HG/T 2871-2022 Determination of flex resistance of whole rubber shoes
1 Scope
This document provides the test methods for determining whether there are abnormal conditions, such as degumming and cracks between uppers, soles and foxing strips after repeated flex resistance tests on the whole rubber shoes under specified test conditions. This document gives two methods: Method A and Method B.
This document is applicable to tests for flex resistance of whole rubber shoes. The test method may be used as a reference for other types of shoes.
2 Normative references
The following documents contain provisions which, through reference in this text, constitute provisions 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 2941 Rubber - General procedures for preparing and conditioning test pieces for physical test methods
3 Terms and definitions
No terms and definitions are listed in this document.
4 Principle
While being flexed repeatedly, rubber shoes will be subjected to stress-induced deformation and material fatigue under the action of repeated tensile stress. In this case, degumming will occur between the upper and the foxing strip, between the upper and the outsole, and between the sole and the foxing strip; cracks (gaps) or fracture will occur on the upper, sole, and foxing strip. This test method is based on this principle above. In the test, take a whole rubber shoe assembled with a suitable bendable last or pressing block, and then place it on the shoe flexing tester, and carry out the flex resistance test for a specified times at the specified angle and frequency. Then measure the length of the crack (gap) on the sole of the rubber shoe and the degumming length between the foxing strip and the upper or between the upper and the outsole, and observe whether there are cracks, ruptures, or other abnormalities present on the upper, sole, and foxing strip.
5 Apparatus
5.1 Vernier caliper
Vernier caliper with a division value of 0.02 mm.
5.2 Inner length gauge
Inner length gauge with a division value of 1.0 mm.
5.3 Retractable tape measure
Retractable tape measure with a division value of 1.0 mm.
5.4 Folding resistance test instrument for Method A
5.4.1 The flexing angle is adjustable and falls in the range of 35° to 60°.
5.4.2 The flexing frequency is adjustable and falls in the range of 50 times/min to 300 times/min.
5.4.3 The function of automatic shutdown according to the preset number of flexing times is available.
5.4.4 A blowing device shall be provided to dissipate heat from the flexing portion of a specimen.
5.4.5 Bendable last: The bendable last is equipped with a steel shaft of φ (5.5±0.5) mm × (40.0±2.0) mm on the vertical line from the first metatarsophalangeal joint to the axis of the last bottom; the maximum bending angle is not less than 60°. After the steel shaft is installed, the surface of the last bottom shall not be concave or convex.
5.5 Folding resistance test instrument for Method B
5.5.1 The flexing angle is adjustable and falls in the range of 0° to 90°.
5.5.2 The flexing frequency is adjustable and falls in the range of 50 times/min to 180 times/min.
5.5.3 The function of automatic shutdown according to the preset number of flexing times is available.
5.5.4 Pressing block: It is installed at the front sole area of the specimen for fixation. Its specifications are shown in Table 1 and Figure 1. It is made of rubber with a Shore A hardness greater than 75.
Foreword i
1 Scope
2 Normative references
3 Terms and definitions
4 Principle
5 Apparatus
6 Specimen conditioning and test atmosphere
7 Test conditions
8 Test procedures
9 Test results
10 Test report
Annex A (Informative) Determination of flexing line in Method B
