1. BELT MATERIAL 2. IDLERS(ROLLERS) 3. DRIVING
4. TENSIONING 5. HOLD BACK 6. CLEARING DEVICE
A belt conveyor is rubber or textile structure with a belt shape
closed ring, with a vulcanized or metallic joint, used for material
Belt conveyors are the most used for transport of solid objects and
bulk materials at great speed, covering great distances (up to 30
Conveyor belts generally are composed of three main components:
There are two types of belt available:
1. Rubber belt
2. Steel Cord
The reinforcement usually found on the inside of a conveyor belt is normally
referred to as the “carcass.” In a sense, the carcass is in the conveyor belt since it
1. Provide the tensile strength necessary to move the loaded
2. Absorb the impact of the impinging material being loaded
onto the conveyor belt.
3. Provide the bulk and lateral stiffness required for the load
The most common carcass design is made up of layers or “plies” of woven
fabrics bonded together.
This “conventional plied” belt construction, generally employs a plain
weave or twill weave carcass which is built up into as many layers as is
required to provide the necessary belt strength…usually bound together with
Conventional plied belting constructions, employing all synthetic carcasses
and elastomer covers appropriate to the end use, are particularly
I. Hard Rock Mining
(A) Aggregate, sand and ore
II. General purpose applications
III. Forest products
IV. Soft Minerals
(A) Coal (B) Potash, Phosphates (C) Grain
V. Unit Handling
(A) Parcels (B) Baggage (C) Mail
The strength of fabric and the number of plies in the carcass of the belt may be varied
together to suit the strength requirement.
However if the belt is too tough, troughing of the belt and bending it round the terminal
pulleys will be very difficult. Therefore the belt with lesser number of plies with stronger
fabric is generally preferred because it is more flexible.
Steel cord belting is used when good trough ability, small specific elongation and higher
operating tensile forces are required.
PVC belting is generally selected for underground mining applications where fire hazard
The rubber, PVC or urethane between plies is called a “skim.” Skims are
important contributors to internal belt adhesions, impact resistance, and
play a significant role in determining belt “load support” and
Improper or marginal “skims” can adversely affect belt performance in
general and can lead to ply separation and/or idler junction failure.
Covers are used in conveyor belt constructions in order to protect the base
conveyor belt carcass and, if possible, to extend its service life. In
addition, covers do provide the finished belt with a wide variety of
desirable properties, including the following:
To increase friction
To increase inclination
To control product
C. A specific coefficient of friction
D. A specific color
E. Cut resistance
F. Enhanced impact resistance, etc.
H. Fire Resistance, Oil & Chemical Resistance
In addition to selecting proper compounds for cover material, it is
also necessary to determine the proper cover thickness.
The thickness of a cover is influenced by the amount of abuse and
wear the belt will receive. The cover is usually the lowest cost
component of the belt. The severity of the wear depends on the
nature of the material and on the size, weight, shape and trip rate
of the Material conveyed.
Sharp edges, particularly on large pieces, can quickly cut a cover
badly. On the other hand, if loading conditions are ideal, with the
material being loaded in the direction of travel of the belt, and with
only a slight impact onto the belt, even very sharp material may not
seriously cut or wear the belt surface.
Types and Selection of Drives:
Single Unsnubbed Bare / Lagged pulley Drive
Snubbed Bare / Lagged Pulley Drive
Single Unsnubbed Bare / Lagged Pulley
This is the simplest drive arrangement consisting of a steel pulley connected to a
motor and the belt wrapped round it on an arc of 180°. This can be used for low
capacity short center conveyors handling non-abrasive material. The pulley may
be lagged to increase the coefficient of friction.
Snubbed Bare / Lagged Pulley Drive:
Here the angle of wrap is increased from 180° to 210° or even up to 230°, by
providing a snub pulley to the driving pulley. In majority of medium to large
capacity belt conveyors, handling mild abrasive to fairly abrasive
materials, 210° snub pulley drive with load pulley lagged with hard rubber is
Here belt tension estimated to be high; the angle of wrap is increased by adopting
tandem drives. Both of tandem pulleys are driven. The tandem drive with arc of
contact from 300° to 480° or more can operate with one or two motors. The location of
such drive is usually determined by the physical requirements of the plant and
Special drives with snub pulleys and pressure belts used in heavy and long
All belt conveyors require the use of some form of take up device
(Tensioning Arrangement) for the following reasons:
1. To ensure adequate tension of the belt leaving the drive pulley so us to
avoid any slippage of the belt.
2. To ensure proper belt tension at the loading and other points along the
3. To compensate for changes in belt length due to elongation.
4. To provide extra length of belt when necessary for splicing purpose.
Usually there are two types of take up arrangements.
1.Fixed take up device that may be adjusted periodically by manual
2.Automatic take up devices for constant load type
Manual Screw Take Up:
The most commonly used manual take up is the screw take up. In a screw
take up system the take up pulley rotates in two bearing blocks which may
slide on stationery guide ways with the help of two screws. The tension is
created by the two screws which are tightened and periodically adjusted
with a spanner. It is preferable to use screws with trapezoidal thread to
decrease the effort required to tighten the belt.
The main problem with the use of manual take up is that it requires a vigilant
and careful operator to observe when take up adjustment is required. Perfect
tension adjustment with this system is also not possible. For these reason these
devices are used only in case of short conveyors of up 60m length and light
Automatic Take Up:
In automatic take up arrangement the take up pulley is mounted on slides
or on a trolley which is pulled backwards by means of a steel rope and
deflecting pulleys. The carriage travels on guide ways mounted parallel to
the longitudinal axis of the conveyor, i.e., horizontally in horizontal
conveyors (Ex.: Gravity type automatic take up arrangement) and at an
incline in inclined conveyors. Hydraulic, Pneumatic and electrical take up
devices are also used
Inclined conveyors require an anti-runback device to prevent reverse
movement of the belts. Such a device is referred to as a backstop, or
Though backstops are most likely to be found on inclined conveyors, they
are also employed on flat, overland conveyors to avoid the unusually
severe shock loading on start-up where the loaded belt sags between
idlers. This paper will direct its attention to backstops installed on inclined
Without a backstop, a reversing conveyor can rapidly accelerate to a
runaway condition, which can kill or injure personnel, damage or destroy
drive train components, tear or rip expensive belting, or cause considerable
Without a backstop, a reversing conveyor can rapidly accelerate to a
runaway condition, which can kill or injure personnel, damage or
destroy drive train components, tear or rip expensive belting, or cause
considerable other damage.
A backstop is essentially a safety device which acts to prevent reversal
thereby protecting against any of the above from occurring, as well as
the massive clean up of material spillage than can occur.
Backstops can be classified either for :
i) low-speed ii) high-speed use.
LOW-SPEED BACKSTOP DESIGN TYPES
There are three basic backstop designs that are or have been used to
prevent anti-runback throughout the many years of conveying materials;
1.rachet and pawl
2.differential handbrake and
3.the overrunning clutch design