Page 138 - Injection Molding Advanced Troubleshooting Guide

14 Mold Cooling

„ „14.1„ Mold Cooling Importance

At its core injection molding is a thermodynamic process that relies on heat ex-
change. One of the critical aspects of a mold is to act as a heat exchanger to remove
the heat energy from the molten plastic. If a mold is not doing an efficient job act-
ing as a heat exchanger the cycle time of the molding process will be limited.
It is important to understand that a part can only be cooled as fast as the plastic
can give up heat energy and as fast as the mold can transfer heat energy from the
plastic.
The mold must be cooled as uniformly as is possible. If the mold has hot spots
these locations will end up dictating the cycle time due to the reduced cooling
capacity.
In most molding processes the overall cycle time is at least 50% cooling time and
often up to 80%; see Figure 14.1 (bear in mind that the plastic is cooling as soon as
it contacts the mold surface). This means that there is a great opportunity avail-
able to optimize cycle times if cooling efficiency is optimized.