04Lecture-Calc - Manufacturing Production Processes...

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Manufacturing & Production Processes - ENGR3190U – Lecture 04 Chapter 13 - 13.2.2 Analysis of Extrusion Calculations For Plastics What is the flow rate of polymer melt in extruder? Refer to Figure 13.5 in textbook As screw rotates inside barrel, the melt is forced to move forward towards die, this is drag flow . A w A D d A DN Q f c d cos ) tan ( ) cos ( 5 . 0 - = π π Q d = volume drag flow rate (m 3 /s) D = screw diameter (m) N = screw rotational speed (rev/s) d c = screw channel depth (m) A = flight angle = D p A π = tan where p = pitch w f = flight land width (m) If we assume flight land width is negligibly small then formula simplifies to A A Nd D Q c d cos sin 5 . 0 2 2 π = Compressing the melt through downstream die creates back pressure flow . = dl dp A Dd Q c b η π 12 sin 2 3 Q b = back pressure flow (m 3 /s) η = viscosity (N-s/m 2 ) 1
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dp/dl = the pressure gradient (Mpa/m) – stronger at die end, weaker at hopper end. (Figure 13.6) If we approximate dp/dl by straight line then formula simplifies to L A Dd p Q c b η π 12 sin 2 3 =
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