Meaning
Extrusion equipment utilizes specialized localized chambers to extract moisture and volatile organic compounds from molten polymer before shaping. In double vent or single vent compounding lines, the degassing vent dome provides the necessary volume and sealing to apply a deep vacuum to the melt. This extraction is critical when processing hygroscopic polymers like polycarbonate or recycled polyester.
Volatile Removal
High temperature melt streams release vaporized monomers and water molecules into the open flight channels of the screw. As these gases escape, the degassing vent dome directs them toward the vacuum pump while preventing the molten plastic from climbing into the extraction ports. If the dome becomes clogged, the volatile gases are trapped within the barrel, which forces them back into the polymer stream and creates bubbles in the final extrudate.
Pressure Management
Extrusion lines must operate under tightly controlled negative pressures to prevent material surging and ensure stable output. Proper design of the degassing vent dome maintains a steady vacuum level without causing excessive shear heat or polymer degradation. When the vacuum level fluctuates, the melt density varies, leading to inconsistent pellet weights.
Defect Prevention
Melt contamination and surface imperfections often arise when volatilization is incomplete. Undegassed resin produces moulded parts with splay marks, internal voids and reduced tensile strength. A well functioning degassing vent dome ensures that the final compound meets the specifications required for optical or structural applications.
