Overview
ISO 1432:2021 specifies the Gehman test - a static torsional procedure for determining the low-temperature stiffening behavior of vulcanized or thermoplastic rubber. The standard covers measurement of torsional stiffness from room temperature down to approximately −120 °C, defining apparatus, calibration, specimen preparation, conditioning and stepwise or continuous test procedures for both liquid and gaseous heat-transfer media.
Key topics and technical requirements
- Test principle: torsional stiffness is measured by connecting the specimen in series with a calibrated spring wire, turning the wire 180° and recording the angular twist (Gehman test).
- Apparatus: torsion head with friction-free angle indication, test piece rack, temperature control and circulation (stirrer or fan), and suitable bath or chamber.
- Torsion wires: tempered spring wires with nominal torsional constants of 0.7, 2.8 and 11.2 mN·m (2.8 mN·m is the reference wire in disputes).
- Specimen dimensions & preparation: length 40 mm ± 2.5 mm, width 3 mm ± 0.2 mm, thickness 2 mm ± 0.2 mm; prepare and condition per ISO 23529.
- Temperature control & measurement: sensor near specimens, measurement accuracy to within ±0.5 °C, medium maintained to ±1 °C.
- Heat-transfer media: liquids or gases that remain fluid and inert at test temperatures. Examples used in practice:
- silicone fluids (down to ≈ −60 °C)
- ethanol (down to ≈ −73 °C)
- methylcyclohexane cooled by liquid nitrogen (down to ≈ −120 °C)
- Procedure highlights:
- reference measurement at 23 °C ± 2 °C in air or liquid;
- turn specimens 180°, record angle after 10 s;
- cool to minimum test temperature, then increase temperature either stepwise (5 °C steps) or continuously (~1 °C/min) while recording stiffness.
- Results and calculations: the standard prescribes expression of results as torsional modulus, relative modulus and apparent torsional modulus of rigidity, with calibration requirements given in Annex A and precision information in Annex B.
Applications and users
ISO 1432:2021 is used to:
- Evaluate low-temperature performance and stiffening of elastomers for automotive seals, hoses, gaskets, cryogenic components and cold-climate products.
- Support materials selection, formulation development, quality control and compliance testing where cold flexibility and stiffness are critical.
Primary users include rubber manufacturers, materials and test laboratories, R&D teams, OEMs in automotive and aerospace, and standards/quality engineers.
Related standards
- ISO 23529 - specimen preparation and conditioning for rubber tests (normative reference)
- ISO 18899 - guide to calibration of test equipment (normative reference)
Keywords: ISO 1432:2021, Gehman test, low-temperature stiffening, rubber testing, torsional modulus, torsion apparatus, cryogenic rubber testing.
Open preview (PDF)Rubber, vulcanized or thermoplastic — Determination of low-temperature stiffening (Gehman test)
