Machinery Lubrication

Machinery Lubrication Jan Feb 2016

Machinery Lubrication magazine published by Noria Corporation

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BACK PAGE BASICS seal will need to be resized for the added sleeve. When installing lip seals, make certain the job is done correctly. I've seen guys install seals with a punch so they wouldn't have to take the extra time to locate the right tool. One wrong thump from a hammer can tear sealing material, puncture the seal casing or push the seal through the housing. Always take time when installing lip seals, and lubri- cate the shaft and seal adequately to prevent tearing or sticking. Also, verify that the lip seal is the correct size. There must be an interfer- ence fit in the bore and on the shaft. Not having the proper size can result in the seal rotating on the shaft or becoming dislodged from the equipment. Maintaining Lip Seals To help your lip seals stay as healthy as possible, you must keep your oil clean, cool and dry. Any contamination in the oil will get into the contact patch and deteriorate the shaft and elastomer. Likewise, the hotter the oil becomes, the more wear and tear will be exerted on the seal. Lip seals should also be kept as clean as possible. Painting over a seal or having dirt built up around it can create exces- sive heat and quickly degrade the elastomer. Failure Causes If you've ever pulled out a lip seal and seen a groove cut into your shaft, this is probably due to particle contamination. Without good breathers, all the dust and dirt that gets into your equipment can destroy not only your bearings and gears but also your shafts and lip seals. Of course, it is always better to exclude contaminants than to try to remove them. Too tight of a fit between the lip seal and the shaft can also create a groove. Excessive temperature is the leading cause of seal failures. As temperatures rise, the lubricating film becomes thinner, resulting in dry running conditions. Elevated tempera- tures can also lead to the elastomer cracking or blistering. Nitrile seal life decreases by a factor of two for every increase in tempera- ture of 57 degrees F. The oil level can be another factor in a lip seal's lifespan if it is too low. In this situa- tion, the seal will eventually become hard and not be able to follow the shaft, resulting in leakage. Cold temperatures can cause seal embrittlement. Selecting the proper lubri- cant and seal material can help in these colder environments. Seals may also fail due to shaft runout. This can be caused by misalignment, shaft imbalance and manufacturing inaccuracies, to name a few. Different elastomers will tolerate varying amounts of runout. Adding a garter spring will help with any runout that can be measured. Excessive pressure is another potential cause of lip seal failure. If you've ever walked past a pump or gearbox and noticed oil leaking out the seal, the sump has somehow overpressurized and leaked to the point of least resistance. This can be attributed to clogged breathers or non-vented sumps. Applications with higher pressures should employ a special seal design . How to Inspect a Lip Seal Among the things to look for when inspecting lip seals include deteriorated or cracked elastomer. This is a telltale sign that heat is an issue. Also, verify that the lip seal is still in place. I've seen a few pumps that had the wrong seal installed. Upon startup, the vibration and movement caused the seal to come out of the bore and spin on the shaft. Any oil leaks around the seal should be a red flag to investigate further. Worn seals can cause leakage, plugged breathers or damaged bearings that allow radial motion. When analyzing any lip seal failure, look at the seal, shaft and bore. While inspecting the shaft, you typically will see a contact or wear zone where the lip seal was riding. This will appear as a black scuffmark where the elas- tomer has transferred to the shaft. Remember, in order to keep your lip seals in good operating order, you must maintain the sump. Cover all seals before painting, keep the oil at the proper level, make sure oil coolers are functioning correctly, and select the right seal design and material. If you are proactive in your approach to rebuilding and installing equipment, you can give your lip seals and machinery a fighting chance at survival. About the Author Garrett Bapp is a technical consultant with Noria Corporation, focusing on machinery lubri- cation and maintenance in support of Noria's Lubrication Program Development (LPD). He is a certified lubrication specialist through the Society of Tribologists and Lubrication Engineers (STLE) and holds a Machine Lubrication Technician (MLT) Level I certification through the Interna - tional Council for Machinery Lubrication (ICML). Contact Garrett at gbapp@noria.com. 70% of lubrication professionals say their plant uses lip seals to control contam- inant ingression, based on a recent survey at MachineryLubrication.com 64 | January - February 2016 | www.machinerylubrication.com Lip Seal Inspection Checklist Check for cracked or deteriorated elastomer Check for case damage Check to see if the breather is plugged Check equipment for excessive temperatures Check for oil leaks around the lip seal Lip seals are vital machine components. They keep oil or grease in and help keep contaminants out.

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