Polymer Production Machines Polymer Engineering Fundamental Polymer

1. Fundamentals of Polymer Engineering
Polymer Processing
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Course Code: PE-2102
Credits: 3-0-3
Teacher: Engr. Asra Tariq
Email Id: asra.tariq@ntu.edu.pk

2. Extrusion Process
Definition:
It represent the processing operation in which fluid/melt is pumped
through a die orifice to produce a shape of constant cross-section.
 The term has a Greek root which means
‘Push out’.
 Squeezing a tube of toothpaste is an extrusion process.
 Extrusion is the most efficient process
for melting plastics as well as
mixing fillers, colorants and other
additives into the molten plastics.
 When the extruder is used to shape the parts
directly then the process is called extrusion.
e.g. manufacturing of pipes
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3. Extrusion Process
The heart of extruder is ‘The Screw’
 The polymer granules are fed from hopper onto the screw, conveyed along the barrel and heated by
conduction from barrel heaters & shear due to the movement of screw.
 The depth of the screw channel is reduced along the length of the screw for compaction.
 At the end of the extruder, the melt is passed through the die to produce an extrudate of the desired shape.
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4. Extrusion Process
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5. Extrusion Process
Extruder with vented zone
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6. Extrusion Process-Screw geometry
It consists of helical screw rotating inside the cylindrical barrel.
The screw geometry is as follows;
Shank: Fitted into the quill of screw drive
Flight: Each turn of the helix
is called a Flight.
Root dia: It is the measure of the
dia of the shaft of the screw.
Flight depth/Channel depth:
the difference between the top of
flight and the root dia.
The flight depth varies with the
variation of root dia.
Helix angle: angle of the flight with the shaft
(most common pitch angle = 17.5o)
Pitch: The distance between the crests of two flights next to each other.
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7. Extrusion Process-Screw geometry
It consists of helical screw rotating inside the cylindrical barrel.
The screw geometry is as follows;
Clearance:
The distance between
the tip of flight and the barrel wall
It is constant over the length of the screw.
Flighted Length: It consists of
80% of the length of the screw.
(This is the portion of the screw
which receives the pellets that are
conveyed to the metering zone by
the rotation of the screw)
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8. Extrusion Process
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9. Extrusion Process
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10. Extrusion Process
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11. Injection Molding
Injection Molding machine (IMM) is a simple process in which,
 A Polymer in the form of granules/powder passes from feed hopper into the barrel
 It is heated in the screw/barrel assembly to melt the granules
 It is then forced through nozzle into the mold which is tightly closed
 When polymer becomes solid in the mold, it is opened and the article is ejected from the mold
Major Advantages:
 Versatility in molding wide range of products
 Manufacturing of products with close tolerances
 High production rate
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12. Injection Molding-Equipment
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13. Injection Molding
Other IMM making companies are,
Arburg, Boy, Kraus Maffai etc
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14. Injection Molding
Now a days in Injection molding,
 The ‘Reciprocating Screws’ are used, performing dual role;
i) On one hand, it rotates in the normal way like the extruder screw to transport, pressurize
and melt the polymer material in the barrel
ii) On the other hand, it is also capable of moving like a plunger to inject the melt into the mold
Due to the availability of ‘Reciprocating Screws’, the IMM with plunger types are seldom used.
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15. Injection Molding-Mechanism
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16. Melting
Injection of
Polymer/Resin
Screw retraction
& part cooling
Part Removal
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17. Injection Molding-Terminology
Shot Size:
It is the quantity of the melt injected into the mold. (measured in g or ounces)
Cycle Time:
The time required to complete one cycle is called cycle time. (It can vary from few
Seconds to several minutes)
Stroke:
The specified distance which is allowed for the screw to move back & forward to
act as a plunger/ram
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18. Injection Molding-Clamping Unit
The Clamping unit performs the following functions;
i) Holds the mold
ii) Closes the mold
iii) Keeps the mold closed under injection pressure
iv) Opens the mold to allow the ejection of the part
v) Accommodate the ejector system which ejects the part
The Clamping mechanism provides the force to keep the mold closed during the injection &
holding pressure stages of the machine cycle.
Types of Clamping Mechanism:
i) Hydraulic clamping
ii) Toggle clamping
iii) Combination of both hydraulic and toggle
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19. Injection Molding-Platen
 Designing molds for injection molding is far more complicated than for extrusion dies.
 The mold is between the stationary platen and the moveable platen of the IMM.
 The connection from the injection unit to the mold is through nozzle.
The injection Mold is the element that,
1) Receives the molten polymer from injection unit
2) Forms the shape of the desired polymer part
3) Provides the necessary cooling to solidify the part
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20. Injection Molding-Ejector System
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21. Injection Molding
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22.  Blow Molding
 Modified extrusion and injection-molding process
 Characteristics
 Hollow thin-walled parts of various sizes
 High production rates
 Low cost for making beverage and food containers
Blow Molding 22

23. The process can be simplified into 3 steps
1) Melting the resin
2) Forming a preform tube
3) Blowing the preform tube into the shape desired
Steps 1 and 2 can be done either in an extruder or in an injection molding
machine.
http://upload.wikimedia.org/wikipedia/en/9/97/Recip_Machine_Trimmer.png
General Process 23

24. Step 1
Step 2
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25. Step 3
Step 4
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26. Process Parameters
Parison characteristics
size, shape, straightness, wall thickness, mechanical
properties
Inflation pressure
Mold design
cooling, venting
Blow ratio= Mold diameter/Parison Diameter (1.5 to 3 are
common
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27. Most thermoplastics can be blow molded
Some typical applications are
HDPE : High Density Polyethylene (stiff bottle, toys, cases,
drum)
LDPE : Low Density Polyethylene (flexible bottle)
PP : Polypropylene (higher temperature bottle)
PVC : Polyvinyl Chloride (clear bottle, oil resistant containers)
PET : Polyethylene terephthalate (soda pop bottle)
Application
(Courtesy : http://industrialblowmolding.com/?page_id=22)
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28. Compression Molding
 Molding is the forming process .
 Compression molding process is followed by two step first one
preheating and pressurizing
• Compression molding is generally used for
thermosetting plastic.
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29. Process Description 29

30. Parameters
1.The quantity of charge(molding material)put into the mold
2.Pressure of the molding process
 Range of pressure 2000-3000 psi(13.8-20.7 MPa) [4]
3.Mold temperature
 Temperature range 300ºF to 375ºF (149⁰C- 191⁰C)[4].
4.Cure time variables.
 The period required to harden thermosetting material to partial and complete
polymerization is called cure time [4].
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31. Mold
Press
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32. Advantages
 Lowest cost
 More uniform density
 Uniform shrinkage due to uniform flow
 Improved impact strength due to no degradation of fibers
during flow
 Dimensional accuracy
 Internal stress and warping are minimized
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33. Disadvantages
 Curing time large
 Uneven parting lines present
 scrap cannot be reprocessed.
Applications & products
 Dinnerware
 Buttons
 Knobs
 Appliance Housings
 Radio Cases
 Automotive exterior panels especially for commercial
vehicles
 ash trays & electrical parts
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