Seal manufacturers are responding to the need for commercial vehicle operators to reduce maintenance and downtime through improved seal designs. In general, seals are designed to work with either grease or oil lubrication systems in wheel bearing applications. For greased wheels, the main design criterion is to ensure that contaminants are excluded. For oil lubrication systems, the seal must retain oil while also excluding contaminants such as water and dirt from the road.
Increasing the life of seals means meeting customer requirements for maintenance-free seals over the ownership of the vehicle. Many suppliers offering all-wheel seals now offer their products with extended warranties, for example, that provide guaranteed service life. With a global market of around eight million seals for this sector annually, it’s vitally important to deliver products that live up to customer expectations. In its response to market needs, SKF’s sealing technology company, Chicago Rawhide, has introduced a new grease seal, Enduro, and has upgraded one of the products within its established Scotseal range.
For grease lubrication, Enduro has been designed especially for commercial vehicle trailers using greased bearings (for example, ROR axle applications). One of the key features of this seal is a three-lip design that offers superior performance in relation to the exclusion of water and other contaminants. Each lip acts as an individual barrier to contamination, and between each lip a bead of grease provides additional protection. The nature of the lip design also provides superior sealing and long life. The grease beads inserted during manufacture also help the sealing system deal with the high temperature profiles found in grease lubrication systems. Heat is a major cause of seal and bearing failure, and the new seal design can withstand wheel end temperatures up to150C.
Improved material technology is also incorporated into the Enduro seal. The seal is fabricated using hydrogenated nitrile butyl rubber (HNBR) which is impervious to attack and degradation by synthetic fluids and additives that can attack conventional nitrile butyl compounds. In addition, the material has a high resistance to abrasives that can become embedded in other compounds, thus causing leakage. The seal design also incorporates an outer covering of Bore-Tite material, with its characteristic green color, that provides a perfect seal against outer diameter leakage.
Other aspects of the grease seal design are a metal-to-metal press fit that prevents leaks occurring at the spindle. The sealing elements remain stationary with the axle such that the effects of centrifugal force are eliminated.
Scotseal PlusXL for oils
Oil lubrication places heavy demands on the seal design and the ScotsealPlusXL is a result of further development by Chicago Rawhide. The XL is an upgrade of an existing member of the Scotseal family, which has application in heavy trucks and trailer wheels. The XL also benefits from the incorporation of HNBR for the sealing side of the design and an ethylene propylene (EPDN) blended nitrile for the sleeve. These materials can resist temperatures well beyond the peak wheel end temperatures that can spike at 135C at start-up.
The ScotsealPlusXL design incorporates four sealing lips that prevent ingress of dirt and road splash while sealing in the lubricant. Grease packs between the sealing lips provide an added protection against road contamination. Also, the design incorporates a patented wave seal that helps sweep the oil back into the bearings. Its unique sinusoidal shape runs cooler and lasts longer than conventional straight-lip designs. The seal lips and sealing surfaces are locked inside the body of the seal so that it is protected from installation damage.
Careful control during manufacture means perfect matching. A key feature of the ScotsealPlusXL is that it can be mounted without the need for special tools. All that is required is to lightly lubricate the inside and outer diameter of the new seal with the lubrication being retained.
Written by Leslie Kern, Doug Fike and Ken Lark of Chicago Rawhide, USA, part of the SKF Group. Learn more at www.skf.com or www.chicago-rawhide.com