Chapter 15 part 2

Drape Forming Eliminates inconsistent wall thicknesses found in vacuum forming Sheet of plastic is clamped then heated Then drawn down over the mold Sometimes the mold is forced into the plastic Vacuum is applied

Extrusion 2nd most common process Similar to squeezing toothpaste to Injection molding Similar to squeezing toothpaste Extruder heats plastic into a continuous melt The melt is forced through a die to produce long shapes Used to make House siding Garden hose Pipe Straws Rods

Pultrusion Pulls continuous roving through three basic stages Pulled through a resin bath Pulled through a preforming fixture to partially shape and remove excess air Pulled through heated dies for final forming Cured in an oven

Film Blowing Polymer is melted into a single screw extruder Then pumped into a tubular die Air is forced into the die The tubular plastic shape is air chilled Then collapsed by pinch rollers Anything less than .01 thickness is considered a film Used to make: Plastic bags Plastic sheets

Wire Coating Extrusion process to coat wire Wire is pulled through a mandrel and surrounded by liquid plastic Plastic is cooled Wire is inspected then coiled by a machine

Extrusion Blow Molding Heated plastic is melted in an extruder Plastic is forced through an extrusion die form a parison Parison is expanded by air pressure against mold

Open Molding Processes that use mold that doesn’t completely surround the workpiece Two types: Hand layup Spray layup Uses thermosetting resin, fiberglass reinforcement and a catalyst

Casting Some thermoplastics and thermosets can be cast Thermoplastics require an additive

Sheet casting High viscosity syrup poured in one end of highly polished stainless steel belts Heating and curing takes place while transported down the belt Most common for acrylics Used to produce plastic sheets Skylights Greenhouse panels Mirrors

Nylon Casting Casting nylon can be more economical than injection molding and extrusion Four steps Melting the nylon lactam monomer Adding the catalyst and activator Mixing Pouring

Potting and Encapsulating Used to add insulation materials to electronic devices and components Protect from moisture and mechanical abrasion

Potting Encapsulating Done by applying compound through a dispensing gun or through automation Device is placed in a mold or pot, and resin is added until it is filled Encapsulating Can be done just to cover a specific area of the part Can be done with a squirt applicator Can cover the entire part Done by a dip coating

Centrifugal casting Create pipe, tubing and other round parts Saturated fiberglass strands are placed in a hollow mandrel that serves as the mold Mandrel is heated in an oven and rotated Centrifugal forces throw the material against the outside walls of the mandrel