Mill, hammer-type

Rietz Mill - A type of hammer mill supplied by Bepex Corp., Santa Rosa, CA. See also Hammer Mill. 

Crusher A machine for crushing rock or other materials—among the various types of crushers are the ball mill, gyratory crusher. Handsel mill, hammer mill, jaw crusher, rod mill, rolls, stamp mill, and tube mill. 

The grinding/powder mills may be of a hammer type, or consist of a classifier and rotating rotor fitted with pins or bars. The classifier may be separate or an integral part of the mill itself. 

Tornado Mill - A type of hammer mill supplied by... 

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. 

Mech nic l Impact Mills. The mechanical types include cmshers, hammer mills, pin disk mills, turbine mills, and mills with air classifiers. Impact Crusher. Feed material is introduced through a feed opening onto a rotor moving at between 25 and 50 m/s (Fig. 11). The initial impact by the rotor causes some size reduction, and the material is accelerated up to the speed of the rotor and flung against the impact plates, where further size reduction occurs. It is possible to wear-protect these units quite well, so that abrasive materials can be handled. The final end particle size can be varied by the inclusion of an outlet grid to vary the residence time in the machine. 

HammerMills. One of the most versatile, economical, and widely used impact mills is the hammer mill (Fig. 12). Many variations are produced, with special types available for specialized appHcations, eg, quick screen change for animal feed, heavy duty for minerals, and light constmctions for woodchip. The principle employed is similar to that of the impact cmsher however, the rotation speed can vary from 20 up to 100 m/s with high speed fine-grinding versions. The oudet screen is used to vary the residence time, which in turn affects final particle size. The size of the end product is an order of magnitude finer than the size of the perforations in the outlet screen. 

Manufacturers of various types of mills maintain laboratories in which grindability tests are made to determine the suitability of their machines. When grindability comparisons are made on sm equipment of the manufacturers own class, there is a basis for scale-up to commercial equipment. This is better than relying on a grindabihty index obtained in a ball mih to estimate the size and capacity of different types such as hammer or jet mihs. 

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. 

Pin MiUs In contrast to peripheral hammers of the rigid or swing types, there is a class of high-speed mills having pin breakers in the grinding circuit. These may oe on a rotor with stator pins between circular rows of pins on the rotor disk, or they may be on rotors operating in opposite directions, thereby securing an increased differential of speed. See also the Mikro-ACM pulverizer described later. 

Colloid mills which are employed for dispersion or for emulsification fall into four main groups the hammer or turbine, the smooth-surface disk, the rough-surface type, and valve or orifice devices. 

Inorganic salts often do not require fine pulverizing, but they frequently oecome lumpy. In such cases, they are passed mrough a double-cage mill or some type of hammer miU. 

If the rock is abrasive, the first stage of crushing may use gyratory or jaw crushers, otherwise a rotor-impact mill. Their reduction ratio is only 1 12 to 1 18, so they often must be followed by a hammer mill, or they can feed a roll press. Rotor crushers have become the dominant primaiy crusher for cement plants because of the characteristics. All of these types of crushers may be installed in moveable crusher plants. 

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