1
MINING EQUIPMENT PRODUCTIVITY INCREASE AND
WORKER'S SAFETY IMPROVEMENT BY WEAR MATERIALS
DEVELOPMENT: CASE HISTORY CARRIED OUT AT VALE,
BRAZIL
Cláudio Gonçalves de Oliveira
Mechanical Engineering Student; Maintenance Engineering Specialist; Vale's Specialized Technician
Email: Claudio.goncalves.oliveira@vale.com
Gilmar dos Santos Mascarenhas
Electrician Engineer; Vale's Senior Engineer
Email: gilmar.mascarenhas@vale.com
Abstract
Wear materials are largely used at mining industrial
installations and equipment maintenance for worn out
material replacement is a frequent occurrence which
generates important downtime with consequent
productivity loss, on top of offering several risks of
accidents and occupational diseases. The highly abrasive
ore, the transportation speed and the high volume of
transported material provoke severe wear on transfer
chutes coating plates of Long Distance Belt Conveyors
and consequent equipment interruption every 15 days,
which represents 700 hours downtime per year,
productivity loss of 2,8 million/tons of non-transferred
ore, plates costs, and ergonomic risks for workers due to
heavy load and inadequate operational position. The
present work developed at Maintenance Engineering
Dept. of Vale mining company in Brazil objectivated the
analysis, project and development of new white cast Iron
alloys for purposes of prolonged service life, weight
reduction and easier installation. Wear material suppliers
were requested to present their best alloys for abrasion
resistance and tests were carried out simulating
operational conditions until an ideal plate with proven
durability and adequate weight could be obtained. A
wear plate alloy has been developed according to ASTM
standards, offering 90 days service life, using new
fastening method with metallic insert screw and mass
relief at base. This new project permitted better thickness
utilization and weight reduction from 23 to 20kg, so
reducing risks of conveyor belt to tear, as well as
avoiding ergonomic risks and human accidents. Long
Distance Belt Conveyor planned interruptions for
maintenance could be extended from 15 to 21 days,
providing better equipment availability; 200 hours/year
could be recuperated for transportation of additional
800.000 tons of ore for production at processing plant
where pilot tests have been carried out.
Keywords: maintenance engineering; wear materials;
industrial and human development.
1
Introduction
This article is the result of a work made by Industrial
Maintenance Engineering from Vale-Brazil and derived
from a request of industrial areas for better availability
of Long Distance Belt Conveyors
The highly abrasive ore, the transportation high speed
and the high volume of transported material provoke
wear on conveyor transference coating plates and
consequent programmed downtime every 15 days for
components replacement, on top of other corrective
interruptions for patching on damaged chutes; all these
interruptions generate productivity loss due to
millions/tons of non-transferred ore; there are also risks
of belt lacerations due to plates detachment and
ergonomic risks due to heavy load and inadequate
operational position.
Taking the Complexo Vargem Grande conveyor as
reference, productivity loss generated by 700 hours
downtime/year for preventive maintenance interventions
amounts to 2,8 million/tons of non-transported ore.
The number of work accidents registered during
wearplates replacement is also quite significant. The
main factors contributing for such accidents occurrence
are: plates weight, fastening project, plates localization
and method of activities execution which expose
operators to several risks. Plates assembling and
disassembling are performed by two operators using
stone-mason's hammer, lever, screw-key and stairs.
In front of such critical situations it has been found out
an urgent need to develop specific projects for anti-wear
materials improvement, mainly conveyor chutes coating
plates, due to their importance in equipment availability
and also due to several material and personal losses
already registered generated by their low service life and
fastening execution, factors which are not satisfactory
since equipments started operating.
According to Xenos (1998, p.20) maintenance activities
have distinguished objectives: some are directed to
correct eventual irregularities or failures observed in
equipments, while others objectivate continuous
improvement or "kaizen" in order to improve original
operating conditions, performance and inherent
reliability through modifications or alterations in
equipment project or original configuration.
One of the indispensable knowledge areas in industrial
processes optimization in mining sector is the material
engineering:
Which objectivates projects development, materials selection
and utilization. (...) It is common to face problems of low
equipment performance allied to materials and in many cases
the solution is the selection of the exactly correct material
among thousands of available ones. For this, the principles of
materials processing-structure-properties-performance have
to be taken into consideration. (Callister Jr., 2002, ps. 2-3).
For sake of equipments gradual and continuous
improvement, surpassing their original specifications,
2
this work objectivates Long Distance Belt Conveyors
(TCLD) productivity optimization and increased
availability by means of development of a new wearplate
made out of white cast Iron, offering increased service
life, lighter weight and new fastening project in order to
maximize their utilization and facilitate their remotion
and replacement, so avoiding above mentioned
problems.
2
Materials And Methods
2.1
Description of used wearplates
Wearplates normally used in TCLD tranference chutes
are rectangular, measuring 390 x 190 x 40mm, 23kg
weight, fabricated with white cast Iron Class II, type D,
chemical composition containing 18 to 23% Chromium
and average hardness of 550 Brinell (HB), not submitted
to thermal treatment, as per ASTM A 532 standard.
White cast Iron is an Iron-Carbon-Silicon basis alloy
with Carbon content over 2% and light-coloured fracture
which gives origin to its name. Its main properties are
high hardness and wear resistance and consequently
provides difficult machining even with best available
cutting materials. (Chiaverini, 1982, p. 439).
For fastening on chute wall purposes, plates are provided
with 200mm centered holes through full plate thickness
where 3/4" x 1 1/2" hexagonal or square screws are
fastened with 3/4" nuts, as per Figure 1.
microstructure, hardness and weight have been
differentiated by each manufacturer.
 First test: 390 x 190 x 40mm plate, white cast Iron
alloy, predominantly martensitic matrix containing
M7C3 primary carbides, M23C6 secondary carbides,
18 to 23% Chromium, 14,7kg weight.
 Second test: 390 x 190 x 50mm plate, white cast Iron
alloy, 25% Chromium, 66 Rc hardness, wafer at end
with 85 Rc hardness, 28kg weight.
 Third test: 390 x 190 x 40mm plate, white cast Iron
alloy, 27% Chromium (ASTM A 532, Grade III, Type
A modified), thermal treatment by tempering and
annealing, final hardness 57 to 62 HRC (approx. 600
to 685 HB), 23kg weight.
 Fourth test: 390 x 190 x 40mm plate, white cast Iron
alloy, 23,8% Chromium (ASTM A 532, Grade III,
Type A), thermal treatment by tempering and
annealing, final hardness (approx. 670 to 675 HB),
23kg weight.
2.4
Once the need for development of a new wearplate
offering extended service life and better cost-benefit rate
has been attended, search has been then directed to the
development of a project for plate fastening in order to
optimize plate utilization and reduce risks of material
and personal accidents.
3
Figure 1: Wearplate 390 x 190 x 40mm with introduced
screws and nuts.
This fastening method does not allow plates satisfactory
utilization since after 40% only of thickness wear,
screws head protection area becomes exposed causing
their detachment. Plates have to be then replaced after
utilization of less than half of their thickness, what
represents high material waste.
Fastening method modification
Results and Discussion
As far as service life is concerned, original plate
presented a duration of 15 days while second test plate
offered 90 days. But this high performance is due not
only to alloy chemical composition and thermal
treatment, but mainly to mass increase providing a
10mm higher thickness and 5kg higher weight in relation
to original plate and 13,3kg higher weight in relation to
plate in the first test, as per graphic 2.
2nd t est (25% Cr )
90
3r d t est (27% Cr )
84
4t h t est (23, 8 % Cr )
78
1st t est (18 - 23% Cr )
41
Or i gi nal pl at e (17- 21% Cr )
15
0
2.2
10
20
30
40
Adopted procedures for research
50
60
70
80
90
In order to develop a new wearplate offering higher
abrasion resistance and extended service life, Industrial
Maintenance Engineering has searched in various wear
materials manufacturers both in local and international
markets the most adequate material to attend company's
requirements.
This lead us to select white cast Iron which offers the
best cost-benefit rate. But such material presents ten
different manufacturing classes with different chemical
composition, hardness and microstructure and definition
of ideal specification had to be made through tests "in
situ".
Graphic 1: Plates service life in days
2.3
As it can be observed in graphic 2, plate weight in third
test is same as original plate but offered additional 69
days of service life. As far as transported tonnage during
plates testing period (graphic 3), third test showed a
Description of tested plates
Fastening method of plates being tested was according to
original project, that is, with full thickness holes for
screws introduction. But ther chemical composition,
100
Days
2nd t est
28,00
Chapa Original
23,00
3rd t est
23,00
4t h t est
23,00
1st t est
14,70
0,00
5,00
10,00
15,00
20,00
25,00
We i ght ( k g)
Graphic 2: Weight of tested plates
30,00
3
highly satisfactory result in comparison to all evaluated
plates, offering a total of 6.690.000 tons transported
during 84 operating days, surpassing second test plate
which offered extended service life in days.
Considering cost of transported millions/tons, third test
also presented the best results: R$32,14 as per graphic 4.
3r d t est (27% Cr )
6. 690
2nd t est (25% Cr )
Figure 2: Former plate project with holes, at background
and new project with metallic inserts and screws at
foreground.
6. 157
4t h t est (23, 8 % Cr )
4. 965
1st t est (18-23% Cr )
3. 155
Or i gi nal pl at e (17 - 21% Cr )
4
1. 112
0
1. 000
2. 000
3. 000
4. 000
5. 000
6. 000
7. 000
8. 000
T o n s ( mi l l i o n s )
Graphic 3: Transported tonnage during testing period
3r d t est (27% Cr )
32, 14
4t h t est (23, 8% Cr )
36, 65
1st t est (18-23% Cr )
44, 18
46, 33
2nd t est (25% Cr )
Or i gi nal pl at e (17-21% Cr )
Conclusion
Due to observed satisfactory results in terms of
productivity, costs reduction, equipments and operators
safety, the new wearplate has been included in Vale's
materials register system in substitution to former plate.
A supply agreement has been settled where annual cost
reduction of approximately R$1,7 millions and 80%
reduction in plates consumption can be reached, on top
of direct labour reduction for replacement as
demonstrated in table 1.
121
0
20
40
60
80
100
120
140
R $ / t r a n s p o r t e d mi l l i o n s / t o n s
Application
Analysed item Um
Specification
-
Face to tests results, the best alloy developed in within
established criteria for service life and cost evaluation in
relation to transported tonnage, was test 3 plate: 390 x
190 x 40mm, white cast Iron alloy, 27% Chromium
(ASTM A 532, Grade III, Type A, modified), with
thermal treatment by tempering and annealing, final
hardness of 57 to 62 HRC (approx. 600 to 685 HB),
23kg weight.
Test 3 plate better performance can be explained by the high
Chromium content in alloy composition, which "(...) when
utilized in high contents produces very hard Chromium
carbides which provide resistance to abrasion wear."
(Chiaverini, 1982, pg.442).
Thermal treatment with tempering and annealing used in
this plate also contributed for the formation of a more
homogeneous microstructure with high quantities of
Chromium carbides and uniform hardness through entire
thickness with minimum superficial hardness of 600 HB.
As per new project, on top of alloy chemical
composition alterations and thermal treatment
application, holes for screws introduction have been
eliminated and substituted by two metallic inserts made
out of easily machinable material allowing thread
opening and fastening of two grub Allen screws 3/4" x 1
1/2" at plate base. Plate also received a mass relief of
8mm in its thickness so reducing its weight from 23kg to
20kg (figure 2).
Such alterations allow 70% utilization of plate thickness,
which was originally 40%. On top of plate utilization
optimization, 3kg weight reduction could be observed
and the new easier assembling/disassembling method
could reduce detachment risks and consequent belt
lacerations. Ergonomic and accidents risks could be
minimized as well.
Abrasion
Graphic 4: Plates cost per transported millions/tons
Manufacturing
process
Code
Annual hours for
replacement
Weight
Annual
consumption
Cost per unit
Annual cost
Difference
Prior
After
Reduction %
ASTM A ASTM A
532, Grade 532, Grade
II, Type D III, Type A
-
Cast
Cast
-
-
96034647
96120891
-
Hh
13246
2650
80
Kg
23
20
13
Pç
13246
2650
R$
126,00
168,60
1.669.000,0
R$
447.000,00
0
R$
80
-34
73
1.223.000,00
Table 1: Comparison between former plate and new
project
We believe this project is the first of several
improvements still to be searched and implemented by
Industrial Maintenance Engineering as far as Vale's wear
materials are concerned since they represent
considerable industrial installations input where
performance is tightly connected to the equipments
availability and reliability, what generates direct impact
on more and more challenging production objectives.
References
XENOS, Harilaus Georgius D’Philippos. Gerenciando
a Manutenção Produtiva. Belo Horizonte: Editora de
Desenvolvimento Gerencial, 1998.
CALLISTER JR. William D. Ciência e Engenharia de
Materiais: uma introdução. Rio de Janeiro: LTC, 2002.
CHIAVERINI, Vicente. Aços e Ferros Fundidos. São
Paulo: ABM, 1982.
SOUZA, Sérgio Augusto de. Composição Química dos
Aços. São Paulo: ABDR, 2001.