PLATINUM

AMANDELBULT
COMPLEX
ENGINEERING & ASSET MANAGEMENT

FAILURE & ROOT

CAUSE ANALYSIS
INVESTIGATION REPORT
151-ML-04 BARRING GEAR BRAKE FAILURE

Prepared by: Thomas Conolly

Reviewed by: Walta Viljoen

Willem van Loggerenberg
Table of Contents
Introduction................................................................................................................................................3
Current Infrastructure.............................................................................................................................4
Root Cause Analysis.................................................................................................................................6
Investigation Findings..................................................................................................................................6
Remedial Actions.......................................................................................................................................10
Appendix A: Laboratory Analysis...............................................................................................................11

List of Figures
Figure 1 - Incident scene showing the damaged guard and missing brake drum and callipers...................3
Figure 2 - 151-ML-04...................................................................................................................................4
Figure 3 - 151-ML-04 mill barring gear arrangement..................................................................................4
Figure 4 - Barring gear brake set arrangement............................................................................................5
Figure 5 - Barring gear dog-clutch interlock................................................................................................5
Figure 6 - Manufacturer's mark displayed on failed brake set....................................................................7
Figure 7 - Close-up on brake liner fragment showing signs of glazing.........................................................8

Disclaimer: The information contained in this document is not prescriptive. It is indicative of good practice and is intended as
information for site specific interpretation and application by the responsible parties within the Anglo American plc Group. The
material contained herein is based on information believed to be reliable, however, no representation or warranty, express or
implied, as to the accuracy or completeness thereof is made. No responsibility is accepted by Anglo American plc or any of its
subsidiaries or associated companies for any loss or damage of whatsoever nature arising out of the use of, adherence to or the
lack thereof to any part of this information.

2
Introduction
At approximately 11:50am, on the morning of Thursday the 25 th of January 2018, employees of the
contractor company Picabiz were busy performing the relining of the Merensky plant Tertiary mill no.2
(151-ML-04), at the Amandelbult Concentrator.

One employee, an assistant appointed by Picabiz, was stationed at the barring gear controls, which were
being used to reposition the mill, as is normal during such relining activities. The employee then saw
smoke being generated from beneath the guard of the barring gear brake set. Reacting to the smoke
which was emanating from below the guard, the assistant immediately applied the brake to stop the
barring process. It was at this application of the barring gear brake that the assistant heard a loud bang.

The barring gear brake drum had seemingly exploded, sending shards of metal flying in all directions.
Two persons were struck by pieces of shrapnel, namely the assistant operating the barring gear controls,
as well as one other contractor employee standing on the opposite side of the mill. The both sustained
relatively minor lacerations to the forearm, which were immediately treated by the emergency response
personnel, following which they were taken to the Amandelbult hospital for further treatment and
observation.

Owing to the potentially severe nature of this incident, a complete investigation was launched by the
on-site management and safety personnel - in order to determine which controls failed to cause this
incident. In addition to the safety report generated this report was generated as a response to the
equipment failure experienced during this incident - in an effort to eliminate the defect or defects which
allowed for this incident to occur.

Figure 1 - Incident scene showing the damaged guard and missing brake drum and callipers

Disclaimer: The information contained in this document is not prescriptive. It is indicative of good practice and is intended as
information for site specific interpretation and application by the responsible parties within the Anglo American plc Group. The
material contained herein is based on information believed to be reliable, however, no representation or warranty, express or
implied, as to the accuracy or completeness thereof is made. No responsibility is accepted by Anglo American plc or any of its
subsidiaries or associated companies for any loss or damage of whatsoever nature arising out of the use of, adherence to or the
lack thereof to any part of this information.

3
 Current Infrastructure
The Merensky Plant Tertiary Mill no.2, designated as 151-ML-04, is a 14-by-22 foot, Fuller-Vecor (F.L.
Smidth) ball mill. The mill is driven by a 1.8MW, 744rpm AC slip-ring motor, through a David-Brown
850CRS gearbox and a 710mm, 30-tooth pinion gear.

Figure 2 - 151-ML-04

The mill is fitted with a barring gear arrangement, which is driven at 1425rpm by a 18.5kW, 4-pole,
squirrel-cage motor, through dual worm-gear sets and a hand-operated dog-clutch, onto the input shaft
of the primary drive gearbox of the mill, as shown in figure 3.

Mill drive gearbox

Barring gear second
worm gearbox

Barring gear first

worm gearbox
Barring gear dog-
clutch handle
Barring gear drive
motor
Barring gear brake
set

Barring gear control

panel

Figure 3 - 151-ML-04 mill barring gear arrangement

Disclaimer: The information contained in this document is not prescriptive. It is indicative of good practice and is intended as
information for site specific interpretation and application by the responsible parties within the Anglo American plc Group. The
material contained herein is based on information believed to be reliable, however, no representation or warranty, express or
implied, as to the accuracy or completeness thereof is made. No responsibility is accepted by Anglo American plc or any of its
subsidiaries or associated companies for any loss or damage of whatsoever nature arising out of the use of, adherence to or the
lack thereof to any part of this information.

4
Between the barring gear motor and the first of the worm-gear sets, the input shaft of the barring gear
is fitted with an external calliper, spring applied/actuator released, drum brake, no dissimilar to the one
shown in figure 4. This brake is intended to stop the barring gear motor once barring has been
completed and power has been removed, as well as to hold in position the barring gear at the point
where the mill is required to stop.

Figure 4 - Barring gear brake set arrangement

The mill barring gear is further fitted with an interlock to ensure that the mill cannot be started whilst
the barring gear dog-clutch is engaged, as shown in figure 5.

Figure 5 - Barring gear dog-clutch interlock

Disclaimer: The information contained in this document is not prescriptive. It is indicative of good practice and is intended as
information for site specific interpretation and application by the responsible parties within the Anglo American plc Group. The
material contained herein is based on information believed to be reliable, however, no representation or warranty, express or
implied, as to the accuracy or completeness thereof is made. No responsibility is accepted by Anglo American plc or any of its
subsidiaries or associated companies for any loss or damage of whatsoever nature arising out of the use of, adherence to or the
lack thereof to any part of this information.

5
Root Cause Analysis
An in-loco investigation was launched on the day of the incident. The purpose of the in-loco
investigation was to gather information and establish the possible sequence of events, possible root
cause and identify the system failures. Furthermore, an investigation was conducted together with all
applicable stakeholders. From this investigation a preliminary investigation report was generated and
distributed for review and comments.

The revision and comments received on the preliminary findings, as well as further evidence from
laboratory analysis, were collated into this final investigation report.

Investigation Findings
From the evidence gathered and interviews conducted on-site, the following details of the incident were
determined:

1. Concerns were raised at the time of the incident, as to whether the mill was started with the
barring gear clutch engaged. It was confirmed during the investigation that the mill was not
started, deliberately or inadvertently, at any time leading up to the failure – The mill had been
isolated and locked-out, with the breaker racked-out, for relining.
2. According to the SAP-PM data available, the barring gear installed on this particular mill has
been in use since April 2008. The brake set which was installed on the barring gear at the time of
the incident is manufactured by a company called, Jingu – the manufacturer’s tag can be seen in
figure 6. According to the OEM of the barring gear, David-Brown, this variant of barring gear
brake is not endorsed by them. When barring gear sets are refurbished or supplied new from
the OEM they are fitted with a brake set manufactured by Pedi-Grip.
 The installation of a barring gear brake set which is not approved by the OEM brings into
question the quality of the brake set. Fragments of the failed brake drum and calliper
were sent to Imp-labs laboratories for analysis. The results of this analysis can be seen in
Appendix A. These analysis result clearly show the poor quality of the material used in
the manufacture of the barring gear brake set. The OEM supplied specification requires
these brake drums to be manufactured from Wrought Steel, to specification BS970-
1983, it was however found that the failed component had been manufactured from
Grey Cast Iron.

Disclaimer: The information contained in this document is not prescriptive. It is indicative of good practice and is intended as
information for site specific interpretation and application by the responsible parties within the Anglo American plc Group. The
material contained herein is based on information believed to be reliable, however, no representation or warranty, express or
implied, as to the accuracy or completeness thereof is made. No responsibility is accepted by Anglo American plc or any of its
subsidiaries or associated companies for any loss or damage of whatsoever nature arising out of the use of, adherence to or the
lack thereof to any part of this information.

6
 Figure 6 - Manufacturer's mark displayed on failed brake set

3. As the contractor employee was barring the mill, the barring gear brake actuator released the
brake as expected when power was applied to the barring motor. However, the brake calliper
did not move completely clear of the brake drum and the brake lining was rubbing against the
brake drum during barring. The close-up image, shown in figure 7, of the brake liner pieces
found at the scene shows signs of glazing on the surface of the brake liner; the brakes rubbing is
also confirmed by the smoke generated just before the incident.
 The cause for the brake calliper to not move completely clear of the brake drum may be
due to either; the brake actuator becoming less effective and thus not being able to
move the brake calliper against the spring, or alternatively the brake gap was incorrectly
set prior to the use of the barring gear. There was, at the time of the incident, a PMO3
works-order in place for the fitter to examine the barring gear arrangements on a month
basis, including the barring gear brake. This examination consists of inspecting the brake
assembly for any abnormalities, such as brake liner wear, but does not include any
inspection of the brake gap, or the effectiveness of the brake actuator.

Disclaimer: The information contained in this document is not prescriptive. It is indicative of good practice and is intended as
information for site specific interpretation and application by the responsible parties within the Anglo American plc Group. The
material contained herein is based on information believed to be reliable, however, no representation or warranty, express or
implied, as to the accuracy or completeness thereof is made. No responsibility is accepted by Anglo American plc or any of its
subsidiaries or associated companies for any loss or damage of whatsoever nature arising out of the use of, adherence to or the
lack thereof to any part of this information.

7
 Figure 7 - Close-up on brake liner fragment showing signs of glazing

4. Barring was performed for between a third and half a drum rotation of the mill, according to the
contractor employees engaged in the relining activities at the time of the incident. During this
time, the brakes which were rubbing against the brake drum caused the generation of heat,
raising the temperature of the brake drum; simultaneously initiating the generation of smoke
from the brake lining.
 According to sources researched during the investigation of this failure; the yield
strength of grey cast iron can decrease by up to 60%, if the temperature rises to the
range of 500°C. It has been shown in the laboratory analysis of the brake drum
fragments that the drum was indeed constructed out of grey cast iron. Further tests
conducted on the barring gear brake which was installed as a replacement to this failed
component, showed that the temperature of the brake drum was raised from ambient
temperature to almost 100°C within 10 seconds of operation, when the brake lining was
rubbing against the drum. It is therefore not difficult to speculate that the brake drum
may have reached significantly higher temperatures when operated for extended
periods with the brake lining rubbing against the brake drum.
5. When the contractor assistant observed the smoke being generated he attempted to stop the
barring motor by pressing the stop button on the barring gear control panel. Once the stop
button is depressed, the power to the barring motor and the brake actuator are cut,
instantaneously applying the brakes fully through the action of the spring.
 The now heated and weakened brake drum, still rotating at approximately 1400rpm, is
subjected to the full clamping force of the brake calliper – the material of the drum can’t
withstand this force at this elevated temperature and undergoes a brittle failure. Due to
the energy being carried by the drum in its rotation the fragments generated by the
failure are flung into the surrounding guard - the guard is unable to hold back the

Disclaimer: The information contained in this document is not prescriptive. It is indicative of good practice and is intended as
information for site specific interpretation and application by the responsible parties within the Anglo American plc Group. The
material contained herein is based on information believed to be reliable, however, no representation or warranty, express or
implied, as to the accuracy or completeness thereof is made. No responsibility is accepted by Anglo American plc or any of its
subsidiaries or associated companies for any loss or damage of whatsoever nature arising out of the use of, adherence to or the
lack thereof to any part of this information.

8
 fragments and they break through the top of the guard, subsequently injuring the two
contractor employees.
6. Some witnesses to the incident said that the mill ran back following the failure of the brake.
 It was confirmed in the field that this mill can in fact run back if the barring gear brake is
released at a point of imbalance. It was however also confirmed in the investigation,
through interviews with witnesses to the incident, that the mill did not run back before
the failure of the brake drum, but immediately after the failure. This concludes that the
run-back of the mill was not a contributing factor in the failure of the brake drum.

Disclaimer: The information contained in this document is not prescriptive. It is indicative of good practice and is intended as
information for site specific interpretation and application by the responsible parties within the Anglo American plc Group. The
material contained herein is based on information believed to be reliable, however, no representation or warranty, express or
implied, as to the accuracy or completeness thereof is made. No responsibility is accepted by Anglo American plc or any of its
subsidiaries or associated companies for any loss or damage of whatsoever nature arising out of the use of, adherence to or the
lack thereof to any part of this information.

9
Remedial Actions
The following remedial actions have been put in place to prevent reoccurrence of this event:

1. The mill barring procedures need to be revised to reflect the two different barring processes and
the requirements of each, namely; barring for mill start-up and barring for maintenance
purposes. (Completed – 19th March 2018)
2. The barring procedures is to be updated to make specific reference to the plant processor that is
to execute barring activities. (Completed – 19 th March 2018)
3. The maintenance plan is to be revised to include a weekly inspection on the brake unit
conducted by the fitter, as well as the addition of a monthly brake gap measurement to be
added on the current monthly works order. The monthly brake gap measurement is to ensure
that the brakes open fully upon activation, with no rubbing of the brake liner whilst the barring
motor is in motion. (Completed – 6th February 2018)
4. Both the maximum and minimum torque setting are to be determined for each brake and
visually marked on the spring. The mill OEM is to provide the actual required torque setting for
each mill. (Completed – 8th March 2018)
5. The barring gear control panels on each mill need to be changed so that the provision of the
brake release button is not accessible to the processor. It should be available only for the fitter
when measuring the brake gaps. (In Progress – 30 th March 2018)
6. Means should be provided to supply visual indication on the mill shell of mill position when
barring. (Planned Completion – 5th April 2018)
7. An audit was conducted of the manufacturer of the brake sets currently installed. A
replacement plan has been drawn-up to phase out brake sets manufactured by companies not
approved by the barring gear OEMs. (Planned Completion – 5 th July 2018)
8. A means should be provided to monitor whether the barring gear brakes are clear of the drum
during normal barring activities. Currently a trial is underway to prove the effectiveness of an
infrared sensor placed inside the guard of the barring gear brake, to monitor the temperature of
the brake drum. (Trial In Progress)

Disclaimer: The information contained in this document is not prescriptive. It is indicative of good practice and is intended as
information for site specific interpretation and application by the responsible parties within the Anglo American plc Group. The
material contained herein is based on information believed to be reliable, however, no representation or warranty, express or
implied, as to the accuracy or completeness thereof is made. No responsibility is accepted by Anglo American plc or any of its
subsidiaries or associated companies for any loss or damage of whatsoever nature arising out of the use of, adherence to or the
lack thereof to any part of this information.

10
Appendix A: Laboratory Analysis

Disclaimer: The information contained in this document is not prescriptive. It is indicative of good practice and is intended as
information for site specific interpretation and application by the responsible parties within the Anglo American plc Group. The
material contained herein is based on information believed to be reliable, however, no representation or warranty, express or
implied, as to the accuracy or completeness thereof is made. No responsibility is accepted by Anglo American plc or any of its
subsidiaries or associated companies for any loss or damage of whatsoever nature arising out of the use of, adherence to or the
lack thereof to any part of this information.

11
Disclaimer: The information contained in this document is not prescriptive. It is indicative of good practice and is intended as
information for site specific interpretation and application by the responsible parties within the Anglo American plc Group. The
material contained herein is based on information believed to be reliable, however, no representation or warranty, express or
implied, as to the accuracy or completeness thereof is made. No responsibility is accepted by Anglo American plc or any of its
subsidiaries or associated companies for any loss or damage of whatsoever nature arising out of the use of, adherence to or the
lack thereof to any part of this information.

12
Disclaimer: The information contained in this document is not prescriptive. It is indicative of good practice and is intended as
information for site specific interpretation and application by the responsible parties within the Anglo American plc Group. The
material contained herein is based on information believed to be reliable, however, no representation or warranty, express or
implied, as to the accuracy or completeness thereof is made. No responsibility is accepted by Anglo American plc or any of its
subsidiaries or associated companies for any loss or damage of whatsoever nature arising out of the use of, adherence to or the
lack thereof to any part of this information.

13
Disclaimer: The information contained in this document is not prescriptive. It is indicative of good practice and is intended as
information for site specific interpretation and application by the responsible parties within the Anglo American plc Group. The
material contained herein is based on information believed to be reliable, however, no representation or warranty, express or
implied, as to the accuracy or completeness thereof is made. No responsibility is accepted by Anglo American plc or any of its
subsidiaries or associated companies for any loss or damage of whatsoever nature arising out of the use of, adherence to or the
lack thereof to any part of this information.

14
Disclaimer: The information contained in this document is not prescriptive. It is indicative of good practice and is intended as
information for site specific interpretation and application by the responsible parties within the Anglo American plc Group. The
material contained herein is based on information believed to be reliable, however, no representation or warranty, express or
implied, as to the accuracy or completeness thereof is made. No responsibility is accepted by Anglo American plc or any of its
subsidiaries or associated companies for any loss or damage of whatsoever nature arising out of the use of, adherence to or the
lack thereof to any part of this information.

15
Disclaimer: The information contained in this document is not prescriptive. It is indicative of good practice and is intended as
information for site specific interpretation and application by the responsible parties within the Anglo American plc Group. The
material contained herein is based on information believed to be reliable, however, no representation or warranty, express or
implied, as to the accuracy or completeness thereof is made. No responsibility is accepted by Anglo American plc or any of its
subsidiaries or associated companies for any loss or damage of whatsoever nature arising out of the use of, adherence to or the
lack thereof to any part of this information.

16