Transcript Polymer Casting - Welcome to AML 883

Polymer Casting
Presented By:
Madan Lal
2008AMD2920
Contents:
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Introduction to polymer
Historical Development
Polymer Casting and various processes
Brief introduction to :
Thermoforming
Compression molding
Rotational Molding
Polymer
Polymer:
Large number of molecules joining together repeatedly in
the form of long and flexible chains.
Types of Polymers:
1.Thermoplastics :
•These can be melted by heating, solidified by cooling
and re-melted repeatedly.
2.Thermosets:
• Hardened by application of heat and pressure.
•These cannot be softened by heating for reprocessing
or cannot re-melted.
•Because due to cross-linking of structure, these create
permanent 3-D network.
Historical Development
•In 1811, Henri Braconnot did pioneering
work in derivative cellulose compounds
which was the earliest important work in
polymer science.
• In 1907, Leo Baekeland created the first
synthetic polymer, Bakelite, by reacting
phenol and formaldehyde.
•Bakelite was then publicly introduced in
1909.
Polymer Casting:
•Operations carried out on polymeric materials to increase their utility.
•The conversion of polymeric raw materials into useful finished
products.
Processes of polymer casting:
1. Thermoforming
2. Compression and transfer molding
3. Rotational molding and sintering
4. Extrusion
5. Extrusion-based processes
6. Injection molding
7. Blow molding
8. Plastic foam molding
Selection of a process depends upon:
- Quantity and production rate.
- Dimensional accuracy and surface finish.
- Form and detail of the product.
- Nature of material.
- Size of final product.
Phases of polymer processing:
1. Heating - To soften or melt the plastic.
2. Shaping / Forming - Under constraint of
some kind like application of specific pressure
etc.
3. Cooling - So that it retains its shape.
•Thermo plastics start as regular pellets or sheet
and can be re-melted.
•Thermosets start as liquids often called "resins",
or powders which need heat for the shaping
phase.
•For shaping a chemical reaction is required,
which means that the material does not soften
on reheating.
Thermoforming
•Only thermoplastics sheet can be processed by this
method.
This sheet is heated so that it can soften.
•This softened sheet is placed in the mould and
pressure is applied to form it into the shape of mould.
Fig: http://pioneer.netserv.chula.ac.th
Applications:
•For food packaging industries.
• Other industries like toiletries, pharmaceuticals
and electronics.
Fig: http://pioneer.netserv.chula.ac.th
Compression and transfer molding
Fig: http://pioneer.netserv.chula.ac.th
• Place a pre-weighed or fixed amount of material
in a matched metal mold and closing the mold.
• Heat and pressure cause the material to liquify
and flow into the voids in the tool where it
chemically reacts and hardens into the final
shape.
Rotational molding :
Fig: http://pioneer.netserv.chula.ac.th
•Charge of plastic powder is placed in one half of a metal
mold.
•The mold halves are then clamped together and heated
while the mold rotates.
•The powder particles melt and form a homogenous
layer on the surface of the mold during rotation.
•The mold is then cooled to solidify.
Application:
This process is used to produce hollow complex shapes.
References:
1. http://www.cheric.org
2. http://pioneer.netserv.chula.ac.th
3. http://en.wikipedia.org
4. http://www2.kmutt.ac.th
5. http://teaching.ust.hk
6. www.gatech.edu