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Design, Fabrication and Testing of a Torsional Compression Thread-based
Gari Screw-type Press
(Cassava Pulp Mechanical Dewatering Machine)
Daniel Amoshie 1, Marshall Dzwene 2, Munashe Nyazenga 3 and Simbarashe Tanyanyiwa 4
Engineering Department, Ashesi University
1 Electrical Engineering; daniel.amoshie@ashesi.edu.gh
2 Electrical Engineering; marshall.dzwene@ashesi.edu.gh
3 Computer Engineering; munashe.nyazenga@ashesi.edu.gh
4 Electrical Engineering; simbarashe@ashesi.edu.gh
Abstract: Gari is a popular type of food in Africa obtained from the dry frying of dewatered cassava pulp. Unfortunately, small scale
Gari producers in Africa are hampered by adoption of inefficient and inappropriate pressing methods. This delays Gari production
and results in low quality products. The purpose of this study is to design, fabricate, and test a torsional thread-based cassava pulp
mechanical dewatering screw press which will provide a cheaper way of pressing cassava compared to the modern methods which
are too expensive for the ordinary farmer due to the complexities involved in their processes and the components used in
manufacturing them. The aim is to make a more hygienic system by enclosing the cassava pulp in a confined cylindrical space and
providing a way of trapping the liquid emanating from the compressed cassava pulp during pressing. The screw will make it easy to
drive and press the cassava pulp. The research also gives details of the manufacturing processes, tools, materials, that will be used
if the product is fabricated. Cassava was not utilized in the testing process, rather, a wet napkin to test the pressing mechanism by
reducing its moisture content. It was found that the machine could dewater 2 kg wet a napkin with 70 % to 15 % moisture in about
3 minutes. The maximum stress reported on the screw shaft handle was 2.773 ×107 N/m2 which was less than the yield strength of
the material used for the simulation.
Keywords: Dewatering, Cassava, Press, Gari, Torsional, Ferritic
1.
Introduction
Gari, the most commercialized cassava product in
Ghana, continues to increase in production due to the
increasing urban demand and export market potential [1].
Cassava is a plant that originated in South America but is
now grown in most African countries [2]. Small-scale Gari
processing methods in Ghana are primarily traditional,
leading to a limited range of finished products from
cassava [3]. Old and inefficient local gari pressing
methods are time-consuming (taking up to 4 days or more),
less hygienic, and result in poor/low product yields.
Existing methods need to ensure product quality
consistency or scale economies [3].
Current dewatering operation is mainly carried out
manually in rural communities. One of the approaches is a
"twisting sack to effect dewatering" method, where the wet
cassava mash is placed in a porous sack and manually
twisted to squeeze out the excess water [4]. Another
approach is placing a "heavy stone on top of mash sack,"
where wet cassava mash is put inside a porous sack, and a
heavy stone is placed on top of the sack to press out the
excess water [4]. These methods are labor-intensive and
time-consuming, especially for large-scale production.
Additionally, modern methods are too expensive for
the ordinary farmer due to the complexities involved in
their processes and the components used in manufacturing
them. An example is the design and fabrication of an
electric motor driven press (cassava dewatering machine)
by O.P. Akinmolayan et., which uses an electric motor and
a screw press where cassava mash is fed into a hopper, and
the screw press applies pressure to the mash, forcing the
water out through the perforations on the press. The
narrow range of processed products and poor processing
technologies could also affect the commercialization of the
crop in Africa [3].
Based on the challenges with current approach to gari
dewatering, this project therefore aims to design, fabricate,
a mechanical gari dewatering system which will provide a
cheaper way of processing cassava. Another goal is to
create a more sanitary system by enclosing the cassava in
a confined cylindrical space and providing a method of
trapping the liquid emitted from the compressed cassava
pulp during pressing to make the whole process more
hygienic. The research gives details of the manufacturing
processes, tools, materials, that will be used if the product
was to be fabricated. Cassava was not utilized in the testing
process, rather a wet napkin to test the pressing mechanism
by reducing its moisture content.
2.
Equipment and Methods
One of the top priorities of this research study was to
identify the best material for making the gari press.
Several factors were considered when deciding on the
materials that will be used to construct the gari press. Such
factors include mechanical strength, corrosion resistance,
impact resistance, and cost.
2
2.1.
Equipment
In this study, SolidWorks 2019, was used to design and
perform mechanical analyses on the desired solution
concept. The scrap materials used in making the low fidelity
prototype of the desired solution concept were obtained
from Kumasi, Ghana. Microsoft Excel was used to plot
graphs the collected data, for further analysis.
2.1.
Methods
2.1.1.
Brainstorming
Several solution ideas were generated during a
brainstorming session to address a problem. Sketches were
drawn to conceptualize the designs. Four design ideas were
presented. The first design idea was a hydraulic jack gari
press, which would use a hydraulic cylinder on a sliding
piston to force liquid out of cassava pulp as shown in Figure
1a. The second design was an electric motor drive press,
which would lower a pressing lid slowly to press liquid out
of the cassava pulp using an electric motor and gear as
shown Figure 1b. The third design was a torsional
compression thread based gari screw-type press, which
would use a thread connected to a handle to press cassava
pulp and force liquid out through perforated holes as shown
in Figure 1c. The fourth design was a centrifugal press,
which would rotate cassava pulp at high speed to separate
it from liquid using centrifugation shown in Figure 1d.
Figure 1: (a, b, c, d) show the four sketches of the design solution
ideas for the identified problem (hydraulic jack gari press, electric
motor driven press, torsional compression thread based Gari Screw-
type Press, centrifugal press)
2.1.2.
Selection
After evaluating the different concepts from the
brainstorming session, a torsional compression thread
based Gari Screw-type press was selected the final design
solution. This design was chosen for its numerous benefits.
Firstly, this type of press applies torsional force to compress
the cassava pulp, which is highly effective in removing
excess water and ensuring high-quality Gari. Secondly, the
screw-type press allows the cassava pulp to be confined in
a cylindrical space during pressing, resulting in a more
hygienic process that reduces the risk of contamination.
The screw also simplifies the process of driving and
pressing the cassava pulp, which is important for small-
scale Gari producers.
Furthermore, the torsional compression thread-based
Gari screw-type press is more cost-effective than modern
methods that involve complex processes and expensive
components. This makes it a more viable option for small-
scale Gari producers in Africa who may have limited
financial resources. In summary, the torsional compression
thread-based Gari screw-type press is the best design for
Gari dewatering due to its effectiveness, hygiene, ease of
use, and cost-effectiveness.
The prototype was designed to take a load of about
20KN. Since load is transmitted under compression, the
screw was made from Ferritic Stainless steel with yield
stress of 200 N/mm. The screw was subjected to the
equation given by,
Where W is load, As is the area of screw, is yield stress
and is the factor of safety.
This informed the choice of screw diameter for building.
2.1.3.
SolidWorks Engineering Design
2.1.3.1.
3D Isometric
As mentioned earlier, SolidWorks 2019, was used to
design the torsional compression thread based Gari Screw-
type press. The SolidWorks design is shown in Figure 2
below.
Figure 2: Shows the SolidWorks Design of the Gari Press (a-b) 3D
Views of the Different Components of the Press (c) Exploded View
of the Gari Press (d) Fully Assembled Gari Press
2.1.3.2 Third Angle Autographic view
The fully assembled SolidWorks Design of the Gari
Press by dimension (See Figure 2), can be put in a box with
a vertical height of 723.41 mm, a horizontal width of 350
mm and a horizontal length of 370 mm. The cylindrical
container has a diameter of 300 mm and a height of 280.78
mm, while the circular plate connected to the central screw
shaft has a diameter of 280 mm. The frame with the mid-
3
joint nut for the screwing system has a vertical height of
427.50 mm and is 30 mm above the cylinder to give room
for screwing. The cylindrical container has circular
perforated holes (10 mm in diameter) which allow liquid
from the cassava pulp to seep through during mechanical
compression into the collection canal. The collection canal is
large enough (370 mm by 350 mm by 50 mm) to hold the
liquid emanating from the compressed cassava through the
perforated holes for a while as it flows out through the
connected outlet tap (10 mm in diameter). The screw shaft
handle (12 mm thick) is what will provide the required
torsional force to drive and press the cassava pulp.
Figure 3: Shows the 3rd angle autographic projection with all
detailed drawings and dimensions in mm.
2.1.4 Cost Analysis
Before prototyping and simulation, a cost analysis of
the gari press was conducted to determine the total amount
required to make the gari press by breaking down the costs
into unit costs of the respective part’s dimensions and
material type.
Table 1: Cost analysis for the Gari Press
Part
Dimensions
(
±
.
~
.
)
Material
Type
Unit Price ($)
Cost ($)
Frame (40 ×
mm
square tubes)
1.70 m
length,
0.04 m
thickness
Ferritic
Stainless
Steel
4.57/m
7.77
Flat circular
press
plate
0.3 m
outer
radius,
0.03 m
thick
Ferritic
Stainless
Steel
10.99/kg/m
10.99
Screw shaft
0.05 m
radius, 1m
height
Ferritic
Stainless
Steel
1.94/m
1.94
Perforated
Cylindrical
Container
0.3m inner
radius,
0.84 m
height
Ferritic
Stainless
Steel
11.21/m
11.21
Outlet
Pipe/Tap
0.05 m
thickness
Brass
9.35
9.35
Total Cost
38.06
41.26
2.1.5. Mechanical Simulation
Selective simulations were performed on the Gari
Press. A mechanical simulation was conducted on the
frame with the mid-joint nut for the screwing system and
the screw shaft handle (See Figure 2). It was necessary to
determine the response of the screw shaft handle and the
frame with the mid-joint nut for the screwing system when
an equivalent torsional force of 120 N was applied during
the screwing process on the Gari Press. Quantitative stress
data was then obtained from the simulated results by
probing across the screw shaft handle, near the joint.
2.1.6. Prototype Fabrication
A prototype of the Gari Press was fabricated to mimic the
3D model presented earlier in Figure 2. Parts were welded
together. Major parts used include a cylindrical container,
screw shaft, round bar, metal plate, nut, and square tubes.
3.
Results & Discussion
3.1.
Mechanical Simulation
From the simulation conducted on the T-shaped screw
shaft of the gari presser, assuming a torsional force of 120
N, the maximum stress reported on the screw shaft handle
was 2.773 ×107 N/m2. This strength was less than the yield
strength of the material used for the simulation (ferritic
stainless steel) ~ 1.723 ×108 N/m2, which implies that under
static torsional loading, the T-shaped screw shaft of the gari
presser (made from ferritic stainless steel) would sustain
the applied force without plastic deformation. Therefore, it
would not yield due to any evidence of permanent plastic
deformation, which leads to failure. Quantitative stress data
was also obtained from the simulated results by probing
across the screw shaft handle near the joint (Figure 4a). The
graph (Figure 4b) suggested higher stresses near the join
where the screw shaft connected with the screw shaft
handle. Stress distribution was found to increase from
2×106 N/m2 to 1.25×107 N/m2.
Figure 4:(a) Qualitative Model of the Simulation of the Gari Press
after applying a Torsional Force of 120 N and (b) Quantitative
Data Obtained from probing across screw shaft handle near the
joint shown in (a)
An upward reaction force was then induced on the
circular press to counter the net downward force, and to
determine the response of the frame with the mid-joint nut
for the screwing system. The maximum stress reported on
the frame with the mid-joint nut was 2.348×106 N/m2 which
4
is less than the yield strength of the material used for the
simulation (ferritic stainless steel) ~ 1.723 ×108 N/.
Quantitative stresses near the fixing point, where the threads
flashed with the middle nut. Stress distribution was found to
increase from 1x105 N/m2 to 2.1x105 N/m2. However, the
result was reduced at the midpoint of the screw, halfway
between the two points where the threads flashed with the
middle nut, to a value of about 1.55 × 105 MPa.
Figure 5: Qualitative model of the simulation of the gari press after
applying a torsional force of 120 N and an upward reaction force
was then induced on the circular press to counter the net
downward force (b). Quantitative Data Obtained from probing
across the frame with the mid-joint nut for the screwing system
shown in (a)
3.2.
Manufacturing
Process
The design is quite simple. The joints in the frame are
welded, first to the nut in the middle, then to the main four-
legged frame. The T-shaft screw with a welded handle is then
screwed into the mid-joint nut with a circular press plate
attached to its bottom that easily fits into the cylindrical
container, which is welded as part of the main four-legged
frame. The curved surface of the cylindrical container is
perforated to allow collection of drained fluid emanating
from the compressed cassava pulp into the collection
channel, then out through an outlet pipe to trap the liquid for
other uses. The cylindrical container is welded from beneath,
to hold casava during the pressing process. Tools required:
Spare parts – None; Fuel Type – None; Pressure Source -
Screw. Materials: Ferritic Stainless steel for the whole
design and Brass for the outlet pipe or tap.
Figure 6: (a) Prototype of the torsional compression thread-based
gari screw-type press (cassava pulp mechanical dewatering machine
4.
Conclusion
From this project, it was found that a mechanical
dewatering screw press provides a cheaper way of
processing cassava compared to modern methods. Also, it
was discovered that the moisture content of cassava pulp is
dependent upon the pressure applied, volume of cassava,
and mass of cassava which are parameters that can be
considered for further research. However, further research
should be done on how to increase the quantity of gari that
can be produced from cassava per batch.
One of the major lessons learned was the procedure
for selecting the suitable materials by considering their
mechanical properties. Simulation and 3D modeling prior
to fabrication proved to be of high importance when it
comes to working with different materials to produce a
final product. Stainless steel was selected based on its
BCC structure (high tensile strength) and its moderate
ductility, derived from solid solution strengthening and
strain hardening. Stainless steel was also selected due to
its excellent resistance to corrosion, weldability, and its
relative cheapness. discovered that chromium is what
makes stainless steel stainless. Chromium is also a ferrite
stabilizing element. Chromium causes the austenite region
to shrink, while the ferrite region increases in size.
Acknowledgments
Much appreciation and thanks go to Dr. Danyuo
Yiporo and Mrs. Miriam Abugre, our project supervisors, for
their unwavering support throughout this project.
References
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[2] Olusegun, H. D. & Ajiboye, T. K. (2009). The Design, Construction
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