The calculation formula and results of the adhesive strength of corrugated cardboard show that the former national standards are different from the industrial standards and the concepts are more confusing. At present, the actual testing involves standards such as GB6548 "Determination of Adhesive Strength of Corrugated Paperboard", GB5034-85 "Procedures for Inspection of Corrugated Paperboard for Export Commodity Packaging," and "Corrugated Cardboard Box" approved by the State Bureau of Technical Supervision in June 1992. Production License Quality Inspection Rules (abbreviated as details).
1. GB6548-88 provides that the formula for calculating the bond strength is:
P=F/s (1)
P-bonding strength in the formula, N/m; the maximum force required for F-samples to be completely separated, N; S-sample area, cm2;
It is not difficult to see that (1) The medium-sized units on both sides do not match, that is, N/m≠N/cm2, and the concept is not established. Obviously the standard is wrong. This result of adhesive strength in practice means that it is not used.
2. The result of the bond strength is expressed in N/m2 in the “Detailed Rulesâ€, from which (1) the unit of S in the formula is m2. At present, this result of the bond strength is expressed in a more uniform understanding and in technical supervision. Systematic quality checks are commonly used. This representation essentially refers to the maximum separation force required to strip the corrugated board per unit area.
3. The results of the bond strengths given in GB5034-85 and SN/T0262-93 are expressed as kgf/楞·10cm and N/m·楞, respectively. The two units are the same in meaning, and the two are just one. Coefficient conversion. The test methods prescribed by the two standards are all GB6548, and neither formula is given. According to the meaning of the units expressed, the calculation formula should be:
P=F/L·n (2)
Where L is the length of the sample, m; n—the number of flutes that the sample contains;
The resulting bond strength value (N/m·楞) essentially refers to the maximum separation force required to peel a single length of corrugated board in unit length. At present, the use of this formula and result expression is more common in the inspection of corrugated paper boxes for export of commodity inspection systems. However, due to the limitation of testing methods, the number of corrugated sheets that are stripped during actual testing is at most n-1, so there are two views and approaches for the value of the number of corrugated sheets, one is to take all the samples contained on the sample ( (Intact) Number of turns, the other is to take only the number of peeled turns of the actual pin on the sample, ie at most n-1. According to this recognition, formula (2) becomes P=F/L·(n-1) or in formula (2), n is the actual stripping parameter. Therefore, the value of the adhesive strength of the same sample will vary greatly depending on the value of the number of turns of the tester. This is a problem that is urgently needed in practice.
4. The revised GB 6548-98 stipulates that the result of bond strength is expressed as N/m, and the calculation formula is:
P=F/L (3)
Where L-sample length, m;
The value of the adhesive strength obtained by the formula (3) substantially means the maximum separation required for peeling a corrugated paperboard having a unit length when the width, that is, the twisting length, is constant (25 mm). The concept of bond strength is more similar to (1), ie, N/m2, and there is a mathematical conversion relationship between them: 1N/m2 = 0.024 N/m.
The new standard expresses new regulations on the results of the adhesive strength of corrugated cardboard and clarifies some of the erroneous concepts in the old standard. However, due to the current revision of the corrugated box production standard that is not synchronized with the method standard, the change in the bond strength result in the new standard causes a vacuum in the adhesion quality evaluation criteria of the corrugated box.
There are two main product standards, the standard value of bond strength in the “Detailed Rules†is not less than 58800N/m2, and not less than 588N/m•inch in SN/T0262-93. In addition, in the inspection practice, if the same sample is calculated under the same conditions using equations (1) and (2), respectively, and judged according to the above two criteria, two completely different conclusions may be obtained.
For Type B samples (with 12 samples), the maximum peel force for the test is F=120N. Calculate P=60000N/m2 according to formula (1); the sample is judged to be acceptable and press ( 2) The formula calculates P = 400N/m·楞; the sample is judged to be unqualified. In view of this, it is imperative that the unity of the corrugated box product standard is revised and the standards are united.
Concluding remarks GB6548-98 is equivalent to the Japanese standard JZS0402-88 "Test method for the adhesion of corrugated cardboard", which has also been adopted by many developed countries in the world. To make this standard practically implemented in China, it requires the joint efforts of people in the industry and related departments.
1. The relevant departments should speed up the revision of the "Detailed Rules" and GB6544-86 "Corrugated Cardboard", GB5034-85, SN/T0262-93 and other product standards, so that the standard value, calculation formula and results of the corrugated board adhesive strength As soon as possible unified to GB6548-98 up.
2. Unified detection methods, in which the non-standard tools, ie, double-sided comb stripping frames, were completely eliminated in the testing practice, while standard single-sided steel pins and support frames were used.
3. Before the relevant standards have been revised, regarding the value of the number of corrugations in formula (2), the author believes that in the actual test, the number of corrugated sheets that were not stripped at the end of the specimen is an indeterminate value, ie, it is non-representative. Because of the regularity, (2) the corrugated data is not suitable for (n-1). If calculated according to the actual stripping factor, many human factors will be added, resulting in inconsistent data processing and even misjudgement.
In addition, from the meaning shown by F, F refers to the maximum separation force required for the sample to be completely separated. At this time, even if corrugations are still connected to the face paper or the core paper in the sample, if the sample continues to be pressurized The force value will not increase again. Therefore, from the perspective of a correct understanding of the standard and the harmonization of methods, the first viewpoint and approach is taken for the value of the number of corrugations in (2), that is, the number of all (complete) turns contained on the sample is correct. of.
4. In the current situation, inspectors should be familiar with and master the relevant national standards and industry standards. In particular, they should thoroughly understand and understand GB6548-98, and be aware of the differences between the various standards and test methods. Try to eliminate the influence of objective factors and human factors on the test of the adhesive strength of corrugated cardboard. This point is particularly important for quality inspection agencies that hold product quality judgments.