PREVENTING MELT ACCUMULATION WITHIN THE DEGASSING AND MELT RETURN DELIVERY THREAD OF AN EXTRUSION SCREW.

摘要

An apparatus including a single screw extruder for extruding a fused molten mass of thermoplastic material and for reverse degassing the melt. The device includes an extrusion screw rotatable in a hollow cylindrial barrel, and a hopper for introducing the melt into the barrel. The screw has at least one flight for conveying the introduced melt and a return delivery flight disposed upstream, in the direction of extrusion, of the hopper. Reverse degassing of the melt is effected by a vacuum source disposed upstream of the hopper in communication with the return delivery section, and provided with a degassing dome generating a reduced pressure or vacuum. At least one radially adjustable separating member for effecting mechanical separation of fused mass from the gas is provided in at least one location in the return delivery section. The method includes degassing of the melt by producing a reduced pressure in the return delivery section. The gas extracted from the melt is discharged. However, the degassing will cause some of the fused mass to enter the return delivery section. The fused mass is separated from the gas by mechanical separators in the return delivery section.