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LECTURE 11 : PLASTIC SHAPING TECHNOLOGY - Coggle Diagram
LECTURE 11 : PLASTIC SHAPING TECHNOLOGY
2 types of plastic
a) Thermoplastics -Chemical structure remains unchanged during heating and shaping
-More important commercially, comprising more than 70% of total plastics tonnage
b) Thermosets
-Undergo a curing process during heating and shaping, causing a permanent change (called cross-linking) in molecular structure
-Cannot be remelted
Classification of Plastic Shaping Processes by Product Geometry
Extruded products with constant cross-section
Continuous sheets and films
Continuous filaments (fibers)
Molded parts which are mostly solid
Hollow molded parts with relatively thin walls
Discrete parts made of formed sheets and films
Castings
Foamed products
EXTRUSION (A manufacturing process where a billet of material is pushed and/or drawn through a die to create a shaped rod, rail or pipe)
Compression process in which material is forced to flow through a die orifice to provide long continuous product whose cross-sectional shape is determined by the shape of the orifice
-Used for thermoplastics and elastomers to mass produce items such as tubing, pipes, hose, structural shapes, sheet and film, continuous filaments, and coated electrical wire
POLYMER SHEET AND FILM SHEET
Sheet
Thickness from 0.5 mm (0.020 in.) to about 12.5 mm (0.5 in.)
Used for products such as flat window glazing and stock for thermoforming
Film
-Thickness below 0.5 mm (0.020 in.)
-Used for packaging (product wrapping material, grocery bags, and garbage bags)
Thicker film applications include pool covers and liners for irrigation ditches
MATERIAL
Thermoplastic polymer
Polyethylene, mostly low density PE
Polypropylene
Polyvinylchloride
Cellophane
Process use are comtinue, high production operation - Process include
a) Slit-Die Extrusion of Sheet and Film
b) Blown-Film Extrusion Process
c) Calendering