Oil seal knowledge

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Oil seal: An oil seal is a mechanical component used to seal oil – the most common liquid in transmission systems. It separates the parts of the transmission that require lubrication from the output components, preventing lubricant from leaking out as well as allowing external dust, mud, and other impurities from entering. Any part of a rotating housing that contains liquid lubricant and is connected to the outside world requires an oil seal. The shaft seal of the first internal combustion engines was a simple packing, which was replaced by leather lip seals in the 1920s. In the 1930s, after synthetic rubbers compatible with mineral lubricants were introduced, a wide variety of lip seals with different appearances made from them began to appear. Currently, they can be roughly classified into: felt oil seals, rubber oil seals, composite material oil seals, labyrinth-type oil seals, spiral-type oil seals, mechanical oil seals, etc., and there are also various split-type oil seals that are easy to install. Felt oil seals were among the earliest types of oil seals to be used; however, due to their poor sealing performance, rapid wear, and short service life, they are no longer widely used. Currently, rubber bone oil seals are widely used due to their good sealing performance. However, due to limitations in their material, their sealing life is short and they need to be replaced frequently, which results in downtime costs associated with replacing these seals being much higher than the cost of the seals themselves. ●The sealing principle of traditional rubber skeleton oil seals is such that, before use, the inner diameter of the seal’s lip is smaller than the shaft diameter (for rotary shafts, the outer diameter of the seal’s lip is larger than the diameter of the hole), resulting in a certain degree of interference. After installation, the oil seal exerts a certain radial pressure on the rotating shaft due to the interference fit of its lip and the contraction of the self-tightening spring (oil seals with springs). At the same time, under the clamping force generated by the contraction of the spring, the oil seal is able to overcome the gaps caused by shaft vibration and runout while the shaft is rotating, allowing the lip of the oil seal to remain in close contact with the surface of the shaft. During operation, the oil seal lip and the surface of the rotating shaft form a sealed contact ring. Under the action of oil pressure in the sealed chamber, the lubricating oil seeps between the oil seal lip and the rotating shaft to form an extremely thin layer of oil film. Driven by the surface tension of the oil, an oil film forms a \"crescent shape\" between the surface of the rotating shaft and the outer edge of the oil seal lip, preventing the oil from leaking out and thus serving a sealing function ； On the other hand, it can also serve as a lubricant between the oil seal lip and the shaft surface. http://www.aigindustries.com.cn/cptp/image2.jpg ●Material properties of traditional rubber-skeleton oil seals. The quality of an oil seal’s sealing performance depends to a large extent on the properties of the material used in that seal. Therefore, understanding the properties of oil seal materials is a prerequisite for achieving an ideal sealing effect. Common materials for rubber oil seals are as follows: Nitrile rubber (NBR): It exhibits good resistance to mineral oils and vegetable oils, is wear-resistant and age-resistant, and also has excellent elasticity. It is a versatile elastic material that can handle inorganic substances, alkalis, and acids at low concentrations or low temperatures. Fluororubber (FKM): Fluororubber maintains excellent physical properties even at high temperatures (up to 250 degrees Celsius). They usually also have very good resistance to oils, fuels, solvents, and chemicals. It is not recommended for use with low-molecular-weight esters and ethers, as well as homocyclic amines. Under operating conditions that readily lead to rapid aging and deterioration of other elastomeric materials, fluororubber is the first choice to consider. Silicone rubber (SIL): The physical and mechanical properties of silicone rubber—such as tensile strength, breaking strength, and ultimate elongation—are inferior to those of other rubbers. However, it has a very low coefficient of friction and minimal compression set, making it suitable for use under certain specific conditions. It has good resistance to mineral oils, but is not resistant to gasoline, acids, and chlorinated solvents. With the development of modern industry, there is an increasing demand for oil seals that can withstand harsh operating conditions such as high temperature, high pressure, and high speed. Moreover, the continuity of production requires these oil seals to have a longer service life. Therefore, more new types of oil seals have been developed, such as lip-type oil seals made from new composite materials, labyrinth-type oil seals, spiral-type oil seals, and mechanical oil seals. These new types of oil seals have been upgraded from various aspects such as materials, sealing design, and structural design, in order to meet the requirements of high temperatures, high pressures, and high speeds; they also improve the sealing performance, reduce wear, and extend service life. The introduction of split-type oil seals with stable performance has effectively eliminated the need for complicated equipment disassembly and assembly, making the replacement of oil seals simpler and faster, and thereby maximizing the continuity of production. The latest oil seal technology not only prevents oil leakage but also stops external contaminants from entering the bearing housing, thus protecting the bearings; for this reason, it is also referred to as a bearing protector.