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MMET 281 Exam #2 Questions And Answers
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MMET 281 Exam #2 Questions And Answers
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MMET 281 Exam #2 Questions AndAnswers
Why is there a delay in the extrusion process at the very beginning? -
correct answer ✅Back pressure resists the extruded part from exiting
the die
Define back pressure. - correct answer ✅A resistance or force
opposing the desired flow of fluid
Define Expanded Materials. - correct answer ✅Materials containing
pores
True or False: Cellular materials come in closed and open cell forms. -
correct answer ✅True
Describe the structure of the cells in a closed cell material. - correct
answer ✅Cells are discrete and separate
Describe the structure of the cells in an open cell material. - correct
answer ✅Cells have openings between them
Interconnected
True or False: Only thermoplastics can be foamed/expanded. - correct
answer ✅False
(This process works for both TP and TS)
,MMET 281 Exam #2 Questions And
Answers
Name some of the applications foamed materials are used in. - correct
answer ✅Thermal Insulation
Sound Insulation
Filler/cushions
Flotation
True or False: Styrofoam is extruded Polyurethane. - correct answer
✅False
(Polystyrene)
Polystyrene is commonly used in expansion processes. How does the
chemical expansion of polystyrene work? - correct answer ✅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? - correct answer
✅Component that liberates gas is added to the resin via a chemical
reaction
Name the three main ways in which physical expansion is attained. -
correct answer ✅Volatizing moisture
,MMET 281 Exam #2 Questions And
Answers
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. - correct answer
✅Air is whipped into the resin and rapidly cured or cooled
Define syntactic plastics. - correct answer ✅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. - correct
answer ✅False
(Closed-cell)
What are some uses of syntactic plastics? - correct answer ✅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 - correct answer ✅d.) polystyrene
, MMET 281 Exam #2 Questions And
Answers
True or False: Two-stage Molding materials are pre-expanded by heat or
radiation. - correct answer ✅True
Describe properties and examples of Two-stage Molding. - correct
answer ✅Can expand up to 40 times their original size
Closed-cellular structure
Packaging, bean bag chairs
Describe the Reaction Injection Molding process. - correct answer
✅Two materials enter the mold, and the resultant chemical reaction
causes the material to foam
Describe the casting process for foaming products. - correct answer
✅A mix of resin, catalysts, and chemical expanding agents is placed in
a mold. The mix then expands into a cellular structure
What are some foaming products made with casting? - correct answer
✅Flotation devices
Sponges
Mattresses
Cushions
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