Comminution is the reduction of
solid materials from one average
particle size to a smaller average particle size, by
crushing,
grinding,
cutting,
vibrating
Oscillation is the repetitive or periodic variation, typically in time, of some measure about a central value (often a point of equilibrium) or between two or more different states. Familiar examples of oscillation include a swinging pendulum ...
, or other processes.
In
geology, it occurs naturally during
faulting in the upper part of the
Earth's crust
Earth's crust is Earth's thin outer shell of rock, referring to less than 1% of Earth's radius and volume. It is the top component of the lithosphere, a division of Earth's layers that includes the crust and the upper part of the mantle. The ...
.
In
industry, it is an important
unit operation in
mineral processing,
ceramics,
electronics, and other fields, accomplished with many types of
mill. In
dentistry
Dentistry, also known as dental medicine and oral medicine, is the branch of medicine focused on the teeth, gums, and mouth. It consists of the study, diagnosis, prevention, management, and treatment of diseases, disorders, and conditions o ...
, it is the result of
mastication
Chewing or mastication is the process by which food is crushed and ground by teeth. It is the first step of digestion, and it increases the surface area of foods to allow a more efficient break down by enzymes. During the mastication process, th ...
of food. In general medicine, it is one of the most traumatic forms of
bone fracture
A bone fracture (abbreviated FRX or Fx, Fx, or #) is a medical condition in which there is a partial or complete break in the continuity of any bone in the body. In more severe cases, the bone may be broken into several fragments, known as a '' ...
.
Within industrial uses, the purpose of comminution is to reduce the size and to increase the surface area of solids. It is also used to free useful materials from
matrix
Matrix most commonly refers to:
* ''The Matrix'' (franchise), an American media franchise
** ''The Matrix'', a 1999 science-fiction action film
** "The Matrix", a fictional setting, a virtual reality environment, within ''The Matrix'' (franchis ...
materials in which they are embedded, and to concentrate minerals.
Energy requirements
The comminution of solid materials consumes energy, which is being used to break up the solid into smaller pieces. The comminution energy can be estimated by:
*
Rittinger's law, which assumes that the energy consumed is proportional to the newly generated surface area;
*
Kick's law, which related the energy to the sizes of the feed particles and the product particles;
*
Bond's law, which assumes that the total work useful in breakage is inversely proportional to the square root of the diameter of the product particles,
mplyingtheoretically that the work input varies as the length of the new cracks made in breakage.
[Bond, F.C. The third theory of comminution.Trans. AIME, vol. 193, 1952.
pp. 484–494.]
*
Holmes's law, which modifies Bond's law by substituting the square root with an exponent that depends on the material.
Forces
There are three forces which typically are used to effect the comminution of particles:
impact
Impact may refer to:
* Impact (mechanics), a high force or shock (mechanics) over a short time period
* Impact, Texas, a town in Taylor County, Texas, US
Science and technology
* Impact crater, a meteor crater caused by an impact event
* Impact ...
,
shear
Shear may refer to:
Textile production
*Animal shearing, the collection of wool from various species
**Sheep shearing
*The removal of nap during wool cloth production
Science and technology Engineering
*Shear strength (soil), the shear strength ...
, and
compression.
Methods
There are several methods of comminution. Comminution of solid materials requires different types of
crusher
A crusher is a machine designed to reduce large rocks into smaller rocks, gravel, sand or rock dust.
Crushers may be used to reduce the size, or change the form, of waste materials so they can be more easily disposed of or recycled, or to reduce ...
s and
mills depending on the feed properties such as hardness at various size ranges and application requirements such as throughput and maintenance. The most common machines for the comminution of coarse feed material (primary crushers) are the
jaw crusher (1m > P
80 > 100 mm),
cone crusher
A crusher is a machine designed to reduce large rocks into smaller rocks, gravel, sand or rock dust.
Crushers may be used to reduce the size, or change the form, of waste materials so they can be more easily disposed of or recycled, or to red ...
(P
80 > 20 mm) and
hammer crusher
A crusher is a machine designed to reduce large rocks into smaller rocks, gravel, sand or rock dust.
Crushers may be used to reduce the size, or change the form, of waste materials so they can be more easily disposed of or recycled, or to re ...
. Primary crusher product in intermediate feed particle size ranges (100mm > P80 > 20mm) can be ground in
autogenous (AG) or
semi-autogenous (SAG) mills depending on feed properties and application requirements. For comminution of finer particle size ranges (20mm > P
80 > 30 μm) machines like the ball mill, vertical roller mill, hammer mill, roller press or high compression roller mill, vibration mill, jet mill and others are used. For yet finer grind sizes (sometimes referred to as "ultrafine grinding"), specialist mills such as the
IsaMill
The IsaMill is an energy-efficient mineral industry grinding mill that was jointly developed in the 1990s by Mount Isa Mines Limited ("MIM", a subsidiary of MIM Holdings Limited and now part of the Glencore Xstrata group of companies) and Netzsch F ...
are used.
Trituration
Trituration (Latin, ''grinding'') is the name of several different methods used to process materials. In one sense, it is a form of comminution (reducing the particle size of a substance). In another sense, it is the production of a homogeneous pow ...
, for instance, is comminution (or substance breakdown) by rubbing. Trituration can further be described as levigation (trituration of a powder with a non-solvent liquid), or pulverization by intervention, which is trituration with a solvent that can be easily removed after the substance has been broken down.
See also
*
*
*
References
{{Extractive metallurgy
Industrial processes