ISO 4647:2021

Overview - ISO 4647:2021 (H-pull test)

ISO 4647:2021 specifies a standardized laboratory method to determine the static adhesion between textile cord and vulcanized rubber using the H-pull test. The procedure measures the force required to pull a single cord axially out of a vulcanized rubber block (the test-piece resembles an “H”). It applies to cords made from natural or man‑made fibres and is primarily intended for tyre cord, with applicability to similar rubber products. The method is limited to cords of linear density up to 800 mg/m (tex) and yields comparative data useful for judging service quality, bearing in mind results are influenced by cord history and rubber compound.

Key topics and technical requirements

• Test principle: Shear adhesion measured by axial pull of a cord embedded in rubber strips (H-shaped test piece).
• Test-piece dimensions: Nominal strip width 6.4 mm and thickness 3.2 mm; embedded cord length typically fixed (can be 5 mm to 10 mm for very high/low adhesion - different lengths are not directly comparable).
• Materials: Any agreed combination of rubber compound, textile cord and adhesive; protective fabric (e.g., cotton) and protective film used during moulding.
• Mould and preparation: Mould designs and cord groove widths recommended (0.8 mm for ≤560 tex; 1.2 mm for >560–800 tex); care required to remove rubber “flash”.
• Apparatus:
  • Tensioning device providing ~0.49 N ± 0.1 N during assembly (e.g., 50 g ±1 g mass).
  • Tensile-testing machine per ISO 5893 with traverse rate 100 mm/min ± 10 mm/min and class 1 force accuracy.
  • Test-piece grips (two types described - note: grip type can affect results).
• Calibration and quality control: Calibration schedule provided (Annex B); Annex A describes preparation of silicone‑rubber‑faced bars used in some mould methods.
• Environmental/handling: Specifies conditioning, timing between vulcanization and testing, test temperature (standard and elevated), and reporting requirements.

Practical applications and users

Who uses ISO 4647:

• Tyre manufacturers and tyre-cord suppliers for quality control and supplier acceptance.
• Rubber compound formulators assessing adhesion performance of compounds.
• Test laboratories and R&D teams comparing cord treatments, adhesives or vulcanization conditions.
• Product certification and failure‑analysis labs evaluating cord–rubber interface integrity.

Why it’s used:

• To compare adhesion performance across cord types, rubber compounds and processing variants.
• To support material selection, batch acceptance, and process optimization for tyre and rubber-product manufacture.

Related standards

• ISO 5893 - specification for tensile test machines (constant rate of traverse).
• ISO 18899:2013 - guide to calibration of rubber test equipment.
• ISO 23529 - general procedures for preparing and conditioning rubber test pieces.

Keywords: ISO 4647:2021, H-pull test, static adhesion, rubber vulcanized, textile cord, tyre cord, adhesion test, test piece, mould, tensile-testing machine.