Heat deflection temperature

The heat deflection temperature is a measure of the temperature stability of plastics. Due to their viscoelastic material behavior, there are no plastics for strictly defined upper operating temperature, a surrogate measure instead determined under a defined load. These are two standard methods.

Heat distortion temperature ( HDT)

This in DIN EN ISO 75-1, -2, -3 ( precursor: DIN 53461 ) Method of temperature of deflection described (HDT = heat deflection temperature) used standard test specimens of rectangular cross section, which are preferably flat edge of a three-point bend subjected to constant load. Depending on the level of the sample is thereby to achieve a so-called surface stress? F of 1.80 (Method A), 0.45 (Method B) or 8.00 N / mm ² (method C) weights and / or springs a force

Applied.

  • B: sample width
  • H: height of the sample
  • L: support distance

Subsequently, the loaded sample to heating at a constant heating rate of 120 K / h (or 50 K / h) to be suspended. Achieved thereby the deflection of the sample has a outer fiber strain of 0.2 %, the corresponding temperature is the heat distortion temperature HDT ( heat deflection temperature or german heat distortion temperature).

Typical HDT values ​​for some unreinforced plastics are:

Vicat method

The Vicat softening temperature (VST Vicat softening temperature = ) according to DIN EN ISO 306 ( precursor: DIN 53460 ) is measured with a needle ( with a circular area of ​​1 mm ²). This is loaded with a test load of 10 N (Test A) or 50 N (Test B). The specimen and having a maximum thickness of 3 to 6.4 mm is subjected to a defined heating rate of 50 and 120 K / h. VST is reached when the penetration reaches a depth of 1 mm. The test is to be applied according to standard only for thermoplastics and gives an insight into the practical continuous use limit, which is about 15 K below the Vicat temperature.

By varying the boundary conditions, four parameter combinations are:

  • VST/A50
  • VST/A120
  • VST/B50 (preferred method for comparative testing (ISO 10350-1 )
  • VST/B120

Typical Vicat softening temperatures ( VST/A120 ) are:

  • Material testing
  • Plastics Technology
Polybutylene terephthalate
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