This report analyzes recent bearing failures on a coke car. The analyses found that the axle diameter did not meet the manufacturer's specifications, causing looseness and wear between the bearing and axle. This led to premature failure of the bearings before their recommended service life. To prevent future failures, the report proposes reordering axles that meet the correct diameter specifications to ensure a proper interference fit between the axle and bearing. Continuous monitoring of future failures is also recommended to verify if the proposed solution prevents recurrences.

1. Bearing Failure Analyses on Coke Car
Liam McCabe
Mechanical Summer Placement 2016
Morfa Coke Ovens
22/09/2016

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Table of contents
Table of Contents
Introduction..................................................................................................................2
Analyses.......................................................................................................................2
Proposals......................................................................................................................2
Next Steps....................................................................................................................2
References....................................................................................................................2
Appendicies..................................................................................................................3
Appendix A...................................................................................................................4
Appendix B...................................................................................................................5
Abstract
This report provides an overview of the recent bearing failure on the Coke Car.
This is a re-occurring failure where the bearing isn’t fulfilling its recommended service
life. An explanation is given on the failure, the possible failure modes which have been
explored and how they were ruled out, the analyses of the bearing, final conclusions of
the failure mode and the next steps to ensure Coke Car bearings last their service life.
This reduction of failures will have a cost saving benefit through part costs as well as
the costs associated through a “shuffle” of cars.
Acknowledgments
I would like to thank the help and guidance of Dean Reynolds, Rotational
specialist for Brammer in assisting with this analyses and Sean Peat, Service Engineer
from Timken Bearings for producing the report on the failure analyses of which this
report relies heavily upon.
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Introduction
On the 8 of July 2016 the north east side bearing on the Coke Car failed
dramatically. This follows two other failures of a similar fashion within the past two
years on both Coke Car, in all 3 situations leaving the respective Coke Car out of use
until a replacement is fitted. These failures have all occurred notably before the service
life of the bearings providing the need for an investigation.
Analyses
The current bearing is a TIMKEN HM133444 – 90239 double roller tapered
type. It is fitted to the axle via an interference fit with a difference of internal diameter
of 0.082 with an axle tolerance of ±0.002mm. The operation the bearing is involved in
includes high, uneven loads, high temperatures, steam presence, and thermal and load
cycling of high difference and frequency.
From analyzing the drawing of the axle (see appendix a) and comparing it to the
manufacturers axle specification (see appendix b), the tolerances are out or the
diameters actual and specified. The diameter of the axle used is 157.234mm-
157.230mm and what Timken specifies is 157.264mm-157.238mm. This loose fit can
lead to wear and heat due to relative motion between moving parts causing fretting.
This fretting generates fine metal particles which accelerate this process of loosening
and damaging the parts (Barden Precision Bearings (Unknown).
From consulting one of Timken’s service engineers along with a Brammer
rotational specialist, this was found to be the main cause of the failure because of
heavy wear on rollers and race as well as “heavy metal particle contamination”. Other
modes of failure mentioned include heavy impact which could be due to the un-clean
coke car track. (Peat, S. 2016).
Proposals
The proposed improvement to prevent this premature failure reoccurring is to re
–order the correct sized axle for the bearing being used to ensure a suitable
interference fit. This will reduce roll wear and increase the service life of the bearing.
The costs incurred of ordering new axles will be offset as every failure which occurs
(approximately 2 a year) damages the axle beyond use as well as the bearing and end
cap.
The possibility of impact having caused the damage, most likely due to waste
on the track will be addressed in another project looking to improve the state of the
track to make it consistently clean.
Next Steps
Following this failure analyses project, the next step is to continuously record if
any future failures occur before the service life again. If this does occur, then the
causes which are familiar with this failure should be compared. If they compare, then
the proposals for improvements should be reviewed again and if appropriate re-
investigate the failure.
References
Unknown. (Unknown). Bearing Failrue: Causes and Cures. Unknown: Barden
Precisions Bearings.
Peat, S. (2016). MCO Coke Car Brg Report 08 16. Coventry: Timken.
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Appendices
Appendix A- Drawing no. 1816.37.02.12.003, drawing of axle used on Coke Car with
dimensions shown
Appendix B- Timken guide of AP Bearing for industrial applications, pg. 31
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Appendix A- drawing of axle used on Coke Car
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Appendix B- Timken guide of AP Bearing for industrial
applications, pg. 31
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