ZZ (double shields)
Very similar to the 2RS construction, shielded bearings have metallic enclosures rather than rubber seals. These shields are secured to the outer ring and rotate with it, maintaining a close running clearance to the inner ring. Even with a restrictive lubrication path, metallic shields cannot provide a total enclosure of the bearing cavity due to this slight clearance between the shield and inner ring
Advantages:
- lubricant is retained at the rolling elements
- the metal shield acts as a slinger feeding grease to the inner ring
- rolling elements are shielded from large contaminants during operation
- Friction Losses are reduced versus similar size 2RS sealed bearings
Disadvantages:
- excessive pressure or impact can force the shield against the cage or balls
- removal of shields is not possible, so relubrication is impossible
