20 Plastic Parts

List common names and abbreviations used in the manufacture of plastic parts. Explain the difference between thermoplastic and thermoset plastics. Explain the processes used in the plastics industry. Describe methods used to fasten and join plastics. Read and interpret prints from the plastics industry.

Plastic Parts Plastic: –Product of polymer chemistry –Synthetic material formed by chemical reaction, rather than a substance of natural origin Thermoplastics: Soften when heated and solid when cooled Thermoset plastics: Cannot be softened once cured, neither by heat nor solvent

Thermoplastics

Thermosets

Plastic Processes Molding: Forcing molten plastic into a hollow mold Thermoforming: Forcing a sheet of softened plastic onto a mold using vacuum or positive pressure Extrusion: Pumping molten plastic through a heated die Casting: Pouring molten plastic into an open mold without using pressure

Plastic Processes Bottles manufactured by blow molding (Uniloy)

Plastic Processes Car model manufactured by thermoforming (MAAC Machinery)

Plastic Processes Plastic pipe manufactured by extruding (Polygon Company)

Fastening and Joining Plastics Mechanical fasteners: Thread-cutting screws, rivets, and press-in inserts Mechanical fits: Press-in and snap-on fits Welding: Ultrasonic welding, heat welding, and spin welding Adhesives: Elastomers, epoxies, and solvents

Fastening and Joining Plastics An ultrasonic plastic welding machine (Dukane)

Plastics Terminology Mold: Hollow form into which material is placed to give the material its final shape Cavity: Depression or set of matching depressions in the mold Parting line: Edge of the mold cavity where mold halves come together

Plastics Terminology Ejector pin: Pushes the product out of a mold Knockout: Any part of the mechanism of a mold used to eject the molded articles Core: Various meanings, including a portion of a mold that hollows out a section of the part Draft: Slight outward taper in a mold wall designed to facilitate removal of the molded object

Plastics Terminology Sprue: Main feed channel that connects the mold orifice to the runners Runners: Usually circular channel that connects the sprue with the gate Gate: Connects the runner to the part cavity; often 1/8  diameter or less Flash: Thin web of excess material forced into crevices between mating mold surfaces

Plastics Terminology Boss: Circular protrusion from the plastic body Gusset: Angular piece of material designed to strengthen two adjoining walls Insert: Material placed into the mold cavity prior to molding that is then surrounded by the molded material Overmold: Process of injection molding a plastic over an existing plastic

List three common amorphous thermoplastics. Polystyrene (PS), polyvinyl chloride (PVC), and polycarbonate (PC)

What is the basic difference between a thermoplastic and a thermoset plastic? A thermoplastic can be softened by heat, while a thermoset plastic cannot be made liquid again by heat or solvent.

List at least three processes used in industry to form plastics. Molding, thermoforming, extrusion, and casting

What are the four principal techniques used to join plastics? Mechanical fasteners, mechanical fits, welding, and adhesives

How does reading a print for a plastic product differ from other types of products? The process is the same; drawing layout, title block, notes, and dimensioning practices are the same.