GB/T 2679.5-1995 Determination of folding endurance of paper and paperboard (MIT folding endurance tester method)

This standard specifies the method for determining the folding resistance of paper and paperboard using the MIT folding tester. This standard applies to paper or paperboard with a thickness of less than 1.00 mm. GB/T 2679.5-1995 Determination of the folding resistance of paper and paperboard (MIT folding tester method) GB/T2679.5-1995 Standard download decompression password: www.bzxz.net

National Standard of the People's Republic of China
Determination of folding endurance of paper and board
(MIT folding endurance tester method)
Paper and board-Determination of folding endurance (MIT tester)
GB/T 2679.5—1995
Replaces GB2679.5—81
This standard is equivalent to the MIT method part in the international standard ISO5626-1978 "Paper—Determination of folding endurance". 1 Subject content and scope of application
This standard specifies the method for determining the folding endurance of paper and board using the MIT folding endurance tester. This standard is applicable to paper or board with a thickness of less than 1.00 mm. 2 Reference standards
GB/T450 Paper and paperboard sample sampling
GB/T10739 Standard atmosphere for handling and testing of pulp, paper and paperboard samples3 Terms
Folding endurance refers to the number of reciprocating double folds of 135° that paper or paperboard can withstand under a certain tension, expressed as the number of reciprocating double folds or the logarithm of the number of double folds with 10 as the base. 4 Instruments
Folding endurance is measured using an MIT type folding endurance tester that meets the following requirements. 4.1 Adjustable spring tension chuck, spring tension 4.91~14.72N. For every 9.81N of tension, the spring is compressed by at least 17mm. 4.2 Folding angle 135°±2°, folding speed 175±10 times/min. 4.3 The width of the folding head is 19±1mm, and the arc radius of the fold is 0.38±0.02mm. 4.4 The distance between the folding head gap is 0.25, 0.50, 0.75, 1.00mm. 4.5 The tension change caused by the eccentric rotation of the folding head is not more than 0.343N (35gf). 4.6 The friction force of the spring tension rod is not more than 0.245N (25gf). 4.7 The folding heads of the instrument should be precisely matched with the host machine and must not be skewed or misplaced. 5 Sampling and processing
Sampling according to GB/T450, the sample is placed in the atmospheric conditions specified in GB/T10739, and after balancing, at least 10 longitudinal and transverse samples with a width of 15±0.1mm and a length of not less than 140mm are cut, and the test is carried out under the standard atmospheric conditions. 6 Test steps
6.1 Calibrate the instrument level, adjust the required spring tension and fix it. For conventional tests, 9.81N spring tension is selected, and 4.91N or 14.72N spring tension can also be used according to requirements. Select the folding chuck required for the sample thickness. Clamp the sample vertically between the two clamps of the folding head, loosen the spring fixing screw, and observe whether the spring tension pointer is in the required position. If there is a position difference, readjust it. Start the instrument and start folding back and forth until the sample breaks. It should be noted that half of the sample is folded to the front first, and half of the sample is folded to the back first. Read the indication value of the counter when it breaks. Reset the counter and perform the next test.
6.2 Repeat the above test procedure and test 10 samples in the vertical and horizontal directions. 6.3 Calculate the average value of the double folding times of each measured value or the average value of the logarithm of the double folding times with 10 as the base. 7 Precision of test results (logarithm of double folding times with base 10) 7.1 Repeatability (same laboratory): When the folding endurance value is about 1.5, the repeatability is about 8%, and when the folding endurance value is about 3.5, the repeatability is about 2%.
7.2 Reproducibility (between laboratories): When the folding endurance value is about 1.5, the reproducibility is about 10%, and when the folding endurance value is about 3.5, the reproducibility is about 4%.
7.3 If the provisions of this standard are not strictly implemented, the above-mentioned error may be twice as high. 8 Test report
a. Number of this national standard;
b. Report the arithmetic mean or coefficient of variation of the longitudinal and transverse measured values ​​respectively as needed. The logarithm of the calculated result shall be rounded to two decimal places, and the double folding times shall be rounded to integers. bzxZ.net
Temperature and humidity conditions used in the test:
d. The spring tension used in the test, whether the sample has delamination, the instrument model used in the test: any deviation from this standard method. g. GB/T2679.5—1995 Appendix A Maintenance and calibration of MIT folding endurance tester (supplement) A1 Calibration of spring tension: Put a special code with a mass of 1kg on the support cap at the upper end of the tension rod, press the tension rod down, adjust the pointer to align with the 9.81N scale line of the tension scale, and then use special magnetic codes with masses of 0.5 and 1.5kg to calibrate the two points of 4.91 and 14.72N respectively, and record the difference between 4.91N and 14.72N for correction when using. A2 Calibration of tension change caused by eccentric rotation of folding head: clamp a paper strip of appropriate thickness and certain strength on the chuck, apply 9.81N tension or the tension used in the test, and slowly rotate the folding head for a whole circle, i.e., one reciprocating, and observe the displacement change of the spring, accurate to 0.1mm. The force indicated by the displacement change shall not be greater than 0.343N (35gf). A3 Calibration of friction of spring tension rod: measure the friction of spring tension rod by adding magnetic code. Under the load tension of 9.81N or the test required, add magnetic code on the support cap, and the mass of magnetic code when the pointer displacement can be observed indicates the friction force, which shall not be greater than 25g (equivalent to 0.245N).
A4 Frequently wipe the round part of the folding head with soft non-linting fabric to keep it clean. Appendix B
Report on the theoretical analysis of the folding endurance using the logarithmic number of double folds with a base of 10 (reference)
The main reason for the fluctuation of the folding endurance value is that the folding stress is only applied to a very small part of the paper surface, and the break occurs at this point of the paper surface, rather than at the weakest point of the test paper strip as in a normal tension test, so the folding endurance value fluctuates greatly. In addition, the folding endurance test is a cumulative operation, and the strength at the test point decreases in an approximately exponential relationship. Therefore, for two samples with similar tensile strength at the test point and the same strength loss during the folding process, very different folding endurance numbers will be given. Unfortunately, the folding endurance has always been expressed in terms of the logarithmic number of double folds with a base of 10. The folding endurance expressed in terms of the logarithmic number of double folds with a base of 10 provides a more realistic result with less error. Additional notes:
This standard is proposed by the China Light Industry General Association.
This standard is under the jurisdiction of the National Technical Committee for Standardization of Papermaking Industry. This standard was drafted by the Tianjin Papermaking Technology Research Institute. The main drafters of this standard are Hou Weiling, Zhang Jingyan and Gao Rui567
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