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International
Academic
Journal
of
Innovative Research International Academic Journal of Innovative Research Vol. 3, No. 11, 2016, pp. 1-20. ISSN 2454-390X
1
www.iaiest.com
International Academic Institute for Science and Technology
Design and Fabrication of Compression Molding Machine for
Plastic Waste Recycling in Nigeria
Ejiroghene Kelly Orhorhoroa*, Eruero Victor Atuma
b, Ayodele Samuel Adeniyi
c
aCemek Machinery Company, Technology Incubation Centre, Federal Ministry of Science and Technogy, 188, Sapele Roadd,
Benin City, Edo State, Nigeria b
Department of Mechanical Engineering Engineering, ,Faculty of Engineering, Delta State Polytechnic, Ote-Oghara, Delta State. cDepartment of Mechanical Engineering, Faculty of Engineering, University of Benin, Benin City, Edo State, Nigeria
Abstract
The current study was aimed at the design and fabrication of compression molding machine for plastic
waste recycling in Nigeria. The machine was designed, fabricated and assembled from locally available raw materials in Nigeria. The machine consists mainly of threaded screw, hopper, heater, heating
chamber, forming chamber, steel frame, and control switch. The raw materials (waste plastics) were
loaded through the hopper and heated within a temperature range of 1800C-220
0C and under a pressure of
3.77 MN/m2. The control switch was used to control the system. Newtonian fluid flow and Non-
Newtonian fluid flow were applied. The working temperature was determined as 2200C. Thus at that
temperature, the polythene solid plastic waste material undergo change of state from solid to completely
liquid. Others parameters calculated for are molding temperature (420C), material plasticizing rate
(1kg/hr), heat transfer per unit mass (2520W), total force (142.58KN), pressure distributed in the barrel
(3.77MN/m2), volume flow rate (1.178 x 10
-5m
3/sec), and factor of safety (1.33). From the results
obtained based on the quality of mold produced by the compression molding machine, the fabricated
machine performance was satisfactory and can be used locally and industrially in small scale.
Keywords: Waste, plastic, compression molding machine, recycling, Nigeria
Introduction:
The rapid growth of plastic products industry in Nigeria accounts in part for its attractiveness to
entrepreneurs. Almost every storage containers, eating plates, sockets, household appliances are made
with plastic products. The continuous increase in quantity of plastic waste generated in Nigeria is due to
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larger volume purchases of finished product made of plastics (Orhorhoro et al., 2016). Plastic product
after used and dumped, contribute about 8.69% of total municipal solid waste generated in Nigeria
(Igbinomwanhia, 2011; Gideon et al., 2014) as shown in Table 1.
Table 1: Average component of solid waste generated per person per day in Oredo LGA, Benin
City, Edo State, Nigeria (Igbinomwanhia, 2011)
Type of solid wastes Weight (kg) % Component
Food waste 0.334 78.59
Plastic/Rubber 0.037 8.65
Paper 0.016 3.67
Metal waste 0.017 4.11
Glass 0.012 2.83
Other waste (Textile, foam, ceramics, ash, etc.) 0.009 2.10
Total solid waste (ppd.) 0.425 100
Nigeria has poor policy of waste management and this is of concern and threat to the entire populace.
Plastic waste poses a serious threat to average Nigeria household and if something urgent is not done, it
will become uncontrollable (Figure 1). Continuous dumping of plastic waste in water way, road side,
institution, market places, churches, mosque, event centres, etc. is of health concern. This indiscriminate
dumping of waste is the major causes of blockage of drainage systems, causing erosion and flooding.
They are a breeding ground for mosquitoes, thus, posing a serious health risk to the entire populace. Due
to the inadequacy of local recycling facilities in Nigeria, the generation of plastic waste has multiplied
steadily over the years as a result of rising population, urbanization and industrialization (Nkwoh, 2006;
Oziegbe, et al., 2016). The problem of solid waste started in Nigeria with the rapid increase in urban
growth resulting partly from the increase in population status (Eguniobi, 1996). No town in Nigeria can
boast of finding a lasting solution to the problem of filth and huge piles of solid waste, rather the problem
continues to assume monstrous dimensions (Okpala, 2002). To urban and city dwellers, public hygiene
starts and ends in their immediate surrounding and indeed the city would take care of itself. The situation
has so deteriorated that today the problem of solid waste has become one of the nations most serious
environmental problem (Titus and Anim, 2014). In Nigeria, the commonly practiced waste management
option is basically the collection of mixed waste materials and subsequent dumping at designated
dumpsites. It is not a practice to separate waste materials at source or any point during its management
(Akintokun et al., 2011).
The problem of plastic waste is not only limited to Nigeria. It is a global phenomenon. The worlds
annual consumption of plastic materials have increased from around 5 million tons in the 50s to more
than 100 million tons; thus, twenty (20) times more plastic is produced today than 50 years ago (UNEP,
2009). This implies that more resources are being used to meet the increased demand for plastic, on the
other hand, more plastic waste is being generated (UNEP, 2009, Orhorhoro et al., 2016). Looking at the
volume of plastic waste generated in Nigeria, there is urgent need for proper plastic waste management,
thus, this research work. This research work is centre on plastic waste management via compressor
molding technology. Solid plastic waste can be recycled by the process of compression molding and this
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will not only reduce environmental pollution as a result of plastic waste but it will also lead to production
of useful plastic materials for both home and industrial use.
Figure 1: Blockage of drainage by used PET bottles
Compression molding is a major technology in the plastic industry, and is one of the original processing
methods for manufacturing plastic and it components (Figure 2). The technology has evolved from the
production of the simple things like combs and buttons to major consumer, industrial, medical, and
aerospace products. In fact, it was widely used in the bakery industry for cookie or cake molding before
plastic materials exist. Although is also applicable to thermoplastics, compression molding is commonly
used in manufacturing thermoset parts. The raw materials for compression molding are usually in the
form of granules, putty like masses. The main concept of plastic molding is placing a polymer in a molten
state into the mold cavity so that the polymer can take the required shape with the help of varying
temperature and pressure. The mold is then closed and pressure is applied to force the materials to fill the
cavity. A hydraulic ram is often utilized to produce sufficient force during the molding process. The heat
and pressure are maintained until the plastic is used.
Figure 2: Pictorial view of Compression molding machine (Kamal, 2009)
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Operation of Compression molding
The operations required to produce plastics products by compression molding include:
1. Preparation of molding material
2. Melting the material
3. Forcing the material through a nozzle and into a mold
4. Ejecting the molded part
5. Machining and finishing the product
Figure 3 shows the various operation of compression molding. As showed in Figure 3a, the molding
compound is placed in an open heated mold cavity, where the mold is closed and pressure is applied to
force the material to fill up the entire mold cavity (Figure 3b). Excess materials are usually channeled by
the overflow grooves. The heat and pressure are maintained until the plastic materials are cured. The
produced final product is removed as shown in Figure 3c.
Figure 3: Various operation of compression molding
Primary factors of compression molding
There are four major primary factors in a successful compression molding processes
1. Quantity of materials
2. Heating time and techniques
3. Force applied to the mold, and
4. Cooling time and techniques
Critical process parameters of compression molding method
The critical process parameters of compression molding method are as follow (Figure 4) 1. Time
2. Temperature, and
3. Pressure
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Figure 4: Critical process parameters of compression molding method
Research Methodology
The amount of requires heat and pressure is applied for a define period of time. The material is placed in
between the molding plates flows, and this is to ensure that there is application of pressure and heat for
the sole purpose of acquiring the required shape of the mold cavity with high dimensional accuracy.
Temperature and pressure facilitate the process of flow raw material into the cavity, which has been
generated between the two mold halves. This was allowed for the curing process to takes place. The
temperature accelerates the curing process. Curing is done at an elevated temperature. The two mold
halves are open and the final product taken out. Figure 5 shows the process flow chart.
Figure 5: Process flow chart
Conceptual Design
The main aim of the research work is to design and fabricate a perfectly working compression molding
machine for the sole purpose of waste management in Nigeria. To achieve the said aim, a conceptual
design was generated (Figure 6).
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Figure 6: Conceptual Design
Functional requirement and Design parameter
To achieve the said aim, a set of functional requirements and design parameters were drawn. Any design
that satisfies all of the functional requirements will fulfill the aim, and the design parameters specify how
each functional requirement must be satisfied. The summary of functional requirement and design
parameter used for the research work is showed in Table 2.
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Table 2: Functional requirement and Design parameter
Functional Requirement Design Parameter
A temperature that can supply enough heat to melt
the materials
A temperature range of 1800C to 220
0C
A pressure that will be able to sustain the process A pressure of 15.8MPa
Prevent molten leakage from heating chamber to
mold former
Airtight in both heating chamber and mold forming
chamber
Efficiency and Performance A perfect working compression molding machine
Durability Lifetime of at least 10 years
Detail Design
Flow of fluid along a channel of uniform circular cross section
Figure 7 shows flow of fluid along a channel of uniform circular cross section
Figure 7: Element of fluid in a channel
Assumption: Flow is steady (Newtonian)
0 ZF
dz
z
ppdrF 21
(1)
pdrF 22 (2)
dddF zr23 (3)
ddtdzpdzpdrpdr .222
(4)
zpd
d r
2
(5)
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dzdprd 2 (6) But,
Maximum shear stress is at r =R, suppose there is pressure drop of P over length L
Therefore,
L
PR
2
(7)
But,
r
v
dd
(8)
Where,
=shear viscosity
= shear strain rate
V = Velocity
Combining equation (6) and equation (8);
22271
27
1
2
22 Rr
dzdp
V
rdrdz
dpdv
dzdprr
v
v
o
r
R
oVVrAt ,20
2
471 R
dz
dpVo
(9)
2
1R
rVV o (10)
Isothermal flow in channel (Non-Newtonian fluids)
The simplest model for analysis is given by the power law equation
1
n
oo Y
Y (11)
nn
oo T
1
(12)
Where,
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oY = shear rate at a chosen standard state
o = shear stress at a chosen standard state
o = shear viscosity at this state
From equation (416)
n
ooYY
1
no YY (13) Then,
Yo (14) Newtonian fluids are special cases of power law fluid with
n=1
Design of the compression molding machine wall (thick wall)
Figure 8: Stresses acting on element of radius r and dr
Where,
r1= internal radius
r2= External radius
Figure 9 shows stresses acting on an element of radius r and thickness dr subtending an angle d at the
centre
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Figure 9: Stresses acting on section of the cylinder
Radial stress r and circumferential stress c are both assumed to be tension, considered positive.
Resolving the forces on the element
2
2
d
cdrrddddrrd rrr (15)
rcrrr ddrd
c
r
rr
d
rd
(16)
Assumption,
If longitudinal strains are uniform along the length of the barrel
.constcr
acr 2
rc a 2 (17) Substituting equation (17) into equation (16)
022
2
2
ard
drr
ad
rd
r
rr
r
r
rr
Multiply through by r
022 arrd
dr
r
barrr 22
2r
bar
(18)
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11
22
r
baa rc
(19)
Considering a common case of a cylinder with internal pressure only such as the threaded screw type
plastic compression molding machine, the distribution of stresses on the wall thickness is showed in
Figure 10.
Figure 9: Distribution of stresses on the wall thickness
This implies,
2
2r
bap
(20)
Also,
2
2
2
1
2
2
2
1
0
rr
rpa
r
ba
2
2
2
1
2
2
2
1
rr
rprb
But, from equation (18),
2r
bar
(21)
Therefore,
2
2
1
2
2
2
1
2
2 1r
r
rr
prr
(22)
2r
bac
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12
2
2
1
2
2
2
1
2
2 1r
r
rr
rp
(23)
But the maximum radial and circumferential stresses occur at,
2rr
Where,
pr
2
2
2
1
2
2
2
1
rr
rrpc
(24)
Negative sign indicate high compression
For a thin wall compression molding machine
From,
2
2
2
1
2
2
2
1
rr
rrpc
tdttdtpd
c
2
22 22
(25)
Where,
dtk
rd
rrt
/
2 2
21
If rc is constant across thickness which is reasonable enough, then
t
pdc
2
(26)
kp
c
21
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Design for Heat Transfer
Figure 10 shows heater on barrel
Figure 10: Heater on barrel
From;
t
T
x
T
12
2
(27)
Where equation (27) is Fouriers equation for non-steady heat flow in one dimension
T = Temperature
= thermal diffusivity But;
pc
k
(28)
Where,
= Density
k=Thermal conductivity
Cp= Specific heat capacity
Where,
sec/101 27 m (Thermoplastic)
Temperature gradient
21
23
TT
TTT
(29)
Where;
T1 = initial uniform temperature of the melt
T2 = temperature of heating or cooling medium
T3 = temperature at time, t
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Design for Heater energy
Melting temperature of thermoplastic = 220oC (High density polyethene-measured)
Molding temperature = 42oC (measured)
Material plasticizing rate = 1kg/hour (measured)
q=Heat transfer per unit mass
W =Work transfer per unit mass
H= Enthalpy
W=0 (for plunger compression molding)
Therefore;
hmq (30)
q=56x45= 2520W
Younesi et al., 2009 reported 2000W for injection compression molding
Estimated threaded screw speed
The estimated threaded screw speed was determined as follow shown in Table 3
Table 2: Estimated threaded screw speed
Number Threaded screw speed mm/sec
1 6.5
2 5.5
3 5.7
4 7
5 6
6 6
7 5.5
8 6.5
9 6
10 6
Average = 10665.65.566755.55.6
= 6mm/sec
Working temperature = 220oC
Volume flow rate
Volume flow rate Q = Area x Velocity
Assumption,
Flow is Newtonian and Isothermal
That is;
Q = AV (31)
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4
1050
50
4
sec/106sec/6
23
2
3
A
mmD
DArea
mmmV
323
1064
1050
Q
sec/10178.1 35mQ
Distance between the torpedo and barrel
22 rRx
22
dDdDx
(31)
2
2550
2
2550x
(32)
mx
x
x
310473.1
0125.00375.0142.3
1000
5.12
1000
5.37142.3
Apparent strain rate
x
QY
6
(33)
sec/10259.2
10473.1
10178.16
4
3
5
mY
Y
Also,
L
px
2
(34)
And,
Y
Where,
mN /1043.15 3 , a constant value
Y
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MN3.6810259.2
1043.154
3
From,
L
px
2
(35)
x
Lp
2
Where,
P = pressure
2
3
33
/77.310473.1
1043.15101802mMN
mp
Force due to pressure
prF 2 (36)
Where,
F = Force due to pressure
r = internal radius
KNF 14.1421077.31012142.3 63
Surface area of torpedo DLSA (37)
Where,
SA= surface area of Torpedo
Viscous drag force DLVDF (38)
Where;
VDF = Viscous drag force
D = External diameter of barrel
=shear stress
NVDF 33.4361043.15101801050142.3 333
Total Force
VDLFTF (39) Where,
TF = Total force
F = Force due to pressure
VDL = Viscous drag force
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KNTF 58.14233.436140,142
Pressure distribution in barrel
Recalling,
Pressure P = 3.77MN/m2
Diameter D = 50 x 10-3
m
Thickness of barrel t=3mm = 3x10-3
m
Yield stress (max) mild steel 1050 hot rolled = 4.13x108N/m
2
Failure will occurs when the greatest principle stress exceed the elastic limit stress in a simple tension test
irrespective of the other principal stresses
Assumption,
Since machine is a threaded screw type compression molding machine, force is applied only by the
threaded screw
Thus,
oy Where,
y = stress by the application of force by the plunger
o = safe working stress of the barrel
t
pdy
2
(40)
2
3
36
/42.311
1032
10501077.3
mMNy
y
Therefore, the stress at the wall of the barrel is 311.42MN/m2 which is far below the yield stress (i.e.
4.13x108Nm
2)
Factor of Safety
Safety factor = 33.1/1042.311
/1013.426
28
mN
mN
o
y
Therefore, a barrel with a thickness of 3mm is adequate
Figure 11 shows the isometric view of the fabricated compression molding machine
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Figure 10: Isometric view of compression molding machine
Discussion
In this research work, design of a compression molding machine was carried out for performance
evaluation. With the manufacturing process in mind, it was essential to choose a material (polythene) that
can withstand the properties of real time mold. In making the mold it was necessary to have the best
possible product design so that it would not complicate the mold designing process. With all the required
dimensions and by the help of conceptual design which mainly based on functional requirement and
design parameters, detail design of the compression molding machine was achieved. It was crucial to find
out if there were any defects in the product design. The working temperature was determined as 2200C.
Thus at that temperature, the polythene solid plastic waste material undergo change of state from solid to
completely liquid. Others parameters calculated for are molding temperature (420C), material plasticizing
rate (1kg/hr), heat transfer per unit mass (2520W), total force (142.58KN), pressure distributed in the
barrel (3.77MN/m2), volume flow rate (1.178 x 10
-5m
3/sec), and the factor of safety (1.33). With all the
parameters calculated for, the compression molding machine was fabricated and tested. The quantity and
quality of plastic waste recycle via the technology prove that the machine can be used domestically and
for small scale industrial use.
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19
Conclusion
Test performance was carried out on the fabricated compression molding machine. Polythene materials in
pellet and small size particles were completely melted between 2000C to 220
0C. The time to melt and
mold forming were taken note of respectively. From the results obtained based on the quality of mold
produced by the compression molding machine, the fabricated machine performance was satisfactory and
can be used locally and industrially in small scale.
Recommendation
Considering the huge economic and environmental importance of the use of polyethenes and plastics, the
government of Nigeria and research centres should bring to the awareness of the society the importance
of recycling wastes polyethenes and plastics through compression molding technology. The government
of Nigeria should invest more on compression molding as this will not only help in re-cycling of waste
polythene and plastics but as well provide jobs among the millions unemployed Nigerian youths.
Contributions to knowledge
The following important results where attained which can be used for future fabrication of a compression
molding machine.
1. It was established that a temperature range of 1800C-220
0C and under a pressure of 3.77MN/m2 can be
used to change the polythene waste plastic materials from solid state to liquid state.
2. It was equally established that a threaded screw speed of 6mm/sec can be used for subsequent project
work.
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