Lecture 7. Plastic Part Manufacture, Injection （讲座7。）.pdfVIP

1 Lecture 7. Plastic Part Manufacture, Injection Molding In the last 30 years, plastics have become the most dominant engineering material for most products. We take a brief look at the most common types of plastics, and how they are processed. All plastics are polymers; these polymers are further divided into two basic types: thermoplastics and thermosets. Thermoplastics melt when heated – so they can be melted and re-formed again and again. Thermosets harden when they are heated, if heated further, they will break down chemically and lose their properties. Some thermosets have properties very similar to rubber, and are used as synthetic rubber; they are categorized as elastomers. Here are some typical plastics and their uses: Thermosets General properties: more durable, harder, tough, light. Typical uses: automobile parts, construction materials. Examples : • Unsaturated Polyesters: lacquers, varnishes, boat hulls, furniture • Epoxies and Resins: glues, coating of electrical circuits, composite materials like fiberglass used in helicopter blades, boats etc Elastomers General properties: these are thermosets, and have rubber-like properties. Typical uses: medical masks, gloves, rubber-substitutes Examples : • Polyurethanes: mattress, cushion, insulation, toys • Silicones: surgical gloves, oxygen masks in medical and other applications, joint seals,… Thermoplastics General properties: low melting point, softer, flexible. Typical uses: bottles, food wrappers, toys, … Examples : • Polyethylene: packaging, electrical insulation, milk and water bottles, packaging film • Polypropylene: carpet fibers, automotive bumpers, microwave containers, prosthetic body parts for disabled people • Polyvinyl chloride