The pillow block bearing in Figure 1 is from a fan assembly. It started making noise, and although the lube mechanic kept putting more grease in it until grease was oozing out the sides, the noise and the heat persisted. Assured that the bearing had enough grease, the maintenance foreman believed without a doubt that the problem was in the process and not in the bearing. This puzzled the production staff because they believed quite strongly that they weren’t doing anything wrong. The growing consensus between production and maintenance personnel was that it was time to install a new rotor wheel assembly. Prior to the installation, vibration analysis was performed on the entire unit. Vibration diagnostics showed that the bearing in Figure 1 had developed a small spall in the outer raceway and was confirmed upon disassembly.

Figure 1. Pillow block bearing from fan assembly.

What was more obvious than the spall was the amount of grease in the bearing. The bearing contained very little grease, which was baffling considering how much grease was around the outside of the pillow block. Based upon these facts, the bearing should have contained ample grease, maybe even too much grease. So why didn’t the bearing have any grease in it when there was grease visibly oozing out of the pillow block?

Figure 2. Bearing partially removed from housing.

The bearing was removed from the pillow block, and suspicion quickly mounted. The suspicion wasn’t whether the lube mechanic did his job, but whether the grease ever got to the bearing in the first place. Figure 2 shows the bearing insert partially removed from the housing. 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 photo. However, this was not the case when the team inspected the bearing. The orientation of the bearing was offset relative to the fitting, much like the one pictured in Figure 3.

Figure 3. Bearing offset relative to fitting.

It was obvious that at some point during the equipment’s operation, the bearing’s outer race shifted circumferentially.

Figure 4 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.

Figure 4. Inside of the pillow block.

Figure 5 is a close-up of the shiny spot shown in Figure 4.

Figure 5. Close-up of the shiny spot.

What is the shiny spot doing on the inside of the pillow block? It was no coincidence that the pattern of the shiny spot was exactly the same shape as the grease zerk hole. Figure 6 shows a close-up of the grease zerk hole in the outer race. The irregular pattern of discoloration was evidence of fretting damage between the outer diameter of the outer race and the inner diameter of the pillow block. The fretting, or cyclic metal-to-metal contact, occurred because of vibration. The shiny spot on the pillow block was where the grease zerk hole of the outer race came to rest and stayed for quite some time. It was shiny because there was very little cumulative fretting damage in that region, given that metal-to-metal contact was not possible.

Figure 6. Grease zerk hole in the outer race.

Here’s a lesson that was learned the hard way: Just because the grease was pumped through the grease zerk, didn’t mean that the bearing was getting any grease. The lube mechanic should have suspected something when the grease began oozing out between the pillow block and the outer diameter of the bearing; he should have inspected his equipment more closely.

This leads to another point: training. The lube mechanic had no idea what was happening. All he knew was how much and how often he needed to pump grease into the bearing. It would have been helpful to have some common knowledge and training in general equipment design with regard to common grease port configurations.

Don’t fall into the same trap; lube mechanics aren’t clairvoyant. They need more training than just knowing how much and how often to grease a machine. Remember, once the grease gets past that grease zerk, it’s a whole new world.

Editor’s Note: Rick has presented a great and practiced lesson here. Increasingly, technicians rely on ultrasonic acoustic analysis to confirm that the lubricant film is present and effective.

Author Richard Adler has more than 25 years experience within the fields of maintenance and
maintenance engineering. He has worked for several companies in the petrochemical, oil refining, specialty chemical and pharmaceutical industries. Photos and articles about actual failure analysis events can be viewed on his Web site: www.RESnapshot.com.

Photos © 2002 R.H. Adler