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Screw right-handed elements

Three-flight conveying screw elements Left-handed kneading element Right-handed kneading element... [Pg.524]

Polyesters, polyetherimide, melamine-formaldehyde, polyurethanes, polyurethane-ureas and polyamides (nylons) are examples of condensation polymers prepared by REX. " Because a small molecule is produced in condensation reactions, vent ports are employed. Between the ports are melt sealing screw sections, to prevent back mixing of volatilizing melt. Sealing screw sections are constructed by a right handed-left handed sequence of screw elements. Another chemistry feature of step-growth reactions is their sensitivity to errors in stoichiometric feed proportions. This poses problems with solid feed materials, which are normally converted to liquid form for more... [Pg.2532]

In addition, the combination of three-dimensional symmetry elements gives rise to a completely new symmetry operator, the screw axis. Screw axes are rototranslational symmetry elements, constituted by a combination of rotation and translation. A screw axis of order n operates on an object by (a) a rotation of 2n/n counter clockwise and then a translation by a vector t parallel to the axis, in a positive direction. The value of n is the order of the screw axis. For example, a screw axis running parallel to the c-axis in an orthorhombic crystal would entail a counter-clockwise rotation in the a - b plane, (001), followed by a translation parallel to +c. This is a right-handed screw rotation. Now if the rotation component of the operator is applied n times, the total rotation is... [Pg.93]

Figure /. Screw designs used in extrusion (right hand side is exit from barrel). Design A has positive kneader elements design B has reverse screw elements. Figure /. Screw designs used in extrusion (right hand side is exit from barrel). Design A has positive kneader elements design B has reverse screw elements.
Left-handed kneading elements Right-handed kneading elements Melt homogenizing screw elements... [Pg.216]

Right-handed or neutral elements Left-handed elements Screw elements... [Pg.33]

Screw rotation. The symmetry element is a screw axis. It can only occur if there is translational symmetry in the direction of the axis. The screw rotation results when a rotation of 360/1V degrees is coupled with a displacement parallel to the axis. The Hermann-Mauguin symbol is NM ( N sub M )-,N expresses the rotational component and the fraction M/N is the displacement component as a fraction of the translation vector. Some screw axes are right or left-handed. Screw axes that can occur in crystals are shown in Fig. 3.4. Single polymer molecules can also have non-crystallographic screw axes, e.g. 103 in polymeric sulfur. [Pg.15]

Twin-screw extruder Flow of Newtonian fluids in kneading disc elements and (right and left handed) screw elements. Szydlowski et al., 1987... [Pg.598]

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See also in sourсe #XX -- [ Pg.285 ]



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