Page 94 - Engineering Plastics Handbook

68 Introduction

plastics processing equipment, according to the company. It provides real-
time controls in milliseconds. The company’s Moldwatcher complements
its XTREEM. The University of Massachusetts-Lowell, Plastics Engineering
Department, has HPM, Battenfeld, and other injection molding models.
The University of Massachusetts-Amherst [8] polymer and plastics
research facilities include the Silvio O. Conte National Center for Polymer
Research and the Polymer Science and Engineering Department with (1)
a Center for UMassachusetts/Industry Research on Polymers (CUMIRP)
which links industry and government agencies, established by the National
Science Foundation, and (2) a Materials Research Science and Engineering
Center sponsored by the National Science Foundation.
Virginia Tech has (1) a National Science Foundation, Science and
Technology Center for High Performance Polymers, Adhesives, and
Composites and (2) a Polymer Materials and Interface Laboratory [9].
Injection molding processes using Stat-Ease Inc. response surface meth-
ods for process optimization are developed with design of experiments
(DOE) and a multifactor linear constant (MLC) [10].
Injection molding pressure is determined by the hydraulic pressure,
hydraulic cylinder area, and plasticating screw cross-sectional area [3]

 A 
P = P h
i h 
 A 
s
where P = injection pressure, MPa (psi)
i
P = hydraulic pressure, MPa (psi)
h
3
3
A = area of hydraulic cylinder, mm (in )
h
3
3
A = cross-sectional area of screw, mm (in )
s
The injection molding clamp force is directly proportional to the pro-
jected area of the part, or to the empirical pressure or viscosity factor.
Clamp force can be related to melt flow length and part thickness [3] by
F =ƒ A
η
c
where F = clamp force, N (tons)
c
ƒ = empirical pressure of viscosity factor
η
2
2
A = projected area of part, cm (in )
When actual or estimated peak cavity pressure P max is used,
= P A
F c max
When clamp force is a function of melt flow length and part thickness,
F = L
c
H