CHAPTER ONE INTRODUCTION 1.1
Preamble
Nigeria has rich and favorable climatic zones making her suitable for the cultivation and production of a wide variety of vegetables. Majority of Nigerians live in the rural areas and are predominantly engaged in agriculture. Thus, to guarantee access to food, reduce rural-urban migration and encourage sustainable development, the processing of agricultural products like vegetables into more valuable products must be promoted and encouraged. Vegetables which are excellent sources of certain vitamins and minerals and often the main source of dietary fiber consist of a large group of plants consumed as food globally ( Gave, 2008). Consumption of vegetables has increased significantly. The increase in its consumption can be accounted for by the increased health consciousness of the consumers. Vegetables can be perishable when fresh but able to be preserved using a number of processing method such as blanching, dehydrating, canning, freezing, fermenting and pickling, and irradiating (Gave, 2008). The perishable nature of the fresh produce has confined the international trade in these products in the processed form. The classification of vegetables can be done based on different criteria some of which are; by edible parts into root (e.g., potatoes and carrots), stem (asparagus and celery), leaf(lettuce and spinach), immature flower bud (broccoli and Brussels sprouts ), and fruit (tomatoes and cucumbers ( Neidhardt, 2008). Differences in the structure, size, shape, and rigidity of the individual cells are dependent on the class of vegetable (Odior and others,
1
2009). The processing requirements and fresh market life are also different for
varying classes. The variations in the sizes in which these products are obtained have made it expedient for certain reduction techniques to be to be utilized. Reducing its size either for further processing or to improve the eating quality or suitability for direct food consumption becomes very necessary. Certain processes such as; cutting, slicing, mincing and pulping has being utilized to ensure the s ize reduction of these products. One of the processes commonly used is the slicing process. The slicing process from time immemorial has involved the use of knives. But with the advent of time, technology technology advances has being seen seen to be on an increase increase hence efforts efforts were being made to eradicate the inefficiencies posed by the use of knives which are evident in the time wastage and injuries incurred during its use. The increased consumption of vegetables either domestically or commercially has greatly influenced the variations in the slicing technology, with the basic principle of the action of shearing by blades and other types of cutters remaining the same. The invent of the slicing technology has made the t he size reduction of the vegetables more efficient. The vegetable slicing machine has being utilized in reducing the varying sizes of vegetables. The machine consists of two cutting blades, a vegetable feeder (hopper), a slicing/processing chamber, two electric motors, and a discharge unit. Some certain factors such as safety, power consumption, economic value and efficiency of cut have greatly informed the modification of this machine to meet up with present demand. This machine is capable of automating the cutting process increasing efficiency and enhancing the hygiene of slicing vegetable for both domestic and commercial consumption. consumption.
2
2009). The processing requirements and fresh market life are also different for
varying classes. The variations in the sizes in which these products are obtained have made it expedient for certain reduction techniques to be to be utilized. Reducing its size either for further processing or to improve the eating quality or suitability for direct food consumption becomes very necessary. Certain processes such as; cutting, slicing, mincing and pulping has being utilized to ensure the s ize reduction of these products. One of the processes commonly used is the slicing process. The slicing process from time immemorial has involved the use of knives. But with the advent of time, technology technology advances has being seen seen to be on an increase increase hence efforts efforts were being made to eradicate the inefficiencies posed by the use of knives which are evident in the time wastage and injuries incurred during its use. The increased consumption of vegetables either domestically or commercially has greatly influenced the variations in the slicing technology, with the basic principle of the action of shearing by blades and other types of cutters remaining the same. The invent of the slicing technology has made the t he size reduction of the vegetables more efficient. The vegetable slicing machine has being utilized in reducing the varying sizes of vegetables. The machine consists of two cutting blades, a vegetable feeder (hopper), a slicing/processing chamber, two electric motors, and a discharge unit. Some certain factors such as safety, power consumption, economic value and efficiency of cut have greatly informed the modification of this machine to meet up with present demand. This machine is capable of automating the cutting process increasing efficiency and enhancing the hygiene of slicing vegetable for both domestic and commercial consumption. consumption.
2
1.2 Aim and Objectives
The aim of this project is to design and fabricate a Modified Vegetable Slicing Machine. This aim is achieved through the following objectives: ● Reduction of human effort in the process of vegetable slicing, as the machine is designed to operate automatically using a set of motor and set of mechanisms, enabling power/torque to be transmitted to the vegetable to be sliced ● Allowing variation of slicing speed by the user based on the nature of the vegetable to be sliced, as a variable speed motor is utilized. ● Processing Processing of different sizes of vegetable with the aid of the mechanical components of the machine. ● Ensuring safety of the user by employing standard design requirement. requirement. ● Ensuring that a level of hygiene is maintained and the vegetable is safe for consumption through proper selection of material. 1.3 Scope and limitation of study
The project will put into consideration basic design concept which will be limited to
material
and
stress
analysis
and
specification
for
fabrication.
The design would cover some essential components of the machine such as the ● Base/Machine frame ● Cutter blade ● Slicing chamber The electric motor design will not be covered in this project however, proper selection on the appropriate size required would be made.
3
1.4 Road map of study
This work is intended to improve an existing design of Vegetable Slicer. The analysis was divided in parts. First, design considerations and material selection, followed by design analysis on each component, economic analysis before fabrication using basic design methods. AutoCAD was used for detailed geometry of the design showing the various views, to also implement the design and enable simulations by varying operating parameters and observing their effects on the indices. While Computations of the design analysis was done using Microsoft excel
4
CHAPTER 2 LITERATURE REVIEW
This chapter presents a review of related past works. It is divided into two parts; Section 2.1 reviews the history of slicing machines while section 2.2 reviews recent works in which slicing machines have been applied. 2.1
Historical Background
The design and the production of a machinery as part of the technological development of a country requires the acquisition of technology and development of capacity in the three activities of design, fabrication or production and engineering research and development. Engineering development and testing of machinery and equipment is a compliment to any design and manufacturing process. It is through such testing and subsequent development that operational problems of the machines produced locally can be investigated and solved and the quality of product maintained. The invent of slicing technology can be dated back to the 1900’s, with a number of authors studying the principles of slicing and slicing machines. The first slicing machine was invented by an American in 1873 (Hardin, 2001), the machine made use of an oblique knife in a vertical slicing frame for slicing dry beef and it worked the frame holding the meat while slicing against the cutting blade (Odior and others, 2009). Otto Rohwedder designed and manufactured the first slicing machine that would slice and wrap bread in 1925 (Frank, 2004). The machine made use of an oblique knife in a vertical sliding frame for slicing dry beef and it worked with the frame holding the meat while slicing it against the cutting blade. The conventional slicing machine was originally designed to slice meat into pieces of uniform thickness. It was also used for slicing cheese, vegetables, ham, onions green peppers and sandwich ingredients. 5
Slicing technology has already been developed mature in the western world in 1970s, in the mid-eighties most of the slicers can process monocrystal with large diameter up to 125 mm (5 inches), like the horizontal inside diameter slicing machine manufactured by Mayer Bbu Geyer company in Switzerland which sliced materials with the maximum diameter up to φ304.8 mm (12 inches). During the period of industrialization, automatic machines have proven to reduce the time needed to do a specific task; hence they are essential part of human life. Nowadays, human life becomes more competitive and faster than before. Slicing vegetables are a risky and time-consuming task in our busy life. In the mid-1980s, the slicing technology has experienced its peak of development, many of the automatic multi-function slicers have been commercialized (Xie, 1996). Wire saw, a cutting machine was developed during this period. It had a unique design and was totally different from the traditional slicing technology. It uses a steel wire to coil the four guide wheels to form hundreds of saw bands. When they operate in a high speed, the silicon carbide will be taken to the machine to produce the effect of cutting. Its advantages are to cause less kerf, small deviation, even cut surface, big quantity and less costs. Its application in the st
market created a new chapter for the cutting technology in the 21 century (Huang and others, 1996). The function of the slicer has been very complete, composite and the way of slicing is diverse. The comb shape cutting machine in 1980s is not new anymore. It has been replaced by the cutting and rotating one, surface grinding one and the one with an air cushion which can prevent the blade from bending and distorting, which can repair and maintain the blade automatically (Jiang, 2011). The chip material can roll and grind by itself while cutting, which can reduce the bending of the monocrystal.
6
2.2 Recent development
Current design consists basically of two cutting blades, a vegetable feeder (hopper), a slicing/processing chamber, a control unit, two electric motors, vegetable discharge unit. The machine was designed to enhance the hygienic slicing of vegetable for both domestic and commercial consumption. It takes an average of 10 seconds to cut a bunch of vegetables and one hour for 1,673 tonnes. The traditional method of slicing plantain with a kitchen knife is laborious, timeconsuming and prone to injury, and can only be practiced on a very small scale of production. (Obeng and others, 2004) developed a mechanized plantain slicer for cutting of bulk plantains into chips. The mechanized slicer seeks to reduce the drudgery associated with traditional cutting of large-scale plantains into chips. The machine takes 5-7 seconds to slice a finger of an average-size plantain into chips of 2-3mm in thickness compared to the 40-80 seconds with a kitchen knife, which gives non-uniform thickness of plantain chips. It was found to be very convenient, and the average thickness of plantain chips produced with the slicer compares favorably with commercial standards. (Owolarafe and others, 2007) developed a manually operated lady’s finger (okra) (Abelmoschusesculentus) slicing device suitable for on-farm use. It was designed, fabricated and tested based on the engineering properties of the vegetable. The machine, simulates the traditional method of okra slicing, consists of the feeder, slicer and receiver. It was made simple for ease of operation and maintenance. The machine was tested with replicated experimental runs using 100, 200, 300, 400 and 500 g of okra. The thickness of the slices (about 10 mm) corresponds evenly to the spacing of the cutting discs. The machine has a slicing efficiency of about 77.4% and through put of about 8.4 kg/h.
7
(Megan, 2008) developed a Slicer featuring simplified controls, improved geometry and enhanced carriage design and other innovations that make it easier to use with clean and deliver improved slice quality. With a 50-degree cutting plane and glass-bead-finished gauge plate and top knife cover, the slicers have a smoother glide against the knife while improving visibility of the sliced product. A lighter tray makes repeated loading and unloading easier. (Neidhardt, 2008) developed the tomato slicer, equipped with a disposable blade cartridge. Features include Razor-sharp blades cut with trouble-free precision, thanks to a unique selflubricating track material that resists misalignment problems that cause nick sand broken blades. Vertical handle and protective guards improve user comfort and safety. (Gave, 2008) developed a vegetable cutter which uses 40 different cutting discs to replicate most hand-cutting styles. Features include a large hopper opening, ¾-hp gear-driven motor, stainless-steel body and base, removable hopper head, and a food pusher, which has antimicrobial protection. (Suryanto and others, 2009) developed a chopper for chopping bunches of palm into small pieces using knife blades and an experimental cylinder-type chopping machine. The knife edge angle had a significant effect on the specific cutting force and the cutting energy. For the impact cutting, the specific torque requirement was affected by the peripheral cutting speed. Increasing the speed from 5.3 to 14.3 m s1 reduced the cutting torque by 14.3%. An experimental chopping machine with a capacity of 3540 kg h-1 has been developed and tested for the empty fruit bunches (Azizet and others, 2011) developed a Slicing machine for fresh cut Pineapple. Intensive research had been conducted in developing a suitable slicing machine to cater for the needs of the local pineapple processors. The development of the slicing machine was based on two systems, namely rotary and centrifugal type
8
working condition. This paper emphasizes machine development and its operating system. At normal rate, the slicing machine is capable of processing 360 fruits per hour. The slicing machine is easy to operate, of simple design, cost effective and easy to clean. The present existing designs of vegetable slicing machine is too numerous to mention in this work, however, these machines operate on similar principles with a difference in the methods of cutting/slicing. The two broad methods of slicing are identified as; rotary slicing method and reciprocating slicing method. The rotary slicing method is achieved with the use of electric motor. Here, the cutter blade is attached directly to the electric motor. The slicing effect of the food is achieved via the rotation of the cutter blade attached to the motor. The reciprocating method is usually manual or semi-automated. It is of a lower efficiency compared to the rotary method which is fully automated. 2.3
Expected Contributions Due to Knowledge Gaps
From the literatures reviewed it was discovered that the different machines utilized different slicing techniques such as the reciprocating and rotary slicing method. They also had different blade designs, varying power consumption and different material selection which had an overall effect on the machines performance. These performances include the time required for cutting, the power consumption and the cutting efficiency. Our design proposes to improve on the existing performance characteristics of the machine. This will be achieved through the use of improved blade design, proper motor and material selection. The fact that little effort is required makes the machine efficient. Above all, the process is highly hygienic time saving and promotes the cause of ergonomics.
9
CHAPTER THREE DESIGN ANALYSIS
In this section all design concepts developed are discussed and based on evaluation criteria and process developed, and a final design was chosen. However, some features of the selected design were modified to further enhance the functionality of the design. The modifications are also discussed. The equations and formulas used were also presented in sequence. Detailed drawings and CAD presentations were made. 3.1 Operating Principle
The vegetable slicing machine was redesigned to slice fresh vegetable into finer finishes and improved performance. The vegetable slicing machine uses rotary motion transferred by the motors to the blades to cut the vegetable. It is made up of a frame with electric motor, the slicing/processing chamber, the wedge bar, the vegetable feeder/hopper, the tray which stores the sliced vegetable after the slicing process in the slicing chamber. It consists of three cutting blades which are spaced 120 degree from each other to give a slice thickness of 0.2mm. The vegetable is separated from the stem and introduced into the machine via the hopper. The quantity of leaves to be introduced at a time depends on the size and texture of the leave. The leave is then cut into smaller sizes by three rotating knife blades spaced at120 degrees. A wedge bar place just beneath the rotating blades traps the vegetable for a while for slicing action to take place before allowing the cut leave to fall into a collector just below the slicing chamber. The speed of the motor can be regulated depending on the size of the slices desired by the operator and the operator may also re-introduce the sliced leaves into the hopper for a finer and better slice
10
The machine is designed to produce fine and hygienic slices. It consists of the following main components; 1. Stainless steel cutter blades(rotating) 2. Slicing/processing chamber with a Wedge bar attached to the side plate 3. Feeder/hopper, 4. Slide plate 5. Electric motor and control unit. 3.2
Design Considerations
The importance of this device has made it necessary for some proper design Considerations to be made. Some of those considerations made during the design and fabrication of the Vegetable slicing machine are; a. The Functionality and Manufacturability of the design b. Economic viability, that is general cost implication of materials and fabrication techniques employed. c. The durability and maintainability of the machine. d. The potential of the machine for modification, Safety and Ergonomics The strength required of each element was also used as a factor in determining the geometry and the dimensions of that element to avoid failure of components. Also, the height of the column and the area of base were designed and materials carefully selected for rigidity, stability and portability of the machine. To ensure an improvement in the shape of the machine, the Aesthetics design was also put into consideration. Finally, ergonomics principle was considered in this design for convenience of the operator.
11
3.3
Component Parts of the Machine
To ease design effort, the system is divided into the following subsystems which include: a. Frame b. Rotating Disc Cutter c. Slide Plate/Tray Carriage d. Hopper e. Motor and Regulator Frame
The frame is a carriage (the skeleton of the system) which serves as a support for the occupant and the other components to be added on. The frame is made of stainless steel. The only modification to be carried out on this frame is the geometric changes from Rectangular to cylindrical shape, and the base of the platform which will be joined with bolts and nuts for easy maintenance. Tripod Stand
The machine is being placed on this component. It is made of cast iron and serves as a support to the weight of the machine. The top has a circular design that fits the
°
shape of the machine, with its leg equally spaced 120 to maintain a perfect balance. Also for easy mobility and to curb any form of vibration that may occur, tires are attached to the legs. The Rotating Disc Cutter
The rotating cutter blade is a tapered flat disc made of stainless steel material. It is 130mm in length. The cutter blade fixed at one end of the electric motor, is a tiny flat metal bar and razor sharp. The blade upon receiving a rotational motion slices
12
the vegetable into edible sizes. The blade rotates at a speed of 1500 revolutions per minute. The Slide Plate / Tray Carriage
The slide plate or tray carriage is the steel component that conveys the sliced vegetable from the slicing chamber to the outlet. In modifying this component, a moveable tray carriage is adopted in the place of a framed one. This modification aids in reducing vegetable wastage due to the compactness of the design. Hopper
The hopper is the part through which the vegetables to be sliced are fed towards the blade in the slicing chamber. For safety purpose, there is a considerable distance from the top of the hopper to the point where the blade performs the slicing action. It is made of stainless steel. Electric Motor
This produces the torque/power which is transmitted via the spindle connecting the cutter blade of the machine. The continuous rotary motion of the blade ensures continuous slicing of the vegetable in the slicing chamber of the machine. Regulator
It regulates the speed of the cutter blade. The regulator allows variation of different cutting speeds to be applied to the vegetables to be sliced. The current coming from the power source is split between the regulator and motor. 3.4
Material Selection
The knowledge of engineering material properties is of great importance to a design engineer. The machine components should be made of materials which have properties suitable for the operating conditions. Besides, the designer must be
13
familiar with the effects which the manufacturing processes and heat treatment have on the properties of the materials. Selection of the most suitable material for a given component is one of the greatest challenges in engineering design, as such careful and enduring attention was exercised to ensure that material chosen for a given element is one which serves the desired objective at the minimum cost. Most engineering works are involved with materials on a daily basis in manufacturing, processing, design and construction of components and structures. The materials selected to be incorporated into any design must withstand failure analysis, (Hedge, 1995). In ensuring adequacy of design certain considerations were being made some of which are; a. Whether the material can consistently be machined to dimensional tolerance and maintain form in use. b. Ease of joining with other parts of an assembly. c. Whether material can be machined economically to save costs. The materials used in this project includes: Mild steel for the frame, the hopper, the carriage tray and the rotating disc cutter, the base, and other parts of this machine will all use this material. The choice of the materials used were influenced by some of the under listed factors
Availability of the material.
Suitability of the material for the working conditions in service.
The cost of the material.
The important properties which determine the utility of the material are its physical, chemical and mechanical properties. The physical properties of the 14
material include luster, color, size and shape, density, electric and thermal conductivity, and melting point. The mechanical properties of the material are its strength, stiffness, elasticity, plasticity, ductility, brittleness, malleability, toughness, resilience, creep and hardness. While the material chemical properties reveal among others, its ability to resist corrosion. 3.4.1
Material for Base and Machine Frames
The base and column material require properties such as high compressive strength, good damping characteristics, machinability, rigidity and fluidity. As such, grey cast iron is selected while plastic was selected as the damper which helps to reduce vibration. 3.4.2 Material for Cutter Blade and Slicing / Processing Chamber
One of the most important properties required of any metal used as cutting tool in food processing is high resistance to corrosion. Within the limit of cost and availability, austenitic stainless steel is selected because it is not poisonous. 3.4.3 Summary of material selection
The adequate material selection for the various parts of the machine can be summarized in the table below; Table 3.1 materials for machine components Machine components
Manufacturing materials
Base and Machine Frame Cutter blade
Grey cast iron Austenitic stainless steel
15
Food Slicing/Processing Chamber
Austenitic stainless steel
Vegetable Feed/Hopper
Austenitic stainless steel
Tray Carriage
Austenitic stainless steel
Tripod stand
Cast iron
3.5 Analysis of Machine Components
In order to ensure that this design is not only efficient but also cost effective, detailed analytical estimation of size/capacity of the desired elements was carried out. The results of the analytical processes were compared with established standard stock values and adjusted where necessary, to ensure that during manufacturing, special cutters and other manufacturing equipment will not be made. 3.5.1 Analysis of electric motor
For this work, the motor analysis was restricted only to motor selection. The actual motor design was not considered. This selection was being made based on the following criteria; ● Increased torque ● Low weight ● Adequate power 3.5.2 Shaft design
A shaft is a rotating machine element which is used to transmit power from one place to another. The power is delivered to the shaft by some tangential force and 16
the resultant torque (or twisting moment) set up within the shaft permits the power to be transferred to various machines linked up to the shaft. The shaft adopted for this design is a transmission shaft which has a steel cutte r blade attached to its end. The design of the Shaft is based on strength, rigidity and stiffness. The following stresses are induced in the shaft:
Shear stress due to transmission of torque
Bending stress due to the forces acting on the shaft (the weight of the cutter blade) Stresses due to combined torsional and bending loads
3.5.3
Analysis of Transmitted Torque
The torque transferred to the cutting blade due to transmitted power from the electric motor can be estimated using the relationship below;
6× = 2××
(3.1)
Where; T
=
Transmitted torque (Nm),
P
=
Power of electric motor (watt),
N
=
Rotational speed of motor (rpm),
=
pi (constant).
3.5.4
Analysis of Bending Moment
The shaft is subjected to a load at the end. According to Negan (1977), the density of a material is given as ρ=
(3.2a)
17
i.e mass per unit volume From equation 3.2, m = ρ x v
(3.2b)
The weight of the cutter blade,
= ρ × V × g
(3.3)
But the volume of the blade is, V=
x
(3.4)
Substituting this into equation 3.3 yields
= ρ g
(3.5)
Where; 2
Wc = Weight of cutter blade (kgm/s ) 2 ρ = Density of cutter blade (N/m )
Ac = Area of cross-seection of cutter blade (m2) Lc = Length of cutter blade (m) 2
g = Acceleration due to gravity (m/s ) Hence, the maximum bending moment of the shaft can be gotten from the expression below; M=
×
(3.6)
Where; M L
= =
Maximum bending moment (Nm) Length of the shaft/spindle (m). 18
3.5.5 Analysis of Shaft/Spindle Diameter
In designing the adequate shaft diameter that can withstand the stresses that acts on them, considerations would be made for the various stress conditions. The larger diameter would be chosen. For a shaft subjected to twisting moment (or torque) only, then the diameter of the shaft may be obtained by using the torsion equation. According to Khurmi and Gupta (2005)
τ =
(3.7)
Where; T = Twisting moment (or torque) acting upon the shaft (Nm), 4
J = Polar moment of inertia of the shaft about the axis of rotation (m ), Τ = Torsional shear stress (pa), r = Distance from neutral axis to the outer most fibre (m), but r = d / 2 Where; d is the diameter of the shaft (m),
For a round solid shaft, the polar moment of inertia is given as;
32
4
J = ×d
(3.8)
Re-writing equation 3.6 yields T=
(3.9)
3 × τ × d 6
For a shaft subjected to bending moment only, the maximum stress (tensile or Compressive) is given by the bending equation below;
=
(3.10)
Where,
19
M = Bending moment (Nm), I = Moment of inertia of cross-sectional area of the shaft about the 4 axis of rotation (m ),
= Bending stress (Pa), and y = Distance from neutral axis to the outer-most fibre (m) For a round solid shaft, the moment of inertia is given as; I =
4 6×d
(3.11)
Rewriting equation 3.8 yield M =
3 × × d 32
(3.12)
For shaft subjected to combined twisting and bending moment, the maximum shear stress theorem is applicable. From this theory, the maximum shear stress in the shaft is;
max =2 2 + 4 2
(3.13)
Putting equation 3.8 and 3.11 into 3.12 the allowable or working shear can be given by the expression;
= 6 √ 2 + 2 =
(3.14)
Where; =
working shear stress (Pa)
max
=
maximum allowable shear stress (Pa)
Fos
=
Factor of safety
20
From Maximum normal stress theorem, the maximum normal stress in the shaft is,
max = 2 + 2 2 + 4 2 =
(3.15)
= 32 [2 { + √ 2 + 2}]
(3.16)
Where;
max
=
Maximum normal stress (pa) working normal stress (pa)
3.5.6 Analysis of Angular Deflection of Shaft
For the angular deflection of shaft;
=
(3.17)
Where;
=
Angular deflection (rad),
G
=
modulus of rigidity (N/m )
2
3.5.7 Analysis of Equivalent Torque and Bending Moment The equivalent torque (Te) which the shaft is subjected to is given as;
= √ 2 + 2
(3.18)
The equivalent Bending moment (Me) is also given as;
= 2 ( + )
(3.19)
21
3.5.8 Cutting force of the blade
The force required to produce shearing action can be gotten from the expression; P=F×V
`
(3.20a)
From the equation above,
F=
(3.20b)
Where; F = cutting or impact force on the blade (N) V = cutting velocity of blade or cutter (m/s) 3.5.9 Cutting velocity of blade
This is the velocity at which the applied shearing force produces a cutting action. it depends on the diameter of the blade and also on the speed of the motor i.e; V=
×× 6
Where; V = cutting velocity of blade (m/s) D = blade diameter (m)
(3.21)
The cutting force of the blade can be gotten using the following relations 3.6
Machine Efficiency
The efficiency of the machine can be estimated by weighing different fraction of sliced, partially sliced, vegetables not sliced and losses. Considering continuous feed without any halt, the theoretical efficiency can be gotten from; 22
= ×100
(3.22)
Where; E = Efficiency of the machine
= Average weight of slices from one vegetable
= Average weight of vegetable
23
CHAPTER FOUR RESULTS AND DISCUSSION
The presentation of the input and output data are being made in this section. The results are obtained using MICROSOFT EXCEL environment based on the evaluation of the design models previously presented. Tables are utilized in presenting the input and output data for more clarity. Graphs are also used to show relationships between various parameters. 4.1
Input data
The data used in in carrying out the design analysis incorporates both data gotten from adequate selection of some components such as the electric motor and some which are considered standards in engineering design. The table below gives an outline of the available input data; Table 4.1 S/N
Quantity
1
Power of electric motor
2
Rotational speed of motor
3
Input parameters
Symbol
Unit
Value
P
watts
1119
N
Rpm
1500
Density of cutter blade
Kg/m
4
Cross-sectional area of cutter blade
m
0.000233
5
Length of shaft
m
0.07
3
2
24
7850
6
Maximum allowable shear stress
Pa
56000000
7
Factor of safety
Fos
---
4
8
Maximum normal stress
Pa
112000000
4.2
Output data
From the input data, the values of the required output parameters from calculations are gotten. The larger value of the diameter from the various theories was being considered as the shaft diameter. These values can be seen in the table below; Table 4.2 S/N
Quantity
Output parameters
Symbol
Unit
Value
1
Transmitted torque
T
Nm
7.123
2
Maximum bending moment of shaft
Nm
0.164
3
Cutting velocity of blade
m/s
10.2115
4
Cutting force
N
110
5
Weight of cutter blade
N
2.337
6
Shaft diameter
D
M
0.014
25
7
Working shear stress
Pa
14000000
8
Working normal stress
Pa
28000000
9
Shaft polar moment of inertia
J
m
10
Angular deflection of shaft
Rad
0.001585
11
Equivalent twisting torque
Nm
7.125
12
Equivalent bending moment
Nm
3.643
13
Efficiency
E
-
95.79
4.3
Performance evaluation
4
× 10−9
3.495
In the evaluation of the machine performance, the physical characteristics of the vegetable were taken into consideration. The effect of the slicing blade and operating speed on the slicing of the vegetable was carefully observed and the relationship between the slicing speed and other parameters were also stated. 4.3.1 Physical characteristics of the vegetables
600g of vegetables of similar size and shape were bought from the local market. The oval shaped medium size vegetables were chosen on visual basis. The weight of the samples of 5 vegetables (25g, 50g, 100g, 150g and 200g) were measured with the help of a digital weighing balance.
26
4.3.2 Effect of slicing blade and operating speed
To evaluate the performance of the machines, the vegetables were divided into five batches of the above listed weights and fed into the slicing machine. Each operation was performed at five different speeds (Very low, Low, Medium, High and Very high). The effect of the varying speed were considered in terms of the time duration involved in the slicing process, the weight of the leaf after the slicing process and the losses involved during the slicing process. Table 4.3 shows the results of the slicing experiment using 3 rotating blades spaced
°
120 apart. With the different speed level represented as 5 for very high, 4 for high, 3 for medium, 2 for low and 1 for very low. The time duration, weight of slices and the loss in weight were noted for the different speed levels. At each rotor speed, different weights of vegetables were sliced and respective time taken for slicing was noted. This excludes the time taken for sorting the vegetable and feeding the vegetable. A significant reduction in the time required to perform cutting action can be seen with a corresponding increase in speed. Slicing at maximum speeds produced finer cuts with reduced thickness than that of lower speed the reason being increase in the cutting area. The improvement in the geometry of the leaf at increase speed was at the expense of its weight, as can be seen from the table. This reduction in the weight of vegetable slices with increase in speed of the cutting blade could be due to improper feeding of the vegetable, difference in relative speed of fall of vegetable into the hopper and the speed with which the blade strike the vegetable during slicing. From the given data, calculations for maximum efficiency can be made considering various parameters.
27
Table 4.3 Regulator Position
Effect of slicing speed on time duration and weight
Speed of Weig ht Of the vegeta Motor ble (g) (rpm)
Time duration of Slicing (sec)
Weight of fully sliced vegetable
Weight of partially sliced vegetable (g)
1Very Low 800
25
7.37
23.30
1.70
2 Low
950
25
7.15
22.41
2.59
3 Medium
1150
25
6.93
21.06
3.94
4 High
1350
25
6.70
21.03
3.97
5Very High
1500
25
6.24
21.00
4.00
Table 4.4 Regulator Position
Effect of slicing speed on time duration and weight
Speed of Weig ht Of the vegeta Motor ble (g) (rpm)
Time duration of Slicing (sec)
Weight of fully sliced vegetable
Weight of partially sliced vegetable (g)
1Very Low 800
50
13.7
48.20
1.80
2 Low
950
50
13.3
47.81
2.19
3 Medium
1150
50
12.8
46.34
3.66
4 High
1350
50
12.4
45.21
4.79
5Very High
1500
50
11.5
45.05
4.95
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Table 4.5 Regulator Position
Effect of slicing speed on time duration and weight
Speed of Weig ht Of the vegeta Motor ble (g) (rpm)
Time duration of Slicing (sec)
Weight of fully sliced vegetable
Weight of partially sliced vegetable (g)
1Very Low 800
100
28.48
97.40
2.60
2 Low
950
100
28.43
96.20
3.80
3 Medium
1150
100
26.89
95.27
4.73
4 High
1350
100
26.50
94.89
5.11
5Very High
1500
100
25.96
93.91
6.09
Table 4.6 Regulator Position
Effect of slicing speed on time duration and weight
Speed of Weig ht Of the vegeta Motor ble (g) (rpm)
Time duration of Slicing (sec)
Weight of fully sliced vegetable
Weight of partially sliced vegetable (g)
1Very Low 800
150
34.85
146.5
3.50
2 Low
950
150
34.25
145.7
4.30
3 Medium
1150
150
33.95
145.2
4.80
4 High
1350
150
33.67
144.7
5.30
5Very High
1500
150
32.95
143.5
6.50
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Table 4.7 Regulator Position
Effect of slicing speed on time duration and weight
Speed of Weig ht Of the vegeta Motor ble (g) (rpm)
Time duration of Slicing (sec)
Weight of fully sliced vegetable
Weight of partially sliced vegetable (g)
1Very Low 800
200
42.65
195.70
4.3
2 Low
950
200
42.20
194.30
5.7
3 Medium
1150
200
41.86
193.90
6.1
4 High
1350
200
41.25
193.50
6.5
5Very High
1500
200
40.50
192.30
7.7
The data gotten from the test and shown in the table depends greatly on operator’s experience. The rate at which the vegetables is fed into the machine has a considerable effect on the time duration of the cutting process hence different results can be gotten from different operators based on their experience level. The relationships between the cutting speed, weight of vegetable slices and the time duration for the various weights can also be seen in the graphs attached in the appendices. From the data above, the efficiency of the machine was calculated to be 95.79%.These value however showed a significant increase in efficiency when compared to the previous one.
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CHAPTER FIVE CONCLUSION AND RECOMMENDATION
5.1
Conclusion
Over the years, the traditional process of slicing vegetable has always been slow, tedious, boring, time consuming and in some cases unhygienic. Designing and fabricating a machine capable of slicing vegetable which will mechanize the slicing process for both domestic and commercial consumption becomes a necessity. The design demonstrates that simple member elements can be assembled to make a functional engineering device. Engineering materials that are rust free were selected. Simple design equations involving Cutting force, Torque, Bending moment and shear forces, etc were related in the course of going through the design process. The results and fabrication of this project has shown the possibility of manufacturing a relatively cheap, easy to use and reliable machine for slicing vegetable which reduces human effort, variation of slicing speed by the user based on the nature of the vegetable to be sliced, as a variable speed motor is utilized. Its flexibility and wide range of applicability is an added advantage. The machine was safely operated. This design is environmentally friendly as it does not use an internal combustion engine but requires power for just the electric motor, thus the production of fumes is entirely eliminated. Almost Every home in Nigeria eats vegetables. Hence, the vegetable slicing machine would serve perfectly in slicing of these vegetables into edible sizes.
5.2
Recommendations
Despite the huge success recorded in the fabrication of this machine, some areas might still need attention should the need for further research and improvement
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