One of the most confusing topics for customers seems to be "Shelf Life."

It is not uncommon that even experienced Quality Mangers sometimes do not appreciate the distinction between Preservative Oils versus Lubricants when it comes to bearings.  It is important to understand the difference between the preservative that protects the bearing while it is in its packaging, or the lubrication contained inside the bearing (usually a grease) that lets it spin properly in the application for which it was designed.  Typically bearings that are "open" (meaning that they don't have any seals or shields), will be in a preservative oil, as determined by the bearing material. An open bearing that has been preserved in oil is cleaned prior to installation, and it is likely that it was designed to be lubricated by the oil inside the unit into which it is installed.

For example, a preservative oil such as MIL-PRF-6085, has corrosion inhibitive properties, and is only intended to protect the bearing until the time of installation. Bearings preserved in oils, properly packaged and stored are considered to have a shelf-life that is "on-condition", meaning if the corrosion inhibitor has done its job, there will be no evidence of corrosion on the bearing. 

Unless there was not enough preservative oil to begin with, or if the packaging is damaged and the oil leaks out, there should not be any corrosion. Therefore the "shelf life" of a preservative oil is indefinite. Nevertheless, to insure quality, our own established internal control procedures dictate that prior to dispatch, an inspection of the bearing, its packaging and lubrication is conducted.

For Sealed Bearings "Shelf-life" may or may not be more of a consideration.  Sealed bearings have 2 seals or shields, which keep the grease inside and keep dirt out. Numerous factors can extend or reduce a bearings’ shelf life. These include proper preservation and packaging in a temperature controlled storage environment.

It is important to note that lubricant manufacturers who might make general recommendations on shelf life will make them based on the storage life of the lubricant in the original container. Once the lubricant has been applied to a bearing or other device, factors which the manufacturer can neither predict nor control will govern lubricant life. Therefore the responsibility falls upon the end user to establish a different policy regarding either storage or operating life.

The lubricants that are in the bearings that we supply are high-quality lubricants that are typically qualified to certain military lubrication specifications. It is interesting to note that the majority of these publications make absolutely no reference to "shelf life."

Our own established internal control procedures call for a periodic review of the product, and also prior to shipment. The scheduled time for review does not presuppose that the lubricant has aged beyond its service life. Our policy here is that lubrication is "on-condition" unless the bearing manufacturer indicates a specific expiration date.

In other words, the bearing and packaging should be evaluated by inspecting the package integrity and the visual appearance of the grease or oil for hardening, caking, discoloration, separation, etc. If the package is unbroken and the bearing lubrication appears normal, that review date of that part is extended accordingly. In the event the lubrication is ever questionable, we would send the bearing out for re-lubrication. It should be noted that bearings that we have in stock are inventoried in a controlled environment in sealed containers.

Click here to read an informative article from ExxonMobil on shelf life.

If you require a bearing’s lube date to be less than 3 years, for example, it would be best if you mention that on your RFQ when requesting price & delivery so that we can accurately respond and quote accordingly.

For bearings you have that you feel do need re-lubrication, even if you didn’t buy them from us, please contact us. We would be happy to help you with your requirement.