Heat resistance
The heat resistance is a measure of the temperature resistance of plastics . Because of their viscoelastic material behavior, there is no strictly defined upper operating temperature for plastics; instead, a substitute value is determined under a defined load. Two standardized methods are available for this.
Heat deflection temperature (HDT)
This in DIN EN ISO 75-1, -2, -3 (predecessor: DIN 53461) method described heat distortion temperature (HDT = heat deflection temperature ) using standard test specimens of rectangular cross section, preferably flat edge of a three-point bending at constant load to be suspended. Depending on the sample height of a so-called here is to achieve surface stress σ f of 1.80 (Method A), 0.45 (Method B), or 8.00 N / mm (Method C) by weights and / or springs , a force
upset.
- b: sample width
- h: sample height
- L: support spacing
The loaded samples are then subjected to heating at a constant heating rate of 120 K / h (or 50 K / h). If the deflection of the sample reaches an outer fiber elongation of 0.2%, then the associated temperature is the heat deflection temperature HDT ( English heat deflection temperature or heat distortion temperature ).
Typical HDT values for some unreinforced plastics are:
| Abbreviation | method | HDT [° C] |
|---|---|---|
| SECTION | A. | 79 |
| POM 1 | 91 | |
| POM 2 | 160 | |
| PBT | 50 | |
| PET | 65 | |
| PP 1 | B. | 82 |
| PP 2 | 115 |
Vicat method
The Vicat softening temperature (VST = Vicat softening temperature ) in accordance with DIN EN ISO 306 (precursor: DIN 53460) is measured with a needle (with a circular area of 1 mm²). This is loaded with a test force of 10 N (test force A) or 50 N (test force B). The test specimen with a permissible thickness of 3 to 6.4 mm is exposed to a defined heating rate of 50 or 120 K / h. The VST is reached when the indenter reaches a penetration depth of 1 mm. According to the standard, the test is only to be used for thermoplastics and provides information about the practical continuous use limit, which is around 15 K below the Vicat temperature.
By varying the boundary conditions there are four parameter combinations:
- VST / A50
- VST / A120
- VST / B50 (preferred method for comparative tests (ISO 10350-1)
- VST / B120
Typical Vicat softening temperatures (VST / A120) are:
| Abbreviation | VST [° C] |
|---|---|
| SECTION | 108 |
| PMMA | 125 |
| PP | 146 |
| Pc | 154 |