House Blends Shipped under a Branded Resin Grade Name
House blends sold under branded grade names alter molecular weight distribution and melt rheology, requiring lot-level shear, thermal, and impact testing.
Screen Pack Mesh
Meaning
The metal wire screens arranged inside the breaker plate of an extruder filter out unmelted resin, degraded gel particles, and foreign contamination from the polymer melt. This assembly, designated by its screen pack mesh size, governs the cleanliness of the melt and the back pressure generated inside the extruder barrel. The specification applies to sheet, film, and profile extrusion lines and is not used in standard injection molding barrels.
Filtration Mechanism
Wire screens of different opening sizes are layered together to trap particles of varying diameters. The screen pack mesh density is chosen based on the sensitivity of the extrusion die and the contamination level of the resin. A typical setup utilizes coarser screens on the outside to support the finer filtration screens in the center.
Pressure Impact
Finer mesh screens generate higher flow resistance and raise the melt temperature through shear heating. This pressure increase improves the mixing and homogenization of the polymer blend. However, excessive pressure can lead to melt degradation or leakage around the extruder head seals.
Process Maintenance
Captured debris gradually clogs the screen openings, which causes the melt pressure ahead of the screen pack to rise. Extrusion lines use pressure transducers to monitor this buildup and signal when the screens must be changed. Using a manual or continuous screen changer avoids prolonged downtime during these screen changes.