Overview
ISO 16945:2014 - "Corrugating medium - Determination of the edge crush resistance after laboratory fluting" defines laboratory procedures to measure the edge crush resistance (CCT) of a corrugating medium after it has been fluted. The standard is intended for corrugating mediums used in the manufacture of corrugated fibreboard and describes two widely used test methods: immediate testing after fluting (20–25 s) and testing after reconditioning (30–35 min). Results are reported as edge crush resistance (kN/m) and optionally as an edge crush resistance index (Nm/g) normalized by grammage.
Key topics and technical requirements
- Test principle: Pass paper between heated corrugating rolls (laboratory fluting), mount the fluted strip with flutes vertical, apply compressive load and record maximum force per unit length.
- Two methods:
- Immediate test (CCT0): compress 20–25 s after fluting.
- Reconditioned test (CCT30): recondition 30–35 min under standard atmosphere before test.
- Specimen preparation: Cut at least 10 test pieces, nominally 12.7 mm ± 0.1 mm wide and 152 mm ± 0.5 mm long (length in machine direction), edges parallel within 0.01 mm.
- Fluter and fluting conditions: Rolls heated to 175 °C ± 8 °C; typical roll speed 4.5 r/min ± 1.0 r/min and specified inter-roll force (documented specification). Roll geometry and matching are specified to ensure reproducible flute profiles.
- Apparatus: Matched corrugating rolls (fluter), a holder that grips 6.35 mm width of specimen with flutes vertical, and a motor-driven fixed-platen compression tester conforming to ISO 13820.
- Conditioning and sampling: Conditioning per ISO 187 and sampling per ISO 186.
- Calculations & reporting:
- Edge crush resistance CCT = F / l (report to 0.01 kN/m).
- Edge crush resistance index Y = 1000 × CCT / grammage (report to 0.1 Nm/g; grammage per ISO 536).
- Test report must include method used (CCT0 or CCT30), mean, standard deviation, number of valid tests and any deviations from the standard.
- Precision: Annex A summarizes round-robin precision data and repeatability/reproducibility guidance.
Practical applications and users
ISO 16945:2014 is used for:
- Quality control at paper mills and corrugating medium suppliers to verify edgewise compression performance after fluting.
- Incoming inspection by corrugated-board manufacturers and converters to accept or qualify medium lots.
- R&D for developing flute profiles, adhesive/process settings and new medium formulations.
- Failure analysis and box design validation where edgewise strength of the medium influences the compression strength of corrugated boxes.
Primary users: test laboratories, packaging engineers, quality managers, material suppliers and standards/technical committees.
Related standards
- ISO 186 - Sampling to determine average quality
- ISO 187 - Standard atmosphere for conditioning and testing
- ISO 536 - Determination of grammage
- ISO 13820 - Calibration/description of compression-testing equipment
- ISO 7263 - (related fluting equipment specification)
- Relevant TAPPI methods and ISO technical reports referenced in Annex A for precision data
Keywords: ISO 16945:2014, edge crush resistance, CCT, corrugating medium, laboratory fluting, corrugated fibreboard, edge crush resistance index, compression tester, grammage, conditioning.
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