Beater mill

Depending on the design of the impactor, these mills can be divided into subclasses such as pinned disc mills, baffle plate mills, beater mills, hammer mills or swing hammer mills. 

Beater mills, hammer mills, baffle plate mills, pin mills and universal mills consist of a horizontal shaft with a rotor and, optionally, an impact surface (Fig. 14.12). Impact bar mills and impact hammer mills with vertical shafts are also used. 

Herbage. Herbage samples must be milled to pass a 1 mm aperture before analysis. This can be achieved by means of a beater mill with a carbon steel construction (as produced by Christie and Norris Ltd., Broomfield Road, Chelmsford, Essex, U.K.). This device introduces no detectable concentration of foreign metals into the sample. A small hammer mill is also satisfactory, but may contaminate the sample slightly with traces of nickel and chromium. 

Coarse grinding of the raw materials with crushers, pan grinders, hammer mills or cross beater mills is often carried out by the raw material suppliers. Thus in ceramic manufacture only fine grinding is required, for which wet grinding in ball mills, in which greater communition effects are realized than in dry mills, is satisfactory. 

Rotor beater mill Precrushing to fine grinding Up to 300 kg/h Soft to medium hard materials Down to < 100 pm... 

Pulverised limestone may be produced economically in impact crushers, such as hammer and beater mills. For use in agriculture, the product should be at least 95 % less than 3.35 mm and substantially less than 600 pm (see chapter 10). 

The coarser products may be produced relatively cheaply in a single pass through a beater mill fitted with an integral basket, which acts as a screen. Finer products are generally produced in tube mills and vertical roller mills [17.2]. In the latter case, a variable speed classifier is fitted above the mill to control the grading of the product, and recycle over-sized particles. 

FIGU RE 51.19 Mill-shaft dryer (beater mill including separators). 

Kek Mill. Trade-name (1) A pin-disk mill depending for its action on highspeed centrifugal force (2) a beater mill in which a four-armed beater revolves horizontally at high speed between upper and lower serrated disks. (Kek Ltd., Manchester, England.)... 

Acids and alkaUes were used to decompose the fiber to cellulose. The alkaU digester process, developed in 1899, is stiU used. Fiber glass reinforcement must be removed mechanically before the mbber can be reclaimed. A highly efficient method involves hammer mills and reel beaters to separate the fiber from the mbber an air current subsequentiy drives off the fiber. 

Paper may be colored by dyeing the fibers in a water suspension by batch or continuous methods. The classic process is by batch dyeing in the beater, pulper, or stock chest. Continuous dyeing of the fibers in a water suspension is adaptive to modem paper machine processes with high production speeds in modem mills. Solutions of dyestuffs can be metered into the high density or low density pulp suspensions in continuous operation. 

The Lawrie Tea Processor (LTP) is used in Africa to macerate lightly withered leaf. A hammer mill, in which final particle size can be controlled by degree of wither and adjustment of the tungsten-carbide-tipped beaters, is essential. 

The Alpine universal mill with turbine beater and grinding track shown in Figure 2.12 is suitable for both brittle and tough materials. The high airflow from the turbine keeps the temperature rise to a minimum. 

Pulping (grinding) nitrocellulose in beaters and in mills respectively. 

Raczynski [9] replaced the beaters for pulping nitrocellulose by disk mills (Fig. 157). A nitrocellulose water suspension flows down from a tank (7) through... 

The introduction of the Raczynski mill revolutionized the pulping of nitrocellulose fibres. Their most important advantage is that they require only 25-30% of the power needed for beaters. The design of the Raczynski mill has since been improved by Wroclawski [11]. 

Attempts have also been made to replace the beaters by conical mills in which conical knives on the rotor mesh with fixed knives. Owing to its shape and to the inclination of the knives, the mill also acts as a pump, drawing the suspension of nitrocellulose from the tank and returning it to the same or to another tank. These mills have not been wider adopted in practice, since they have no material advantage over conventional beaters. 

After being pulped, the nitrocotton fibres are pumped into the poacher. If the consistency is insufficiently liquid then water is added to the slurry during pumping. The beaters or mills are emptied through a discharge pipe in the base. 

A diagram illustrating the layout of a beater or a mill with a poacher, the position of the mixer and the final purification unit, is outlined in Fig. 159. 

Between the beaters or mills and the boilers, an apparatus for separating long fibre nitrocellulose from the cut fibres is inserted. This is a tank carrying a vertical cylindrical screen drum, with apertures 0.4 mm dia. The drum rotates and the cut fibres pass through the sieve into the drum, whence the contents flows to the boilers. The uncut fibres are caught on the surface of the screen from which they are removed by means of a brass knife and recycled to the beaters. 

The hollow fibers still contain an acid solution within them. In order that this acid may be washed out, they are pulped or broken up into short lengths by means of apparatus like that which is used in the manufacture of paper. A Jordan mill cuts the fibers off rather sharply, leaving square ends, but a beater tears... 

A variation of the Bead Beater is the freezer mill, which uses small magnetic bars rather than beads to pulverize the sample. Cooling is provided by immersing the sample chambers in a liquid nitrogen bath. The freezer mill is intended for larger samples (>500 mg) but may be customized for smaller samples. Both the freezer mill and the Bead Beater require that the sample be placed in secondary containers, which may or may not be disposable. Disposable secondary containers offer the very attractive advantage of reduced time and effort for cleaning. 

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