I was asked this screw design question last week…
What is the optimal length for the feed zone of the screw?
note: this is for an injection molding machine
Generally speaking, the feed zone of the screw should be at least 1.5 times the total injection stroke. This allows the material in front of the feedthroat to properly convey to the transition zone with a low likelihood of blow-back.
When processing materials which tend to melt better with conductive heating such as ABS, PP, and Nylon, the feed zones are often longer to allow more material heating to take place before reaching the transition (compression) zone. An ABS screw, for instance, typically has a feed zone approximately half the overall length of the screw.