MMET 281 Exam 2 Questions and Answers Graded A+

MMET 281 Exam 2 Questions and Answers Graded A+ Why is there a delay in the extrusion process at the very beginning? Back pressure resists the extruded part from exiting the die Define back pressure. A resistance or force opposing the desired flow of fluid Define Expanded Materials. Materials containing pores True or False: Cellular materials come in closed and open cell forms. True Describe the structure of the cells in a closed cell material. Cells are discrete and separate Describe the structure of the cells in an open cell material. Cells have openings between them Interconnected True or False: Only thermoplastics can be foamed/expanded. False (This process works for both TP and TS) Name some of the applications foamed materials are used in. Thermal Insulation Sound Insulation Filler/cushions Flotation True or False: Styrofoam is extruded Polyurethane. False (Polystyrene) Polystyrene is commonly used in expansion processes. How does the chemical expansion of polystyrene work? Chemical blowing agent causes a thermal breakdown, freeing a gas within the plastic particles Polyurethane is commonly used in expansion processes. How does the chemical expansion of polyurethane work? Component that liberates gas is added to the resin via a chemical reaction Name the three main ways in which physical expansion is attained. Volatizing moisture Dissolving a gas that expands at room temperature in the resin Adding liquid/solid component that vaporizes when heated in the melt Explain how the mechanical expansion method works. Air is whipped into the resin and rapidly cured or cooled Define syntactic plastics. Materials made up of the blending of small glass or plastic bubbles into the resin binder True or False: Syntactic materials are open cell materials. False (Closed-cell) What are some uses of syntactic plastics? Thermal and acoustic insulation High compression strength flotation devices Two-stage molding is extensively used for __. a.) polyethylene b.) polyvinyl chloride c.) polypropylene d.) polystyrene d.) polystyrene True or False: Two-stage Molding materials are pre-expanded