Overview
ISO 8942:2010 - Rubber compounding ingredients - Carbon black - Determination of individual pellet crushing strength - defines standardized laboratory procedures to measure the individual pellet crushing strength (hardness) of pelletized carbon black used in the rubber industry. The standard specifies two test methods: Method A (pellets 1.4–1.7 mm, referenced to ASTM D5230) and Method B (pellets ~1.0 mm) and gives rules for sampling, testing, calculation and reporting of results.
Key topics and requirements
- Scope: Two methods for determining crushing strength of carbon black pellets for rubber compounding.
- Sampling: Use ISO 1124 sampling procedures and a single-stage riffle sample splitter to obtain a representative ~100 g sample.
- Pellet selection (sieving):
- Method A: sieve aperture range typically 1.4 mm–1.7 mm (ASTM D5230 approach).
- Method B: 1.0 mm sieve to select ~1 mm pellets for tighter distributions and higher precision.
- Test equipment:
- Manual pellet hardness tester: two parallel plates, constant force rate (5–25 cN/s), force measurement accuracy 1 cN.
- Automatic pellet hardness tester: automated loading, constant-rate force application, endpoint detection, data storage; accuracy ±0.4 cN.
- Sieve shaker and ISO 565-compliant sieves.
- Procedure:
- Method B manual: position pellet, apply force at 25 cN/s until fracture, record force in centinewtons.
- Automatic: follow manufacturer instructions; test 20, 50 or 100 pellets depending on required precision.
- Results & reporting:
- Report average force (centinewtons) rounded to nearest millinewton and maximum individual crushing strength.
- For 50 or 100 pellets, optional reporting of top-five average and highest 10% averages.
- Test report must reference ISO 8942:2010, method used, sieve details, number of pellets, any deviations, and test date.
Practical applications and users
- Quality control and process control in rubber compounding and carbon black production.
- Suppliers and buyers of carbon black specifying pellet hardness to ensure good dispersion, bulk handling and conveying performance.
- Laboratory analysts performing physical characterization of pelletized carbon black.
- Engineers optimizing pelletization processes or troubleshooting pellet breakage during transport and mixing.
Performance precision
- Annex A reports precision data. For Method B the pooled repeatability is about 18.1%; reproducibility is provided for interlaboratory context - use these figures when assessing measurement variability.
Related standards
- ISO 1124 - Carbon black shipment sampling procedures
- ISO 565 - Test sieves (nominal opening sizes)
- ASTM D5230 - Automated individual pellet hardness (Method A reference)
- ISO/TR 8942:1988 - previous technical report replaced by ISO 8942:2010
Keywords: ISO 8942:2010, carbon black, pellet crushing strength, rubber compounding, pellet hardness, Method A, Method B, ASTM D5230.
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