Question

ratios....

Answer 1

so i have an extruder that has a length to diameter ratio of 26. how do i find the diameter from that?

Answer 2

the full question is: An extruder has a length to diameter ratio of 26. The flight angle, A, on the screw is 15 degrees while the pitch of the screw is 4.2 in, and the channel depth, d_c, is 0.15 in. The barrel heats the polypropylene melt to 500 degrees Fahrenheit, which provides a melt viscosity of 0.0025 lb-s/in^2. In operation the screw rotates at 50 rev/min (0.833 rev/s) and a volume flow rate of 3.5 in^3/s at the end of the barrel is generated. What is the head pressure generated by the die end?

Answer 3

equations....
resulting flow\[Q_x=Q_d-Q_b\]\[Q_d=\frac{1}{2}\pi^2D^2Nd_csinAcosA\]\[Q_b=\frac{p\pi Dd_c^3\sin^2A}{12 \eta L}\]\[\tan A=\frac{p}{\pi D}\]\[\frac{L}{D}=26\]D= screw diameter
N= screw rotational speed
d_c= screw channel depth
A= flight angle
L= screw length
p= head pressure (die)
n=melt viscosity.

Answer 4

so far i have\[Q_b=\frac{p\pi (L\frac{1}{26})(0.15)^3(\sin 15)^2}{12(0.0025)L}=9.11*10^{-4}p\]\[Q_d=\frac{1}{2}\pi^2\frac{L^2}{26^2}(0.833)(0.15)(\sin 15)(\cos 15)=7.26*10^{-5}L^2\]

Answer 5

What course is this for?

Answer 6

this is my EGR 218 class. Materials and Manufacturing. i got all the equations from the teacher's slides. i have all the information to fill the slides but i don't have the length of the screw which is what i need to find the diameter of the screw in order to find the head pressure.

Answer 7

Where is the pitch of the screw in your equations?

Answer 8

that was a hint...

Answer 9

oh...

Answer 10

no.. the flight angle is not the screw pitch

Answer 11

p in your equations is pitch..

Answer 12

tanA=p/πD

you can solve for D from this because you know A (flight angle ) and p (pitch)

Answer 13

Gotta run...

Answer 14

ok thanks for helping.

Answer 15

you are welcome!

Answer 16

so for D i get 4.989 and then i found L as 129.7

Answer 17

so the p in that equation is different than the p in the other equation. the p in the Q_b equation is the head pressure which is what i have to find.

Answer 18

exactly!

Answer 19

yes and I would suggest you use capital P for head pressure and lower case p for screw pitch so you can keep them separate.

Answer 20

yeah. the slides confused me. thanks. i got head pressure to be 57.56

Answer 21

units for pressure...don't forget those.
and now as you study for finals...
https://www.youtube.com/watch?v=hkMaBy6EX0w

Answer 22

always try...

Answer 23

thank you for the encouragement. you were a huge help in everything!

Answer 24

you are welcome and don't hesitate to contact me as you prepare for finals!