04Lecture-ch13 - Manufacturing and Production Processes...

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Manufacturing and Production Processes ENGR 3190U – Lecture 04 Chapter 13 - Shaping process for plastics Sections 13.1, 13.2, 13.3, 13.4, 13.6.1 – 13.6.5 1. Properties of polymer melt 2. Extrusion 3. Production of sheet and film 4. Fiber and filament production 5. Injection molding 6. In class video clips: Injection molding 7. Analysis of Extrusion Calculations For Plastics (04Lecture-Calc.doc)
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Plastic Shaping Processes are Important Almost unlimited variety of part geometries Plastic molding is a net shape process Further shaping is not needed Less energy is required than for metals due to much lower processing temperatures Handling of product is simplified during production because of lower temperatures Painting or plating is usually not required 2 types of plastics: Thermoplastics, Thermosets
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Classification of Shaping Processes Extruded products with constant cross‑section Continuous sheets and films Continuous filaments (fibers) Molded parts that are mostly solid Hollow molded parts with relatively thin walls Discrete parts made of formed sheets and films Castings Foamed products
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Polymer Melts To shape a thermoplastic polymer it must be heated so that it softens to the consistency of a liquid In this form, it is called a polymer melt Important properties of polymer melts: Viscosity – the resistance to flow, decreases with temperature, “better flow” Viscoelasticity – “bounces back to its original form”, important in “die swell”
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Extruded polymer "remembers" its previous shape when in the larger cross section of the extruder, tries to return to it after leaving the die orifice Figure 13.3 Die swell, a manifestation of viscoelasticity in polymer melts, as depicted here on exiting an extrusion die. Die Swell
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Extrusion 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 Widely 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 Carried out as a continuous process; extrudate is then cut into desired lengths
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Extruder Figure 13.4 Components and features of a (single‑screw) extruder for plastics and elastomers
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Extruder Barrel Internal diameter typically ranges from 25 to 150 mm (1.0 to 6.0 in.) L / D ratios usually between 10 and 30: higher ratios for thermoplastics, lower ratios for elastomers Feedstock fed by gravity onto screw whose rotation moves material through barrel Electric heaters melt feedstock; subsequent mixing and mechanical working adds heat which maintains the melt
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