Introduction to Basic Manufacturing Processes and ... - always yours

256 Introduction to Basic Manufacturing Processes and Workshop Technology
Ejector pin
Moulded
part Heaters Granular
plastic
Torpedo
Plunger
Nozzle
(a) Using heated manifold and heated torpedo
Hopper
Nozzle
13.11.2 Extrusion Molding
Circulating water in
electrodes
Injection
ram
Preheating
chamber
(b) Used for thermosetting plastics
Fig. 13.11 Typical injection molding
Generally all thermo plastic materials are highly suitable for extrusion in to various shapes
such as rods, tubes, sheets, film, pipes and ropes. Thermosetting plastic is not suitable for
extrusion molding. In this process the powder polymer or monomer is received through
hopper and is fed in to the heated chamber by a rotating screw along a cylindrical chamber.
The rotating screw carries the plastic powder forward and forces it through the heated orifice
of the die. As the thermoplastic powder reaches towards the die, it gets heated up and melts.
It is then forced through the die opening of desired shape as shown in the sectional view of
the extrusion molding process through Fig 13.12. On leaving the product from the die, it is
cooled by water or compressed air and is finally carried by a conveyor or belt. The process
is continuous and involves low initial cost.
Hopper
Rotating screw
Heater
Air or water
Product
Die opening
Raw material (Powder)
Fig. 13.12 Schematic extrusion molding
Conveyer