Presentation by Andreas Schleicher Tackling the School Absenteeism Crisis 30 ...
plastic
1.
2. Polymer family
Large size molecules-long chain molecules
formed by polymerization
Low cost
Low density
Low electrical and thermal conductivity
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4. Bond between adjacent long chain molecules (secondary bond)
Covalent bond between mers (primary bond)
•The overall strength of plastic depend on the secondary bond
•Increased temperature (Tm and Tg) weaken secondary bond (thermal vibration of
long molecules) and the chain are easily move by external shaping.
5. Also known as thermosoftening plastic
Can be remelted, recycled and remoulded.
More elastic and flexible
Example: vinyl ,acrylic, polycarbonate,
Polyamide, polyethylene and polypropylene.
Application : lense, bubble top, windshield,
zipper.
6. Cannot be melted and re-shaped after it is
cured
Cannot be recycled
Better suited to high-temperature applications
Generally stronger than thermoplastic
materials due to this 3-D network of bonds
Example : Polyester, Bakelite, Vulcanized
rubber, epoxy, melamine, polyamides
Application : Electrical insulators and plastic
ware, car parts, body parts of modern airplanes
and printed circuit boards
7.
8.
9. Raw material (pellet, granules, powder) are placed into hopper
and fed into the barrel of screw extruder.
Helical screw blend the pellet and convey them down the barrel
toward the die
Barrel heater and the screw internal friction heat the pellet and
liquidizes them.
Molten plastic was then forced through the die.
Extruded part was then cooled by exposing it to blowing air or
pass through water-filled chanel
10. Parts- Solid rod, sections, channel, sheet,
tubing, pipe, architectural parts.
Defects- surfaces fractures (uneven die shapes),
bambooing and sharkskin effect ( friction at
die-polymer interface and elastic recovery and
non-uniform deformation of product outer
layer.
11. Control parameters- extruder screw rotational
speed, barrel wall temperature, die design, rate
of cooling, drawing speed.
The flowrate- control by the shape, pitch and
flight angle of helical screw
Cooling rate and uniformity – control by
cooling medium such as air and water
Design of die and extruder
Pressure and heat rate
Continuous supply of raw material
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14.
15. Has high production rates (fast cycle time)
Good dimensional control
Complex shapes with good dimensional
accuracy
Parts generally weigh 100g-600g (small parts)
or heavier ( automobile components)
High tooling cost (die)
16.
17.
18. Product - Cup, container, housing, knob, toy,
electrical and telecommunication devices
Examples of product
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20.
21. Design capabilities
Proper control of temperature and pressure
Mold design modifications
Good control of flowrate in the die cavities
Defect
Weld lines- molten plastic flows in from 2 opposite
runners and meet in the middle of cavities
Void/Porosity-runner section too small, premature
solidification, preventing full filling of mold cavity
Flash- die do not close completely
Sink marks/ Pull in- thick molded section
25. A tube or pre form (parison) is first extruded.
It is clamped into the mold with cavity much
larger than the parison diameter
It is then blown upward to fill the mould
cavity
The pieces was then cooled and ejected from
mold
26. Short tubular pieces (parison) is injection molded in
cool dies.
The dies then open and the parison is transferred by
an indexing mechanism.
Hot air is injected from the blow pin into the parison,
expanding to the wall of mold cavity
The pieces was then cooled and ejected from mold
after the blow pin is removed
27.
28. Parts produces are hollow tubing and
containers
Sufficient blowing pressure
Strong and rigid die ( typical material : steel,
aluminum, beryllium copper)
Improper filled molds
The blow pressure of hot blasting ranging from
350 to 700 kPa depending on the material types
Blow ratio can be up to 7:1.
Drum with volume up to 2000 liters can be
made through this process
29. Process of forming thermoplastic sheet/film
over a mold through the application of heat
and pressure.
Sheet is clamp and heated to sag point ( above
Tg) by radiant heating.
It was then force using vacuum or pressurized
air against the mold surfaces.
30.
31. Typical parts- tray, house appliances, panel for
shower stall, etc
Cannot made part with holes/opening due to
unable to maintain pressure during forming
Material had to exhibit high and uniform
elongation.
The molds is made from aluminum due to low
strength and low cost requirement
The mold has small holes (<0.5mm) to help
vacuum forming
32. Tearing of sheet during forming
Non-uniform wall thickness
Improper filled molds
Poor part definition
Lack of surfaces details
33. Made through roll method or doctor blade
method.
In roll method, the polymer coating material is
squeeze against the substrate (fabric, paper,
cardboard, metal foil), by mean of opposing rolls.
This cause the polymer to uniformly cover the base
material and the take-up reel will roll and gather
the coated material
In doctor blade method, a sharp knife edge control
the amount of polymer melt that is coasted in the
substrate. Similarly, the coated material will be
collected through a take up reel.