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ISO 75 and ISO 306 with Zwick's HDT/Vicat instruments

Zwick's HDT/Vicat instruments are designed to enable easy, convenient testing in research and development, goods inwards checks and product monitoring, as well as for education and training purposes. Different versions of the instruments are available, with up to 6 testing stations according to requirements. A connected PC allows convenient test-sequence parameterization and measured-value display (option).


Convenient parameterization and evaluation via testXpert II

Vicat ISO 306 - HDT ISO 75

Heat deflection temperature to ISO 75 and ISO 306

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.

  1. Heat deflection temperature to ISO 75 (HDT) Heat deflection / distortion temperature)
  2. Vicat softening temperature (VST) to ISO 306

Heat deflection temperature to ISO 75

Heat deflection temperature to ISO 75 (HDT)

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.

Test sequence

  • A specimen is placed in a 3-point flexure test kit and loaded with the test weight required to achieve the flexural stress specified in the standard.
  • The temperature of the oil-bath is then increased at a uniform heating rate of 120K/h.
  • The temperature at which the specimen reaches the deflection specified in the standard is determined.

Vicat softening temperature to ISO 306

Vicat softening temperature (VST) to ISO 306

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.

Test sequence

  • The indenter is placed on the plastic specimen and loaded with a defined test weight.
  • The specimen is then heated at a specified rate.
  • The VST is obtained when the needle penetrates to a depth of 1 mm.
  • ISO 306 and ASTM D1525 are identical with regard to the test sequence.

ISO 306 distinguishes between 2 procedures and 2 different heating rates, giving 4 different test methods in all:

  1. Method A = 10 N load, heating rate 50 K/h
  2. Method A = 10 N load, heating rate 120 K/h
  3. Method B = 50 N load, heating rate 50 K/h (preferred method for comparative tests ISO 13050-1)
  4. Method B = 50 N load, heating rate 120 K/h

Vicat Dry and dry method (ISO 306)

Vicat Dry and 'Dry Method'

The classical medium used for heat transfer is oil. An alternative is the 'dry method', in which heat transfer is via heating blocks. A special version of the Zwick instrument, the Vicat Dry, is available for this method.


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