1. The document discusses screw presses, which are used to separate solids and liquids through compression and shear. It describes the types, construction, working principle, design considerations, and performance of screw presses. 2. Key aspects of screw press design include the diameter of the shaft, load lifted by the screw thread, and pressure developed. Performance is determined by parameters like capacity, power requirement, oil yield, efficiency, and extraction loss. 3. Examples are provided to calculate screw press specifications and performance metrics like oil efficiency and effectiveness based on given operating conditions and extraction results.

1. Screw press and its performance
Pragati Singham
M.Tech (FPEM)

2. CONTENTS
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Introduction
Types
Construction & working
Principle
Performance(design)
References

3. INTRODUCTION
• It is the simplest machine for separation of solids and liquids.
• It is a cage style press.
• It is used for separation of –
– Oils from various oilseeds
– Fruit juices
• Screw pressing is a continuous operation, hence these are
also known as “expellers”

4. TYPES OF SCREW
PRESS
Horizontal screw press
Huber inclined screw press

5. CONSTRUCTION & WORKING

7. PRINCIPLE
• It works on the principle of ‘compression and shear’.
Compression curve
Compression ratio = volume displaced per revolution at the feed end
volume displaced per revolution at discharge end

8. DESIGN OF SCREW PRESS
•
Diameter of shaft (ds)
where,
T = torque transmitted by shaft
δ0 = yield stress
•
Load lifted by screw (We)
where, Dm = mean thread diameter
T = torque transmitted by shaft
µ = coefficient of friction
α = tapering angle
θn = thread (lift) angle
•
Pressure developed by screw thread (Pr)
where, Ap = pressing area
h = screw depth at max. pressure
area (discharge end)
n = no. of threads
Hall et al., 1961

9. Capacity (Qe)
where, Ds = diameter of the screw thread
ds = base diameter of the screw shaft
Ps = screw pitch,
Ns = rotational speed of the screw shaft
φ = filling factor,
ρ = bulk density
Power requirement(Pe)
where, Qv = volumetric capacity of the screw shaft
ls = length of screw shaft
g = acceleration due to gravity
F = material factor
Hall et al., 1961

10. PERFORMANCE OF SCREW PRESS
• Design a screw press whose specifications areDs = 100 mm,
Ns = 90.63 rpm,
δ0 = 200 N/m2,
µ = 0.15 ,
h = 5mm,
ls = 500 mm ,
1.
ds = 50 mm,
Φ = 0.8,
T = 928.571 Nm,
θn = 150,
n = 9,
g = 9.81 m/s,
Diameter of shaft
2. Load lifted by screw (We)
Ps = 50mm
Ρ = 740kg/m3
Dm = 75 mm
θ = 30
Qv = 1.281m3 / hr
F = 0.4
= 16 x 928.571 = 44.407mm
0.27 x 3.14 x 200
= tan-1 (tan150 . Cos 30)
=14.980

11. = 928.571 x 75/2 tan30 + 0.15
(1-0.15 tan 30 cos 14.980)
=72.88KW
Pressure developed by screw thread (Pr)
= 3.14 x 75 x 9 x 5
= 72.88 x 1000
10602.88
Capacity (Qe)
740
= 10602.88 mm2
= 6.87 N/mm2
= 60 x 3.14/4 (100)2 - (50)2 x 50 x 90.63 x 0.8 x
= 948.249 kg/hr
Power requirement(Pe)
= 4.5 x 1.281 x 500 x 740 x 9.81 x 0.4
= 8.369KW

12. YIELD , EFFICIENCY, EXTRACTION LOSS
• Oil yield (OY) =
• Oil efficiency (OE) =
• Extraction loss (EL) =
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•
•
•
•
•
•
•
where,
OE = % extraction efficiency
OY = % oil yield
EL = % extraction loss
WOE = weights of oil extracted(g)
WRC = residual cake (g)
WFS = feed sample (g)
x
= oil content of seed in decimal.

13. 1. NUMERICAL
• Soybean seeds contain 40% oil on weight basis and 4.2 g of oil is
extracted by screw press from 100 g of soybean seeds. Calculate
the oil efficiency of the soybean seeds.
weight of soybean(WFS)
Amt. of oil present(x)
Amt. of oil extracted(WOE)
Oil efficiency (Oy)
= 100 g
= 0.40
= 4.2 g
=
= 100 x 4.2 %
0.4 x 100
= 10.5 %

14. 2. NUMERICAL
•
Calculate the effectiveness of an screw press, which yields 3.7 kg oil containing 5%
impurities from 100 kg mustard seeds. The oil content of the mustard seeds is
38%.
Weight of mustard seeds
Expected yield
Oil extracted
Effectiveness
= 100kg
= 38 kg
= 3.7 – (3.7 of 5%)
= 3.7- 0.185
= 3.515kg
= calculated yield x 100
Expected yield
= 3.515 x 100
38
= 9.25 %

15. REFERENCES
• Deli, S., Farah Masturah, M., Tajul Aris, Y. and Wan Nadiah, W. A.
The Effects of physical parameters of the screw press oil expeller on
oil yield from Nigella sativa L seeds. International Food Research
Journal 18(4): 1367-1373 (2011)
• Hall, A. S., Holowenko, A. E., & Laughlin, H. G. (2002). Schaum’s
outline series theory and problems of machine design. (1st ed.).
New York: McGraw-Hill Companies, Inc., (Chapter 12).
• Handbook of Food Processing Equipment by Geōrgios D.
Sarabakos, Athanasios E. Kosaropoulos
• http://www.reinartz.de/index.php?id=27&L=1
• http://www.fao.org/docrep/t0532e/t0532e04.ht
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