Milling attrition mills

The general pieces of equipment used in grinding flake mica or mica concentrate into saleable mica products are hammer mills of various types, fluid energy mills, Chaser or Muller mills for wet grinding, and Raymond or WiUiams high side roUer mills. Another method is being developed, called a Duncan mill (f. M. Huber, Inc.), that is similar in many respects to an attrition mill. AH of these mills are used in conjunction with sieves, and all but some types of hammer mills incorporate air classifiers as a part of the circuit. 

The second class of grinding equipment is used to prepare dispersions. Typical of this class are baU and pebble mills, ultrasonic mills, and attrition mills. SoHds, eg, sulfur, antioxidants, accelerators, and zinc oxide, are generaUy ground on this equipment (see Size reduction). BaU mill action is assisted in some mills by a combination of dispersion circulation by an external pump and mechanical osciUation of an otherwise fixed nonrotary mill chamber. Where baU mill chambers are rotated it is necessary to experimentally estabHsh an optimum speed of rotation, the size and weight of the baU charge, and ensure the mills do not overheat during the grinding period. 

With hafQes Horizontal drum Double cone revolving around long axis Twin shell Ciihe Twin rotor Tiirhine Paddle mixer Sifter (tiirhosifter) Attrition mill Elevator loading Pneumatic conveying Vibrating... 

In the second type of mill (Fig. 20-28), a cyhndrical grating is provided beneath the rotor for product discharge. Some hammer crushers are symmetrically designed so that the direction of rotation can be reversed to distribute wear evenly on the hammer and breaker plates. When such a Pennsylvania nonreversible hammermill is used for reduction, material is broken first by impacl against hammers and then by rubbing action (attrition) against screen bars. Performance data of Pennsylvania reversible hammer mills are shown in Table 20-14. 

Turbo pulverizers and turbo mills (Pallmann Pulveiizer Co.) combine tne action of hammer and attrition mills, finding special apphcation for grinding plastic materials that would be softened under high-energy warm-mill conditions. 

Ring-roller mills should be distinguished from roller mills. Paint roll mills are described under Disk Attrition Mills, and flour roll mills under Cereals and Other Vegetable Products. ... 

FIG. 20-51 Double-runner attrition mill. And ritz-Sprout-Baner Inc. )... 

Soybeans, Soybean Cake, and Other Pressed Cakes After granulation on rolls the granules are generally treated in presses or solvent extracted to remove the oil. The product from the presses goes to attrition mills or flour rolls and then to bolters, depending upon whether the finished product is to be a feed meal or a flour. 

The method used for grinding pressed cakes depends upon the nature of the cake, its purity, residual oil, and moisture content. If the whole cake is to be pulverized without removal of fibrous particles, it may be ground in a hammer mill with or without air classification. A 15-kW (20-hp) hammer mill with an air classifier, grinding pressed cake, had a capacity of 136 kg/h (300 Ib/h), 90 percent through No. 200 sieve a 15-kW (20-lm) screen-hammer mill grinding to 0.16-cm (Vi6-in) screen producea 453 kg/h (1000 Ib/h). In many cases the hammer mill is used merely as a preliminaiy disintegrator, followed by an attrition mill. Typical performance of the attrition mill is given in Table 20-25. A finer product may be obtained in a hammer mill in closed circuit with an external screen or classifier. 

Most gums and resins, natural or artificial, when used in the paint, varnish, or plastic industries, are not ground veiy fine, and hammer or cage mills will produce a suitable product. Typical performance of the di attrition mill is given in Table 20-25. Roll crusners will often give a sufficiently fine product. 

The following materials may be ground at ordinary temperatures if only the regular commerci fineness is required amber, arabac, tragacanth, rosin, olibanum, gum benzoin, myrrh, guaiacum, and montau wax. If a finer product is required, hammer mills or attrition mills in closed circuit, with screens or air classifiers, are used. 

The white cast irons and their low alloys have good abrasion resistance properties [2,3]. White cast irons are used for grinding balls, segments for mill liners and slurry pumps. In the ceramic industry they are used for muller tyres and augers in the pulp and paper industry for attrition mill plates and chip feeders and in the paint industry for balls for grinding pigments. 

Attrition mills (for grain processing)—starting unloaded 100 60 175 3-15... 

Leuco dye and coreactant are individually milled in an aqueous solution of binder such as poly(vinyl alcohol) or hydroxyethylcellulose by means of an attrition or sand mill until the particle size of the solid materials is about 1 pm or less in diameter. Smaller particles provide superior performance. 

Despite the little experimental data, there are two models available in the literature. Adams etal. (1992) considered dense phase conveying. They tried to predict the amount of attrition as a function of conveying distance by coupling a Monte Carlo simulation of the pneumatic conveying process with data from single-particle abrasion tests. Salman et al. (1992) focused on dilute phase conveying. They coupled a theoretical model that predicts the particle trajectory with single particle impact tests (cf. Mills, 1992). 

Organic pigments can be dispersed readily in plasticizers, for example with the aid of triple-roll mills. However, the throughput here is low because of the lack of smoothness of such pastes compared to other systems such as letterpress or offset inks, which is why attrition mills are better. 

---