Mineral processing – Milling
Practical Action
Carbon
Pharmaceuticals
Chalk
Spices
Talc Sugar
Pigments
Resins
Dyestuffs
Table 9: Material suitability for pin, air classifying and turbo mills
Vibratory mills
Description:
This is the first mill we will consider which does not rely on rotation for the main grinding
action. The vibrating mill is a grinding chamber which is filled to about 65 - 80% of its
capacity with grinding media such as balls or rods. The chamber is vibrated at a frequency of
between 1000 and 1500 times per minute (can be variable speed) by cams or imbalanced
weights.
The grinding action is efficient and thorough. Grinding media material and chamber lining can
vary depending on application.
Characteristics:
Vibrating mills can grind hard or soft materials. Maximum throughput is in the order of 20
t.p.h. but feed size should be kept fairly small. Although final product size can be as low as
0.005mm this type of mill is often used for less fine applications. Product size and shape is a
function of the time spent in the mill, media type and size, and frequency of vibration.
Commonly the mill is used as a batch process.
Lime
Calcium carbide
Gypsum
Bauxite
Limestone
Sillimanite
Pigments
Dolomite
Table 10: Material suitability for vibratory mills
Alumina
Chromite
Fluorite
Magnesite
Stirred media mills
Description:
Stirred media mills are usually constructed in the form of a cylindrical drum inside which
there are a series of rods, arms or perforated discs which are rotated on a central shaft. The
drum is loaded with grinding media, such as metal balls or glass sand. The media and the
charge is ‘stirred’ together and thus the grinding takes place.
Characteristics:
The mill is suited primarily to the very fine grinding of soft materials. Usually used with wet
grinding but can be used for dry grinding also. Product size is as small as 0.005mm.
Pigments
Kaolin
Colorants
Table 11: Material suitability for stirred media mills
Fluid energy mills
Description:
The general principle of operation in a fluid energy mill is that the mineral to be ground is fed
into a grinding chamber in a high speed, high pressure and, often, high temperature jet of air
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