Milling equipment commonly used

The generally accepted definition of micronization is the size reduction of particles down to 1-30 m in diameter. Although it is possible to use some of the previously discussed equipment to reduce the particle size distribution of a product down to this range they are not ideally suited to the application as the distribution curve can be fairly wide spread and possibly even bimodal where as a tight PSD and single node curve is the goal of most manufacturers (Fig. 21). The equipment commonly used are pin mills, hammermills, fine grind, and jet mills. 

For fine dispersion of curatives and colorants a paint mill is commonly used. This equipment consists of 3 rolls turning at slightly different surface speeds relative to each other. The adjustable nip between the rollers allows dispersion with exceptional fineness of grind. 

FIGURE 7.7 Equipment commonly used in rice-milling operations, (a) Schema of rubber roll dehuller (courtesy of American Association of Cereal Chemists), (b) Schema of abrasive disc dehuller (courtesy of American Association of Cereal Chemists). 

FIGURE 7.9 (Continued) Equipment commonly used in wheat-milling operations. (b2) photograph (courtesy of Buhler AG, Switzerland) of roller mills, (c) Plansifter (courtesy of Buhler AG, Switzerland). 

FIGURE 7.7 Equipment commonly used in rice-milling operations.198... 

FIGURE 7.9 Equipment commonly used in wheat-milling operations.204... 

FIGURE 7.11 Equipment commonly used in oat milling operations.214... 

FIGURE 8.2 Equipment commonly used in wet-milling operations.228... 

The selection guides given by Lowrison (1974) and Marshall (1974), which are reproduced in Tables 10.12 (see p. 465) and 10.13, can be used to make a preliminary selection based on particle size and material hardness. Descriptions of most of the equipment listed in these tables are given in Volume 2, Chapter 2 or can be found in the literature Perry et al. (1997), Hioms (1970), Lowrison (1974). The most commonly used equipment for coarse size reduction are jaw crushers and rotary crushers and for grinding, ball mills or their variants pebble, roll and tube mills. 

Water rinses are used in surface preparation operations such as acid pickling, alkaline cleaning, and nickel deposition to remove any process solution film left from the previous bath. A water rinse may also follow the neutralization step. Another common water use is in the ball milling process, which uses water as the vehicle for the enamel ingredients, as a cooling medium, and for cleaning the equipment. Coating application processes normally use wet spray booths to capture oversprayed enamel particles. Water wash spray booths use a water curtain into which the enamel particles are blown and captured. 

The commercial importance of this metal was first recognized in 1950s when its high strength/density ratios were found attractive in aerospace applications. The corrosion resistance in a variety of conditions led to its use in wet chlorine gas coolers for chlor-alkali cells, chlorine and chlorine dioxide bleaching equipment in pulp/paper mills, and reactor interiors for pressure acid leaching of metallic ores. The metal and its alloys were used in seawater power plant condensers, with over 400 million feet installed in application.65,66 The most commonly used alloys and their composition are given in Table 4.48. 

Wood grinders arc used to shred large pieces of wood (e.g., yard wastes, construction debris, palettes) into chips. Tub grinders are the most commonly used equipment, but horizontal flail mills can be used as well. 

Forces commonly used in food processes for particle size reduction are compressive, impact, attrition (or shear), and cutting forces. More than one force usually participates in the comminution operation in industrial size-reduction equipment. In particular, crushing rolls use mainly compressive forces, hammer mills are based on impact, disc mills cause particle attrition through shear force application, and rotary knife cutters use cutting forces. 

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