Vertical mixers

Both horizontal and vertical mixers are used for biscuit doughs and both have their advantages and disadvantages. Vertical mixers usually have a removable bowl that can be wheeled across the shop floor to move dough. Spare bowls can be held ready to use. 

Arosolvan A-Methylpyrrolidone 308 Vertical mixer-settler column... 

Figure 11. 300-Gallon vertical mixer with bowl in lowered...

A general recommendation with vertical mixers is that about 15 min mixing time is adequate after the last ingredient has been added to the mixer. With horizontal and drum mixers the mixing time is shorter, about 5-10 min after addition of the last ingredient. 

Numerous equipment types can be used for agglomeration, including horizontal ribbon and vertical mixers, rotary drums, zig-zag mixers, and pan agglomerators. Horizontal ribbon mixers as shown in Fig. 36.41 are used primarily for dry mix formulating, where only limited agglomeration occurs. They are comprised of a U-shaped trough and a ribbon or paddle-type agitator. Liquids are sprayed onto the surface of the dry material and slowly dispersed into the mix. Mixer operations can be either batch or continuous. 

Vertical mixers have become more commonly used due to low space requirements and high efficiency of operations. The vertical mixer shown in Fig. 36.42 utilizes high speed agitation to intimately mix and uniformly blend liquids and dry raw materials prior to discharge. The contact time is reduced to less than five seconds. The rotary drum units generally contain baffles that roll or lift the product... 

Although most solid propellants are manufactured in a vertical mixer batch process, a continuous mixing process has been used successfully in the production of the first stage A-3 Polaris propellant and in the NASA 260 inch demonstration motor program. The use of a continuous mixing process, in which propellant chemicals are metered into a helical kneader, offers considerable benefit in terms of safety and cost for large-volume propellant production. 

High speed dispersion vertical mixers which are fitted with a variable speed drive and a toothed disc at the end of the vertical shaft. This type suits the lower viscosity plastisols used in wall and floor coverings. 

Mixer-granulators Continuous high-shear (e.g., Shugi mixer) Batch high-shear (e.g., vertical mixer) 0.1-0.5 0.1-2 Low Moderate to high Up to 50 tons/h Up to 500-kg batch Handles cohesive materials, both batch and continuous, as well as viscous binders and nonwettable powders Fluid-bed, tray, or vacuum/ microwave on-pot drying Chemicals, detergents, clays, carbon black Pharmaceuticals, ceramics, clays... 

Figure 86. Methods used for spherical agglomeration in suspensions , (a) Container with stirrer, (b) container with liquid circulation, (c) inclined disc, (d) horizontal drum, (e) colloid mill , (f) shaking container, (g) vertical mixer, (h) continuous mixer...

Auger shaft vertical, mixer shaft horizontal. 

FIGURE 32.19 Osmotic dehydrator—a vertical mixer. (1) worm screw (2) vessel (3) shaft (4) spout. (Adapted from Marouze, A. et ah, Food Eng., 49, 207, 2001. With permission.)... 

For a simple vertical mixer design, the key dimensions are the impeller diameter D, which is usually equal to the bowl diameter, the chopper diameter Dc, and the fill height H. The dimensionless groups that need to be held constant for geometric similarity are... 

In vertical mixers, the rotor is installed in a 90° angle to the bottom of the vessel and for horizontal mixers the rotor is parallel to the ground. The cylindrical vessel form is used for horizontal mixers. In case of vertical mixers, it can have a conical or a cylindrical form. 

Vertical mixers are very frequently used for laboratory purposes, because they are somehow easier to operate and require less space. For the manufacturing of bigger volumes, the choice of the mixer type depends on items like how are the raw materials likely to be charged, the final product likely to be discharged, and it depends on the available floor space. O Figure 37.3a... 

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