Lecture 3 Material Handling Equipment (Hoisting Equipment)

MATERIALS HANDLING EQUIPMENT
LECTURE Three
Hoisting Equipment
Outlines
 Theory of hoisting equipment
 Flexible hoisting appliance
 Pulleys, sprockets, Drums and
 Load handling attachments
 Arresting gear and brakes
 Hoisting and travelling gear
By: Amanuel DIriba
9/7/2019 1By: Amanuel Diriba

Theory of hoisting equipment
• The hoisting is a device used for lifting or lowering a load by
means of drum or lift – wheel around which rope or chain
wraps.
• It may be done with a wide range of equipment from the small
hand operated simple screw or hydraulic – jack to modern high
powered cranes and elevators.
• It may be manually operated, electrically or pneumatically driven
and may use chain, fiber or wire rope as its lifting medium.
• Hoisting equipment can be a stationary, portable or travelling.
• There are different types of hoisting equipment whose accurate
classification is difficult.

Cont..
• There are three groups of hoisting equipment having the
following main distinctive features.
i. Hoisting machines
- a group of periodic action devices designed as self-lifting
gears for hoisting and moving loads.

Cont..
ii. Cranes
- a combination of separate hoisting mechanism with a frame
for lifting and/or moving loads

Cont..
iii. Elevators
- a group of periodic action machine intended for raising loads
with guide – ways.

Cont..
• The main technical parameters of hoisting machines
are:
– lifting capacity : the maximum safe load a machine is
designed to handle
– Dead weight of the machine : the total weight of the
machine without load
– Speed of various movements: this may be the hoisting
speed, the bridge travel speed and the trolley traveling speed
– lifting height : the height to which the load is intended to be
raised;

9/7/2019 7
Flexible hoisting appliances
- Hemp – rope
- Welded loaded chains
- Roller chain
- Steel wire ropes
Fastening of
chains and ropes Load handling attachments
- Hook’s
- Electric lifting magnets
- grabs
By: Amanuel Diriba

• The needs of hoisting machinery in flexible members are met
widely by hemp rope, welded and roller chains, and steel wire
ropes.
1. Hemp – Ropes
 Because of their poor mechanical properties (rapid abrasion,
inadequate strength, rapid damage from sharp materials and
atmospheric effects, etc), they can be recommended only for hand-
operated hoisting machinery (rope pulleys).
 The diameters of the sheaves over which the rope runs should be at
least 10d,where d is the nominal rope diameter.

Cont..
• By the mode of manufacture and number of strands, hemp
ropes are classified as
i. plain-laid
ii. cable-laid
• The latter being from twisted from three ordinary ropes twisted
from three ordinary ropes.

Cont..
2. Welded loaded chains
 They are widely used in hoisting installations as flexible
members.
 Depending on the ratio between the pitch and the diameter of
the chain bar, welded chains are classified into
i. Short – link chains with t ≤ 3d
ii. Long – link chains with t ˃ 3d

Cont..
 Manufacturing accuracy divides welded chains into:
i. Calibrated – with permissible deviation from the nominal
size within t +/- 0.03d and B+/- 0.05d
ii. Uncalibrated – with permissible deviation from the
nominal size within t +/- 0.1d and B +/- 0.1d
 Links for welded chain are formed most commonly hammer
(forge) and electric resistance welding.
 Because of the short comings, welded chains are used only in
some hand – operated mechanism (where Dmin > 20d) and in
few power drive mechanism (where Dmin > 30d)
 They are employed for low capacity hoisting machines (hoists,
winches, hand – operated cranes, etc)

Cont..
 Advantage of welded chain
– Good flexibility in all direction
– Possibility to use small diameter pulleys and drums
– Simple design and manufacture
 Disadvantages of welded chains
– Heavy weight
– Susceptibility to jerks and overload
– Sudden failure
– Concentrated wear at the link joints and
– Low safe speed f movement.

Cont..
3. Roller chains
 Roller chains are composed of plates hinge – jointed by pins and
rollers.
 For light loads, two plates are used. For very heavy loads the
number of plates can be increased upto 12.
 The maximum allowable speed of roller chain is V = 0.25m/s
 Roller chains are used for hand operated hoists, power – driven
winches and hoisting mechanisms of high load lifting capacity,
operating at low speed, if the weight is lifted between guide –
ways.

Advantage of roller chains
Roller chains are superior to welded chains in a number of ways such
as:
- The reliability of operation is higher since the plates are solid.
- Roller chain have good flexibility
- The friction in the joints is considerably less than that in the
joints of welded chains.
But roller chains should not be allowed:
– To carry weight acting at an angle to the plate(to prevent
excessive wear and pin breakage)
– To be used in dusty premises (unless the chain is sealed by
cover which would cause excessive wear)

Cont..
4. Steel wire Ropes
 The steel wire ropes are extensively used in hoisting machinery as
flexible lifting appliance.
 The wire is drawn cold and given heat treatment as well as
chemical treatment between the drawing stages in order to obtain
required strength, structure, appearance and surface finish.
 They are most popular types used in hoisting machinery.
 Normally steel wire ropes consist of 6 or 8 strands and a core.

Cont..
 Comparing to chains they have the following advantages:-
– Lighter weight
– Less susceptibility to damage from jerks
– Silent operation even at high speeds
– Greater reliability in operation

Cont..
 Non –spinning wire ropes
 Each individual wire and strand being laid is performed to
correspond to its disposition in the rope.
 As a result of unloaded wires are not subjected to internal stresses
and tend to spin.
 Advantages of non – spinning wire ropes over the general
purpose ropes:-
- Uniform load distribution over the individual wires, which
reduces internal stresses to a minimum
- Better flexibility
- Less wear of the wire ropes running over drum or sheaves
- Greater operation safety.
 The disadvantage of non- spinning wire ropes is that it is more
expensive.

Cont..
4. Fastening of chains and Ropes
• Various methods are used to secure the ends of chains and
ropes.

• A pulley is a wheel on an axle or shaft that is designed to
support movement and change of direction of a rigid cable or belt,
or transfer of power between the shaft and cable along its
circumference.
• Pulleys are used in a variety of ways to lift loads, apply force, and
to transmit power.
Pulleys

Classification of pulleys
• Pulleys are either fixed or movable in design.
1. Fixed Pulleys
• Fixed pulleys are used to change the direction of the flexible
appliance.
• Disregarding the resistance of the pulley, the pulling force Zo
equals Q (weight to be pulled) I.E Zo = Q, without considering
pulley resisting.

Cont..
2. Movable pulley
• Movable pulleys are used to gain mechanical advantage or speed/force.
• Movable pulleys are classified into two
a. Pulleys for gain in force:
• Used to increase amount of force applied and it doesn’t change direction
of the force.
• The distance that effort moves is double that of the load, and the speed at
which the load is raised is half of that of the effort.
S = 2h
C = 2v
Figure : Single movable pulley for a gain in force
Where C= Speed of force
v = speed of load
s = distance the force moves
h = distance the load moves

Cont..
b) Pulleys for gain in speed
• Used to increase amount of load speed and it doesn’t change
direction.
• The effort is applied at the axle of the pulley and moves at half the
speed of the load.
• The distance moved by the load is twice that of the effort.
s =
ℎ
2
c =
𝑣
2
Z=Q = So
Figure : Single movable pulley for a Gain in speed9/7/2019 23
Where C= Speed of force
v = speed of load
s = distance the force moves
h = distance the load moves
By: Amanuel Diriba

Cont..
3. Block and Tackle pulley
• A block and tackle is a pulley system made up of fixed and
movable pulleys.

Cont..
Pulley Systems
• Several fixed and movable pulleys are combined in order to form a
pulley system for a gain in force or a gain in speed.
Figure: pulley system for a gain in force Figure: pulley system for a gain in Speed

9/7/2019 27
- Hemp – rope
- Roller chain
- Steel wire ropes
Sheaves
• Used for ropes and welded
chains
Sprockets
• Used for welded chains and
Roller chain
Drums
• used for Hemp rope and steel
wire ropes
By: Amanuel Diriba

Sheaves
• A sheaves is a pulley with a grooved wheel for holding belt, wire
rope or rope.
• A sheaves are grooved rims used for guiding ropes or chains.
• The sheaves are usually mounted freely on their axles.

Cont..
• Rope life depends on the material of the groove.
• Practical experience goes to show that ropes operating over steel
sheaves wear down more rapidly than those used in conjunction
with cast-iron sheaves apparently due to higher contact stresses
and poorer conditions of slipping of the rope over the steel
sheave.
• To increase rope life, sheave grooves are lined with aluminum,
rubber, and plastics.
 Sheaves for welded chains:
– These sheaves are usually made of cast iron.
– They are mainly used for hand operated hoists and rarely they
are used for power driven devices.

Sprockets
• A sprocket or sprocket-wheel is a profiled wheel with teeth,
that mesh with a chain, track or other perforated or
indented material.
• As a rule , sprockets are manufactured with a small number of
teeth and are small in size ensuring compactness and low cost of
the driving mechanism .

Cont..
Sprockets for welded chains:
• Sprockets are used as driving chain wheels of hand operated
hoists and winches.
Sprockets for rollers chains:
• Sprockets are manufactured from cast iron and forged steel
casting.
• They are mainly used for hand- operated hoists and winches.

Drums
• Drums is a grooved wheel on which the rope is wound in more
than one layer.
• During operation the drum is subject to the combined action of
torsion bending and compression.
• The machined grooves increase the drum bearing surface,
prevent friction between the adjacent rope turns and
consequently reduce the contact stresses and rope wear.

Cont..

Friction Drums of ropes
• Friction drums are rope – driving drums in which motion is
transmitted by friction between the rope and drum.
• They have the advantage of being able to raise loads for great
height.
• Are used for winches and railway cars.
• Friction drums are capable of handling long ropes by means of a
small drum.

Cont..
• There are three types of friction drums
a) Simple friction drums
– They are provided with helical grooves for the rope, which
coil around in one or several turn.
b) Double drum friction drive
– In this case the rope is wound several times around two
parallel drums rotating in the same direction and driven by
a single motors.
c) Capstan
– Capstans are usually arranged vertically, driven by
electromotor through a worm gear drive and used to move
railways cars.

9/7/2019 37
- Hemp – rope
- Roller chain
- Steel wire ropes
Fastening of
- Hook’s
- grabs
• Sheaves
• Sprockets
• Drums
By: Amanuel Diriba

LOAD HANDLING ATTACHMENTS
• The load is usually handled by many various methods.

Cont..
• They are three most commonly used load handling
attachment
i. Hook’s
ii. Electric lifting magnets
iii. Grabs
i. Hook’s
• The load is usually handled by means of chain or rope
slings attached to hooks.
• One – piece forged hooks are used for lifting loads upto
100 tons while triangular and laminated hooks can be
employed to carry over 100 tons.
• Hook are forged from low carbon steel.

Cont..
• In the process of production hooks are carefully annealed after
forging and machining.
• Generally hooks have trapezoidal section made wider on the
inside for better material utilization.

Cont..
ii. Electric Lifting Magnets.
– Lifting magnets are used to handle magnetic materials of
diverse form (ingots, beams, rails, steel sheets and plates,
scrap, metal chips etc.).
– These drastically reduces the time required for manual
suspension of loads.

Cont..
iii. Grabs
• These are the holding attachments which are special type of
buckets which mechanically grab and automatically dump the
materials.
• The grabs are designed considering the type of material to be
bold.

9/7/2019 By: Amanuel Diriba 44

9/7/2019 45
- Hemp – rope
- Roller chain
- Steel wire ropes
Fastening of
- Hook’s
- grabs
• Sheaves
• Sprockets
• Drums
By: Amanuel Diriba

Arresting Gear
• Arresting gear is used to hold the being lifted without
interfering in the hoisting process but preventing the load from
coming down due to gravity.
• They are three most common arresting gear types:-
i. Ratchet gearing
ii. Friction arresters
iii. Roller ratchets
Arresting gear and brakes

Cont..
i. Ratchet gearing
• Ratchet gearing consists of ratchet gear and pawl.
• The teeth in the ratchet(internal teeth or external teeth) and so
arranged that the ratchet gear runs free when the load is being
raised.
• The pawl engaging the ratchet assist its motion when the load is
being lowered.

Cont..
ii. Friction Arresters
• Friction arresters operate noiselessly compared to the operation of
toothed arresting gear.
• However, the pressure on the pawl pivot and shaft is considerably
high. They have a limited application.
• To avoid unidirectional action, the arrester is always provided
with two pawls arranged at diametrically opposite points.

Cont..
iii. Roller Ratchets
• This mechanism arrest the load within a minimum distance.
• The whole system relies on friction for its successful operation.
• A roller wedged between the follower and the driver is
subjected to the action of normal forces N1 and N2 and tangential
friction forces µ1N1 andµ2N2.
• With the roller in equilibrium, the resultant force R1 = R2. for
equilibrium N1= N2

Brakes
• A brake is a mechanical device that inhibits motion by absorbing
energy from a moving system.
• It is used for slowing or stopping of moving vehicle, wheel axle
or to prevent it’s motion, most often accomplished by means
of friction.
• In hoisting machinery, brakes are employed for controlling the
speed of load lowering and holding the suspended load at rest.

Cont..
• Depending on the purpose, brakes can be classified as
i. Stopping brakes – These bring the drive at rest at the
end of motion.
ii. Regulating brakes – These are serving to maintain the
speed of motion within prescribed limits.
• From operational aspect they can be classified as
i. Automatic brakes – These brakes are applied
automatically irrespectively of the operator’s will at the-
instant the motor of the mechanism is de-energized.
ii. Controlled brakes – These are set and released by the
operator irrespectively of whether or not the relevant drive
is in operation.

Hoisting and Travelling Gear
– In any lifting drive the hoisting mechanism is considered to be
the vital element.
– Hoisting mechanisms are subdivided into three groups
a) Hand power drives
b) Individual power drives
c) A common drive for several mechanisms

Cont..
a) Hand power drives
• A hand drive" is employed in mechanisms with a low lifting
capacity, or where the load has to be moved a short distance, or
for occasional lifts;
• Application area of Hand drives are:- winches with small lifting
height, in jacks, and sometimes in travelling overhead and gentry
cranes and in light-duty rotary cranes.

Cont..
b) Individual electric drives
• An electric motor driven hoist has one or two rope
drums for coiling and uncoiling the hoisting wire rope.
• The hoisting motor drives the drum through a
planetary gearing system.
• Electrically driven cranes designed to handle up to 2000
tons are available. The drives can be hydraulic drive ,
pneumatic drive , diesel electric drives etc.

Cont..
Electric motor is generally preferred in most hoisting
installations owing to the following advantages.
1) Immediate readiness for operation.
2) Possibility of driving every motion by a separate motor.
3) Higher economic efficiency as compared with other
drives.
4) The ease of speed control over a wide range.
5) Convenient reversing of motions.
6) Safe operation, simplicity of construction, and high
reliability of safety devices.
7) Ability to cope with short-time overloads of significant
magnitude.

Lecture 3 Material Handling Equipment (Hoisting Equipment)

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