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without producing any appreciable velocity differences, so that almost no mixing oc-curs. By installing a stationary baffle, some mixing capability is added. This works well on materials with viscosities from 5000-25,000 centipoise. For the best results, with products between 100,000 and 250,000 centipoise, a counterrotating set of crossbars provides excellent blending. Such equipment is illustrated in Fig. 15. Some designs use the same motor, turning a pinion gear between two opposing bevel gears to provide rotation in opposite directions. Others provide a greater degree of flexibility by driving the two shafts on separate motors. In either case, there will be a hollow shaft driving the anchor agitator and an additional shaft located inside the hollow shaft to drive the inner crossbars [21]. B. High-Speed Dispersers A simple yet powerful device used extensively in industries other than pharmaceutical manufacturing for dispersion of solid particles in liquids is the high-speed disperser. Sometimes called a saw-blade disperser for the shape of the mixing impeller, this ma-chine consists of a variable-speed shaft connected to an impeller with a serrated edge. The mixer is designed to rotate at a high speed in order to produce shear and pumping (Fig. 16). This type of equipment is designed specifically to disperse powders, usually pig-ments, into liquids. Much has been written that high-speed dispersers are capable only of dispersing "easy" pigments [23]. This is true if the particles are hard agglomerates or individual hard particles with some strength. Furthermore, the high-speed disperser design is ineffective if the viscosity is low. The only shear stress that is delivered to Darticles is due to the hydraulic shear that is a product of the shear rate and the viscos-Fig. 15 Counterrotating agitator. (From Ref. 21.)
DOI link for without producing any appreciable velocity differences, so that almost no mixing oc-curs. By installing a stationary baffle, some mixing capability is added. This works well on materials with viscosities from 5000-25,000 centipoise. For the best results, with products between 100,000 and 250,000 centipoise, a counterrotating set of crossbars provides excellent blending. Such equipment is illustrated in Fig. 15. Some designs use the same motor, turning a pinion gear between two opposing bevel gears to provide rotation in opposite directions. Others provide a greater degree of flexibility by driving the two shafts on separate motors. In either case, there will be a hollow shaft driving the anchor agitator and an additional shaft located inside the hollow shaft to drive the inner crossbars [21]. B. High-Speed Dispersers A simple yet powerful device used extensively in industries other than pharmaceutical manufacturing for dispersion of solid particles in liquids is the high-speed disperser. Sometimes called a saw-blade disperser for the shape of the mixing impeller, this ma-chine consists of a variable-speed shaft connected to an impeller with a serrated edge. The mixer is designed to rotate at a high speed in order to produce shear and pumping (Fig. 16). This type of equipment is designed specifically to disperse powders, usually pig-ments, into liquids. Much has been written that high-speed dispersers are capable only of dispersing "easy" pigments [23]. This is true if the particles are hard agglomerates or individual hard particles with some strength. Furthermore, the high-speed disperser design is ineffective if the viscosity is low. The only shear stress that is delivered to Darticles is due to the hydraulic shear that is a product of the shear rate and the viscos-Fig. 15 Counterrotating agitator. (From Ref. 21.)
without producing any appreciable velocity differences, so that almost no mixing oc-curs. By installing a stationary baffle, some mixing capability is added. This works well on materials with viscosities from 5000-25,000 centipoise. For the best results, with products between 100,000 and 250,000 centipoise, a counterrotating set of crossbars provides excellent blending. Such equipment is illustrated in Fig. 15. Some designs use the same motor, turning a pinion gear between two opposing bevel gears to provide rotation in opposite directions. Others provide a greater degree of flexibility by driving the two shafts on separate motors. In either case, there will be a hollow shaft driving the anchor agitator and an additional shaft located inside the hollow shaft to drive the inner crossbars [21]. B. High-Speed Dispersers A simple yet powerful device used extensively in industries other than pharmaceutical manufacturing for dispersion of solid particles in liquids is the high-speed disperser. Sometimes called a saw-blade disperser for the shape of the mixing impeller, this ma-chine consists of a variable-speed shaft connected to an impeller with a serrated edge. The mixer is designed to rotate at a high speed in order to produce shear and pumping (Fig. 16). This type of equipment is designed specifically to disperse powders, usually pig-ments, into liquids. Much has been written that high-speed dispersers are capable only of dispersing "easy" pigments [23]. This is true if the particles are hard agglomerates or individual hard particles with some strength. Furthermore, the high-speed disperser design is ineffective if the viscosity is low. The only shear stress that is delivered to Darticles is due to the hydraulic shear that is a product of the shear rate and the viscos-Fig. 15 Counterrotating agitator. (From Ref. 21.)
ABSTRACT
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