Definition of extrusion
 Extrusion is defined as ”The process by
which moistened, expansible, starch and/or
proteinous materials are plasticized and
cooked in a tube by a combination of
moisture, pressure, temperature and
mechanical shear”.
 Extrusion of feed is a combination of heat;
shear and pressure build up in the
presence of water.
Extrusion Basics
•Thoroughly mixed before entering the pre-bin
•The feed here (FôrTek are volumetric, not
gravimetric 
•The feeder needs to be calibrated before
each new material (hazzle)
coater
•The bin should be equal filled all time to
ensure constant pressure on material (
constant feeding)
Prebin
I
•Wet material has quite another density than
Prebin dry material (you need to calibrate)
II
(Pre)conditioner
extruder
dryer
cooler
mixer
Extrusion Line
surge bin
ingredient feeder
water addition
agitator
to vacuum pump
volumetric feeder
steam to conditioner
conditioner
steam to conditioner
venting
direct steam additon
slurry pump
72 kW at ca. 450 rpm
to suction pneumatic
Pre-conditioner (NOT a mixer)
Raw Material
Steam and
liquids
High
rpm
Mixing unit
Retention unit
Conditioned
Material
Low
rpm
The Screw Elements
1st
2nd
3rd
4th
5th
2: Feeding
4: Pressure generation, heat
transfer  high fill
6: Reverse conveying elements
4
6 10: Forward Polygon:
Kneading effect. High shear,
(Can be both forward and
backward, i.e. Left and right
handed) (interrupted melt flow)
Advantages Extrusion/Expansion
 increased temperatures
 increased fat addition
(90°C to 160°C)
(30% or more)
 increased molasses addition
 gelatinization of starch
(70% to 95%)
 pasteurized/sterilised feed
 improved pellet durability
(up to 15%)
(90°C to 160°C)
(up to 20%)
 increased production capacity
 lower dust quantities
 a more flexible process
(up to 50%)
Disadvantages
Bigger energy consumption compared with
other processes.
More expensive than pelleting with regular
conditioning.
Processing parameters: extrusion
Graph provided by Bühler AG
Extrusion processing: SME
Graph provided by Bühler AG
Energy justification: Extrusion
E (total) = SME (specific mechanical E) + STE (specific thermal E)
50
45
40
35
SME
30
25
20
15
10
5
0
Wheat
Oats
Wheat
Oats
Zimonja and Svihus (2008)