Overview
ISO 13145:2023 - Rubber - Determination of viscosity and stress relaxation using a rotorless sealed shear rheometer - specifies a laboratory method to measure the rheological behaviour of raw or compounded rubber under defined conditions. The standard defines procedures to determine viscosity (via constant strain, temperature and frequency oscillatory testing) and stress relaxation (via constant static strain and temperature tests), providing the elastic and loss components of the complex shear modulus (G′, G″) and the torque decay during relaxation.
Key topics and requirements
- Measurement principle: Torque is measured for a rubber test piece sealed in a temperature-controlled cavity with one die oscillating; complex torque S* is resolved into elastic (S′) and loss (S″) components and converted to G* using geometric factors.
- Apparatus: Requirements for a rotorless sealed shear rheometer include:
- Two heated, sealed dies forming a test cavity; die surfaces with anti-slip grooves and low-friction seals.
- Dies manufactured from stiff, wear-resistant material (recommended minimum hardness ~50 HRC) and dimensional control (cavity dimensions typically controlled to ±0.2%).
- Die closure system capable of sustaining a specified closing force (guideline minimum ~7 kN).
- Torsional oscillation drive for one die and a sensitive torque-measuring system.
- Heating and temperature control with measurement resolution ±0.1 °C and steady-state control accuracy ~±0.3 °C (range 60 °C to 200 °C).
- Test variables: Specified strain amplitude, frequency (single frequency selected in the standard), and temperature for viscosity tests; constant static strain for stress relaxation tests. The relation between oscillation angle and strain is given (y = θ/φ for conical dies).
- Calibration and reporting: Calibration schedule and precision data are addressed; test report and result expressions (G′, G″, tan δ, torque decay) are specified for reproducibility.
- Scope limits: Applies to raw or compounded rubbers; intended as an alternative to Mooney viscometer measurements under comparable shear-rate conditions.
Applications - who uses it
- Rubber manufacturers and compounders for processability and mixing control.
- R&D laboratories studying viscoelastic properties and formulation effects.
- Quality control labs needing reproducible viscosity and relaxation metrics.
- Test instrument manufacturers developing or validating rotorless sealed shear rheometers.
- Useful where a rapid, repeatable rheological assessment is required, and as an alternative or complement to Mooney viscometer testing.
Related standards
- ISO 1382 - Rubber vocabulary (terms and definitions referenced).
- ISO 18899:2013 - Guide to the calibration of test equipment (normative reference).
- ISO 289-1 (Mooney viscometer) is discussed in the introduction as a common comparative method.
Keywords: ISO 13145:2023, rotorless sealed shear rheometer, rubber viscosity, stress relaxation, rheological properties, Mooney viscometer, complex shear modulus, G′ G″ tan δ.