9.1 Introduction

Oil seals and "O" rings are used in all hydraulic systems, pumps, pistons, pipe connections, etc. An oil seal used for sealing a rotating member is called a rotary seal. "O" rings are also used for a similar purpose. Oil seals are used to protect shafts and bearings from ingress of dirt and foreign matter and egress of oil or grease. An oil seal generally consists of an outer circular metal part and an inner flexible member that does the actual sealing and is bonded to the metal part by chemical adhesive agents. The sealing member is made of rubber, either synthetic or natural as the case may be. The sealing lip of the flexible member is prepared by cutting away the flash that forms at the sealing edge during molding. A fine sealing edge provides adequate pressure on the shaft to prevent leakage.

The "O" rings are light and flexible and under compression they deform to follow the component parts to be sealed. "O" rings have a long life. They provide effective sealing under constant or varying pressure, high vacuum, and high or low temperatures. Rubber "O" rings have a circular cross section. In the molding of "O" rings, the flash line at 180 is avoided and the same is preferably provided at 45 on the cross section so that the sealing face is smooth. This is achieved using a proper mold design.

Natural rubber seals and rings are suitable for air, acetylene, cold ammonia gas, alcohols,...