Abstract: A plastic extruder screw tip having a conical inwardly and forwardly tapering melt converging surface; having first and second dashers fixedly attached to and extending laterally outwardly from the melt converging surface, the dashers being opposingly arranged and having curved distal ends; the plastic extruder screw tip further having a helically threaded screw root mounting cylinder fixedly attached to and extending rearwardly from the melt converging surface, the screw root mounting cylinder having annular outer “O” ring seals nestingly received within “O” ring receiving channels, the screw root mounting cylinder further having an interior oil return conduit.

Abstract: A screw for a double-screw extruder has its flight defining an outer cone and an inner cone of different convergencies with the inner cone converging more steeply than the outer cone from the feed end to the exit end of the extruder. Where A is the outer diameter at the feed end, B is the outer diameter at the exit end, C is the flight height at the feed end and D is the flight height at the exit end, the screw is defined by the relationship m.times.(A-B)/B=(C-D)/D where m is less than zero and greater than -0.75, the screw having a length L.gtoreq.15B.

Abstract: A double worm extruder has the ribs of its screws of trapezoidal cross section between divergent flanks to minimize wear of the housing surface.

Abstract: An embossing apparatus in an extrusion line for the production of sheet extrusions like vinyl siding, can include a revolver above the backing roll and supported in a pair of cradles so that selected embossing rolls can be juxtaposed with the backing roll and can define the embossing gap therewith. The revolver is indexed in position by pneumatically-operated locking members on the cradles. The revolver allows embossing roll change on the fly, if desired.

Abstract: A triple-wall foam coextrusion apparatus in which inner and outer layers of one synthetic resin material are coextruded with an intermediate layer of another synthetic resin material, and wherein the passages for the first material are inclined to the axis along which the second material is extruded around a spider to ensure uniform flow.

Abstract: A triple-wall foam coextrusion apparatus in which inner and outer layers of one synthetic resin material are coextruded with an intermediate layer of another synthetic resin material, and wherein the passages for the first material are inclined to the axis along which the second material is extruded around a spider to ensure uniform flow.