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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. The instrument continuously records pressure and temperature at the gaps as well as the torque applied to the screws by their drive.

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First Claim