Page 93 - Engineering Plastics Handbook

Processing 67

where N = screw speed, rpm
P = pressure, Pa
K = thrust bearing constant
1
The thrust bearing constant is described in C. Rauwendaal.
Among other machinery and equipment considerations critical to good
performance are the land length and gearbox. When the land length is too
long, excessive shear can generate; when the land length is too short,
insufficient molecular alignment and extrudate swell can occur. The two
main properties to look for with a gearbox are strength and torque.

Injection Molding
Injection molding machinery and processes using engineering thermo-
plastics were introduced at K2004 [18]. Nestal Machinery (Devens, Mass.,
USA) all-electric 132-ton Elion series molds PC/ABS cellphone shell halves.
Arburg Inc. (Newington, Conn., USA) and Engel Canada Inc. (Guelph,
Ontario, Canada) introduced machines for injection comolding of nylon and
liquid silicone rubber (LSR), a thermosetting synthetic rubber. Arburg
has an Allrounder 570C injection molding machine and an Engel tiebar-
less Victory injection molding machine. Engel’s Duo Combo CS system com-
bines injection-compression with a rotary stack mold.
Principal injection-molded parts considerations that influence process-
ing conditions, machinery, and mold design include wall thickness, part-
ing line and ejection, appearance, ribs, boss designs, holes and depressions,
and corners, radii, and fillets [5].
Computer controls for injection molding monitor the viscosity, temper-
ature, and pressure. Many important injection molding technology
advances with computer software come from universities. Cornell Injection
Molding Program (CIMP) at Cornell University [6] has about 30 software
programs for injection molding such as its TM series, which includes mold-
filling analyses and capillary-rheometer viscosity. The University of
Massachusetts-Lowell, Plastics Engineering Department [7] software
includes AutoCAD, Cadkey, Pro/Engineer, and SolidWorks. The University’s
CAE program funded by Moldflow is linked to state-of-the-art Ferromatik
Milacron injection molding machines, which include all-electric models.
Moldflow software is applied to molding processes and manufacturing.
Ferromatik Milacron North America (Batavia, Ohio, USA) controls can be
“wired” from the plant to other machines and to all departments in the com-
pany and globally. The company’s XTREEM Control was the first PC-
based control to be developed for the plastics processing industry and

1
C. Rauwendaal, ed., Polymer Extrusion, 2d ed., Hanser Publishers, Munich, Germany,
1990.