Mixer Muller

Uniform sand mixes can be prepared by adding the binder to the sand in conventional foundry mixer, muller, or mix-mixers, or laboratory or kitchen mixers, and mixing for sufficient time to obtain a good admixture of the sand and binder, e.g., for several minutes. When added separately, it is desirable to mix each component for less than 2 min to avoid undue drying. 

The muller is useful for mixing problems requiring certain types of aggregate breakdown, fricdional anchorage of particles to one another, and densification of the final mix. Materials which are excessively fluid or sticky should be avoided. The muller mixer is generally used for batch operations (Fig. 19-9g), although Fig. 19-9/j shows a continuous muller. 

Muller W, Rumpf H. Mixing of powders in mixers with axial motion (in German). Chem Ing Tech 1967 39 365-373. 

Figure 10.15. Some mixers and blenders for powders and pastes, (a) Ribbon blender for powders, (b) Flow pattern in a double cone blender rotating on a horizontal axis, (c) Twin shell (Vee-type) agglomerate breaking and liquid injection are shown on the broken line, (d) Twin rotor available with jacket and hollow screws for heat transfer, (e) Batch muller. (f) Twin mullers operated continuously, (g) Double-arm mixer and kneader (Baker-Perkins Inc.), (h) Some types of blades for the double-arm kneader (Baker—Perkins Irtc.).

In muller mixers the rotation of the circular pan or of the plows brings the material progressively into the path of the mullets, where the intensive action takes place. Figure 18-46 shows one type of mixer, in which the mullets and plows revolve around a stationary turret in a stationary pan. The outside plow moves material from the crib wall to the path of the following muller the inside plow moves it from the central turret to the path of the other muller. The mullets crush the material, breaking down lumps and aggregates. 

Vacuum or Pressure Most tumbling mixers can have provision for vacuum or pressure. Mixers which cannot be adapted to these conditions are mullers with rotating pans. Continuous mixers introduce problems of sealing the charge and discharge ends. 

Pan mullers are the modern industrial equivalent of the traditional mortar and pestle. Typical mullers have two broad wheels (Ml and M2) on an axle (Fig. 18-54). The mixer rotates about the approximate midpoint of the axle, so that the wheels both rotate and skid over the bottom of the mixing chamber (A). Plow blades (PI and P2), which rotate with the mixer, push material from the center (T) and walls (C) of the mixing chamber into the path of the rollers. The mixing action combines both crushing and shearing to break lumps or agglomerates and evenly distribute moisture. 

Mullers can be used if the paste is not too fluid or sticky. The main application of muller mixers is now in the foundry industry to mix small amounts of moisture and binder with sand for both core and molding sand. Muller mixers also handle such diverse materials as... 

FIG. 21-49 Classification of bunker or silo mixers following Muller [W. Muller, Methoden und derzeitiger Kenntnisstand fur Auslegungen beim Mischen von Feststoffen [Methods and the current state of the art in solids mixing configurations], Chem. Eng., 53. 831-844 (1981)]. 

Fig. 5 Mix muller-type mixer. (Courtesy of Sud-Chemie Inc.) (View this art in color at www.dekker.com.)...

Figure 139(g) and (h) depicts muller mixers (B.l). The batch machine, less muller rollers, is essentially identical with the mixer described in the early patent of Eirich. 5 While this modified equipment (B.3) is still used extensively for agglomeration (Figure 138), the continuous type (Figure 139(h)) is only... 

Table VIII, which is a combination of two of Smith s tables, shows the necessity for choosing the proper mixer for the particular soil to be mixed for example, although the two-arm kneader and muller mixed very well with sand, they did not do well with the Marshall clay. The reciprocating conveyor, however, while it did not mix sand too well, did the best job on Marshall clay.

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