In any application proper attention to cage design and materials selection is essential to ensure reliable and long-term bearing performance.

The role of cages, or separators as they are sometimes known, covers:

• They space the rolling elements apart equally and help lubricant distribution within the bearing.
• Separating the elements halves their running contact speed, allowing higher bearing speeds.
• They facilitate handling and installation of separable type bearings.

Since they may be required to accelerate rapidly, bearing cages should be lightweight and be manufactured from materials that have superior strength/weight ratios. Traditionally used brass or bronze cages have good wear characteristics but steel cages are offered which provide excellent service but at a lower cost. They are favoured in applications for harsh environmental conditions or where bearings are subject to very high levels of vibration or extremes of heat. Alternatively, in some price sensitive applications, cages manufactured from high performance plastics are preferred.

Other factors affecting cage design and selection:

• Low coefficient of friction with ball and race materials.
• Compatible expansion rate with ball/ring materials.
• low tendency to gall or wear.
• The ability to absorb lubricant.
• Dimensional and thermal stability.
• Suitable density.
• Adequate tensile strength.
• Creep resistance