Oils seals need to form a very tight barrier with metal. The material best suited for this job is usually rubber. The rubber is treated to make it resistant to wear and corrosion by the oil and other present elements then shaped into specific contours depending on what type of seal it is making. Most oil seals are round, but the rubber used to make them can be smooth, undulating or cut in particular patterns. To keep the seal firm and in place, the base is created from an equally resistant metal around which the rubber is formed.
Different types of rubber are used depending on what type of fluid is being sealed. Nitrillic rubber is used with mineral oils, grease, diesel oils and water. Polyacryllic and silicon seals are used for motor oils, while flourelastomer rubber seals are used in a wide variety of fuel-related oils and can withstand a wide range of temperatures.
Orientation of Seal
Oil seals can be used in many different situations. Some may be placed inside machines in moving rods that need to have a seal as they move along their shafts. Others are used externally, such as piston seals that are exposed to other elements and need to keep contaminants from reaching the oil as well as keep the oil from escaping. Some seals are made to perform equally well both internally and externally.
V-ring seals have two different sections of rubber, divided into a thick base and thinner flap that extends out forming a right angle space between the two pieces. When the seal is placed on a pipe, the outer flap bends in, contracting a forming a tighter v-shape with the base rubber section. They are easy to install and do not need a perfect fit to perform well, but can only withstand so much pressure before breaking or wearing apart.
Labyrinth seals are wide seals created with many parallel grooves carved into the rubber, in effect creating a series of more simple seals designed to fit inside a shaft. This creates a tight maze that obstructs the oil from escaping, since leaks that make it past the first part are usually stopped later on by another groove of the seal. These seals are especially common in rotating mechanisms, where the rod needs to turn inside the shaft.
Many oil seals also include a thin spring next to the rubber. This spring is designed to force the rubber against the metal it forms that seal with, ensuring a stronger barrier against the oil. Springs create much stronger seals, but they also cause the rubber to wear away more quickly.