Archive: Jun 2016

Extension of Service Life – The Role of Sealing

Bearings are fundamental to operating machinery across a diverse array of sectors, ranging from mining, electric motors, and machine tools to transportation, power generation, and robotics. Ensuring their longest possible service life is essential to preventing excessive wear; such wear can lead to system failures, often resulting in costly downtime to rebuild equipment.

Engineers can use a standard bearing lifespan expectation to calculate the likely longevity of their bearing supplies. Known as the L10 life (or also known as B90 or C90 life), the theorem explains that 90% of bearings will meet or exceed a particular number of revolutions when employed in particular work environments. However, this expectation is not guaranteed; bearing failure in real-world applications is actually much more common and significantly more complicated, affecting most systems long before the end of their predicted lifespan.

 Though many factors can maximize bearing service life, the most important consideration is proper sealing — recent studies indicate that the majority of bearing failures are caused by contaminated bearing oil. By using the best quality seals available, engineers can prevent or substantially lessen contamination, extending bearing life significantly while improving equipment uptime and protecting against system breakdowns.

Two Principal Sealing Systems

To protect bearings, seals help to reduce excessive temperatures by efficiently retaining lubricant, which reduces wear. Perhaps even more importantly, seals keep foreign debris from entering the bearings, preventing damage that can worsen bearing performance and eventually cause them to stop working entirely.

The two most common sealing arrangements are known as radial lip, or rubbing contact seals, and labyrinth, or non-contact seals. Both sealing systems help to protect bearings and extend service life. Individual designs vary according to application and ultimately determine the level of protection these seals provide.

Rubbing Contact Seals

Early rubbing contact seals were built to consistently maintain contact with the sealing surface; today’s models maintain maximum protection with a more efficient design by using specialized shapes and geometries to create a hydrodynamic effect. This design allows the seal to reduce friction and abrasion by recirculating lubricant into the bearing system from under the lip of the seal — creating an advanced process that increases longevity and efficiency.

There are a number of rubbing seal designs that provide premium performance for a slightly higher cost, such as a face seal with spring elements that provide automatic adjustments or a seal featuring two collars surrounding a grease trap with automatic grease refilling. In addition to these options, the next best cost-effective options include collars that are regularly or occasionally greased and renewed from the bearing. The least expensive options include collars that are not renewed, felt rings that are occasionally renewed, and felt ring rings that are never renewed.

Non-Rubbing Seals

Non-contact seals continue to grow in popularity. The most common type is the labyrinth seal, which is designed with complex pathways that retain lubricants and fluids while blocking the entrance of contaminants. Another option is a hybrid design, which incorporates centrifugal force, drain back design, and other methods of retention and exclusion to provide the best possible sealing performance.

The most efficient (and costly) labyrinth sealing arrangements include multi-passage models with either automatic or otherwise regular replenishment of grease. Multi-passage labyrinths with occasional grease replenishments from the bearing are the next best options, followed by seals with run-in simple Nilos rings and long gaps. More economic models with shorter service lives include short gap, Z shielding, and open bearing non-contact seals.

Seal Solutions from Emerson Bearing

At Emerson Bearing, we have led the industry in providing seals, ball bearings, and roller bearings for more than 50 years. Working with suppliers throughout the United States, Asia, and Europe, we strive to offer products that meet our customers’ exact specifications at some of the industry’s most competitive prices.

For more information about oil seals and how to increase the lifespan of your bearings, check out our Bearing Failure Analysis guide. The eBook outlines bearings deterioration over time and highlights the best methods to remedy such equipment failures. If you have further questions or would like to request a custom quote for your particular bearing needs, contact us today.