HDT/Vicat Allround for Convenient Testing
Many plastics applications are placing increasing demands on heat resistance. An important value with regard to the temperature resistance of plastics is the heat deflection temperature. This can be divided into Vicat softening temperature and HDT (heat deflection temperature). In both methods an oil-bath is heated at a defined rate and the temperature is recorded at a deflection or indentation depth specified by the standard.
Vicat softening temperature (VST) provides a value for the temperature at which a thermoplastic material begins to soften rapidly. This temperature is determined using a needle-shaped indenter with a round cross-sectional area of 1 mm².
ISO 306 distinguishes between 2 procedures and 2 different heating rates, giving 4 different test methods in all:
Heat deflection temperature (HDT) (ISO 75-1/2/3) indicates the relative behavior of different types of material under load at elevated temperatures. It is determined for materials such as thermoplastics, hard rubber and duroplastic laminates.