Hafiz Luqman Khalil (032)
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Engr. Waqas Qamar
5th Semester, Chemical Engineering
Subject: Particle Technology
Topic: Size Reducing Equipment
Size Reduction Equipment
Size reduction equipment is divided into crushers, grinders, ultrafine grinders and cutting
machines. Crushers do the large work of breaking large pieces of solid material into small lumps.
A primary crusher operates on run-of-mine material, accepting anything that comes from the face
of mine and breaking it into 150-250 mm lumps. A secondary crusher reduces these lumps to
particles perhaps 6 mm in size. Grinders reduce the crushed feed to powder. The product from a
intermediate grinder might pass a 40-mesh screen; most of the product from a fine grinder would
pass a 200-mesh screen with a 70 μ mm opening. An ultrafine grinder accet feed particles no larger
than 6 mm; the product size is typically 1-50 μ mm. Cutters give particles of definite size and
shape, 2 to 10 mm in length.
Primary crushing reduces this run-of-mine rock to 150-250 mm lumps. The different types
of primary crushers are: jaw crushers, gyratory crushers, impact crushers, and autogenous
1. Jaw Crusher:
The jaw crusher squeezes rock between two surfaces, one of which opens and closes like
a jaw. Rock enters the jaw crusher from the top. Pieces of rock, that are larger than the
opening at the bottom of the jaw, lodge between the two metal plates of the jaw. The
opening and closing action of the movable jaw against the fixed jaw continues to reduce
the size of lodged pieces of rock until the pieces are small enough to fall through the
opening at the bottom of the jaw.
2. Gyratory Crusher:
A gyratory crusher is among the main kinds of primary crushers in a mine or ore processing
plant. Gyratory crushers are designated in dimensions either by the gape and mantle
diameter or from the size the receiving opening. Gyratory crushers can be utilized for
primary or secondary crushing. Because, the gyratory crusher design is broken product
quality and production capacity as the primary factor to consider. Gyratory crusher is
developed for both dry and wet crushing of brittle, medium-hard materials for the mining,
cement, coal, metallurgic material, construction material, road building, and petroleum &
chemical industries. A gyratory crusher breaks rock by squeezing the rock between an
eccentrically gyrating spindle, which is covered by a wear resistant mantle, and the
enclosing concave hopper. As run-of-mine rock enters the top of the gyratory crusher, it
becomes wedged and squeezed between the mantle and hopper. Large pieces of ore are
broken once, and then fall to a lower position （because they are now smaller） where
they are broken again. This process continues until the pieces are small enough to fall
through the narrow opening at the bottom of the crusher.
3. Impact Crusher:
Impact crushers, which are also called hammer mills, break rock by impacting the rock
with hammers that swing on a rotating shaft. The practical use of impact crushers is limited
to soft materials, such as phosphate, gypsum, weathered shales, etc. Impact crushers
cannot handle as large a top sized material as jaw, or gyratory, crushers can; however,
impact crushers can make a finer sized product.
4. Autogenous Crusher:
In recent years, autogenous crushers have been adapted for crushing run-of-mine rock in
primary crushing circuits. Consequently, autogenous mills have increased in importance
as a means of crushing and grinding. In autogenous crushers, the rock to be crushed also
provides the crushing force. Crushing is accomplished by the tumbling action of the rock.
Flexible crushing circuits can be constructed so that hard ores, as well as soft ores, can be
processed. Wet, sticky ores can be processed in autogenous mills, while the same ore
would present difficulties for other types of crushers.
The term grinder refers to a variety of size reduction machines for intermediate duty.
Product from a crusher is often fed to a grinder for further reduction. Common commercia l
grinder machines are hammer mills, attrition mills, tumbling mills etc.
1. Hammer Mill:
A hammer mill is a machine whose purpose is to shred or crush aggregate material into
The material can be put into the machine from the inlet and then under the influence of the
guiding plate into the pulverizing cabin. Later on, the materials will be ground with the
hammer plates striking and sieve plates friction at fast speed, at last, with the help of
centrifugal force and air current, the pulverized materials will be discharged from the
foundation through sieve holes.
The basic principle is straightforward. A hammer mill is essentially a steel drum containing
a vertical or horizontal rotating shaft or drum on which hammers are mounted. The
hammers are free to swing on the ends of the cross, or fixed to the central rotor. The rotor
is spun at a high speed inside the drum while material is fed into a feed hopper. The material
is impacted by the hammer bars and is thereby shredded and expelled through screens in
the drum of a selected size.
The hammer mill can be used as a primary, secondary, or tertiary crusher.
2. Roller Mill:
Roller mills are mills that use cylindrical rollers, either in opposing pairs or against flat
plates, to crush or grind various materials, such as grain, ore, gravel, plastic, and others.
Roller grain mills are an alternative to traditional millstone arrangements in gristmil ls.
Roller mills for rock complement other types of mills, such as ball mills and hammer mills,
in such industries as the mining and processing of ore and construction aggregate; cement
milling; and recycling.
3. Attrition Mill:
The Attrition Mill produces particles within a relatively narrow particle size spectrum, from
granular (10 to 200 mesh). It is employed primarily for reduction of fibrous materials, but
is also suitable for friable products. It is available in three sizes with single- or dual
(counter-rotating) powered discs, and an extensive selection of plate designs for optimum
performance. In addition to general process applications, Munson Attrition Mills are often
utilized for conditioning of materials prior to packaging.
The attrition mill is a device for mechanically reducing solid particle size by intense
agitation of a slurry of material being milled and coarse milling media. For example, in 10
hours of milling, specific surfaces of 40 and 25 m2/g were obtained for alumina and barite,
corresponding to 38 and 56 nm equivalent spherical diameter, respectively. Size reduction
rates for relatively coarse particles were first-order and increased linearly with power input
to the mill. Optimum milling medium concentration corresponded to medium particles
moving a distance of approximately 0.7 of their diameter before collision with another such
particle. Power characteristics of the attrition mill were essentially the same as those of a
radial flow turbine mixer. Laminar flow became disrupted at NRe ≈ 200, while turbule nt
flow was established at NRe > 8000. Slurries of fine powders exhibited the same linear
power-average density dependence as single-phase liquids. However, a differe nt
dependence was observed with large particles.
4. Tumbling Mill:
Tumbling Mill / Ball Mill consists of a cylindrical shell which slowly turns about a
horizontal axis & is filled about half its volume with a solid grinding media. The shell is
lined with a replaceable liner which may be of high carbon steel, Manganese steel,
Porcelain or rubber. The grinding media is metal or rubber balls in a ball mill, Pebbles or
Porcelain in a Pebble Mill & metal rods in a Rod Mill.
In Tumbling Mills the material to be grinded is carried up the side of the shell upto the top
from where they fall on the particles underneath. In Ball / Pebble Mill the most of the
grinding is achieved by the impact of the Ball / Pebble which drop from nearly the top of
the shell whereas in a Rod mill the most of the size reduction is due to rolling attrition &
The Tumbling Mills may be batch type or continuous.
C. Ultrafine Grinders
Ultrafine grinding mill is a high-efficient ultrafine powder grinding mill, comparable to
air-blast mill, newly designed on the basis of industrial mill manufacturing experience for
many years, which adopts the theory of fluidics and successfully solves the problem of
high cost in domestic air-blast mill.
The new type of grinding roll assembly changes the traditional structure, using various
means of sealing, getting rid of three defects of old assembly, i.e. oil leak, dust coming in,
With a wide range of capabilities in toll powder processing including grinding, flash drying
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1. Fluid Energy Mills:
Fluid energy mills are used because of their advantages in fine grinding. The materials fed into
a jet stream are accelerated to a relatively high velocity from 10 to 200 m/s and although these
values are much higher than those encountered in the breeding process of crystals, there are
some similarities between these two operations. In both tiny fragments are produced by the
attrition of particles when they collide with each other, with the mixer or the wall of the
A size-reduction unit depending for its action on collisions between the particles being ground,
the energy being supplied by a compressed fluid, (e.g., air or steam) that enters the grinding
chamber at high speed. Such mills will give a product of 5 mu m or less; they have been used
for the fine grinding of frits, kaolin, zircon, titania, and calcined alumina, but the energy
consumed per ton of milled product is high.
2. Colloid Mill:
A colloid mill is a machine that is used to reduce the particle size of a solid in suspension in
a liquid, or to reduce the droplet size of a liquid suspended in another liquid. This is done by
applying high levels of hydraulic shear to the process liquid. It is frequently used to increase
the stability of suspensions and emulsions.
In Colloid Mill the product is subjected to high shearing, cutting, and rubbing forces between
two toothed surfaces. The product, while passing down the hopper, initially gets seized in the
preliminary breaking drum where it is broken and thrown in to the centrifugal effect of the
rotor rotating at a speed of 2800 RPM, the material is forced in to second tooth stage. The tooth
design of the grinding set causes powerful vibrations, which subject the particles with high
degree of forces. Intense whirling multiplies the grinding and mixing effect. The process is
continued till the material reaches the lowest grinding stage. The ground material continuously
leaves the mill through the outlet pipe, if required, it can be recalculated.