Page 342 - Plastics Engineering

Processing of Plastics 325

I

Force, F Annular element
I /of fluid

Fig. 4.63 Analysis of compression moulding

12q dH
-.-=-- 2dP (4.44)
H3 dt r dr
This simple differential equation is separable and so each side may be solved
in turn.
2 dP
Let -- - -A where A = f(H)
r dr
P r
so jdp = 4 Jrdr
0 R
A
or P = -(r2 - R~)
4
Now the force on the element is 2rcrdr(P) so the total force, F, is given by
integrating across the platen surface.

RAR4
F = ]2nr (a) (r2 - R2)dr = --
8
0
This may be rearranged to give

where V = xR2H
Substituting for A in (4.44)

12qdH
8rcFH2
--- - --
V2 H3 dt