Rubber O-ring plane static sealing introduction

Plastic and rubber looks a clear distinction between two kinds of substances or materials, it is not true ,numbered security seals they are the same substance in different rendering. They are polymers, and at a certain temperature conditions can be transformed into each other . This transformation temperature is the polymer glass transition temperature Tg, which is one of the characteristic temperature of polymer .
Tg is bounded to , polymers exhibit different physical properties : Tg less polymer material is plastic ; Above the Tg , the polymer material is rubber . From the engineering point of view , the glass transition temperature is the upper limit temperature engineering plastics , use lower limit of rubber .
If a recipe EPDM sample test measured by obtaining the glass transition temperature is -53.6 ℃, after the glass transition sample starts to melt ( elasticity began to recover ) , near the peak position at 31.4 ℃ . This peak temperature is the maximum melting temperature of the material at this temperature for maximum heat absorption , and thus also the largest of its expansion , the greatest contribution to the sealing .
January 28, 1986 , the U.S. space shuttle Challenger exploded, the reason is on solid fuel propulsion rubber O-ring seal structure caused by improper design :
1, O -ring material selection improperly ;
2 , the night before take-off extremely low temperatures , resulting in decreased elasticity O-ring seal compression decline ;
3, O -ring should be designed to the outside rather than the inside , as in the inside of the combustion and expansion of the metal rapid heat transfer , so that compression of the O- ring is insufficient , security seals resulting in tragedy. So the problem is not trivial seal , seal design or choice worth pondering.