Overview
ISO 7323:2006 defines a laboratory method - the parallel-plate plastometer technique - for measuring the plasticity number and recovery number of raw, unvulcanized compounded and reclaimed rubber stocks. These two indices quantify aspects of the material’s viscoelastic behaviour: the plasticity number indicates flow/softness under compression, while the recovery number indicates the elastic recovery after load removal. The method is widely used in rubber testing and quality control to predict processability (ease of forming, die swell) of unvulcanized rubber materials.
Key topics and technical requirements
- Principle: A cylindrical test piece of volume 2.00 ± 0.02 cm3 (typically 16 mm diameter × ~10 mm height) is preheated, compressed at a total force of (49 ± 0.5) N, and its height under load (h1) and after recovery (h2) are measured.
- Plasticity number = 100 × h1 (mm).
Recovery number = 100 × (h1 − h2) (mm).
- Apparatus:
- Parallel-plate plastometer with parallelism within 1° and dial indicator gauge calibrated to 0.01 mm.
- Oven (circulating-air) controllable to ±1 °C to house the plastometer.
- Dial micrometer with a presser foot (≈25 mm diameter) and dead weight load (800 ± 30) mN for recovery height measurement.
- Test conditions:
- Preferred test temperatures: (70 ± 1) °C and (100 ± 1) °C; other temperatures may follow ISO 23529.
- Preheat test piece for (15 ± 0.5) min.
- Typical reading intervals: plasticity at 3 min under load; recovery at 1 min after removal of load (user may select other intervals and must report them).
- Sampling and preparation: Follow ISO 1795 and ISO 23529 for sampling, cutting and conditioning. Test three specimens and report the median values.
- Reporting: Include sample description, preparation method and timings, test temperature, load and timing, and the reported plasticity and recovery numbers.
Applications and users
- Quality control and incoming inspection in rubber manufacturing and compounding plants.
- R&D and formulation labs assessing processability, die swell, and handling characteristics of unvulcanized rubbers.
- Suppliers and purchasers requiring standardized material property data for specification compliance.
- Testing laboratories performing comparative or acceptance testing of raw, compounded, or reclaimed rubber stocks.
Related standards
- ISO 1795 - Sampling and preparative procedures for raw natural and synthetic rubber.
- ISO 23529 - General procedures for preparing and conditioning test pieces for rubber physical tests.
Keywords: ISO 7323:2006, plasticity number, recovery number, parallel-plate method, plastometer, unvulcanized rubber testing, viscoelastic properties, rubber processability.
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