Mate 447 Review Paper

Review for Exam 3
MatSE 447
Wednesday, April 23 (in class) 2:30 - 3:20
Bring: Pen or pencil, calculator and one 8.5” x 11” paper with anything you want to write on one side
Review: Homeworks, Notes
Polymer Processing: Injection Molding,
Single Screw Extrusion, Twin Screw
Extrusion, various uses of Extruders

Injection Molding

Economics: What impacts cycle time t ? part cost = material cost + (mold cost)/N
+ (molding machine cost per hour) t / n
Clamping Force is how injection molding machines are sized (the force required to hold the mold closed during injection and packing) F=PA

Injection Molding Window

Injection Molding Window

Injection Molding Thermodynamics

only pack until the gate freezes

Injection
The roughly triangular left screw flight region shown in red has large pressure induced backflow, making the NOCT have the steepest extruder characteristic.

 WHvb cos 
Q  1  f  
2


3
 WH  P 

  Q12

12   Z 


barrel right screw flight First two terms are nearly identical to the usual terms for extruders



or f is the fraction of the arc on each screw that sees the red triangle f 
2
360

L
Third term is the backflow
Q12  0.017  H a  0.61Wa  Wa 3  s in the two red triangles
 e

  P 


 L 

Single Screw / Twin Screw
• Single screw extruder is the workhorse of the plastics industry, offering a useful range of pumping and mixing of polymer melts
• Twin screw extruders provide intensive mixing
(NOCT) or shorter residence time (CICT) die characteristic
CICT extruder characteristic

Q