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Reference.org
Mill (grinding)
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<p>A mill is a device, often a <a href="/facts/Structure/xQDPtqDQ">structure</a>, <a href="/facts/Machine/wTCxFRfs">machine</a> or <a href="/facts/Home_appliance/JYKalzw6">kitchen appliance</a>, that breaks <a href="/facts/Solid/hj5UsXno">solid</a> materials into smaller pieces by grinding, crushing, or cutting. Such <a href="/facts/Comminution/P9nhjTW6">comminution</a> is an important <a href="/facts/Unit_operation/7TAe9XH0">unit operation</a> in many <a href="/facts/Process_(engineering)/ntHyBWHg">processes</a>. There are many different types of mills and many types of materials processed in them. Historically, mills were powered by hand or by animals (e.g., via a <a href="/facts/Crank_(mechanism)/1a3bCxyE">hand crank</a>), <a href="/facts/Working_animal/LRENovAW">working animal</a> (e.g., <a href="/facts/Horse_mill/6BIl6EbH">horse mill</a>), wind (<a href="/facts/Windmill/D7rzFXT2">windmill</a>) or water (<a href="/facts/Watermill/UTvzQY8S">watermill</a>). In the modern era, they are usually powered by <a href="/facts/Electricity/hNC8D65W">electricity</a>. </p><p>The grinding of solid materials occurs through mechanical forces that break up the structure by overcoming 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. </p><p>Milling also refers to the process of breaking down, separating, sizing, or classifying aggregate material (e.g. mining <a href="/facts/Ore/kgc9DssX">ore</a>). 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. </p><p>Grinding may serve the following purposes in engineering: </p> <ul><li>increase of the surface area of a solid</li> <li>manufacturing of a solid with a desired grain size</li> <li>pulping of resources</li></ul>