Oil Seals 101 - Part 1 | Global O-Ring and Seal

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.

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 makes up the interior of the oil seal, and the materials commonly used are:

• a. Nitrile Rubber (NBR) – this is the most commonly used material. It has good heat resistance properties and has good resistance to salt solutions, oils, hydraulic oils, and gasoline. Operating temperatures are recommended from -40 to 248⁰ F (-40 to 120 deg.C). Nitrile also functions well in a dry environment, but only for intermittent periods. The disadvantage of this material is poor chemical resistance.
• b. Polyacrylate Rubber (PA) – also known as acrylic rubber, this material has better heat resistance than nitrile. PA is also recommended for a high surface speed environment. Operation temperatures are recommended from -4 to 302⁰ F (-20 to 150⁰ C). Polyacrylate rubber should not be used with water or in temperature below -4⁰ F (20⁰ C).
• c. Silicone Rubber (SI) – these compounds operate effectively in a broad temperature range of -58⁰ F to 356⁰ F (-50 to 180⁰ C). Silicone rubber is a leading choice for its resistance to both low temperatures and heat. The high lubricant absorbency of the material minimizes friction and wear. These oil seals are usually used as crankshaft seals. Silicone has poor resistance to hydrolysis and should not be used in oxidized or hypoid oils.
• d. Fluorocarbon Rubber (FKM) – is widely known under the Chemours (formerly Dupont™) trade name of Viton® and offers the best resistance to chemicals and superior performance to high temperatures.

2. Metal Case

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:

• a. Carbon Steel – the most common material used in oil seals.
• b. Stainless Steel – for applications that require resistance to water, chemicals, or corrosion. (Stainless steel metal cases are also recommended for many FDA applications.)

3. Garter Spring

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:

• a. Carbon Steel – which is used in conjunction with regular lubricants.
• b. Stainless Steel – which is used when resistance to water, seawater, and chemicals are involved.

Oil Seals From Global O-Ring and Seal

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.

Oil seals play an important role in many machines and industrial equipment. Oil is commonly used as a lubricant. It reduces friction so that machinery parts can move more smoothly and with less resistance. Leaks, however, can result in the loss, which leaves machinery parts susceptible to damage and failure.

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What Are Oil Seals?

Oil seals are ring-shaped mechanical seals that are designed to prevent the leakage of oil or other lubricants. Also known as lip seals and grease seals, they are commonly used around shafts and similar rotating or moving machinery parts.

Most machines with moving parts need lubricant to reduce friction. Lubricant, however, is only effective if it stays in place. Oil seals help to contain oil or other lubricants to the machinery parts with which they are used. They fit snugly around rotating shafts, thereby containing the oil. At the same time, oil seals also protect machinery parts from environmental contaminants like water, dirt, dust and debris.

How Oil Seals Work

Oil seals work by filling the space around the parts with which they are used. When placed around a shaft, for instance, the oil seal will form a barrier that contains the shaft’s oil while simultaneously preventing external environmental contaminants from entering the shaft.

When the shaft rotates, the oil seal’s lip follows the shaft’s surface, maintaining a dynamic seal. The garter spring ensures constant contact between the lip and the shaft, providing the necessary radial tension to create an effective seal. This design ensures that lubricants are retained, friction is reduced, and wear and tear are minimized.

Parts of an Oil Seal

They may look like ordinary O-rings consisting of a single piece of elastomeric material, but oil seals feature multiple parts. Oil seals typically feature a lip, case and spring.

The case is the part of an oil seal that holds it in place. The spring is a ring of energized material that provides radial tension. Finally, the lip is an outer rim or edge that serves as the primary sealing element. Once installed, the lip will sit directly on the surface of the shaft while the spring applies tension.

In Conclusion

Oil seals do a lot of heavy lifting to keep machines running smoothly. Their main job is to keep oil and other lubricants where it belongs. Additionally, oil seals keep out dirt, water and other junk from reaching machinery parts, which could otherwise result in damage.

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