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Transport in Open Pits
Unit-5
LIST OF TOPICS
1
Introduction
Overview of transport in Open pits, types of material haulage system in open pits
2
Dumpers
Overview, Types, applicability and limitations, computation of their productivity,
Shovel-Dumper synchronization
3
Rail transport and conveyors in Open pits
Suitability, IPCC, High angle conveying, specialized conveying
4
Automation in open pit transport
Truck dispatch system, Overview of excavation and haulage
Haulage operation in Open pits - Overview
13%
12%
12%
48%
15%
Open pit production costs
Drill and Blast Roads and Dumps
Loading Haulage
Overhead
• Haulage system is a key and the most expensive unit operation of
open pit mining.
• The hauling of material (such as coal, ore, sand, gravel, or top-soil)
from one point to another in a safe, efficient, and cost-effective
manner is critical for mining operations.
• Selecting the type of surface hauler requires a thorough
understanding of the selected mining method and its associated
advantages and disadvantages along with the machinery available
to the industry.
• Rigid-frame haul trucks have dominated haulage in open-pit
mining operations for decades.
• Although in some cases articulated dump trucks (ADTs) have
proven a viable alternative, and sometimes rail haulage is still
being used.
• Furthermore, longer haulage distances in many large pits,
availability problems with haul trucks, and improvements in
technology have revived interest in conveyor transport including
in-pit crushing and conveying (IPCC).
Introduction – Automobile transport in Open pits
• A number of haulage options are
available for mining, all of them with
unique characteristics that can be
optimal for a particular mine site and
haul distance.
Articulated dump trucks Off-highway articulated trucks are
a hauling alternative primarily for
middle-to-large-scale construction
projects. They are often used for
pre-stripping, road construction,
and material hauling for ground
preparation for buildings and
other infrastructure. When used
with small hydraulic excavators or
wheel loaders, they can constitute
an effective loader and hauler
fleet for a mass excavation
project. They are widely used for
pre- and postmining construction
in soft-underfoot conditions, in
small loading and dump areas, or
on steep (10%–15%) grades
An articulated dump truck (ADT) is a three-axle machine with
an articulation point between the front axle and the two rear
axles. The articulation, which is unique to this truck type, is
useful where there is limited area in which to operate.
ADTs providing the
surface mining industry a
hauling solution that is
adaptable to tough
hauling conditions.
However, because of
their limited hauling
capacity, they are not
viable as primary
production machines.
Trolley assisted Dump
trucks
Trolley-assist haul trucks are haul trucks that
have been adapted from the standard
diesel–electric system to a system that relies
on pantographs to connect to an electrified
over-head line for power supply. Historically,
use of this system has been concentrated in
southern Africa, but with rising diesel prices,
interest in trolley-assist hauling from other
parts of the world is increasing. Major
infrastructures that need to be installed for
the use of trolley-assist haulage include the
overhead lines, truck conversion packages,
and trolley substations. These conversion
packages can be fitted on the majority of
diesel–electric trucks.
Increased power supply from the overhead line, compared to a truck-based diesel
generator, allows maximum use of the capacity of the electric motor in a truck. As a
result, reduced cycle times are possible, and consequently, truck fleets can be reduced.
This allows for productivity increases and possibly reduced capital investment costs
related to purchasing fewer trucks. Furthermore, as the diesel engine is idling while on
trolley assist, fuel consumption and ultimately time between engine overhauls can be
reduced significantly. Lastly, energy can be recovered into the trolley supply grid when
trucks are moving downgrade.
Dumpers or Haul Trucks
Most popular haulage system in open-pit
mining operations for decades.
Haulage trucks have superior Payload capacities that
range from around 25 t to over 360 t.
Better speeds in most road conditions and
have lower maintenance requirements.
There is a choice between mechanical drive and
electrical drive systems.
Rigid-frame trucks, with or without trolley
assist, and are the preferred choice for
haulage in most open-pit mines.
Truck models by size class and manufacturer
• Trucks for surface mining currently have
payload capacities of 90–360 t (100–400
st).
• These values have evolved over time,
driven by the mining industry’s desire to
go larger in order to maintain or increase
production while decreasing fleet size
and operating costs.
• Within this payload range, there are five
distinct classes, designated according to
size:
1. 90-t (100-st) class
2. 135-t (150-st) class
3. 180-t (200-st) class
4. 220-t (250-st) class
5. >290-t (320-st) ultra-class truck
(UCT)
Mechanical drive train
• The mechanical drive train contains five major
components: engine, torque converter,
transmission, differential, and planetary gear
sets (wheels).
• The power source is the diesel engine plus
torque converter; the latter transmits
rotational power from the engine to the main
driveshaft.
• The transmission controls machine torque and
speed during operation.
• The differential transfers output torque to the
wheels.
• Two hydraulic brake packs are mounted on
each of the axle shafts on the two rear wheels.
• The entire system is activated by means of a
variety of electronic control modules and
hydraulic control systems.
Electric drive train (DC and AC)
• DC and AC electric drive trains contain six major com-
• ponents: engine, generator, power converter, wheel
motors, planetary gear sets (wheels), and retarding grid.
• The power source is the diesel engine plus generator;
the latter converts mechanical power from the engine
into electric power.
• AC current from the generator is then converted into
useable form.
• In a DC-drive truck, a rectifier converts it into DC power;
in an AC-drive truck, a rectifier converts it into DC
power and inverters convert it back to a controllable
version of AC power suitable for managing the
amperes, volts, and frequencies of the wheel motors in
order to create machine speed and torque.
• The DC or AC wheel motors receive the electric power
and feed it mechanically to the planetary gear sets
(wheels).
• Diesel - Electric AC systems dominate the larger truck
sizes (>150- t payload).
Dumpers - Productivity
• Cycle times determines the
productivity of haul truck which in
turn depends on the type of
excavator, truck capacity and
haulage distance.
• Assuming good truck - excavator
capacity matching and good
digging conditions, trucks should
be loaded in approximately 100 to
150 seconds, this is longer for
front end loaders.
• Spotting at the excavator typically
takes between 40 and 60 seconds.
• Productivity of the haulage system
is highly dependent on the
performance of other activities in
the mine, notably the haul road
and dump conditions, excavator
efficiency etc.
One sided loading Two sided loading
One-sided loading has several disadvantages. Mining shovels and hydraulic shovels cycle in
30–35 seconds and spotting takes 40–60 seconds, so the shovel must wait for the truck,
reducing production levels. In addition, the time required for a cleanup dozer to work in the
spot area can delay operation. These disadvantages can be addressed to some extent by
two-sided loading
Factors influencing the productivity of dumpers
Many times problems with poor haul truck productivity and reliability can often be traced back to poor
performance of other parts of operations. Some of these factors are;
• Haul road performance: Poor haul road performance (e.g., haul road defects and high rolling resistance) can
reduce productivity and reliability of dump trucks.
• Loading & Dump Face Conditions: Poor floor conditions in active loading and dumping areas (e.g., benches
and dumps) can also affect productivity and reliability of dump trucks.
• Poor Material Quality: Retention of material in both excavator bucket and the truck bed can pose a
challenge to operations (in adverse climatic conditions or where material has a high clay or moisture
content). Adaptation of the truck bed design, e.g., rubber floor mats or circulation of exhaust fumes through
the bed to prevent freezing can alleviate this problem.
• Good communication between truck and excavator operators: Good operator training as well as a high
degree of coordination, communication, and visual confirmation on the part of both the excavator and the
truck operator is crucial for truck spotting at the Excavator. Excavator operators should communicate the
correct position for a truck, rather than relying on his judgment to get the truck in the right place. Good
communication is especially crucial when double-spotting trucks. This method has the potential to reduce
excavator and truck idle time.
Productivity of dumpers – Key terminology
Relationship between calendar hours and operating hours
• Although there are about 8,760 calendar hours
in a year, excavators typically operate for 6,000–
7,000 hours per year.
• For initial estimating, it is adequate to combine
availability and utilization values into a single
operating efficiency factor.
• Typical availability and utilization values are each
about 85%, which provides an operating
efficiency of about 72% of the scheduled hours.
𝐴𝑣𝑎𝑖𝑙𝑎𝑏𝑖𝑙𝑖𝑡𝑦 𝑓𝑎𝑐𝑡𝑜𝑟 =
𝐻𝐴
𝐻𝑠
𝑈𝑖𝑙𝑖𝑧𝑎𝑡𝑖𝑜𝑛 𝑓𝑎𝑐𝑡𝑜𝑟 =
𝐻𝑈
𝐻𝑆
=
𝐻𝐴 − 𝐻𝐷𝑈
𝐻𝑆
Productivity of dumpers – Key terminology
• In the mine, the material which is to
be loaded into the dipper must
generally first be loosened from its
“in-place (in situ)” or “bank”
position.
• Assuming that the material occupies
a volume of 1 m3 in place (denoted as
1 bank cubic metres, or 1 bcm), that
same amount of material would be
expected to occupy a larger volume
in the loose condition.
• The weight of one cubic metre of
loose material (one lcm), due to the
presence of void (air) spaces between
the pieces, would be less than the
weight of one bcm.
Bank Cubic Metres and Loose Cubic Metres
Swell is the ratio of the bank to loose weight densities.
Swell factor is inverse of swell.
𝑆𝑤𝑒𝑙𝑙 =
𝑏𝑎𝑛𝑘 𝑑𝑒𝑛𝑠𝑖𝑡𝑦
𝑙𝑜𝑜𝑠𝑒 𝑑𝑒𝑛𝑠𝑖𝑡𝑦
𝑃𝑒𝑟𝑐𝑒𝑛𝑡 𝑠𝑤𝑒𝑙𝑙 = 100(𝑠𝑤𝑒𝑙𝑙 − 1)
Material filling
𝑆𝑤𝑒𝑙𝑙 𝑓𝑎𝑐𝑡𝑜𝑟 =
1
𝑠𝑤𝑒𝑙𝑙
=
𝑙𝑜𝑜𝑠𝑒 𝑑𝑒𝑛𝑠𝑖𝑡𝑦
𝑏𝑎𝑛𝑘 𝑑𝑒𝑛𝑠𝑖𝑡𝑦
The “fillability” or the “fill-factor” refers to the ratio of the loose volume
of rock contained in the dipper to the rated dipper capacity.
𝐹𝑖𝑙𝑙𝑎𝑏𝑖𝑙𝑖𝑡𝑦 =
𝑙𝑜𝑜𝑠𝑒 𝑣𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑟𝑜𝑐𝑘 (𝑚3
)
𝑟𝑎𝑡𝑒𝑑 𝑐𝑎𝑝𝑎𝑐𝑖𝑡𝑦 𝑜𝑓 𝑑𝑖𝑝𝑝𝑒𝑟 (𝑚3)
Productivity of dumpers – Key terminology
Some properties for various materials which are important for loading
machine evaluation
Rock
Specific
gravity
(bank)
Weight density
Swell
Percent
Swell
Swell
factor
Fillability
kg/bcm kg/lcm
Bauxite 1.90 1898.45 1406.07 1.35 35.02 0.74 0.90
Coal (Bituminous) 1.25 1245.88 922.54 1.35 35.05 0.74 0.90
Iron Ore (60% Fe) 3.85 3856.30 2487.61 1.55 55.02 0.65 0.75
Limestone (hard) 2.60 2610.42 1631.51 1.60 60.00 0.63 0.80
Sandstone (porous) 2.50 2491.76 1557.35 1.60 60.00 0.63 0.80
In estimating fill factors, the
following rules of thumb apply:
• a typical value is about 0.85 but
higher values are sometimes
quoted.
• fill factors will be higher where
the material is easy to dig and
lower where digging is hard.
• where material breaks finely, the
fill factors will be higher
• fill factors are higher for large
equipment and lower for small
equipment
An example of this type of calculation as applied to a Coal (bituminous) is given below:
𝑆𝑤𝑒𝑙𝑙 =
𝑏𝑎𝑛𝑘 𝑑𝑒𝑛𝑠𝑖𝑡𝑦
𝑙𝑜𝑠𝑠𝑒 𝑑𝑒𝑛𝑠𝑖𝑡𝑦
=
1245.88
922.54
= 1.350482 ≈ 1.35
𝑆𝑤𝑒𝑙𝑙 𝑓𝑎𝑐𝑡𝑜𝑟 =
1
𝑠𝑤𝑒𝑙𝑙
=
𝑙𝑜𝑜𝑠𝑒 𝑑𝑒𝑛𝑠𝑖𝑡𝑦
𝑏𝑎𝑛𝑘 𝑑𝑒𝑛𝑠𝑖𝑡𝑦
=
922.54
1245.88
= 0.740476 ≈ 0.74
Shovel-Dumper Synchronization
Truck and Shovel system is the most popular equipment system for Surface Mining Operation. Total
volume moved by this system exceeds all other excavation systems combined. The main advantages
of this system is its excellent flexibility which results into excellent ability to meet production and cost
targets. Their flexibility enables a mining operation to adapt quickly to changes in commodity prices,
geology, and other influences that cause the original mine plan to change.
Shovel-Dumper Synchronization
In a fully mechanized iron ore mine with an annual production target of 2.5
million tonnes, the rock excavation is carried out with shovel-dumper
combination. The excavated rock must be transported to an unloading point
of beneficiation plant at a lead distance of 5 km. Further, it was observed
that on the haul road, loaded dumpers travel at an average speed of 20
km/h, while empty dumpers travel at 25 km/h. Assuming the following data,
determine the appropriate fleet size for shovels and dumpers required for
efficient operation and synchronize the equipment accordingly:
• Number of working days in a calendar year = 300;
• Availability factor = 0.85;
• Utilization factor = 0.85;
• Swell factor for iron ore = ?;
• Bucket fill factor = ? ; and
• Weight density = ?
• Number of passes required to fill a dumper = 5
• Average cycle time of the shovel = 36 s
Determine the cycle time of truck selected. The cycle time consists of
the following operations:
– Loading time (180 s )
– Travel time of the loaded truck
– Discharge or unloading time (30 s) assumed
– Travel time of empty truck
– Spot or change over time from one truck to another. (45 s) assumed
Step-I: Estimate the available machine time
Step-II: Estimate the utilizable machine time
Step-III: Calculate the target production volume
Step-IV: Calculate the material swell (after breakage)
Step-V: Estimate the hourly production target
Step-VI: Determine the required bucket size of shovel
Step-VII: Determine cycle time of dumper
Step-VIII: Determine the fleet size
Transport of material
through trucks and
excavators relies on
diesel power, has
several
disadvantages
including high
operating costs for
fuel, personnel,
accommodation,
travelling and
maintenance; high
safety risk created by
weather conditions
or human factors;
and environmental
damage caused by
carbon and noise
emissions.
IPCC systems typically consists of
a gyratory, impact, cone, or jaw
crushers to feed an overland
conveyor belt that transports
material to the beneficiation
plant or to the overburden
dump. They can be classified into
mobile and semi-mobile systems.
IPCC systems are an
alternative to conventional
truck haulage. Longer haulage
distances in many large pits,
availability of haul trucks, and
improvements in IPCC
technology have made IPCC a
viable alternative in a open pit
transportation system.
Mobile systems are crawler mounted
and are often fed directly by an
excavator. Having capacities of less
than 1,500 t/h, these systems are
usually found in small open-pit mines
or quarries.
Semi-mobile systems are mostly based on gyratory crushers fed
either directly from trucks or from truck fed apron feeders. They
can only be moved with specialized equipment, hence the name
semi-mobile. Having far higher capacities (up to 14,000 t/h) than
fully mobile systems, these systems are suitable for mines with
very large production tonnages.
IPCC – In-Pit Crushing & Conveying
After being crushed, the material is
transported out by means of a
conveyor.
Mobile IPCC system
IPCC – In-Pit Crushing & Conveying
As a general rule, it can be said that
• If production exceeds approximately
100,000 t/d,
• When haulage distances surpass 5 km or
when the vertical lift exceeds 250 m and
• If the installation can be in operation for
at least 10 years,
the benefits of IPCC can offset the higher
capital costs of this installation.
Economic viability of IPCC depends on
• Production tonnages,
• Duration of the operation,
• Haulage distance, and
• Vertical lift.
The economic benefits of IPCC rely on the potential to significantly reduce truck
haulage distances and consequently, fuel consumption, haul road and truck
maintenance costs, and labor requirements.
Furthermore, operations using IPCC are less prone to tire, equipment, or labor
problem. Other advantages over conventional truck haulage systems include lower
carbon emissions and improved safety.
The main disadvantage of IPCC system is reduced operational flexibility of a mining
operation with respect to pit expansion and pushbacks.
Additionally, crusher moves and unplanned downtime of the conveyor belt can
have serious impacts on the overall productivity of the system. Careful selection of
crusher locations should minimize downtime due to crusher relocation.
Benefits
Disadvantages
Applicability & Viability
High angle conveying
A high angle conveyor can be
defined as any conveyor that
transports material along a
slope exceeding the dynamic
stability angle of the
transported material. Typical
recommended inclination
angles of conventional
conveyors for open-pit mine
products (such as excavated
earth including anthracite coal,
bituminous coal, lignite and
crushed rock) vary from 15° to
22° with respective angles of
repose from 29° to 44° , but
the high angle conveyors may
carry the material at an angle
more than this and in some
cases even at 90°.
High Angle Conveying (HAC) The most common conveyor belt configuration is a standard trough-type conveyor. However,
this type of conveyor belt suffers from limited curve radii and slope angles (maximum of 16°–
18°).
High angle conveying
Pipe conveyors is a relatively recent development used to negotiate
tighter curves. They are essentially rubber conveyor belts folded into
a pipe shape with idler rollers. As idlers constrain the belt from all
sides, far tighter curves can be negotiated. A further advantage is the
reduction of spillages and fugitive dust generation. The disadvantage
of a pipe conveyor is its limited capacity.
Several high angle conveying systems are available to meet the requirement of
high angle conveying such as the sandwich design or the pocket lift design. The sandwich design
sandwiches materials
between two conveyor
belts kept in place by
idlers.
The pocket-lift
design relies on
material being
carried in pockets
created by wrinkling
the belt. A system
similar to the pipe
conveyor can also
be used for high-
angle conveying,
provided that
material is
sufficiently confined
Automation in Open-pit transport - TDS
The main purpose of truck
dispatching systems is to increase
equipment productivity. Since
productivity is measured in tonnage
or volume over time, productivity
increases are made by decreasing
truck and shovel cycle time.
An important side benefit to truck dispatching systems, is the routine acquisition of
detailed cycle time data. These data can be used to quantify the effects of changes in the
mining operation. For example, the cost of incremental improvements to haul roads could
be compared with the savings accruing from a decrease in travel time. Since monitoring
and dispatching systems record all time increments for all mobile units, the average times
can be used for accurate and sensitive statistical cost studies.
This decrease can be translated into
more production with the existing
operating equipment or constant
production with a smaller equipment
fleet.
Concurrent objectives are product
quality maintenance and
minimization of rehandle. Also,
longer term mine planning goals
cannot be sacrificed for short term
productivity maximization; this
point is dealt with through shift
planning.
The data is
presented to mine
management in two
forms. Real-time
data is used to make
immediate decisions
in the current shift.
Summary data is
tabulated into shift
reports. Shift
reports are used
together with a
mine plan to
formulate shift
plans.
A dispatching system
gathers data from the
equipment operating in the
pit, analyses it, compares it
to the mine’s current shift
plan, and then directs the
equipment to locations and
activities which will enable
the mine to meet its
objectives in the most cost
effective manner. A mine’s
data acquisition program
gathers information from
the mobile equipment and
the field supervisors.
Essential functions common to all dispatching systems
The two primary
data types are time
and material
movement, i.e.
how long has it
taken to move
material A from
location X to
location Y.
Secondary
information relates
to fuel
consumption,
length of delays,
etc.
The real-time data and
the targets set by the
shift plan are then
used by the dispatch
logic to formulate
dispatch instructions
to the mobile
equipment.
Automation in Open-pit transport - TDS
Yao, J.; Wang, Z.; Chen, H.; Hou, W.; Zhang, X.; Li, X.; Yuan, W. Open-Pit Mine Truck Dispatching System Based on Dynamic Ore Blending Decisions. Sustainability 2023, 15,
3399. https://doi.org/10.3390/su15043399
Automation in Open-pit transport - TDS
Yao, J.; Wang, Z.; Chen, H.; Hou, W.; Zhang, X.; Li, X.; Yuan, W. Open-Pit Mine Truck Dispatching System Based on Dynamic Ore Blending Decisions. Sustainability 2023, 15,
3399. https://doi.org/10.3390/su15043399
Automation in Open-pit transport - TDS
Yao, J.; Wang, Z.; Chen, H.; Hou, W.; Zhang, X.; Li, X.; Yuan, W. Open-Pit Mine Truck Dispatching System Based on Dynamic Ore Blending Decisions. Sustainability 2023, 15,
3399. https://doi.org/10.3390/su15043399
Different types of TDS
Manual: A purely manual system is one in which the pit
supervisors gather data from the field by listening to the
voice radio and by visual observation. All the dispatch
logic is in the supervisor’s head. This is the current
practice at most mines.
Computer Aided Manual: This system uses a non real-
time computer to assist the pit supervisors tabulate data
and dispatch equipment. Data is gathered over the voice
radio and a computer operator manually types the data
into a computer. The computer stores and summarizes
the data and, when required, suggests a dispatch
instruction. This dispatch instruction is relayed to the
field over the voice radio. This type of system was used
in the early days of truck dispatch. There is still current
interest in these systems due to their simplicity and low
cost. Their chief disadvantage is their inability to handle
a large number of radio messages in a short period of
time.
Automatic Monitoring: There is a significant benefit to automatic
data acquisition without dispatching. Data is transmitted from the
pit directly to a computer over a communications data channel.
The data is summarized and real-time statistics are presented to
the central dispatcher.
These statistics (e.g. cycle times, product blend) are used by the
dispatcher as a guide to the dispatching process. Another
important benefit is the timely generation of shift reports. A
detailed shift report can be printed before a crew goes home
providing immediate positive feedback.
Automatic Dispatch: An automatic dispatch system combines
automatic monitoring with a computer program containing a
dispatch algorithm that estimates the optimum destination for a
mobile unit. Dispatch messages are sent directly to the unit using
the data communication system. The destination is displayed on a
mobile data terminal located in the equipment’s cab.
All truck and shovel mines currently have a truck dispatching system of some sort in place, they range in type from purely manual to
sophisticated automatic systems. There are four types of dispatching systems in use today.
Front End Loaders
A front end loader is either a crawler track or wheel
mounted tractor having a bucket at the front of the
mainframe. It is used for loading coal or ore from a
smaller height bench (say a height around 3 m to 15
m) onto the trucks, rail wagon or other conveying
system. It also loads and transports material, ore or
coal to a smaller distance.
During stripping it piles up blasted rock mass or
mineral to assist power shovel for loading, handling
etc. It also spreads rock or ore in the stockpile of
material handling station. The machine can nicely
be used for the removal and hauling of top soil for
a distance of 150 m and a thickness of bench
around 2m.
The crawler track mounted front end loader is used where the ground
condition is soft, terrain is rough and also where high digging force is
required to excavate the loose or blasted rock mass or mineral.
It can be used efficiently on the soft to hard floor
condition. It has a high digging capability and
moderate to high production capacity.
The wheel mounted front end loader has a very high degree of
mobility. It is a highly speedy loading machine and has a high degree
of flexibility and a high degree of productivity and longevity. The
machine is highly efficient for unconsolidated rock, good fragmented
rock mass or ore, but less efficient of handling blocky poor
fragmented rock mass.
Front End Loaders
Combination of loading by front
end loader and transporting by
dumper can transport
economically ore to a distance of
more than 3 km for a very low to
very high production rate.
When a front-end-loader is not
being used for loading coal/ore/
overburden rock, it can be used
for the road construction, spot
filling, floor cleaning around the
shovel, lifting and transporting
equipment/component of the
equipment, etc.
• The cutting edge (made from manganese steel) of the bucket of the loader may
be either straight type for maximum cleaning and loading efficiency and also for
higher flexibility of operation whereas the 'vee' type cutting teeth are used for
better penetration in the muck pile.
• Size of the bucket depends on the requirement of production capacity, cycle time,
bucket fill factor, digging factor, operating efficiency, swell factor, machine
availability, propel time factor, etc. Based on the capacity of the bucket the size of
the front-end- loader is selected.
• Sometimes counter weight is provided onto the loader for higher stability of the
machine and to increase the operating load capability.
• The bucket may be either powered controlled or gravity controlled.
• The gravity controlled bucket has an arrangement to release the loaded bucket
under gravity and also the bucket can be lifted up either by hydraulic mechanism
or by rope pulley system.
• Power operated buckets are controlled by the hydraulic system. The efficiency of
the loader is lowered down while digging the harder and coarser materials.
Buckets are generally arranged overturning type.
The Bucket and Other Main Units
Front End Loaders
• Beside bucket the loader consists the units like
a) engine,
b) arms,
c) power transmission system,
d) undercarriage unit or frame.
• Generally the power is provided to the loader driving
wheel (in case of the wheel mounted front end loader) or
to the driving sprocket (in case of the crawler track
mounted front end loader) by the diesel engine via
torque converter, reduction gear box, propeller shafts and
differential gearing systems.
• Mechanical linkage arms are actuated by the double
acting hydraulic pistons.
• Raising or lowering of the bucket, tilting, floating and
holding of the same are governed by the hydraulic system
which consists oil tank, oil pump, lift and tilt cylinders,
relief and other control valve system etc.
• The loader consists two types of brakes which are-(a)
Hydraulic operated main brakes and (b) Parking brakes.
The Loader
Front End Loaders
• For crowding the bucket is
lowered down and the
whole front end loader unit
is pushed forward towards
the bench for digging.
• After digging is over the
bucket unit is raised up
slightly by the lifting
cylinder.
• The loaded loader is then
reversed back and
maneuvered in position to
the dumping point or unload
the material over the
dumper by overturning the
bucket by the tilt cylinders.
The loader is then again
maneuvered to the right
position and move forward
towards the production
bench for loading.
• As compared to a shovel, a front-end-loaders are more versatile, can efficiently clean the
face, grade the muck pile and blend well, cheaper in price and has less operating cost.
• Beside this a front-end-loader requires less capital intensive back-up equipment.
Operators of the front-end-loader trained up within a very short time and the loader can
be used for road making too.
Operation
• However as compared to a shovel, a front end loaders life is very short (5 to 6 years), has
less salvage value, repair and maintenance costs are also very high.
• In operation as compared to a shovel machine it suffers form more shock loading,
requires more space for back and turning, requires good fragmented rocks to be loaded,
machine can not crowd and dig as smooth as a shovel, reach is poor, less efficient to
reach for loading materials up to the end of a truck, bucket is very wide and weak.
• It may require the help of a dozer to push the material as well as sometimes to push the
loader itself, requires good roadway (sometimes fines are sprayed over the road for
good padding) and also it's tire life is also very small.
• Since turning of the machine is achieved by steering the whole front end loader unit, it's
digging, loading and unloading cycle of operations are slower as compared to a shovel
and hence the capacity is also less as compared to the latter.
• For gaining maximum loading efficiency it would be better if the loader is moved within
the radius of 5 m and the turning angle does not exceed more than 40° to 45°.
Merits and Demerits of a Front-End-Loader as Compared to a Shovel
Scrapers
It is a diesel operated four wheel drive
rubber tired tractor or a crawler tractor
having a bowl attached with a cutting
blade at the bottom.
The scraper can cut a thin slice of unconsolidated material soft rock or soil (thickness of the slice is approximately varying from 70
mm to 250 mm) and can nicely be used within a radius varying from 150m to 1500 m. Size of the material which it can handle varies
from very fine to more than 550 mm in good and dry ground condition. However wet ground condition hampers the scraper
efficiency. It is very much flexible under wide varied conditions and can handle wide rate of production ranging from very small to
very high total tonnage. Maximum efficiency is achieved at a very flat gradient (say 4°) but it can negotiate a gradient even more
than 15°. Scraper cut and load or simply load, haul, dump and return back for recycling of operation.
Applicability
The speed of a tractor wheel mounted scraper is around 60 km/h to
65 km/h. Because of higher mobility the wheel mounted scraper is
preferred over the crawler track mounted scraper. However where
steep gradient, seasonal variations, etc., are to be encountered and
where mobility is not a factor of selection, the crawler track mounted
tractor will yield a very good result.
Scrapers
• Scraper can also be
used for hauling blast
fragmented hard rocks
or minerals. Scraper
should be used for
removal of top soil or
unconsolidated rocks
or minerals of
thickness 2 m to 3 m.
• The tractive effort of
the scraper depends
on power, weight of
the machine, gear
efficiency, type and size
of the tyres, condition
of the surface
topography over which
it moves, etc.
A scraper consists of the following
main units and components:
• bowl,
• apron,
• cutting blade,
• steering system,
• power transmission system,
• cable or hydraulic type of
control unit, braking system etc.
Main features
The scrapers are basically divided into two categories i.e.
Self propelled type and Towed type.
• Rubber tired self propelled scrapers are available as four
wheel units or as two wheel overhung units. Because of
the stability, smoothness of movement, ease of
operation, higher speed (around 45 km/h to 50 km/h),
higher safety, four wheeled scrapers are widely used.
• The towed scrapers are mounted over four wheeled
machine body and attached to the rear side of the
tractor.
• The available struck
capacity of a scraper
may be more than 12
m3 whereas the
heaped capacity of
more than 16 m is
also possible.
Scrapers
During cutting most of the times a bulldozer is necessary to
push the scraper from the backside. The scraper may be used
over a ripped or hard mineral or rock surface for loading and
transporting purposes. It is also used for leveling purpose.
However it requires a very good traveling ways. It is
unsuitable in hard ground condition and sites having big
boulders.
• After retracting the tailgate to the extreme position,
the apron is opened partially and the bowl is
lowered till the cutting blade touches or penetrates
in the loose ground with high hydraulic pressure.
• The scraper thereafter moves forward taking a slice
of 100 mm to 200 mm of the soft, unconsolidated
and loose ground material which fed into the bowl
till it is filled up.
• Thereafter bowl is raised up and the excavated
material is hauled and dumped to the required
place.
Operation
• Whilst operating on a bench, a scraper should not
approach within 2 m of the bench crest.
• No scraper should be permitted to move backwards
downhill when unloading.
• Scrapers hauled by wheeled tractors should not be
permitted to negotiate access roads having a gradient
greater than 15° in the case of a loaded machine or 25° in
the case of an empty machine.
Precautions
https://www.youtube.com/watch?v=tldOKQiMvAk
Transport in Open Pits______SM_MI10415MI

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Transport in Open Pits______SM_MI10415MI

  • 1. Transport in Open Pits Unit-5
  • 2. LIST OF TOPICS 1 Introduction Overview of transport in Open pits, types of material haulage system in open pits 2 Dumpers Overview, Types, applicability and limitations, computation of their productivity, Shovel-Dumper synchronization 3 Rail transport and conveyors in Open pits Suitability, IPCC, High angle conveying, specialized conveying 4 Automation in open pit transport Truck dispatch system, Overview of excavation and haulage
  • 3. Haulage operation in Open pits - Overview 13% 12% 12% 48% 15% Open pit production costs Drill and Blast Roads and Dumps Loading Haulage Overhead • Haulage system is a key and the most expensive unit operation of open pit mining. • The hauling of material (such as coal, ore, sand, gravel, or top-soil) from one point to another in a safe, efficient, and cost-effective manner is critical for mining operations. • Selecting the type of surface hauler requires a thorough understanding of the selected mining method and its associated advantages and disadvantages along with the machinery available to the industry. • Rigid-frame haul trucks have dominated haulage in open-pit mining operations for decades. • Although in some cases articulated dump trucks (ADTs) have proven a viable alternative, and sometimes rail haulage is still being used. • Furthermore, longer haulage distances in many large pits, availability problems with haul trucks, and improvements in technology have revived interest in conveyor transport including in-pit crushing and conveying (IPCC).
  • 4. Introduction – Automobile transport in Open pits • A number of haulage options are available for mining, all of them with unique characteristics that can be optimal for a particular mine site and haul distance.
  • 5. Articulated dump trucks Off-highway articulated trucks are a hauling alternative primarily for middle-to-large-scale construction projects. They are often used for pre-stripping, road construction, and material hauling for ground preparation for buildings and other infrastructure. When used with small hydraulic excavators or wheel loaders, they can constitute an effective loader and hauler fleet for a mass excavation project. They are widely used for pre- and postmining construction in soft-underfoot conditions, in small loading and dump areas, or on steep (10%–15%) grades An articulated dump truck (ADT) is a three-axle machine with an articulation point between the front axle and the two rear axles. The articulation, which is unique to this truck type, is useful where there is limited area in which to operate. ADTs providing the surface mining industry a hauling solution that is adaptable to tough hauling conditions. However, because of their limited hauling capacity, they are not viable as primary production machines.
  • 6. Trolley assisted Dump trucks Trolley-assist haul trucks are haul trucks that have been adapted from the standard diesel–electric system to a system that relies on pantographs to connect to an electrified over-head line for power supply. Historically, use of this system has been concentrated in southern Africa, but with rising diesel prices, interest in trolley-assist hauling from other parts of the world is increasing. Major infrastructures that need to be installed for the use of trolley-assist haulage include the overhead lines, truck conversion packages, and trolley substations. These conversion packages can be fitted on the majority of diesel–electric trucks. Increased power supply from the overhead line, compared to a truck-based diesel generator, allows maximum use of the capacity of the electric motor in a truck. As a result, reduced cycle times are possible, and consequently, truck fleets can be reduced. This allows for productivity increases and possibly reduced capital investment costs related to purchasing fewer trucks. Furthermore, as the diesel engine is idling while on trolley assist, fuel consumption and ultimately time between engine overhauls can be reduced significantly. Lastly, energy can be recovered into the trolley supply grid when trucks are moving downgrade.
  • 7. Dumpers or Haul Trucks Most popular haulage system in open-pit mining operations for decades. Haulage trucks have superior Payload capacities that range from around 25 t to over 360 t. Better speeds in most road conditions and have lower maintenance requirements. There is a choice between mechanical drive and electrical drive systems. Rigid-frame trucks, with or without trolley assist, and are the preferred choice for haulage in most open-pit mines.
  • 8. Truck models by size class and manufacturer • Trucks for surface mining currently have payload capacities of 90–360 t (100–400 st). • These values have evolved over time, driven by the mining industry’s desire to go larger in order to maintain or increase production while decreasing fleet size and operating costs. • Within this payload range, there are five distinct classes, designated according to size: 1. 90-t (100-st) class 2. 135-t (150-st) class 3. 180-t (200-st) class 4. 220-t (250-st) class 5. >290-t (320-st) ultra-class truck (UCT)
  • 9. Mechanical drive train • The mechanical drive train contains five major components: engine, torque converter, transmission, differential, and planetary gear sets (wheels). • The power source is the diesel engine plus torque converter; the latter transmits rotational power from the engine to the main driveshaft. • The transmission controls machine torque and speed during operation. • The differential transfers output torque to the wheels. • Two hydraulic brake packs are mounted on each of the axle shafts on the two rear wheels. • The entire system is activated by means of a variety of electronic control modules and hydraulic control systems.
  • 10. Electric drive train (DC and AC) • DC and AC electric drive trains contain six major com- • ponents: engine, generator, power converter, wheel motors, planetary gear sets (wheels), and retarding grid. • The power source is the diesel engine plus generator; the latter converts mechanical power from the engine into electric power. • AC current from the generator is then converted into useable form. • In a DC-drive truck, a rectifier converts it into DC power; in an AC-drive truck, a rectifier converts it into DC power and inverters convert it back to a controllable version of AC power suitable for managing the amperes, volts, and frequencies of the wheel motors in order to create machine speed and torque. • The DC or AC wheel motors receive the electric power and feed it mechanically to the planetary gear sets (wheels). • Diesel - Electric AC systems dominate the larger truck sizes (>150- t payload).
  • 11. Dumpers - Productivity • Cycle times determines the productivity of haul truck which in turn depends on the type of excavator, truck capacity and haulage distance. • Assuming good truck - excavator capacity matching and good digging conditions, trucks should be loaded in approximately 100 to 150 seconds, this is longer for front end loaders. • Spotting at the excavator typically takes between 40 and 60 seconds. • Productivity of the haulage system is highly dependent on the performance of other activities in the mine, notably the haul road and dump conditions, excavator efficiency etc. One sided loading Two sided loading One-sided loading has several disadvantages. Mining shovels and hydraulic shovels cycle in 30–35 seconds and spotting takes 40–60 seconds, so the shovel must wait for the truck, reducing production levels. In addition, the time required for a cleanup dozer to work in the spot area can delay operation. These disadvantages can be addressed to some extent by two-sided loading
  • 12. Factors influencing the productivity of dumpers Many times problems with poor haul truck productivity and reliability can often be traced back to poor performance of other parts of operations. Some of these factors are; • Haul road performance: Poor haul road performance (e.g., haul road defects and high rolling resistance) can reduce productivity and reliability of dump trucks. • Loading & Dump Face Conditions: Poor floor conditions in active loading and dumping areas (e.g., benches and dumps) can also affect productivity and reliability of dump trucks. • Poor Material Quality: Retention of material in both excavator bucket and the truck bed can pose a challenge to operations (in adverse climatic conditions or where material has a high clay or moisture content). Adaptation of the truck bed design, e.g., rubber floor mats or circulation of exhaust fumes through the bed to prevent freezing can alleviate this problem. • Good communication between truck and excavator operators: Good operator training as well as a high degree of coordination, communication, and visual confirmation on the part of both the excavator and the truck operator is crucial for truck spotting at the Excavator. Excavator operators should communicate the correct position for a truck, rather than relying on his judgment to get the truck in the right place. Good communication is especially crucial when double-spotting trucks. This method has the potential to reduce excavator and truck idle time.
  • 13. Productivity of dumpers – Key terminology Relationship between calendar hours and operating hours • Although there are about 8,760 calendar hours in a year, excavators typically operate for 6,000– 7,000 hours per year. • For initial estimating, it is adequate to combine availability and utilization values into a single operating efficiency factor. • Typical availability and utilization values are each about 85%, which provides an operating efficiency of about 72% of the scheduled hours. 𝐴𝑣𝑎𝑖𝑙𝑎𝑏𝑖𝑙𝑖𝑡𝑦 𝑓𝑎𝑐𝑡𝑜𝑟 = 𝐻𝐴 𝐻𝑠 𝑈𝑖𝑙𝑖𝑧𝑎𝑡𝑖𝑜𝑛 𝑓𝑎𝑐𝑡𝑜𝑟 = 𝐻𝑈 𝐻𝑆 = 𝐻𝐴 − 𝐻𝐷𝑈 𝐻𝑆
  • 14. Productivity of dumpers – Key terminology • In the mine, the material which is to be loaded into the dipper must generally first be loosened from its “in-place (in situ)” or “bank” position. • Assuming that the material occupies a volume of 1 m3 in place (denoted as 1 bank cubic metres, or 1 bcm), that same amount of material would be expected to occupy a larger volume in the loose condition. • The weight of one cubic metre of loose material (one lcm), due to the presence of void (air) spaces between the pieces, would be less than the weight of one bcm. Bank Cubic Metres and Loose Cubic Metres Swell is the ratio of the bank to loose weight densities. Swell factor is inverse of swell. 𝑆𝑤𝑒𝑙𝑙 = 𝑏𝑎𝑛𝑘 𝑑𝑒𝑛𝑠𝑖𝑡𝑦 𝑙𝑜𝑜𝑠𝑒 𝑑𝑒𝑛𝑠𝑖𝑡𝑦 𝑃𝑒𝑟𝑐𝑒𝑛𝑡 𝑠𝑤𝑒𝑙𝑙 = 100(𝑠𝑤𝑒𝑙𝑙 − 1) Material filling 𝑆𝑤𝑒𝑙𝑙 𝑓𝑎𝑐𝑡𝑜𝑟 = 1 𝑠𝑤𝑒𝑙𝑙 = 𝑙𝑜𝑜𝑠𝑒 𝑑𝑒𝑛𝑠𝑖𝑡𝑦 𝑏𝑎𝑛𝑘 𝑑𝑒𝑛𝑠𝑖𝑡𝑦 The “fillability” or the “fill-factor” refers to the ratio of the loose volume of rock contained in the dipper to the rated dipper capacity. 𝐹𝑖𝑙𝑙𝑎𝑏𝑖𝑙𝑖𝑡𝑦 = 𝑙𝑜𝑜𝑠𝑒 𝑣𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑟𝑜𝑐𝑘 (𝑚3 ) 𝑟𝑎𝑡𝑒𝑑 𝑐𝑎𝑝𝑎𝑐𝑖𝑡𝑦 𝑜𝑓 𝑑𝑖𝑝𝑝𝑒𝑟 (𝑚3)
  • 15. Productivity of dumpers – Key terminology Some properties for various materials which are important for loading machine evaluation Rock Specific gravity (bank) Weight density Swell Percent Swell Swell factor Fillability kg/bcm kg/lcm Bauxite 1.90 1898.45 1406.07 1.35 35.02 0.74 0.90 Coal (Bituminous) 1.25 1245.88 922.54 1.35 35.05 0.74 0.90 Iron Ore (60% Fe) 3.85 3856.30 2487.61 1.55 55.02 0.65 0.75 Limestone (hard) 2.60 2610.42 1631.51 1.60 60.00 0.63 0.80 Sandstone (porous) 2.50 2491.76 1557.35 1.60 60.00 0.63 0.80 In estimating fill factors, the following rules of thumb apply: • a typical value is about 0.85 but higher values are sometimes quoted. • fill factors will be higher where the material is easy to dig and lower where digging is hard. • where material breaks finely, the fill factors will be higher • fill factors are higher for large equipment and lower for small equipment An example of this type of calculation as applied to a Coal (bituminous) is given below: 𝑆𝑤𝑒𝑙𝑙 = 𝑏𝑎𝑛𝑘 𝑑𝑒𝑛𝑠𝑖𝑡𝑦 𝑙𝑜𝑠𝑠𝑒 𝑑𝑒𝑛𝑠𝑖𝑡𝑦 = 1245.88 922.54 = 1.350482 ≈ 1.35 𝑆𝑤𝑒𝑙𝑙 𝑓𝑎𝑐𝑡𝑜𝑟 = 1 𝑠𝑤𝑒𝑙𝑙 = 𝑙𝑜𝑜𝑠𝑒 𝑑𝑒𝑛𝑠𝑖𝑡𝑦 𝑏𝑎𝑛𝑘 𝑑𝑒𝑛𝑠𝑖𝑡𝑦 = 922.54 1245.88 = 0.740476 ≈ 0.74
  • 16. Shovel-Dumper Synchronization Truck and Shovel system is the most popular equipment system for Surface Mining Operation. Total volume moved by this system exceeds all other excavation systems combined. The main advantages of this system is its excellent flexibility which results into excellent ability to meet production and cost targets. Their flexibility enables a mining operation to adapt quickly to changes in commodity prices, geology, and other influences that cause the original mine plan to change.
  • 17. Shovel-Dumper Synchronization In a fully mechanized iron ore mine with an annual production target of 2.5 million tonnes, the rock excavation is carried out with shovel-dumper combination. The excavated rock must be transported to an unloading point of beneficiation plant at a lead distance of 5 km. Further, it was observed that on the haul road, loaded dumpers travel at an average speed of 20 km/h, while empty dumpers travel at 25 km/h. Assuming the following data, determine the appropriate fleet size for shovels and dumpers required for efficient operation and synchronize the equipment accordingly: • Number of working days in a calendar year = 300; • Availability factor = 0.85; • Utilization factor = 0.85; • Swell factor for iron ore = ?; • Bucket fill factor = ? ; and • Weight density = ? • Number of passes required to fill a dumper = 5 • Average cycle time of the shovel = 36 s Determine the cycle time of truck selected. The cycle time consists of the following operations: – Loading time (180 s ) – Travel time of the loaded truck – Discharge or unloading time (30 s) assumed – Travel time of empty truck – Spot or change over time from one truck to another. (45 s) assumed Step-I: Estimate the available machine time Step-II: Estimate the utilizable machine time Step-III: Calculate the target production volume Step-IV: Calculate the material swell (after breakage) Step-V: Estimate the hourly production target Step-VI: Determine the required bucket size of shovel Step-VII: Determine cycle time of dumper Step-VIII: Determine the fleet size
  • 18. Transport of material through trucks and excavators relies on diesel power, has several disadvantages including high operating costs for fuel, personnel, accommodation, travelling and maintenance; high safety risk created by weather conditions or human factors; and environmental damage caused by carbon and noise emissions. IPCC systems typically consists of a gyratory, impact, cone, or jaw crushers to feed an overland conveyor belt that transports material to the beneficiation plant or to the overburden dump. They can be classified into mobile and semi-mobile systems. IPCC systems are an alternative to conventional truck haulage. Longer haulage distances in many large pits, availability of haul trucks, and improvements in IPCC technology have made IPCC a viable alternative in a open pit transportation system. Mobile systems are crawler mounted and are often fed directly by an excavator. Having capacities of less than 1,500 t/h, these systems are usually found in small open-pit mines or quarries. Semi-mobile systems are mostly based on gyratory crushers fed either directly from trucks or from truck fed apron feeders. They can only be moved with specialized equipment, hence the name semi-mobile. Having far higher capacities (up to 14,000 t/h) than fully mobile systems, these systems are suitable for mines with very large production tonnages. IPCC – In-Pit Crushing & Conveying After being crushed, the material is transported out by means of a conveyor. Mobile IPCC system
  • 19. IPCC – In-Pit Crushing & Conveying As a general rule, it can be said that • If production exceeds approximately 100,000 t/d, • When haulage distances surpass 5 km or when the vertical lift exceeds 250 m and • If the installation can be in operation for at least 10 years, the benefits of IPCC can offset the higher capital costs of this installation. Economic viability of IPCC depends on • Production tonnages, • Duration of the operation, • Haulage distance, and • Vertical lift. The economic benefits of IPCC rely on the potential to significantly reduce truck haulage distances and consequently, fuel consumption, haul road and truck maintenance costs, and labor requirements. Furthermore, operations using IPCC are less prone to tire, equipment, or labor problem. Other advantages over conventional truck haulage systems include lower carbon emissions and improved safety. The main disadvantage of IPCC system is reduced operational flexibility of a mining operation with respect to pit expansion and pushbacks. Additionally, crusher moves and unplanned downtime of the conveyor belt can have serious impacts on the overall productivity of the system. Careful selection of crusher locations should minimize downtime due to crusher relocation. Benefits Disadvantages Applicability & Viability
  • 20. High angle conveying A high angle conveyor can be defined as any conveyor that transports material along a slope exceeding the dynamic stability angle of the transported material. Typical recommended inclination angles of conventional conveyors for open-pit mine products (such as excavated earth including anthracite coal, bituminous coal, lignite and crushed rock) vary from 15° to 22° with respective angles of repose from 29° to 44° , but the high angle conveyors may carry the material at an angle more than this and in some cases even at 90°. High Angle Conveying (HAC) The most common conveyor belt configuration is a standard trough-type conveyor. However, this type of conveyor belt suffers from limited curve radii and slope angles (maximum of 16°– 18°).
  • 21. High angle conveying Pipe conveyors is a relatively recent development used to negotiate tighter curves. They are essentially rubber conveyor belts folded into a pipe shape with idler rollers. As idlers constrain the belt from all sides, far tighter curves can be negotiated. A further advantage is the reduction of spillages and fugitive dust generation. The disadvantage of a pipe conveyor is its limited capacity. Several high angle conveying systems are available to meet the requirement of high angle conveying such as the sandwich design or the pocket lift design. The sandwich design sandwiches materials between two conveyor belts kept in place by idlers. The pocket-lift design relies on material being carried in pockets created by wrinkling the belt. A system similar to the pipe conveyor can also be used for high- angle conveying, provided that material is sufficiently confined
  • 22. Automation in Open-pit transport - TDS The main purpose of truck dispatching systems is to increase equipment productivity. Since productivity is measured in tonnage or volume over time, productivity increases are made by decreasing truck and shovel cycle time. An important side benefit to truck dispatching systems, is the routine acquisition of detailed cycle time data. These data can be used to quantify the effects of changes in the mining operation. For example, the cost of incremental improvements to haul roads could be compared with the savings accruing from a decrease in travel time. Since monitoring and dispatching systems record all time increments for all mobile units, the average times can be used for accurate and sensitive statistical cost studies. This decrease can be translated into more production with the existing operating equipment or constant production with a smaller equipment fleet. Concurrent objectives are product quality maintenance and minimization of rehandle. Also, longer term mine planning goals cannot be sacrificed for short term productivity maximization; this point is dealt with through shift planning. The data is presented to mine management in two forms. Real-time data is used to make immediate decisions in the current shift. Summary data is tabulated into shift reports. Shift reports are used together with a mine plan to formulate shift plans. A dispatching system gathers data from the equipment operating in the pit, analyses it, compares it to the mine’s current shift plan, and then directs the equipment to locations and activities which will enable the mine to meet its objectives in the most cost effective manner. A mine’s data acquisition program gathers information from the mobile equipment and the field supervisors. Essential functions common to all dispatching systems The two primary data types are time and material movement, i.e. how long has it taken to move material A from location X to location Y. Secondary information relates to fuel consumption, length of delays, etc. The real-time data and the targets set by the shift plan are then used by the dispatch logic to formulate dispatch instructions to the mobile equipment.
  • 23. Automation in Open-pit transport - TDS Yao, J.; Wang, Z.; Chen, H.; Hou, W.; Zhang, X.; Li, X.; Yuan, W. Open-Pit Mine Truck Dispatching System Based on Dynamic Ore Blending Decisions. Sustainability 2023, 15, 3399. https://doi.org/10.3390/su15043399
  • 24. Automation in Open-pit transport - TDS Yao, J.; Wang, Z.; Chen, H.; Hou, W.; Zhang, X.; Li, X.; Yuan, W. Open-Pit Mine Truck Dispatching System Based on Dynamic Ore Blending Decisions. Sustainability 2023, 15, 3399. https://doi.org/10.3390/su15043399
  • 25. Automation in Open-pit transport - TDS Yao, J.; Wang, Z.; Chen, H.; Hou, W.; Zhang, X.; Li, X.; Yuan, W. Open-Pit Mine Truck Dispatching System Based on Dynamic Ore Blending Decisions. Sustainability 2023, 15, 3399. https://doi.org/10.3390/su15043399
  • 26. Different types of TDS Manual: A purely manual system is one in which the pit supervisors gather data from the field by listening to the voice radio and by visual observation. All the dispatch logic is in the supervisor’s head. This is the current practice at most mines. Computer Aided Manual: This system uses a non real- time computer to assist the pit supervisors tabulate data and dispatch equipment. Data is gathered over the voice radio and a computer operator manually types the data into a computer. The computer stores and summarizes the data and, when required, suggests a dispatch instruction. This dispatch instruction is relayed to the field over the voice radio. This type of system was used in the early days of truck dispatch. There is still current interest in these systems due to their simplicity and low cost. Their chief disadvantage is their inability to handle a large number of radio messages in a short period of time. Automatic Monitoring: There is a significant benefit to automatic data acquisition without dispatching. Data is transmitted from the pit directly to a computer over a communications data channel. The data is summarized and real-time statistics are presented to the central dispatcher. These statistics (e.g. cycle times, product blend) are used by the dispatcher as a guide to the dispatching process. Another important benefit is the timely generation of shift reports. A detailed shift report can be printed before a crew goes home providing immediate positive feedback. Automatic Dispatch: An automatic dispatch system combines automatic monitoring with a computer program containing a dispatch algorithm that estimates the optimum destination for a mobile unit. Dispatch messages are sent directly to the unit using the data communication system. The destination is displayed on a mobile data terminal located in the equipment’s cab. All truck and shovel mines currently have a truck dispatching system of some sort in place, they range in type from purely manual to sophisticated automatic systems. There are four types of dispatching systems in use today.
  • 27. Front End Loaders A front end loader is either a crawler track or wheel mounted tractor having a bucket at the front of the mainframe. It is used for loading coal or ore from a smaller height bench (say a height around 3 m to 15 m) onto the trucks, rail wagon or other conveying system. It also loads and transports material, ore or coal to a smaller distance. During stripping it piles up blasted rock mass or mineral to assist power shovel for loading, handling etc. It also spreads rock or ore in the stockpile of material handling station. The machine can nicely be used for the removal and hauling of top soil for a distance of 150 m and a thickness of bench around 2m. The crawler track mounted front end loader is used where the ground condition is soft, terrain is rough and also where high digging force is required to excavate the loose or blasted rock mass or mineral. It can be used efficiently on the soft to hard floor condition. It has a high digging capability and moderate to high production capacity. The wheel mounted front end loader has a very high degree of mobility. It is a highly speedy loading machine and has a high degree of flexibility and a high degree of productivity and longevity. The machine is highly efficient for unconsolidated rock, good fragmented rock mass or ore, but less efficient of handling blocky poor fragmented rock mass.
  • 28. Front End Loaders Combination of loading by front end loader and transporting by dumper can transport economically ore to a distance of more than 3 km for a very low to very high production rate. When a front-end-loader is not being used for loading coal/ore/ overburden rock, it can be used for the road construction, spot filling, floor cleaning around the shovel, lifting and transporting equipment/component of the equipment, etc. • The cutting edge (made from manganese steel) of the bucket of the loader may be either straight type for maximum cleaning and loading efficiency and also for higher flexibility of operation whereas the 'vee' type cutting teeth are used for better penetration in the muck pile. • Size of the bucket depends on the requirement of production capacity, cycle time, bucket fill factor, digging factor, operating efficiency, swell factor, machine availability, propel time factor, etc. Based on the capacity of the bucket the size of the front-end- loader is selected. • Sometimes counter weight is provided onto the loader for higher stability of the machine and to increase the operating load capability. • The bucket may be either powered controlled or gravity controlled. • The gravity controlled bucket has an arrangement to release the loaded bucket under gravity and also the bucket can be lifted up either by hydraulic mechanism or by rope pulley system. • Power operated buckets are controlled by the hydraulic system. The efficiency of the loader is lowered down while digging the harder and coarser materials. Buckets are generally arranged overturning type. The Bucket and Other Main Units
  • 29. Front End Loaders • Beside bucket the loader consists the units like a) engine, b) arms, c) power transmission system, d) undercarriage unit or frame. • Generally the power is provided to the loader driving wheel (in case of the wheel mounted front end loader) or to the driving sprocket (in case of the crawler track mounted front end loader) by the diesel engine via torque converter, reduction gear box, propeller shafts and differential gearing systems. • Mechanical linkage arms are actuated by the double acting hydraulic pistons. • Raising or lowering of the bucket, tilting, floating and holding of the same are governed by the hydraulic system which consists oil tank, oil pump, lift and tilt cylinders, relief and other control valve system etc. • The loader consists two types of brakes which are-(a) Hydraulic operated main brakes and (b) Parking brakes. The Loader
  • 30. Front End Loaders • For crowding the bucket is lowered down and the whole front end loader unit is pushed forward towards the bench for digging. • After digging is over the bucket unit is raised up slightly by the lifting cylinder. • The loaded loader is then reversed back and maneuvered in position to the dumping point or unload the material over the dumper by overturning the bucket by the tilt cylinders. The loader is then again maneuvered to the right position and move forward towards the production bench for loading. • As compared to a shovel, a front-end-loaders are more versatile, can efficiently clean the face, grade the muck pile and blend well, cheaper in price and has less operating cost. • Beside this a front-end-loader requires less capital intensive back-up equipment. Operators of the front-end-loader trained up within a very short time and the loader can be used for road making too. Operation • However as compared to a shovel, a front end loaders life is very short (5 to 6 years), has less salvage value, repair and maintenance costs are also very high. • In operation as compared to a shovel machine it suffers form more shock loading, requires more space for back and turning, requires good fragmented rocks to be loaded, machine can not crowd and dig as smooth as a shovel, reach is poor, less efficient to reach for loading materials up to the end of a truck, bucket is very wide and weak. • It may require the help of a dozer to push the material as well as sometimes to push the loader itself, requires good roadway (sometimes fines are sprayed over the road for good padding) and also it's tire life is also very small. • Since turning of the machine is achieved by steering the whole front end loader unit, it's digging, loading and unloading cycle of operations are slower as compared to a shovel and hence the capacity is also less as compared to the latter. • For gaining maximum loading efficiency it would be better if the loader is moved within the radius of 5 m and the turning angle does not exceed more than 40° to 45°. Merits and Demerits of a Front-End-Loader as Compared to a Shovel
  • 31. Scrapers It is a diesel operated four wheel drive rubber tired tractor or a crawler tractor having a bowl attached with a cutting blade at the bottom. The scraper can cut a thin slice of unconsolidated material soft rock or soil (thickness of the slice is approximately varying from 70 mm to 250 mm) and can nicely be used within a radius varying from 150m to 1500 m. Size of the material which it can handle varies from very fine to more than 550 mm in good and dry ground condition. However wet ground condition hampers the scraper efficiency. It is very much flexible under wide varied conditions and can handle wide rate of production ranging from very small to very high total tonnage. Maximum efficiency is achieved at a very flat gradient (say 4°) but it can negotiate a gradient even more than 15°. Scraper cut and load or simply load, haul, dump and return back for recycling of operation. Applicability The speed of a tractor wheel mounted scraper is around 60 km/h to 65 km/h. Because of higher mobility the wheel mounted scraper is preferred over the crawler track mounted scraper. However where steep gradient, seasonal variations, etc., are to be encountered and where mobility is not a factor of selection, the crawler track mounted tractor will yield a very good result.
  • 32. Scrapers • Scraper can also be used for hauling blast fragmented hard rocks or minerals. Scraper should be used for removal of top soil or unconsolidated rocks or minerals of thickness 2 m to 3 m. • The tractive effort of the scraper depends on power, weight of the machine, gear efficiency, type and size of the tyres, condition of the surface topography over which it moves, etc. A scraper consists of the following main units and components: • bowl, • apron, • cutting blade, • steering system, • power transmission system, • cable or hydraulic type of control unit, braking system etc. Main features The scrapers are basically divided into two categories i.e. Self propelled type and Towed type. • Rubber tired self propelled scrapers are available as four wheel units or as two wheel overhung units. Because of the stability, smoothness of movement, ease of operation, higher speed (around 45 km/h to 50 km/h), higher safety, four wheeled scrapers are widely used. • The towed scrapers are mounted over four wheeled machine body and attached to the rear side of the tractor. • The available struck capacity of a scraper may be more than 12 m3 whereas the heaped capacity of more than 16 m is also possible.
  • 33. Scrapers During cutting most of the times a bulldozer is necessary to push the scraper from the backside. The scraper may be used over a ripped or hard mineral or rock surface for loading and transporting purposes. It is also used for leveling purpose. However it requires a very good traveling ways. It is unsuitable in hard ground condition and sites having big boulders. • After retracting the tailgate to the extreme position, the apron is opened partially and the bowl is lowered till the cutting blade touches or penetrates in the loose ground with high hydraulic pressure. • The scraper thereafter moves forward taking a slice of 100 mm to 200 mm of the soft, unconsolidated and loose ground material which fed into the bowl till it is filled up. • Thereafter bowl is raised up and the excavated material is hauled and dumped to the required place. Operation • Whilst operating on a bench, a scraper should not approach within 2 m of the bench crest. • No scraper should be permitted to move backwards downhill when unloading. • Scrapers hauled by wheeled tractors should not be permitted to negotiate access roads having a gradient greater than 15° in the case of a loaded machine or 25° in the case of an empty machine. Precautions https://www.youtube.com/watch?v=tldOKQiMvAk