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IMPROVEMENT AND EVALUATION OF A

MINI MOTORIZED CORN SHELLER

Undergraduate thesis proposal submitted in partial fulfillment of the requirements

for the degree of Bachelor of Science in Mechanical Engineering from the Mariano
Marcos State University, City of Batac, Ilocos Norte. Prepared under the guidance of
Engr. Romaric G. Ascaño.

JOSEPH PAOLO S. DELA CRUZ

INTRODUCTION

Background of the Study

A corn sheller is a hand-held device or a piece of machinery to shell corn kernels

of the cob for feeding to livestock or for other uses. The Corn Sheller is a low-cost device

for removing corn kernels from the cob that makes it possible to shell corn several times

faster than manual shelling. Maize shellers can be made in many ways using a variety of

materials.

Shelling is the process of removing seed or grain from their respective cobs for

both human and industrial use. Shelling is best attained when the moisture content is as

low as 13%. Primitive method of shelling includes, beating with stick, crushing with

mortar and pestle, hand shelling and therefore consume much human energy and time.
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Maize production in the Philippines increased at an annual rate of 1.7% over a 20-

year period (1980-2000) (Table 8, Annex 1). After production peaked in 1990 at 4.9

million metric tons, a sharp decline was posted in 1998 when the El Niño phenomenon

affected the region. Total area planted to maize was also highest in 1990, at 3.8 million

hectares, but was observed to be on the decline at 1.9% per year from 1985 to 2001

(Gonzales and Lapiña, 2003). These long-term figures reflect a sharper decline in white

maize area in contrast to that planted to yellow maize. Further, while average yields for

white maize are consistently low, yellow maize yields increased by an annual rate of

4.9% over a 17-year period beginning in 1985 (Gonzales and Lapiña, 2003). The

adoption of improved technology for yellow maize production has resulted in significant

yield increases. Yellow maize accounted for 23% of total maize production in 1985, and

for 58% by 2001. It should be noted, however, that the national average yield of 1.82 tons

per hectare for white and yellow maize (in 2001) is low when compared to maize yields

in other Asian countries (Gonzales and Lapiña, 2003).

Most common in upland areas, maize production peaks from July to September;

the lean months are from January to June. The upland regions of Mindanao have the most

area planted to maize, and the highest production in the Philippines. Maize is also grown

in the rainfed lowlands, where it is planted during the dry season after the rice crop has

been harvested. The production of maize after rice increases the productivity of irrigation

systems during the dry season, while supplying needed grain during an otherwise lean

period. Integrating livestock into the system provides high value products and increases

the income of maize farmers with small landholdings (FSSRI, 2000; Eusebio and Labios,

2001).
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Conceptual Framework

INPUT PROCESS OUTPUT

Design of a mini model Evaluation of the mini

Review of the existing
based on the existing corn sheller
Motorized Corn Sheller
corn sheller

Fabrication of the mini

Capacity of the mini
corn sheller
corn sheller

Figure 1 Conceptual framework of mini motorized corn sheller

General Objectives

This study will focus on the improvement, and evaluation of the mini motorized

corn sheller for faster and more efficient corn shelling for home purposes.

Specific Objectives

1.) To design the mini corn sheller

2.) To fabricate the mini corn sheller

3.) To evaluate the capacity of the mini corn sheller

Significance of the Study

This study provides a fast, efficient, and convenient way to shell corn. It will also

benefit small scale farmers for this will be a low cost machine. It is also environment

friendly because it will use electricity as source of energy.

Scope and Limitations of the Study

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This study focuses on the design, fabrication, and evaluation of mini motorized

corn sheller. The design will be based on the existing corn shellers.

REVIEW OF LITERATURE
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Review of Related Studies

To obtain a better understanding of this research, a review on the historical

development and composition of corn shellers will be presented in this section.

For this dissertation the literature related to the following topics will be reviewed.

1.) Conventional corn shelling machines

2.) Non-conventional corn shelling machines

Conventional Corn Shelling Machines

The two types of shelling mechanisms commonly used for field shelling of corn

are the axial flow cage sheller and the cylinder-concave sheller. Both shellers have a

relatively high capacity. The popularity of the cylinder sheller has increased with the

practice of field shelling high moisture corn.

The cage sheller (Figure 2) consists of a cylinder with lugs, helical flutes, or

paddles which turns inside a cage. The cage has a perforated surface with holes large

enough to let kernels fall through but retain the cobs. The ears are fed into an opening at

one end of the cage. The helical flutes feed the ears through the cage and at the same time

shell them by a rolling and crushing action against the cage surface and each other. An

adjustable cob gate serves to retain the ears in the cage long enough to be completely

shelled. The ability to shell high-moisture corn is important when field shelling. Tests

conducted by Burrough and Harbage (1953) showed cage sheller losses of 5 to 10% when

kernel moisture was 29.6% and cob moisture was 56.5%, wet base. Part of the loss was

due to unshelled corn remaining on crushed cob sections, and part to difficulty in
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separating the damp kernels from the cobs. The percentage of kernels left on the cobs and

the percentage of kernels damaged by shelling were almost directly proportional to the

moisture content of the kern

Figure 2 The axial flow cage type sheller

The second basic shelling mechanism, commonly used in combines, consists of a

cylinder and a concave (Figure 3). The corn is shelled by the impact of bars on the

periphery of the cylinder as the corn is fed between the cylinder and the concave bars.

The most common type of cylinder bar used is the rasp-bar. These bars were shown to

cause less damage than an angle-bar type cylinder (Pickard, 1955). These cylinders are

commonly 55.9 cm (22 inches) in diameter and range from 61 to 152 cm (24 to 60

inches) in length, depending on the size of the combine. For corn shelling, they turn at

speeds of 400 to 700 rpm. The concave assembly nearly conforms to the periphery of the

cylinder. It forces the corn to be in contact with the cylinder through about 90 degrees of

cylinder rotation. The concave bars are channel, rectangular, or half round in shape and

are oriented parallel to the cylinder axis. The severity of the shelling action is controlled

by the cylinder speed and the cylinder to concave clearance. Clearance at the front of the

concave is approximately 3 cm. This allows ears to easily enter the threshing crescent
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between the cylinder and concave assembly. The cylinder-concave clearance tapers to the

rear and is about 1.5 cm at the rear of the concave. The severity of the shelling action

determines the amount of unshelled corn remaining on the cob and the level of kernel

damage. Cylinder adjustments are a compromise between high speeds for kernel removal

and low speeds for reduced kernel damage. Reducing the concave clearance also

increases the thoroughness of shelling and the level of kernel damage.

Kernel moisture content is another factor that has a great influence on kernel

damage (Hopkins and Pickard, 1953; Barkstrom, 1955; Goss et al., 1955; Pickard, 1955;

Fox, 1959; Brass, 1970; Hall and Johnson, 1970; Mahmoud, 1972). These 11 researchers

reported that mechanical kernel damage increased rapidly with increasing moisture

content over approximately 20%, However, corn shelled at moisture contents

considerably below 2056 moisture also suffered high levels of damage. Minimum kernel

damage was generally found to occur at kernel moisture contents of 18 to 22%.

Figure 3 The rasp bar cylinder-concave sheller

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Non-conventional Corn Shelling Machines

Corn shelled by the conventional combine cylinder suffers a high level of kernel

damage. Several com shelling machines have been developed by different research

workers in an attempt to shell corn with a relatively low damage compared to that caused

by the high impact action of the combine cylinder. Although the new experimental

machines succeeded in reducing the level of kernel damage, they lacked other functional

requirements such as high shelling efficiency, high capacity, and durability. An

experimental sheller that handles corn gently during the shelling process was designed by

USDÀ agricultural engineers (1967). This shelling device (Figure 4) consisted of two

endless rubber belts rotating in opposite directions at different speeds. The ears of corn

were rolled through the unit and were shelled with an intensifying squeezing action

provided by an adjustable pneumatic spring located at the discharge end. In laboratory

tests with this device, corn at 15% moisture content was shelled with no apparent damage

to the kernels. However, the low durability of the belts, low capacity of the sheller, and

the decrease in shelling efficiency at high moisture are major problems of this shelling

system.
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Figure 4 The USDA sheller uses two endless rubber belts operating in opposite directions to accomplish

shelling

The principle of rolling and squeezing was used in another experimental sheller

designed by Fox (1969). This machine consisted of two smooth-surfaced tires mounted

with their axes parallel as shown in (Figure 5). The two rollers rotate in the same

direction but at different speeds. A feeder plate shaped to the contour of the tire was used

to orient and feed the ears between the rollers. The hypothesis was that the combination

of compression, low impact and centrifugal force induced by the sheller reduced the

strength of the kernel attachment to the cob. The wedging action of the kernels and the

centrifugal force cause failure of the weakened attachment and the kernels are shelled as

the ear is rotated between the rollers. Fox ran comparative damage studies using the

rubber roller sheller and a combine cylinder. Kernel damage of corn shelled by the rubber

roller sheller ranged from 6% damage at 22% moisture content to 9% damage at 30%

moisture content, while corn shelled in the combine cylinder ranged from 15% to 30%

damage for 22% and 30% moisture content, respectively. However, the rubber roller

sheller was reported to have feeding problems, and its shelling of unhusked ears was
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unsatisfactory. Fox did not report the shelling capacity of the rubber roller sheller and

how it compared to the capacity of a conventional combine cylinder.

Figure 5 The compression-type sheller designed by Fox uses two pneumatic tires operating at differential

speeds

Peprah (1972) hypothesized that spring-mounting the rasp bars of conventional

rasp-bar cylinders would reduce damage to kernels during shelling. Laboratory tests were

performed in which corn was shelled with a modified combine cylinder with spring

mounted rasp bars (Figure 6). Shelling efficiency and percent kernel damage for various

spring constants were determined. The test results revealed that the spring-mounted rasp-

bar sheller had objectionably low shelling efficiency at low speeds. However, shelling

efficiency increased with increasing speed, especially when softer springs were used.

Comparative damage studies showed that the spring-mounted rasp-bar sheller had a

slightly lower percent damage than the conventional combine cylinder. The percent

damage decreased with a decrease in the spring constant and increased with speed.
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Figure 6 Schematic diagram of the spring-mounted rasp-bar sheller (Peprah, 1972)

Review of Related Literature

Design of the Shelling Cylinder with spikes

NUMBER OF SPIKES ON SHELLING CYLINDER

Lc π d
Np= x
Ssr Ssc

Where:

Np = number of spikes on shelling cylinder

Lc = length of shelling cylinder

Ssr = spike spacing on row

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Ssc = spikes spacing on circle

d = diameter of shelling cylinder

TORSIONAL MOMENT OF SHAFT

P
Mt=
2π N

Where:

Mt = torsional moment (Nm)

P = power (watts)

N = speed (rpm)

MAXIMUM BENDING MOMENT

Mb=√ M BV 2 + M BH 2  

Where:

Mb = maximum bending moment (Nm)

Mbv = maximum vertical bending moment (Nm)

Mbh = maximum horizontal bending moment (Nm)

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SHAFT DIAMETER

The following formulas were used in determining power transmitted on shafts. This was

taken from Philippine Mechanical Engineering (PME) Code.

D3 N
P=
80

Where:

P = Power transmitted in Hp,

D = Shaft diameter in inches, and

N = Rotational Speed in Rpm.

V-belts and V-belt pulleys

V-Belts are friction based power or torque transmitters. The power is transmitted

from one pulley to the other by means of the friction between the belt and pulley. The

rubber used as the base material plays a very vital role in this. This is quite similar to the

friction between the Tyre and road in the automobiles that enables the automobiles to

move on the road.

V-belt pulleys are devices which transmit power between axles by the use of a v-

belt, a mechanical linkage with a trapezoidal cross-section. Together these devices offer a

high-speed power transmission solution that is resistant to slipping and misalignment.

Design of V-belt and Pulley

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LENGTH OF V-BELT

π ( D 2−D 1 )2
L=2 c + ( D 2+ D 1 ) +
2 4c

Where:

c = center distance

D2 = pitch diameter of bigger pulley

D1 = pitch diameter of smaller pulley

ARC OF CONTACT

D2−D1
θ=π +
c

Where:

Ɵ = arc of contact in radian

c = center distance

POWER OF THE MOTOR

Design HP=Power Transmitted (Nsf )

Where:

Nsf = service factor

RATED HP/BELT
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0.09
103 Vb 2
Rated HP
Belt
=a
[( )
Vb
−
c
Kd ( D 1 ) ( )] ( )
−e
106
Vb
103

Where:

a, c, and e = constants

Vb = velocity in fpm

Kd = correction factor

D1 = pitch diameter of smaller pulley in inches

ADJUSTED RATED HP/BELT

Adjusted Rated HP Rated HP

Belt
=( K θ ) ( K L ) (
Belt )
Where:

KƟ = correction factor

KL = correction factor

Rated HP/Belt in HP

Adjusted Rated HP/Belt in HP

NUMBER OF V-BELTS

Design HP
No .of Belts=
Adjusted Rated HP

DESIGN OF PULLEY
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The following formula was based from the “Design of Machine Elements” by

V.M. Faires, 1969,

V = πDN
Where:

V = Linear velocity of the pulley

N = Rotational speed of the pulley

D = Diameter of the pulley

METHODOLOGY
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This chapter will show the discussion on how this study will be accomplished by

the researcher.

Design of the Mini Motorized Corn Sheller

The related studies and literature will be applied in the designing of the mini

motorized corn sheller. The design will be based on the existing motorized corn sheller.

The design, fabrication, and evaluation of the mini motorized corn sheller will

start from the selection of sheet metal to be used as housing of the machine and the rating

of motor to be used on the corn sheller. A table comparing the capacity of corn being

shelled with different speeds will also be made in order to measure the capacity of the

machine.

Fabrication of the Mini Motorized Corn Sheller

The designing of the shelling cylinder will be based on some formulas. The

number of spikes on the shelling cylinder will then be computed. Then the torsional

moment of the shaft and maximum bending moment will also be computed as well as the

diameter of the shaft.

Evaluation of the Mini Motorized Corn Sheller

For the evaluation of the mini corn sheller, the individual parts of the machine

will be evaluated first to ensure that each part will work properly as it should then the

machine will be assembled and will be evaluated as a whole. The capacity of the corn

sheller will also be measured after the evaluation of the motorized corn sheller the

capacity will be based on how much corn it can shell with a given time.
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LITERATURE CITED
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Al-Jalil, Hamid Fadhil (1978)., "Design and performance of low damage corn shelling
machines” Retrospective Theses and Dissertations. 6477.
http://lib.dr.iastate.edu/rtd/6477

Idowumi Olugbenga Adewumi (May 2015), “Design, Fabrication and Performance

Evaluation of a

Motorized Maize Shelling Machine”

http://researchgate.net/publication/281274006

Oriaku E.C, Agulanna C.N, Nwannewuihe H.U, Onwukwe M.C and Adiele, I.D (2015)

“Design and Performance Evaluation of E. a Corn De-Cobbing and Separating Machine”

S.B. Patil, J.S. Ghatge and P.R. Sable (2018), “Study on Shelling Techniques of Sweet
Corn”

https://doi.org/10.20546/ijcmas.2018.704.062

Anirudha G. Darudkar Dr. C. C. Handa (2015), “Literature Review of Corn Sheller

Machine”