Material handling equipments : conveyors and elevators

Material handling equipments; conveyers
and elevators
Protected Cultivation and Secondary Agriculture
By Ajaz Ahmad Malla

Material handling Equipments
Material handling includes a number of operations that
can be executed either by hand (manual) or by
mechanical means or devices to convey material and to
reduce the human drudgery. The most common types
of mechanical devices for grain handling are;
• 1. Belt conveyor
• 2. Bucket elevator
• 3. Screw conveyor
• 4. Chain Conveyor
• 5. Pneumatic conveyor

Selection of material Handling machines and Conveyors
The selection of proper conveying system is important for ease in
operation and getting desired capacity for a particular product.
Principles based on which the material handling equipment is
selected:
• Based on the characteristics of the products being conveyed
• Working and climatic conditions.
• The capacity of conveying
• In a conveying system possibility of use of gravity.
• The capacity of handling / conveying equipment should match with
the capacity of processing unit or units.
• Spillage of conveyed products should be avoided.
• Pollution of the environment due to noise or dust by the conveying
system should also be avoided.

1. Belt conveyors
• Principle of operation:
A belt conveyor is simply an endless strap of flexible
material stretched between two pulleys and supported
at intervals on idler rollers. When the pulley is rotated
by the driving motor, the belt will move with roller due
to frictional resistance, there by the material placed on
the belt will be transported from one place to other.

• A belt conveyor is an endless belt operating between
two pulleys with its load supported on idlers. One of
the pulley is driven by motor. The belt may be flat for
transporting bagged material or V-shaped. The belt
conveyor consists of a belt, drive mechanism and end
pulleys, idlers and loading and discharge devices.
• On the belt conveyor baggage/ product lie still on the
surface of belt and there is no relative motion
between the product and belt. This results in
generally no damage to material.
• Belt can be run at higher speeds, so, large carrying
capacities are possible. Horizontally the material can
be transported to longer distance.

• conveyor with a specified conveying capacity is to determine
the speed and width of the belt. The belt speed should be
selected to minimize product spillage or removal of fines due
to velocity of the belt.
• For transportation of grains, the belt speed should not
increase 3.5 m/s. Generally, for grain conveying, belt speed of
2.5 to 2.8 m/s is recommended.
• The selection of belt width will depend upon the capacity
requirement, speed of operation, angle of inclination of belt
conveyor, trough angle and depth.
• A trough angle of 20° is best suited for paddy as paddy forms
a surcharge angle of 20° and most other grains also. Other
common trough angles are 30° and 45°.

2.Bucket Elevator
Working Principle :
The product is fed into the moving bucket belt
at a controlled rate in a similar manner to
feeding a normal belt conveyor. At the end of
conveyor, the buckets are emptied by gravity
into the discharge section.

• A bucket elevator consists of buckets attached to
a chain or belt that revolves around two pulleys
one at top and the other at bottom.
• The vertical lift of the elevator may range
between few metres to more than 50 m.
• Capacities of bucket elevators may vary from 2
to 1000 t/hr.
• Bucket elevators are broadly classified into two
general types
(1) spaced bucket elevators and
(2) continuous bucket elevators.

The spaced bucket elevators are further
classified as,
• (1) centrifugal discharge elevators,
• (2) positive-discharge elevators,
• (3) marine leg elevators and
• (4) high-speed elevators.
The continuous bucket elevators are classified as
• (1) super capacity bucket elevators and
• (2) internal-discharge bucket elevators.

• The spaced bucket centrifugal discharge type is
most commonly used for elevating the grains.
• The bucket elevator is a very efficient device for
the vertical conveyance of bulk grains.
• Bucket elevators with belts are employed in food
industries for vertical conveyance of grains,
derivatives and flours.
• Bucket elevators are usually mounted at a fixed
location, but they can also be mounted in a
mobile frame.
• It requires limited horizontal space and the
operation of conveying is enclosed in housing,
thus it is dust free and fairly quite.

• They are suitable for conveying material vertically
and widely used in building, mining, power station,
cement, concrete plants, chemical industry, light
industry and grain, etc.

3.Screw Conveyor
• Working Principle :
Using Screw Conveyor material is transported
by rotation of helical screws which moves
material in forward direction in tube from
feed point to discharge point.

• The screw conveyor consists of a tubular or U-
shaped trough in which a shaft with spiral screw
revolves. The rotation of screw pushes the grain
along the trough.
• The main parts of a screw conveyor are, screw
blade, screw shaft, coupling, trough, cover, inlet
and outlet gates, bearings and drive mechanism.
• The screw basically consists of a shaft and the
screw blade.
• The screw conveyor is used in grain handling
facilities, animal feed industries and other
installations for conveying of products generally
for short distances.

• The pitch of a standard screw which is the
distance from the centre of one thread to the
centre of the next thread is equal to its
diameter. For example a 10 cm diameter
screw has a pitch of 10 cm.
• As the screw conveyor's driving mechanism is
simpler, and no tensioning device is required,
the initial cost of the conveyor is lower than
any other conveyor with the same length and
capacity.

• The screw conveyor is generally used to move
grains horizontally. However, it can also be
used at any angle up to 90° from the
horizontal, but the capacity correspondingly
reduced as per the inclination of conveyance.
• Screw conveyor requires relatively high power
and is more susceptible to wear than other
types of conveyors.

4.Pneumatic Conveyor
• Working Principle :
The bulk materials or granules are transferred
through an enclosed conveying pipeline by the
collective force of pressure and the gas used
(commonly air).

• Pneumatic conveyors are continuous
conveyors for bulk material in which material
is conveyed in an enclosed tube system by
means of compressed air or by means of a
vacuum.
• This type of conveyor is extremely flexible in
terms of routing.
• Both compressed air and vacuum systems are
based on the same principle, according to
which solid particles—when the air velocity is
fast enough—are picked up by the conveyor’s
air flow and conveyed along the pipe.

• The pneumatic conveyor moves granular
materials in a closed duct by a high velocity air
stream. Pneumatic conveying is a continuous
and flexible transportation method.
• The material is carried in pipelines either by
suction or blowing pressure of air stream.
• The granular materials because of high air
pressure are conveyed in dispersed condition.
• For dispersion of bulk material, air velocities in
the range of 15-30 m/s is necessary.

• The pneumatic conveying system needs a
source of air blowing or suction, means of
feeding the product into the conveyor, ducts
and a cyclone or receiving hopper for
collection of product.
• There are three basic systems of pneumatic
conveying.
1. Pressure or blowing system
2. Suction or vacuum system
3. Combined push-pull

• For separation of product particles from air,
air-product separators are used.
• Cyclones are mostly used to collect the
particles.
• Cyclone is a device which removes the bulk of
the product particle from the conveying air
stream by centrifugal force.

Limitations of Pneumatic Conveying
• Erosion of solid surfaces and equipment
surfaces by solid particles with conveying air
stream.
• In case of bends or misaligned sections, the
erosion problem becomes severe.
• Chances of repeated impacts between the
particles and the solid surfaces are high. Due
to such impacts, product degradation results.

5.Chain Conveyor
• These conveyors are similar in working
principles to the belt conveyors. In this case a
chain is made to run over the head and tail
sprockets.
• Just as in belt conveyors , idlers are provided
to support the chain in the load carrying.
• Chain conveyors have a better ability to
absorb impact loads and have less
stretchability under load.

• They can transport large loads and can be
used in applications where the conveyed
material is hot.
• These conveyors are more expensive and are
also noisy as compared to belt conveyors.
• They require proper lubrication and the chains
wear faster, if conveying speeds are increased.
• Chain conveyors are generally suitable for unit
loads.

Material handling equipments : conveyors and elevators

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