Recycled Polyethylene Terephthalate Moisture Testing Methods
Accurate moisture testing below 50 ppm via Karl Fischer oven titration prevents hydrolytic intrinsic viscosity degradation in recycled PET during melt processing.
Extrusion Feed Throat
Meaning
Machine components positioned at the entry point of a plasticating extruder receive solid polymer pellets from the hopper and channel them into the screw channel. The extrusion feed throat is typically water-cooled to prevent the resin from melting prematurely and forming a solid plug that blocks the flow of material. This component is situated directly between the hopper and the heated barrel zones of the extruder or injection moulding machine.
Thermal Management
Polymer pellets must remain in a solid, free-flowing state until they are gripped by the rotating screw flights. If the feed throat temperature rises above the softening point of the polymer, the pellets will stick together and bridge, stopping the feed stream entirely. This temperature is maintained using a dedicated cooling water circuit, which prevents the heat from the barrel zone from migrating upward.
Precise control of this cooling circuit is essential when processing low-melting-point polymers or soft regrind materials.
Moulding Efficiency
Unstable feed behavior leads to pressure fluctuations in the extruder, resulting in part weight variation and cosmetic defects in injection moulding. A properly cooled feed throat ensures a consistent bulk density of the feed, which stabilizes the output rate of the screw. This consistency is particularly important when feeding high-regrind blends, which often have irregular pellet shapes and varying friction behavior compared to virgin resin.
Maintenance Protocol
Over time, calcium buildup or scale inside the cooling channels of the feed throat can reduce heat transfer efficiency, leading to gradual temperature rise and feeding issues. Routine flushing of these channels with descaling solutions maintains the required cooling performance. This preventative maintenance avoids unplanned production stops and maintains the consistency of the moulding process.