Bearings Shelf Life
Below is some interesting information from Bearingnet News about the shelf life on bearings and the lubricants within them.
It goes without saying that all bearings and lubricants should be stored in a protected area that is relatively vibration and dirt free and not subjected to temperature extremes or excessive humidity.
Some Basic Rules of Good Housekeeping: All Bearing Types
Store bearings flat, in a vibration-free, dry area with a cool, steady temperature. Control and limit the relative humidity of the storage area as follows:
75% at 20 °C (68 °F)
60% at 22 °C (72 °F)
50% at 25 °C (77 °F)
Keep bearings in their original unopened packages until immediately prior to mounting to prevent the ingress of contaminants and corrosion. Bearings that are not stored in their original packaging should be well protected against corrosion and contaminants. It is particularly important to protect them when stored for long durations.
Bearings: Closed and Open
Tom McDermott, Sr. Applications Engineer at the SKF USA Solution factory in Houston, TX says that the difference is simple. “Most small consumer electronics such as blenders are designed using sealed bearings that have lubricants built into them.
“Equipment such as large industrial electric motors, gearboxes, and fans used for rugged applications use open bearings that need to be re-lubricated on a calculated schedule.”
The maximum storage interval for all types of sealed bearings is dictated by the lubricant inside the bearings. “Lubricant deteriorates over time as a result of aging, condensation, and separation of the oil and thickener. For closed bearings – sealed or shielded – that contain the standard domestic grease (GJN), and that are still in their original, unbroken packaging, the recommended shelf life is five years. All other grease filled bearings have a shelf life of two years or three years depending on the specific grease,” McDermott says.
“By design, SKF can easily determine what grease is in each bearing and when it was produced by way of our extensive designation marking. By exceeding this shelf life limit, the oil may bleed out of the grease rendering the grease unreliable for long-term use in these closed bearings. However, it is impractical to remove the seals, clean the bearing, re-grease it and then re-fit the seals. More importantly by doing this, the seals could be damaged and contaminants could be introduced into the bearings in the process,” McDermott adds.
Open bearings that remain in original, unbroken packages can be effectively stored for up to eight years. “The shelf life of open bearings is based on the continuing ability of the corrosion inhibitor to protect the bearing surfaces during storage. Although open bearings older than eight years, based on the package date, may be acceptable for use, we do not sell nor restock bearings of that age,” McDermott says. “This is simply the best way to be certain that our customers receive the latest available bearing technology.
“Bearings that have exceeded the recommended shelf life still may be suitable for the application. However, they should be reviewed by both the end user and also the original supplier, for obsolescence or refurbishment,” he adds.
It is important that all types of bearing lubricants and all greases and oils are always kept in their original packaging until they are going to actually be used.
Heat can cause greases to separate and moisture to contaminate both oils and greases. “While this affects closed bearings that come pre-greased, it also includes separate lubricants used for maintaining open type bearing assemblies, stored on a shelf,” McDermott says. “It is important that all types of bearing lubricants and all greases and oils are always kept in their original packaging until they are going to actually be used. This minimises the risk of contamination from the entry of moisture, dust and debris.”
“Most 55 gallon lubricant drums for instance have a specific cap seal that is in place to keep the contents protected. That seal should be checked on a regular basis to ensure it is working properly. A can of grease is like a can of paint. If you don’t put the lid back on properly the grease can go bad just like paint does. Also, storage temperature is critical. The higher the temperature, the faster the lubricant will degrade,” he adds.
Keep up to date
Bearing companies are continually improving their bearings, materials and designs. Therefore, just like anything else, bearings eventually become obsolete. “At SKF we upgrade the features of our bearings between every three to five years.”
McDermott says that design engineers should stop thinking “we’ve always done it this way so let’s just go for the same components.” Whenever creating a new design or upgrading an existing one, stop and re-evaluate what innovations may benefit the product, including bearings. One good example to check out is SKF CARB.
“Stay up to date on the latest catalogs or websites such as SKF, and make sure you are always using the best bearings available for the application. Better components not only create a better product but allow for a better warranty on the product. Learn what is available to make your products better.”
For more information go to http://news.bearingnet.net/shelf-life-affect-bearings-and-their-lubricants/