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
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 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®, 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.
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.