Figure 1. Photo of seperation of base oil from grease thickener

Grease is comprised of a base oil, a thickener and various additives (refer to Brenco Technical Forum 92-2, "Introduction to Grease Lubrication Fundamentals"). The separation of base oil (figure1) from the grease is the primary concern when considering bearing storage life. Base oil is the essential lubricating element that prevents metal-to-metal contact and provides corrosion protection. Separation of the base oil leads to reduced bearing life. This separation is time and temperature dependent and will vary according to the lubricant’s formulation and storage environment. Most AAR approved grease manufacturers recommend limiting the storage life of grease to two (2) years. To ensure optimal bearing performance, Brenco recommends any bearing stored for more than two years be re-qualified by a Brenco Service Engineer or returned to an authorized reconditioner.

Figure 2. Photo of wear ring surface rust	Figure 3. Photo of axle scoring

During these inspections corrosion damage on wear rings was noted (figure 2). Corrosion damage on the wear rings and inner races is a potential source of axle journal scoring during bearing installation (figure 3). In addition, abrasive material from this corrosion can lead to component fretting wear during service life (refer to Brenco Technical Forum 93-2, "Improved Bearing Retention – The Answer to Journal Fretting Damage").

Figure 4. Photo of damaged packing material	Figure 5. Photo of rusted and dirty bearing

Other bearing storage issues (figures 4 and 5) can be minimized or eliminated through the use of proper storage and handling procedures. Proper handling during transportation from the manufacturer/reconditioner to the storage area and finally to the application area will ensure the packaging material is not damaged. If this packaging material is damaged, the bearings must be inspected and repackaged before long term storage. To insure that the bearings’ reliability is not compromised, they need to be store where they are protected from extreme temperatures. Bearings also need to be protected from dirty-dusty conditions, water, and high humidity. Optimum storage humidity should remain below 60%. These outlined conditions can cause internal / external corrosion and accelerated base oil separation, all of which are detrimental to bearing performance.

Figure 6. Photo of date on packing	Figure 7. Photo of locking plate date

Time of bearing storage can be determined by two methods. The first and easiest method is the date printed on the packaging material (figure 6). If the date on the packaging material is missing or illegible refer to the manufacturing or reconditioning date stamped on the locking plate (figure 7).

These bearing storage issues make it clear that rotating your inventory is critical for the following reasons. First, bearings are lubricated with AAR approved greases, which have a practical shelf life of two years. Second, bearings’ storage environment can have detrimental effects on a bearing’s appearance and more importantly its performance. Brenco recommends that bearings stored for more than two years be re-qualified and re-lubricated. Brenco Service Engineers are available upon request to assist you in evaluating the condition of your bearings.

Recommendations

The following recommendations are made in the interest of optimizing bearing performance and service life:

1. Limit the storage life of bearings to two (2) years.
2. Establish a FIFO (first in first out) inventory method.
3. Use proper storage and handling procedures to protect packaging integrity.
4. Avoid extreme temperatures in your storage area.
5. Store bearings in a clean, dry environment (below 60% relative humidity).

The Technical Forum is an information resource for the rail industry and is provided as a courtesy of Amsted Rail Group. Suggestions, inquiries or comments are welcomed and should be directed to:

Editor, Technical Forum
BRENCO, Incorporated
P.O. Box 389
Petersburg, Virginia 23804
804-863-1713

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