Machinery Lubrication magazine published by Noria Corporation
Issue link: http://www.e-digitaleditions.com/i/629709
nyone in the mainte- nance field who has repaired a pump or gearbox knows the one component that always seems to get replaced during a rebuild is the lip seal. It usually is damaged when being extracted or during disassembly. Perhaps the lip seal is the reason the piece of equipment was pulled from service due to leakage. Regardless, the fact remains that lip seals are vital machine components. They keep oil or grease in and help keep contami- nants out. Lip seals seem to be on almost every piece of plant equipment, so why not take the time to learn how to correctly select and install them. Purpose of Lip Seals The primary purpose of a lip seal is to exclude contaminants while retaining lubri- cants. By nature, lip seals function by maintaining friction. They can be used in a variety of applications from slow-moving equipment to high-speed rotation and in temperatures from below freezing to more than 500 degrees F. To be effective, a lip seal must maintain proper contact with its rotating counter- part. This will be influenced by proper selection, installation and care of the seal once it is installed. I've often seen a new lip seal start to leak as soon as it was put into service. This typically is due to improper installation. Other seals will leak initially but then stop leaking once the seal material has seated to the shaft. Selecting a Lip Seal Maintaining functional lip seals begins with the selection process. When choosing a material, you must consider the operating temperature, the lubricant in use and the application. The most common lip seal material is nitrile (Buna-N). This material functions well at temperatures of minus 40 degrees F up to 275 degrees F. Nitrile lip seals cover most applications in industry from new equipment to replacement seals. They have excellent resistance to petroleum oils, water and hydraulic oils, but what really sets these seals apart is their low cost. Another affordable option is Viton. Its temperature range is minus 40 degrees F to 400 degrees F, depending on the specific compound. Viton seals provide good resis- tance to petroleum oils and can be employed with gasoline and transmission fluid. Other seal materials that can be used with petroleum oils include Aflas, Simiriz, carboxilated nitrile, fluorosilicone, highly saturated nitrile (HSN), polyurethane, polyacrylate, FEP and silicone. All of these materials have specific applications and precise temperature ranges. Be sure to take into account the process and environ- ment before selecting a seal material or making a switch, as the correct material can prevent a costly failure. Lip Seal Construction Once the seal material has been selected, the next step is to consider the seal's construction. In the past, a simple lip seal consisted of a leather strap on a wheel axle. Today's lip seals have multiple parts that affect how the seal performs. There are various contacting patterns as well as IMPORTANCE of Lip Seals in Controlling A BACK PAGE BASICS C o n t a m i n a t i o n C o n t r o l g A rre t t BA pp | Nori a Corpor at ioN 62 | January - February 2016 | www.machinerylubrication.com The CONTAMINATION