Page 55 - Plastics News Issue November - 2024
P. 55
TECHNOLOGY NEWS
Impact of Temperature on
Molded Part Quality
Let us consider the first one: a higher tempera-
ture in the melt will help you fill better the mold,
it will increase the part gloss, and it will give you
better quality in the weld lines, where two flow
fronts collide.
There is an additional advantage of molding at
higher temperatures. You may have heard about
viscoelasticity, which is a behavior particular to
certain substances – plastics amongst them.
Viscoelasticity- The Dual Nature of Polymers
emperature in injection molding process-
es plays a crucial role in part quality, ei- At lower temperatures polymers will exhibit
Tther improving or compromising essential a more evident elastic behavior, as a solid. At
attributes. higher temperatures, the viscous behavior will
dominate, and the material will relax stresses, as
Injection molding is a complex process, where a liquid.
several variables interact to determine the
outcome. Quality, measured as compliance of Mold at higher melt temperatures whenever the
dimensions, appearance, resistance and per- part will face higher loads, especially at low work-
formance attributes, is determined by the com- ing temperatures, to prevent internal stresses
bination of several factors.
Also, higher melt temperature will of course
lower the viscosity and improve homogeniza-
However, most of the defects normally encoun-
tered in injection molding parts come one major tion. So if you have dispersion problems, make
source: temperature – either the excess or lack sure to increase the parameters affecting melt
of it in the melt or in the mold. Understanding shear and heat dissipation: back pressure and
how temperature affects your part can help you rotational speed of the screw.
solve variations in product quality. On the other hand, excessive melt temperature
The Effect of Melt Temperature will lead you to higher cooling times, and under
extreme circumstances it may induce degrada-
Energy in polymers is the source of molecular tion. It will also increase the molecular move-
movement. There will be some scenarios where ments, and at the gate or in thicker regions of
you want to have more movement, and other the part it may induce shrink marks.
scenarios where you want to have less.
November 2024 PLASTICS NEWS 55
