MECH 3503 - Polymer - Midterm Review

  1. properties of polymers
    • Low density relative to metals and ceramics
    •  Good strength-to-weight ratios for certain (but not all)
    • polymers
    •  High corrosion resistance
    •  Low electrical and thermal conductivity
  2. limitations of polymers
    • Low strength relative to metals and ceramics
    •  Low modulus of elasticity (stiffness)
    •  Service temperatures are limited to only a few
    • hundred degrees
    •  Viscoelastic properties, which can be a distinct
    • limitation in load bearing applications
    •  Some polymers degrade when subjected to sunlight
    • and other forms of radiation
  3. what makes thermosets set
    cross linking, covalent-ly bonded structure 

    chemical reactions associated with cross linking are called curing or setting
  4. mechanical properties of thermoplastics
    • low E  = low stiffness 
    • low tensile strength = easy to break
    • lower hardness 
    • greater ductility
  5. properties of thermosets
    •  Rigid - modulus of elasticity is two to three times
    • greater than thermoplastics
    •  Brittle, virtually no ductility
    •  Less soluble in common solvents than thermoplastics
    •  Capable of higher service temperatures than
    • thermoplastics
    •  Cannot be remelted - instead they degrade or burn
  6. whats the relationship between viscosity and shear rate
    • viscosity of a polymer melt decreases with shear rate
    • vis
  7. how to extrude polymers
    you do the big screw boi and the barrel get hot hot hot
  8. good and bad of calendaring
    • feedstock passed thru series of rolls
    • expensive equipment, high production rates
    • process good for good surface finish and high gage accuracy
    • good for rubber or rubbery thermoplastics
  9. how to make fibres and filaments
    • ya spin it boi
    • spinning is extrusion of polymer melt or solution through a spinnerret, then drawing and winding it onto a bobbin

    • different types
    • melt spinning - starting polymer is heated to molten state and pumped through spinneret, filaments are drawn and air cooled before being spooled 
    • dry - starting polymer is in solution and solvent can be separated by evaporation
    • wet - solvent is non-volatile, polymer is in solution, separate polymer in liquid chemical that precipitates the polymer into strands
  10. advantages between two plate and three plate and hot runner
    three plate disconnects the runner and the part 

    hot runner eliminates solidification of sprue and runner, saves material that wouldve been scraped
  11. How do you extrude polymer
    • A large screw extruder
    • Barrel is heated 
    • goes thru breaker plate to make flow straighter through the die where extrudate comes out

    For hollow shapes, a mandrel is placed
  12. How does slit die extrusion work?
    goes drippy drippy into a manifold thru a thin af die slit to make an extruded film
  13. blown film process
    extruder goes out where there's air that goes blowy blowy and guide rolls help make the shape. pinch rolls make it smol
  14. how 2 make continuous filaments of fibres of polymers
    feed hopper with polymer granules goes in a heating unit 

    gets pumped into a spinny boi and a yam driving roll collects all the stringies
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MECH 3503 - Polymer - Midterm Review