| 摘要 |
<p>Oil seals having, on an inner periphery thereof, a flat surface with a first predetermined shape helical pumping ribs, is provided. The oil seals have an excellent sealing properties for a long time of period as well as its initial stage in use. The oil seals further have a second helical pumping ribs on its frustoconical air-side surface, giving the oil seals a long life pumping property even after the first helical pumping ribs disappear from the flat surface. <IMAGE></p> |
