Reliability Engineering Snapshot TM

Illustrated Case Studies in the Maintenance Reliability Engineering World of Failure Analysis, Predictive Maintenance, and Non Destructive Evaluation



Lubrication - Case Study No. 19: Grease Passageway Misalignment Starves Bearing

Pillow Block Brng with Bearing In PlaceThe pillow block bearing to the left was on a fan assembly. It started making noise, and although the mechanic kept putting more grease in it, the noise and the heat never went away. Assured that the bearing had enough grease, the maintenance foreman believed without a doubt that the problem was in the process and not the bearing. This of course put undue stress on the production people because they weren't doing anything different. The consensus was leading toward a new rotor wheel assembly. Prior to doing any of this work a vibration analysis was performed on the entire unit.

Vibration diagnostics showed that the bearing to the left had developed a small spall in the outer raceway. Without further analysis, one would tend to assign the cause for the premature failure on lack of lubrication, and once again the Lubrication Mechanic would bear the brunt of the blame.

Bearing Pillow Block With Brng Partially Removed - Correct PositionBearing Pillow Block With Brng Removed - Actual LocationHowever, no stone should be left unturned in a good failure analysis. The bearing was removed from the pillow block and immediately there was suspicion as to whether the bearing had really been able to be lubricated all of this time. The picture to the left shows the bearing insert partially removed. The orientation of the grease hole which would allow the grease to get to the bearing is purposely lined up correctly with the grease zerk for this picture. In actuality, the orientation of the bearing was like that in the picture to the right. It is obvious that at some time in the past the bearing outer raceway shifted.

Of course there was speculation as to whether this really was the truth, or whether this was an elaborate attempt to save face for the Lubrication Mechanic. The pictures below show the complete story.

Pillow Block Bearing With Brng Removed - Reveal Brng Insert Lube Hole Location versus Actual Lube Hole
Bearing Insert Outer Raceway Showing Grease Hole and FrettingBearing Pillow Block With Bearing Removed - Reveal Lube Hole Location of the Bearing Outer RacewayThe picture above shows the inside of the pillow block, depicting the grease zerk, the grease zerk hole, and a very distinctive shiny spot well below the grease zerk hole.

What is this shiny spot? It is no coincidence that the pattern of the shiny spot assumes the shape of the grease zerk hole. A close up of the shiny spot is shown in the picture to the right. Imagine if you will for a moment, the fact that the bearing outer raceway is banging around in the pillow block. There is fretting damage evident on the raceway as shown in the picture to the left. This is where there was metal to metal contact in the form of banging. The shiny spot is where there was no metal to metal contact.

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