Meaning
Dynamic barriers created by fully molten polymer within an extruder screw prevent the backflow of gases. The melt seal forms where the resin transitions from a solid bed to a continuous molten phase, filling the screw flights entirely. Maintaining this pressure boundary allows for high vacuum levels in degassing zones without drawing air from the feed throat or venting molten material into the vacuum system.
Separation Zone
Pressure isolation between different functional areas within the barrel relies on the integrity of this viscous plug.
Screw Geometry
Design of the flight depth and the use of restrictive elements help to establish the barrier at a specific location. Reverse flighted elements or neutral kneading blocks are often employed to force the polymer to fill the channel completely. These components create the local resistance needed to maintain the melt seal under varying screw speeds.
Degassing Efficiency
Removal of moisture and trapped air improves when the seal provides a clear boundary for the vacuum. If the seal fails, the vacuum draws atmospheric air through the hopper, which can cause oxidation of the polymer melt. Consistent performance of the melt seal ensures that the final extruded product is free from bubbles and structural defects.
