Plastics lines blame resin lot when line speed creeps down to hold gauge. Often the screw has opened clearance in the compression section and the barrel has bell-mouthed at the feed throat. Melt thermocouples still read in band because the extruder works harder, not because the process is stable.
This is not die lip buildup alone and not dryer moisture on its own. It is screw–barrel wear geometry as a slow variable.
Wear signals that precede scrap
| Signal | Likely mechanism | First check | |--------|------------------|-------------| | Specific energy up 8–12% at same rate | Flight tip wear, more slip | Screw depth gauge at compression | | Melt pressure ripple at constant RPM | Barrel scoring or ovality | Bore gauge, pull screw if trend persists | | Feed throat temperature rise | Solids bed slipping early | Throat ID, feed roll bite | | Color streaks after a “good” purge | Dead zone behind worn flights | Screw profile map vs. spare |
Pull schedule discipline
Log flight depth at pull, barrel ID at three zones, and hours since last pull. Replace as matched sets when clearance exceeds the OEM map—mixing a fresh screw in a worn barrel buys weeks, not quarters.
Do not approve a rate increase on a worn pair because the gauge still meets nominal. You are borrowing melt quality.
Change control
Screw steel, coating, and barrel liner grade are process. A resin change that raises abrasives without moving the pull interval is MoC. So is running regrind above the wear model assumed.
The panel shows RPM and amps. The screw and barrel decide whether that power becomes useful melt or slip heat.