Bearing closure designs evolve to meet demands of modern manufacturing

The role of bearing closures is becoming increasingly important as manufacturing industry demands more consolidated bearing assemblies that reduce costs in a wide range of products, from machine tools to cars and white goods. Once, the overriding primary role of closures was to protect the bearing and prevent the ingress of contaminants. However, in today's more integrated climate, where bearings are routinely sealed with grease for lifetime operation, the role of the closure is just as likely to be one of retaining lubricant within the bearing assembly.

Bearing closures fall into two basic categories, seals and shields, both of which can be ordered as integral components of deep groove ball bearings. Closures are attached to the bearing outer ring. If they contact the inner ring, they are seals. If they clear the inner ring, they are shields.

Determining the best type of closure for an application often involves a trade-off, usually balancing the benefits of sealing efficiency against its negative effects on speed capability and bearing torque. On the one hand, shields do not raise bearing torque or limit bearing speed, but they have low sealing efficiency and are not suitable for applications where external contamination is heavy. Seals, on the other hand, are more efficient, but the greater friction experienced when using them may restrict operating speed and increase bearing torque and operating temperature.

A further consideration when selecting closure types is whether there is airflow through the bearing. Airflow is detrimental because it carries contamination into the bearings and dries out the grease lubricant. Consequently, seals should always be used where this condition is likely to occur.

As the choice of closure type is always application specific, bearing manufacturers such as Barden offer a wide range of sealing and shielding options. (see Fig 1). These are produced in a variety of material types - stainless steel, rubber, aluminium/fibre laminate, Teflon filled glass fibre, polyacrylic rubber and high temperature Viton rubber, to ensure the best operational match of the closure to the application.

In recent years it would be true to say that the design focus for bearing companies has mainly been centred on producing more efficient types of seals for rolling element bearings. These seal designs have sought to achieve improved levels of sealing, while at the same time reducing friction and, hence, bearing temperature rise, to a minimum.

Barden is at the forefront of seal design, as evidenced by a recent success in developing a solution to the previously intractable problem of providing seals in standard angular contact bearings. Barden has solved this problem with its revolutionary RSD seal, a unit that enables machine tool spindle builders and users to enjoy the cost, life and maintenance-free benefits of grease lubrication, while enjoying complete bearing interchangability.

The RSD seals have retention characteristics equal to standard seal designs, but are fitted in such a way that there is minimal contact with the bearing inner rings. As a result, friction is minimised and there is no rise in the bearing operating temperature. The Barden design also overcomes problems of ring distortion from seal radial pressure. And it provides additional operational benefits as the space between seals and balls serves as a grease reservoir.

Up To 5 Times The Life.

Operational test have shown that even after many operating hours the Barden sealed bearings are still much cleaner inside than non- sealed types. The effectiveness of the seals not only means that foreign particles are excluded from the bearing, but also that more grease is retained because airflows are unable to dry it out.

The lubrication life of the grease is prolonged, therefore, and this, combined with Barden's unique bearing material specification, results in significantly improved bearing life - up to 5 times that of standard open type angular contact bearings.

This impressive improvement in bearing life means reduced costs to the user over the longer term. However, with the new seal developments even greater cost savings can be made at the "front end" of new spindle investments. This is because the package of sealed, greased -for- life spindle bearings, supplied with new high technology greases and ceramic balls, is increasingly being used as a replacement for complex, and costly, re-circulating oil lubrication systems in many applications.

About The Author:

Mark Harris is a successful author and regular contributor to http://www.bearing-n-bearings.com. Keep things running smoothly with ball bearings, roller bearings, ball thrust bearings and tapered bearings.