1. Designing a Machine Element: Screw Press
A report submitted to the Department of Mechanical Engineering, Khulna University
of Engineering & Technology in partial fulfilment of the requirements for the
“Course of ME 3118”
Submitted to Submitted by
Dr. Md. Arifuzzaman MD. Mahedi Hasan
Assistant Professor Roll: 1405024
Department of Mechanical Engineering Section:A
Khulna University of Engineering & Technology
July 2017
Department of Mechanical Engineering
Khulna University of Engineering & Technology
Khulna 9203, Bangladesh
2. 1.0 Executive Summary:
This report contains a technical analysis on a project to be carried out on design
and development of screw press. The project focuses on qualitative analysis of
existing screw presses and modifying them for production in local workshops.
The analysis will be based on both technical and financial appraisals.
Limitations therefore will include complexity of the turbine, easy of fabrication
and production costs among others.
The first screw press model was consuming relatively more energy and needed
high power source for its operation. The other problems were unsmooth
operation, oiling up, heavy foots, high oil content in cake fibre, and
comparatively high cost of maintenance. The model was found inefficient for
heavy lifting.The avobe enlisted shortfalls necessitated further research and
development.
3. 1.0 Introduction:
The press consists of a cylindrical perforated cage through which runs a pair of
closelyfitting screws. The screw presses, due to the turbulence and kneading
action exerted on the fruitmass in the press cage can effectively break open the
unopened oil cells and release more oil.Digested fruit is continuously conveyed
through the cage towards an outlet restricted by a cone,which creates the
pressure to expel the oil through the cage perforations (drilled holes).The
crude oil pressed, which consists of water, dirt and palm oil is passed to
the purification section. At the same time, the press cake, which discharged
from the end of the press, contains mainly the fiber and nuts. There is a
relationship between nut breakage and the percentage of fibre passing to the
clarification section. Nut breakage should be properlymeasured by the
presence of broken shells as with Tenera material the variation in shellthickness
can at times be heuristic, as some of the kernels have little or no shells
surroundingthem. The appearance in the press cake of smashed kernels
normally indicates that the press pressure requires immediate adjustment or that
the worm screws are in need of rebuilding.
The optimum conditions for operation of the twin-screw press will depend
uponconditions of the fruit when it enters the screw press to achieve effective
use of the press. Toestablish the proper condition, an accurate and true record
of press expelled material samples isessential. Considerable efforts have been
made in the past to improve the oil extraction efficiencyof screw presses.
Most of them have focused on optimization of process variables such asapplied
pressure, pressing temperature and moisture conditioning of the fed samples
(Ohlson,1992). Attempts to improve upon existing screw presses by
developing a suitable and efficient oilexpression device have remained isolated.
4. 3.0 Objectives:
The main objectives of this sessional are:
1) To continue technical developments in optimizing the approximately
better design for screw press.
2) To evaluate the performance of the newly developed screw press during
field trials.
4.0 Methodology and Calculation:
4.1 Methodology:
The methodology used in this project shall be as follows:
The screw press which are available are studied and performance data
compared. Among the expellers available, locally fabricated small
sizeexpeller shall be selected for further improvement or adaptation. Based on
the qualitative data obtained, sketches will be made. The design will then be
evaluated using the evaluation matrix method. The optimum screw press
design will be selected using the set criterion. Further analysis on this press
type will then be carried out. Theoretical design and performance
parameters will then be developed. Modifications on the design will
be carried out and final design carefullysketched. Detailed engineering
drawings will then be produced and based on this, the press will be fabricated.
4.2 Calculation:
Here,
Material AISI C1020
F=10 Kips, F1 = 10/2=5,(for each column)
5. N=3, L=10 in fixed ends,
Le / k = 5 / (D/4) = 20 / D,
Sy=48 ksi , E=30000ksi,
K=√
I
A
I = √(𝜋D4
/64),
A=πD2
/4,
K=√ ( πD4
/64)*(4/πD2
) = D/4,
Le = L/2 = 10 / 2 = 5 in
Now,
F
A
= Se[1 −
Sy(
Le
k
)
2
4π2E
]
5
πD2
4
=
Sy
N
[1 −
Sy(
20
D
)
2
4π2E
]
10
πD2 = 16[1 −
48(
20
D
)
2
4π2∗30∗103]
D= 0.669 ≈ 0.70 in
Fig 4.2.1: Column
6. For Fixed Plate:
Area, A=3.1416*D*t
=3.1416*0.669*t
Now,
F
A
=
sy
N
Or,
5
π∗0.669∗t
=
48
3
Or, 𝑡 =
5∗3
0.669∗48∗3.1416
Or, t=0.149 in
Fig 4.2.2: Fixed Plate
8. Fig 4.2.3: Moving Plates
Design of Power Screw:
For material AISI C1020, as rolled, from table AT-7,
Sy=48 ksi
Let, Design Factor N=3
F=10 kips
We know,
Sd =
F
A
=>
Sy
N
=
F
A
=>
48
3
=
10
π
4
d2
=> d = √
10∗3
π
4
∗48
=> d = 0.9 1
9. From Table 8.1, proportion of power threads,
Size, D0=1 inch (Standard)
Dr=0.781 inch
Thread per inch = 4
Mean Diameter, Dm =
1
2
∗ (Do+Dr)
=
1
2
∗ (1+0.781)
= 0.891 in
Lead, Pc =
1
Thread Per inch
=
1
4
= 0.25
Pitch angle, = tan−1
(
Lead
πDm
)
= tan−1
(
0.25
π∗0.891
)
= 5.10o
Let, Co-efficient of friction, f = 0.15
f = tan β = 0.15
=> tan−1(0.15) = β
=> β = 8. 53o
Here β > , so the screw is self locking.
Torque required to press the load:
10. We have,
W= 10 kips
Dm= 0.891 in
β = 8.53o
= 5.10o
T=
WDm
2
∗tan(β − )
=
10∗0.891
2
∗ tan(8. 53o
− 5.10o
)
T = 0.268 kips
Number of thread and length of the threaded portion:
W = 10 kips
P = 1000 psi
Do= 1 in
Dr = 0.781 in
h = length of threaded portion
Nt = Number of thread
Pressure, P =
4W
π(Do−Dr)∗Nt
=> Nt =
4W
π(12−0.782)∗p
=
4∗10
π(12−0.782)∗1
= 32.63 33
11. Length of the threaded portion, h = Nt*Pc
= 33 * 0.25
= 8.25 in
Efficiency, η =
tan (1−f tan )
tan +f
=
tan (1−0.15 tan 5.10o)
tan 5.10o+0.15
= 0.368
= 36.8%
Figure 4.2.4: Power Screw
12. Fig 4.2.5: Power Screw and fixed plate with dimension
Fig 4.2.6: Isometric View
13. 5.0 Summary:
In this project a prototype of screw press which can be operated by hand has been
fabricated. The screw press has been designed to pay a load of 10 KN. All the
elements of the screw press are fabricated in the machine shop. The assembly of the
component was achieved in no time literally. The elements which are useful are
readily available in the commercial market and with very little cost. For the reduction
of cost we have used wood instead of steel to make the certain parts of the prototype.
6.0 Parts used for Screw Press
All the dimensions are given Inch.
Name Specification Material
Handler D=0.4; L=6.5 Material AISI C1020 as rolled
Power screw D=0.5; L=11 Material AISI C1020 as rolled
Column D=0.6; L=12 Material AISI C1020 as rolled
Lower Fixed Plate 11 x 6.5 x .8 Wood
Upper fixed plate 11 x 6.5 x .8 Wood
Movable Plate 11 x 6.5 x .8 Wood
16. 6.0 Discussion:
The purpose of the course was to study screw press mechanism and using
that method design & construct a power screw at the workshop. For this first
of all we calculated the dimensions of the different parts of the prototype of
the machine that was suppose to be made. Using the dimensions, the parts
were drawn in SolidWorks software then assembled and simulated with
motion. After the approval of the design the machine parts were fabricated
in the machineshop. There some machine parts in the machine that was
thought to be fabricated using metal AISI C1020. But due to the
unavailability of that metal and as the model is possible and less costly using
wood we fabricated the screw press successfully.
7.0 Conclusion:
The screw press was constructed according to the dimension mentioned
above. During the construction of the prototype, workshop skill and
mechanical knowledge was enhanched. The fabricated machine is easy to
operate and easy to produce. The computer aided design was helpful in
terms of construction of the project. Although there were many complications
in terms of manufacturing the design, we successfully ended up making the
prototype.
