Thermoplastics testing.

Tests for the heat deflection temperature (HDT) and the Vicat softening temperature (VST) are said to form part of the fundamental characterization methods for plastics, and are described in ISO 10350-1. Thermoplastic materials do not exhibit an exact melting point marking the transition from a solid to liquid, so the Vicat softening temperature was introduced as a substitute for the melting point for measurement and test purposes. It defines the temperature at which a thermoplastic material begins to soften. The heat deflection temperature is an additional measurement parameter. A prismatic test specimen is flexed and then heated with a defined increase in temperature. The heat deflection temperature is reached when the specimen reaches a flexure value defined in the standards. Since this temperature result is dependent on the applied load, specimen geometry, heating rate and the chosen flexure value, the HDT is a value which allows different materials to be compared with one another. The company's product line includes manually operated HDT/Vicat Standard models with computerized calculations from the measured data. The HDT/Vicat Allround models additionally have computer controlled functions such as motorized lowering of the measuring stations, and the motor-driven application of test weights. Both models are available in different variants with one to six measuring stations. (Zwick) www.zwick.de