High speed fluid mixers

High Speed Fluid Mixers The agitation is accomplished by a rotor at the base of the mixing chamber, rota g at a speed up to few thousand... 

Various types of equipment are used commercially to manufacture dispersed pigment concentrates or finished dispersion products used by printing ink, and die coatings and plastics industry. These include kneaders or internal mixers close tolerance mills high speed fluid energy mills ball and pebble mills san, bead, and shot mills. 

Most plastics e.g. polyolefins and polystyrenes and their derivatives such as ABS (acrylonitrile-butadiene-styrene) and SAN (styrene-acrylonitrile) are supplied by the manufacturers in ready-to-use form with most of the above-mentioned stabilizers or simply need to be additionally stabilized with other additives, e.g. antistatic agents and HALS stabilizers, as required. On the other hand, in the case of other materials (e.g. PVC) it is the end user who adds the additives, pigments or preparations. This is normally done on fluid or high-speed mixers, although in the past gravity mixers or tumble mixers were also used. The mixture is then homogenized on mixing rolls, kneaders, planetary extruders or twin-screw kneaders and further processed. 

With the Flexomix, dry powders are fed into the mixer where the paddles mix the powder with liquid that is introduced close to the paddles, which turn at high speeds. The wet mass which exits the mixer is dried in a fluid bed system. The product from this system is an open structure granulate which exhibits instant behavior upon dissolution. 

Conical mixers are also known as Nauta mixers (Fig. 18-53). Material placed in the conical bin is lifted by the rotation of the helical screw, which in turn is rotated around the wall of the cone. The lifting actions of the screw combined with motion around the cone provide bulk mixing for flowable dry powders, paste materials, and even viscous fluids. The specific energy input is relatively small, and the large volume of the mixers can even provide storage capacity The mixers may have multiple screws, tapered screws, and high-speed dispersers for different applications. At constant speed, both the mixing time and power scale up with the square root of volume. Sizes from 0.1 to 20 m3 (3.3 to 700 ft3) are available. 

For mixing operations which require the continuous production of finely dispersed solids, emulsions, stable foams, etc., the in-line dynamic mixer in one of its several forms could be used. These usually consist of a rotor which spins at high speed inside a casing and the feed materials are pumped continuously to the unit. Inside the casing the fluid is subjected to extremely high shear forces which are required for the dispersing operation, see Figure 7.10. 

The literature is small on rotor-stator devices, as discussed in Chapter 8. [They are also discussed in Chapter 12, since this is the process result (liquid-liquid and solid-liquid) that these devices are most used for.] It should be mentioned that because of their very high speed they can produce turbulent motion in some rather high viscosity fluids. Also see Cohen (1998), Dietsche (1998), and Myers et al. (1999) for general information about the industrial application of rotor-stator mixers versus other mixing options. 

Recent developments and adaptations of high-speed seal technology have brought gas barrier seals into mixer applications. With a gas such as nitrogen as the barrier fluid, process contamination is virtnally eliminated, and a pressure monitor can be used to detect leaks. The problem is that gas is a poor lubricant for the seal surfaces. However, by machining swirls or pockets in the inside surface of the seal faces, gas pressure can be raised locally to lift the seal surfaces apart. 

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