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A mill is a device that breaks solid materials into smaller pieces by grinding, crushing, or cutting. Such comminution is an important unit operation in many processes. There are many different types of mills and many types of materials processed in them. Historically mills were powered by hand (e.g., via a hand crank), working animal (e.g., horse mill), wind (windmill) or water (watermill). Today they are usually powered by electricity. The grinding of solid matters occurs under exposure of mechanical forces that trench the structure by overcoming of the interior bonding forces. After the grinding the state of the solid is changed: the grain size, the grain size disposition and the grain shape. Milling also refers to the process of breaking down, separating, sizing, or classifying aggregate material. For instance rock crushing or grinding to produce uniform aggregate size for construction purposes, or separation of rock, soil or aggregate material for the purposes of structural fill or land reclamation activities. Aggregate milling processes are also used to remove or separate contamination or moisture from aggregate or soil and to produce "dry fills" prior to transport or structural filling. Grinding may serve the following purposes in engineering: *increase of the surface area of a solid *manufacturing of a solid with a desired grain size *pulping of resources ==Grinding laws== In spite of a great number of studies in the field of fracture schemes there is no formula known which connects the technical grinding work with grinding results. To calculate the needed grinding work against the grain size changing three half-empirical models are used. These can be related to the Hukki relationship between particle size and the energy required to break the particles. In stirred mills, the Hukki relationship does not apply and instead, experimentation has to be performed to determine any relationship. *Kick for ''d'' > 50 mm : *Bond〔(Mineral Beneficiation – The Third Theory of Comminution – Document Summary ). Onemine.org. Retrieved on 2010-10-09.〕 for 50 mm > ''d'' > 0.05 mm : *Von Rittinger for ''d'' < 0.05 mm : with ''W'' as grinding work in kJ/kg, ''c'' as grinding coefficient, ''d''A as grain size of the source material and ''d''E as grain size of the ground material. A reliable value for the grain sizes ''d''A and ''d''E is ''d''80. This value signifies that 80% (mass) of the solid matter has a smaller grain size. The Bond's grinding coefficient for different materials can be found in various literature. To calculate the KICK's and Rittinger's coefficients following formulas can be used with the limits of Bond's range: upper ''d''BU = 50 mm and lower ''d''BL = 0.05 mm. To evaluate the grinding results the grain size disposition of the source material (1) and of the ground material (2) is needed. Grinding degree is the ratio of the sizes from the grain disposition. There are several definitions for this characteristic value: *Grinding degree referring to grain size ''d''80 : :Instead of the value of ''d''80 also ''d''50 or other grain diameter can be used. *Grinding degree referring to specific surface : :The specific surface area referring to volume ''S''v and the specific surface area referring to mass ''S''m can be found out through experiments. *Pretended grinding degree : :The discharge die gap a of the grinding machine is used for the ground solid matter in this formula. File:Simple Grinding Forces.png 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Mill (grinding)」の詳細全文を読む スポンサード リンク
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