|
Thermal Resistance
Thermal Resistance The thermal resistance of PTFE ranges from -260°C up to +260°C, with short-term resistance up to +300°C. (e.g. no brittling in boiling helium at -269°C). This temperature range is not achieved by any other plastic. Permanent service temperatures, however, depend on the respective load and stress factors. With regard to field applications, this means that PTFE exposed to moderate mechanical stress can be used at temperatures from -200°C up to +260°C.
Temperature Limits of Selected Fluoroplastics 2)
Thermal Expansion of PTFE and Modified PTFE
|
Relative change in length of unfilled PTFE depending on temperature(2)
Crystallite transformation at 19°C (triklinc -> hexagonal)
|
Linear expansion coefficient of unfilled PTFE depending on temperature(2)
 Crystallite transformation at 19°C (triklinc-> hexagonal)
|
When designing assembly components the relatively high thermal expansion of these materials must be taken into consideration:
10 – 30 °C: = 21 x 10-5 1/K
30 – 100 °C: = 11 x 10-5 1/K
30 – 200 °C: = 13 x 10-5 1/K
30 – 300 °C: = 19 x 10-5 1/K
If PTFE assembly components are cooled down from +20°C to -260°C this will result in an app. 2% shrinkage in length. The development of the linear expansion coefficient shows two conspicuous ranges:
- At 19°C there is a transformation within the crystal lattice (<19°C triclinic, >19°C hexagonal).
- At app. 327°C there is an even higher degree of unsteadiness, the crystal melting point
Note
- When performing accurate measurements of PTFE components with narrow tolerance specifications it is imperative to perform the measurements at a temperature of 23 +/- 2°C.
- PTFE compounds generally have a lower thermal expansion. The correlation between temperature and thermal expansion is shown below
Thermal expansion of unfilled PTFE and PTFE compounds, measured lengthwise and crosswise to the pressing direction(2)
Test piece: diameter 16 mm, length 40 mm
 crosswise  lengthwise  crosswise = lengthwise
PTFE virgin
 |
PTFE with 60% bronze
 |
Compound HS 21059
 |
PTFE with 25% glass fibers
 |
Compound HS 21037
 |
PTFE with 10% glass fibers and 10% graphite
 |
PTFE with 25% carbon
 |
PTFE with 30% carbon and 3% graphite
 |
(2) Diagrams
The information provided in these diagrams is based on comparative values determined by ElringKlinger. These values have been obtained under specifically defined conditions and may not be transferred exactly to other applications. The diagrams, however, allow you to draw a basic comparison between our compounds and semifinished products.
|
|
|
|
|
