Sealing is the primary defence against premature bearing failure in industrial environments. Open bearings depend on external lubrication and housing seals; sealed bearings retain grease and block contaminants. Shielded bearings sit between the two. Across UAE manufacturing, HVAC, and outdoor material handling sites, choosing the wrong sealing level is a leading cause of repeat failures within months of installation.
Open bearings
Open bearings have no factory-installed shields or seals on the raceways. They require either periodic re-greasing through the housing or operation inside a sealed bearing chamber with external oil or grease supply.
Use open bearings where maintenance teams have scheduled lubrication routes, where speed and heat require specific grease types not compatible with contact seals, or where the bearing housing already provides effective contamination protection.
- Clean indoor machine rooms and controlled process areas
- High-speed spindles with dedicated lubrication systems
- Large housed units where grease nipples are accessible
- Applications where bearing must be washed down without seal damage (with proper re-lube)
Shielded bearings (Z / 2Z)
Metal shields create a gap seal — better than open, but not fully contact-type. Fine dust can still enter over time, especially in abrasive environments.
2Z (shields both sides) is common on motor bearings where moderate protection is needed and some internal grease exchange is acceptable.
Sealed bearings (RS / 2RS)
Contact rubber seals on both sides (2RS) provide the best protection for typical industrial MRO where re-lubrication is infrequent. Factory fill grease is intended to last the bearing's service life under normal load.
Contact seals create slightly higher friction and limit maximum speed compared to shields — for most conveyor, pump, and fan applications up to standard motor speeds, this is not a limiting factor.
| Environment | Recommended sealing |
|---|---|
| Clean indoor, regular maintenance | Open or 2Z |
| General factory floor | 2RS |
| Dusty (cement, quarry, woodworking) | 2RS + external housing seal |
| Humid / coastal outdoor | 2RS stainless or housed unit |
| Food washdown (if applicable) | Stainless housed unit, food-grade grease |
Re-lubrication and sealed-for-life
Many maintenance teams assume all sealed bearings are truly 'lubricated for life.' In high-temperature or heavy-load duty, grease can break down before the bearing reaches expected life. If your plant runs extended shifts in summer ambient temperatures, discuss re-lubrication intervals or consider C3 clearance with appropriate grease fill.
Never remove seals to add grease unless the bearing design allows it — damaged seals admit contamination immediately.
Common mistakes
- Using open bearings on outdoor conveyors without adequate housing seals
- Replacing 2RS with open to reduce friction without assessing contamination
- Pressure-washing directly at exposed open bearings
- Mixing shielded and sealed bearings on the same motor without engineering review