Development and Evaluation of a Motorized Plantain Slicing ... · development of a more efficient...

135 Chilakpu et al., Development and Evaluation…

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Volume-4, Issue-1, pp- 135 - 142

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Research Paper July 2018

Development and Evaluation of a Motorized Plantain Slicing

Machine.

*1Chilakpu, K. and 2Ezeagba, A. C.

1Agricultural and Bioresources Engineering, Federal University of Technology, Owerri, Nigeria.

2Agricultural and Bioresources Engineering Department, University of Nigeria, Nsuka, Nigeria.

*Corresponding Author’s Email: [email protected]

Abstract

A motorized slicing machine was developed using locally available materials for size reduction of some freshly harvested farm products. The machine consists of 520 x 400 x 580 mm size main frame. The frame is made of 30 x 30 mm mild steel materials. The feeder assembly consists of a cylindrical hopper with three feeding chutes of different diameters; 50, 47 and 45 mm for big, medium and small peeled plantain. The cutter assembly comprises of three stainless steel blade fixed at an angle of 120 degrees to each other. Below the cutter blades is an adjustable plate which serves as a restriction to prevent the plantain from dropping into the collection tray without being cut. The machine works on the rotational principle whereby the peeled plantain is fed vertically into the cutting edges of the rotating blades. The slicing machine was powered by a 0.75kw electric motor running at a speed of 360 revolutions per minutes (rpm). It has a throughput capacity and slicing efficiency of 63.23kg/hr and 95.43% respectively when used for the slicing of fresh plantain thickness of 6.5 – 7.5 mm.

Keywords: Motorized, plantain, Slicing, Development, t-distribution.

1. Introduction

1.1. Background Study.

Plantain (Musa paradisiaca L.) is a crop which is generally grown in tropical and temperate

region of the world, and is a good source of vitamins and dietary fiber. Plantain provides a

well balanced diet compared to any fruits and satisfies the definition of good food that is

which is easily digested and absorbed in our body. It contains energy 510KJ (120kcal),

carbohydrates 31.9g, sugars 15g, dietary fibers 2.3g, fat – 0.37g, thiamine (vitamin B1)

0.052mg (5%). A bunch consists of several „fingers‟ (several plantains attached in a single

bunch), each having a length in the range of 63.5 - 304.8 mm, and width of between 19.50 -

50.80 mm, (CRFG, 1997).

Industrially, plantain fruit serves as composite in the making of baby food, bread, biscuit and

others (Ogazi, 1996; Ayeampong, 1999). Most of the methods of processing plantain pass

through the slicing process. The nutritional demand for plantains and its by-products in this


part of the world call for serious effort aimed at developing more efficient processing

machine to meet the product demand.

Obeng (2004) reported a highly mechanized plantain slicing machine produced at Kwame

Nkrumah University of Science and Technology Kumasi Ghana with a capacity of 100kg/hr

of plantain slices. However, this machine has not been attractive to farmers because it slices

plantain longitudinally inform of shreds. Bello, et.al, evaluated a plantain slicing machine

produced by National centre for Agricultural Mechanization (NCAM). The NCAM slicing

machine is not only limited by its low reported slicing efficiency of 63.03% it can only handle

a plantain finger at a time. The developed plantain slicing machine cut the plantain “fingers”

in transverse section with additional advantage of handling up to three different sizes of

plantain in a batch.

1.2. Statement of Problem

Locally, plantain slicing is manually done with knives by family members or hired labour. This

method is slow and labour intensive as only about 35 kg of plantain pulps could be sliced by

a labourer in a day. The existing plantain slicing machines do not seem to be acceptable to

most farmers due to low efficiency and the shape of slices produced. This calls for the

development of a more efficient machine that will cut plantain into shapes acceptable to the

farmers.

1.3. Justification of the Study

Plantain and it‟s by products has become a staple part of the cuisine of many families.

Plantains are readily eaten in form of chips at home, cinemas and other public places as

snacks. To meet the ever increasing demand for this product, there is need to mechanize

the processing to overcome the drudgery associated with the manual slicing method. To

ensure more acceptability in the market, there is every need to improve on the design of a

transverse plantain slicing machine to meet individual and commercial requirements.

2. Materials and Methods

Motorized slicing machine considering the need for hygienic processing of plantain as food,

stainless steel materials were used for the part of the machine in direct contact with the

product while mild steel was used for other parts such as the frame work to reduce

production cost. This new machine frame is made of 50 x 50 mm mild steel angle. The

frame length, breath and height are 520 x 400 x 580 mm respectively. These sections are

firmly joined with arc welding. The bearings, connecting shaft, housing cover and prime

mover are mounted on this frame. All these accessories were mounted with the help of

fasteners. The feeder assembly consists of a cylindrical hopper with three feeding chutes of

different diameters; 50, 47 and 45 mm for big, medium and small (feed tubes) were selected

for round slices considerably the maximum effective width and diameter of the peeled

plantain. The length of the feeding chutes (tubes) is 75 mm for providing sufficient space for

feeding the plantain from the top. The cutter assembly comprises of a three cutting blades of

75mm long and 1.5mm thick. The blades are mounted at an angle of 120 degrees to each

other on a disc which is fastened to a 30mm drive shaft as shown in Figs.4 and 5. Below the

cutting blade arrangement is a restriction plate to prevent the plantain to be sliced from

dropping into the collection tray without being cut.


A number of researchers that include; O‟Dogherty, (1981); Persson, (1987);

Balasubramanian, Sreenarayaanan and Visvanathan, (1993); Kachru, Balasubranian and

Kotwaliwale, (1996) and Akande and Onifade, (2015) in their studies reported that cutting

of agricultural materials are influenced by the cutting velocity, shear force of cut and the

power available to the cutting tool.

2.1. Force Required for Shearing the Raw Plantain

According to the work of Odekunle (1986), the force required to shear the raw plantain was

given by equation 1;

where:

= Force required for shearing the raw plantain (Newton)

= Area under shear (m2)

= Shear stress of the raw plantain (N/m)

where:

D = Diameter of raw plantain

2.2. Cutting Power Requirement

The power required by the cutter to slice the raw plantain may be obtained from the

expression by Saeed, (2001)as shown in equation 3;

where:

= Power required by the cutter (watt)

= Linear velocity of the cutting blade

The linear velocity was given by equation 4;

where:

= Angular velocity of rotating disc

r = Radius of cutting disc (on which the blades are mounted)

2.3. Torque Requirement

The torque acting on the shaft was calculated for the cylindrical shaft using equation 5;

where:

P = Power to be transmitted by shaft = 0.75KW (electric motor).

T = Allowable torque on shaft (N/m2)

N = Rotating speed of shaft (rpm)

2.4. Determination of Pulley Speed and Size

The electric motor transmit power through the pulleys to the shaft carrying the cutting blades.

The diameters of the pulleys were calculated as shown in equation 6 according to the work

reported by Kachru (1996).


where,

N1 = Speed of the pulley on the motor (rpm)

N2 = Speed of the pulley on the shaft (rpm)

D1 = Diameter of the pulley on the motor (mm)

D2 = Diameter of the pulley on the shaft (mm)

2.5. Shaft Design

In designing the driving shaft, a combination of twisting moment and bending moment were

considered as the major forces acting on it as shown in Figure 1. According to the work of

Khurmi and Gupta (2010), by limiting the maximum shear stress ( max) equal to the

allowable shear stress ( ) for the material, the equivalent twisting moment was calculated

using equation 7.

√

where;

Tq= Equivalent twisting moment (Nmm)

m = Bending moment (Nmm)

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

= Shear stress induced due to twisting moment/allowable shear stress (N/mm2)

d = Diameter of shaft (mm)

Figure 1: Load, Shear Force and Bending Moment Diagram.

The orthographic diagram of the developed machine and the cutting blade arrangement are

as shown on Fig.2 and 3 respectively.


Figure 2 Orthographic Projection of New Machine Figure 3 Plan View of the Cutting blade Arrangment

The shaft – blade arrangement and the Isometric view without the outside cover of the

developed machine is as shown on fig.4 and fig.5 respectively

Figure 4 The shaft – blade arrangement. Figure 5 Isometric view without the

outside cover of the developed machine

The plate of the fabricated machine with the outer cover showing the three feeding holes for

various sizes of materials and the product out let is as presented on plate 1.

Plate 1. Photograph of developed machine


3. Operational Principle of the Developed Machine

The developed machine works on shear cutting principle as presented by Clarke (1987).

The machine has three stainless blades mounted on upper end of the power shaft rotating at

a speed of 360 rpm slicing of the products. The peeled plantains were manually fed vertically

through the feeding hole to the rotary blades. A stainless steel base with an adjustable

height is placed below the cutting blades to prevent the products from passing through

without being cut, and also to ensure uniform thickness of the sliced products.

3.1. Performance Evaluation

To evaluate the performance of the machine, the approach recommended by Kachru,

Balasubranian and Kotwaliwale (1996) was adopted for its simplicity. One hundred fingers of

plantain was used for this experiments. The clearance between the cutting blades and the

restriction base which determines the thickness of the plantain slice was varied between 6.0,

6.5, 7, 7.5 and 8.0 mm in line with the thickness of the manually cut slices in the open

market which has an average of about 7 mm. The plantain fingers were peeled manually,

weighed and sorted according to the feeding holes sizes. They were manually fed into the

matching feed hole while the machine was running; the time taken to completely slice each

plantain finger was recorded. This experiment was repeated five times for each slice

thickness at different speed range of 250, 360, 460 and 500 rpm and the average results

recorded.

3.1.1. Operating/Slicing Efficiency of the Machine (Es)

This was obtained by feeding some plantain into the machine and after each operation the

products (slices) are weighed irrespective of damaged slices per unit operation. The

damaged or products with uneven cut thickness were manually picked out of each trial

operation and weighed separately. Five independent trials were carried out at each speed

level and their average weights recorded. The operating/slicing efficiency of the machine

was determined using equation 8

8

3.1.2. Throughput Capacity, (Tc)

The quantity of material that the machine can handle in a given time was determined using

equation 9;

9

4. Variation of Slicing Force of Plantain For Days of Storage

It was observed in the course of evaluating the performance of the developed machine that

the ripeness or length of storage of a feedstock affects the amount of force required for the

slicing of a given product as shown in Fig 6.


Figure. 6 Slicing force required for transverse and longitudinal plantain cutting against days of Storage.

4.1. Discussion

The developed slicing machine was powered by a 0.75kw electric motor, various ranges of

machine speed (250,360,460 and 500rpm) were used to determine the optimum operational

speed for plantain slicing. The optimum results were obtained at a machine speed of 360

revolutions per minutes and a throughput capacity and slicing efficiency of 63.23kg/hr and

95.43% respectively when used for the slicing of fresh plantain thickness of 6.5 – 7.5 mm.

The machine was quite stable (not wobbling) in operation and took an average of 5 seconds

to complete each slicing batch. It was observed in the course of evaluating the performance

of the developed machine that the ripeness or length of storage of a feedstock (plantain)

affects the amount of force required for the slicing. Fig 6 gave a graphical presentation of the

effect of storage on the cutting force requirement of plantain. The trend of graphs for

transverse and longitudinal force requirement indicated that the slicing force decreases as

days in storage increases. This could be as a result metabolic activities and deterioration

going on within the product. A linear regression equation was developed for transverse

cutting force and longitudinal cutting force as shown in equation 10 -13.

Equation 10 gave the R2 for transverse cutting force while eqn. 11 gave the R2 for

longitudinal cutting force. The developed linear regression equations for transverse and

longitudinal cutting force are as presented by equation 12 and 13 respectively.

where:

= Number of days.

= Transverse cutting force

= Longitudinal cutting force

The implication is that when the number of days of storing plantain is known, equations 12

and 13 could be used to determine the required cutting force in the transverse or longitudinal

y = -4.9853x + 29.836 R² = 0.9881

y = -6.0146x + 42.276 R² = 0.9789

0

5

10

15

20

25

30

35

40

1 2 3 4 5

Tran

sve

rse

an

d L

on

gitu

din

al C

utt

ing

Forc

e (

N)

Number of Storage Days

TRANSVERSE CUTTINGFORCE (N)

LONGITUDINALCUTTING FORCE (N)

Linear (TRANSVERSECUTTING FORCE (N))

Linear (LONGITUDINALCUTTING FORCE (N))


sections. The result of this work has buttressed the point that it requires higher cutting force

to slice plantain in the longitudinal section than the transverse section.

4.2. Conclusion

A motorized slicing machine was developed with locally available materials for the slicing of

freshly harvested farm products (plantains). The develop machine in addition to slicing

peeled and unpeeled plantain can also be adjusted to slice other agricultural products such

as; banana, cucumber, carrot among others. Based on the results of the test obtained, the

machine proved to be a better design than the existing in that the slicing time of plantain is

reduced from 25- 30 minutes to 5-6 minutes. In addition, the use of stainless materials in

area in direct contact with the product ensured that there was no discoloration of the sliced

chips produced.

.

References

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