Case Studies and Stories  

Poor Lubrication – Brass Cages Are Boon

Akhil jeet Rathore
Akhil jeet Rathore | Condition Monitoring, Indorama Petrochemicals & Fertilizers

An antifriction bearing generally has 4 major components.

  • Inner ring
  • Outer ring
  • Rolling Elements
  • Cage

The primary purposes of a cage are:

  • separating the rolling elements to reduce the frictional heat generated in the
  • keeping the rolling elements evenly spaced to optimize load distribution
  • guiding the rolling elements in the unloaded zone of the bearing
  • retaining the rolling elements of separable bearings when one bearing ring is removed during mounting or

Cage is normally the weak link & seen as the first component to fail. When cage fails bearing seizes which is undesired.

It is experienced that during overhauls, bearings when replaced bearing suffixes are overlooked. Stock available bearings are used. Type of cage suffixes are fixed per manufacturer and during replacement care to exercise is to check OEM recommended bearing v/s replacement to ensure recommended components are used.

This case study shows how brass cages are better in a highly dusty & contaminated poor lubrication condition.

Machine Description

Integrally Geared Air compressor drive motor. Motor details

Power – 970 Kw Rpm – 2975

DE & NDE Bearings – 6319M/C3

Air compressor HT motor of 970 Kw was showing high enveloping acceleration values with some bearing defect peaks after 2 years of continuous operation. The motor was having maximum 2    mm/s overall vibration. The acceleration values were trending high & there were fault frequencies      in FFT. Equipment monitoring frequency was  increased  as  pipe  line  quantity  delivery  was awaited. After receipt of correct bearings overhaul to replace bearing was planned.

Figure 1 Enveloping Trend

 

Bearing  pics  after removing

                                                    Figure 2 Contamination                                                             

Figure 3 Wear in the cage

Figure 4 Wear in cage

Observations

  • The DE bearing showed excessive contamination in
  • There was heavy wear on the Its thickness reduced by @ 40% of its original size.
  • The cage guiding surfaces dia enlarged & the cage was completely distorted which resulted in creation of knife edges at the cage inner
  • The bearing was monitored for 6
  • Soft foot in motor was

 

Analysis & action taken

  • Contamination in grease was the main damage mechanism that started the wear and further aggravated damaging the cage. The bearings were
  • Grease path was cleaned, Motor exchanger over the NDE blower was cleaned, and grease storage & handling were

Conclusion

  • Brass cages are very good in poor lubrication environment. Brass being a softer material when compared to steel, the cage wear gradually. Gradual wear allowed plant to operate machine (@6 months) till replacement bearings were
  • If this bearing had a steel cage, specifically the riveted  steel  cage  which  is standard for the deep grove ball Operation of machine with

contaminated grease would have created heavy loads causing sudden failure   of cage and resulting in a catastrophic failure. Such catastrophic failure generally damage other components (housing, shaft).

  • Take extra care of the equipment & while greasing when it is close to a

construction site.

 

Comparison of Brass cage vs Steel cage for this application

 

Brass (M) Steel (J)
Poor lubrication
Contamination
Shock Loads
High temp Up to 250°C Up to 300°C

 

END OF REPORT

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About the Author

Akhil jeet Rathore
Akhil jeet Rathore Condition Monitoring, Indorama Petrochemicals & Fertilizers

I am a Mechanical Engineer by qualification, passed out my university in 2008 since then till today working as condition monitoring engineer. Total 11+ years of experience in the CBM field. Worked with industries like Cement, Automobile, Petrochemicals, Refinery & fertilizer, was associated with SKF India for 5 years as reliability engineer. Currently I am working with Indorama Eleme Petrochemicals & fertilizers, Nigeria.

I hold Mobius VA CAT-II, BINDT CAT-I, SKF India VA Level-II, SKF Nigeria MCSA CAT-I, ASNT UT-II certificates.