制造方法第7章.ppt

CHAPTER 7 PLASTICS TECHNOLOGY Expandable polystyrene (EPS) Carbon dioxide gas producing reagents are incorporated in the Styrofoam resin known as EPS, When the Styrofoam is injection molded at 95deg C, the reagent react under heat to give carbon dioxide and foams the material. Figure 7-18 Foam molding process for expandable polystyrene CHAPTER 7 PLASTICS TECHNOLOGY JOINING PLASTICS How a plastic can be joined depends on the nature of the particular plastic. Some methods work better for one plastic than for another. Below are general guidelines for joining various plastics. Table 7.2 Method Principle Applications Solvents Cohesion For amorphous (non-crystalline) plastics, e.g. acrylic, styrenes, cellulosics. Fusion by Heat Cohesion For all thermoplastics, especially those with a crystalline structure, e.g. polyethylene, vinyls, nylon. Not for thermo sets. CHAPTER 7 PLASTICS TECHNOLOGY Adhesives Adhesion For all plastics and for joining plastics to wood, metals, ceramics, composites. However, each type of adhesive is only suitable for joining certain materials. Mechanical fasteners Mechanical linkage For any plastic that has low notch sensitivity. For joining plastics to wood , metals, ceramics, composites. Friction welding Cohesion For some thermoplastics, especially those with a crystalline structure. Ultrasonic welding Cohesion For some thermoplastics, especially those with a crystalline structure. CHAPTER 7 PLASTICS TECHNOLOGY Notch sensitivity is the property that causes a material to crack through very quickly once the surface is damaged, or once there is a discontinuity in the component. Food for Thought Q: Most of us have given little consideration to the plastic containers that are used to contain our food .Can you think of the material(s)employed and the appropriate manufacturing process (es) for these containers? Post your answers on the IVLE forum to brain storm with your classmates. A: Figure 7-19 plastic containers of different sh