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RELIABILITY

Causes of Bearing Failures

The lubrication needs of rolling element bearings operating under mild, clean conditions are relatively undemanding.  However, conditions of this nature are uncommon in many Australian industries due to the effects of contamination, elevated temperatures and vibration. 

Commonly accepted estimates suggest that more than 50% of rolling element bearings fail due to lubrication related maintenance deficiencies such as lubricant starvation, contamination by moisture or abrasive particles, incorrect lubricant or over lubrication.  Less than 10% of bearings reach their rated fatigue life.

For industries where the presence of moisture and particulate contaminants is high, such as the mining, quarrying and cement industries, the portion of bearings which suffer premature lubrication related failures is likely to be higher.

One of the most common causes of bearing failure is contamination with hard particles which enter the bearing via poorly maintained seals during operation or during manual greasing as a result of poor manual greasing practices.

The lubricating film between interacting surfaces of bearing elements ranges in thickness from a few tenths of microns to several microns when lubrication conditions are good.  If hard particles which are larger in size than the film thickness pass through the loaded zone of a bearing the resulting indentations then act as stress raisers which eventually lead to premature fatigue related wear.

Figure 1 below demonstrate a typical installation of perma STAR VARIO lubricators installed on a spherical rolling element bearing with taconite seals. 

Figure 1 - Lubrication maintenance for labyrinth and taconite type seals

 

Relubrication Intervals

Harsh operating conditions which increase the likelihood of solid contaminants entering bearings demand that re-lubrication intervals be reduced. 

A number of prevailing unfavorable conditions quickly reduce the re-lubrication interval to the point where manual lubrication is not practical.

Automated lubrication provides the ideal solution to achieving the required greasing regime for bearing which are subject to harsh conditions, while containing labour costs and reducing the likelihood of human error. 

 

Limitations of Manual Lubrication

Evidence of poor manual lubrication is often identified via the inspection bearing seals.  In harsh operating environments, lack fresh grease usually indicates that lubrication starvation and contamination entry may be occurring.

Common practices for manual lubrication lead to a feast or famine lubrication regime whereby relatively large quantities of grease are injected at long and often inconsistent intervals.  The chart below demonstrates this common problem.

Figure 2 - Manual Lubrication Regime

Potential causes of poor manual greasing practices:

  • Lack of resources to do the job on time
  • More urgent maintenance tasks take priority at the detriment of good manual greasing practices
  • Lack of care to avoid the introduction of abrasive contaminants and moisture.
  • Lack of care to ensure that the correct amount of grease is applied.
  • Limited opportunity to access all lubrication points due to access restrictions around running equipment.

 


Advantages of Automated Lubrication

Automated greasing provides the most practical, realistic and cost effective way of reducing wear of bearings.

Figure 3 - Automated Lubrication Regime

Automated lubrication provides:

  • Regular injections of small quantities of grease
  • Reduced drain on labour resources, therefore liberating time which can be invested into other maintenance tasks
  • Reduced time around working equipment – lower chance of injury, lower noise exposure etc.
  • Prevent the ingress of contaminants.

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