How to avoid bearing failure: Guide to bearing storage
Bearing reliability has significantly increased in the last 10-15 years owing to the improvement in bearing technology and quality. SKF [1] shares that more than 90% of bearings outlive the equipment they are part of. Most of the remaining are replaced to prevent sudden failure, leaving very few to fail over time.
The small number of bearings that have to be replaced is still a cause of concern for production. Given their integral importance in the working of critical equipment, spare bearings are always required on the shelf. Therefore, we should know how to properly store them and care for them to prevent problems arising from inappropriate stocking as shown in the figure below.
Storage of bearings
For storing bearings, we must look into both the storage conditions and the permitted shelf life. The table below gives the general recommendations regarding those. Still, you should go through the text underneath it for developing a thorough understanding.
| Parameter | Recommendations | |
|---|---|---|
| Temperature | 10-25 °C (50-77 °F) | |
| Relative Humidity | Below 60% | |
| Location | 30 cm above ground Dry and vibration-free Away from sunlight and outside walls |
|
| Handling | Kept in unopened packages Large bearings should be kept horizontal |
|
| Shelf Life | Open Bearings | 5 years* |
| Sealed Bearings | 3 years | |
*Shelf life can be extended after inspection and renewal of rust-inhibiting coating
Storage conditions for bearings
The top bearing manufacturers suggest similar storage conditions for their bearings.
Temperature
Most bearing manufacturers suggest that the ideal temperature for storing bearings is 20-25°C [2]. Still lower temperatures, to about 8-10°C, are permitted [3]. On the other end, higher temperatures of 30°C are only allowed for brief durations. Exceeding the limit on either side of the temperature range is harmful to the bearing. At temperatures lower than 0°C, the lubricant may crystallize, while at temperatures above 30°C, the lubricant would lose its effectiveness.
In addition to these temperature limits, the variation between day and night temperature should also be limited. Most manufacturers recommend a temperature variation of less than 8°C [4] to avoid condensation.
Relative Humidity
Moisture corrosion, as shown in the figure above, is the primary concern for stored bearings. To prevent that, most manufacturers recommend that the bearing storage should be dry i.e. the relative humidity should be below 60-65%. Still, SKF permits a relative humidity of as high as 75% at 20°C [1]. Therefore, if need be, a higher relative humidity at a lower temperature is permissible, but it should be certain that temperature variation does not cause condensation as a result.
Location
Ideally, bearings should be stored in a way that shields them against outside influences. They should be placed on shelves at least 30 cm [5] above the ground to prevent dust contamination. They should be away from direct sunlight and from contact to outer walls to prevent high-temperature variations.
In addition, the location of bearings should be protected against vibrations as it can cause damage to the raceways of bearings.
Handling
Bearings should be kept in their original unopened packages to protect them from corrosion and contamination. Also, larger bearings with relatively thin walled rings and precision rolling bearings must be laid horizontally. Placing them upright causes raceway deformation.
Moreover, NTN recommends that bearings should not be stacked too high, as it squeezes out the rust-inhibiting compound from the bearings at the bottom.
Shelf Life of Bearings
The shelf life of a bearing depends upon whether it is an open bearing or a sealed bearing. In an open bearing, the control factor is the rust-inhibiting compound that is applied to it as a coating. Its protection lasts for 5 years [1]. Therefore, you need to remove the bearing from the package, inspect it for damage, and reapply the coating after that, before storing it again.
On the other hand, in sealed bearings, the lubricant inside the bearing dictates the shelf life. Over time, the lubricant changes its chemo-physical behavior because of condensation and separation of the oil and the thickener. Thus, sealed bearings should not be stored for more than 3 years [1].
After reading this piece, you should be well-equipped to handle bearing storage. Nonetheless, if you have any confusion or any specific query, you can always feel free to contact us. We would be happy to assist you.
References
- [1] SKF Group, SKF bearing maintenance handbook. 2011.
- [2] NTN, Ball and Roller Bearings. 2020.
- [3] Schaeffler, Mounting and Dismounting of Rolling Bearings. Schweinfurt, Germany, 2013.
- [4] Schaeffler Korea Corporation, Rolling Bearings. 2020.
- [5] NACHI, Precision Rolling Bearings. 2019.
