Overview
EN ISO 306:2022 - Plastics - Thermoplastic materials - Determination of Vicat softening temperature (VST) - specifies laboratory methods to measure the temperature at which thermoplastics begin to soften rapidly. The standard defines four standardized test methods (A50, B50, A120, B120) that differ by applied load and heating rate, producing comparable VST values used for material specification, quality control and design.
Key topics and technical requirements
- Test methods:
- Method A50: 10 N load, 50 °C/h heating rate
- Method B50: 50 N load, 50 °C/h heating rate
- Method A120: 10 N load, 120 °C/h heating rate
- Method B120: 50 N load, 120 °C/h heating rate
- Principle: temperature at which a flat-ended indenter penetrates 1 mm into the specimen under a specified load while temperature rises uniformly.
- Apparatus:
- Rigid frame with vertically moving rod and hardened steel indenter (flat tip diameter ≈ 1.128 mm ± 0.008).
- Heating media options: liquid-filled bath, fluidized bed, or direct-contact heating unit; specimens immersed ≥ 35 mm when non-gaseous media used.
- Temperature and penetration measurement devices per referenced thermocouple/RTD standards.
- Quality checks:
- Blank tests on low-expansion specimens (e.g., Invar) to determine apparatus correction; corrections ≥ 0.02 mm must be recorded and applied.
- Test conditions & reporting: specimen preparation, conditioning (ISO standard atmospheres), precision and test-report requirements are defined. Informative annexes compare heating methods and give repeatability/precision data.
Applications and who uses it
- Material suppliers: specify VST in data sheets to indicate softening behavior of thermoplastics.
- Quality control laboratories: routine testing for lot acceptance and production control.
- R&D and product design engineers: select materials and assess service temperature limits where softening is critical (e.g., housings, components under load).
- Certification and regulatory bodies: verify compliance with material performance requirements.
- Test-equipment manufacturers: design instruments compatible with EN ISO 306 methods and universal testers (note: 2022 edition updated to support commercial universal equipment covering ISO 75 and ISO 306).
Related standards (normative references)
Keywords: EN ISO 306, ISO 306:2022, Vicat softening temperature, VST, Vicat test, thermoplastic materials, plastics testing, material specification, heating rate, penetration test.
