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Grinders

A grinding mill is a unit operation designed to break a solid material into smaller pieces. In materials processing a grinder is a machine for producing fine particle size reduction through attrition and compressive forces at the grain size level. A grinding mill crushes material between two closely placed, heavy objects like stones. They are rotating with respect to one another so the material gets crushed like in a mortar and pestle. The rotating motion of the partially filled industrial grinder can make cascading effect that decreases the material to a very fine and give it powder shape or convert it in to powder form. There are many different types of grinding mills and many types of materials processed in them.

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. Dry chemicals can be ground to a uniform particle size (to a specified fineness) which enables optimal dispersibility, reactivity, and processing uniformity.

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.

In industrial and manufacturing process there are different types of industrial grinders used for breaking down and mixing rough material like paints, chemicals and ores. Industrial grinder can cut, shape and reshape metal and it can grind any thing into small pieces or some can present in a powder form.

Grinding machines are mainly applied for the powder processing of mineral products in the industries of metallurgy, construction materials, chemicals, mining, etc. A grinding machine can produce powder from various non-flammable and non-explosive mineral materials, such as quartz, feldspar, talcum, barite, cinder, cement clinker, activated carbon, dolomite, granite, soft coal, coking coal, lignite, gold ore, red clay, clay, coke, coal gangue, porcelain clay, bentonite, pyrophyllite, shale, red stone, basalt, gypsum, graphite, carborundum, heat insulating material, etc.

One of the most commonly used industrial grinders is called a ball mill. It rotates on a horizontal axis and has a cylindrical design. A slightly inclined or horizontal rotating cylinder is partially filled with balls, usually stone or metal, which grinds material to the necessary fineness by friction and impact with the tumbling balls. Ball mills are characterized by comparatively smaller diameter and longer length. The feed is at one end of the cylinder and the discharge is at the other. Ball mills are commonly used in the manufacture of Portland cement. These industrial ball mills are mainly big machines. Small versions of ball mills can be found in laboratories where they are used for grinding sample material for quality assurance.

Different type of materials can be used as grinding media in an industrial grinder, such as flint pebbles, stainless steel balls and ceramic. Sometimes the final stage of crushing and the preliminary stage of grinding are economically combined into one operation.

Impact crushers can be used to combine crushing and grinding, in one operation. Impact crushers involve the use of impact rather than pressure to crush material. These machines offer the lowest capital cost of any grinding mill. Hammer speeds of 4,000 ft/min. will suffice for a course product, but upwards of 15,000 ft/min, may be required for fine grinding. With different forms of crushing chambers, grinding elements and discharge screens, they can be built to handle and reduce almost any material that is not too abrasive: as coal, seeds, limestone, gypsum or soft metallic ores. Impact crushers can be adapted for wet crushing and grinding to produce a slurry, in this way serving an additional purpose, but there is some loss of machine capacity and an increase in power consumption when the machine is used in wet operations. They are used for grinding and classifying non-metallic minerals and dry chemicals to a fineness ranging from 800 to 35 microns with a high degree of uniformity.

4. Answer the questions to the text:

1) What is a grinding mill designed for?

2) How does a grinding mill work?

3) What purposes in engineering may grinding serve?

4) What mineral materials are used for producing powder by a grinding machine?

5) What is the most commonly used industrial grinder

6) How does a ball mill operate?

7) What machines are used to combine crushing and grinding in one operation?

8) What materials are impact crushers designed to handle and reduce?

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