I've had an interesting question from a Design Engineer that I would like to share. He is installing new pumps and the manufacturer has built the pumps with rolling element bearings that have non metallic cages in the gearbox. In the past he has been informed by Reliability Engineers in the Petrochemical Industry that these cages prevent them capturing "clean" vibration spectra from this type of bearings. So the question I pose is, does the quality of vibration data captured on bearings diminish depending on the type of cage (ie metallic or non metallic cages). My limited experience would say that you really are more concerned with the races and rolling elements and that the bearing loadpath would be where most of the data would be dependant upon. Anyway over to you guys. Thanks

It has been my experience that these only affect the ability to detect sidebanding around the BPFO. The FTF signiture is a more pronounced with a metal cage.

To add a bit more info to JB comments:

It was presented several years ago at a conference, that vibration data was collected on a pump and before the data was downloaded, the pump failed due to a collapsed bearing cage. The vibration data was scrutinised and no evidence of a bearing defect could be found. This led many people to specify to only install metallic style cages in their equipment. There are a few specific, typically high speed applications, where the OEM will only fit NON-Metallic cages and advise against fitting metallic cage bearings. For all other applications it is expected that metallic cages provide extra operational life during the failure of the bearing, allowing additional time for detection of the bearing fault. This would be expected to allow enough time to typically initiate an action prior to catastrophic bearing failure.
Hope this helps
Tony s
Disclaimer: These comments are my own and not neccessarly those of my employer.

Non metallic bearing cages are also prone to siezure more rapidly than metallic ones which tend to hold the whole mess together as failure progresses. One of the reasons that oil and gas people spec metallic cages is their increased resistance to siezing and heat generation which is not something you want around hydrocarbons. So its a safety issue as much as a CM issue. Also its much harder to detect cage wear using oil analysis. OEM's use plastic cages because they are cheap not because they have any advantage in performance.