The document provides information on various types of mechanical material handling devices used for grain handling. It discusses belt conveyors, bucket elevators, screw conveyors, pneumatic conveyors, roller conveyors, chute conveyors, and slat conveyors. For each conveyor type, it describes the main components and how it functions to horizontally or vertically convey granular materials like grains in an efficient manner with reduced human labor.

1. LECTURE - 15
Material handling

2. Material handling
 After harvesting, the grains are moved, transported or conveyed
from place to place. In earlier periods all these operations were
manual.
 The grains were threshed and bagged by human labour.
 Grains were transported several times through storage and
milling plants, and the milled food products were conveyed
manually to consumers.
 Thus, grains were handled too much involving increased costs
and human drudgery.
 But in modern times, some mechanical devices have replaced
human labour, other supplement it or in some case make

3. Material Handling
 Material handling is the function of moving the
right material to the right place in the right time, in
the right amount, in sequence, and in the right
condition to minimize production cost.
 The cost of MH estimates 20-25 of total
manufacturing labor cost

4. Goals of Material Handling
 The primary goal is to reduce unit costs of
production
 Maintain or improve product quality, reduce
damage of materials
 Promote safety and improve working
conditions
 Promote productivity
 material should flow in a straight line
 use gravity! It is free power
 move more material at one time
 mechanize material handling
 automate material handling

5.  The most common types of mechanical
devices for grain handling are;
 Belt conveyor
 Bucket elevator
 Screw conveyor

6. Principles
 The selection of proper conveying system is important
for ease in operation and getting desired capacity for
a particular product. Before selecting a conveying
system, the following principles should be taken into
account.
1. The conveying device has to be selected according
to the characteristics of the products being
conveyed
2. The stability of the conveyor must be ensured under
all normal working and climatic conditions.
3. The capacity of conveying and speed rating should
be maintained at specified limits.

7. 4. The dead load of the conveyor should be low in
relation to the weight of transported product.
5. In a conveying system possibility of use of gravity
should be taken into consideration.
6. The capacity of handling/conveying equipment
should match with the capacity of processing unit or
units.
7. Spillage of conveyed products should be avoided.
Pollution of the environment due to noise or dust by
the conveying system should also be avoided.

8. Parts of belt conveyor
1. Belt
2. Drive mechanism
3. Pulleys
4. Idlers
5. Loading and discharging device

9. 1.Belt
Materials :
A. Rubber
• used for bulk material
• Made up of carcass
B. Woven cloth
• Light weight material
C. Steel
• For metal industries

10. 2. Drive mechanism
 For single pulley drive up to 30-50 kW is
required.
 We can provide up to 250 kW.
 Depends on pulley drive.

11. Pulleys
• Head Pulley - turns belt back
around
to return - may be coupled to drive
• Tail Pulley - turns empty belt
around for loading - occasionally
coupled to drive
• Drive Pulley - Coupled to motor
pulls belt - usually special grip
surface

12. 5. Idlers
• Supports Belt and Material Load
• Built with
– Shaft surrounded by bearings
– Then roll of steel or rubber
• Two main types
– Carrying for material and belt
– return supports belt on return trip
• Efficiency of conveyor largely dependent on this.
• Its diameter ranges from 4 to 7 inches.

13. Idler type
1. Flat belt idler
 Used for granular materials of
angle of repose not less than 35º.
Preferred for low capacity where
inexpensive conveying is required.
2. Toughing idlers with 20º trough
Used for conveying all kinds of
bulk material
3. Toughing idlers with 35º and 45º
trough
Mainly used for transportation of
small particle light weight materials
like grains, cotton seed etc.
 used for carrying heavier,
medium size lumps like crushed
stones.

14. 6. Loading device

15. 6. Unloading device
Plough scrapper
oMore than one point
discharge
oGenerally used in flat and
horizontal conveyor
oScrappers or ploughs are
diagonally mounted usually at
30º across the direction of
travel
oMay damage the belt if
speed is higher than
60m/min.

16. Unloading device
Tripper
oUsed
to
discharg
e the
material
at a
number
of fixed

17. Design of belt conveyor
Design of belt conveyor system is based on:
Available space
Horizontal conveying length
Characteristics of material to be conveyed
Capacity requirement

18. Design parameters
1. Speed and width of belt
- Speed should not increase 3.5 m/s.
- For grain conveying: 2.5 to 2.8 m/s.
- Belt width in meter;
where is coefficient of cross sectional area of load on belt
is coefficient of load reduction of load layer cross
section on an inclined portion of conveyor

19. 2. Thickness of belt
3. Diameter of pulleys and idlers
- for rubber-fabric belt
Where is coefficient depending on strength of
ply fabric
I
is coefficient depending on type of pulley
is number of plies
- For rubber-cable belt
i

20. 4. Required horsepower
- It depends on the capacity of belt conveyor.
- The capacity of belt conveyor in m³/hr is given by:
5. Belt tension
Effective tension,
kW is power in kilowatt
S is the belt speed, m/s
T = kW / S
(area of cross-section of belt, m²) * (belt speed, m/min) * 60

21. Belt tension
 The tension developed at the drive pulley in
transmitting the required power to move the loaded
belt is known as effective tension.
 The effective tension is the sum of tension to move
the empty belt, the tension to move the load
horizontally and the tension to lift the material.
 The effective tension is related with the power
required to move the belt and belt speed in the
following manner.

22. 6. Trough angle and surcharge angle in idlers

23. Idler spacing
 The incorrect idler spacing may result in belt
undulation
 The space between the successive idlers should be
approximately equal to the width of belt. The spacing
should not exceed 1·2 metres.
 The upper idlers and the return idlers are usually
placed at an equal distance from one another.
 Additional idlers are provided at loading points to
support the product load and to maintain the trough.
This avoids spillage of materials.

24. Advantages
 High load carrying capacity (up to 30000t/h)
 Large length of conveying path (up to 3-4 km in
single conveyor)
 Simple design
 Easy maintenance
 High reliability for operation
 More flexible

25. Disadvantages
Vertical transportation can not be done.
A separate arrangement for material
handling is required.
Hot materials can not be transported .
High initial cost for short distances.

26. Belt conveyor

27. Belt conveyor

28. Bucket elevator
 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 bucket elevator is a very efficient
device for the vertical conveyance of
bulk grains.
 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.

29.  In a bucket elevator, the conveyor belt with buckets
runs over pulleys at the upper and lower ends.
 The top pulley is driven pulley while the lower pulley is
return and tension pulley.
 Buckets are usually made of steel or plastic and are
bolted onto the belt.

30.  The curved hood is designed for proper
centrifugal discharge of the grains.
 The boot can be loaded from the front or back or
both

31.  The product flow is discharged either by means of
gravity or centrifugal force.

32.  The bucket elevator's capacity mainly depends on bucket
size, conveying speed, bucket design and spacing, the
way of loading and unloading, the bucket and the
characteristic of bulk material.
 Belt speed is the first critical factor to consider.
 Bucket elevators with a belt carrier can be used at fairly
high speeds of 2.5 to 4 m/ s.
 The speed of the belt depends on the head pulley speed.
 If the belt speed is too low, the discharge of the grains
becomes more difficult, with too high speed the buckets
are not fed well.

33.  The gravitational discharge occurs with non-adhesive bulk
material elevated at low speed and by means of buckets
mounted closely together.
 With purely centrifugal discharge, complete contents of a
bucket are projected towards the discharge chute. Such
type of discharge is obtainable with high belt speeds and
smaller diameter drive pulleys.
 In elevating of grains the discharge from bucket elevators
is a combination of centrifugal and gravitational
discharge.
 Part of the bucket contents is projected by the centrifugal
force, the rest flows out by gravity.

34.  The main parts of a bucket elevator are,
(1) elevator head section
(2) elevator boot section,
(3) elevator legs,
(4) belts for bucket elevator and
(5) buckets.

35. Head Section
 The discharge side of the head should
be shaped so that material thrown
from the buckets may not deflect into
the down leg.
 When the product is not thrown well
clear of the buckets into the discharge
chute, it will fall in the down leg. This
is called as ''back logging".
 The back logged material has to be
re-elevated, thus it reduces the
capacity of the elevator.
 To avoid back logging, an adjustable

36.  In the boot section, the
loading chute should be
located at such point that,
the pick-up of the product
by the buckets takes place
above the centre line of the
return pulley.
 Grain entry may be on
either side of the boot
 Additional power is
required to overcome the
"‘dredging effect" while
pulling the buckets through
Boot section

37. Elevator belts
 The total stretch of the belt under maximum load
should not exceed 1-2% of the belt length.
 Most conveyor belts consist of synthetic fibres like
polyesters and polyamide and are built up with
synthetic rubber or PVC.
 To increase tensile strength of belt, several layers of
fibres are put together to build a carcass.
 Such carcass is able to withstand very high tensile
forces with a minimum of stretch.

38. Buckets
 Digging in of buckets in the elevator boot and the
centrifugal discharge at the elevator head influence the
shape of buckets.
 For centrifugal discharge the resultant of product weight
and the centrifugal force should preferably be directed
towards the lip of the bucket.
 The buckets should have a wide open mouth for digging
and discharging the product .
 But at the same time the lip of bucket must not be too low
and the bottom angle should not be too big. This will
cause spillage of product.

39.  The common shape of bucket is shown in Figure.
 The top angle is generally taken as 80° while the
bottom angle is between 20-30°.
 Such buckets have fairly large capacity, high side
walls which prevent spilling.

40. Bucket conveyor

41. Bucket conveyor

42. Screw conveyor
 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 pitch of a standard screw is equal to its
diameter.

43.  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 conveyor is generally used to move grains
horizontally.
 However, it can also be used at any angle upto 90°
from the horizontal, but the capacity correspondingly
reduced as per the inclination of conveyance.

44.  The screw basically consists of a shaft and the screw
blade or flight.
 The flight is a continuous one piece helix, shaped
from a flat strip of steel welded onto the shaft.
 The screw shaft is usually a jointless tube with thick
sides and a high tensile strength to reduce the weight.
 The thickness of the steel strip helix decreases from
the inner edge to the outer edge.

45. Troughs of screw conveyor
 Most common is U shaped trough.
 In an enlarged or flared trough the side
walls become wider at the top.
 This type of trough is usually used for
conveying non-easy flowing materials
which may have lumps.
 The tubular trough is completely closed
with circular cross-section and mostly used
for conveying materials at inclination or for
vertical lift.

46.  If the screw conveyor is used to convey different
materials, mixing of products is possible.
 Also when the kernels are pressed between the screw
edge and trough walls, they can be damaged.
 The product can be discharged, either at the end of
the screw or the intermediate discharge can be
achieved through an opening in the bottom of the
trough
 The capacity of screw conveyor is influenced by the
screw diameter, inclination of the screw blade, speed
of the blade, shaft diameter and cross-section of
loading.

47. Screw conveyor

48. Screw conveyor

49. Pneumatic conveyor
 The pneumatic conveyor moves granular materials in a
closed duct by a high velocity air stream.
 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.

50.  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.

51.  In blowing or positive pressure systems, the product
is conveyed by using air pressures greater than the
atmospheric pressure.
 This system consists of a fan or blower, an air-lock
feeder for introducing the product into the system,
ducts and suitable air and product separating
device.
 The product is fed into the pneumatic conveying
system from the bottom of a hopper.

52.  For separation of product particles from air, air-
product separators are used.
 Cyclones are mostly used to collect the particles.
 In some cyclone, a fabric filter is attached to
remove residual dust and fine product particles
from the air stream.
 The conveying air is first passed through the
cyclone and then it goes to the fabric filter for
secondary separation of finer particles.

54. Roller conveyor

55. Chute conveyor

56. Chute conveyor

57. Slat conveyor