Leather Fold Fastness: Ultimate Durability Testing Guide

This standard specifies the method for determining the fold fastness of dry or wet leather and leather coatings.

This standard applies to all types of leather with a thickness less than 3.0mm.

Principle of the test

The upper test face of the specimen folds inward and is clamped inside a movable fixture; the lower test face folds outward and is clamped inside a fixed fixture. The upper moving clamp drives the specimen to move, and after a specified number of cycles, changes in the specimen are evaluated.

Test method

Sample preparation

(1) Sampling: Conducted according to QB/T 2706.

(2) Sample preparation: According to QB/T 2707, use a mold knife to cut at least 4 samples from the grain surface, ensuring that at least 2 long sides are parallel to the ridge line and at least 2 are perpendicular to the ridge line.

(3) Dry-state regulation: Air conditioning is performed according to the requirements of QB/T 2707 for dry-state samples.

(4) Wet preparation:

• Place the sample in a glass dish containing distilled or deionized water with a depth of no less than 10mm.
• Place the glass tray in the dryer, vacuum it to ≤4 kPa and hold for 2 minutes, then release the pressure.
• Repeat the vacuum and release processes twice.
• Remove the sample, use absorbent paper to absorb excess moisture, and immediately perform the wetness test.

Clamping and testing

(1) Initial Settings:

• Open the upper and lower fixtures, ensuring the gap is at least twice the specimen thickness.
• Start the motor so that the EF edge of the upper fixture is parallel to the upper edge of the lower fixture.

(2) Specimen clamping:

• Fold the test face of the sample inward so that the two long edges are close together, then clamp into the upper clamp (the folded edge should be tightly pressed against the lower edge of the upper clamp and one end against the screw).
• Wrap the fixture with the two corners that are not clamped outward and downward on the specimen, so that the two surfaces make contact.
• Fix the free end of the specimen in the lower fixture, allowing it to extend vertically, with the force applied to just tighten the specimen.

(3) Selection of test counts:

• Dry state: can be selected from 500, 1000, 5000, 10000, 20000, 25000, 50000, 100000, 150000, 200000, 250000 cycles.
• Wet state: selectable from 500, 1000, 2500, 5000, 10000, 20000, 25000, and 50000 cycles.
• Wet state over 50,000 times: Every 25,000 tests, the sample must be removed for observation and recording, then rewetted and returned for further testing.

Inspection and evaluation

(1) Examination method:

• Stop the testing machine, remove the sample, and fold it in reverse along the longitudinal axis.
• Under good lighting, inspect any damage to the bent part with the naked eye and magnifying glass (ignore the clamping part).

(2) Damage assessment (if needed):

• Bend the specimen along its axis and gently stretch it with a finger or metal clip.
• The damage is divided into:

– Cracks: visible to the naked eye.

– Small cracks: visible under a magnifying glass.

– Microcracks: Visible under a 25x stereomicroscope.

• Record content:

– Coating color variation.

– The number and development trends of coating cracks.

– Abnormal changes in coating adhesion or interlayer adhesion.

– Powder or flake appearance in the coating.

– Color contrast of cracks, powders, or flakes.

(4) Special Operations:

If you need to assess loose leather structure, cut the bent part (it is recommended to cut after all tests are completed to avoid damaging the sample).