0

DESIGN & FABRICATION OF A MANUALLY OPERATED CARROT

WASHING MACHINE FOR SMALL SCALE FARMERS

A DISSERTATION SUBMITTED TO THE DEPARTMENT OF

AGRICULTURAL ENGINEERING

SCHOOL OF ENGINEERING SCIENCES

UNIVERSITY OF GHANA, LEGON

IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE AWARD

OF BACHELOR OF SCIENCE DEGREE IN AGRICULTURAL ENGINEERING

BY

KINGSFORD KORANTENG

(10399395)

AGRICULTURAL ENGINEERING DEPARTMENT

SCHOOL OF ENGINEERING SCIENCES

UNIVERSITY OF GHANA

LEGON

MAY, 2016

i

DESIGN & FABRICATION OF A MANUALLY OPERATED CARROT

WASHING MACHINE FOR SMALL SCALE FARMERS

A DISSERTATION SUBMITTED TO THE DEPARTMENT OF

AGRICULTURAL ENGINEERING

SCHOOL OF ENGINEERING SCIENCES

UNIVERSITY OF GHANA, LEGON

IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE AWARD

OF BACHELOR OF SCIENCE DEGREE IN AGRICULTURAL ENGINEERING

BY

KINGSFORD KORANTENG

(10399395)

AGRICULTURAL ENGINEERING DEPARTMENT

SCHOOL OF ENGINEERING SCIENCES

UNIVERSITY OF GHANA

LEGON

MAY, 2016

i

DECLARATION

I, hereby declare, that this work submitted to the school of Engineering sciences, UG, legon, with

the exception of references of other researchers which have been duly acknowledged, is the result

of my own research and that this project has never been presented anywhere for a degree.

MR. KINGSFORD KORANTENG ........................... ........................

(STUDENT) SIGNATURE DATE

DR. MALCOLM .N. JOSIAH ……..................... ..........................

(SUPERVISOR) SIGNATURE DATE

DR. S. ABENNEY MICKSON ........................ ........................

(HEAD OF DEPARTMENT) SIGNATURE DATE

ii

DEDICATION

This dissertation is dedicated to my wonderful parents, Nana Yaw Koranteng and Magaret Akoto

Konadu for raising me to be the person I am today and also to my lovely siblings Priscilla

Koranteng and Patrick Koranteng, for support, inspiration and love throughout my education.

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ACKNOWLEDGEMENT

The best of my thanks and appreciation goes to the Almighty God for His grace, strength,

protection and health to witness the end of this work. My heartfelt gratitude goes to my supervisor

Dr. Malcolm N. Josiah, for his untiring assistance, direction, comments, encouragement,

continuous guidance and supportive ideas.

I would like to express my heartfelt gratitude to all the lecturers in the Agricultural Engineering

department for their knowledge imparted to me and also a big thanks to the workshop manager,

Mr. Richard Nudekor for his technical advice and useful suggestions at every stage of the work.

To my entire family, especially my father, Nana Yaw Koranteng and mother, Magaret Akoto

Konadu and lastly to my lovely siblings, Priscilla Koranteng and Patrick Koranteng for their moral,

spiritual and material support. God richly bless you.

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ABSTRACT

Carrots after harvesting from the field need to be pre-cleaned of soil and other foreign particles

before processing or transporting to the market. Currently, farmers/traders in Ghana use the

traditional method in which carrots are washed by hand. A carrot washing machine was developed

to give the best solution to this problem. The carrot washing machine consist of wood drum made

of wood planks and two shafts (hollow shaft and solid shaft), and a center pipe made of aluminum

with holes drilled on it for water spraying. The carrot washing machine was designed to use either

the immersion and non-immersion type of wash. The carrot washing machine was put to test

against two labourers in the agricultural field and the machine proved to be time efficient. The

appropriate rotation of the drum was found to be between 12 to 13 rpm. Performance trial on the

machine shown that the average washing efficiency is approximately 94.3%.

Keywords: Immersion, Non-immersion, Carrot etc.

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Contents page

DECLARATION.......................................................................................................................................... i

DEDICATION............................................................................................................................................. ii

ACKNOWLEDGEMENT ......................................................................................................................... iii

ABSTRACT ................................................................................................................................................ iv

LIST OF FIGURES .................................................................................................................................. vii

LIST OF TABLES ................................................................................................................................... viii

CHAPTER 1 ................................................................................................................................................ 1

1.0 INTRODUCTION ................................................................................................................................. 1

1.1 Washing ........................................................................................................................................... 2

1.2 Problem statement ................................................................................................................................ 3

1.3 Significance of the study ....................................................................................................................... 4

1.4 Aims of the study ................................................................................................................................... 4

1.5 Objectives of the study .......................................................................................................................... 4

CHAPTER 2 ................................................................................................................................................ 5

2.0 LITERATURE REVIEW .................................................................................................................... 5

2.1 Immersion wash system ........................................................................................................................ 5

2.2 Non-immersion system ......................................................................................................................... 6

2.2.1 Commercial Washer ...................................................................................................................... 6

2.2.2 Small Scale Washer ........................................................................................................................ 7

2.2.3 Manually Operated Washer .......................................................................................................... 8

2.2.4 Wooden drum ................................................................................................................................. 9

CHAPTER 3 .............................................................................................................................................. 10

3.0 MATERIALS & METHODOLOGY ................................................................................................ 10

3.1 Materials selection .............................................................................................................................. 10

3.2 Cost Analysis ....................................................................................................................................... 11

3.2.1 Material Cost Estimation ............................................................................................................ 11

3.2.1.1 Material for Fabrication ....................................................................................................... 11

3.2.1.2 Standard Purchased Parts .................................................................................................... 11

3.2.2 Machining Cost Estimation ......................................................................................................... 11

3.2.3 Calculation for Material Cost ..................................................................................................... 11

3.3 Design consideration ........................................................................................................................... 13

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3.4 Carrot ................................................................................................................................................... 13

3.5 Description of the machine ................................................................................................................. 14

3.6 Main components ................................................................................................................................ 16

3.6.1 Washing drum .............................................................................................................................. 16

3.6.2 Main frame ................................................................................................................................... 18

3.6.4 Shaft .............................................................................................................................................. 20

3.7 The Prototype ...................................................................................................................................... 22

3.7.1 Principle of operation of the machine ........................................................................................ 22

3.8 Design calculation & mathematical formulas................................................................................... 23

3.8.1 The shaft design calculations ...................................................................................................... 24

3.9 Design of Bearing ................................................................................................................................ 26

CHAPTER 4 .............................................................................................................................................. 27

4.0 RESULTS & DISCUSIONS ............................................................................................................... 27

4.1 Testing for efficiency ........................................................................................................................... 28

4.2 Effect of Drum speed on Washing Efficiency ................................................................................... 30

5.1 CONCLUSION ................................................................................................................................... 31

5.2 RECOMMENDATIONS .................................................................................................................... 31

REFERENCES .......................................................................................................................................... 32

vii

LIST OF FIGURES

Figure page

Figure 2.1 Traditional method of washing carrots..........................................................................3

Figure 3.1 Small scale carrot washer..............................................................................................8

Figure 6.1 Isometric view of the carrot washing machine............................................................15

Figure 6.2 Orthographic view of the carrot washing machine......................................................16

Figure 6.3 Wash drum.................................................................................................................. 17

Figure 6.3.1 Orthographic view of the washing drum..................................................................17

Figure 6.4 Metal disc................................................................................................................... 17

Figure 6.5 Fabricated frame..........................................................................................................18

Figure 6.5.1 Orthographic view of the frame................................................................................18

Figure 6.6 Water trough............................................................................................................... 19

Figure 6.6.1 orthographic view of the water trough.....................................................................19

Figure 6.7 Hollow shaft................................................................................................................20

Figure 6.7.1 Orthographic view of the hollow shaft.....................................................................20

Figure 6.8 Solid shaft....................................................................................................................20

Figure 6.8.1 Orthographic view of the solid shaft........................................................................21

Figure 6.9 Fabricated carrot washing machine.............................................................................22

Figure 7.1 Dimensions for the shaft design..................................................................................24

Figure 7.2 Free body diagram of a section of the drum and the shaft..........................................24

Figure 9.1 Graph of time against quantity....................................................................................26

Figure 9.2 determination of the initial weight of the carrots…...………….……………………29

viii

LIST OF TABLES

Table Page

Table 3.1 Summary of materials selected.....................................................................................10

Table 3.2 Summary of the cost of components.............................................................................12

Table 3.3 Summary of the physical properties of carrot...............................................................13

Table 4.1 Time taken by labourers and the machine to wash carrots...........................................27

Table 4.2 Summary of washing results.........................................................................................29

Table 4.3 Effect of drum speed on washing efficiency.................................................................30

1

CHAPTER 1

1.0 INTRODUCTION

Processing is very important in transforming raw harvested agricultural products into valuable

products in the market. Processing of agricultural products is done to reduce wastage, raises the

quality of the product, enhance food security etc. According to Onwuala et al. (2006), process of

agricultural product increases the yield from a raw farm product by either causing an increase in

the amount of finish product, the number of finished product or both and to improve the total

economic value of a product. For an agricultural product to be processed, it has to undergo various

unit operations such as cleaning, sorting, grading, size reduction etc. Cleaning of agricultural

product is one of the most important unit operation in processing.

This project seek to focus on the cleaning operation of harvested carrot. Carrot (Daucus carota) is

a vegetable that belongs to the Umbelliferea (Apiaceae) family (Manosa, 2011). It is cultivated in

many countries throughout the world such as the Americans, Europe, south-west Asia and Africa

(Rubatzky et al., 1999) and this is mainly due to the fact that carrots have high nutritional value

(Al-Harbi et al., 1997; Munro & Small, 1997). The edible roots are nutritious and contain water,

protein, ash, vitamins and mineral (Norman, 1992).Vegetables (carrots) are the major sources of

vitamins and minerals in the human diet (Pamplona, 2008). There is no substitute to the role

vegetables (carrots) play in our meals (Drechel et al., 2010).

Carrots after being harvested from the field may have soil particles and other foreign materials

attached to them hence there is the need to remove these materials before processing. The removal

is accomplished by dry or wet brushes, rinsing or immersion in tap water, hot water or solutions

2

containing one of a number of cleaning or sanitizing agents, using equipment designed for the

commodity (Asamoah, 2014; Fallik, 2004).

1.1 Washing

Washing is a process of cleaning and sanitization of produced by dipping, rinsing, rubbing or

scrabbling. It plays an important role in processing of crop produce by adding value and also

improving on the quality and safety of the produce in post-harvest operation. In order to effectively

weigh, sort, grade harvested carrots there is the need to wash them (Oladip et al., 2006) in clean

water to remove dirt and other debris and surface contaminants (Asamoah, 2013). There are

different principles used in washing of agricultural product which include soaking in still water,

moving water over the product, spraying water on product, using rotary drum cleaner, brush

washing and shuffle or shaker washer (Henderson & Perry, 1980; Diamante, 2007). Different

washing machines have been developed for washing some Agricultural products such as potato,

melon seeds, cassava root and coffee (Oladip et al., 2014). Basically there are two main categories

of washing used by the industries. They are the immersion wash which employs the principles of

dumping, submerging or floating of the produce in water and the non-immersion wash which is

done by spraying or rinsing produced in a basket, wash bed drum or barrel washer (Henderson &

Perry, 1980). The effectiveness of washing is determined by the availability of water as the

cleaning liquid (Oladip et. al., 2014). This project is design to inculcate both type of wash, giving

the user options to switch to which ever method he/she prefers.

Ten (10) carrot farms in Accra were visited and a case study conducted on their harvest wash. The

method used by these farms were labor intensive and time consuming. This project seeks to find a

possible solution by designing a washing machine for carrots to alleviate the stress traders/farmers

go through to have their carrot wash.

3

1.2 Problem statement

In Ghana, carrot is one of the exotic vegetable which has high demand and value in urban centers

and it is a potential export crop (MOFA, 2002). Carrots after harvesting from the field needs to be

cleaned before transporting to the market. The act of cleaning harvested carrot is not normally

done by small scale farmers in Ghana. This is mainly due to the absence of appropriate mechanized

ways of cleaning the harvested root crops.

Most farmers/traders in Ghana normally use a traditional method to clean their harvested carrots

in which the carrots are washed manually using metal sponge, water and some preservative such

as potassium permanganate or salt.

A case study conducted by Asamoah (2014) at the Asante Mampong municipality and he showed

that processing of carrots by traders was either by washing and scrapping or washing only. He

finds out that in all, 84% washed carrots using metal sponge, 14% used brush to scrape whiles 2%

wash with bare hands. This is as a result of the expensive nature of washers. These methods, aside

the fact that they are laborious and time consuming, the process tends to contaminate the carrots

especially use of metal sponge. It is with this reasons we have looked into a mechanized way of

designing a low cost washing machine for carrots.

a) b)

Figure 2.1 Traditional method of washing carrots

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1.3 Significance of the study

The proposed design will help farmers to:

Reduce the time used to wash harvested carrots.

Reduce the cost of labor employed to wash harvested carrots

Reduce the risk of contaminating harvested carrots with stones, metal sponge etc. during

washing.

1.4 Aims of the study

The design aims at:

• Developing a low cost manually operated carrot washing machine which will effectively

and efficiently wash carrots with reduce time and labor requirement.

1.5 Objectives of the study

The study was conducted to peruse the following objectives:

To design and fabricate a carrot machine suitable for small scale farmers

To compare the time required by the machine to wash crop effectively as against the

traditional methods.

To determine the efficiency of the washing machine for carrots.

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CHAPTER 2

2.0 LITERATURE REVIEW

Carrots are very important to mankind due to its high nutritional value. They are consumed fresh

or cooked either alone or with other vegetable (Asamoah, 2012).In some cases, fresh carrots are

grated and use in salads and the tender root are pickled (Sharma et al., 2006). Bunyaphlanan (1973)

worked on the mechanical properties of carrots. In order to process harvested carrots, it is a

necessity to wash them. Most farmers/traders use the traditional method to wash harvested carrots

from the farm.

In other to improve on the traditional methods used by farmers in processing harvested carrots,

various researchers have looked into ways of designing machines which could manually or

automatically wash harvested carrots with minimum constraints. Oladip et al. (2014) worked on a

continuous processing multi-crop washing machine for seeds. The machine is an improvement on

existing batch melon washer developed by the National Centre for Agricultural Mechanization,

NCAM. Kenghe et al. (2015) worked on a mechanical fruit washer. Washing of produce can be

carried out by immersion or non-immersion by spray/showers or by combination of the two

process. (Kenghe et al., 2015)

2.1 Immersion wash system

This system is an effective and simple method of washing root crops (carrots). It involves

immersing the crop directly into water. It is normally preferred for processes requiring extended

soaking time because of the type of contaminate to be removed or the shape of the part. Le–Bohec

(1993) stated that conventional washing methods for carrots, consisting of rotary washing systems

6

in which carrots are not immersed, tend to damage carrots. The root crop (carrot) washing machine

for immersion type of washing consist of a perforated washing drum with perforation or horizontal

hole mounted about a horizontal axis. It has a water trough mounted beneath the washing drum for

partial immersion of the drum. This type of system makes use of no sprayers hence makes it simple

and less expensive.

2.2 Non-immersion system

This system involves spraying of the produce with water. It comprises of a washing drum mounted

about a substantially horizontal axis. The washing drum is of perforated material or of slatted

construction and is usually driven by drive rollers or pinion gears. Water is applied to the produces

in the drum using spray nozzles. The water is sprayed under high pressure onto the produce in the

drum. The shape and arrangement of the nozzles and the spray force have a major influence on the

degree of cleaning that is provided in this system. The efficiency of a spray of water for washing

depends upon the pressure of the water, its volume, and also the distance of the spray nozzle from

the vegetable to be washed (Diamante, 2007). According to Antony (1987) a product that is heavily

contaminated with soil should be thoroughly soaked in water to loosen the soil before passing it

under sprays. Jayashree and Viswanathan (2010) reported that the bruise index of produced

increased with increase in operating drum speed for washing of ginger rhizomes.

2.2.1 Commercial Washer

The most common proposed design by researchers is the non-immersion rotary washing type

system. Mandenshall et al. (1988) discussed several ways in which vegetable can be washed with

7

principles similar to common washing machines such as an automobile washer, household dish

washers etc. Most commercial washers are designed based on the rotary drum system.

Stark et al. (2000) worked on a commercial carrot washer whose cylindrical washer had a length

of 5m (16.4ft) and a diameter of 0.9m (2.95ft). The design had a full length spray bar to supply

water in the drum. The design make use of 4 rollers with 600kg (1320Ib) capacity each and operate

at a speed of 12 to 13 rpm by means of 7.5KW (10HP) electric motor.

This commercial washer, although very useful, is cumbersome and expensive which makes it

difficult for most farmers to purchase and unsuitable for small scale farmers to use due to their

large capacity.

2.2.2 Small Scale Washer

In order to develop a simple and affordable washer, Moss et al. (2012) developed a low mechanical

carrot washer which has a cylindrical barrel made of a high density polyethylene (HDPE) unlike

the design by Ravdeep et al. (2014) and our proposed design which is made of wood planks. The

cylindrical barrel has a length of 0.86m and a diameter of 0.58m. Slots are provided along the side

of the barrel to provide drainage.

The barrel has it outside wrapped with a rubber belt which is 0.46m wide and 1.85m long to provide

friction between the barrel and the drive rollers. Within the barrel is a center pipe for spraying

water unto the sample (Mandenshall et al., 1988). A V–belt transfer’s power from the hydraulic

motor to the pulley on one of the roller and the roller is powered by means of 0.75kw electric

motor (Ravdeep et al., 2014).

8

The design, construction and operation of the mechanical washer by Moss et al. (2012) pose

inherent hazards of entanglement of bodily parts, slippage, electrical shocks etc. For instance, the

design of the linkage between the barrel and the roller pose risk of slippage and, also, there is the

possibility of the barrel creeping off the roller as a result of no guide provided to support the barrel.

2.2.3 Manually Operated Washer

In order to ensure simplicity of design and to provide convenience in using the mechanical washer

at places where there is no electricity, Ambrose & Annamalai (2013) designed a manually operated

washer for carrots.

The washer is made of a stainless steel washing drum of length 470mm and a diameter of 390mm,

a detopper and a center shaft with fine holes for spraying water. The drum has a chute of 20 mm

length and a slope of 84° for feeding the vegetables. The washing drum was provided with different

matting namely 5 mm thickness rubber, 1.5 and 3.5 mm thickness plastic, respectively for effective

cleaning of the vegetables. Le–Bohec (1993) tested designs involving carpeting as a way to reduce

carrot breakage and improve the storage characteristics of carrots.

Figure 3.1

Figure 3.1 small scale carrot washer by Moss et al. (2012)

9

The design by Ambrose & Annamalai (2013) could only accommodate samples up to 10kg and

also the material (stainless steel) selected for the washing drum will increase the cost if larger

capacity is to be constructed, which will make most small scale farmers unable to purchase

2.2.4 Wooden drum

The design using wooden drum as the washing system is seen as the appropriate design used by

indigenous farmers due to the fact that wood is a locally available material and it is less expensive.

The wooden washer drums are made of wooden planks with even horizontal spacing between them

for the passage of contaminated water all along its circumference. A hollow shaft or pipe runs

along the center of the drum. This shaft/pipe has holes on it for sprinkling pressurized water inside

the drum (Ravdeep et al., 2014). The shaft is mounted on bearings on both sides and rotates with

the drum. The drum is rotated by hand or means of a high torque hydraulic motor. A V–belt

transfers power from hydraulic motor to a pulley on a roller (Moss et al., 2012). Water is pump

into the hollow shaft through a pipe or by gravity.

10

CHAPTER 3

3.0 MATERIALS & METHODOLOGY

3.1 Materials selection

The cost, availability, properties and weight of the materials were some of the major factors

considered for the selection of material for each of the machine component. Table 3.1 shows the

summary of the material selected for each machine component.

Table 3.1 summary of the materials selected

MACHINE COMPONENT

MATERIAL USED SIZE/TYPE QUANTITY

REASONS FOR SELECTING THE MATERIAL

Wash drum Wood plank (red wood) 6500mm×50mm×25mm

25 Readily available Low cost

Steel metal sheet 5mm thickness

1 Readily available

Counter sunk screw & nut

6mm 50 Low cost

washer NA 50 Readily available Frame mild steel square pipe 1¼ inch 2ft. Good tensile

properties Water trough Galvanized steel sheet 1.5mm

thickness 1 Excellent corrosion

resistance Spraying

system Aluminium pipe Ø 10mm 1 Excellent corrosion

resistance Garden hose Rubber 1 ft. 1 Low cost Pipe to hose

connector Aluminium 80 mm 1 Low cost

Bearing NA UCP 203 2 Resist corrosive environment

Paddle Steel 200mm 1 Readily available

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3.2 Cost Analysis

3.2.1 Material Cost Estimation

It is the overall amount needed to acquire the raw material which has to be processed or fabricated

to desire size and functioning of the components. These materials can be divided into two

categories.

3.2.1.1 Material for Fabrication

Here, the material in obtained in raw condition and is manufactured or processed to finished size

for proper functioning of the component.

3.2.1.2 Standard Purchased Parts

These are the materials that are readily available in the market and do not need to be fabricated.

Examples are the pillow ball bearing, bolts & nuts

3.2.2 Machining Cost Estimation

This cost estimation is an attempt to careful forecast the total expenses that may include

manufacturing, labor, materials etc.

3.2.3 Calculation for Material Cost

The general procedure for calculation of material cost estimation is: After designing a project a

bill of material is prepared which is divided into two categories.

I. Fabricated components.

II. Standard purchased components.

12

The cost of the items used in the fabrication of the design is based on 2016 Ghana price.

Components generally available from local hardware or retailers. Table 2. Shows a summary of

the cost of the component parts of the machine.

TOTAL: GH¢ 470.10

ITEMS QUANTITY COST PER-UNIT (GH¢) TOTAL COST

Pillow ball bearing

2 30.00 60.00

Bolts & nuts (12mm)

4 1.50 6.00

Bolt & nut (6 mm)

4 0.80 3.20

Paddle

1 15.00 15.00

Shaft

2 20.00 40.00

Mild steel square

pipe 1¼ inch 2 feet 30.00 60.00

Screws with nut

50 0.30 5.10

Pipe to hose

connector

1 5.00 5.00

Door handle

Ι 2.00 2.00

Galvanized steel

1

2sheet

90 45.00

Garden hose

1 10.00 10.00

Clips

2 1.00 2.00

Transportation

50.00

Paint

2 10.00 20.00

Workmanship

1 100.00 100.00

Wood planks

25 1.80 45.00

hinge 2 0.90 1.80

Table 3.2 Summary of the cost of component parts

13

3.3 Design consideration

A variety of factors were considered in the design process of the carrot washing machine, some of

which are:

1. The relevant physical and mechanical properties of carrots were determined and obtained

from literature.

2. The machine was design to be relatively cheap and be within the buying capacity of small

scale farmers.

3. The material used for the fabrication are readily available materials and are locally sourced.

4. The wood selected for the construction of the drum is of a variety which can withstand

water

5. The maintenance and repair of the machine can be carried out with ease.

6. The dimensions, speed, capacity and efficiency of the machine were considered

3.4 Carrot

The physical and mechanical properties of carrots were obtained from literature. Table 3.3 shows

the physical properties of carrot. (Ambrose & Annamalai, 2013).

Table 3.3 summary of the physical properties of carrot

14

3.5 Description of the machine

The component parts of the carrot washing machine are the drum, water trough, frame, bearing,

spraying system (pipe with holes), paddle, shaft, bolts & nuts, screws and circular metal disc with

a flange. One unique feature about this design is that it provides the user an option to choose

whether to use immersion or non-immersion wash or both process.

The wash drum is made of wood planks of dimensions 650mm x 50mm x 25mm with an even

horizontal spacing of about 4mm to 8mm between them for the passage of contaminated water

and, also, running through the center of the drum is the water spraying system which provides

pressurized water onto the produced in the drum. The water trough is located beneath the drum for

partial immersion of the drum. In the case of the non-immersion, the pipe is used to sprinkle

pressurize water onto the produced. The pipe has small holes, running along it length, having

diameters ranging from 2mm to 3mm drilled on it for spraying. The holes are used in place of

nozzle to minimize the cost of design. For the immersion wash, the water trough which is beneath

the drum is used for the partial immersion of produced.

The system is design such that in both cases, excess water can be collected and re-used for other

purposes such as irrigation. The drum rotates freely on a shaft by means of a pillow block ball

bearings. Rotation of the drum is done, manually, by driving a stirring/paddle provided on one end

of the drum. The whole system is supported by the frame which is made of mild steel square pipes.

15

Figure 6.1 isometric view of the carrot washing machine

16

ORTHOGRAPHIC VIEW OF THE CARROT WASHING MACHINE

3.6 Main components

The carrot washing machine consist of four main components as follows: wash drum, main-

frame, water trough and shaft

3.6.1 Washing drum

The washing drum is made up of wood planks each having a dimension of 650mm x 50mm x

25mm. The wood planks are fastened onto a circular disc having a flange by means of a

countersunk screw. The rotation of the drum causes the carrots to move to and fro within the drum.

Figure 6.2

17

This further causes the carrots to rub against each other and also against the wood planks resulting

in effective washing.

Figure 6.3 wash drum

ORTHOGRAPHIC VIEW OF THE WASHING DRUM

Figure. 6.4 Metal disc

Figure 6.3 Figure 6.4

Figure 6.3.1

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3.6.2 Main frame

The main frame is the skeletal structure of the carrot washing machine on which all other

components are mounted. In this work, two factors were considered in the determination of the

material required for the frame, they are the weight and strength .A mild steel square pipe was

used to construct the frame. The frame is of trapezoidal shape.

ORTHGRAPHIC VIEW OF THE FRAME

Figure 6.5

Figure 6.5.1

Figure 6.5 fabricated frame

19

3.6.3 Water trough

The water trough is in the form of a semi-cylinder made of galvanized sheet of 1.5mm having a

diameter of 470mm and a length of 720mm. It serves the purpose of holding water for washing the

carrots in the drum and also serves as a channel through which contaminated water passes to the

outlet in the case of non-immersion wash. It is situated beneath the washing drum and it is fastened

onto the frame by means of bolts and nuts.

ORTHOGRAPHIC VIEW OF THE WATER TROUGH

Water trough

Figure 6.6

Figure 6.6.1

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3.6.4 Shaft

The design consists of two shafts (i.e. a hollow shaft and a solid shaft) which are welded to the

center of the metal disc on each end of the drum and are supported by bearing onto a frame. A

paddle is mounted onto the solid shaft and a pipe is passed through the hollow shaft to run through

the center of the drum.

ORTHGRAPHIC VIEW OF THE HOLLOW SHAFT

Figure 6.7 hollow shaft

Figure. 6.7.1

Figure 6.8 solid shaft

21

ORTHGRAPHIC VIEW OF THE SOLID SHAFT

Figure 6.8.1

22

3.7 The Prototype

The prototype was built and tested at the agricultural engineering workshop at University of

Ghana.

3.7.1 Principle of operation of the machine

The muddy samples are dumped gently into the wash drum through a door provided on the

circumference. A tap which is provided to regulate the spray of the water is opened to allow water

to be sprayed onto the carrot. In the case of the immersion type of wash, the trough provided

beneath the drum is filled with water to a reasonable quantity such that when samples are placed

in the drum they come into contact with the water in the trough. In both method, the drum is set to

rotate by manually rotating a paddle provided. The rotation of the drum which causes produce to

move to and fro within the drum and the water supply clean the carrots from soil and other foreign

materials

(A) (B)

Figure 6.9 fabricated carrot washing machine

23

3.8 Design calculation & mathematical formulas

Volume of the wash drum =πr2l …………………………………….eqn. (1)

The volume of the drum was calculated using eqn.1

=π× (0.40m) 2× (0.65m)

=0.326m3

Where l = length of the drum

r=radius of the drum

Volume of the trough = 𝟏

𝟐πr2l…………………………………………eqn. (2)

The capacity of the water trough is computed using eqn. 2

=1

2π× (0.25m) 2×0.75m

= 0.0736m3

Washing efficiency

Efficiency=𝑤𝑒𝑖𝑔ℎ𝑡 𝑏𝑒𝑓𝑜𝑟𝑒 𝑤𝑎𝑠ℎ𝑖𝑛𝑔

𝑤𝑒𝑖𝑔ℎ𝑡 𝑎𝑓𝑡𝑒𝑟 𝑤𝑎𝑠ℎ𝑖𝑛𝑔 × 100.......................................eqn. (3)

The washing efficiency of the machine is computed using equation 3.

24

3.8.1 The shaft design calculations

Assuming the wooden drum and the two metal disc has a load of (Wd) =100N and loaded with

carrots (Wc) of 120N. Hence the safe load acting on the shafts is W=P=Wd+Wc =220N .The shafts

are supported by two pillow ball bearing. Since the load will be shared equally by the drum, half

the section of the drum is considered for the calculation of the moment. The Figure 7.1 below

shows the shaft and its dimensions.

Figure. 7.2 (a) shows half the section of the drum and (b) shows the free body diagram and the

forces acting on it

Figure 7.1 dimensions for the shaft design

(A)

(B)

Figure 7.2 Free body diagram of the drum and the shaft

25

Assumptions are made for W1, W2, W3 and W4.

At B-E

• Moment = -P×BE+ [-W1× (CE+0.5BC) +-W2× (DE+0.5CD) +-W3×DE× (centroid of load

from E)]…………………………………………………………….eqn. (4)

AT F-G

• Moment = -W4 × (RF+0.5FG)………………………………….….eqn. (5)

The shaft which is made of mild steel is assumed to rotate at 12 rpm. The shaft here is subjected

to both bending moment and torsional stresses. The ultimate shear stress of a mild steel shaft

from design data is 265Mpa. The safe load is 220N (22Kg) but will be carried equally by both

shaft. The shaft of length 110mm (0.11m) is subjected to bending moment and torsion stresses.

The maximum torque (Mt) can be calculated using the following equation:

Torque = W × R, Khurmi and Gupta (1984)……………………………..eqn. (6)

Where W= force needed to cause drum to rotation (N)

R = radius of the paddle (m)

= 220N ×0.2m

= 44N-m

By compensation, then the maximum torque equal to 50N-m

Using maximum shear stress theory

D3= (16

𝑛𝜋𝑠𝑠√(𝐾𝑏𝑀𝑏)2 + (𝐾𝑡𝑀𝑡)2 Khurmi and Gupta (1984)………….eqn. (7)

D = Shaft diameter,

Ss = Allowable shear stress for steel= 40×106N/m

26

Kb= combine shock and fatigue factor applied to bending = 3

Kt = combine shock and fatigue factor applied to torsional = 3

Mb = Maximum bending moment (N-m),

Mt= Maximum torque (N-m). There are no forces acting on the shaft except the weight of the drum

and produced.

The diameter of shaft taken is 20 mm which is safe.

𝑃𝑜𝑤𝑒𝑟(𝑃) =2𝜋𝑁𝑇

60………………………………………………………eqn. (8)

P= power required (kW)

N=number revolution of the drum per seconds

T = Torque transmitted in N-m,

Power is calculated using equation 6.

𝑃𝑜𝑤𝑒𝑟(𝑃) =2×𝜋×(12)×44

60

= 0.060kw

3.9 Design of Bearing

Depending upon the nature of contact UCP 203 pillow ball bearing has been chosen.

27

CHAPTER 4

4.0 RESULTS & DISCUSIONS

Tests were conducted on the machine to ascertain its performance. The manually operated carrot

washing machine was put to test against two labourers in the agricultural fields at Weija. Both the

carrot washing machine and laborers were given some quantity of harvested carrots and the time

taken by each of them were recorded corresponding to the quantity of carrot washed by hand

(sponge and water) and for the machine The results were recorded and a graph of time as against

quantity is plotted as shown in figure 9.1

Table 4.1 Time taken by labourers and the machine to wash carrots

Number of

carrots

Time (seconds) taken to

wash samples by labourers

Average time

(seconds) taken by

the labourers

Time taken to wash

carrots by the

machine T1 T2

10 60 75 67.5 39

20 140 170 155 56

30 149 180 164.5 59

40 223 260 241.5 60

50 271 310 290.5 66

60 310 365 337.5 69

70 351 408 379.5 NA

80 384 440 412 NA

28

Figure 9.1 graph of time as against carrot quantity.

4.1 Testing for efficiency

The initial weight of the carrots were first determine before placed into the carrot washing machine

to be washed. This was done at the university of Ghana physic laboratory using an electronic

balance. The weight were again determine after washing with the prototype and the corresponding

efficiencies are tabulated as shown in table 4.2.

67.5

155 164.5

241.5

290.5

337.5

379.5

412

39

5659 60

6669

0

10

20

30

40

50

60

70

80

0

50

100

150

200

250

300

350

400

450

0 10 20 30 40 50 60 70 80 90

Tim

e ta

ken

to w

ash

sa

mp

les

by

th

e

mach

ine

(seco

nd

s

Tim

e ta

ken

to

wash

sam

ple

s b

y h

an

d

(seco

nd

s)

quantity of carrots

Graph of time vrs quantityTime taken by hand

Time taken by the machine

Figure 9.1

29

Number of carrots Weight before

washing(g)

Weight after

washing (g)

Washing efficiency

10 152 135 0.89

20 244 224 0.92

30 358 338 0.94

40 473 452 0.96

50 610 589 0.97

60 750 736 0.98

(A) (B)

Figure 9.2 determination of the initial weight of the carrots

Table 4.2 summary of weighing results

Samples of unwashed carrots Weighing samples using an

electronic balance

30

4.2 Effect of Drum speed on Washing Efficiency

The washing efficiency of the carrot washing machine were recorded by varying the drum speed

for 10rpm, 11rpm, 12rpm, 13rpm and 14rpm. It was observed that higher (97.4 %) efficiency was

recorded for 13 rpm and Lower efficiency (89.1%) was recorded for 10 rpm. It was also observed

that drum speed at 14rpm there were some bruises.

Revolution per minute (rpm) Efficiency (%)

10 89.1

11 96.8

12 97.4

13 98.4

Table 4.3 Effect of the drum speed on washing efficiency

31

CHAPTER 5

5.0 CONCLUSION AND RECOMMENDATIONS

5.1 CONCLUSION

From the graph in figure 9.1 the machine proved to be more time efficient as compared to the

traditional method of washing. The average efficiency of the machine was found to be 94.3%.

Increasing the speed of the drum beyond 13rpm resulted in an increase in bruises. An efficient

wash with minimal bruise index was achieved when the revolution per minute of the drum was

between 12 to 13rpm.

5.2 RECOMMENDATIONS

Despite the appreciable performance of the carrot washing machine in terms of machine efficiency

and time, I will recommend that:

1. The carrot washing machine should be motorized so that farmers who cannot rotate the

drum manually can use it.

2. The inside of the drum should be mated with an appropriate material to improve the

washing efficiency.

3. Farmers should use both the immersion and non-immersion during washing to conserve

water and also for effective wash.

32

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