C ONVEYORS By SidraJabeen Department of Chemical Engineering,
University of Engineering & Technology Lahore
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Conveying is a term used to transport, transfer or transmit.
Conveyor is a device that transports or transmits something
Conveyors are machines that transport material fed to them at
controlled rate to desired location. 2 Conveyors
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Screw Conveyor Belt Conveyor Bucket Elevators Vibrating or
Oscillating Conveyor Pneumatic Conveyors 3 Types of Conveyors
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The screw conveyor is one of the oldest and most versatile
conveyor types. It consists of a helicoid flight (helix rolled from
flat steel bar) mounted on a pipe or shaft and turning in a trough.
Power to convey must be transmitted through the pipe or shaft.
Screw-conveyor capacities are generally limited to around 10,000 ft
3 /h. Screw conveyors can also be adapted to a wide variety of
processing operations in addition to their conveying ability 4
Screw Conveyors
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Contd.. Screw conveyor can be used for mixing, heating,
cooling, and drying operations. A further advantage is the fact
that the casing can be designed with a drop bottom for easy
cleaning to avoid contamination when different materials are to be
run through the same system. 5
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The belt conveyor is almost universal in application. It can
travel for miles at speeds up to 1000 ft/min and handle up to 5000
tons/h. It can also operate over short distances at speeds slow
enough for manual picking, with a capacity of only a few kilograms
per hour. Belt-conveyor slopes are limited to a maximum of about
30, with those in the 18 to 20 range more common. Direction changes
can occur in the belt path and must be carefully designed as flat
bends. 8 Belt Conveyors
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Contd.. Belt conveyors inside the plant may have higher initial
cost than some other types. Temperature and chemical activity of
the conveyed material play important roles in belt selection.
Moisture can cause poor discharge conditions because of material
sticking to the belt. 9
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Bucket elevators are the simplest and most common units for
making vertical lifts. They are available in a wide range of
capacities and may operate entirely in the open or be totally
enclosed. 11 Bucket Elevator
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Most vibrating conveyors consist of a spring-supported
horizontal pan vibrated by a any of the vibrating mechanism. The
motion imparted to the material particles may vary, but its purpose
is to throw the material upward and forward so that it will travel
along the conveyor path in a series of short steps. 13 Vibrating or
Oscillating Conveyors
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14 Vibrating / Oscillating Conveyor
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One of the most important material-handling techniques in the
chemical industry is the movement of material suspended in a stream
of air over horizontal and vertical distances ranging from a few to
several hundred feet. Material is dropped into an air stream by a
rotary air-lock feeder. The velocity of the stream maintains the
bulk material in suspension until it reaches the receiving vessel,
where it is separated from the air by means of an air filter or
cyclone separator. 15 Pneumatic Conveyors
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17 Conveyor Selection Selection of the correct conveyor for a
specific bulk material in a specific situation is complicated by
the large number of interrelated factors: Capacity requirement
Length of travel Lift Material characteristics
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Capacity requirement is a prime factor in conveyor selection.
Belt conveyors, which can be manufactured in relatively large sizes
to operate at high speeds, deliver large tonnages economically. On
the other hand, screw conveyors become extremely bulky as they get
larger and cannot be operated at high speeds without creating
serious abrasion problems. 18 Capacity Requirement
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Length of travel is definitely limited for certain types of
conveyors. The length limit on belt conveyors can be a matter of
miles. Pneumatic conveyors are limited to 305 m (1000 ft);
vibrating conveyors, to hundreds of meters or feet, Screw conveyors
can travel upto 50 m. 19 Length of travel
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Lift can usually be handled most economically by vertical or
inclined bucket elevators, but when lift and horizontal travel are
combined, other conveyors should be considered. Conveyors that
combine several directions of travel in a single unit are generally
more expensive. 20 Lift
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Material characteristics, both chemical and physical, should be
considered, especially flow ability. Abrasiveness and lump size are
also important. Chemical effects (e.g., the effect of oil on
rubber) must be considered Moisture or oxidation effects from
exposure to the atmosphere may be harmful to the material being
conveyed and require total enclosure of the conveyor. 21 Material
Characteristics
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22 Conveyors for bulk materials
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Conveyor drives may account for from 10 to 30 percent of the
total cost of the conveyor system, depending on specific job
requirements. They may be of either fixed-speed or adjustable-speed
type. 23 Conveyor Drivers
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Fixed-speed drives are used when the initially chosen conveyor
speed does not require change during the course of normal
operation. In any event, the conveyor must be shut down while the
speed change is made. Adjustable-speed drives are designed for
changing speed either manually or automatically while the conveyor
is in operation, to meet variations in processing requirements.
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