Overview
ISO 7763:2024 - Testing of paper and board - Compressive strength of a sample held in S-shape specifies an S‑test method for measuring the compressive strength of paper and board strips fixed into an S‑shape in the machine direction. The method is intended for papers with a grammage of 80 g/m² to 220 g/m² and produces an S-test value expressed in kN/m. The test is analogous to the Short‑Span Compression Test (SCT) and shows good correlation with corrugated medium test (CMT) load‑curve behaviour.
Key topics and technical requirements
- Scope and applicability
- Test applicable to papers with grammage 80–220 g/m²; other grammages can give unreliable results.
- Test principle
- A 15.0 ± 0.1 mm wide strip is clamped so that it undergoes double bending and assumes an “S” shape; compressive force is applied parallel to the paper plane until buckling/failure.
- Apparatus and dimensions
- Test piece width: 15.0 ± 0.1 mm; minimum length 90 mm.
- Free clamping length: 4.0 ± 0.1 mm; lateral offset between clamps: 1.00 ± 0.05 mm.
- Clamping jaw length: 30 ± 2 mm.
- Clamping force: (2 300 ± 500) N and jaws must grip full width without burrs.
- Test speed: 3.0 ± 1.0 mm/min (movable clamp toward fixed clamp).
- Procedure and measurements
- Follow specified clamp closing sequence to avoid pre‑stressing the strip.
- Record maximum load F (nearest 1 N) or S directly in kN/m (two decimal places).
- Calculation: S = F / b (F in newtons, b in millimetres → result in kN/m).
- Minimum requirement: obtain at least 20 valid measurements for a test series.
- Calibration, inspection and conditioning
- Force measuring device calibration (load cell) across the application range; clamp spacing and offset checks; sample conditioning per ISO 187; sampling per ISO 186.
- Precision
- Repeatability and reproducibility evaluated by interlaboratory study (see Annex A).
Applications and users
- Who uses ISO 7763:2024
- Paper and board manufacturers, quality control laboratories, R&D teams, converters of corrugated board.
- Practical applications
- Predicting compressive performance of corrugating medium and corrugated board.
- Quality assurance during production and material selection for packaging.
- Correlation with SCT and CMT helps troubleshoot corrugator performance and board strength issues.
- Providing standardized test data for supplier specifications and product comparisons.
Related standards
- ISO 186 - Sampling to determine average quality (normative reference).
- ISO 187 - Standard atmosphere for conditioning and testing (normative reference).
- Related test types: SCT (Short‑Span Compression Test) and CMT (Corrugated Medium Test) - for comparative and correlative evaluations.
Keywords: ISO 7763:2024, S-test, compressive strength, paper testing, paper and board, grammage, clamping jaws, corrugated medium, SCT, CMT, ISO 186, ISO 187.
