Apr. 17, 2023
Oil seals, also referred to as shaft seals, are widely used to prevent the leakage of medium (such as oils and grease) along a rotating shaft. This leak prevention is primarily achieved by the sealing element which can be made from a wide range of materials that are chosen according to each application. They are commonly used in gearboxes, hydraulic cylinders, and related components.
An oil seal is designed to perform three major functions: to prevent lubricants from leaking outside the seal even under high pressure, to act as a barrier to retain the lubricating oil, and to prevent dirt and other contaminants from entering the unit.
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Oil seals normally consist of three basic components: the sealing element, the metal case, and garter spring.
The sealing element makes up the interior of the oil seal, and the materials commonly used are:
The metal case is the exterior (or frame) of the oil seal, the principal function of which is to give rigidity and strength to the seal. The material of the case must be selected depending on the environment where the seals are to be used. Often the metal case is covered by the same rubber material used in the sealing element, which also helps seal the exterior of the oil seal in the housing bore. Common case material types are:
The garter spring is located at the end of the primary sealing lip and used to apply pressure to the sealing lip against the shaft. Common garter spring material types are:
Global O-Ring and Seal carries a full line of oil seals in all industry standard sizes and has the ability to create custom oil seals. If you are a distributor or user of oil seals who may have need for our services, contact us today to speak with one of our team members, request a no-obligation quote, or place an order from our extensive inventory at GlobalOring.com.
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Want to learn more? Read “Oil Seals 101, Part 2”.
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Bill has served in the sealing industry for more than 25 years, and founded Global O-Ring and Seal nearly 10 years ago.
What is Oil Seal | Purpose , Types of Oil Seal , Advantages
OIL SEAL
Oil seals, also known as shaft seals, are radial lip type seals which are primarily used for retaining lubricants in equipment having rotating, reciprocating or oscillating shafts. The rotating shaft application is most common.
An oil seal normally consists of three basic components: the sealing element, the metal case and the spring. The purpose of the sealing element is to stop the fluid from leaking between the shaft and housing. The metal case will give rigidity and strength to the seal while it is being held in the bore or recessed groove. The garter spring ensures constant pressure and maintains the radial force to the shaft, flattening the sealing edge to a defined width. The garter spring maintains the radial force exerted by the sealing lip around the shaft surface. All materials must be selected depending on the environment in which the oil seal will function.
The performance of these seals depends to a large extent on a suitable unit load being maintained at the seal-shaft interface. These seals withstand a pressure of 15PSI and their working depends on parameters like shaft diameter, shaft speed, working temperature, service conditions, etc
Oil seals or shaft seals are an integral part in any rotating and moving part assembly. Oil seals find great deal of usage in gearboxes, hydraulic cylinders, etc. The usage of the seals in areas concerned with motion also earns them a name of “Dynamic Oil Seals.”
The purpose of the oil seals is
To act as a physical barrier retaining the lubricating oil where it is bound to be.
To prevent thelubricating oil from leaking outside even under high pressure of the oil.
To act as a barrier and prevent dirt, contamination and other external entities from entering the system containing the lubricating oil.
Constructional Aspects of an Oil Seal:
1. The oil seal consists of a metal ring as the inner skeleton which provides the structural stability to the oil seal.
2. The outer skin is made of nitrile rubber and various other materials which are used based on the requirement.
3. The spring on the lip of the oil seal tends to provide support to the lip and prevents the lubricant from leaking outside and also prevents the entry of contaminants from outside.
TYPES OF OIL SEAL
Double Lip Oil Seals
In this an auxiliary lip is provided along with the regular sealing lip. The additional dust lip protects the main sealing lip against dust and other fine solid contaminants and therefore this type is recommended for use in polluted environments. To achieve a long lifetime a suitable lubricant between the two sealing lips should be applied.
Advantages:
– Good static sealing
– Compensation of different thermal expansion
– Reduced risk of fretting corrosion
– Effective protection against air side contaminants
– Higher bore surface roughness is allowed
– Installation in split-housings
– Modern lip design provides low radial forces
Duplex Oil Seals
Sometimes, two different kinds of fluids leak from one chamber to another and gets mixed up. Here, this type comes as a boon. This is a metal inserted duplex type oil seal recommended on such assembly where mix-up of two different fluids is to be prevented.
Oil Seals without Spring
This type of oil seal can withstand only low speed and friction. It is recommended in places where thick fluid or grease is to be sealed. This is not recommended for difficult applications.
Material:
Oil seals are made out of nitrile synthetic rubber with steel stiffener rings. Other rubbers such as viton, silicon, neoprene or poly acrylic can be used for specific applications. The stiffener rings may be stainless steel or brass where highly corrosive fluids are to be sealed. Springs are generally made of spring steel to IS: 4454:Gr.ll or from stainless steel or bronze for corrosion resistance
Type A Oil Seals
Sealing of lip type seal is normally a result of an interference fit between the flexible sealing element, usually augmented by spring pressure and a shaft. Fluid retention is based on the precise amount of lip contact pressure. In most lip seals, increased fluid pressure in the sealed area causes lip contact pressure on the shaft to increase.
Advantages:
– Good static sealing
– Compensation of different thermal expansion
– Reduced risk of fretting corrosion
– Higher bore surface roughness is allowed
– Installation in split-housings
– Modern lip design provides low radial forces
Type B Oil seals
This is almost similar to that of ‘A’ type seal. But this has the metal case placed outside. When the housing is rough, temperature is high and working conditions are severe, this type is preferred.
Type C Oil seal
Type ‘C’ oil seal has an additional cup inserted into the outer cup of ‘B’ type. The supplementary metal inner ring provides a superior stiffness. This type is recommended for use in heavy polluted environments. As the static sealing between housing and metallic shell is limited, low viscosity media can “creep”.
Advantages:
– Very good fitting stability avoiding pop-out of the seal
– Modern lip design provides low radial forces
– Superior radial stiffness, especially for very large diameters
– Cost effective for expensive elastomer materials
– Suitable for use in combination with axial seal
Material used for Oil Seal :
Based on the application of the oil seal, the outer skin layer tends to differ. Here are some types of the materials used for the outer skin of the oil seal.
1. Nitrile rubber – The commonly used material for oil seals
2. Silicone – Used in specific applications where only light loads are applied.
3. Poly acrylate
4. Fluroelastomer also popularly known as Viton. – The high temperature resistant material used in places where temperature is more than 120 Degree Celcius.
5. PolytetraFluroEthylene (PTFE)
The oils seals require certain prerequisites to be maintained for their proper working. They are as follows:
a) The shaft on which the oil seal is to be mounted should be ground with the surface finish or surface roughness between 0.2 to 0.8 Microns. It is best for the shaft to be hardened atleast to 40 – 45 HRc in order to prevent groove formation on the shaft due to the pressure exerted by the spring.
b) The area where the oil seal is seated is to be plunge ground in order to prevent wear grooves that normally tend to wear out the lip of the oil seal at a faster rate.
Sachin Thorat
Sachin is a B-TECH graduate in Mechanical Engineering from a reputed Engineering college. Currently, he is working in the sheet metal industry as a designer. Additionally, he has interested in Product Design, Animation, and Project design. He also likes to write articles related to the mechanical engineering field and tries to motivate other mechanical engineering students by his innovative project ideas, design, models and videos.
All About Oil Seals
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.
The basic principle of an oil seal is fairly straightforward. It is installed adjacent to the bearing, with the flexible lip against the rotating shaft and the casing pressed into the housing to hold the seal in place. It’s important that the sealing lip is lubricated to prevent it from overheating as a result of any generated friction. It’s also crucial to understand which type of seal is appropriate for your particular machinery. Before selecting your seal, consider the environment, temperature, pressure and shaft speed of your machine, as well as the type of medium the seal will come into contact with during operation. These considerations will all determine the size, colour, and type of lip material or sealing element to choose, and whether it can be sealed in or sealed out.
Oil seals are made from multiple compounds and materials. Some of the oldest, still in use today, are leather and felt compounds. The trend in mass production, however, has seen a move towards synthetic rubber or elastomers. Nitrile is by far the most popular material but developments in PTFE have created a surge of interest in buyers needing seals for high-speed shaft rotation applications. Viton is taking over from the polyacrylic and silicone, as it works better in high-temperature applications and has a high-resistance to abrasion and harmful chemicals.
There are various sizes of industrial and ordinary oil seals, ranging from 0 to 33cm (13in). These varieties are also designed for different temperatures. As long as your seal matches the original equipment it’s intended for, you can be sure your machine will perform at its best. For further guidance and information regarding oil seals, don’t hesitate to contact our knowledgeable team. We are always available to assist you with your bearing, seal and gasket needs.
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FOUNDED IN 1993
China SBT Oil Seal is an international company integrating design, research and development, production and processing.
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