CHAPTER-5
HOISTING AND CONVEYING EQUIPMENT
5.1 HOISTING EQUIPMENT:
CRANE:
A crane is a type of machine, which is generally equipped with a hoist rope, wire ropes or chains,
and sheaves, that can be used both to lift and lower materials and to move them horizontally. It is mainly used
for lifting heavy things and transporting them to other places. The device uses one or more simple machines to
create mechanical advantage. Cranes are commonly employed in the transport industry for the loading and
unloading of weight, in the construction industry for the movement of materials, and in the manufacturing
industry for the assembling of heavy equipment.
Different types of Cranes:
1. TOWER CRANE:
Tower cranes are a modern form
of balance crane that fixed to the
ground on a concrete slab (and
sometimes attached to the sides of
structures), often give the best
combination of height and lifting
capacity and are used in the
construction of tall buildings,
bridges, power plants etc.
Principles and Working of
Tower Crane:
The construction of the tower
crane is such that it can work and
then dismantled in restricted space.
It is fixed to the ground on a
concrete slab, called base of tower
crane. The base is then attached to
the mast (or, tower), which gives
the crane its height. Further, the
mast is attached to the slewing unit
(gear and motor) that allows the
crane to rotate. On top of the
slewing unit there are three main
parts which are: the long
horizontal jib (working arm),
shorter counter-jib, and the operator's cab.
The long horizontal jib is the part of the crane that carries the load. The counter-jib carries a
counterweight, usually of concrete blocks, while the jib suspends the load to and from the center of the crane.
The crane operator either sits in a cab at the top of the tower or controls the crane by radio remote control
from the ground. In the first case the operator's cab is most usually located at the top of the tower attached to
the turntable, but can be mounted on the jib, or partway down the tower. The lifting hook is operated by the
crane operator using electric motors to manipulate wire rope cables through a system of sheaves. The hook is
located on the long horizontal arm to lift the load which also contains its motor.
In order to hook and unhook the loads, the operator usually works in conjunction with a signaler. They
are most often in radio contact, and always use hand signals. The signaler directs the schedule of lifts for the
crane, and is responsible for the safety of the rigging and loads.
Each model and distinctive style of tower crane has a predetermined lifting chart that can be applied to
any radii available depending on its configuration. A tower crane may lift an object of greater mass closer to
its center of rotation than at its maximum radius. The tower cranes have 360 degree slewing capability. An
operator manipulates several levers and pedals to control each function of the crane.
Depending upon the nature of the task, tower cranes can be grouped into following categories:
(a) Stationary Cranes: These tower cranes are supported on foundations, and their mast bolted to a fixed
position. The height of these cranes can be increased further (up to 100m) by bracing the mast with the
building structure.
(b) Travelling Cranes: The steel base of these cranes is mounted on travel gear, resting on rail tracks
embedded in the foundation. This enables the crane to travel along the track with load. This increased
coverage of the work area. The height of these cranes should not be exceeding about 70m.
(c) Climbing Cranes: These cranes are useful where the shortage of sufficient external spaces around the
constructing building that does not permit the erection of other tower cranes. Structurally supported by
the floors of the buildings that is being constructed, the crane climbs on special climbing collars that
are fitted to the buildings completed structural floors. The weight of both the crane and the load lifted
is transmitted to the structure of the building.
2. MOBILE CRANES:
A mobile crane is a cable-controlled crane mounted on crawlers or rubber-tired carriers with a telescoping
boom mounted on truck-type carriers. They are designed to easily transport to a site and use with different
types of load and cargo with little or no setup or assembly.
The mobile cranes have four motions i.e. hoisting and derricking, slewing and travelling. Mobile cranes
are either crawler mounted or wheel mounted.
1. Crawler mounted cranes: Crawler mounted cranes are highly maneuverable and have the ability to
operate on unmade ground. Long wide crawler mountings and wide crawler shoes give low ground bearing
pressures and they can travel with their maximum load suspended from the hook. This improves crane
stability. Since these move slowly, they are used in rough terrain where truck- mounted cranes cannot travel
and hence are economically used where ground conditions are poor and required to operate in a limited area.
The boom of these cranes comes in sections which are joined by pin connections. The straight boom thus
formed can lift loads over a radius of 30 to 40 meters.
The full revolving super structure of crawler crane is
mounted on a pair of continuous, parallel crawler tracks. Many
manufacturers have different option packages available that
enable configuration of the crane to a particular application. The
crawlers provide the crane with good travel capability around the
job site. Shifting a crawler crane between projects requires that it
be transported by the truck, rail or barge. As the size of the crane
increases, the time and cost to dismantle and load the crane,
investigate the haul routes, and assemble the crane will also
increase.
2. Wheel mounted mobile cranes: Wheel
mounted mobile cranes are generally truck
mounted or self-propelled and have high
mobility, and can travel upto 70 to 75 km per
hour on good roads. These are designed for long
distance travel with high road speeds. The
number of axles and drive depends upon load
lifting capacity and the length of the boom. These
cranes can operate on firm ground. For increasing
base width and to improve stability during
operations, out-riggers are used.
Self-propelled rubber-tyred wheel cranes
have greater mobility over hard surfaces and
are widely used for shifting and transporting light
loads over short distances, and for off- loading of
medium to heavy loads.
Truck mounted cranes are available with
telescopic-jib and strut-jib. Telescopic-jib cranes
provide flexibility in adjusting distances and
heights of lifts. These have greater mobility on
roads than other cranes. Strut-jib cranes are
suitable for shifting small loads at a distance,
where ground obstruction restricted the utility of the crane.
3. DERRICK CRANE:
Derrick cranes consist of a mast, a boom, bull wheel on
which it rotates about a vertical axis, and supporting
members (also known as guys). These cranes are very
widely used in construction projects, industrial and
multi-storied building construction, loading and
unloading of cargoes at ports, in ship building etc.
When used with grabs it can handle loose materials like
sand, ballast, coal etc.
The most of the derrick cranes are supported by
a number of guys (As shown in the figure). The boom
can revolve through 360° and can pass below these
guys. A bull wheel is attached to the mast and rotates
it. These are operated by either a diesel engine
or by an electric motor.
As mentioned above, mast is generally
supported by guy ropes but when this is
replaced by trussed structure it becomes stiff-
leg derrick. In this case the mast is supported at
its upper end by two braced stiff-leg, therefore
the boom rotates through angle of 270° to
290°.
The derrick cranes are sometimes
mounted on rail wagons for quick
transportation and for working near rail lines,
and are known as as Whirler cranes. The
Derrick cranes can be used as Tower cranes for
the purpose of erection of high industrial and
residential buildings of height 100 meter or
above. The Derrick cranes are also designed to
work as port tower cranes (for use in ports for container and general cargo handling) and as shipyard cranes
(for use in ship building and ship repairing works with longer capacities and larger working radii).
4. OVERHEAD (GANTRY) CRANES:
These are used for handling loads over a long rectangular area
in factories, power stations, in shipyards and in workshops.
The simplest form mainly consists of (i) structural bridge
support on elevated track, and (ii) supporting a lifting block or
hoist trolley. Control is from a cabin on the bridge or by
pendant at floor level. Due to freedom from floor
obstructions, these are widely used in steel plants, power
houses, shipyards etc.
The bridge consists of two main girders which are
fixed at the end and supported on tram wheels and can move
on gantry rails. The hoist trolley also known as crab is
supported on these girders and is capable of travelling across
main girders. Thus load hook has three motions viz. hoisting i.e. lifting and lowering; cross travelling with
trolley in both directions; and longitudinal traversing with the bridge in both directions.
5.2 CONVEYING EQUIPMENT:
BELT CONVEYOR:
Belt conveyor is one of the most common forms of material handling system used in mining industries and in
construction projects. Heavy industries like steel, fertilizer, chemical and cement etc. cannot function without
the belt conveyors. In construction projects the belt conveyors are used for handling the materials in Asphalt
plants, aggregate mixing plants etc. In coal mining and other mining industries these are used for handling of
coal or other raw material. The belt conveyors are capable of conveying large quantities of material
continuously over long distances at a fast speed. For transporting the material for short distance, conveyor
may be a portable or a fixed unit. When a belt conveyor system is used to transport materials for a
considerable distance, up to several kilo-meters in some cases,
the system consists of a number of flights. Each flight is
complete conveyor unit discharging its load onto the tail end of
the successive unit.
Belts used in the system are costly and perishable item
and hence need to be carefully maintained. The belts are
generally made of rubber covered over cotton or rayon laid up
in plies. The strength of a rubber belt depends on number of
plies. Canvas plies, woven wire mesh and steel belts are also
used depending upon the strength required for the conveyors to
convey various types of materials, their temperature, quantity to
be transported etc. Belts are specified by width, number of plies,
and weight of each layer of ply.
Belt conveyors consist of a belt running over drums or pulleys provided at the end and are supported at
intervals by a series of rollers known as idlers. These idlers are supported on the conveyor frame, and help to
support the conveyors and reduce the sag of the belt and prevent the loose material from spilling. These 3
idlers are free to move on bearings. Since 1000 to 1200 idlers per kilometer of belt length are provided, it is
important to design, select and maintain them for maximum life and to give best performance. Selection of
proper bearings with minimum friction value, standardization, strict quality control and proper finish/tolerance
of shifting is essential. The dust proof bearings packed with lubricant with efficient seals require no further
attention for years. The spacing of idlers depend upon the weight of the material handled, if the idlers are
widely spaced, the sag between them becomes excessive, which will result in wastage of power, increase in
belt wear, chances for spillage of material due to impact at each idlers.
Advantages: Following are the main advantages of belt conveyors:
(i) It is capable of handling light or heavy, fine or coarse, wet or dry material.
(ii) It can handle, thousands of tons of material per hour for several kms.
(iii) It can handle hot materials up to 160°C or so.
(iv) It is lighter in weight, and consumes less power.
(v) It operates without noise.
(vi) It gives a continuous discharge and quantity of which can be varied by varying the speed of
conveyor belt.
(vii) It can carry the material horizontally or in an inclination.
Types of Conveyor Belts:
Some most commonly used belt and their applications:
(i) Solid, general-use belts: The most common conveyor belts are general-use belts. These solid belts
typically feature materials including rubber or a fabric such as nylon, polyester, neoprene etc. Belt properties
determine the conveyor belt’s primary applications. For example, mining and milling industries commonly
use rubber to handle bulk materials including raw ore and aggregates..
These materials may feature different coatings, thicknesses, and arrangements to deliver a range of
handling properties.
(ii) Filter belts: Some belts allow particulates to pass through rather than ride along the conveyor system.
Industries may use filter belts to drain excess liquid from parts or to filter out toxins. Water treatment
companies often use these types of conveyor systems during water treatment processes. Manufacturers may
use metal or synthetic fibers to create filter-capable belts.
(iii) Woven metal belts: Woven belts feature interlinking chains of metal or wiring designed to allow
airflow as an item moves along. Businesses commonly use woven belts to facilitate drying, cooling, and
heating processes in the food, electronics, and glass-working industries, among others. Manufacturers may
offer pre-fabricated woven belt designs or may custom design a woven belt to meet a customer’s specific
application needs.
(iv) Hinged belts: Hinged belts often feature metal construction. The hinged quality of the belt gives it a
flat, solid surface capable of rotating around the pulley system via interlocking hinges. Companies use hinged
belts for small product, scrap, and recycling applications. Metal hinged belts are durable and can stand up to
rigorous use.
(v) Plastic interlocking belts: Plastic belts provide manufacturers and material handlers with a modular
alternative to metal and fabric belts. Businesses may use plastic belts in food handling and packaging
processes or in the automotive industry. Modular plastic belts work well in applications that require frequent
cleaning and belt replacement.
