Abstract: An apparatus for the laboratory testing of plastic compositions as to their extrudability comprises a housing with two mutually parallel, intersecting cylindrical bores occupied by two counterrotating plasticizing screws each having two sections with threads of mutually opposite pitch separated by a gap. The gaps of the two screws are relatively offset to define a recirculation zone in which a plastic mass to be tested, fed in axially by intermeshing thread sections of these screws, is transported in one axial direction by an extension of a thread section of one screw and in the opposite axial direction by an overlapping extension of a thread section of the other screw. In the recirculation zone, in which the turns of the overlapping thread-section extensions have the same pitch, clashing is avoided by reducing the sum of the radii of these turns to less than the spacing of their axes or providing the turns with discontinuities enabling them to pass by one another.

Abstract: A double-worm press, especially an extrusion or plastifying press for thermoplastic materials and particularly high viscosity thermoplastics, has generally conical worms, at least the discharge zones of which are formed so that the material is treated generally adiabatically therein. For this purpose, the end of the discharge zone has a depth of the worm flight which is between 24 and 33% of the worm diameter, preferably between 26 and 30%, with the ratio of the depth of the flight (or height) to the diameter of the worm increasing progressively away from the discharge end, counter to the direction of feed of the material.

Abstract: An extruder for thermoplastic or elastomeric materials has a mastication stage with one or more feedscrews preceded by a preheating zone in which the incoming bulk material is circulated and possibly recirculated by two screw-type conveyor members or augers in a loop within a heated extension of the extruder housing. The augers may be counterrotatingly disposed in two juxtaposed cylindrical compartments or may be coaxially nested and corotating with opposite pitch.

Abstract: A scraper flight conveyor for preheating thermoplastic bulk material and feeding it to a screw extruder comprises a succession of controllably heated slideways arranged in superposed series, a plurality of scraper flights in sliding contact with each slideway and spaced along a path of travel over the surface thereof, and a drive operable to move the scraper flights on each slideway along the path of travel. The scraper flights push discrete portions of the thermoplastic bulk material along the path of travel. The delivery rate of the material to the slideways is controlled.

Abstract: An extruder has a housing in which is rotatable a pair of axially tapered screws of like construction but opposite hand. The thread of each screw meshes with that of the other screw so that the screws' major diameters overlap by a distance that forms a constant ratio with the major diameter along the entire length of the screws.

Abstract: A transmission for a multiscrew extruder comprises a central spur gear meshing with several peripheral spur gears disposed symmetrically therearound, each gear having herringbone teeth with an annular gorge separating its sections of opposite pitch. The central gear is axially immovably journaled at its ends in two roller bearings, which may also be combined with thrust bearings, mounted in opposite walls of a housing. The peripheral gears are each journaled with axial play in terminal roller bearings and in an intermediate roller bearing, the latter having individual inner and outer races large enough to slip over the toothed sections of these gears. The intermediate bearings are supported by split bushings in the gorges of the peripheral gears and are embraced, over a major fraction of their circumferences, by an annular housing partition surrounding the central gear; the free minor circumferential portions of these bearings extend into the gorge of the central gear.