3 More Reasons For Premature Bearing Failure (And How To Avoid Them)

Listening to what your failed bearings are telling you today can help minimize problems tomorrow.

This is a follow-up to an NSK-supplied article on three other reasons for bearing failure—creep, flaking and smearing—that ran in the September/October 2009 issue of LMT.

You've heard it before: Every failed bearing tells a story—one that can help you identify machinery problems, maintenance issues, bearing-selection errors, installation problems and more. Are you listening?

Premature bearing failure is costly, both in terms of component replacement and unscheduled downtime. Fortunately, many types of bearing damage can be spotted, assessed and addressed—before failure occurs. The ability to proactively identify issues that affect bearing performance and wear is key to ensuring that your facility stays up and running as required.

Understanding types of bearing damage, along with their causes and solutions, can help boost reliability and cut maintenance. A previous article discussed creep, flaking and smearing. In this follow-up, the focus is on three more killers: seizure, cage damage and fretting.

#1. Seizure
When sudden overheating occurs during rotation, bearings can become discolored. The raceway rings, rolling elements and cage begin to soften, melting and becoming deformed as damage accumulates.

WHAT TO LOOK FOR: Discolored bearing elements and melting of the roller surface, resulting in adhesion of worn particles from the cage

Possible causes...

• Poor lubrication
• Excessive load
• Excessive rotational speed
• Excessively small internal clearance
• Entry of water and debris
• Poor precision of shaft and housing, excessive shaft bending

• Review lubricant and lubrication method.
• Investigate suitability of bearing type.
• Study the preload, bearing clearance and fitting.
• Improve the sealing mechanism and mounting method.
• Check precision of the shaft and housing.

#2. Cage damage
Several types of cage damage can affect the life of a bearing. These include fracture of the cage pillar, deformation of the side face and wear of pocket or guide surfaces.

WHAT TO LOOK FOR: Fractured cage

Possible causes...

• Poor mounting or bearing misalignment
• Poor handling
• Large moment load
• Shock or large vibration
• Excessive rotation speed, sudden acceleration and deceleration
• Poor lubrication
• Rise in temperature

Solutions...

• Review mounting method.
• Reduce vibration.
• Re-select cage type, lubrication method and lubricant.
• Assess temperature, rotation and load conditions.

#3. Fretting
Fretting is the specific type of wear that occurs as a result of repeated sliding between two surfaces. It occurs at the fitting surface and the contact area between the raceway ring and rolling elements.

WHAT TO LOOK FOR: Reddish-brown or black worn particles

Possible causes...

• Poor lubrication
• Vibration with a small amplitude
• Insufficient interference

Solutions...

• Use appropriate lubrication for bearing type and application.
• Apply a preload.
• Check the interference fit.
• Apply a film of lubricant to the fitting surface.

Remember this
When a bearing is damaged, it doesn't affect just a single piece of equipment: It can cause entire operations to grind to a halt. No facility or machinery is immune to unexpected bearing failure. When this type of failure occurs, the right response is crucial.

While your immediate concern may be to install a replacement component, a proper assessment of the bearing damage should follow in order to pinpoint its actual cause. Failure to find the root cause of the problem increases the risk of unnecessary repeated failures, downtime and expense.

Proactive bearing-failure analysis pro-longs bearing life, improves productivity and reduces maintenance costs. Take the time to identify and resolve issues around bearing selection, mounting, lubrication and application. When additional technical expertise is needed, ask an industrial specialist from the manufacturer to perform a failure analysis and recommend the most appropriate solution. LMT

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