Bearing seals are protective components that shield the internal rolling elements and lubricant from external contaminants such as dust, moisture and chemicals. Selecting the right seal type directly determines bearing service life and operational reliability across industrial applications.
Common bearing seal types
Three main seal families cover the majority of industrial use cases. Each offers a distinct trade-off between contamination protection and friction.
| Seal type | Designation | Material | Typical application |
|---|---|---|---|
| Contact seal | 2RS, LLU | Nitrile rubber (NBR) | Pumps, electric motors, conveyors |
| Metal shield | 2Z, ZZ | Pressed steel | Industrial fans, high-speed gearboxes |
| Labyrinth seal | — | Steel / engineered polymer | Machine tool spindles, turbines |
Contact seals (2RS) press a rubber lip against the inner ring to form a physical barrier between the environment and the grease cavity. They offer the strongest protection against dust and water ingress. The trade-off is friction-generated heat, which reduces the permissible speed limit by roughly 20-30% compared to metal shields.
Metal shields (2Z) maintain a small radial gap with the inner ring, producing virtually no contact friction. This allows the bearing to reach higher limiting speeds. However, fine particulate can still migrate through the gap over time, making shields less suitable for heavily contaminated environments.
Labyrinth seals route contaminants through a tortuous path of narrow channels without any rubbing contact. They are the preferred solution for very high-speed applications or situations where minimizing heat generation is critical.
Selecting seals by operating environment
Seal selection hinges on three factors: contamination level, rotational speed and operating temperature.
In dusty environments such as cement plants, quarries or woodworking shops, a 2RS contact seal paired with an external V-ring seal provides the most robust protection. The V-ring mounts on the shaft, rotates with it and acts as a first line of defense before contaminants reach the primary seal.
For high-speed, clean-room or climate-controlled installations, 2Z shields or labyrinth seals reduce parasitic friction losses and keep operating temperatures lower. This translates directly into longer grease life and extended maintenance intervals.
When operating temperatures exceed 120 C, standard NBR rubber seals degrade rapidly. Two alternatives exist: switch to FKM (Viton) material rated up to 200 C, or adopt a non-contact labyrinth design that eliminates the rubber element entirely.
Water exposure adds another layer of complexity. If water jets or washdown procedures are part of the operating routine, stainless steel housings combined with 2RS seals and appropriate grease (such as a calcium sulfonate complex) will resist corrosion far better than standard configurations.
Key Takeaways
- 2RS contact seals deliver the best dust and water protection but reduce permissible speed by 20-30% versus 2Z shields.
- 2Z metal shields suit high-speed applications in relatively clean environments.
- Labyrinth seals eliminate contact friction entirely, ideal for spindle-class speeds.
- Heavily contaminated settings benefit from combining a 2RS seal with an external V-ring for layered defense.
- Temperatures above 120 C require FKM seal material or a non-contact seal design.