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Over 40 specimens of mixers of various designs were presented at the exhibit. These machines were fabri-
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cated by MKF [VEB Maschinenbau - Kombinat Freital] Weast (East Germany), Drais, Werner-Pfleiderer, Henschel,
Ehrwecka, Vibau (West Germany), Anger (Austria), Covema, Comerio (Italy), Bonnet-Calade (France), Buss, Bachof-
fen (Switzerland), Smurmans en Vanginneken (Netherlands), Niipon (Japan). The models exhibited can be differen-
tiated by design features into gate mixers, anchor mixers, propeller mixers, turbine mixers, disk mixers, conveyer-
blade mixers, ribbon mixers, mixers with shaped arms (sigma or Z blades), roll mixers, and screw mixers. Well
known designs met competition from mixers of types which have only recently come into use in industry; the latter
include in particular the mixers deve!oped for processing polyvinyl chloride polymer compositions.
Drais exhibited the Helimat laboratory model mixer (Fig. 1) designed for mixing and plastication processes
in the treatment of suspension and emulsion type polyvinyl chloride compositions. These machines are to replace
rollers and Banbury mixers based on the internal mixing principle. In internal mixing, there are shear stresses re-
sulting in wear on the material and heating of the material as layers of process material moving at different speeds
come into direct contact.7843
The Helimat mixer has a cylindrical split chamber enclosing a horizontal side-entering shaft with four pairs
of plane paddies set at an angle to the rotation axis. The process polymer mass is forced to the wails of the mixing
chamber by centrifugal force generated by the high rotation speed of the shaft (1500 to 3000 rpm) and is worked by
blades at the walls; this leaves a space free of process material at the center of the mixing chamber. The place-
ment of blades around the shaft brings about circulation of the process material, so that an external mixing effect is
achieved, i.e., constant renewal of the surface of the process mass. The heat liberated by transformation of the
mechanicai energy is used in plasticizing the polymer.
The mixer can be loaded with slightly moistened or pasty mass; premixing of the components is not man-
datory. As soon as a certain temperature in the chamber indicating the process of kneading has been completed is