Sealed Bearings Explained: Do They Later Need Oil?

 

Sealed bearings do not need to be refueled time and again. Therefore, they are also known as “lubricated for life.” They have seals on both sides which could either be a rubber sealing cover or a steel stamping sealing cover.

These seals are usually filled with grease which can be retained for life time. Therefore, with lubrication for life, sealed bearings are used in applications where loads are normal to light at moderate/low speeds - such as electric motors, fan motors, and automation equipment.

So, what are the two primary main functions of these seals?

• These seals inhibit the leakage of lubricant
• They do not allow contaminants such as dust or water inside the bearing.

Bearings must be properly lubricated to avoid direct metal-to-metal contact between the rolling elements, raceways, and cages, which helps reduce wear and shields the bearing surfaces from corrosion.

Types of Bearing Seals

The following are the two bearing seal types:

Non-Contact Seals:

These types of seals do not physically touch the bearing's inner ring. Non-contact seals, as the name suggests, leave a small gap between the inner diameter of the seal and the shaft, which is filled with lubricant - mostly grease - to improve seal performance and longevity.

Contact Seals:

Contact seals function by having a rubber lip that directly presses against the shaft, forming a 

secure, tight barrier. These seals are usually made from Buna-N rubber.

However, because the rubber lip touches the shaft directly, it creates more friction, which can cause some heat to build up. Also, the part of the seal that touches the shaft rotates along with it, so how fast it can spin safely depends on the type of seal being used.

Contact vs Non-Contact

To increase the shelf life of bearings, selecting the right type and proper lubrication is essential.

If maximum grease retention and contamination protection are the priority, contact seals would make a better choice.

If low friction and speed are the priority, provided that the environment is clean, non-contact seals are ideal.

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