Plastics Processing Test 2

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  1. Definition of Transfer molding
    Auxiliary or external pot and Integral ram 

    Has a pt connected by runners and gates. The mold is closed and the material is placed into the pot. Its then pushed out through runners and gates into the cavities.
  2. Terms for material-loading chamber
    • Pot 
    • Material Well
  3. Advantages of Transfer molding 
    • Less flash on parts since mold is closed 
    • Dimensions are more accurate across the parting line 
    • Delicate inserts can be molded in place 
    • Cure is rapid due to frictional heat and pressure
    • Smoother finishes 
  4. Disadvantages of Transfer Molding
    • Warpage due to uneven filling and gate location 
    • Knit lines, weld lines, and flow lines in black of pins and inserts 
    • Loss of material due to cull, runner, gate and sprue 
    • Erosion is common in gates, runners and cavities 
    • high bulk or highly filled material are difficult to mold 
  5. Problems caused by overly thick sections
    • Longer cycle times 
    • Shrinkage 
    • Warpage 
  6. Problems caused by over thin sections 
    • Warpage 
    • Brittle 
    • More ware on mold 
  7. Importance of radii and fillets on parts 
    • Cause damage and failure in parts 
    • Cause damage and failure in molds 
    • Longer molding time 
  8. Mold Cost- Integral ram vs. Auxiliary ram 
    Auxiliary mold cost is more expensive than Integral mold cost 
  9. Type of Transfer molding is our machine 
    Auxiliary Ram or External Pot (well)
  10. Which machine is best for encapsulation
    Auxiliary ram because you have better control of the rams speed and pressure 
  11. Location of gates 
    Want them on the thick sections of parts 
  12. Transition- thick to thin sections 
    Rounded out sections, no abrupt changes in material flow 
  13. Insert use in "gate area"
    To replace gate for wear and tear, instead of taking out entire mold 
  14. Function of gates
    • Break off point between runner an parts 
    • Creates back pressure 
    • Directs flow 
  15. Ultimate Density 
    Best part and properties possible. 

    Above U.D.: Short shots, higher shrinkage and lower properties overall 

    Below U.D.: Over densification and part expands and swell, there is warpage 
  16. Composite molding is made up of tow more more materials and two or more processes 
  17. Changes required to go from T.P. to T.S.
    • Cooling Barrel 
    • 1:1 compression ration screw 
    • Change nozzle and runner system 
    • High heat from molds 
    • Inhibitors used in molding compound 
    • Wear resistance of barrel and screw is critical 
    • Cannot use valves 
  18. Advantages of Injection molding of T.S. 
    • Elimination of electronic or other preheating 
    • High bulk factor material used 
    • Continuous feeding of materials 
    • Less critical control problems 
    • Reduction in cycle time which provides more production 
    • Better plastication of material 
    • Interchangeability of T.P. and T.S. machine use 
    • T.S. become more competitive to T.P
  19. Disadvantages of Injection molding of T.S.
    • High equipment cost 
    • Wear on screw and barrel 
    • Cant use "non-return" valve 
    • Must choose T.S. materials to use 
    • Cant mold inserts as easily as vertical
Card Set:
Plastics Processing Test 2
2013-02-09 05:03:04
PP2 T2

notes for processing test 2
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