Oil Seals 101 - Part 1

Oil Seals 101 - Part 1

What is an Oil Seal?

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.

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Purpose of an Oil Seal

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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Construction of an Oil Seal

Oil seals normally consist of three basic components: the sealing element, the metal case, and garter spring.

1. Sealing Element

The sealing element forms the interior part of the oil seal, made from materials such as:

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• a. Nitrile Rubber (NBR) – the most commonly used material. It has good heat resistance and is resistant to salt solutions, oils, hydraulic oils, and gasoline. Operating temperatures range from -40 to 248°F (-40 to 120°C). Although effective in a dry environment, it's not recommended for prolonged use. This material, however, has poor chemical resistance.
• b. Polyacrylate Rubber (PA) – known as acrylic rubber, this material offers better heat resistance than nitrile and is suitable for high surface speed environments. Recommend operating temperatures range from -4 to 302°F (-20 to 150°C). It should not be used with water or at temperatures below -4°F (-20°C).
• c. Silicone Rubber (SI) – effective in a broad temperature range of -58 to 356°F (-50 to 180°C), it is chosen for its resistance to both low temperatures and heat. Its high lubricant absorbency reduces friction and wear, making it ideal for crankshaft seals. It does, however, have poor resistance to hydrolysis and should not be used in oxidized or hypoid oils.
• d. Fluorocarbon Rubber (FKM) – known under the Chemours trade name Viton®, it offers excellent chemical resistance and superior high-temperature performance.

2. Metal Case

The metal case forms the exterior or frame of the oil seal, providing rigidity and strength. The choice of material for the case depends on the operating environment. Sometimes, the metal case is coated with the same rubber material used in the sealing element for added sealing effectiveness in the housing bore. Common case materials include:

• a. Carbon Steel – the most typical material used in oil seals.
• b. Stainless Steel – used for applications requiring resistance to water, chemicals, or corrosion, including many FDA applications.

3. Garter Spring

The garter spring is located at the end of the primary sealing lip, applying pressure to the lip to ensure it presses against the shaft. Common materials for garter springs include:

• a. Carbon Steel – used with regular lubricants.
• b. Stainless Steel – used when resistance to water, seawater, and chemicals is necessary.

Oil Seals From Global O-Ring and Seal

Global O-Ring and Seal offers a comprehensive range of oil seals in all industry-standard sizes and can produce custom oil seals. Distributors or users in need of our services are encouraged to contact us to speak with a team member, 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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