Final Hit 300. Batsie

8/3/2019 Final Hit 300. Batsie

http://slidepdf.com/reader/full/final-hit-300-batsie 1/67

1

HIT 300 (DESIGN AND INNOVATION PROJECT)

REDESIGN AND IMPROVING THE MODEL OF A ROTARY

GRAIN DE-WEEVIL

BY

BATSIRAI WEBSTER MASHAVA

REG. NUMBER: H0810835T

PROGRAM: B.TECH. FOOD PROCESSING TECHNOLOGY (HONOURS)

SUPERVISOR: MR. W. GWALA

DATE: 28 JUNE 2011

This document is submitted in partial fulfillment of the requirements of the course HIT 300offered in Part III of a Bachelor of Technology Degree program in Food Processing Technology(Honours).



2

Dedications

This work is dedicated to all those who played a role in this work with particular emphasis

directed to my parents and friends.



3

Acknowledgements

It is with great honour and privilege to have had an opportunity of carrying this design project.

Many persons have given their utmost support and encouragement and the few names singled out

here represent all those without whose indispensable support, this phase could not have been

successful.

Many thanks go to Mr W. Gwala, project supervisor and lecturer, Eng. M. Mukurunyorowa,

project fund facilitator, and G.M.B whose guidance and dedicated support cannot be

overemphasised.

I would like to thank the Almighty God for his providence.

Great appreciation and thanks go to my colleagues for their assistance and support during the

design process.



4

Abstract

This project is a contribution towards improving grain cleaning preparation by efficiently

removing weevils at an industrial level making it easy and less time consuming. It is aimed at

redesigning and improving the rotary grain de-weevil by increasing capacity, cleaning efficiency

and reducing resident time comparing to manual cleaning.

Design principles were employed to come up with detailed illustrative diagrams of the design.

The materials used in the design was mild steel in place of stainless steel for the purpose of

producing the prototype since the material was readily available and easy to acquire unlike the

stainless steel.



5

Contents

Dedications ........................................................................................................................................... 2

Acknowledgements ............................................................................................................................... 3

Abstract ................................................................................................................................................. 4

List of tables…………………………………………………………………………………………………………………………………………6

Executive summary ................................................................................................................................. 10

1.1 Rationale ....................................................................................................................................... 10

1.2 Aim ................................................................................................................................................ 11

1.3 Objectives ...................................................................................................................................... 11

1.4 Benefits ......................................................................................................................................... 11

1.5 Delimitation .................................................................................................................................. 11

1.6 Limitations ..................................................................................................................................... 12

LITERATURE REVIEW ............................................................................................................................... 14

2.4.0 Grain Weevils ............................................................................................................................. 19

2.4.1 Appearance ................................................................................................................................ 19

2.4.2 Life Cycle .................................................................................................................................... 20

2.4.3 Type of Damage ......................................................................................................................... 20

2.4.4 Maize Weevil Resistance ............................................................................................................ 21

2.5.0 Machine Design .......................................................................................................................... 21

2.5.1 Engineering Material .................................................................................................................. 21

2.5.2 Material Type ............................................................................................................................. 22

2.6.0 Electric Motors ........................................................................................................................... 23

2.6.1 Determining Motor Loads .......................................................................................................... 23

2.6.1.1 Reasons to Determine Motor Loads ....................................................................................... 23

2.6.2 Input Power Measurements ...................................................................................................... 24

2.6.3 Torque of Shafts ......................................................................................................................... 25

2.7.0 Frustums .................................................................................................................................... 27

2.7.1 Volumetric Formula of a Frustum .............................................................................................. 28

2.7.2 Surface Area Formula of a Conical Frustum............................................................................... 28



6

2.7.3 Conical Frustum Slant Angle ...................................................................................................... 29

2.8.0 Safety, Health and Environmental Issues .................................................................................. 30

2.8.1 Safety ......................................................................................................................................... 30

2.9.0 Existing Grain Cleaning Machines .............................................................................................. 30

2.9.1 The Clipper ................................................................................................................................. 30

2.9.2Fanning-mills or winnowing-machines ....................................................................................... 31

2.9.3 Rotary Cleaners .......................................................................................................................... 32

2.9.4.1 Function: ................................................................................................................................. 33

DESIGN METHODOLOGY ......................................................................................................................... 35

3.1 Data Gathering .............................................................................................................................. 35

3.2.0 Experimental Procedures ........................................................................................................... 36

3.3.0 Parameters Measured ............................................................................................................... 36

3.3.1 Determination of the grain size ................................................................................................. 36

3.3.3 Determination of time ............................................................................................................... 37

3.3.4 Determination of Shaft diameter ............................................................................................... 37

3.3.5 Determination Feed Rate ........................................................................................................... 37

3.3.6 Determination of Cleaning Efficiency ........................................................................................ 37

3.4.0 Design Process ........................................................................................................................... 38

3.4.1 Research Design ......................................................................................................................... 38

Chapter 4 ..................................................................................................................................................... 40

4.0 Research Design Process ................................................................................................................... 41

4.1 Design Brief ................................................................................................................................... 41

4.1.0 Product Design Specifications .................................................................................................... 41

4.2.1 Capacity ...................................................................................................................................... 42

Rotary sieves’ internal dimensions (capacity dimensions)................................................................. 42

4.2.2 Height of the machine................................................................................................................ 43

4.2.3 Orifice diameters of the sieves .................................................................................................. 44

4.2.4 Width and Length of the machine ............................................................................................. 44

4.3.0 Alternative Concept Design ....................................................................................................... 44

4.3.1 Alternative Solution No. 1 .......................................................................................................... 45

4.3.1.1 Principle of Operation: ............................................................................................................ 45

4.3.2 Alternative Solution No. 2 .......................................................................................................... 47



7

Dimensions of the Second Alternative................................................................................................ 47

4.3.1.2 Principle of Operation ............................................................................................................. 48

4.4.0 Concept Evaluation (Comparison of the two Alternatives) ....................................................... 49

4.4.1 Evaluation based on capacity ..................................................................................................... 50

4.4.3 Evaluation based on Capital Cost ............................................................................................... 50

4.4.4 Evaluation based on Maintenance Cost..................................................................................... 51

4.4.5 Floor Space Consumption .......................................................................................................... 51

4.5.0 Detailed Design .......................................................................................................................... 51

4.5.1 Dimensions of the machine ....................................................................................................... 51

4.5.2 Machine parts ............................................................................................................................ 51

4.5.3: Calculating the torque of the shaft ........................................................................................... 52

4.5.4 Calculating the forces acting on the shaft: ................................................................................ 52

4.5.5 Calculation of the shaft diameter .............................................................................................. 55

4.5.6 Calculation of the Maximum Revolutions per minute (rpm) that could be attained under load

............................................................................................................................................................ 57

4.5.7 Calculation of Power required Under Load ............................................................................... 57

4.5.7 Cost Evaluation .......................................................................................................................... 58

Chapter 5 ..................................................................................................................................................... 59

5.0 Calculation and Discussion ................................................................................................................ 60

5.1 Calculation of Speed required for Efficient Cleaning .................................................................... 60

5.2 Calculating the required power to sustain this speed under a load. ............................................ 60

5.3 Calculating Capacity of the design ................................................................................................ 61

Chapter 6 ..................................................................................................................................................... 63

6.0 Conclusion and Recommendations................................................................................................... 64

Bibliography ................................................................................................................................................ 65



8

List of tables

Table 1 NEMA‟s Service Factor at Synchronous Speed (RPM) for drip proof motors ..…24

Table 2 Sieve dimensions …………………………………………………………………...42

Table 3 Gradient angle of the frustum …………..……………………………………….42 Table 4 Height of the design ……………………………………………………43

Table 5a Alternative no. 1 dimensions …………...……………………………………….44

Table 5b material costing of Al No.1 ……………………………………………………47

Table 6a Alternative no. 2 dimensions ……………………………………………………47

Table 6b material costing of Al No.1 ……………………………………………………49

Table 7 Alternative evaluation and analysis ……………………………………………………50

Table 8 Recommend values of Km and Kt ……………………………………………………55

Table 9 Details of the existing machine …..........................................................................60



9

Chapter 1



10

EXECUTIVE SUMMARY

1.1 Rationale

Food Incorporated is a company located in Waterfall and it is under Super Sands industrial

sector. It was founded in 2003 and it is owned by Mr. Mukunyorowa. The company is involved

in the mass production of maputi, cooking oil and soy chunks. The company has primarily two

prime raw materials in operation, which are maize and beans. The company receives an average

of 60 - 80 tonnes of maize per week during the harvesting season and 42 - 49 tonnes per week is

popped into maputi. Grain cleaning operation done at this company is manual which has

therefore lead to various problems with weevil infestation on the maize grain. The problem with

these weevils is associated with failures in popping out of the maputi. The efficiency of manual

cleaning at Food Incorporated is substantially below production capacity (12%) that is 250 Kgs

per hour in which it can be increased mechanically by 42% to meet maximum production

capacity per day. This cleaning operation is done by three people, which means its both labour

intensive and time consuming.

Calculating with the company‟s monthly delivery which adds to approximately 240 tonnes

subtracting with the monthly production of 168 tonnes, which means 72 tonnes are vulnerable of

weevil destruction and damage. This possible since the female corn weevils lay between 36 and

254 eggs which in just 14 days the larva hatch and begin to grow, within 21days the larvae grows

and repeat the reproductive process.

The rotary grain cleaner found at G.M.B consists of a single cylindrical rotating sieve. The

machine is only capable of remove a fraction of weevils, smaller impurities and does not remove

any impurities bigger than the grain such as stones and stalks. The capacity of the machine is 1100kg/h and its cleaning efficiency is 87.2% which is not a sufficient percentage of maize grain

cleaning at Food Incorporated. According to G.M.B‟s statistical maize grain reception (of about

100 -200 tonnes per week, such a machine is very slow in its returns. Regularly G.M.B process

30 tonnes of maize grain per day with that compromised cleaning efficiency.



11

1.2 Aim

To improve the rotary grain cleaner by redesigning a machine that will increase its

capacity and cleaning efficiency in relation to time.

1.3 Objectives

To increase the daily production of maputi from 6 tonnes per day to more than 10 tonnes

per day at Food Incorporated.

To increase the capacity and cleaning efficiency of the current rotary de-weevil to meet

the requirements of 10 tonnes per day.

1.4 Benefits

The project was to insist Food Incorporated, GMB and farmers to improve their grain

quality prior to storage and processing, and it was a platform to the nation in creating

room for employment and bringing about the power of innovation to the nationalindustry.

This project will help the designer to partially fulfill his Bachelor of technology degree in

Food Processing Technology and to gain valuable knowledge and experience in the

design process and subject under study.

1.5 Delimitation

This project is rational and it will limit itself to the conceptual design and producing a

working product model by including a blower and another sieve on the current machine.



12

1.6 Limitations

The project is done concurrently with internship therefore becomes strenuous and energy

consuming.

Acquiring information from the Internet was also limiting since some most websites

require registered membership in order to access information.

The project was limited by the time allocated to it hence the prototype for

demonstrations‟ sake is still in progress.

The project‟s working prototype was limited to tools and to material unavailability

especially sieves.



13

Chapter 2



14

LITERATURE REVIEW

2.1 Introduction

The highest ever standards for grain quality, required by both customers and governmental

agencies, have sharply increased the importance of precision grain cleaning methods for today's

Markets. Fines, dust and dirt must be removed to much more critical tolerances of less than ….

Thus to meet this need grain cleaning methods were improved from generation to generation.

According to Brennan (2006) defined “Cleaning” as the phase or phases of the post-harvest

system during which the impurities mixed with the grain mass are eliminated.

Clean grain has a higher value than grain that is contaminated with straws, chaff, weed seeds,

soil, rubbish, and other non-grain materials. There are three main importance of grain cleaning

and these are:

i. Cleaning improve the ability of the grain to be safely stored, reduce unwanted materials

(dockage) for milling, and improve milling output and quality.

ii. Cleaning is essential for protection of process equipment as well as the final consumer,

for example, it is essential to remove sand, stones or metallic particles from beans/maizeprior to milling to avoid damaging the machinery.(Brennan, 2006)

iii. Impurities lower the quality of the product and are also a focal point for potential

infestation during storage. Dirty grain can attract certain insects or fungus that might

damage the grain. Therefore cleaning is greatly required.

2.2 Grain Cleaning Process

All food raw materials are cleaned before processing. Increased mechanization in harvesting and

subsequent handling has generally led to increased contamination with mineral, plant and animal

contaminants. (Brennan, 2006)

There are a number of cleaning methods available, classified into dry and wet methods, but this

project focuses on dry cleaning methods.



15

2.2.1 Dry Cleaning Methods

The main dry cleaning methods are based on screens, aspiration or magnetic separations. Dry

methods are generally less expensive than wet methods and the effluent is cheaper to dispose of,

but they tend to be less effective in terms of cleaning efficiency. Precautions may be necessary to

avoid the risk of dust explosions and fires (Brennan, 2006).

2.2.2 Winnowing

Winnowing is an agricultural method developed by ancient cultures for separating grain from

chaff, which uses wind or a fan to remove the light elements from the grain. It is also used to

remove weevils or other pests from stored grain (Harrison, 1922). Wind winnowing method

involves tossing the grain into the air and letting the wind carry off the lightest impurities. Such

impurities include unfilled grains, chaff, weed seeds, and straw can be removed from the grain

by using wind (Harrison, 1922).

This method has its disadvantages, labour intensive, time consuming and it does not eliminate

the heavier impurities, nevertheless it simple and no energy is required. Fig 1.1, illustrates how

winnowing is done.

Fig 1.1 wind winnowing

Advances have been made to improve the wind winnowing operation. Techniques included using

a winnowing fan (a shaped basket shaken to raise the chaff) or using a tool (a winnowing fork or

shovel) on a pile of harvested grain (Thompson, 1991).



16

Mechanical winnowers use a fan and several superimposed reciprocating sieves or screens are

now used in many countries. Winnowers are simple machines that consist mainly of a hopper to

receive the grain, a fan and a set of sieves. These can be manually powered or motorized and

have capacities from 100kg to 3 tons per hour (www.knowledgebank.irri.org). Fig 1.2 shows a

winnowing machine

Fig 1.2 winnowing machine

The rotary winnowing fan is used to crank a fan to produce the air stream (Thompson, 1991).

2.2.3 Screen and Shifting

Smaller materials such as weed seeds, soil particles and stones can be removed by sieving the

grain through a smaller sized screen (2.5mm or less sieve opening). (Hanson, 1985)

Screens are essentially size separators based on perforated beds or wire mesh . Larger

contaminants are removed from smaller food items: e.g. straw from cereal grains, or pods and

twigs from peas. This is termed „scalping‟, see Fig. 1.3 a. alternatively, „dedusting‟ is the

removal of smaller particles, e.g. sand or dust, from larger food units, see Fig. 1.3 b (Brennan,

2006).

http://www.knowledgebank.irri.org/






17

Fig 1.3 Screening of dry particulate material: (a) scalping, (b) dedusting

2.3.0 The Maize Grain

Maize is originally from Mesoamerica, it is very adaptable to different weathers, and nowadays

its consumption is worldwide. In fact, the maize is the most widely grown cereal crop. In the

global production of cereals crops, the maize ranks first after rice (paddy) and wheat. Likewise,

corn is the leading cereal crop in Zimbabwe in terms of volume and value. It is a staple grain

mainly dominant and cheap (FAO, 1992)/ (Mangelsdorf and Reeves, 1939).

The corn ranges from white to dark brown or purple in color but white and yellow are most

common. According to Coleman and Larkin (1999), the botanical name for maize is Zea mays

and it belongs to the grass family (Gramineae).

The maize kernel consists four main principle parts:

i. Bran/Hull (Outer layer) – It constitutes approximately 5-6% of the kernel. It is important

due to the presence of vital minerals, fiber and vitamins. The hull is the pericarp.



18

ii. Germ – Covers 10-14% of the kernel. It contains high crude oil and oil soluble vitamins

iii. Endosperm – It mainly constitute starch and proteins; and it covers 80-85% of the kernel

iv. Tip-cap

Fig 3, illustrate the structure of the maize kernel.

Fig 2 Maize kernel, source Illinois (1964)

The approximate chemical compositions of maize kernel are 9.5% protein, 2.2% fiber, 4.3% ash,

33% crude oil and 12% moisture. (Burge and Duensing, 1989)

Maize is grown seasonally and to that effect storage is important to encourage availability

through the year. Therefore cleaning is considered to be one of the most important procedures

required to improve the shelf-life of maize especially against weevils.



19

2.4.0 Grain Weevils

Weevils are beetles that are attracted to many grain crops such as wheat, rice, barley and corn

that are grown. Weevils and insects degrade the grain coat integrity and endosperm. Their

damaging effects are largely due to their ability to reproduce quickly and then spread throughout

the corn in a matter of days. (Longstaff, 1981)

The maize weevil‟s scientific name is Sitophilus zeamais. The maize weevil is similar to the

rice weevil in appearance, except that the insects are longer, adults reaching a length of 3-

3.5mm. (ento.psu.edu)

2.4.1 Appearance

The maize adult weevil is a small snout beetle which varies in size, averaging between 1/8- to

3/16-inches long. It varies from dull red-brown to nearly black and is usually marked on the back

with four light reddish or yellowish spots. The maize weevil has fully developed wings beneath

its wing covers and can fly readily. The thorax is densely pitted with somewhat irregularly

shaped punctures, except for a smooth narrow strip extending down the middle of the dorsal

(top) side. (Longstaff, 1981) Fig 3.1 illustrates a detailed maize weevil appearance.

Fig 3.1 Maize weevil (Sitophilus zeamais)

An egg hatches in a few days into a soft, white, legless, fleshly grub which feeds on the interior

of the grain kernel. The grub changes to a naked white pupa and later emerges as an adult beetle.



20

The maize weevil is slightly larger than the rice weevil and has more distinct colored spots on

the forewings. It is a stronger flier than the rice weevil. The habits and life cycle are similar to

the rice weevil.

2.4.2 Life Cycle

The female maize weevil bores a hole into a kernel of grain and lays an egg, sealing the opening

with gelatinous material. Full development of the weevil takes place within the kernel of grain

and is not discernible from the outside. The development phase of the grain weevil depends on

temperature, normally taking minimum life cycle of 28 days. Females can lay more than 200

eggs under favorable conditions. (Longstaff, 1981)

The entire life cycle from egg to adult may be as short as one month during the summer or as

long as 5 months during the winter, being very dependent upon the temperature. There are

usually 4 generations per year with adults living between 7-8 months.

2.4.3 Type of Damage

These weevils are very destructive grain pests. Weevils develop as larvae within the grain

kernels. The weevil (presumably) chews a small hole on the ear of the seed emitting a

pheromone which will attract other maize weevils to the area. They subsequently lays eggs in the

resulting cavity. The larva bores throughout the seed and pupates there, the adult emerging after

it has matured. Since weevils have the ability to reproduce quickly, they frequently cause almost

complete destruction of grain in elevators or bins, where conditions are favorable. Infested grain

will usually be found heating at the surface, and it may be damp, sometimes to such an extent

that sprouting occurs. (Derera et al, 2001)

Corn is a favorite host of the maize weevil, and can become infested in the field as well as in

storage. Like many other stored grain pests, Sitophilus species tolerate or prefer low moisture

levels in their food. Fig 3.2 shows an affected maize grain with weevils



21

Fig 3.2 Destructed grains by weevil

2.4.4 Maize Weevil Resistance

According to Perez-Mendoza (1999), the increasing occurrence of insecticide resistance and

increasing environmental concerns about the use of chemical insecticide mean that alternative

control methods are required. Studies have been carried out focusing on the grain factors

contributing to maize weevil resistance and inheritance mechanism of resistance.

The tactic for control of stored products pests in commercial facilities in Mexico are almost

completely depend on pesticides but in recent years(1991 to 1992), managers of commercial bins

have reported control failures of these chemicals. It was thought to be less insecticide applicationbut the most likely reason was due to insecticide resistance in the target weevil (Perez-Mendoza,

1993 and Subramanyam, 1995).

The factors contributing to weevil resistance have been studied extensively and include

concentration of phenolic compounds in pericap tissue, grain protein content, grain hardness and

completeness/ tightness of husk cover (Classen et al, 1990).

2.5.0 Machine Design

2.5.1 Engineering Material

The selection of a material for a machine part or structural member is the most important job for

a designer before the final dimensions of the designed part are decided. According to Jindal

(2010), technical properties of material can be classified into three:



22

i. Physical properties, such as density, homogeneity, thermal expansion coefficient and

composition.

ii. Technical properties, such as machinability, forgeability, castability, drawability and

defromability.

iii. Mechanical properties, such as strength, toughness, hardness, corrosion resistance, impart

strength, fatigue (a progressive and localized structural damage that occurs when a

material is subjected to cyclic loading [Stephens, 2001]) and creep resistance.

The design of a machine part depends upon the strength and stiffness of the material. Stresses

developed in the machine part and the deflection in members depends on the dimensions of the

member the various types of rigidity, namely torsional rigidity, flexural rigidity and stiffness.

(Jindal, 2010)

In many cases the frictional property of the material also plays an important role in the selection

process, since the coefficient of friction should be low for bearing materials and high for brake

lining.

2.5.2 Material Type

Most of food processing machinery is made up food grade material that is not capable of

imparting any side effects on the processed food, for example, iron rusts therefore using it on

moist food products it owes contamination. Hence each material used is of advantage or

disadvantage to the food industry. Most of food processing machines are made up of stainless

steel or galvanized material. Stainless steel does not react with food either those with moisture or

not.

List of Food Processing material

i. Stainless steel

ii. Aluminium

iii.

Coated or painted ironiv. Cast Iron (good at absorbing vibration)



23

2.6.0 Electric Motors

An electric motor converts electrical energy into mechanical energy. Most electric

motors operate through interacting magnetic fields and current-carrying conductors to generate

force. Electric motors are found in applications as diverse as industrial fans, blowers and pumps,machine tools, household appliances, and disk drives. They may be powered by direct

current (e.g., a battery powered portable device or motor vehicle), or by alternating current from

a central electrical distribution grid or inverter. Electric motors may be classified by the source of

electric power, by their internal construction, by their application, or by the type of motion they

give. (Donald, 1978)

In an electric motor the moving part is called the rotor, and the part that stands still is called

the stator. Magnetic fields are produced on poles, and these can be salient poles where they are

driven by windings of electrical wire. A shaded pole is used in some motors and contains an

inductor to delay the phase of the magnetic field for that pole. A commutator is a device for

varying the direction of flow of current to coils depending on the angle of rotor (Edwin, 1897).

2.6.1 Determining Motor Loads

To compare the operating costs of an existing standard motor with an appropriately-sized energy

efficient replacement, you need to determine operating hours, efficiency improvement values,

and load. Part-load is a term used to describe the actual load served by the motor as compared to

the rated full-load capability of the motor. Motor part-loads may be estimated through using

input power, amperage, or speed measurements.

2.6.1.1 Reasons to Determine Motor Loads

Most electric motors are designed to run at 50% to 100% of rated load. Maximum efficiency isusually near 75% of rated load. Thus, a 10-horsepower (hp) motor has an acceptable load range

of 5 to 10 hp; meaning that the peak efficiency is at 7.5 hp. A motor‟s efficiency tends to

decrease dramatically below about 50% load. Overloaded motors can overheat and lose

efficiency. Many motors are designed with a service factor that allows occasional overloading

(Branan, 2005)

http://en.wikipedia.org/wiki/Electrical_energy

http://en.wikipedia.org/wiki/Mechanical_energy

http://en.wikipedia.org/wiki/Motor

http://en.wikipedia.org/wiki/Magnetic_fields

http://en.wikipedia.org/wiki/Electrical_conductor

http://en.wikipedia.org/wiki/Hard_drive

http://en.wikipedia.org/wiki/Direct_current


http://en.wikipedia.org/wiki/Battery_(electric)

http://en.wikipedia.org/wiki/Alternating_current

http://en.wikipedia.org/wiki/Electrical_grid

http://en.wikipedia.org/wiki/Inverter_(electrical)

http://en.wiktionary.org/wiki/rotor

http://en.wiktionary.org/wiki/stator

http://en.wiktionary.org/wiki/pole

http://en.wiktionary.org/wiki/salient_pole

http://en.wiktionary.org/wiki/windings

http://en.wiktionary.org/wiki/shaded_pole

http://en.wiktionary.org/wiki/commutator




http://en.wiktionary.org/wiki/shaded_pole

http://en.wiktionary.org/wiki/windings

http://en.wiktionary.org/wiki/salient_pole

http://en.wiktionary.org/wiki/pole

http://en.wiktionary.org/wiki/stator

http://en.wiktionary.org/wiki/rotor

http://en.wikipedia.org/wiki/Inverter_(electrical)

http://en.wikipedia.org/wiki/Electrical_grid


http://en.wikipedia.org/wiki/Battery_(electric)



http://en.wikipedia.org/wiki/Hard_drive

http://en.wikipedia.org/wiki/Electrical_conductor

http://en.wikipedia.org/wiki/Magnetic_fields

http://en.wikipedia.org/wiki/Motor

http://en.wikipedia.org/wiki/Mechanical_energy

http://en.wikipedia.org/wiki/Electrical_energy



24

According to Branan (2005), Service factor is a measure of periodically overload capacity at

which a motor can operate without overload or damage. The NEMA (National Electrical

Manufacturers Association) standard service factor for totally enclosed motors is 1.0. A motor

operating continuously at a service factor greater than 1 will have a reduced life expectancy

compared to operating at its rated nameplate horsepower.

Table 1 NEMA’s Service Factor at Synchronous Speed (RPM) for drip proof motors.

Power(HP)

Service Factor - SF

Synchronous Speed (RPM)

3600 1800 1200 900

1/6, 1/4, 1/3 1.35 1.35 1.35 1.35

1/6 1.25 1.25 1.25 1.25

¾ 1.25 1.25 1.15 1.151 1.25 1.15 1.15 1.15

1 1/2 and up 1.115 1.15 1.15 1.15

Therefore, 1hp motor with a service factor of 1.15 can operate at:

1 HP x 1.15

= 1.15 HP

without overheating or otherwise damaging the motor if rated voltage and frequency are supplied

to the motor. Insulation life and bearings life are reduced by the service factor load.

2.6.2 Input Power Measurements

With measured parameters taken from hand-held instruments, an equation can be used to

calculate the three-phase input power to the loaded motor. You can then quantify the motor‟s

part-load by comparing the measured input power under load to the power required when the

motor operates at rated capacity (Bollen, 1999).

Where: Pi = Three-phase power in kW

V = RMS voltage, mean line-to-line of 3 phases; I = RMS current, mean of 3 phases, and PF =

Power factor as a decimal.



25

According to Fairchild (2004), The power factor of an AC electric power system is defined as

the ratio of the real power flowing to the load to the apparent power in the circuit, and is a

dimensionless number between 0 and 1 (frequently expressed as a percentage, e.g. 0.5 pf = 50%

pf). Real power is the capacity of the circuit for performing work in a particular time. Apparent

power is the product of the current and voltage of the circuit.

Where: = Input power at full-rated load in kW

hp = Nameplate rated horsepower, and

= Efficiency at full-rated load.

Where: Load = Output power as a % of rated power

Pi = Measured three-phase power in kW, and Pir = Input power at full-rated load in kW.

Calculating the three phase power and the input power at full rated load, therefore, the load of

the electric motor can be determined using equation 3.

2.6.3 Torque of Shafts

Torque is the tendency of a force to produce rotation about an axis or pivot, also called as

moment or moment of force. Just as a force is a push or pull, a torque can be thought of as a

twist. Torque consists of force acting on distance. In relation to the design, the torque of the

electric motor will determine the power that can be used by a machine under full load (Khurmi,

2005).

Therefore torque can be calculated by the following formulas:

Where T = Twisting moment (or torque) acting upon the shaft,

J = Polar moment of inertia of the shaft about the axis of rotation,


http://en.wikipedia.org/wiki/Ratio

http://en.wikipedia.org/wiki/AC_power#Real.2C_reactive.2C_and_apparent_power


http://en.wikipedia.org/wiki/Power_(physics)

http://en.wikipedia.org/wiki/Power_(physics)



http://en.wikipedia.org/wiki/Ratio




26

τ = Torsional shear stress, and

r = Distance from neutral axis to the outer most fibre

= d / 2; where d is the diameter of the shaft.

And for a round solid shaft, polar moment of inertia,

Therefore substituting equation (5) into (4), hence

Where , and

d = the diameter of the shaft.

The twisting moment (T ) may be also obtained by from power transmitted in a shaft (Khurmi,

2005).

Where N = rpm

Every shaft that is under horizontal load undergoes both twisting and bending moments.

According to Khurmi (2005), when the shaft is subjected to a bending moment only, then themaximum stress (tensile or compressive) is given by the bending equation.

Where M = Bending moment,

I = Moment of inertia of cross-sectional area of the shaft about the axis of rotation,

= Bending stress, and

y = Distance from neutral axis to the outer-most fiber.

But when the shaft is subjected to combined twisting moment and bending moment, then the

shaft must be designed on the basis of the two moments simultaneously. Various theories have

been suggested to account for the elastic failure of the materials when they are subjected to



27

various types of combined stresses. The following two theories are important from the subject

point of view:

1. Maximum shear stress theory or Guest's theory. It is used for ductile materials such as

mild steel.

2. Maximum normal stress theory or Rankine‟s theory. It is used for brittle materials such

as cast iron.

The equivalent twisting moment may be defined as that twisting moment, which when acting

alone, produces the same shear stress (τ) as the actual twisting moment. This moment can be

denoted by ,which is the equivalent bending moment,

* √ +

Where Km = Combined shock and fatigue factor for bending, and

Kt = Combined shock and fatigue factor for torsion.

T = torque M = bending moment

The values of and are represented in table 8 in section 4.5.5

And also,

Where Bending stress (tensile or compressive) induced due to bending moment.

2.7.0 Frustums

In geometry, a frustum (plural: frusta or frustums) is the portion of a solid (normally

a cone or pyramid) that lies between two parallel planes cutting it. There are several types of

frustum, namely conical frustum, pyramidal frustum and square frustum, illustrated in Fig 5

below. These entire type shares the same volumetric formula, but the surface area formula is

different for each. (Boyer, 1991)

http://en.wikipedia.org/wiki/Geometry

http://en.wikipedia.org/wiki/Polyhedron

http://en.wikipedia.org/wiki/Cone_(geometry)

http://en.wikipedia.org/wiki/Pyramid_(geometry)

http://en.wikipedia.org/wiki/Parallel_planes

http://en.wikipedia.org/wiki/Parallel_planes

http://en.wikipedia.org/wiki/Pyramid_(geometry)

http://en.wikipedia.org/wiki/Cone_(geometry)

http://en.wikipedia.org/wiki/Polyhedron

http://en.wikipedia.org/wiki/Geometry



28

(a) Pyramidal frustum (b) conical frustum (c) square frustum

Fig 5 Frustums

2.7.1 Volumetric Formula of a Frustum

The general formula for any frustum shape is:

V = .........................................................................................................Eq.11

where: π is 3.14159… and a, b are the radii of the two bases.

This formula was derived by Hero of Alexandra in the 10th AD. (Boyer, 1991)

2.7.2 Surface Area Formula of a Conical Frustum

The surface area of a right circular cone frustum shown in Fig 5 (b) is:

A = π ( )………………………………………….…Eq.12

where a and b are the base and top radii respectively. The conical frustum is of more concern to

the ideal design since the rotary sieves have a frustum shape.



29

2.7.3 Conical Frustum Slant Angle

The slant angle of a conical frustum is obtained from getting the slant height first through the

application of Pythagoras theorem. Bisecting the conical frustum from the center a triangle is

formed and the slant height is obtained by applying the Pythagoras theorem. (Boyer, 1991)

Pythagoras Theorem

………………………………………………………………………………...Eq. 13

Where s is the slant height, a is the height and b is the base.

Therefore the slant height s is

……………………………………………………………………………….Eq. 14

Obtaining the slant height from equation 11 makes it easy to obtain the slant angle by applying

the cosine rule. According to David (2003), in a triangle ABS in which the side opposite each

vertex is denoted by the corresponding lower case letter illustrated in Fig 6 below. Then thecosine rule entails:

……….…………………………………………………………Eq.15

B

.a s

S b A

Fig 6 a triangle

This rule can be rearranged to give:



30

………………………………………………………………………….Eq. 16

2.8.0 Safety, Health and Environmental Issues

2.8.1 Safety

Safety has become a matter of paramount importance these days in design. Machines must be

designed to serve mankind, not to harm it. Industrial regulations ensure that the manufacturer is

liable for any damage or harm arising out of a defective product. Use of a factor of safety only in

design does not ensure its overall reliability. According to R.S Khurmi, G.K Gupta (2005) some

machines are dangerous to operate, especially those which are speeded up to insure production at

a maximum rate. Therefore, any moving part of a machine which is within the zone of a worker

is considered an accident hazard and may be the cause of an injury. It is, therefore, necessary that

a designer should always provide safety devices for the safety of the operator. The safety

appliances should in no way interfere with operation of the machine

2.9.0 Existing Grain Cleaning Machines

2.9.1 The Clipper

The Clipper is known as a grain cleaning farm machine that is made up wood, several removable

sieves and a fan. The blast within the machine is generated with attached pulleys on the fan

blades with crossed belts. This machine is both manual and automated. When one simply want to

use power, the cog wheel must be substituted by a pulley. Operations done by the use of power

require the shaker shaft to have a speed of 390 to 400 revolutions per minute. This operation will

be valid to secure a strong air blast to blow out all light, chaffy kernels, leaving only the plum,

heavy kernels for seed. (Michigan, 2003)



31

Fig 5 the Hand Powered Clipper.

1. Shoe, with two receiving grooves for screens. The screens are securely held in place by a

compressing rod.

2. Straw spout, for carrying off particles, straw, etc.

3. Screening spout, for removing sand, fine weeds, etc.

4. Vertical Air shaft, through which the draft passes upward, carrying off chaff, dust, etc.,

through dust hood

5. Grain box, which will hold 5 bushels. It has a lifting board at the end which allows the

contents to be easily scooped into sacks

6.

Dust hood, through which chaff, dust and worthless matter are discharged. All light,

imperfect and foreign grain and seeds are discharged at the opening.

7. Fan, with iron arms, fitted on turned steel shafting, equipped with core pulley. This

allows changing the speed of the Fan, which is necessary to property clean grain and

seeds of varying weights.

2.9.2Fanning-mills or winnowing-machines

These clean coffee, grain, etc., from chaff, dirt, and other light impurities. The apparatus shown

in Fig. 5.1 is designed for hand-use. Multiplying gear is placed between the crank-handle and bar

shown. The sieves are vibrated by means of a crank disk-rod and bell-crank. The grain is fed in

at tile top, and passes through the sieves, the uppermost of which is coarse, while the lower ones

are of varying degrees of fineness, the object being to distribute the fanning duty, by arresting the



32

motion of the grain, so that the coarser impurities pass out between the upper and the finer ones

between the lower sieves.

Figure 5.1 Fanning mill

2.9.3 Rotary Cleaners

Rotary Cleaners are a versatile screen cleaner specifically designed for efficient cleaning using arotating sieve joined to. According to Alvan Blanch,



33

2.9.4 Universal Screen Grader/Cleaner KUT

Universal screen graders type KUT are designed for removal of admixtures and impurities from

stream of basic material by aid of screens and air stream. They are namely used for post-harvest

cleaning and pre-cleaning of grain. Universal screen grader is a machine capable to clean all

sorts of cereals and seeds, like poppy, e.g. poppy seed, buckwheat, maize, beans, but also dried

herbs, spices, tobacco, salt, all that according to the type of sieves used. The machine is suitable

for all cases of sieving and sorting even when the crops are frequently changed. All parts coming

in contact with the sorted material can be easily cleaned. (Brenan, 200

2.9.4.1 Function:

The machine is fitted with pair of sieves, which ensure separation of coarse (big) and fine (small)

impurities according to the mesh in the sieves. The screens are cleaned by silicone balls (good

jumping even at low temperatures). The vibrations are created by electric vibrators. And the

casing with the sieves is cushioned by springs. Screens casing is of frame modular construction.

Connected air channel enables separation of light impurities. Pair of sieves is included into the

machine delivery, the size of mesh is recommended to the customer according to the type of crop

for the best result. Fan and cyclone separator are delivered as optional accessories. Universal

screen graders KUT can be widely used in food and agriculture industry.



34

Chapter 3



35

DESIGN METHODOLOGY

The chapter highlights the systematic framework that was used, research design, sampling

techniques, methods of data collection, analysis and presentation and limitation of the research.

The objective of this chapter was to come up with a method that can be used to design an

economically feasible and more efficient grain cleaner.

3.1 Data Gathering

In this design of an efficient de-weevil roto-fanning machine, various sets of data were collected.

This information was Food Incorporated basis of cleaning procedures and G.M.B‟s grain

cleaning plant. Information on weevils‟ infestation was obtained from G.M.B and other various

sources to be highlighted in this chapter. The data was divided into two classes that are primary

and secondary data.

Primary data

This is the type of data that is obtained directly from the field and this data. In the project

primary data was gathered using experiments, brain-storming, questionnaires and interviews.

Experiments conducted included determining the rate of rotation for maximum sieving action,

determining capacity per hour and determining the size of the grain. Interviews and

questionnaires were also conducted in order to get information concerning production from the

personnel.

Secondary data

This is the type of data that is collected from secondary sources such as records, journals,internet and books, in this particular project secondary data concerning the sales of juice was

used in order to evaluate if the project was going to be profitable or not to the company. Another

source of data that was obtained from secondary sources was total mixing time.



36

3.2.0 Experimental Procedures

Twenty kilogram of maize grain samples was taken randomly from a heap of received sacks and

fed into the hopper manually. Feeding time, cylinder speed, blower speed and sieve reciprocation

speed and frequency were recorded experimentally. Approximate feed rate was computed as

weight of crop fed into the machine per unit time in kg/hr. Grain output was expressed in kg/hr

by recording time taken in cleaning operation and weight of grain recovered.

Feed rate of sieve was obtained by the output from the oscillating frustum sieve. Cleaned grains

in each collector box were collected in a transparent polyethylene bag and labeled to be

analyzed. Sample collected in each box was weighed with an electronic weighing balance.

Weight of cleaned grain was recorded for each box. The difference gave weight of impurities.

This was used to determine cleaning efficiency.

The impurity discharge section chaff was collected and weighed using electronic weighing

balance to determine the corresponding loss or grain cleaning efficiency.

3.3.0 Parameters Measured

3.3.1 Determination of the grain size

From the samples, 10 maize grains were selected at random for determining the physical axial

characteristics. For each grain, three linear dimensions were measured, that is length (L), width

(W), and thickness (T) using a micrometer screw gauge (Sheffied S 139 Br) reading to 0.01

mm. After determining all the three linear dimensions, a geometric mean diameter de was

determined as given by Mohsenin (1980)

de = (abc)1/3

,where, a,b,c = diameters/ dimensions along three axes (all in mm).



37

This procedure was done with regards to determine the size of the sieves to be used. Therefore

measurements of all geometric mean diameter where averaged to obtain the maximum and

minimum average sieve diameter.

3.3.2. Bulk Density of Samples

A 20 liter bucket container with an initial weight of 0.9 kg was used. The sample, which filled

the container, was weighed using electronic mettler balance (Sarturious 2355, maximum 160g, d

0.001d). The bulk density of the samples were determined using the method given by

Mohsenin(1980).

,where: m = mass of grain, chaff or straw (kg)

v = volume of container (m3)

3.3.3 Determination of time

Crop feeding times in seconds were measured with stopwatch. A stopwatch was used to

determine the measurement of air velocity in meters per second.

3.3.4 Determination of Shaft diameter

Shaft diameter was determined by considering the shear stress of the material, torque required to

turn the shaft under a load, load in the frustum per unit time and revolutions per minute of the

shaft, shown in section 4.5.3.

3.3.5 Determination Feed Rate Approximate feed rate was computed as weight of crop fed into machine per unit time (hr). This

was done by computing a time/mass table for the samples.

3.3.6 Determination of Cleaning Efficiency



38

Cleaning efficiency (Purity) was obtained by the procedure detailed by

,where: η =cleaning eff iciency, %= weight of pure grain at the outlet, kg = weight of contaminant (MOG), kg

3.4.0 Design Process

The basic five-step process usually used in a problem-solving can also work for design problems.

Since design problems are usually defined more vaguely and have a multitude of correct

answers, the process may require backtracking and iteration. Solving a design problem is a

contingent process and the solution is subject to unforeseen complications and changes as it

develops.

The five steps used for solving design problems are:

1. Define the problem

2. Gather pertinent information

3. Generate multiple solutions

4. Analyze and select a solution

5. Test and implement the solution

3.4.1 Research Design

The mapping of this design was done through design models. The research design initially

followed two design models in coming up with the best evaluated model to use. The design

processes were according to Hertz (2007) and Norman (1995) and in this project Hybrid design

process model was used, taking into account the weaknesses and strengths of each model over

the other. Fig 6 shows the flow diagram of the design process:



39

Fig 6 A Hybrid Design Process Model

According to Hertz (2007) the stage of concept design in the design process, an attempt is made

by the designer to come up with a possible solution to the design problem. The design

specifications were taken into account in coming up with the solution. But, but Norman (1995)

model was voted to be more effective, it gave the designer the room to come with alternative

model which was an effective stage in the designing process. Norman (1995) model allowed the

designer to produce a prototype and finally the evaluation. Norman (1995) model reflected a

weakness in not including costing, but this problem was addressed by Hertz (2007). Therefore

the weakness and strengths of each of the models is accounted for by an alternative model known

as the Hybrid design model.

Design Brief

Product Design Specification

(PDS)

Alternative Concept Design

Detail Design

Working Prototype

Testing and Evaluation

Costing



40

Chapter 4



41

4.0 RESEARCH DESIGN PROCESS

4.1 Design Brief

The constraints at Food Incorporated production capacity per day do not mean its weekly maizeand soy beans delivery rate. Due to this situation the grains are vulnerable to weevil attack and

degradation. Therefore to meet such a problem an improved design of the existing grain cleaning

machine is required. The design should increase Food Incorporated‟s cleaning capacity from 6

tonnes to 10 tonnes per day. The existing design has a single and 4mm orifice rotating sieve and

it only removes particles smaller than the grain. This rational design is therefore going to add

another sieve (which can either be rotary or vibratory) and a blower on the existing machine to

remove anything bigger and smaller than the grain.

4.1.0 Product Design Specifications

According to Hertz (2007), the specification is a statement of the characteristics that a design

must possess in order to be a solution to the human need, and it is more properly known as a

product design specification (PDS). Its aim is to ensure that the subsequent design and

development of a product meets the needs of the user.

The design must remove both bigger and smaller particles than the grain. The main concerns are

on the thorough removal of weevils and dust particulates. The first frustum, 12mm orifice

rotating sieve should allow the grain to pass through and remove any particles bigger than the

grain such as ….., the blower should blow off weevils, dust and anything lighter and the second

frustum, 4mm orifice rotating sieve should remove any smaller particles than the grain including

remain weevils.



42

4.2.1 Capacity

Rotary sieves’ internal dimensions (capacity dimensions)

Table 2

Sieves required dimensions

Dimension mm

Length 1000

Internal Diameter, a 300

Diameter, b 200

The rotating sieves have a conical frustum shape.

Calculations

Total volume of the rotating screens V = ………..………………Eq.11

=

=

=198 967 534.7

=1 989 675.347

Total sieving surface area A =π √ ..Eq. 12

π √

= 5.075 Therefore the volume of the two rotating sieves is 0.796 with a total sieving surface area of 5.075 Table 3

Required gradient angel of the frustum

Dimensions mm

Height a 1000

Base b 100



43

The base b was obtained by taking a common dimension from both sides which was 400mm and

it was subtracted from 600mm. 200mm was the remaining portion but since bisecting the

frustum would make two triangles (the same as the one in Fig 6) therefore each triangle would

be 100mm.

Calculation

From Fig 6, the slant can be calculated:

Slant height …………………………………………………………….Eq.14

s =

s = 1004.988mm (3d.p)

, therefore the gradient angle B of the slant s can be obtained by cosine rule.

…..………………………………...……..………………………………..Eq.16

4.2.2 Height of the machine

Table 4

Required height dimensions

Dimensions mmHeight from ground tothe final grain discharge

700

Diameter a 600

Diameter b 400

Space between rotatingsieves (clearance height)

500

Top height allowance 200



44

Working

Total height of the machine = the sum of all dimensions

= 700+600+400+500+200

=2400mm

The total height of the design is 2.4 meters.

4.2.3 Orifice diameters of the sieves

The machine is consisted of sieves one above the other. The first sieve was made to have an

orifice of 12mm to allow the grain to pass through it and any particle above this diameter is

discharged at the end of the oscillating sieve. The second sieve was made to have an orifice of

4mm to allow anything smaller than the grain to pass through including weevils.

4.2.4 Width and Length of the machine

The machine‟s proposed width was to be about 1 meter and the length was to be 1.65 meters.

4.3.0 Alternative Concept Design

According to Hertz (2007), the third step of design is called conceptualization. At this stage

designer considers the alternative concepts to find the best possible design to solution problem.

The selection of concepts is a decision making process which is carried out in terms of trade –

offs. The success of designer at this stage depends largely on selection of evaluation criteria that

must be relevant to performance specifications of product including also the cost.

Different alternatives were considered and evaluated in order to come up with the best possible

design. Each alternative had its own costing though the main objective in all of these alternatives

was to increase the machine‟s capacity.



45

4.3.1 Alternative Solution No. 1

The first alternative was to design a shaker beneath the rotating sieve with an electric

motor driving a centrifugal shaft and a blower. In trying to increase capacity and reducing

residence time of the existing machine at the same shaft angle, the conical frustum rotary

sieve was designed instead. Designing a conical frustum increased the design‟s capacity

from 0.503 to 0.796.

This model of a design was to achieve the increase of capacity and the removal of

weevils and any undesired materials.

Dimensions of the first alternative

Table 5a

Total height 2000mm

Total width 1000mm

Length 1800mm

Total capacity 0.796

4.3.1.1 Principle of Operation:

The product is fed to the machine by means of a screw conveyor, and then enters the intakesprout where the grain are exposed to blowing process before they enter to the front part of thefirst sieve basket. Blowing serves as a pre-cleaning procedure but removing light material asdust, weevils, chaff and unhealthy small grains. The grains are directed to rotating sieve wherethey are distributed across the whole sieve width. On the first sieve deck, impurities smaller thanthe grain including the grain are separated and moved out of the machine. Any impurities largerthe grain, are removed at the end discharge of the rotary sieve.

The grain from the first sieve deck move to the second sieve deck where impurities smaller thancereal grain are separated. This process in the design is achieved through shaking of the sieve bya vibratory electric motor, shown in fig 6. These impurities are collected in the bottom of thesieve basket from where they are discharged. The overtails from the second sieve deck representthe good grain which leaves the sieve separator clean.



46

First angle of the first alternative design

Fig 6: alternative design no. 1

Average Sieving Surface Area Calculation

From equation 9, the sieving surface area of the conical frustum was 5.075. The shaker sieveis 1000mm x 1000mm, therefore its surface area is:

Surface Area = length x width

= 1 x 1

= 1

Hence the average total surface area =

= 3.038



47

Material Costing

Table 5b

materials Dimensions (mm) Prices ($)

Chanel iron 50 * 100 * 9 200 150.00Angle Iron 60 x 40 x 12 000 120.00

1st Screen (sieve) 2 200 x 1 000 diameter -12 250.00

2nd Screen 1 000 x 1 000 diameter – 4 150.00

2mm stainless steel sheets 40 x 2 500 96.00

Shaft 60 x 2 500 65.00

4 x bearings 40 and 20 55.00

Electric motor with a gearbox(3 x 400v/18kw)

750.00

Shaker electric motor (1hp) 560.00

Flat bar 12 x 30 x 5 30.00

Blower 350.00Bolts and nuts 12 x 60 x 81 10.00

Centrifugal shaft and pulley 20 x 150 45.00

Belt 320 12.00

Sub total 2 643.00

Labour 650.00

Tax @ 15% 97.50

Total 3 390.50

4.3.2 Alternative Solution No. 2

The second design was to design a machine with two rotating sieve and a blower. Thisdesign consists of two rotating shafts in connection by means of a belt running on twopulleys of different sizes. In trying to increase capacity and residence time the cylindricalrotating sieve was substituted by two conical frustum rotating sieves with the samedimension as that of alternative one.

This model of the design was to reduce manufacturing costs and still achieve an increasedrate of weevil removal and capacity.

Dimensions of the Second Alternative

Table 6 a

Total height 2400mm

Total width 1000mm

Total Length 1850mm

Capacity 0.796



48

First angle of the second alternative design

Fig 7: alternative design no. 2

4.3.1.2 Principle of Operation

The maize product is fed to the machine by means of a screw conveyor, and then enters the

intake sprout and the grains enter the front part of the first sieve basket. The grains are directed

to rotating sieve where they are distributed across the whole sieve width. On the first sieve deck,

smaller impurities and the grains are sieved through while any impurities larger the grain, are

removed at the end discharge of the rotary sieve.

Unlike alternative no. 1, the sieved grain enters a chamber of blowing where all lighter

impurities are removed including a small fraction of weevils. The grains from the blowing

section are directed to the second sieve deck where impurities smaller than cereal grains are

separated. This process is achieved through rotation of the sieve in the with the same velocity as

the first sieving basket.



49

Average Sieving Surface Area Calculation

Unlike alternative one, the total surface of the sieve is the same since the design consists two

rotary sieves though with different orifice sizes.

Hence, the average sieving surface area =

= 5.075

Material Costing

Table 6b

materials Dimensions (mm) Prices ($)

Chanel iron 50 * 100 * 9 200 150.00

Angle Iron 60 x 40 x 12 000 120.00

1st Screen (sieve) 2 200 x 1 000 diameter -12 250.00

2nd Screen 1 200 x 1 000 diameter – 4 170.00

2mm stainless steel sheets 40 x 2 500 96.00

2 x Shaft 60 x 2 500 125.00

4 x bearings 40 65.00

Electric motor with a gearbox(3 x 400v/18kw)

750.00

Flat bar 12 x 30 x 5 30.00Blower 350.00

Bolts and nuts 12 x 60 x 81 10.00

Belt 920 22.00

Sub total 2 138.00

Labour 500.00

Tax @ 15% 75.00

Total 2 713.00

4.4.0 Concept Evaluation (Comparison of the two Alternatives)

In comparing the two possible evaluations, several parameters were considered. These included

the following:



50

Table 7

Parameters Current Machine 1st Alternative 2

nd Alternative

Capacity 900 – 1 300 kg/hr 1 200 – 1 800kg/hr 1 200 - 2000kg/hr

Capital Costs $2 300.00 $3 390.50 $2 713.00

Maintenance Cost Moderate Very high Moderate

Floor spaceconsumption

2.154

Average SievingSurface Area

4.66

4.4.1 Evaluation based on capacity

Fig 8: indicating the average capacity (kg/hr) of grain cleaning

The capacity of alternative number one has a lower range than that of alternative number two this

because of the resident time and the average sieving surface area which appears to be less in

alternative number one, illustrated in Fig 8.

4.4.3 Evaluation based on Capital Cost

Alternative design number one have high capital cost than alternative design number two this is

because of the shaker that requires an extra electric motor to move the centrifugal shaft for

shaking to occur.

0

500

1000

1500

2000

2500

current machine alternative no. 1 alternative no. 2

Average Capacity (kg/hr)

Average Capacity (kg/hr)



51

4.4.4 Evaluation based on Maintenance Cost

The maintenance cost of alternative number one is almost twice than of alternative number two.

The main route of having a high maintenance cost in alternative one is because the design

consists of a complex mechanism system that needs regular inspections, for example check of

loose bolts and belt. The machine is not easy to dismantle and it is labour intensive in terms of

dismantling.

4.4.5 Floor Space Consumption

Alternative design number two occupies greater floor space then of alternative number one this is

because of its structural arrangements of parts, i.e. the shaker is supposed to overlap the

oscillating/rotating sieve.

4.5.0 Detailed Design

4.5.1 Dimensions of the machine

The machine dimensions were determined bearing in mind the space available on the floor and

height of the small plant. Food Incorporated‟s plant total height is 4m, and the available area for

the machine installation is 2.2. The machine height is 2,4m, width 1,0m and length is 1,65m.

4.5.2 Machine parts

Electric motor – electric motor on the design consists of a gearbox to promote speed

variations at different feed rates. The AC electric motor of the design has a service factor

of 1.15, a power of 2 hp and maximum RPM of 3 600.

Shaft – the design consists of two shafts with a length of 2.2 meters and a diameter of

35mm (which was determined through bending moments and torque shown in the next

sections). The shafts are in connection by means of chain running on sprocket pulleys to

avoid slipping and to maintain a constant rotation between the shafts. The shafts were

made of mild steel with a mass destiny of ⁄ (Khurmi, 2005).



52

Blower – the design consists of a blower responsible in blowing off dust, weevils and any

other material that is light.

Stainless Frustum Sieve – the sieves of the machine are made from stainless with a

thickness of 2mm. The design contains two sieves with different orifice diameter; with

the top sieve having an orifice diameter of 12mm while the bottom sieve, 3mm. Sieve

metal plates of a length by width of 2000 by 1000 mm were used. The 2000mm length

side was winded into a frustum producing diameters 600mm by 400mm.

The reason for using stainless was that it does not react with the product and at the same

it does not react with any metal to cause rusting as in iron which reacts with water.

Sieve Frame – the sieve frame was made up of mild steel plates. It was made in way to

allow an ease in sieve exchange and firmly hold the sieve during rotation.

4.5.3: Calculating the torque of the shaft

When the shaft is subjected to a twisting moment (or torque) only, then the diameter of the shaft

may be obtained by using the torsion equation (Khurmi, 2005)

which can then reach this by substitution of J equation (5):

Where

Hence,

4.5.4 Calculating the forces acting on the shaft:

The weight of a 1 meter frustum sieve with a thickness of 2mm made up of stainless with 12 mm

orifice was determined by:



53

From chapter two, stainless steel has a mass density of 7.80g/ . Therefore calculating using

the volume:

Mass = volume ( x mass density (g/ )

= 1 563.381 x 7.80

= 12 194.3718g

= 12.194kg

The mass of the stainless = 12.194kg which is equivalent to 121.94Netwons (N), (taking g =

10)

Considering the weight of the frame which was supposed to hold the frustum had a mass of 8kg

which is equivalent to 80N. Therefore the total load acting on the shaft in respect of the sieve and

the frame was 201.94N but this load was not evenly distributed since at one side of the frustum

sieve has a greater diameter than the other. Hence considering a diameter ratio to determine load

distribution: (mm)

Getting the total ratio: = 2 + 3

= 5Therefore distribution of weight at the ends can be considered: ⁄ ⁄ ………………… (ii)

Considering that the frustum holds 15kg (150N) at any given static time and assuming that the

load is uniformly distributed over the shaft therefore:



54

Fig. 9: Analysis of the Shaft under Load.

Resolving moments of inertia shown in Fig 9 – load diagram:

Weight distribution of the frustum was developed from the ratio (i) above:



55

Weight at the 400mm: ⁄

Weight at the 600mm:

⁄

Hence,

Therefore reaction forces and acting on the shaft are 120.48N and 169.69N respectively.

4.5.5 Calculation of the shaft diameter

To determine the diameter of the shaft a formula of equivalent bending moments was used(khurmi, 2005).

[ √ ]

Table 8 Recommended values for K m and K t ., source

Nature of load

1) Stationary shaft

i) Gradually applied loadii) Suddenly applied load

1.01.5 to 2.0

1.01.5 to 2.0

2)

Rotating shafti. Gradually applied orsteady load

ii. Suddenly applied loadwith minor shocks only.

iii. Suddenly applied loadwith heavy shocks

1.5

1.5 to 2.0

2.0 to 3.0

1.0

1.5 to 2.0

1.5 to 3.0



56

And also,

Where

Bending stress (tensile or compressive) induced due to bending moment.

Substituting equation (i) and (10) into (9), hence: * √ +

* +

Where and are given in table 8 and in this particular case and , M is

the highest resultant bending moment (B.M.) shown in Fig. 9 on the moment diagram (N-m). In

this case; and (for En 8 mild steel), hence:

* +

Therefore the required shaft diameter size to with all of these forces is 33.141 mm but in this

design a diameter of 35 mm was adopted.

Now from equation 3, the torque can be calculated by substituting d with the adopted shaft

diameter:



57

, hence the required torque for the shaft was . But since the design consists

of two shafts, therefore it means 9.6487 is the amount of torque found in each

shaft assuming that the loads any give time are at equilibrium.

4.5.6 Calculation of the Maximum Revolutions per minute (rpm) that could be attained

under load

Making RPM the subject of formula:

Data from the type of electric motor required on the design then,

Power =3HP, service factor = 1.15 and (from section 4.5.5)

Hence under load the maximum possible speed is 150.3 rpm.

4.5.7 Calculation of Power required Under Load

Where P = Power (watts)



58

N = revolutions per minute (rpm)

Therefore the maximum power required to sustain the shafts‟ load is 15.18Kw at a speed of 150.3 rpm.

4.5.7 Cost Evaluation

The cost evaluation of the design is represented in table 6b.



59

Chapter 5



60

5.0 CALCULATION AND DISCUSSION

5.1 Calculation of Speed required for Efficient Cleaning

Table 9: Details of the existing rotating cleaning

Capacity (kg/hr) RPM HP Feed Rate(kg/min)

Cylinder size(diameter xlength) mm

1100 14.2 1.5 18 400 x 1000

The existing machine achieves maximum cleaning efficiency of 94.3% grain cleaning process

(that is the removal of dust and weevils) when the oscillating sieve is rotating at a speed of 14.2

rpm. Considering the design‟s electric motor (2HP), it is directly proportional to the related

output (rpm) of the existing machine, therefore to determine the speed at which cleaning process

is most efficient:

Hence by simple proportion of HPs in relation to speed,

Therefore to achieve maximum de-weevil and cleaning of grains in the design a speed of 18.9

rpm is required.

5.2 Calculating the required power to sustain this speed under a load.

Adopting the equation 9 in section 4.5.6:



61

Where

, and

The required power consumption of the design theoretically agrees with the need. Considering

electric rates issued in Zimbabwe by Z.E.S.A (Zimbabwe Electricity Supply Authority), its total

rating in summer including customer charge, distribution service and electricity service is

$0.4266 kWh, Therefore for the design to suit Food Incorporated‟s side of gain this means:

, where (9) represents the working hours per day and (31) number of days in a month.

Considering that at present, three people are involved in the manual cleaning of the maize grain

while the design machine only requires one person to hang and remove the sack at the grain

discharge outlet. Each worker receives a salary of $200.00 therefore eliminating two them the

resultant profit of company prior to machine existence is $180.98.

5.3 Calculating Capacity of the design

Assuming that the shaft of the machines is at the same angel.

If the feed rate of the existing machine is at 18kg/min, therefore to obtain the capacity of the

machine at any given time several factors need to be considered. Angle at which flow is going

through, for example in the design when the shaft is at horizontal, the frustum sieve creates its

own angel of (section 4.2.1) which can influence rate of flow.

Using simple proportion and the assumption,



62

Where x is an approximate feed rate of the design machine, hence:

Multiplying the feed rate by 60mins to get the capacity per hour,

Further multiplying the capacity by 9hours (normal working hours per day),

Therefore:

Applying an error of , hence



63

Chapter 6



64

6.0 CONCLUSION AND RECOMMENDATIONS

The set objective of increasing the machine‟s capacity was theoretically attained and at same

time fulfilling the set objective of increasing Food Incorporated‟s production capacity from 6

tonnes per to more than 10 tonnes per day.

The cleaning efficiency as an set objective was unmeasurable since the prototype is still in

progress. The available spacing in the plant is sufficient for installation of the machine and

creating a well safe environment for operation.

The time to submit the project did not give any room for prototype complete therefore results had

to be calculated. The University‟s Food Department should consider the strenuous of coming up

with a detailed project when students are on attachment by increasing time.



65

Bibliography

1. Harrison (1922), Prolegomean to the study of Greek religion, 3rd Edition, Intermediate

Technology Publications.

2. M.W. Thompson (1991), The Rise of the Castle, Cambridge University Press.

3. Jindal U.C (2010), Machine Design, Pearson Education India.

4. Joseph Edward Shingky; Charles R Mischke and Thomas Hunter Broom (2004), Standard

Handbook of Machine, McGraw-Hill

5. Classen. D Arnason, J. T Serratos, J. A Laubert and Philogene B. J. R (1990); Correlation to

phenol acid content of maize to resistance to zeamais, maize weevil; Journal of Chemical

Ecology.

6. Perez-Mendoza.J (1999), Survey of insecticides resistance in Mexican populations of

maize; Journal of Stored Product Research.

7. Merrian. S (1998), Qualitative Research and Case Studies Application in Edu; Jossey –

Bass Publishers, Sam Francisco

8.

R. S. Khurmi and J. K. Gupta (2005), Machine Design, Erasia Publishing House (PVT.)

LTD

9. Donald G. Fink and H. Wayne Beauty (1978); Standards Handbook for Electrical

Engineering; Eleventa Ed; McGraw-Hill, New York.

10. Edwin J. Houston and Aurthur Kennelly (1902); Recent Types of Dynamo-Electric

Machinery; copyright American Technical Book Co.; Published by P. F. Collier and Sons,

New York

11. Carl Branan (2005); Rules of Thumb for Chemical Engineer’s, Gulf Professional

Publishing.

12. Bollen M. H. J (1999); Understanding Poor Quality Problems, Voltage sags and

Interruption; Piscatary N.J. Wiley Press.

13. Hertz. G (2007); The sage Handbook Of Qualitative Research Methodology; Denzin N

K; Lincoln Y. S.



66

14. Blanchard, Benjamin. S. (1992); Logistic Engineering and Management, 4th Edition;

Prentice-Hall Inc; Englewood Cliffa; New Jersey

Final Hit 300. Batsie

Documents

Transcript of Final Hit 300. Batsie