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Cold Flow Properties PTFE migrates – i.e. flows – under constant tensile or compression stress as early as at room temperature. This property depends on the level of compression or tensile stress applied, the period of exposure to such stress as well as on temperature.
Due to these properties PTFE parts exposed to higher stress or load levels are either enclosed, thus preventing migration, or PTFE compounds with clearly improved pressure resistances are used. The utilization of modified PTFE is another suitable measure to reduce cold flow.
Stress-Strain Diagrams for Unfilled PTFE(2)
 
Deformation under Load (Cold Flow) of PTFE Compounds and Compounds Based on Modified PTFE
The characteristic values for compression stress, which occurs more frequently than tensile stress in field applications, are shown in the following diagrams. These graphs clearly show the lower deformation of PTFE compounds with glass fiber, carbon or bronze fillers. When evaluating cold flow it is obvious that there is a significant gain in performance when using compounds based on modified PTFE.
Deformation under load according to ASTM D621(2)
(15 N/mm2, 100 h load + 24 h restoring time (= permanent deformation), 23°C, compressed specimen: Ø 10 mm, 10 mm high)
 PTFE
 Modified PTFE
Deformation under load of PTFE, PTFE Compounds and the Modified Alternatives(2)
Test temperature: 23°C Test cycle: 100 h, no restoration
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Deformation under load of PTFE, PTFE Compounds and the Modified Alternatives(2)
Test temperature: 150°C Test cycle: 100 h, no restoration
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PTFE unfilled
 Mod. PTFE unfilled |
PTFE + 25% glas
 Mod. PTFE + 25% glas |
 PTFE + 25% carbon
Mod. PTFE + 25% carbon |
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