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This standard is developed in accordance with the rules given in GB/T 1.1-2009.
This standard is revision of QB/T 2714-2005 Leather - Physical and mechanical tests - Determination of flex resistance.
In addition to editorial changes, the following technical changes have been made with respect to QB/T 2714-2005 (the previous edition):
——in 4.1.1, the description of upper clamp is adjusted, and the thickness requirements for its flat metal plate and ledge EF are added, which is consistent with the international standard;
——"4.8 Mandrel", "4.9 Metal clip", "4.10 Stereomicroscope" and their relevant requirements are added, which is consistent with the international standard;
——in 5.2, the number of test pieces is adjusted, which is consistent with the international standard;
——in 6.5, the wet flex cycle 2500 is added, which is consistent with the international standard;
——in 6.6, the evaluation method for crack intensity and description method for damage are added, which is consistent with the international standard;
——in 6.10, the treatment method for the case where only one test piece shows slight damages is added, which is consistent with the international standard.
This standard has been redrafted and modified in relation to ISO 5402-1:2011 Leather - Determination of flex resistance - Part 1: Flexometer method. The international standard is based on Part 1 of Standard IUP 20 of International Union of Leather Technologists and Chemists Societies (IULTCS).
According to the actual situation of China, the following technical modifications have been made in adoption of ISO 5402-1:2011:
——the original ISO standards referenced in "Normative references" are changed to relevant standards of China;
——for the convenience of application, the provisions of 5.1 are divided into 5.1 and 5.2, the following article numbers are postponed accordingly;
——"Note" for reference in 5.1 is deleted to avoid misunderstanding in application;
——“Annex A (Informative) Sources of apparatus" is deleted.
The following editorial changes have also been made in this standard:
——foreword in ISO standard is deleted;
——"this international standard" is changed to "this standard";
——the comma "," used as the decimal point is replaced by ".".
——for the convenience of application, the wording sequence of 6.6 is adjusted.
This standard was proposed by the China National Light Industry Council.
This standard is under the jurisdiction of the National Technical Committee on Leather of Standardization Administration of China (SAC/TC 252).
This standard replaces the former professional standard QB/T 2714-2005 Leather - Physical and mechanical tests - Determination of flex resistance, which is abolished from the implementation date hereof.
The previous editions of this standard are as follows:
—GB 4689.9-1984 (later converted to QB/T 3812.9-1999, with contents unchanged);
—QB/T 3812.9-1999;
—QB/T 2714-2005.
Leather - Physical and mechanical tests - Determination of flex resistance
1 Scope
This standard specifies a method for determining the wet or dry flex resistance of leathers and leather finishes.
It is applicable to all types of leathers which are less than 3.0mm in thickness.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
GB/T 6682 Water for analytical laboratory use - Specification and test methods (GB/T 6682-2008, ISO 3696:1987, MOD)
QB/T 2706 Leather - Chemical, physical and mechanical and fastness tests - Sampling location (QB/T 2706-2005, ISO 2418:2002, MOD)
QB/T 2707 Leather - Physical and mechanical tests - Sample preparation and conditioning (QB/T 2707-2018, ISO 2419:2006, MOD)
3 Principle
A test piece is folded with the upper test surface inwards and clamped in a movable clamp and the lower test surface outwards in a fixed clamp. Movement of the upper clamp causes movement of the test piece. The changes of test piece are evaluated after a specified number of cycles.
4 Apparatus and materials
4.1 Flexing resistance test machine
It shall include the components specified in 4.1.1~4.1.3.
4.1.1 Upper clamp, consisting of a pivoting pair of flat metal plates with maximum thickness of 4mm (see Figure 1). One of the metal plates has the basic shape of a trapezium ABCFD but with a radius of 2mm at F. It has a ledge EF with (4±1)mm in thickness to support and clamp the folded test piece. The other plate has the shape EGHCF. The clamp tightening screw K draws the plates together and also acts as a stop to prevent the test piece from being positioned closer to AB than the vertical through C. A stop near the edge AB and approximately midway between A and B ensures that the plates clamp more effectively near point F. The upper clamp is reciprocated by a motor about a horizontal axis J, descending through an angle of 22°30'±0°30' at a frequency of (100±5) cycles/min.
4.1.2 Lower clamp, fixed and lying directly beneath (planar to) the upper clamp and consisting of a pair of flat plates to hold the test piece. The position of the lower clamp is such that the distance between the ledge EF and the upper edge of the fixed lower clamp, when the ledge EF is horizontal, is (25.0±0.5)mm.
4.1.3 Counter, indicating the number of cycles.
4.2 Press knife
Conforming to the requirements of QB/T 2707, the inner wall of which is a rectangle (70±1)mm × (45±1)mm.
4.3 Magnifier
With a magnification of 4 to 6 times.
4.4 Desiccator
Or other vessels which can be evacuated.
4.5 Vacuum pump
Capable of reducing the pressure in the desiccator to less than 4kPa.
4.6 Distilled or deionized water
Of Grade 3 in accordance with the requirements of GB/T 6682.
4.7 Glass dish
Minimum diameter of 100mm and minimum depth of 25mm.
4.8 Mandrel
Having a diameter of 10mm and a minimum length of 70mm.
4.9 Metal clip
70mm wide, capable of fixing a test piece around the mandrel (4.8) at a slight stretch.
4.10 Stereomicroscope
With a magnification of 25 times.
Foreword i
1 Scope
2 Normative references
3 Principle
4 Apparatus and materials
5 Sampling and sample preparation
6 Procedure
7 Test report
