The basic purpose of the water is to cool the feedthroat to avoid bridging. The feedthroat is the area of the barrel where the material passes through from the hopper the screw.

If this area gets too hot, the material may clump or stick together, creating a blockage known as bridging. If the area is cooled too much, condensation may occur resulting in visual defects or a change in mechanical properties. Condensation in the feedthroat most often occurs during a production delay, such as a mold or material change.

For a related entry on feedthroat cooling, please review: Feedthroat Temperature Differences…

-Andy