Nov. 11, 2024
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:
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.
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.)
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.
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”.
What is an oil seal?
Seals are essential to protecting the bearings of any rotating shaft assembly -They prevent contaminants such as dirt, dust and water, while also preserving the system’s lubricant.
Choosing the right oil seal
Oil seals come in many different types and materials depending on their application. Determining the material is vital to ensuring your equipment is operating at its best performance. For example, your equipment may need to run at higher temperature applications, such as an engine seal for a jet engine, you may need to choose a specific material for your oil seals to run properly. In this article, we will explore the most popular and utilized materials in the industry, as well as touch on some of the more unique options out there.
Oil seal materials
Nitrile
The first material that we are going to look at is Nitrile Buna- N 70 or NBR for short.
NBR is recommended for the majority of standard applications and is the most commonly used rubber (elastomer) material. This is because of Nitrile's compatibility with most environments as well as its relatively low cost. Generally nitrile is used for disposable non-latex gloves, footwear, automotive transmission belts, synthetic leather, hoses, o-rings, gaskets, oil seals, and more.
The temperature range of nitrile is −35° to 120 °C (−30° to 250 °F). Due to this wide range, NBR seals can be used for gas oil, silicone oil, animal/vegetable oils and fat, hydraulic liquid as well as hot and cold water. In addition, NBR is oil resistant and has an excellent abrasion resistance, so for any application that demands shock absorbers, NBR is a perfect choice to go with.
Some disadvantages of NBR are poor ozone, sunlight and weather resistance as well as limited high temperature and flame resistance. For higher temperature resistance, a much better material to use is Silicone.
Silicone
Silicone compounds or “VMQ” offers a wide range of traditional operating temperatures starting at -60°C to 200°C (-140°F to 392°F).
In addition to its excellent temperature resistance, it is also resistant to ozone, light, and weather conditions. Silicone can be typically found in the food and medical industry as well as in hydraulics and pneumatics. It is often the preferred material for o-rings, moulded parts and flat seals but is also commonly used for electric insulators due to the material’s translucency and flexibility.
Although extremely flexible, silicone does have some disadvantages. Many silicone compounds have poor tensile strength, tear resistance, and abrasion resistance. If you are looking for a material that offers a higher tensile strength, while still offering high temperature resistance, look no further than Viton®.
Viton®
Viton®, a trademarked name of The Chemours Company, is a specific brand of synthetic rubber commonly used in o-rings, oil seals, gaskets, chemical resistant gloves, and other molded products.
Due to having a higher density, Viton has the widest temperature range of -40°F to over 400°F (-40°C to over 240°C) making it a perfect choice for higher temperature applications. Viton® also has the largest range of chemical resistance, i.e., it is resistant to silicone oil and grease, mineral/vegetable oil and grease, aliphatic, aromatic, and chlorinated hydrocarbons, non-flammable hydraulic fuels as well methanol fuels, and more.
Although it does have a higher tensile strength and longer wear times than other materials, it is recommended to be used in dry-running applications sparingly or intermittently.
While Viton offers a superior temperature and chemical range than other materials, it can be more expensive than the others as well. Let’s take a look at an alternative that is easier on the wallet, Polyacrylate.
Polyacrylate is a great compromise between cost and quality. It has a high performing temperature and chemical range, but not to the extent of the range of Viton. The temperature ranges from 31°C to 148°C (-25°F to 300°F). Polyacrylate is primarily used in automotive transmissions and hoses but also found in shaft seals, gaskets and o-rings, due to offering a high resistance to hot oil and oxidation. While Polyacrylate is a great alternative to other high temperature resistant materials that are more expensive, it does have a poor water compatibility and cold flexibility. The best situation for Polyacrylate is an environment where heat and oil resistance but cost is the major issue. And while these 4 different materials cover a wide range of applications, there are even more materials out there designed for very specific niches in mind.
Summary
If you are looking for the highest temperature resistant oil seals, Perfluoelastomer can go up to 600°F. If you are more concerned for low temperature, Chloroprene can go all the way down to 40°F, which is why it is used most commonly for refrigeration. And if FDA applications or medical devices are your primary concern, Butyl , the all petroleum compound, will be your best choice. As you can see, when choosing the right material to work with, you must analyze several other key components to help choose the right one.
Hopefully after reading this article, you have a better understanding of why choosing the right materials for oil seals is so important. Remember, if you have any questions about industrial oil seals and supplies, please contact us and we would be more than happy to help.
Oil Seals | Material
Mar 13, 2018
Oil seals play a crucial role in all rotating and moving part assembly as they act as a physical barrier to retain lubricants, whilst excluding dirt, moisture and other contamination. They are manufactured in a wide range of sizes and specifications to meet several demanding sealing applications across industries. This post, which has two parts, discusses some of the must know things about oil seals. Read on to understand the seals better!
General Features of Oil Seals
Designed to offer optimum sealing performance, oil seals guarantee extreme durability even under high-peripheral speed. They are light-weight, compact, and exhibit high self-lubricating performance. As oil seals are manufactured using high-grade materials, they last long without showing the signs of any kind of hardening, softening or ageing.
Types of Oil Seals
As mentioned earlier, oil seals are available in varied designs to best match the applications. A few of the commonly available types include:
Type A single lip rubber coated w/spring
Type ADL double lip rubber coated w/spring
Type AO single lip rubber coated – no spring
Type AODL double lip
Type B single metal lip-metal case w/spring
Type BDL double lip
Type BO single lip – metal case
Type BODL double lip metal case
Type C single lip full metal case w/spring
Choosing the right seal is important as it determines the sealing performance by effectively preventing the leakage of lubricating oils and the ingress of contaminants.
Materials of Choice
Oil seals are made from several materials. However, the material must be chosen considering several parameters including operating temperature, environment, pressure, and maximum shaft surface speed, among others. The most commonly used materials for oil seal construction are as follow:
PolyTetraFluoroEthylene (PTFE)
Fluoroelastomer ( Viton )
Silicon
Poly Acetal
Nitrile
General Purpose Polyurethane
Nitrile Buna Rubber
Fluorocarbon
Perfluoroelastomer
Polyacetal
Thermoplastic Elastomer
PTFE Filled Polyamid
Hot Water Resistant Polyurethane
Hodrogenated Nitrile
Ethylene Propylene
Fluoro-Silicone
Polyetheretherkeytone
Polyamid
Polytetrafluoroethylene*
Composites
Ultra High Molecular Weight Polyethylene
Applications of Oil Seals
Oils seals find immense applications in agriculture, automotive, construction, material handling, mining, oil and gas, and so on. They are used in the assembly of:
Conveyors
Elevators
Engines
Grinding Mills
Pipelines
Wind Turbines
So far, we have discussed features, types, materials used in the construction, and applications of oil seals. In the next post, we will discuss few more general things about oil seals.
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FOUNDED IN 1993
China SBT Oil Seal is an international company integrating design, research and development, production and processing.
No. 68, Hua'an Street, Renze District, Xingtai City, Hebei Province, China
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Won many honorary certificates through a number of patented inventions
