Propylene (fluorinated ethylene)
When included, the garter spring applies pressure to the sealing lip against the shaft, ensuring a tight seal. The choice of material, like that of the case, largely depends on the environment of use.
Vulcanizates of several fluoroelastomers, listed in Table 14.1, were exposed to a standard 5W-30 engine oil, ASTM Service Fluid 105, for up to 6 weeks at 150°C (302°F).5 The oil was changed weekly, but was not aerated. Retained elongation was measured after exposure for 1, 2, 3, and 6 weeks; data are shown in Fig. 14.3. The results indicate that bisphenol-cured FKM-A500 VDF/HFP copolymer, FKM-B600 VDF/HFP/TFE terpolymer, and peroxide-cured FEPM-7456 TFE/P/VDF terpolymer lost most of their original elongation over the course of the test exposure, indicating considerable additional cross-linking occurred by reaction with amine- and phenol-containing oil additives. The other fluoroelastomers showed better retention of elongation, being much less susceptible to additional crosslinking. Note that FEPM-7456 contains a high level of VDF (about 30%), while FEPM-7506 contains a relatively low VDF level (10–15%) to serve as cure site for bisphenol curing. The other FEPM types contain no VDF.
These oil seals are the best for applications involving high temperatures. It’s suitable for temperatures between -4 degrees Fahrenheit and 392 degrees Fahrenheit. Also, it’s highly resistant to acids, dissolvent materials, and other chemicals. Viton (FKM/FPM) oil seals can run at a maximum speed of 38 m/s.