Classification of solidification processes
Principle of the process
Structure/Configuration
Process modeling
Defects/quality control
Design For Manufacturing (DFM)
Process variation
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Shaping Processes For Plastics - Extrusion
1. Introduction
Screen pack
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Shaping Processes For Plastics - Extrusion
1. Introduction
Extrusion is a
process in which the
material is forced to flow through a die orifice
to provide a long, continuous product whose
cross-sectional shape is determined by the
shape of the orifice
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Shaping Processes For Plastics - Extrusion
2. Analysis of Flow Rate
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Shaping Processes For Plastics - Extrusion
Find the flow rate with respect to various parameters
in the system. These parameters include: parameters
of the screw, the clearance between the screw and
the inner surface of the barrel.
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The goal of the engineering analysis:
1. The flow rate or production rate.
2. The pressure of the
or product
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The general idea to meet the goal:
1. Flow rate inside the extruder and at the die ?
2. Flow rate outside the extruder and at the die ?
die
Extruder
The balance
between the two
should lead to
the flow rate as
well as pressure
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Flow rate of the extruder
(not including the die)
Drag flow
w
Screw surface
v
d
Barrel
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Qd  0.5vdw
v  DN cos A
dc
w
v
d
wc   D tan A cos A  wf
Qd  0.5 D Nd c sin A cos A
2
2
(1)
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wc   D tan A cos A  wf
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Back pressure flow
Dd sin A dp
Qb 
( )
12
dl
3
c
2
12
Back pressure flow
Dd sin A dp
Qb 
( )
12
dl
3
c
2
pDd sin A
Qb 
12L
3
c
2
(2)
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Net forward flow Qx
pDd sin A
Qx  0.5 D Nd c sin A cos A 
12L
2
2
3
c
2

Linear relation between the net flow rate and head pressure.

Assumption: viscosity is constant.

The structure: extruder only not including die.
(3)
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Shaping Processes For Plastics - Extrusion
The design parameters: those that define the geometry
of the screw and barrel.
The operating parameter: those that can be changed
during the process to affect the output flow
pDd sin A
Qx  0.5 D Nd c sin A cos A 
12L
2
Variable
2
3
c
2
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Shaping Processes For Plastics - Extrusion
Maximum pressure and maximum net flow rate
0
pDd sin A
Qmax  0.5 D Nd c sin A cos A 
12L
2
2
3
c
2
Maximum head pressure to cause no flow
6DNL cot A
pmax 
2
dc
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Shaping Processes For Plastics - Extrusion
Extruder characteristic
Q
Qmax
pmax
p
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Shaping Processes For Plastics - Extrusion
 Determination of the operating point
Pressure and Flow rate
Qx  K s p
D
Ks 
128Ld
die
4
d
Die characteristic
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Shaping Processes For Plastics - Extrusion
 Determination of the operating point
Qx
Die characteristic
Qmax
Operating point
Extruder characteristic
pmax
p
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Example:
Given: diameter D=120 mm
length =3.0 m
channel depth =8.0 mm
pitch = 95 mm
viscosity = 75 pas
head pressure = 4.0 Mpa
Find: the rotational speed of the screw required to
achieve a volumetric flow rate of 90 cm3/s
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Solution to be filled in the classroom
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Shaping Processes For Plastics - Extrusion
Discussion

A manufacturing process is to
requirements.

Requirements: quality, quantity, time, cost, green and sustainability.

Quantity with respect to time is called production rate.

The whole manufacturing system at the equipment level can be
viewed as consisting of devices and materials.
the material to meet
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Shaping Processes For Plastics - Extrusion
Discussion

Both the device and material are under the manipulation from the
external system that supplies energy or power and material.

There are several parameters and variables in the manufacturing
system: device parameter, process parameter, product parameter.
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Shaping Processes For Plastics - Extrusion
Discussion

Device parameter also system or design parameter: the one
category of parameters that describe the device, e.g., the diameter
of the extruder, length of the extruder, etc.

Process parameter also operating parameter: the one category of
parameters that describe the process on the material, e.g., the
rotational speed of the screw bar, heat energy supply, material
supply rate, etc.

Product parameter: the one category of parameters that describe or
characterize the product which is the output from a manufacturing
system, e.g., the flow rate, etc.
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Shaping Processes For Plastics - Extrusion
Discussion

Manufacturing system design and control:
1. Device design: to determine the device parameter.
2. Process design: to determine the process configuration and
parameter.
3. Product modification: design for process.
4. Device control.
5. Process control.
Product quality, quantity, cost,
time, green and sustainability
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