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1 MFGT 142 Extrusion Professor Joe Greene CSU, CHICO

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  • Slide 1
  • 1 MFGT 142 Extrusion Professor Joe Greene CSU, CHICO
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  • 2 Chapter 11: Extrusion Overview Purpose, advantages, disadvantages, and cost elements Equipment: extruder, die, cooling, puller, removal, special equipment, plant layout and capacity Normal operation and process control: start-up, part dimensional control, maintenance, safety Extrusion problems and trouble shooting Material and product considerations Post-extrusion forming Coextrusion
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  • 3 Introduction Extrusion: (Greek) push out Pump supplies a continuous stream of material to a shaping tool or to some other subsequent shaping process. Materials plastics metals (Al window frames caulking with a caulk gun spaghetti and other noodles cookie dough hamburger toothpaste hot melt glue gun Extrusion useful for shaping parts with extruder dies Extrusion is basis for injection molding and blow molding Melting device to add fillers, colorants, fibers in compounding
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  • 4 Extrusion Principle Continuously shaping a fluid polymer through an orifice of a suitable tool (die), and subsequently solidifying into a product. Equipment Single screw extruder consists of Screw, barrel, feed hopper, and die Common extruders are rated by barrel bore diameter (0.75 to 6) Plastics extruders can be 24 diameter and 48 ft in length Electric heaters for barrels and Air (or water bath) coolers for extrudate Screw is matched to material produced Simple screw has flights and decreasing gaps along channel Screw Aspect (L/D) ratio = screw length to screw diameter (range 20-30) Venting zone for gases that evolve during processing Twin screw- used for shear sensitive materials (e.g., PVC)
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  • 5 Extruder Components Hopper- Feed thermoplastic pellets Heating and shear zone- rotating single or twin screw conveys plastic to heat zone and applies shear (friction) to melt
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  • 6 Extruder Equipment Exit zone- die die imparts shape on the material, e.g., rod, tube, sheet, channel exit material is called extrudate extrudate swells at end of die due to normal forces from the polymer flow, called die swell Cooling zone water bath or air cooled to lower the temperature below Tg Auxiliary equipment puller rollers for proper thickness Wind-up or cut off Die Swell
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  • 7 Extrusion Equipment Tooling (Shaping tool associated with extrusion) filaments: multiple orifices with tapered entrances profile products: without hollow sections with plate dies tubes or pipes: hollow extrudate with use of mandrel films or sheets:several slit die configurations are used T-shaped, coat hanger, fishtail, Difficult to get uniform product thickness across entire width remedy is to use restricter bars and flexible lips Coextrusion of 2 or more plastic materials through a single die Auxiliaries Cooling (water bath), sizing (forced against external sleeve or against a mandrel with vacuum), post forming (jigs, fingers, shoes, rollers), cutting (fly cutters), winding devices
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  • 8 Extrusion Materials Materials (high MW, high viscosity, and melt strength) Polyethylene used for films and pipes, either as LDPE (flexible) or HDPE (rigid) Polypropylene used as oriented film PVC used in rigid form and plasticized form with twin-screw PTFE or UHMWPE processed by screwless (ram) extrusion Products Fibers and monofilaments: PA, acrylics, polyesters (800-6000 ft/min) Profiles (flat strips, simple channels, hollow sections): vinylic, styrenic, and olefinic resins. Profiles with cellular (foam) core and a solid skin: exterior wall siding, window tracks, door tracks, handrail covers, weatherstripping Tubular products: tiny tubing (artificial kidney or drinking straws) to pipes with 63 diameter
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  • 9 Extrusion Products Specialty tubes Pipes made with coextrusion foam core Very long tubes made with helically winding and then bonding a suitable extruded profile Flexible reinforced tubing made by extruding an inner liner, braiding around it a fiber reinforcement, and then extruding over it a cover (jacket) Materials are PVC, LDPE or HDPE Flat products Films (