Key principles.
Stiffness change
Temperature where amorphous plastic transitions stiff to flexible.
Rigid
Below Tg, plastic glassy and rigid. Standard service.
Rubbery
Above Tg, plastic rubbery. Generally avoid.
Tm matters more
Crystalline plastics melting point (Tm) more relevant.
Various Tg
PC 150°C. ABS 105°C. Nylon 50-60°C. PEEK 143°C.
Below Tg
Service temperature below Tg. Safety margin 20-30°C.
FAQ
Plastic loses stiffness above Tg. Service must stay below for structural applications.
Tg: amorphous transition (gradual). Tm: crystalline melting (sharp). Different mechanisms.
PC 150°C. ABS 105°C. Nylon (PA66) 60°C. PEEK 143°C. PVC 80°C. PS 100°C.
Continuous service ≤ Tg minus 20-30°C safety margin. Structural applications.
Glass fiber raises effective service temperature, less Tg dependent.
Specify continuous service temperature. Material/process select per Tg.
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