GB/T 39372-2020 English PDF (GBT39372-2020)

This Standard specifies the method for the determination of percentage extension of leather. This Standard is applicable to the determination of percentage extension of various types of soft leather (especially decorative leather).

GB/T 39372-2020
GB
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
ICS 59.140.30
Y 46
Leather - Physical and Mechanical Tests -
Determination of Percentage Extension
(ISO 17236:2016, Leather - Physical and Mechanical Tests - Determination of Extension Set, MOD)
ISSUED ON: NOVEMBER 19, 2020
IMPLEMENTED ON: JUNE 1, 2021
Issued by: State Administration for Market Regulation;
Standardization Administration of the People’s Republic of
China.
Table of Contents
Foreword ... 3
1 Scope ... 5
2 Normative References ... 5
3 Principle ... 5
4 Instruments and Equipment ... 5
5 Sampling and Specimen Preparation ... 6
6 Test Methods ... 7
7 Result Expression ... 7
8 Test Report ... 8
Foreword
This Standard was drafted in accordance with the rules in GB/T 1.1-2009. This Standard uses the re-drafting method in the modification and adoption of ISO 17236:2016 Leather - Physical and Mechanical Tests - Determination of Extension Set. In comparison with ISO 17236:2016, this Standard has structural adjustments as follows:
---The content of the third paragraph of 5.2 is modified into the NOTE of 5.2, so as to comply with the habits of our country (see 5.2);
---The content of 8 c) about result expression is adjusted to “7 Result Expression” (see Chapter 7).
In comparison with ISO 17236:2016, the technical differences and the causes for these differences are as follows:
---In terms of Normative References, this Standard adjusts the technical differences, so as to adapt to the technical conditions of our country. The adjustments are intensively reflected in Chapter 2 “Normative References”. The specific adjustments are as follows:
 GB/T 39364, which modifies and adopts International standard, is used to replace ISO 2418 (see 5.1);
 QB/T 2707, which modifies and adopts International standard, is used to replace ISO 2419 (see 4.3 and 5.3);
 QB/T 2709, which modifies and adopts International standard, is used to replace ISO 2589 (see 4.2 and 5.4);
 The reference of ISO 7500-1 is deleted;
---In tensile machine, the accuracy level of tensile force recording device is modified (see 4.1);
---The instructions for the sampling of non-standard sites are added, so as to satisfy the demands of routine inspection (or sampling directly from shoes and clothing) (see 5.1);
---The stipulations of horizontal and longitudinal specimens are added to sampling and specimen preparation, so as to facilitate standard compilation and test results recording (see 5.2);
---The calculation formula is adjusted and the unit description of percentage extension is added, so as to comply with the habits of our country (see Chapter 7);
---The requirements for the accuracy of the calculation results are added, which enhances the comparability of results between laboratories (see Chapter 7); ---The test report is adjusted and the requirements for the accuracy of thickness are added, which enhances the comparability of results between laboratories (see Chapter 8).
This Standard also makes the following editorial modifications:
---The title of this Standard is modified into: “Leather - Physical and Mechanical Tests - Determination of Percentage Extension”;
---The description of the tensile machine in 4.1 is modified from two clauses into the itemized form (see 4.1);
---Clause titles are added to “5 Sampling and Specimen Preparation” (see Chapter 5).
This Standard was proposed by China National Light Industry Council.
This Standard shall be under the jurisdiction of National Technical Committee 252 on Leather of Standardization Administration of China (SAC/TC 252).
The drafting organizations of this Standard: Dongguan Weiside Technology Development Co., Ltd.; Chinatesta (Shenzhen) Testing Services Co., Ltd.; Liming Vocational University; China Leather & Footwear Research Institute Co., Ltd.; Jiaxing Fur and Shoe Industry Research Institute; Quality and Technical Supervision Standards and Coding Office of Huizhou City, Guangdong Province; Jinjiang Dongyi Shoes Industry Co., Ltd.
The main drafters of this Standard: Bu Qiaoqiao, Yuan Jingjie, Li Xiang, Chen Xiaohong, Su Guohui, Wen Zhifan, Zhang Wenfu, Dai Ziqiang.
can be mechanically or pneumatically clamped. There shall be certain texture inside the clamp, so as to ensure that when the applied load reaches the maximum, the specimen does not slip, and moves at a constant rate of (50 ± 5) mm/min.
4.2 Thickness gauge, which complies with the stipulations of QB/T 2709. 4.3 Die cutter, which complies with the stipulations of QB/T 2707. The inner wall is a rectangle with a size of (250 ± 5) mm  (10.0 ± 0.5) mm.
4.4 Scale ruler, with an accuracy of 0.5 mm.
4.5 Stopwatch, with an accuracy of 1 s.
5 Sampling and Specimen Preparation
5.1 Sampling
In accordance with the stipulations of GB/T 39364, conduct sampling. If it is not possible to take samples from standard parts (for example, direct sampling from shoes and clothing), sampling shall be conducted at any part within the available area. The specimens shall be representative and indicated in the test report.
5.2 Specimen Preparation
Use the die cutter (4.3) to cut 6 specimens from the grain surface, in which, the long sides of 3 specimens are parallel to the back ridge line (longitudinal specimens), and the long sides of the other 3 specimens are perpendicular to the back ridge line (horizontal specimens).
NOTE 1: for smaller samples, the number of specimens may be reduced; the number of the decreased longitudinal specimens and the decreased horizontal specimens shall be consistent.
NOTE 2: if there are more than 2 samples in the same batch of products that need to be tested, at least 1 specimen shall be cut from each sample in each direction, and the total number of specimens in each direction shall be not less than 3. 5.3 Specimen Conditioning
In accordance with the stipulations of QB/T 2707, conduct specimen conditioning. 5.4 Thickness Determination
In accordance with the stipulations of QB/T 2709, conduct thickness determination.