 1kg. 7.3 Type inspection
7.3.1 The supplier shall produce and supply according to the brand and technical requirements specified in this standard, and conduct type inspection in the following circumstances: a) Newly produced products or products that have been suspended for a long time and resume production; b) Newly mined ore deposits;
c) When there is a change in the production process;
d) When the test results are significantly different from the last type inspection results; e) During normal production, periodic inspections shall be carried out;) When the national quality supervision agency puts forward type inspection requirements. 7.3.2 The items of type inspection are the technical requirements specified in Chapter 4 and Chapter 5. 7.3.3 If any item of type inspection fails to meet the requirements, re-sampling shall be conducted and the re-inspection result shall be the final result. If the final result still fails to meet the requirements, the product shall be judged as unqualified.
7.4 Factory inspection
7.4.1 Each batch of products shall be subject to factory inspection according to the technical requirements specified in this standard. 7.4.2 The factory inspection items are: particle size, wet compressive strength. 7.4.3 If it is necessary to inspect items other than those specified in 7.4.2, it shall be determined by negotiation between the supply and demand parties. 7.4.4 If any item of the factory inspection index fails to meet the requirements, re-sampling can be conducted in the same batch and the re-inspection result shall be the final result. If the final result still fails to meet the requirements, the batch of products shall be judged as unqualified. 7.4.5 The purchaser may conduct acceptance according to the product quality certificate. If there is any product quality problem, the supplier and the buyer shall negotiate to solve it, or entrust the arbitration unit to conduct sampling inspection. The arbitration inspection is the final inspection. 7.5 The dry compressive strength value of bentonite for casting is not specified. When it needs to be measured, it can be carried out according to the provisions of 6.6. 8 Packaging and marking
8.1 Packaging
8.1.1 Various brands of bentonite for casting or clay for casting are supplied in bags to avoid leakage and moisture. 8.1.2 Each bag of product shall be accompanied by a product quality certificate. The content of the product quality certificate includes: product name, grade, production period and batch number, and manufacturer name.
8.2 Label
The words "bentonite for casting" or "clay for casting" shall be printed in bold and eye-catching on the upper part of the outer layer of the packaging bag, the net weight of each bag of product shall be printed in the middle of the bag, and the manufacturer name shall be printed on the bottom of the bag. 594
JB/T9227
Attachment A
(Appendix to the standard)
Method for determination of methylene blue adsorption
A1 Determination method: Weigh 0.20g of the dried sample, place it in a conical beaker, add 50ml of distilled water to pre-mix it. Then add 20mL of 1% sodium pyrophosphate solution, shake it evenly, heat it on an electric stove and boil it for 5min, and cool it to room temperature in the air. Use a burette to drop a 0.2% methylene blue solution (chemical reagent). When titrating, add about two-thirds of the expected amount of methylene blue solution for the first time, and then titrate 1 to 2mL each time. The method of checking the end point is to shake for 3)s after each drop of methylene blue solution, and use a glass rod to dip a drop of test solution on the medium-speed quantitative filter paper to observe whether there is a light blue halo around the central dark blue point. If not, continue to drop methylene blue solution, and repeat this operation. When a blue halo begins to appear, let the test solution stand for 1 minute, and then dip a drop of test solution with a glass rod. If no light blue halo appears around, it means that the end point has not been reached. Methylene blue solution should be added again until an obvious light blue halo appears. The end point is the test end point. The blue absorption of the sample can be calculated according to formula (A1): ab
where B
blue absorption·g/100g sample;
α-the amount of methylene blue contained in each milliliter of methylene blue solution, g, b-the titration amount of methylene blue solution, ml, and the weight of the sample, g.
Note: Preparation of methylene blue solution: Before preparation, methylene blue must be dried at 93°C ± 3°C to constant weight, then weigh 2.000 ml of dried methylene blue and dissolve it in 1000 ml of distilled water to prepare a 0.2% methylene blue solution.8 Determination of refractoriness
The determination of refractoriness of foundry clay shall be in accordance with the provisions of GB/T7322. 6.9 Determination of cation exchange capacity and exchangeable cation content The determination of cation exchange capacity and exchangeable cation content of foundry bentonite shall be in accordance with the provisions of Chapter 12 of JB/T9225-1999. 6.10 Determination of methylene blue adsorption
The determination of methylene blue adsorption of foundry bentonite shall be in accordance with the provisions of Appendix A (Appendix to the standard). 7 Inspection rules
7.1 Batch
The bentonite or clay of different grades delivered at the same time is a batch. 7.2 Selection of inspection samples
7.2.1 The sampling of each batch of products shall be carried out by random sampling method, and the number of samples shall not be less than Vn/2. n is the number of bags of delivered products, and the number of samples for each batch shall not be less than 2 samples.
JB/T9227—1999
7.2.2 The test material is obtained from the selected samples by the "four-point method", and its weight can be determined by the test item, but shall not be less than 1kg. 7.3 Type inspection
7.3.1 The supplier shall produce and supply according to the brand and technical requirements specified in this standard, and conduct type inspection in the following situations: a) Newly produced products or products that have been suspended for a long time and resume production; b) Newly mined ore deposits; c) When the production process has changed; d) The test results are significantly different from the previous type inspection results; e) During normal production, periodic inspections are conducted; d) When the national quality supervision agency puts forward type inspection requirements. 7.3.2 The items of type inspection are the technical requirements specified in Chapter 4 and Chapter 5. 7.3.3 When any item of type inspection fails to meet the requirements, re-sampling shall be conducted, and the re-inspection results shall be the final results. If the final result still fails to meet the requirements, the product is judged as unqualified.
7.4 Factory inspection
7.4.1 Each batch of products shall be inspected according to the technical requirements specified in this standard. 7.4.2 The factory inspection items are: particle size, wet compressive strength. 7.4.3 If it is necessary to inspect items other than those specified in 7.4.2, it shall be determined by negotiation between the supplier and the buyer. 7.4.4 If any of the indicators of the factory inspection fails to meet the requirements, the same batch can be resampled for inspection, and the re-inspection results shall be the final result. If the final result still fails to meet the requirements, the batch of products shall be judged as unqualified. 7.4.5 The buyer may accept the product according to the product quality certificate. If there is a product quality problem, the supplier and the buyer shall negotiate to solve it, or entrust an arbitration unit to conduct sampling inspection. The arbitration inspection is the final inspection. 7.5 The dry compressive strength value of cast bentonite is not specified. If it needs to be measured, it can be carried out according to the provisions of 6.6. 8 Packaging and marking
8.1 Packaging
8.1.1 Various brands of bentonite or clay for casting are supplied in bags to avoid leakage and moisture. 8.1.2 Each bag of product should be accompanied by a product quality certificate. The content of the product quality certificate includes: product name, grade, production period and batch number, and manufacturer name.
8.2 Marking
The words "bentonite for casting" or "clay for casting" should be printed in bold and eye-catching fonts on the upper part of the outer layer of the packaging bag, the net weight of each bag of product should be printed in the middle of the bag, and the manufacturer name should be printed on the bottom of the bag. 594
JB/T9227
Attachment A
(Appendix to the standard)
Method for determination of methylene blue adsorption
A1 Determination method: Weigh 0.20g of the dried sample, place it in a conical beaker, add 50ml of distilled water to pre-mix it. Then add 20mL of 1% sodium pyrophosphate solution, shake it evenly, heat it on an electric stove and boil it for 5min, and cool it to room temperature in the air. Use a burette to drop a 0.2% methylene blue solution (chemical reagent). When titrating, add about two-thirds of the expected amount of methylene blue solution for the first time, and then titrate 1 to 2mL each time. The method of checking the end point is to shake for 3)s after each drop of methylene blue solution, and use a glass rod to dip a drop of test solution on the medium-speed quantitative filter paper to observe whether there is a light blue halo around the central dark blue point. If not, continue to drop methylene blue solution, and repeat this operation. When a blue halo begins to appear, let the test solution stand for 1 minute, and then dip a drop of test solution with a glass rod. If no light blue halo appears around, it means that the end point has not been reached. Methylene blue solution should be added again until an obvious light blue halo appears. The end point is the test end point. The blue absorption of the sample can be calculated according to formula (A1): ab
where B
blue absorption·g/100g sample;
α-the amount of methylene blue contained in each milliliter of methylene blue solution, g, b-the titration amount of methylene blue solution, ml, and the weight of the sample, g.
Note: Preparation of methylene blue solution: Before preparation, methylene blue must be dried at 93°C ± 3°C to constant weight, then weigh 2.000 ml of dried methylene blue and dissolve it in 1000 ml of distilled water to prepare a 0.2% methylene blue solution.8 Determination of refractoriness
The determination of refractoriness of foundry clay shall be in accordance with the provisions of GB/T7322. 6.9 Determination of cation exchange capacity and exchangeable cation content The determination of cation exchange capacity and exchangeable cation content of foundry bentonite shall be in accordance with the provisions of Chapter 12 of JB/T9225-1999. 6.10 Determination of methylene blue adsorption
The determination of methylene blue adsorption of foundry bentonite shall be in accordance with the provisions of Appendix A (Appendix to the standard). 7 Inspection rules
7.1 Batch
The bentonite or clay of different grades delivered at the same time is a batch. 7.2 Selection of inspection samples
7.2.1 The sampling of each batch of products shall be carried out by random sampling method, and the number of samples shall not be less than Vn/2. n is the number of bags of delivered products, and the number of samples for each batch shall not be less than 2 samples.
JB/T9227—1999
7.2.2 The test material is obtained from the selected samples by the "four-point method", and its weight can be determined by the test item, but shall not be less than 1kg. 7.3 Type inspection
7.3.1 The supplier shall produce and supply according to the brand and technical requirements specified in this standard, and conduct type inspection in the following situations: a) Newly produced products or products that have been suspended for a long time and resume production; b) Newly mined ore deposits; c) When the production process has changed; d) The test results are significantly different from the previous type inspection results; e) During normal production, periodic inspections are conducted; d) When the national quality supervision agency puts forward type inspection requirements. 7.3.2 The items of type inspection are the technical requirements specified in Chapter 4 and Chapter 5. 7.3.3 When any item of type inspection fails to meet the requirements, re-sampling shall be conducted, and the re-inspection results shall be the final results. If the final result still fails to meet the requirements, the product is judged as unqualified.
7.4 Factory inspection
7.4.1 Each batch of products shall be inspected according to the technical requirements specified in this standard. 7.4.2 The factory inspection items are: particle size, wet compressive strength. 7.4.3 If it is necessary to inspect items other than those specified in 7.4.2, it shall be determined by negotiation between the supplier and the buyer. 7.4.4 If any of the indicators of the factory inspection fails to meet the requirements, the same batch can be resampled for inspection, and the re-inspection results shall be the final result. If the final result still fails to meet the requirements, the batch of products shall be judged as unqualified. 7.4.5 The buyer may accept the product according to the product quality certificate. If there is a product quality problem, the supplier and the buyer shall negotiate to solve it, or entrust an arbitration unit to conduct sampling inspection. The arbitration inspection is the final inspection. 7.5 The dry compressive strength value of cast bentonite is not specified. If it needs to be measured, it can be carried out according to the provisions of 6.6. 8 Packaging and marking
8.1 Packaging
8.1.1 Various brands of bentonite or clay for casting are supplied in bags to avoid leakage and moisture. 8.1.2 Each bag of product should be accompanied by a product quality certificate. The content of the product quality certificate includes: product name, grade, production period and batch number, and manufacturer name.
8.2 Marking
The words "bentonite for casting" or "clay for casting" should be printed in bold and eye-catching fonts on the upper part of the outer layer of the packaging bag, the net weight of each bag of product should be printed in the middle of the bag, and the manufacturer name should be printed on the bottom of the bag. 594bzxz.net
JB/T9227
Attachment A
(Appendix to the standard)
Method for determination of methylene blue adsorption
A1 Determination method: Weigh 0.20g of the dried sample, place it in a conical beaker, add 50ml of distilled water to pre-mix it. Then add 20mL of 1% sodium pyrophosphate solution, shake it evenly, heat it on an electric stove and boil it for 5min, and cool it to room temperature in the air. Use a burette to drop a 0.2% methylene blue solution (chemical reagent). When titrating, add about two-thirds of the expected amount of methylene blue solution for the first time, and then titrate 1 to 2mL each time. The method of checking the end point is to shake for 3)s after each drop of methylene blue solution, and use a glass rod to dip a drop of test solution on the medium-speed quantitative filter paper to observe whether there is a light blue halo around the central dark blue point. If not, continue to drop methylene blue solution, and repeat this operation. When a blue halo begins to appear, let the test solution stand for 1 minute, and then dip a drop of test solution with a glass rod. If no light blue halo appears around, it means that the end point has not been reached. Methylene blue solution should be added again until an obvious light blue halo appears. The end point is the test end point. The blue absorption of the sample can be calculated according to formula (A1): ab
where B
blue absorption·g/100g sample;
α-the amount of methylene blue contained in each milliliter of methylene blue solution, g, b-the titration amount of methylene blue solution, ml, and the weight of the sample, g.
Note: Preparation of methylene blue solution: Before preparation, methylene blue must be dried at 93°C ± 3°C to constant weight, then weigh 2.000 ml of dried methylene blue and dissolve it in 1000 ml of distilled water to prepare a 0.2% methylene blue solution.2% methylene blue solution (chemical reagent). During titration, add about two-tenths of the expected amount of methylene blue solution for the first time, and then titrate 1-2 mL each time. The method for testing the endpoint is to shake for 3) seconds after each drop of methylene blue solution, use a glass rod to dip a drop of test solution on the medium-speed quantitative filter paper, and observe whether there is a light blue halo around the central dark blue point. If not, continue to add methylene blue solution, and repeat the operation. When a blue halo begins to appear, let the test solution stand for 1 minute, and then use a glass rod to dip a drop of test solution. If no light blue halo appears around, it means that the endpoint has not been reached. Methylene blue solution should be added again until an obvious light blue halo appears. This is the test endpoint. The blue absorption of the sample can be calculated according to formula (A1): ab
wherein B
blue absorption g/100g sample;
α-the amount of methylene blue contained in each milliliter of methylene blue solution, g, b-the titration of methylene blue solution, ml, and the weight of the sample, g.
Note: Preparation of methylene blue solution: Before preparation, methylene blue must be dried at 93°C ± 3°C to constant weight, and then 2.000 of the dried methylene blue is weighed and dissolved in 1000ml of distilled water to prepare a 0.2% concentration methylene blue solution. 5952% methylene blue solution (chemical reagent). During titration, add about two-tenths of the expected amount of methylene blue solution for the first time, and then titrate 1-2 mL each time. The method for testing the endpoint is to shake for 3) seconds after each drop of methylene blue solution, use a glass rod to dip a drop of test solution on the medium-speed quantitative filter paper, and observe whether there is a light blue halo around the central dark blue point. If not, continue to add methylene blue solution, and repeat the operation. When a blue halo begins to appear, let the test solution stand for 1 minute, and then use a glass rod to dip a drop of test solution. If no light blue halo appears around, it means that the endpoint has not been reached. Methylene blue solution should be added again until an obvious light blue halo appears. This is the test endpoint. The blue absorption of the sample can be calculated according to formula (A1): ab
wherein B
blue absorption g/100g sample;
α-the amount of methylene blue contained in each milliliter of methylene blue solution, g, b-the titration of methylene blue solution, ml, and the weight of the sample, g.
Note: Preparation of methylene blue solution: Before preparation, methylene blue must be dried at 93°C ± 3°C to constant weight, and then 2.000 of the dried methylene blue is weighed and dissolved in 1000ml of distilled water to prepare a 0.2% concentration methylene blue solution. 595
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