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HOW TO JUDGE THE SUCCESS OF THE REPAIR AND MAINTENANCE CREWS
MAINTAINING ELECTRIC MINING SHOVELS ? ( MAINTENANCE AND REPAIR
QUALITY INDICATORS OF ELECTRIC MINING SHOVELS )
Conference Paper · January 2011
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HOW TO JUDGE THE SUCCESS OF THE REPAIR AND
MAINTENANCE CREWS MAINTAINING ELECTRIC MINING
SHOVELS ?
( MAINTENANCE AND REPAIR QUALITY INDICATORS OF
ELECTRIC MINING SHOVELS )
Metin ÖZDOĞAN
İdeal Makine Danışmanlık Ltd. Şti., Ankara
Hakkı ÖZDOĞAN
İdeal Makine Danışmanlık Ltd. Şti., Ankara
ABSTRACT : In this paper, maintenance and repair achievement indicators are
cited and described for electric mining shovels with 15 m3 dippers, such as
availability, utilization, reliability, maintainability, failure rate. These indicators
are depicted for five electric mining shovels, for a period of three years,
operating at GLİ Tunçbilek surface mines. The maintenance and repair
parameters of the equipment are calculated and interpreted for a period of three
years .
1 INTRODUCTION
Electric mining shovels are capital equipment and requires a very high capital
investment cost therefore, they are always serviced and maintained on regular
basis ie periodically. Electric mining shovels react divergent to the applied repair
and maintenance programs depending on the design, structural properties, quality
of the replacement parts, sturdiness ratio of the machine (ratio of operating
weight over dipper capacity).
Electric mining shovels’ productivity and profitability are functions of operating
durations (periods) and the longevity of equipment life. Maintenance and repair
programs comprise of 20 % to 40 % of the mining operational cost (Erçelebi and
Ergin, 1997)
2 MAINTENANCE TYPES
Maintenance on the Basis of Failures (Reactive Maintenance) : Reactive
maintenance is repairing & maintaining the machine when it fails. Reactive
maintenance methods were used in mining for a long period of time. In this type
of maintenance, equipment breakdowns occur all of a sudden which causes
destructive production losses and repair and maintenance expenses (Barkhuizen
ve Pretorius, 2008).
Periodical Preventive Maintenance: As a result of devastating component
failures and production lossess mining industry concentrated on periodical
preventive maintenance programs and started replacing and repairing the parts
prior to break downs happen.
Predictive Maintenance: The contemporary maintenance method is predictive
maintenance which involves check up of the health, and estimate life expectancy
of components by using diagnostic devices like vibration meters, infrared
termographs, oil analysers and ultrasonometers etc. (Barkhuizen, 2002). Based
on the inspection and diagnostics, repair and maintenance programmes; parts and
component changes are planned.
3
MAINTENANCE
&
REPAIR
QUALITY
INDICATORS
Table 1. Maintenance and repair parameters of P&H 2300XP (15m3) shovels in
2007, 2008 and 2009.
Shovel #
(A)
%
(n/h) x 10-2
count/h
(U)
%
R,
hours
(M), (n),
hours count
YK34(avg.) 61±5
84±3
25±4
7±2
112±24
(4,05±0,50) x 10-2
YK35
64±4
87±6
39±2
7±2
87±28
(3,04±1,09)
YK36
66±7
88±9
42±2
5±2
69±9
(3,67±2,63)
YK37
65±3
86±7
36±5
6±2
90±25
(3,42±0,77)
YK38
62±4
85±1
28±2
10±3
112±2
(3,55±0,26)
Averages
64±2
86±1
34±7
7±2
94±18
(3,55±0,33)
3.1 Availability and Utilisation
The Utilisation (U) differs from Availibility (A) that the utilisation concept has
both planned and unplanned downtimes. Unplanned downtimes cover
breakdowns and waiting idle. On the other hand, planned downtimes comprise
shift changing times, bench preparations, meal and tea breaks, lubrication,
supplies and maintenance. Utilisation calculation equation is given in the
appendix section (Dhillon 2008).
Table 2. Availability details of electric mining shovel # YK37(15m3)
Year Program Unplanned
(h)
downtime
(Tprg)
(Tupd) (h)
Planned Avail.
downtime (A)
(Tpd)
%
(h)
Utilisation
(U)
%
Real
working
time
(Tg)
(h)
Dig Rate,
Q
(m3/h)
(bank m.)
Annual
Production,
Q (m3/year)
(bank m.)
x 103
Failure
(Tupda)
Idling
(Tupdb)
2007 5715
387
1809
156
62
95
3364
826
2780
2008 6143
678
1272
622
68
85
3572
816
2913
2009 4995
497
1314
684
64
79
2504
820
2054
Avg. 5618
±474
521
±120
1465
±244
487
±236
65±3
86±7
3147
±462
821±4
2582
±378
Figure1. Average availability figures of the shovels for three years.
Figure 2. Average utilization figures of the shovels for three years.
3.3 Equipment (EMS) Reliability (R) (Mean Time Between Failures)
(MTBF)
Reliability is the measure of equipment’s sturdiness and resistance, durability to
daily heavy duty work being carried out. Reliability is also defined as the mean
time between failures and abbrevated as (MTBF).
Figure 3. Average reliability figures of the shovels for three years.
Table 3. Reliability, maintainability and failure rate figures of shovel #YK37
Years
Program
(h)
(Tprg)
Failure
Waiting
time
idle
(Tupda) (h) (Tupdb)
(Tupda)
Real
# of
working failures
time (h) (n)
(Tg)
Mean time
between
failures
(MTBF),(R)
(h)
(M)
(MTTR)
(Tupda) / (n)
(mean time to
repair) (h)
Failure rate,
n/h, n/Tg
2007
5715
387
1809
3364
85
39.57
4,55
3,42 x 10-2
2008
6143
678
1272
3572
122
29.28
5,58
4,36 x 10-2
2009
4995
497
1314
2504
62
40.39
8,02
2,48 x 10-2
Avg.
5618
±474
521
±120
1465
±244
3147
±462
90±25 36±5
6±2
3,42±0,77 x
10-2
3.4 Equipment Maintainability (M) (Mean Time To Repair, MTTR)
Equipment’s maintenance and repair ease is called maintainability. It is also
defined the mean time to repair and its’ abbrevation is MTTR or M and its’unit is
hours (Barkhuizen, 2002). The smaller the M value, the better the maintainability
of the equipment. The smaller M figure indicates that failures are shot in a
shorter time; this in turn implies the success of maintenance and repair team and
management at the mine (Pak, 2010). Figure 4. Depicts, mean time to repair
figures of the five electric mining shovels. YK36 has the best maintainability
figure.
Figure 4. Average maintainability figures of the shovels for three years.
3.5. Failure Rate (n/h)
Failure rate is described as the average number of breakdowns per unit time
which is generally per hour. This parameter shows the frequency of breakdowns
of the machine. Predictive maintenance decisions and intervals are based on the
failure rate figures. Sudden increase in failure rates and increase in frequency of
breakdowns generally imply that the equipment has to be replaced by a new one
(Cebesoy 1998). Failure rate is a measure of quality of the repair and
maintenance conducted by the maintenance administration and the unit is the
number of breakdowns per hour (Pak, 2010). The Figure 5. depicts failure rates
of the shovels studied, and YK35 shovel has the best failure rate ie lowest
number of breakdowns per hour.
Figure 5. Average failure rate figures of the shovels for three years.
3.5.1 Maintenance Frequency
Maintenance frequency indicates the periodical preventive maintenance
intervals. There is some production loss and repair and maintenance expenditures
may increase to a degree due to the fact that the equipment is allocated to
maintenance by taking it off the production. In order to minimise the losses, an
optimum preventive maintenance interval for the equipment to be decided which
is not an easy task, in practice (Cebesoy, 1998). Maintenance intervals
recommended by the OEM may be a clue in this respect. For example, electric
mining shovel manufacturers suggest daily, weekly, monthly, and yearly
intervals for maintenance intervals.
5 CONCLUSIONS
Average availability (A) value of the five shovels was 64±2 percent. Highest
figure was 66±7 percent belonging to YK36 shovel whereas the lowest
availability was that of YK34 shovel with 61±5 percent.
Utilisation (U) figure of the five shovels was 86±1 percent. Highest utilisation
value was 88±9 percent belonging to YK36 shovel whereas the lowest
availability was that of YK34 shovel with 84±3 percent.
Reliability (R) figure ofthe five shovels was 34±7 hours. Longest time between
failures was 42±2 hours belonging to YK36 shovel, whereas the shortest time
between failures was that of YK34 shovel with 25±4 hours.
The increase of (R) value implies that surprise failures diminishes, and sound
operational periods extended (Pak, 2010). Reliability is a function of equipment
sturdiness and quality of the repair and maintenance practices and programs
applied.
Average maintainability (M) figure of the five shovels, in three-years, was 7±2
hours. Longest repair time was 10±3 hours for YK38 shovel whereas the shortest
repair time encountered was that of YK36 shovel with 5±2 hours.
Average number of failures (n) count of the five electric mining shovels, in
three-years, was 94±18 each. The number of breakdowns was highest on YK34
with a count of 112±24 and YK38 with 112±2 each; whereas the least number of
failures encountered was that of YK36 shovel with 69±9 counts.
Average failure rate (n/h) count of five YK(15m3) shovels’ in three-years was
94±18 each. The rate of breakdowns was highest on YK34 with a count of
4,05±0.50 x 10-2 breakdowns per hour; whereas the least rate of failures
encountered was that of YK35 shovel with 3,04±1,09 failures per hour.
As far as the mathhematics of reliability and maintainability are concerned, as
the unplanned (unscheduled) downtimes (breakdowns) decrease, the Reliability
or MTBF increases. Meanwhile MTTR (M) should decrease. As unscheduled
stoppages of equipment get closer to zero (0), MTBF (R ) gets closer to infinite
(∞), and MTTR (M) becomes zero (0) and availability will be (100) hundred
percent (Pak, 2010).
Making use of these indicators, the repair and maintenance teams’ and programs’
performances can be evaluated and judged. Furthermore, success of parts
purchasing and supply systems can also be judged; life and quality of the parts
can be monitored thru these records and calculated parameters. However, to have
meaningful maintenance and repair indicating facts and figures, records and
monitoring should cover at least a period of six months or one year; thus,
indicate trends that may give clues to the maintenance and repair administration
(Barhuizen, 2002, Kruppu (2004).
Unless the maintenance and repair crews are not competent enough and properly
trained, all the efforts spent go down the drain. As far as quality replacement
parts and supply of consumables are concerned, if supply chain is slow and the
quality of components procured are inferior, the efforts of maintenance teams
are wasted off. If the above cited factors prevails, there is no improvement in
maintenance and repair parameters eventhough periodical maintenance and
repair programmes applied; in other words, number of breakdowns can not be
reduced, mean time between failures can not extended; the impact of the
maintenace programmes applied is not as good as expected.
REFERENCES
Barkhuizen, W.F. and Pretorius, L., 2003; Life Cycle Management for Mining
Machinery, University of Johannesburg, South Africa,2008 Available online at:
http://ujdigispace.uj.ac.za:8080/.../ArticleLifeCycleManagementforMiningMachinery.pdf
Barkhuizen, W.F., 2002; Life Cycle Management for Mining Machinery,
University of Johannesburg, South Africa, 2008
Available online at:
http://ujdigispace.uj.ac.za:8080/dspace/.../MastersDegreethesisrev02.pdf
Cebesoy, T.. ; Maden ekipmanları için bir rasyonel bakım planlaması modeli:
Önleyici bakım. Türkiye 11. Kömür Kongresi Bildiriler Kitabı,
1998, Zonguldak, Türkiye, s. -.
Dhillon, B.S. 2008; Chapter 4, Mining Equipment Reliability, Mining Equipment
Reliability, Maintainability, and Safety, 1st edition (book), July 29, 2008,
Springer (publisher), 2008, New York, USA. p.57-70.
Erçelebi, S.G. Ve Ergin, H., 1997; Maden makinalarında koruyucu bakım onarım
planlaması, Türkiye 15. Maden Kongresi, Güyagüler, Ersayın, Bilgen (eds),
Ankara, 1997, s. 31-36.
Kruppu, M.D. 2004; New technologies available to maximizing equipment
reliability, Hardygora, Paszkowska and Sikora (Eds)., 2004; Mine Planning and
Equipment Selection, Taylor and Francis Group, London, pp. 455-459
Pak, C. 2010 ; http://www.cengizpak.com.tr/index.php/periyodik-önleyici-ve-kestirimcibakim-nedir?/
Appendix:
= [Tprg – (Tupda+Tupdb] x 100
Tpd
Where,
A
A
: Availability %
Tprg
: Programmed total working time, h
Tupda
: Breakdown time (repair time) (unplanned downtime), h
Tupdb
: Unplanned downtime, h
Tupd
:Total unplanned downtime, h
Tpd
: Planned downtime (maintenance, lunch breaks, shift changes etc.)
(Dhillon 2008).
U = (Tprg) – Tupd – Tpd x 100
(Tprg) - (Tupd)
Where,
U
Tprg
Tupd
Tpd
: Utilisation
: Total programmed working time, h
: Unplanned total downtime, Tupda +Tupdb, h
: Planned total downtime, h
(Dhillon 2008).
Where,
R = (Tprg)-(Tupd) -(Tpd)
(n)
R
: Reliability, (Mean Time Between Failures),h
Tprg
: Programmed total working time, h
Tupd
: Unplanned total downtime , h
Tpd
: Planned total downtime, h
n
: Number of breakdowns, count
Maintainability: (Mean time to repair) (MTTR)
M= Tupda
(n)
Where,
Tupda
n
: Total downtime due to breakdowns
: Number of breakdowns
Failure Rate :
Breakdown Rate = # of breakdowns (unplanned downtimes)
Working time, h
Breakdown Rate = n/ Tg = Count / h
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