Overview
ISO 306:2022 - Plastics - Thermoplastic materials - Determination of Vicat softening temperature (VST) defines standardized laboratory methods to measure the Vicat softening temperature (VST) of thermoplastic materials. The VST is the temperature at which a flat-ended indenter penetrates 1 mm into a specimen under a specified load while the sample is heated at a controlled, uniform rate. ISO 306:2022 updates prior editions to reflect modern testing equipment and allows use of commercial universal units.
Key topics and technical requirements
- Four test methods:
- A50: 10 N load, 50 °C/h heating rate
- B50: 50 N load, 50 °C/h heating rate
- A120: 10 N load, 120 °C/h heating rate
- B120: 50 N load, 120 °C/h heating rate
- Defining VST: temperature at which the indenter reaches 1 mm penetration into the thermoplastic specimen.
- Apparatus:
- Flat-ended indenter (hardened steel, nominal area 1 000 mm²; diameter ≈ 1.128 mm ±0.008 mm).
- Penetration-measuring device readable to 0.01 mm (dial gauge or LVDT). Spring thrust of analogue gauges must be accounted for; combined downward thrust ≤ 1 N.
- Temperature sensor with 0.1 °C resolution and ±1 °C accuracy; sensor tip located close (≤ 12.5 mm) to indent area and not touching specimen.
- Heating options: liquid-filled bath, fluidized bed or direct-contact heating unit. Liquids must be chemically stable and not affect specimens.
- Control & calibration:
- Heating rate tolerance: (50 ±5) °C/h or (120 ±10) °C/h. Rate-check over every 6 min interval (5.0 ±0.5 °C or 12.0 ±1.0 °C).
- Blank tests and correction terms for frame thermal expansion; if correction ≥ 0.02 mm it must be recorded and applied.
- Specimen preparation, conditioning and reporting: references to ISO specimen preparation and conditioning practices; sections on precision and required test-report information.
Applications and users
- Who uses it: materials and polymer engineers, quality control labs, R&D teams, compliance officers, product designers and procurement professionals.
- Practical uses:
- Material selection and specification for temperature-sensitive applications (housings, connectors, consumer goods).
- Quality control for production batches and supplier acceptance testing.
- Comparative ranking of thermoplastics by softening behavior.
- Input to design limits, thermal performance data sheets and safety assessments.
Related standards
Keywords: ISO 306:2022, Vicat softening temperature, VST, thermoplastics, Vicat test, heating rate, indenter, penetration testing, polymer testing.
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