Shelling of groundnut pods (Arachis hypegea) by hand is tedious, laborious and unhygienic with low efficiencies. As a result farmer get low income due to amount of broken kernels and a lot of time is lost in the tedious shelling operation. To overcome this problem, pertinent parameters that influence shelling efficiency of pedal operated groundnut decorticator were identified. Pedal operated decorticator were designed and fabricated with chain and sprocket of bicycle and aluminum spike tooth is used and evaluation was done in the department of Agricultural and Bio-Environmental Engineering Technology, Kwara State Polytechnic, Ilorin because it was affordable and locally fabricated. A rotary motion mechanism was employed to drive the decorticating drum while concave screen was fixed. The selection of the screen aperture was based on the size and shape of the groundnut seed. The factors considered in this project work were feed rate and operators characteristics (height, weight and knuckle lengths). The evaluation of machine was conducted while time was taken for each tests. The result of the pedal operated groundnut decorticator revealed that operator III has the maximum shelling efficiency of 65% was achieved at 9minutes, 16 seconds and breakage of 9% and throughput capacity of 15.3kg/hr. Operator II was the optimum shelling efficiency of 56% at 12 minutes 44 seconds and breakage of 8% and throughput capacity of 14kg/hr. Operator I has the minimum shelling efficiency of 47% at 11 minutes 44 seconds and breakage of 16% and throughput capacity of 15kg/hr. The total amount used for the fabrication of the pedal operated groundnut decorticator was totaled to Ninety-two Thousand and Seven Hundred Naira only (N92,700.00). The result of the fabricator implies that the characteristics of Operator III is recommended to farmers who shell for seed can now obtained more seed shelled with low breakage and will get more income.


Cover Page i

Title Page ii

Certification iii

Dedication iv

Acknowledgements v

Abstract vi

Table of Contents vii

List of Tables xi

List of Figures xii

List of Plates xiii


1.1 Background to the Study 1

1.2 Statement of the Problems 2

1.3 Objective of the Project 2

1.4 Justification of the Project 3

1.5 Scope of the Study 3


2.1 Physical Properties of Groundnut 4

2.1.1 Determination of Size 4

2.1.2 Determination of Coefficient of Friction 5

2.1.3 Determination of Moisture Content 5

2.1.4 Angle of Repose 6

2.1.5 Porosity 6

2.1.6 Surface Area 6

2.2 History of Groundnut in Nigeria 6

2.3 Agronomy of Groundnut 7

2.4 Post Harvest Losses of Groundnut Seeds 8

2.5 Economic Importance of Groundnut Seed 9

2.6 Factor Affecting Shelling Operation 11

2.6.1 Cylinder-Concave Clearance 11

2.6.2 Sieve Shake 12

2.7 Description of some Threshing Equipment 12

2.7.1 Maize Sheller 12

2.7.2 Maize Dehusker-cum Sheller: 13

2.7.3:    Hand Maize Sheller 13

2.7.4    Groundnut Striper 14

2.7.5:    Groundnut Thresher 15

2.7.6:    Groundnut Decorticator Manually Operated 16

2.7.7    Power Operated Groundnut Decorticator 17

2.7.8    Pedal Operated Thresher (Paddy Thresher): 18

2.8 Terminology Related to Thresher 18

2.8.1 Feed Rate 18

2.8.2 Clean Grain 19

2.8.3 Concave Clearance 19

2.8.4 Cleaning Efficiency 19

2.8.5 Threshing Efficiency 19

2.9     Review of Existing work 19


3.1 Physical Properties of Biological Materials 23

3.1.1 Sample Preparation 23

3.1.2 Determination of Size and Shape 24

3.1.3 Determination of Moisture Content 24

3.1.4 Determination of Mass, Volume and Density 25

3.1.5 Determination of Coefficient of Static Friction 25

3.1.6 Determination of Angle of Repose 25

3.2 Description of the Groundnut Pedal Operated Machine 26

3.3 Design Consideration 28

3.4 Design Calculation and Analysis 28

3.4.1 Design for Hopper 28

3.4.2. Design for Decorticating Unit 29

3.4.3 Design of Chain Drive 32 Determination of Chain Length between the Pedal and Idler Shaft 32 Determination of Chain Length Between the Idler Shaft and Decorticating Shaft 33 Determination of Chain Length Between the Idler Shaft and Blower Shaft 33

3.5 Material Selection 34

3.6 Fabrication Procedure and Assembly 34

3.6.1 Fabrication of Main Frame 34

3.6.2 Fabrication of Hopper 35

3.6.3 Fabrication of Bicycle Pedal and Chain Drive 35

3.6.4 Fabrication of Decorticating Drum 35

3.6.5 Decorticating Screen 35

3.6.6 Operator Seat 36

3.6.7 Aluminum Spike Tooth 36

3.7 Principle of Operation of the Machine 36

3.8 Cost Analysis 37

3.9 Performance Evaluation 38

3.9.1 Sourcing of Experimental Material 38

3.9.2 Sample Preparation 38

3.9.3 Experimental Procedure 38

3.9.4 Instrumentation Used for the Experiment 39

3.9.5 Design Layout 42

3.9.6 Output Parameter 42


4.0 Results And Discussion 45

4.1 Results 45

4.2. Discussion 46

4.2.1 Physical Properties of Groundnut Pods 46

4.2.2 Effect of Operator Parameter Threshing Efficiency 47


5.1 Conclusions 48

5.2 Recommendations 48

References 49

Appendix A 52

Appendix B 59


Table No                                  Description                                                                       Pages


Table 3.1: Sample Preparation 38

Table 4.1 Data Sheet for Physical Properties of Groundnut Pods 45

Table 4.2 Data Sheet for Output Parameters 45

Table 4.3 Data Sheet for Output 46

Table 4.4 Average Performance of Thresher 46


Figure No                                  Description                                                                       Pages

Figure 2.1: Maize Sheller 13

Figure 2.2: Hand Maize Sheller 14

Figure 2.3:  Groundnut Thresher 16

Figure 2.4: Manual Operated Groundnut Decorticator (Oscillating Type) 17

Figure  2.5 Power Operated Groundnut Decorticator 18


Plate No                                  Description                                                                       Pages

Plate 2.1: Groundnut Pod 9

Plate 3.1: Sample of Groundnut Seed 23

Plate 3.2: Determination of Coefficient of Static Friction and Angle of Repose 26

Plate 3.3: Pedal Operated Groundnut Decorticator 27

Plate 3.3: Digital Venier Caliper 39

Plate 3.4: Digital Weighing Scale 40

Plate 3.5: Digital Stop Watch Scale 40

Plate 3.6: Electric Oven 41

Plate 3.7: Tachometer 41



1.1 Background to the Study

Groundnut (Arachis hypogaea) is a species in the legume or beans family (AshishandHanda, 2014; Atiku et al., 2014).  It was first cultivated in Peru. Its seed contain about 63% carbohydrate, 19% protein and 6.5% oil. Groundnuts are grown in tropical and subtropical climate regions and warmer parts of temperature regions and it is low growing annual plant and has a variety of uses.  Prior to its usage however groundnut need to undergo preprocessing which include drying and shelling.  Removing of kernels from the pod is generally referred to as shelling or “decorticating” (Maduako et al., 2006).  In Nigeria groundnut is mainly decorticate by hands (traditional method).  This method is not hygienic as dirt from hands and mouth could pose health risk from the nuts. (FAO. 2001).

Shelling is a fundamental step in groundnut processing as it allows the kernel and hull to be used as well as other post harvesting technologies to take place such as oil extraction or in hull briquetting (Pradhanaet al., 2010). Shelling is usually carried out on the farm just before the farmer sells his product for the following reasons: Kernel do not store as well as nuts in the shell and groundnuts in the shell are fifty per cent heavier than kernels alone and therefore costlier to transport. Shelling can generally be done by hand or machine. Hand shelling is the process in which the pod is pressed between the thumb and first finger so that the kernel is released.  In mechanization now we use large and smaller machinery for groundnut shelling. These machines are used in industries where large production is required. There are different methods of shelling and different machines have been fabricated and used to shell wide variety of crops under different conditions (Nyeaanga et al., 2003., Atiku et al., 2004; Gitau et al., 2013; andMaduakoet al., 2006).  The peasant farmer cannot afford this machine because they are too costly and complex in operation and maintenance.  Also the operator had to be trained and spare part imported.  These factor increase the overall cost production which does not make any economic sense to the farmer.

1.2 Statement of the Problems

Research shows that groundnut has an inherent poor storage life, if not threshed after harvesting unlike some other crops, but in threshed forms, it can be stored for a very long period of time (Onuoha2010). Therefore, to overcome the problem associated with manual threshing and quick rate of insect infestation after harvesting, the development of groundnut decorticating machine is of paramount. Traditionally the seeds are left in the pods which would then be stored in a pot and would only be shelled when they are needed for cooking (Ngugi, 2007), shelling is one by hand or beating with a short stick or pestle and mortar, followed by winnowing (KaulandEgbo,1985). The constraints such as fatigue, high time energy inputs and inefficiency in manual shelling of groundnut led to design and fabrication of pedal operated groundnut Sheller that will go a long way in solving the problem of rural farmers that are engage in groundnut production at small and medium scale level.

1.3 Objective of the Project

The main objective of the project is to design and fabricate a pedal operated groundnut decorticator that will remove and separate the groundnut seed from the hull for domestic and industrial uses.

The Specific Objectives are to:

i) determine the physical properties of groundnut seed in relation to the design of pedal operated ground decorticator.

ii) design and fabricate a pedal operated groundnut decorticator 

iii) evaluate the performance of the decorticator in terms of decorticating. Efficiency, percentage of breakage, percentage of shelled seed throughput capacity.

1.4 Justification of the Project

Due to high lose that are recorded due to lack of adequate power supply, these are expected to be achieve at the end of the project.We can save the time and money by using pedal operated groundnut decorticator, limited number of labour will be required, groundnut will be available for domestic and industrial use. The fabrication of the machine will encourage the farmers to grow more groundnuts.

The machine would overcome the traditional method by reducing wastage due to crack or crushed groundnut, to increase the efficiency, to reduce the hard work and to reduced time to shell the groundnut, to develop a low cost machine which can be used by farmer to convert their semi-finished (shell groundnut) into finished product (groundnut) and it satisfies the need of village people to earn more money.   

1.5 Scope of the Study

Groundnut is the sixth most important oil seed crop in the world and is widely cultivated in Nigeria.  The project work is limited to groundnut seed. The variable factors to be considered in this study were feed rate and characteristics of the operator (weight, height and knuckle length).



2.1 Physical Properties of Groundnut

The physical properties of groundnuts, namely size, angle of repose, co-efficient of friction, bulk density, weight, moisture content and shape were determined.  The angle of repose for the three varieties of groundnuts investigated ICGV, RM.9 and RM – 12 average 28.5; 20.50 and 34.50 for the pods, seeds and shells, respectively, while the coefficient of friction of the pods, seeds and shells were found to be 7.4%, 6.4% and 11.3% on the average, respectively.  These physical properties determine the dimensions of machine parts such as hoper, mattering unit, shelling drum, concave and separating sieves and the angles of inclination and clearances, of these parts in relation to one another.   The choice of construction materials for different machine parts and the computation of power requirement of the machine in view of the desired throughout capacity also depend on a working knowledge of the physical properties.

To avoid breaking and crushing the seeds during the pod shelling operation and thereby reducing the quality and causing seed losses, there is need to characterize the pods in terms of these physical properties before designing the shelling machine (Maduako and Hamman 2004)

2.1.1Determination of Size

Size and Shape

Size is an important physical attribute of foods used in screening solids to separate foreign materials, grading of fruit and vegetables, and evaluating the quality of food materials.

Size can be determined using the projected area method. In this method, three characteristic dimensions are defined.

1. Major diameter, which is the longest dimension of the maximum projected area

2. Intermediate diameter, which is the minimum diameter of the maximum projected area or the maximum diameter of the minimum projected area and

3. Minor diameter which is the shortest dimension of the minimum projected area.

Resch & Daubert, (2001)

Density of a material is the amount of that material occupying a certain space and is expressed in units of mass per unit volume. Materials consisting of particles or grain with interstitial air spaces have different values of particles density and bulk density.(Suter and Brusewiz, (2005)




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