Figure 1: Wear ring groove depth of 0.006.

approximately 1% of the total reconditioned bearings contained in BRENCO's joint inspection data base, have been detected as loose in the five years since the rule changes. Furthermore, since 1988, significant improvements have been made to bearing reconditioning standards with regard to cone facewear and maximum cone bore diameter. These changes should help to further improve bearing clamp and thus reduce the incidence of loose bearing failures among reconditioned bearings.

Although component face wear and cone bore reconditioning standards have been tightened within the past five years, these improved reconditioning standards obviously cannot equal those of a newly manufactured bearing. Nonetheless, the significant improvement in bearing performance that is resulting from these changes has already translated into major cost savings for car owners and improved service for railroads.

As gratifying as these results have been with respect to eliminating loose bearing failures, a second beneficial effect, perhaps even more important from an economic standpoint, has now been confirmed. Developing adequate clamp forces on the bearing has virtually eliminated axle journal fretting damage.

The first evidence of this benefit began to appear within 12 months after the AAR rule changes in May of 1988. At that time, several railroad wheelshops reported to our Service Engineers that wheelsets coming through the shops, due to early wheel related set outs, were showing unusually good condition of the axle journals. Typically, in heavily loaded unit coal train service, wheelsets coming into the shop for shelling damage with as little as 50,000 miles of service would often show fretting damage on the axle in the area of the inboard wear ring fit diameter. (Figure 1) This is the result of the bearing not being adequately clamped and the axle journal deflecting under the heavy loads carried by these unit train coal cars. That journal flexure, in conjunction with low clamp force, permitted the wear ring inside diameter to fret and groove into the axle journal at the inboard wear ring position. Axle fretting and grooving had become such a common occurrence in unit coal train service that the absence of such fretting damage became readily apparent to experienced wheelshop personnel. Figure 2 shows a new axle journal.

Figure 2: New Axle Journal

Figure 3: Visible wear ring and cone contact patterns. No Groove Depth.

Five years have now passed since lateral clamp improvements were realized from the removal of the cap screw seal rings. To assess the effects of those improvements, BRENCO Service Engineering recently conducted an extensive survey of wheelsets in the field to observe and document journal conditions for bearings installed with cap screw seal rings and without cap screw seal rings. A total of 332 axle journals were inspected at four wheelshop locations and measured for any indication of fretting damage at the inboard wear ring interference fit area. The wheelsets included in this study were primarily composed of 61/2 X 12 and 7 X 12 axles but also included a small population of 6 X 11 and 51/2 X 10 axles.

Figure 4:Wear Ring Groove Depth of 0.003." Axle can be plated under current AAR standards (April 1993).

The wheelsets were selected from unit train coal service (34%), from twin stack intermodal service (11%), and from general freight service (55%). Accumulated service mileage for the unit coal train bearings averaged 296,300 miles (with a range that ran from 18,000 miles minimum to 790,000 miles maximum.)

Journal Condition	Bearings Without Cap Screw Seal Rings	Total %	Bearings With Cap Screw Seal Rings	Total %
Returned to Service	249	98.8	61	76.2
Rebuilt by Plating	3	1.2	16	20.0
Journals to be Scrapped	0	0.0	3	3.8
Table 1

Table 1 shows the distribution of journal fretting conditions between bearings that were installed with cap screw seal rings and bearings without cap screw seal rings. For those applications containing cap screw seal rings, 20.0% of the journals exhibited wear ring groove depths between 0.002" and 0.010" (Figure 4), and 3.8% of the journals exhibited groove depths in excess of 0.010" (Figure 5). Current AAR axle specifications require plating wear ring grooves which are greater than .002" but not more than 0.010" deep and require scrapping axles with grooves deeper than 0.010".

Figure 4:Wear Ring Groove Depth of 0.016." Axle is scrap under current AAR standards (April 1993).

BEARINGS WITHOUT CAP SCREW SEAL RINGS
Journal Condition	Total %	5½ x 10	6 x 11	6½ x 12	7 x 12
Returned to Service	98.8	0	12	195	42
Rebuilt by Plating	1.2	0	0	3	0
Journals to be Scrapped	0.0	0	0	0	0

BEARINGS WITH CAP SCREW SEAL RINGS
Journal Condition	Total %	5½ x 10	6 x 11	6½ x 12	7 x 12
Returned to Service	76.2	2	10	49	0
Rebuilt by Plating	20	0	2	14	0
Journals to be Scrapped	3.8	0	0	3	0

Table 2. For applications that did not contain cap screw seal rings, only 1.2% of the journals required reclamation through plating with no journals that exceeded the condemning limit for scrap. THE BOTTOM LINE: for the applications without cap screw seal rings, 98.8% of the journals were acceptable for return to service without further attention or cost and the other 1.2% were recoverable. Table 2. shows this same data broken down by bearing size for the with and without cap screw seal ring categories.

Our most recent study, with data compiled through April 1993, is not included in Tables 1 and 2. This recent data represents Fifty-three (53) - 61/2 X 12 bearings operating in 286,000 pound GRL coal service on Norfolk Southern. The bearings were in service for approximately two years and accumulated an average of approximately 100,000 miles per year. Nine of the twenty-five axles were old style with non-fitted dust guards, and the remaining sixteen axles had fitted dust guards.

Examination of all fifty-three (53) journals after bearing removal revealed no measurable cone seat fretting, and only two journals had any measurable (0.001" depth) wear ring seat fretting.

These results have significant implications for all car owners - especially in view of the trend toward loading to 286,000 pound GRL. Developing adequate clamp load on the bearing is a no cost solution to the expensive problem of journal fretting damage. The results also emphasize the importance of correct bearing installation practice. Adequate clamp load on the bearing not only improves bearing performance but also reduces downstream axle maintenance expenses significantly.

FOR FURTHER INFORMATION

Two related video tapes entitled Bearing Retention and Proper Bearing Mounting Procedures are available to the industry for training and educational purposes at no charge. To order, please contact BRENCO at (804) 732-0202.

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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