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Troughed Belt Conveyors
The troughed belt conveyor is probably the most widely used and well known conveyor design of all
types of belt conveyors.
The troughed belt conveyor has proven to be a reliable and versatile conveyor in many applications
and is probably more forgiving than most other types of conveyors when exposed to adverse
operating conditions.
Improved technology supporting the design of conveyor systems together with innovations in
component design and a better understanding of the dynamics prevalent in conveyor belts during
operation, have propelled troughed belt conveyors into broader applications and higher conveying
capacities.
It is imperative that designers, users and learners are kept informed of the latest developments in
the field of conveyors, and the associated technical and economic benefits which these technologies
hold for the end-user.
Functional Description
A troughed belt conveyor comprises an endless, rubberized flat belt (a) suspended between
pulleys at either end and supported along its length by a number of rotating idler rollers (b). The belt
is driven via one of the pulleys (usually the head pulley (c)) and the tension in the belt is maintained
by using a sliding pulley (d) which is tied to a gravity take-up unit (e).
The material (f) is loaded onto the conveyor at the tail-end via a chute (g) and is transported along
the carrying-side (h) to the head-end where it discharges into a discharge chute (i) which guides the
product onto the downstream equipment.
Impact idlers (j) are located at the loading point to support the belt where the load impacts onto
the belt as it is dropped down the loading chute.
Once the material has been discharged from the carrying belt, the return belt (k) is guided back to
the tail pulley on return idlers (l).
The impact, carrying and return idlers are spaced at different intervals. On the carrying-side, the
mass of the belt plus the load conveyed is greater than the mass to be supported on the return-side
and thus, for the tension in the conveyor belt (by the take-up and induced by the drive unit), the
idler spacing is selected accordingly. This 'sag' in the belt between the carrying and return idler sets
must therefore be designed on the basis of the heaviest load that the conveyor is to transport.
Snub pulleys (m) are sometimes incorporated into the design of a conveyor in order to increase
the angle of wrap (n) of the belt on the drive pulley. The greater wrap angle on the pulley allows
more power to be introduced into the belt as is passes around the drive pulley without slip
occurring. In this way, fewer drives are needed on longer conveyors or conveyors with high
conveying loads.
For a detailed view of a troughed belt conveyor click here to be routed to the "anatomy" of a
trough belt conveyor, or click the appropriate item on the contents bar to the left of your screen
Applications for Troughed Belt Conveyors
Troughed belt conveyors are used extensively throughout the bulk materials handling industry and
examples of applications where this type of conveyor is commonly used are listed below (click
thumbnail for images) :-
Short plant conveyors - horizontal,
inclined or declined
Long overland conveyors - straight or
curved.
Reversible conveyor.
Boom conveyors - stacker-mounted,
slewable.
Inclined mine shaft conveyors. Shiftable conveyors.
Tripper conveyors. Elevated conveyors in gantries. Two-way conveyors.
Material to be Conveyed
Troughed belt conveyors are able to transport a wide variety of materials in bulk. Notwithstanding
this, factors which affect the performance of a conveyor belt, its success or failure often depends on
whether or not the designer completely understands the properties and characteristics of the
material to be transported.
Knowing how a particular material will behave when it is dropped down a loading chute onto a belt
conveyor below and whether a material is dusty, abrasive, free-flowing or extremely wet, is helpful
to the engineer and in the long run, ensures that the client receives a conveyor that meets his
expectations.
Material Class Description
The angle of repose of a material is that angle to the horizontal assumed by the stir-face of a freely
formed pile, The angle of surcharge is that angle to the horizontal assumed by the surface of a
material at rest on a moving conveyor belt. The surcharge angle may be anything up to 20 less than
the angle of repose. The flowability chart on sheet 2 shows the general relationship between the
angles of repose and surcharge.
C.E.M.A. Handbook UNIROYAL Conveyor Belt Selection Guide PROK Handbook
The classification table are based upon nvrm4e conditions and typical materials. The determination
of angles of repose and surcharge and maximum recommended conveyor inclination must be
considered with due regard to such properties as size and shape of fine particles and lumps,
roughness of the surface of the particles, proportion of fines and lumps present, moisture content,
dustiness, stickiness, abrasiveness, corrosive action, etc. Materials or characteristics omitted from
the tables may be roughly appraised by comparison with similar listed materials.
Material Angle of Repose and Surcharge Angle
If details about the material to be conveyed are known and fall within the experience of the
designer, the engineer is able to cater for the specific features necessary on the conveyor which will
ensure that the material can be loaded, conveyed and discharged in accordance with the users
specification. This will in turn lead to a more reliable and efficient troughed belt conveyor operation.
From the above it is obvious that the conveyor designer must have a firm grasp on the properties
of the material which is to be transported along the conveyor in addition to a fundamental
understanding and appreciation of belt conveyor design.
Conveyor Selection Criteria
For the novice, a brief outline of the basic considerations and limitations of the troughed belt
conveyor are given below. Reference is also made to alternative types of belt conveyors which may
be more suitable than troughed belt conveyors in some instances.
As can be seen below, it is incumbent on the engineer to establish the most cost-effective and
practical conveyor system in each application. Where necessary visitors should consult the
appropriate sections dealing with these alternative types of conveyors by clicking on the title bar at
the top of your screen.
Note that detailed design by a competent engineer is required to establish the specific layout
parameters for each conveyor. The information provided below serves merely as a guide.
Layout
For 'short' troughed belt conveyors
(whose length is less than
approximately 500 m) and troughed
belt conveyors installed in factories or
plants should be straight in plan view.
These conveyors may be inclined,
horizontal or declined in elevation, or
parts of a conveyor may be inclined,
horizontal and declined.
For 'long' troughed belt conveyors
(where the conveyors' length is in
excess of 500 m) and where the
conveyor is an overland-type conveyor
following ground line, horizontal
curves of radius greater than 1000 m
can be considered.
As above, these conveyors may
include inclined sections, horizontal
sections and declined portions
between the loading and discharge
points.
Profiles of Troughed Belt Conveyors
The possible profiles which a troughed belt conveyor can follow are almost unlimited. In the process
of determining whether a troughed belt conveyor is the correct type of conveyor for any given
application, the layout of the conveyor plays a significant role.
One aspect of the layout of a conveying system is the profile which the conveyor must follow. To a
large degree the vertical profile is limited by the character of the material being conveyed e.g.
whether the material will roll back along the belt while being transported up an inclined section of a
conveyor. To ensure that this does not occur, the designer must consider the material properties
and must tailor the profile of the conveyor accordingly.
Assuming that the material properties, physical obstacles on the Plant and the process requirements
are taken into consideration, the profile which a troughed belt conveyor can follow is almost
unlimited.
Some examples of troughed belt conveyor profiles commonly seen are provided below :-
At loading points, the
maximum inclination of the
belt should not be greater
than approximately 5
degrees to the horizontal.
This maximum inclination is
dependent on the belt
speed, the material
characteristics and to a
lesser degree the layout of
the feed point. Inclining the
loading point to a greater
angle may result in spillage
at the loading chute.
A further consideration at loading points is the height required above the conveyor belt for the
loading chute work. It is important that material is loaded onto the center of the conveyor belt to
ensure that the belt runs centrally along the conveyor structure. To achieve this the loading/feed
chute must be wide enough at the top of the chute to collect all material being fed into it, while the
bottom of the chute must be no wider than 2/3 of the width of the conveyor belt.
The side walls of the chute must
be steep enough to prevent
material accumulating on the
side walls and corners of the
chute, which could lead to
blockages. Typically side walls of
chutes range between 45
degrees and 70 degrees
depending on the material to be
conveyed.
It can be seen in the sketch
therefore that careful consideration must be given to the layout of the tail station. The height
required above the new conveyor belt for the feeding system and chute work must not be
overlooked.
The discharge of material from a troughed belt conveyor is usually via a chute onto another
conveyor, into a silo, etc. As with the feed chute, the discharge chute must be carefully laid out in
order to establish the required elevation of the head / discharge pulley to ensure that the discharge
chute does not block under full load conditions.
It has been explained above that troughed belt conveyors are generally designed as straight
conveyors (plan view), certainly in the case of short belt conveyors. When a designer is considering
the layout of a conveyor in a factory for example, the desired route which the conveyor is to follow
may not in fact be possible due to physical obstacles located between the feed point and the desired
discharge point.
In such a case the designer
is presented with a number
of options which should be
investigated prior to
finalising the design of the
belt conveyor system to be
used.
A first option may be to use two a troughed belt conveyors with a transfer point between the two
conveyors, as can be seen in this sketch.
A second option may be to use a different type of belt conveyor for example the pipe conveyor or
Sicon conveyor which offer the ability to negotiate corners without the need of transfer points. Each
of these alternative types of belt conveyors has their own layout constrains, advantages and
disadvantages, which the designer must take into consideration as part of the investigation.
The inclination of a belt conveyor is also a factor which must be considered by the engineer, when
selecting the type of belt conveyor to be used. The maximum inclination or decline of a conveyor
generally depends on the characteristics of the material to be transported. To assist the learner in
determining which type of conveyor should be used for a particular application, a graph may be
viewed by clicking here.
Conveyor Duty & Material Specification
It is important that the duty which the conveyor is expected to fulfill is clearly established at the
commencement of the design phase, as this will impact on numerous items in the detailed design of
the conveyor and component selection.
The capacity of the conveyor (in tons per hour or cubic meters per hour) as well as the average
operating hours per day or per year are important design criteria. Details pertaining to the material
to be conveyed must also be specified.
Having established the duty that the conveyor is expected to fulfill and obtained the material
specifications the designer is in a better position to determine the most cost-effective conveying
method to be employed.
Environmental Considerations
The need to improve the local environment at factories and plants is gaining support throughout
the world and is often driven by legislation. As such the type, layout, design and correct operation of
belt conveyors and their associated equipment is becoming more important.
Environmental considerations cover an extremely wide scope of issues ranging from the degree of
pollutants generated by the working conveyor to the visual impact of a conveyor on the local
community. The designer cannot therefore neglect to include the environmental considerations into
the assessment of the most appropriate type of conveyor.
Environmental legislation differs from country to country and from factory to factory and it is
therefore important that the specific environmental legislation and rules be established and
introduced into the overall conveyor feasibility and design procedure.
For the purposes of list Beginners Guide, some of the most obvious environmental-related issues
are itemised below to provide the learner with an holistic approach to conveyor design.
Products which are dusty or which tend to generate dust at transfer points for example
powder cement and dry fly ash, may be conveyed in enclosed conveyors. Examples of
enclosed conveyors include pipe conveyors, Sicon conveyors, bucket elevators, screw
conveyors and pneumatic transportation systems.
In considering the layout of the conveying system, the number of transfer points between
conveyors should be minimised to reduce the number of dust and spillage generating points
in a conveying system, thereby minimising the impact of the system on the local
environment.
Using a pipe conveyor which incorporates a gradual 90 degree curve can eliminate one
transfer point in an equivalent troughed belt conveyor system, where two troughed
conveyors would otherwise be necessary.
Alternatively, a Sicon
conveyor may be a better
solution due to its superior
cornering ability and
increased flexibility. Should
a troughed belt conveyor be
used however, the conveyor
can be installed into an
enclosed gantry or tunnel to
reduce the possibility of
material being blown off of the carrying side. Covers can also be installed over the carrying
belt to reduce the risk of material blowing off of the conveyor and / or contain the dust.
The environment in which the belt conveyor is to operate may be subject to extreme
variations in weather
conditions. A conveyor
located on a jetty for
example, may be subject to
high and low temperatures,
strong wind conditions and
an extremely corrosive
environment. In such a case
issues such as whether or not
the conveyor is to be
enclosed becomes extremely
important. In addition, the
materials of construction of
the structure may be
different to an equivalent conveyor located in a dry, noncorrosive environment. The
corrosion protection specification applicable to the conveyor structure and components
would typically demand a far greater degree of control over the application and
maintenance of the coating.
The material to be conveyed may inherently be a commodity of high value where the client
wishes to limit access to the product and the opportunity for spillage. The transportation of
diamond-bearing Kimberlite to and from a process plant is an example of such an
environment. In such a case Sicon conveyors are employed for their ability to negotiate
difficult conveying routes without the need for transfer points as well as the fact that they
enclose the material.
The 'environment' in which a conveyor is
to be installed may dictate that the
space available for a conveyor is
extremely limited. Transporting material
from ground level to the top of a bin or
silo may require the conveyor to be
installed vertically up the side of the silo.
In this case the equipment to be used
would typically be a bucket elevator or a
pocket belt or a sandwich type
conveyor, all of which are able to
transport material vertically.
The location of the
site where the
conveyor is to be
installed may be in a
cold, mountainous
area. In this case
(assuming ambient
temperatures drop to
well below freezing),
special consideration
must be given to the
selection of the
conveyor belt as well
as to items such as the
mechanical components (bearings) and the lubricant proposed. Starting belt conveyors in
extremely cold conditions requires among other things additional power to overcome the
friction imposed by cold lubricants and a stiffer belt.
In addition to the temperature aspect, it may
be necessary to route the conveyor down the
side of a mountain and the conveyor route
must negotiate the natural contours of the
terrain thereby forcing the designer to
incorporate vertical and horizontal curves into
the conveyor layout. Where the environment
imposes extremely arduous
parameters/limitations on the design of the
conveying system, it may be necessary to
reconsider whether in fact a belt conveyor is
appropriate for the application.
Cost Like any other equipment, there are costs associated with belt conveyors and these costs must be
determined to a reasonable degree of accuracy in order for a commercial evaluation to be
developed which will accompany the technical evaluation.
It is generally accepted practice for the 'costs' of a conveyor to be presented in two categories
namely; the initial capital outlay or capital expenditure for the system i.e. CAPEX and an ongoing
operating and maintenance expense i.e. OPEX which the client will incur for the remaining life of the
conveyor system.
CAPEX should take into consideration costs such as :-
the cost of the mechanical, electrical, civil, structural and instrumentation equipment
purchased and installed on site as part of the conveyor.
the project management fee which a contractor / supplier will charge the user for executing
the project.
the cost of any modifications to existing equipment which may be required on site to
incorporate the new conveyor into the factory.
the cost to install, commission and test the conveyor system on site.
OPEX should take into consideration the following costs :-
the cost of spare parts which the user will have to procure over the operational life of the
conveyor. This cost is based on a projection of the life of components within the conveyor
and the cost of each of those components, based on the duty of the conveyor.
the cost of personnel required to operate the conveyor.
the costs of personnel and equipment required to maintain the conveyor.
the cost of electrical power to drive the conveyor.
Depending on the layout of the conveyor system and possibly the type of conveyor system to be
used, the CAPEX and OPEX costs will differ. It is important therefore that the calculation of the costs
for each option is performed according to the same basic parameters for example, similar costs for
man hours and for electric power.
It is possible for the total life cycle costs (CAPEX and OPEX) for any given option to be represented
in a number of ways. Examples include; all capital and operational costs may be shown as a present
value cost, escalation and/or discount factors may be included or excluded from the financial
analysis, etc.
Standardisation
If a belt conveyor is to be installed on either a new plant or existing facility, the choice of type of
conveyor to be used may depend to a large extent on the need to standardise on the type of
equipment used.
In the case of a new factory for example where a number of troughed belt conveyors are to be
used throughout the facility then, in the interests of standardising and minimizing on spares to be
held by the client and the training of personnel to operate and maintain the conveyors, the type of
conveyor to be used should as far as reasonably possible be kept the same.
Notwithstanding the need to investigate the optimum layout and cost for a particular conveyor,
practicality dictates that standardisation of equipment is very often in the long-term interest of the
end-user of the equipment and the engineer should bear this in mind in his assessment.
Examples of Troughed Belt Conveyors Having understood some of the basic considerations relating to the choice and feasibility of
troughed belt conveyors, it is important that the learner is left with an indication of the capabilities
of this type of conveyor.
The longest single-flight troughed belt conveyor in the world
is installed in Zimbabwe, Southern Africa, by Bateman
Engineered Technologies. The conveyor length measured from
tail pulley to head pulley is 15.6 km (belt length = 31,372 km)
and transports iron ore at a rate of 500 tons per hour. The belt
is 750 mm wide, travels at a speed of 4,7 m/s and the installed
drive power is 1000 kW. The troughing and return idlers are
spaced at intervals of 4.5 m and 9.0 m respectively and the 80
ton counter weight has a travel of 50 m.
The longest multiple-flight troughed belt conveying system is
installed in the Sahara desert and transports phosphate rock at
a rate of 1000 tph over a distance of 110 km. The conveying
system comprises 11 individual conveyors. This system was
designed and installed by Krupp.
Among the highest capacity troughed belt conveyors in the
world are mounted on mobile bucket wheel reclaimers in
Europe. While these conveyors are relatively short
(approximately 100 m pulley centre distance) the belts measure
up to 3.0 m wide and travel at 8 m/s. The peak design capacity
of these conveyors is up to 25 000 m3/hour and material lump
size ranges up to 1.0 m particle diameter.
Conveyor Selection Guide
Choosing the correct
type of the conveyor
for any given
application depends
on a number of
factors including
material
characteristics,
conveyor system
layout, duty,
environment, etc.
The following graph
has been developed
to assist learners with
the selection of the
correct type of belt
conveyor system. This
graph is intended for
use as a guide only
and Users would be
well advised to
approach suppliers of
these conveyor
systems in order to
confirm whether the
preferred type of
conveyor is
appropriate.
Anatomy of a Troughed Belt Conveyor
There are many possible variations in the design of a troughed belt conveyor depending on the
purpose and duty for which the conveyor is being designed. Similarly the choice of individual
components, features and accessories found on a conveyor should be selected on the basis of the
functions which have to be performed by the conveyor.
At this point in the Beginners Guide the learner is introduced to the different components and basic
arrangement and features which are found on the majority of troughed belt conveyors throughout
the world.
In this section a graphic image of a typical troughed belt conveyor is provided together with detailed
images and photographs of specific components. The learner should also study the nomenclature
and terms used by engineers and designers when describing troughed belt conveyors.
