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.
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 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.
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Want to learn more? Read “Oil Seals 101, Part 2”.