- One of the primary functions of the oil seal is to prevent oil from leaking out of the engine. This is achieved through the use of a rubber or synthetic material that forms a tight seal around the shaft of the engine. As the engine operates, the oil seal remains in constant contact with the shaft, ensuring that no oil escapes. Over time, however, this constant friction can cause the seal to wear down, leading to leaks.
Steel or cast iron is generally used as the housing material.
Aluminum alloys and resin (materials with a large difference between the linear expansion coefficients) demand sufficient consideration (as there is a risk of failure due to the increased clearance with the oil seal at high temperatures).
There are a few options to remedy this situation:
Oil seals go by many names, such as shaft seals, dirt seals, grease seals, lip seals, and many other variations of these. They are essentially simple devices used in rotary shaft equipment to prevent lubricant from escaping and for excluding contaminants such as dust, dirt and water. An oil seal’s most important function, however, is that it protects every type of ball, sleeve and roller bearing in the rotating shafts. The seals also prevent the integration of two different fluids that shouldn’t mix, such as oil and water.

Double metal cased
As can be seen from the seal cross-section shown in Fig. 14.2, shaft seals are complex shapes that require advanced mold design and molding techniques (see Section 7.3 for discussion of fluoroelastomer molding). For some time, most shaft seals were made in the United States by compression molding. Injection molding of shaft seals is prevalent in Europe, and is being used increasingly in the United States. An advantage of compression molding is that preforms (usually rings cut from extruded tubing) are used that closely approximate the amount of stock required for the final parts, so compound waste is minimized. For injection molding, the amount of cured stock in the central sprue and runner (actually a thin sheet leading to the seal lip) is often large compared to the stock required for the final part, so the waste of high-cost fluoroelastomer may be high. Such waste is reduced in modern injection molding designs.
B
Oil seal characteristics
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When the bore and shaft centers are misaligned, seal life will be shortened because the wear will be concentrated on one side of the sealing lip.