SHAPING PROCESSES FOR PLASTICS Die Design Production of Sheet, Film, and Filaments ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Die Configurations and Extruded Products The shape of the die orifice determines the cross‑sectional shape of the extrudate Common die profiles and corresponding extruded shapes: Solid profiles Hollow profiles, such as tubes Wire and cable coating Sheet and film Filaments ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Extrusion of Solid Profiles Regular shapes such as Rounds Squares Irregular cross sections such as Structural shapes Door and window moldings Automobile trim House siding ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Extrusion Die for Solid Cross Section Figure 13.8 (a) Side view cross‑section of an extrusion die for solid regular shapes, such as round stock; (b) front view of die, with profile of extrudate. Die swell is evident in both views. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Hollow Profiles Examples: tubes, pipes, hoses, and other cross‑sections containing holes Hollow profiles require mandrel to form the shape Mandrel held in place using a spider Polymer melt flows around legs supporting the mandrel to reunite into a monolithic tube wall Mandrel often includes an air channel through which air is blown to maintain hollow form of extrudate during hardening ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Extrusion Die for Hollow Shapes Figure 13.10 Side view cross‑section of extrusion die for shaping hollow cross‑sections such as tubes and pipes; Section A‑A is a front view cross‑section showing how the mandrel is held in place; Section B‑B shows the tubular cross‑section just prior to exiting the die; die swell causes an enlargement of the diameter. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Wire and Cable Coating Polymer melt is applied to bare wire as it is pulled at high speed through a die A slight vacuum is drawn between wire and polymer to promote adhesion of coating Wire provides rigidity during cooling - usually aided by passing coated wire through a water trough Product is wound onto large spools at speeds up to 50 m/s (10,000 ft/min) ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Extrusion Die for Coating Wire Figure 13.11 Side view cross‑section of die for coating of electrical wire by extrusion. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Polymer Sheet and Film Film - thickness below 0.5 mm (0.020 in.) Packaging - product wrapping material, grocery bags, and garbage bags Stock for photographic film Pool covers and liners for irrigation ditches Sheet - thickness from 0.5 mm (0.020 in.) to about 12.5 mm (0.5 in.) Flat window glazing Thermoforming stock ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Materials for Polymer Sheet and Film All thermoplastic polymers Polyethylene, mostly low density PE Polypropylene Polyvinylchloride Cellophane ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Sheet and Film Production Processes Most widely used processes are continuous, high production operations Processes include: Slit‑Die Extrusion of Sheet and Film Blown‑Film Extrusion Process Calendering ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Slit‑Die Extrusion of Sheet and Film Production of sheet and film by conventional extrusion, using a narrow slit as the die opening Slit may be up to 3 m (10 ft) wide and as narrow as around 0.4 mm (0.015 in) A problem is uniformity of thickness throughout width of stock, due to drastic shape change of polymer melt as it flows through die Edges of film usually must be trimmed because of thickening at edges ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Slit Die Extrusion Figure 13.14 One of several die configurations for extruding sheet and film. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Blown‑Film Extrusion Process Combines extrusion and blowing to produce a tube of thin film Process sequence: Extrusion of tube Tube is drawn upward while still molten and simultaneously expanded by air inflated into it through die Air is blown into tube to maintain uniform film thickness and tube diameter ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Blown-film Process Figure 13.16 Blown‑film process for high production of thin tubular film. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Calendering Feedstock is passed through a series of rolls to reduce thickness to desired gage Expensive equipment, high production rates Process is noted for good surface finish and high gage accuracy Typical materials: rubber or rubbery thermoplastics such as plasticized PVC Products: PVC floor covering, shower curtains, vinyl table cloths, pool liners, and inflatable boats and toys ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Figure 13.17 A typical roll configuration in calendering ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Fiber and Filament Products Definitions: Fiber - a long, thin strand whose length is at least 100 times its cross‑section Filament - a fiber of continuous length Applications: Fibers and filaments for textiles Most important application Reinforcing materials in polymer composites Growing application, but still small compared to textiles ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Materials for Fibers and Filaments Fibers can be natural or synthetic Natural fibers constitute ~ 25% of total market Cotton is by far the most important staple Wool production is significantly less than cotton Synthetic fibers constitute ~ 75% of total fiber market Polyester is the most important Others: nylon, acrylics, and rayon ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Fiber and Filament Production - Spinning For synthetic fibers, spinning = extrusion of polymer melt or solution through a spinneret, then drawing and winding onto a bobbin Spinneret = die with multiple small holes The term is a holdover from methods used to draw and twist natural fibers into yarn or thread Three variations, depending on polymer : Melt spinning Dry spinning Wet spinning ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Melt Spinning Starting polymer is heated to molten state and pumped through spinneret Typical spinneret is 6 mm (0.25 in) thick and contains approximately 50 holes of diameter 0.25 mm (0.010 in) Filaments are drawn and air cooled before being spooled onto bobbin Significant extension and thinning of filaments occur while polymer is still molten, so final diameter wound onto bobbin may be only 1/10 of extruded size Used for polyester and nylon filaments ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Melt Spinning Figure 13.18 Melt spinning of continuous filaments ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Dry Spinning Similar to melt spinning, but starting polymer is in solution and solvent can be separated by evaporation First step is extrusion through spinneret Extrudate is pulled through a heated chamber which removes the solvent, leaving the polymer Used for filaments of cellulose acetate and acrylics ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Wet Spinning Similar to melt spinning, but polymer is again in solution, only solvent is non‑volatile To separate polymer, extrudate is passed through a liquid chemical that coagulates or precipitates the polymer into coherent strands which are then collected onto bobbins Used to produce filaments of rayon (regenerated cellulose) ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Subsequent Processing of Filaments Filaments produced by any of the three processes are usually subjected to further cold drawing to align crystal structure along direction of filament axis Extensions of 2 to 8 are typical Effect is to significantly increase tensile strength Drawing is done by pulling filament between two spools, where winding spool is driven at a faster speed than unwinding spool ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

Thanks ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e