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Contents
CHAPTER ONE..............................................................................................................................1
INTRODUCTION...........................................................................................................................1
1 Background..............................................................................................................................1
1.1 Problem statement.............................................................................................................2
1.2 Project objectives..............................................................................................................2
1.2.1 Main objective...........................................................................................................2
1.2.2 Specific objectives.....................................................................................................3
1.3 Significance of the project................................................................................................3
CHAPTER TWO.............................................................................................................................4
LITERATURE REVIEW................................................................................................................4
2 Introduction..............................................................................................................................4
2.1 Shelling process of maize.................................................................................................4
2.2 The existing maize and shelling techniques......................................................................5
2.2.1 Hand shelling.............................................................................................................5
2.2.2 Squeezer shelling.......................................................................................................6
2.2.3 Shelling by manual operated machines.....................................................................6
2.2.4 Power operated maize shelling..................................................................................6
2.3 Types of shelling mechanisms commonly used................................................................7
2.4 New justification...............................................................................................................8
CHAPTER THREE.........................................................................................................................9
METHODOLOGY..........................................................................................................................9
3 Introduction..............................................................................................................................9
3.1 Reviewing the literature relating to maize shelling machines..........................................9
3.2 Design a concave and cylinder top cover..........................................................................9
3.2.1 To make design calculation.......................................................................................9
3.2.2 Preparation of details drawing of the machine..........................................................9
3.2.3 Selection of material................................................................................................10
3.3 Manufacture and assemble the concave with the cylinder top cover..............................10
3.4 To test the prototype for shelling maize..........................................................................10
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3.5 Cost estimates.................................................................................................................12

REFFERENCES............................................................................................................................13
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CHAPTER ONE
INTRODUCTION
1.0 Background

Maize is an important cereals crop which belongs to grass family, it produces small edible seeds
which was said to have originated from Mexico over years. It is the world’s best adapted crop, a
versatile grain crop and commonly known as corn in America. The nature endowment of high
rainfall, high light intensities, and favorable temperature in the cultivation of maize make it to be
one of the world’s most versatile seed crops.

Maize is the one of the most important food crops in Tanzania; it comprises 45% of the
cultivated area. Though Tanzania is the largest producer of maize in East Africa, the country still
faces lots of challenges of achieving full business potential. Maize mostly produced in Mbeya,
Iringa, Rukwa, Katavi, Manyara, Arusha, Kilimanjaro and Ruvuma.

Tanzania has ranked among the top 25 maize producing countries in the world in the last two
decades. The production of maize accounts for more than 70 percent of the cereal produced in
the country. A sector with high potential for economic growth and trade expansion, but limited
by barriers such as prohibitive government policies, high costs, failure to meet quality
requirements and a lack of financial capacity. 

The crop is grown mainly by smallholder farmers targeting both local and foreign markets but
also now days there are farmers cultivate maize in large scale for commercial purpose only.
Farmers shell the bulk of the maize using the traditional method of beating on the bare ground or
loosely packed in sacks. The method has low productivity, causes high physical damage and
contamination with foreign matter resulting in low market value and reduced shelf life of the
crop. Other methods such as hand priming, shelling using manual and automatic maize shellers
are not productive for commercial farming.
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Concave plays an important role in working efficiency of the maize shelling process as it give
the rubbing mechanism of the maize cobs, when cob rotated with the cylinder rubs on concave
casing wall, cause the grains to left and fall from concave.

Here the objective of the project is to manufacture the a shelling machine that will pealing maize
dried leaves after harvesting from farmer and shelling them from their cobs so as to obtain
quality maize crop without being damaged(breaking) and lost its value. The machine will
simplify shelling process by increasing the production rate, save time and energy and reduce the
number of labours required for shelling and pealing processes.
1.1 Problem statement

Maize shelling process is boring and time consuming process that affect much local and rural
farmers due to poor methods used to detach seeds from the cobs and even the motorized
machines are expensive, most of them using electrical power to operate, and that become
difficult to use for rural areas where there is no electrical power supply

Also the existing maize shelling machines have trend to damage (break) maize grains (seed) as
the maize cobs rubs between rotating drum (cylinder) and concave. This is due to unclear
clearance gap between concave and cylinder, high speed of the cylinder and the manufactured
concave that consisting of the sieve and bars that fails to withstands forces acting on it as maize
cob rotated by the cylinder, the sieve become weak and cause sieve holes increases in diameter
resulting to unshelled maize cob to penetrate instead of shelled grains. this affect the
performance of the machines as many cobs coming out without being shelled, lower the quality
of maize grains when stack on the sieve holes, lower market value and reduced shelf life of the
crop.

The project aim to design and manufacture machine that will be operated with the help of an
diesel engine, a highly efficiency machine with a concave casing that will be able to maintain the
required clearance gap between cylinder and concave, ability to overcomes forces acting on the
wall of the concave and reduces seeds breaking and ensure maize grains detaches compete from
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the cobs, to allow maize seeds to penetrate easily through the concave. The machine will be
affordable for rural farmers even in interior regions where there is electrical power supply
because the source of power will be and engine that requires diesel fuel that is at least available
on those areas.
1.2 Project objectives

The objectives of this project consists two classifications which are:

i. Main objectives

ii. Specific objective

1.2.1 Main objective

Main objective of this project is to design and manufacture concave (housing) for maize shelling
machine.
1.2.2 Specific objectives

i. To reviewing the literatures related to maize shelling machines

ii. To design the concave(drum housing) for maize shelling machine
iii. To manufacture and assemble the concave or drum housing.
iv. To test the prototype
1.3 Significance of the project

i. Increase performance of the machine

ii. Provide quality products
iii. Reduce labour requirements
iv. Save time and energy
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CHAPTER TWO
LITERATURE REVIEW
2 Introduction

Maize is an important cereals crop which belongs to a grass family. A producing small edible
seed which was said to have originated from Mexico over years, it is the world’s best adapted
crop, It is a versatile grain crop and commonly known as corn in America. The natural
endowment of high rainfall, high light intensities, and favorable temperature in the cultivation of
maize make it to be one of the world’s most versatile seed crops [ CITATION Kar88 \l 1033 ]

In industrialized countries, maize is largely used as livestock feeds and as raw material for
industrial products, while in low income countries; it is mainly used for human consumption. In
Sub-Saharan Africa, maize is a staple food for an estimated 50% of the population. Maize is an
important source of carbohydrate, protein, iron, vitamin B and minerals. In Africa, maize is
consumed as a starchy base in wide variety of porridges and pastes. Green maize (fresh on the
cob) is eaten parched, baked, roasted or boiled which play an important role in filling the huge
gap after dry season. [ CITATION Whi96 \l 1033 ]

Maize is a vital raw material in industry. Corn starch, corn oil, corn syrup and sugar are the chief
industrial products obtained from maize. Corn starch is used for starching clothes. The starch is
also employed in the manufacture of asbestos, ceramics, dykes, plastics, oil cloth and linoleum.
Corn syrup is used in shoe polish, glassine paper and rayon in tobacco industries. Corn sugar
finds their use in the manufacture of chemicals, leather preparation, dykes and explosives. The
maize when cooked under acids produces furfural, a compound used in the production of
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adipontrile (nylon) in the restinging of diesel and lubricating oils. The stalks and leaves are
sometimes used for making paper, paper board and wall board. Pulverised maize cobs are used
extensively for removing carbon from airplane motors. [ CITATION Ser10 \l 1033 ]
2.1 Shelling process of maize

Maize shelling is an important step towards the processing of maize to its various finished
products like flour. Threshing or shelling operations of maize follow the harvest and whatever
pre-drying of the crop is undertaken. This operation can be carried out in the field or at the
storage environment. The different methods of maize shelling can be categorized based on
various mechanization technology used. These includes: hand-tool-technology, animal
technology, manual operated, motorized and engine power technology. (Food and agriculture
organization Corporate Document Repository on Agricultural engineering in development - Post-
harvest operations and management of food grains)

In the olden days and in rural communities, primitive method of shelling were involved which
include, beating with stick, crushing with mortar and pestle, hand shelling and therefore consume
much human energy and time. [ CITATION 1OG14 \l 1033 ]

The existing maize shellers are normally large, heavy and require high power input to operate,
they also produces low product quality in terms of percentage seed breakage and purity.
Damaged kernels are susceptible to insect and moulds thereby increasing the incidence of
aflatoxin contamination. [ CITATION Rud18 \l 1033 ]
2.2 The existing maize and shelling techniques
2.2.1 Hand shelling

The easiest traditional system for shelling maize is to press the thumbs on the grains in order to
detach them from the ears (figure 2.1). Another simple and common shelling method is to rub
two ears of maize against each other. However, this method takes of time and man power.
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These methods however require a lot of labour. It is calculated that a worker can hand-shell only
a few kilograms an hour. Shelling of maize,can be more efficiently accomplished by striking a
bag full of harvested maize with a stick. Maize and sunflowers can also be shelled by rubbing the
ears or heads on a rough surface. Small tools, often made by local artisans, are sometimes used to
hand-shell maize. With these tools, a worker can shell 8 to 15 kg of maize an hour. [ CITATION
WAN14 \l 1033 ]

Figure 2.1: Hand shelling [ CITATION Kus18 \l 1033 ]

2.2.2 Squeezer shelling

This was the shelling device found for shelling sweet corn. It operates by varying diameter
aluminum circle is forced through the corn, shelling the kernels off.
2.2.3 Shelling by manual operated machines

This involves use of simple machines powered by human thrust (figure 2.2). A machine consist f
a handle that driven manual by hand. They are relatively higher in performance but not well
compatible with large scale agriculture.
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Figure 2.2: manual maize shelling [ CITATION VIN16 \l 1033 ]

2.2.4 Power operated maize shelling

The Sheller removes the kernel from the cobs in cylinder with rows of internal teeth; the cobs
are inserted into cylinder which is rotating with a motor or engine. There is a cast iron rotating
disk with protrusions on it and the cobs are pushed against the disk and the kernels are knocked
off. Figure 3 shows a powered maize shelling machine, maize cobs placed on hoper to the
rotating drum trough gravity where maize was shelled with a totating drum receiving power from
motor.
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Figure 2.3: powered maize shelling machine [ CITATION Swa07 \l 1033 ]

2.3 Types of shelling mechanisms commonly used

The two types of shelling mechanisms commonly used for field shelling of corn are the axial
flow cage sheller and the cylinder-concave sheller.

The axial flow cage sheller consists of a cylinder with lugs, helical flutes, or paddles which
turns inside a cage. The cage has a perforated surface with holes large enough to let kernels fall
through but retain the cobs. The ears are fed into an opening at one end of the cage. The helical
flutes feed the ears through the cage and at the same time shell them by a rolling and crushing
action against the cage surface and each other. An adjustable cob gate serves to retain the ears in
the cage long enough to be completely shelled.
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The cages are usually from 27.9 to 38.1 cm (11 to 15 inches) in diameter and the cylinders have
rotational speeds of 650 to 790 rpm. The capacity of these shellers is in the order of 4 to 5 metric
tons per hour (150 to 200 bushels per hour). This shelling unit is generally used as a shelling
attachment mounted on a two-row corn picker in place of the husking bed, although self-
propelled corn harvesters using this type of sheller are available.

Cylinder concave sheller commonly used in combines consists of a cylinder and a concave.
The corn is shelled by the impact of bars on the periphery of the cylinder as the corn is fed
between the cylinder and the concave bars. The most common type of cylinder bar used is the
rasp-bar. These bars were shown to cause less damage 10 than an angle-bar type cylinder. These
cylinders are commonly 55.9 cm (22 inches) in diameter and range from 61 to 152 cm (24 to 60
inches) in length, depending on the size of the combine. For corn shelling, they turn at speeds of
400 to 700 rpm.

The concave assembly nearly conforms to the periphery of the cylinder. It forces the corn to be
in contact with the cylinder through about 90 degrees of cylinder rotation. The concave bars are
channel, rectangular, or half round in shape and are oriented parallel to the cylinder axis. The
severity of the shelling action is controlled by the cylinder speed and the cylinder to concave
clearance. Clearance at the front of the concave is approximately 3cm. This allows ears to easily
enter the threshing crescent between the cylinder and concave assembly. The cylinder-concave
clearance tapers to the rear and is about 1.5 cm at the rear of the concave. The severity of the
shelling action determines the amount of unshelled corn remaining on the cob and the level of
kernel damage. Cylinder adjustments are a compromise between high speeds for kernel removal
and low speeds for reduced kernel damage. Reducing the concave clearance also increases the
thoroughness of shelling and the level of kernel damage.[ CITATION Ham78 \l 1033 ]

2.4 New justification

From the above literature review it has been seen that more of existing machine perform single
mechanisms for maize shelling process with concave only but also the concave affect the
performance shelling process and reduce the quality (value) of maize grains shelled.
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Therefore there is a need to develop a maize Sheller with higher efficiency, better product quality
and powered with small engine to reduce human drudgery associated. New design and
manufacture will improve the weakness that seen in existing machine and also will perform two
mechanisms, pealing and shelling of maize at the same time within a single machine. Also the
machine will operate safe and with higher efficiency during pealing and shelling process.

CHAPTER THREE
METHODOLOGY
3 Introduction

This chapter is explaining in detail how this project will be achieved, from literature review,
designing, manufacturing and assembling of the machine in order to fulfill the specific objectives
and achieve main objective.
3.1 Reviewing the literature relating to maize shelling machines
In this area, Literature Review gives an overview of the related topics about maize shelling
machine. It gives the information on the progress of the various types of the existing maize
shelling machines, Mechanism and method used to shell (detach) maize grains(seeds) from the
cobs, material used to manufacture maize shelling machine. This information is mainly obtained
through browsing various internet websites, reading related engineering books, reading previous
projects which done at National institute of transport.
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3.2 Design a concave (drum housing)

3.2.1 To make design calculation

This will be achieved by studying the existing machine to compare the parameters. The
calculation will help to enable the materials selections dimensions such as length and width,
diameter size of the concave and cylinder top cover and the clearance between cylinder and
concave. The concave will consists of two halves circle with the same diameter covers the area
with the dimensions bellow
Length (L) of the concave (housing) = 618 mm
Width (W) of the concave is equal to `diameter (D) of the concave = 350mm
Thickness (T) of the concave metal sheet = 4.5mm
The bottom of the concave will be provided with the sieve of diameter (d) size = 20mm for easy
penetrations of the maize seeds.
The clearance distance between cylinder and concave will be used = 50mm
3.2.2 Preparation of details drawing of the machine

Designing software will be used to prepare the drawings of the proposed parts of the machines in
different views. And my design drawing will be represented by engineering AutoCAD program.
The figure 3.1below shows the proposed concave or drum housing for maize shelling machine
that will works together with the shelling drum (cylinder) and figure 3.2 shows the complete
proposed machine for pealing and shelling maize.

3.2.3 Selection of material

Systematic selection of the best material for a given application begins with properties and costs
of candidate materials. When selecting a material for a given application the material properties
must satisfy the function and the operating conditions of the component or the machine being
designed.
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The following factors should be considered during the material selection.

i. Mechanical Properties involves stiffness, strength, ductility, hardness and toughness.

ii. Physical Properties involves density, electrical conductivity and thermal conductivity.

iii. Chemical Properties involves corrosion resistance in various environments.

iv. Manufacturing Properties involves formability, machinability and eases of joining.

3.3 Manufacture and assemble the concave with the cylinder top cover

To manufacture and assemble the prototype, this involves building of metal structures by cutting,
rolling bending, drilling, joining (welding) and assembling process. The following are
instruments that will be used for accomplishing the task; welding, rolling, drilling and grinding
machines.

Welding machine will be used to join the metal sheet and flats bars, rolling machine will be used
to roll or bend metal sheet plate and flat bars to obtain the required diameter of concave, and
drilling machine will used to drill holes for maize grains penetration after being shelling.

Finally the concave casing parts will be joining (assembling) to the machine frame and fit the
required clearance between concave casing and the drum (cylinder) for ensure the correct
performance of the machine.
3.4 To test the prototype for shelling maize

The testing will be done to check operation and to observe if the concave casing perform the
desired function clear. This will enable to determine the forces acting on the concave, energy
losses due to friction and vibrations, work done, efficiency and the rate of maize grains to
penetrate the concave holes.
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Table 3.1: Schedule of activities

ACTIVITIES WEEKS

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Literature review

Data collection

Information
analysis

Specification
writings

Machine design

Prototype

manufacturing
and testing
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Documentation,
report
completion and
submission.

3.5 Cost estimates

For cost evaluation, the following table presents price list for expenses of material and all
expenditures for this project.

Table 3.2: Cost estimates

S/NO MATERIALS MATERIAL QUANTITY COST IN TZS

USED/DESCRIPTION

Metal sheet Mild steel (4ft × 4ft×3mm)

1 1 70000

2
Electrode For mild steel 2Kg 15000

3
Rebar’s Mild steel (8mm× 6m) 1 10000

4 Painting color Green and red oxide 3lts×3lts 30000

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6 Stationary Printing and binding - 30000

7 - -
Transport cost 20000

TOTAL 175000
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REFFERENCES
Ogunlade, C. A. (August 2014). Design, fabrication and performance evaluation of a power
(motorised) maize shelling machine in Nigeria, Lautech, Ogbomoso: African Journal of
Agricultural Research.

Al-Jalil, H. F. (1978). Design and performance of low damage corn India,Lowa: Ahmad
Kalbasi-Ashtari Iowa State University

Pattanayak, K. J. (2018). Women’s Drudgery and Maize Sheller Intervention, India : Indian
Journal of Hill Farming

Serna-Saldivar, S. O. (2010). Cereal Grains: Properties, Processing, and Nutritional Attributes

in Kenya, Nairobi: Taylor and Francis Group.

Sushilendra, R. C. (4 February 2018). Design and Development of Maize Dehusker cum Sheller.

Swapan Kumar Roy1§, M. A. (March, 2007.). Business Rationale for Investment on Power
Operated Maize Sheller in India, Bangladesh:

Varley, K. K. ( Aug 1988). Characterization of somaclonal variants in maize. Cornell

University.

VINAY. (2016). Design and development of pedal in India, Krishikosh : CCSHAU

WANJALA. (2014).

Whitaker's Almanack., 1. (1996). Account of the Astronomical and Other Phenomena

...information Respecting the Government, Finances, Population, Commerce, and General
Statistics of the Various Nations of the World,. Whitaker's Almanack.