Design and Fabrication of Coconut Dehusking Machine

Jibin Jacob1, Rajesh Kumar S.2 1Post Graduate Student, Department of Mechanical Engineering, Mar Baselios College of Engineering and Technology,

Nalanchira, Trivandrum, Kerala 695015 , India.

2Assistant Professor, Department of Mechanical Engineering, Mar Baselios College of Engineering and Technology, Nalanchira, Trivandrum, Kerala 695015, India.

Abstract-In general, Coconuts are dehusked manually using either a machete or a spike. These methods require skilled labor and are tiring to use. Attempts made so far in the development of dehusking tools have been only partially successful and not effective in replacing manual methods. Considering the drawbacks of manual dehusking methods, and existing automated dehusker, power operated coconut dehusking machine was developed. This power operated coconut dehusking machine operates on 1-phase, 1 hp electric motor. It consists of main parts like frame, electric motor, speed reduction unit and dehusking unit. Single person is required for operating the dehusker. During the tests, average time required for dehusking a coconut was found to be 25 second, and the machine can dehusk 120-150 coconuts per hour.

Keywords- Circular Pitch, Horizontal pitch, Tynes

I. INTRODUCTION India has recently achieved the distinction of being the

highest producer of coconuts in the world, having overtaken the next highest producer, the Philippine Islands. India ranks third on world coconut map and in recent times became the largest producer of coconut with the production of 16.9 billion nuts from acreage under plantation of about 1.89 million hectares [4].

Coconut is being cultivated in an area of over 1.94 million hectares in India. The estimated requirement of coconut seedlings in the country is in the region of 30 million per annum [4].

Dehusking is the important post harvest operation, which is necessary step towards making the coconut ready for the further utilization. Also it gives husk, which is important material for coir processing industry.

A. Present Study We have many methods to dehusk the coconut. It is by

manually, mechanically and also by the use of automated machines. Manual dehusking with knife is a common practice. Need for the improvement in present method is the lack of sufficient manpower. This necessitates the use of appropriate machinery to aid in various tasks in coconut plantation. Traditional devices currently in use, such as the blade and spear are difficult and less productive. Even though limited number of automated

machines was available, the reasons for the failure of these machines include unsatisfactory and incomplete dehusking, breakage of the coconut shell while dehusking, spoilage of useful coir, greater effort needed than manual methods, etc.

Based on this realization the necessity of a new automated machine which simplify as well as increases the productivity of the coconut dehusking, arise. This new mechanism will directly boost any economy that relies on coconut plantations.

The present work involves the design, fabrication and testing of a coconut dehusker that overcomes the previously reported drawbacks. The design and developmental stages called for a closer look at the magnitude and direction of the dehusking forces and their generation mechanisms. In short the main objective of this project work is to introduce a newer machine that can, overcome the disadvantages and limitations of existing machines, which includes manual and automatic coconut dehusker.

II. OVERVIEW Considering all the existing powered and non-powered

coconut dehusking machines, world market require a better coconut dehusking machine, which is both economically viable and efficient.

Major disadvantages of existing power operated coconut dehusker are:

1. High initial cost 2. Low rate of dehusking 3. High power consumption 4. Less availability 5. Lack of better dehusking method 6. Operational difficulty 7. Large in size

III. WORKING PRINCIPLE This power operated coconut dehusking machine

operates on single phase, 1 hp electric motor. It consists of main parts like

1. Frame, 2. Electric motor, 3. Power transmission and speed reduction unit, 4. Dehusking unit.

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Frame was constructed by welding, angle iron to the dimensions of 9000×350×500mm using cast iron. Single phase electric motor of specification 1hp, 1500rpm is used. To transmit the power from motor to the cylinders, with required speed, gear and pulley transmission system are incorporated. The dehusking unit consists of two cylinders, of different diameters with different speed of rotation in order to cause tearing effect over the coconut husk. The two diameters provide different speeds at opposite directions. This eliminates the use of number speed reduction unit in the machine. The tynes are mounted on the cylinders in a particular manner, to get more grip and effective dehusking.

The dehusking process in very simple, place the coconut in between the two rolling cylinders, rotating in opposite directions and press it by a manually operated mechanical linkage. As the cylinders rotate, tynes provided on the periphery will penetrate into the husk and tear it away. Tynes are designed in such a way that it will not cause any damage to the coconut shell. Removed husk is in the form of separated fibers, so these fibers are more useful in coir industry. Thus the dehusking can be done, effectively.

IV. DESIGN In the designing of machine, it is very important to

consider the shape and size of the coconut. After the detailed study, average dimensions of the coconut where found. Those values are described below. Shape : Ovoid Dimension : 300mm long × 200mm wide Thickness of fiber: 20 to 40mm Weight : 1Kg While dehusking the coconut, husk removes as 3 parts. Each of width : 40 to 80 mm.

A. Design of Tynes Tynes are the major component in this machine, which

has direct involvement in the dehusking operation. As shown in the Figure-1, tynes are specially designed in a manner to get effective penetration with the coconut. Shape : conical Height : 27mm Diameter : 25mm

Figure I. Different views of Tynes

B. Design of Cylinders Dimension of cylinders are designed in a manner to obtain effective mesh with coconut husk.

1) Assumptions used: a. Coconut contacts with the cylinder at an average

angle of 300 of contact sector. b. 1/6th of the width of coconut should be inserted

into the intermediate space of cylinders.ie approximately 30mm.for effective dehusking.

c. Angle AOB =300

From Figure-2, since the arc AB is considerably small, we can assume it as a straight line, thereby we get a triangle AOB. From the assumption, the inserted depth of coconut is 30mm. Using the trigonometric relations, length of straight line, i.e. arc AB (L) as 41.41mm. Using this equation, R×θ=L Where, ’R’ is the radius of the cylinder (mm). ’L’ is the length of arc (mm). Diameter of cylinder = 160mm (approximate)

Even though the approximate diameter of cylinder, obtained by the above calculation is 160mm, in the design 163mm and 138mm diameter of cylinders are selected to get different velocities.

Figure II. Design of Cylinder

C. Design of Pitch In the design, we have both Horizontal and Circular

Pitch. Horizontal pitch is the distance between the tynes, that are horizontally arranged, where as circular pitch is the distance between the tynes, circularly arranged around the cylinder. Design of the pitches is same for both the cylinders.

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Assumptions taken for the design:

a. Tynes are arranged on the cylinder to obtain effective mesh with the coconut husk, in a particular manner.

b. Optimum number of tynes is mounted over the cylinder.

1) Horizontal Pitch:

Average length of coconut is founded as 300mm, for making this working model, the length of the cylinder is limited to 400mm. This specially designed tynes are mounted on the cylinder in a manner that maximum number of tynes to be in contact with the coconut. It reduces the load on each tynes and increases the efficiency on the dehusking operation. For that 7 and 6 series of tynes are mounted on the larger and smaller cylinder respectively. Thus, Horizontal Pitch = 50.8mm

Figure III. Horizontal Pitch

2) Circular Pitch:

Average width of coconut is founded as 200mm, for

making this working model, the diameter of the cylinder is limited to 163 and 138mm. To get effective mesh with the coconut, 12 tynes are mounted around the larger cylinder; where as 10 tynes are mounted around the smaller one. Diameter of larger cylinder (d1) = 163mm

Circumferential length = 512.07mm Number of tynes = 12 () Circular pitch = Circumferential length / Number of tynes 42.67mm

Diameter of smaller cylinder (d2) = 138mm Circular pitch = 42.67mm Number of tynes = 10

So on the larger cylinder 12 tynes are arranged in

1 row. There are 7 rows, therefore a total of 84 tynes are mounted on the larger cylinder. Similarly, there are 6 rows on the smaller cylinder and each row contains 10 tynes. Therefore a total of 60 tynes are mounted on the smaller cylinder.

Figure IV. Circular Pitch

D. Power transmission and speed reduction unit:

The power from 1hp electric motor is transmitted to the rotating cylinders through pulleys and gears. The same system is also used to reduce the speed of cylinders. It includes 4 pulleys and 3 gears. Selections of these gears and pulleys are according to the availability in the market. Since the machine is designed and fabricated as a working model, major priority is given to the cost factor. Speed of the motor=1500rpm

1) Dimension of the gear

a. Gear attached to the larger cylinder, GL= 153 mm diameter, Number of teeth=49

b. Gear attached to the smaller cylinder, GS =200mm diameter, Number of teeth=54

c. Gear attached to the second transmission pulley, G4=80mm diameter, Number of teeth=25

2) Dimensions of the Pulley

a. Diameter of the first pulley, attached to the shaft

of motor,D1=31.75mm b. Diameter of the second pulley, D2 = 304.88mm c. Diameter of the third pulley, attached to the shaft

of second pulley,D3=31.75mm d. Diameter of the fourth pulley, D4=254mm

3) Speed:

As per the following steps, the speed is reduced from

1500rpm to an average of 28rpm to the cylinders.

a. Speed of the motor, NM =1500rpm b. Speed of the first pulley, attached to the shaft of

motor,N1 =1500rpm c. Speed of the second pulley,N2 = 156.25rpm d. Speed of the third pulley, attached to the shaft of

second pulley,N3= 156.25rpm e. Speed of the fourth pulley,N4 =19.5rpm f. Speed of the Gear attached to the second

transmission pulley, NG =70rpm g. Speed of the Gear attached to the smaller

cylinder, NS =32.37rpm h. Speed of the Gear attached to the larger

cylinder, NL = 24.7rpm

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4) Tangential Velocity:

Tangential velocity = R × ω

a. Tangential velocity of the larger cylinder, VL = 238.97mm/sec

b. Tangential velocity of the smaller cylinder, Vs= 202.31mm/sec

E. Selection of Motor:

Different types of coconuts are tested using U.T.M. machine (Tensile Test) for finding the maximum force required to dehusk the coconut. The maximum value found to be 1kN. Selection of motor is based on the following: 1. Power require to dehusk the coconut 2. Power require to rotate the mass

1) Power require to dehusk the coconut

Force required to dehusk the coconut =1kN (obtained from UTM test). Torque, (T1) =1kN × perpendicular distance from the centre of motor to the point of action of load (200mm). Torque, T1 = 200Nm Power, P1 = (2π×NA×T)/60 Average Speed, (NA) = 28 rpm Power require to dehusk the coconut, P1 = 0.586kW=0.786hp

2) Power require to rotate the mass

Total mass acting on the centre of cylinder = mass of cylinder + mass of tynes + mass of coconut = 20 kg Force due to the mass = 196.2N Torque, T2 = 196.2 × Perpendicular distance to the line of action of mass on the cylinder (200mm).

=39.24Nm Average Speed, (NA) = 28 rpm Power, P2 = (2π×NA×T)/60 = 0.115kW=0.154hp Total torque and power require operating the machine. Total Torque (T) = T1+T2= 239.24Nm Total power to operate the machine, P = P1+ P2

= 0.786 hp + 0.154hp =0.943hp Power Rating = 0.703 kWh There by, motor is selected with following specification Single phase, 1Hp, 1500 rpm.

V. FABRICATION Mainly, the tynes and cylinders are prepared by lathe

operations; such as turning, cutting, drilling, facing, taper turning etc. The different shafts are turned on the lathe to get smooth and good surface finish. Along with this drilling, milling and shaping machines are also used for many operations. Different types of drilling bits are used to drill holes for the seating of bolts and nuts. Another main operation on this fabrication stages is the welding. Tynes and cylinders, angle irons are joined together using welding operations. The welding methods used here are arc welding and gas welding. The fabrication consists of different steps as follows:

1. Machining of the tynes are done using lathe, manually.

2. Cylinders are machined to 163 and 138mm from 170 and 140mm diameter for larger and smaller cylinders, respectively.

3. Cylinders are welded to the shafts of diameter 30mm, using circular plates.

4. For fixing the tynes, holes are made over the cylinders using drilling machine.

5. Tynes are welded over the cylinders, by inserting the lower portion of tynes in the holes.

6. The major load carrying component, frame was constructed by joining angle irons as in the design.

7. Bearings, Bushes, blocks, etc are welded to the shafts.

8. Using cast iron plate, seating for motor is made on the frame.

9. Transmission system is attached to the frame, as per in the design.

Figure V. Coconut Dehusking Machine

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VI. RESULT AND EVALUATION It is observed that the machine has the capacity to

dehusk the commonly available coconut of different thickness and hardness, effectively. The machine can normally dehusk about 120 to 150 coconuts per hour even though, time require to dehusk is related with the age of coconut. TABLE 1. Shows time taken to dehusk, different aged coconut.

TABLE I. OBSERVATION AND TABULATION

SL. No.

Age of coconut (days)

Dehusking time(sec)

Remarks

1. 0-2 20 Can dehusk easily

2. 2- 6 25 Can dehusk easily

3. 6-10 30 Can dehusk easily

4. 10 – 20 35-45 Difficult to dehusk

From the above table, average time taken to dehusk a

coconut = 25seconds. Major observations during working are:

1. Negligible vibration level was observed. 2. Negligible variations in Speed of component

pulleys are observed. This may due to the slip in pulley.

A. Profit Estimation General Data used for profit estimation are:

• Net cost of the machine = 18,000 • Working cost of machine, per hour = 6 • Number of coconut dehusk per hour=120 • Cost for dehusking one coconut = 6/120=5paise • Cost to dehusk 120 coconuts manually = 96 • Cost for dehusking one coconut, manually

= 0.80paise 1) Per Day Cost analysis: Using machine

• Number of hours of working per day = 8.5 hours • Number of coconuts dehusking per day = 1000 • Cost for dehusking 1000 coconuts

= (6/120) ×1000= 50Rs • Cost for human assistance = 300Rs • Total Cost for dehusking 1000 coconuts

= 300+50 = 350Rs.

2) Per Day cost Analysis: Manually

• Number of hours working per day = 8.5 hours • Number of coconuts husking per day = 1000 • Cost for dehusking 1 coconut = 0.80 • Cost for dehusking 1000 coconuts

= 1000×0.80 = 800

3) Profit Analysis

• Net Profit per 1000 coconut = Cost for manual dehusking – Cost for machine dehusking = 800-350= 450

• Payback period = 18000/450 = 40 days.

B. Advantages: 1. It is user friendly, rapid and can be operated

safely. 2. Compact in size and portable. 3. Husks are separated, in the form of thin fibers; so

it is very useful to make other valuable products. 4. The coconut shell of any thickness and hardness

can be easily removed. 5. Skilled labor is not required to operate the

machine. 6. Less maintenance.

C. Dis advantages: 1. Since the machine is mainly designed for large

scale coconut growers, it is not economic for house hold purposes.

2. Length in between the cylinders is not adjustable.

VII. CONCLUSION In this modern world the time and cost has more

weightage for each and every operation. So a new machine has been designed, fabricated and named as “Coconut dehusking machine” to reduce the cost and to save energy. By comparing with many types of existing methods, includes traditional, and automatic, it can be concluded that this machine require less power and less human effort, and the test results substantiate the above.

VIII. FUTURE WORK 1. By increasing the length of the cylinders, rate of

dehusking can be increase. 2. Length in between the cylinders can be adjusted

so as to accommodate various dimensions of coconuts

3. Tynes can be attached to the cylinder using fasteners; so that replacement can be easily done.

REFERENCES [1] A.V. Gajakos. development of power operated coconut dehusker

February-May 2008, Vol. 3 (1&2):167-170. [2] S.K Hajra Choudhury, S.K. Bose, A.K. Hajra Choudhury, Nirjhar

Roy, Elements of Workshop Technology, Vol: ׀׀, Machine Tools, Media Promoters & Publishers Pvt. Ltd, Edition:1964.

[3] K. Mahadevan, Dr. K. Balaveera Reddy, Design data Hand Book For Mechanical Engineers, CBS Publishers & Distributors, New Delhi, Edition: 1987.

[4] R.K. Singh and B. Subburaj, Market share of Tender nuts - An Estimation - Indian Coconut Journal 8-10, Vol. XXXIV No. 5 September, 2003.

[5] C.V. Sairam S. Arul Raj and Rajagopal Perspectives of Marketing Research for Coconut and its products; (CPCRI, Kasargod Kerala)

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