Page 74 - Plastics News May 2024

IN THE NEWS

At a Glance and features. They can also lead to toring variable. If the pressure is too
ase barrel temperature setup flash. high, it can lead to flash, overpacking,
and voids. Pressure that is too low can
on the material manufactur- Best practice when establishing bar- cause shorts, sinks, and other under
er’s recommended tempera- rel temperatures is to base setup on pack conditions.
ture window. the material manufacturer’s recom-
mended temperature window. The
Lower mold temperatures help to run manufacturer will provide a material Time.
faster cycles, but they can also cause data sheet that gives you the recom- Measurements and setpoints related to
defects and complications.
mended temperature for the material’s time are also key to establishing a ro-
Cooling too fast can result in higher performance range. Start at lower tem- bust process. Primary setpoints relat-
shrink rates, dimensional problems, peratures to benefit from an improved ed to time are hold time, fill time, cool
and heat sinks. cycle, but if scrap is being generated time, and cycle time. Key monitoring

Setting up plastic injection molding because the temperature is set too low, variables such as recovery time, actual
processes can seem like a daunting increase barrel temperature until the fill time, and cycle times are important
task. After all, there are many different material performs optimally. when establishing a process. Cool time
defects that can lead to scrap when a must be longer than screw rotate time
process has been set up incorrectly. Mold temperature. to prevent screw recovery from caus-
The key to developing a robust process Mold temperatures can also create ing inconsistent cycle times.
is understanding the fundamentals of defects in a process. Lower mold tem- Cooling.
plastic injection processing. This arti- peratures help to run faster cycles, but
cle will outline the primary foundations they can also cause shorts, poor part Excessive cooling duration can lead
of a process, as well as detail the de- finish, overpacking, and poor knitting to longer cycles, sticking parts, and
fects that may be caused by incorrect in areas where multiple flow fronts dimensions that are too large or long.
settings. meet. Higher mold temperatures can Cooling too fast can result in higher
cause flow fronts to move too quickly, shrink rates, dimensional problems,
Barrel temperature. leading to gas trap and poorly filled and heat sinks. Long cooling events
Barrel temperatures are key setpoints ribs and details. Higher temperatures can also lead to splay because of lower
that can lead to scrap events. Barrel also can lead to increased part shrink- mold and barrel heat soak conditions.
temperatures that are set too low can age, forcing a processor to run longer Heat, time, pressure, and cooling are
lead to shorts. Higher viscosities can cycles. When stationary and moveable the key foundation blocks of a robust
be harder to control due to an increase half temperatures are different from plastics process. Understanding the
in flow front thickness. each other, they can cause or correct effects they have on a process is key to
warp defects. process setup. These are the first four
Lower temperatures can also lead factors to consider when scrap events
to over packing and sticking parts. Pressure. occur. Knowing this will help you to
Pressure is also one of the primary better understand what adjustments
Higher temperatures result in lower
viscosities and thinner flow fronts. factors in a plastic injection process. need to be made to eliminate scrap and
Hold pressure is a key setpoint, and increase profits.
Faster flow fronts can lead to trapped peak pressure is a key process moni-
gas at end of fill or poorly packed ribs Source – Plastics Today

74 76 PL MA MAY 2024 PLASTICS NEWS 75
PLASTICS NEWSASTICS NEWS
MAY 2024Y 2024