Recovery Issues at Start-Up

[JayDub]

Can you tell whether the material is getting to the screw or hanging up in the throat? If the latter it could be coming out of the drier too hot and soft and bridging. You could try drying at a lower temperature for longer. A technique that is supposed to help with screw feed is to have grooves cut in the back end of the barrel (essentially right under the feed throat), but I don’t have personal experience with it.

[chrisprocess]

Interesting - it's fine once it's running though. So what would cause dosage issues when screw is empty vs screw is full?
The material enters the screw same way in either condition. So that sort of eliminates any potential issues above the screw, right?
You mentioned most solutions that came to mind.
I might try a colder (like cold) rear barrel temp and profile up to a hot temp to the nozzle
if that doesn't work try the other way around

Tried with high and low back pressure? or try to simulate what the screw would do in fully auto?
block the nozzle (with cold slug in sprue maybe?), use back pressure extrude the screw. I might try pulling screw back and trying to extrude in different stages as well; feed zone, mixing zone.

let us know

[rickbatey]

Have you confirmed all is correct inside injection unit? Maybe wear or pellets stuck to the screw after shutting down. How do you shut these machines down and for how long? Run them completely empty one shutdown and see what you get.
I’ve seen this with incorrect barrel temperatures (t/c wrong/damaged) and when the cold screw prevention times were too low. Is there a torque setting on charging drive? Maybe running high speed versus high torque.
Could there be a setting in machines that causes low torque and screw RPM on restarts or a set idle timer? I’ve seen that on several new machines.
Rick