In some cases, customers may notice that the outer surface of a bearing remains clean and free from corrosion, while fine rust appears inside the bearing cavity after long-term storage.

This issue is more common when sealed bearings are stored in high-temperature and high-humidity environments.

The image below shows a typical example of internal corrosion inside a sealed bearing. Although the outer surface remains in good condition, fine rust has developed inside the raceway and rolling element area.

WHAT CAUSES INTERNAL RUST IN SEALED BEARINGS?

Many users believe that sealed bearings are completely airtight.

However, standard rubber sealed bearings are mainly designed to prevent dust and contamination during operation. They are not fully airtight structures.

Under high-temperature storage conditions, humid air may slowly enter the internal cavity through the sealing structure.

When environmental temperatures change, moisture may gradually accumulate inside the bearing chamber.

Because the internal space is relatively enclosed, water vapor cannot easily escape. Over time, oxidation may occur on the raceways and rolling surfaces, resulting in fine internal rust.

IMPORTANT:

Sealed bearings are not completely airtight products.

WHY DOES THE OUTSIDE REMAIN CLEAN?

In many situations, the external packaging remains intact and continues to provide effective protection against direct outside corrosion.

This is also why proper bearing packaging is extremely important during transportation and storage.

As a result, the outer surface may still appear normal, while internal corrosion develops due to trapped moisture inside the sealed cavity.

In most cases, this type of corrosion is related to improper storage conditions rather than bearing manufacturing quality.

RECOMMENDED STORAGE CONDITIONS

To reduce the risk of internal oxidation, sealed bearings should always be stored in:

• Cool environments

• Dry and ventilated warehouses

• Areas away from direct sunlight

• Locations without strong heat sources

Bearing cartons should not be placed near:

• Workshop heating equipment

• High-temperature production areas

• Areas exposed to continuous sunlight

Reducing exposure to heat and humidity can significantly lower the risk of moisture penetration and internal corrosion.

IMPORTANT:

High temperature + humidity + long-term storage are major causes of internal bearing rust.

PROPER STORAGE CAN EXTEND BEARING LIFE

Even high-quality bearings may develop internal corrosion if stored improperly for long periods.

For industrial users, proper warehouse management is extremely important for maintaining bearing performance and service life.

Humidity control, ventilation and stable storage temperatures are all critical factors in preventing internal rust problems.

CONCLUSION

Internal rust inside sealed bearings is usually caused by long-term exposure to high-temperature and high-humidity storage conditions.

Although sealed bearings provide effective protection during operation, they are not completely airtight structures.

Proper storage conditions play a critical role in preventing moisture accumulation and internal oxidation.

For bearing storage recommendations or technical support regarding corrosion prevention, please contact our technical team.

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