Sizing in Mineral processing

1. SIZING
• Sizing is the process of separating a mixture of grains of different size into groups or
grades whose characteristics is that the particles there in are more or less necessary of
same size, that have passed an aperture of certain dimension and failed to pass through
some smaller aperture
• Sizing is the process of Production of a final product having a specific size
• PURPOSES OF SIZING
1. SIZING OR CLASSIFYING - to separate particles by size, usually to provide a downstream
unit process with the particle size range suited to that unit operation;
2. SCALPING - to remove the coarsest size fractions in the feed material, usually so that
they can be crushed or removed from the process;
3. GRADING - to prepare a number of products within specified size ranges. This is
important in quarrying and iron ore, where the final product size is an important part of
the specification;
4. MEDIA RECOVERY - for washing magnetic media from ore in dense medium circuits;
5. DEWATERING - to drain free moisture from a wet sand slurry;
6. DE-SLIMING OR DE-DUSTING - to remove fine material, generally below 0.5 mm from a
wet or dry feed; and
7. TRASH REMOVAL - usually to remove wood fibres from a fine slurry stream.
8. To cut off the fine end from either feeds and thus save power and overgrinding

2. METHODS OF SIZING
• There are two basic types of sizing separator
• Screening (coarse sepatarion)
• Classification(fine separation)
• Screening;-
• is a mechanical separation of particles on the basis of size accomplished on to a screening surface with
with uniformsized aperture
• Screening is characterised by the use of a physical barrier(screen) to bring about a separation
• Screening is generally carried out on realitively coarse material and the efficiency decreases rapidly with
finees.
• Fine screen are very fergile and expensive and tend to become blind rather easily
• Screening - used to screen particles of several inches in size to particles as fine as 0.1 mm. Normally
used to size coarser than 20 mesh screens.
• Sieving;- screening and sieving are distinguised by the fact that screening is a continuous process ans is
used mainly for industrial scale , where as sieving is a batch process and used for laboratory purposes
• Classificatuion;- is a operation in which a mass of grain of mixed sized and specific gravity is allowed or
caused to settel through a fluid medium wich may be either in motion or stationary state
• Classification is separation of particles accorsding to their settlin rate in a fluid
• Classification - used to classify particles of 2-3 mm sizes to 0.02-0.03 mm. Normally used to
size finer than 35 mesh screens.

4. TYPES OF SCREEN

5. GRIZZLY
• Fixed screen with heavy screening surfaces usually made of parallel bars are called
grizzly
• Grizzlies are characterised by parallel steel bars, rods or rails set at a fixed distance
apart with a uniform clear opening and installed in line with the flow of ore. The
gap between grizzly bars is usually greater than 50 mm and can be as large as 300
ram, with feed top size as large as 1 m. The bars have taper from feed end to
discharge end. The bars are inclined usually at an angel of between 20-50degree,
greater the inclination ,the greater the throughput but the lower in efficiency . They
are made of steel or wooden bars having a various cross section.
• The bars are held together by cross rods or by bolts and are spaced the desired
distance apart by thimbles or sleevs on the bolt..

6. • Clogging major problem
• Capacity can be up to 1000tonnes per hour is proportional to area
• Grizzly screens;-used for
1. Scalping out large rock between truck and bin
2. Very coarse material screen.
3. It is used to protect primary crushers against overload.
4. Allow fines to by pass crusher , thus reducing load on machine

7. Types of grizzly
1. Rail grizzly
2. Cantilever grizzly
3. Self cleaning grizzly
4. Moving bar grizzly
5. Chain grizzly
6. Travelling grizzly
7. Roller type grizzly
8. Vibrating grizzly

8. Rail grizzly
• Rail grizzlies are widely used for very coarse sizing where severe service is anticipated These may he
made of 15 to 150-lb. Rail suitably braced and spaced. They are rarely used with spacing's of less than 5
in. -because they clog seriously with the narrower openings.
• Slope of grizzly depends on its purposes . A flat grizzly is used on the top of ore bins fed by skip ,cars or
dumper in order to scalp boulders. When used in the feed chute to primary crusher are set at such slope
that material will just slide over them 25 degree to 35 degree.To ensure free movement of the material
slope the slope should be 35 degree to 45 degree as high as 50 degree. a lower slope may be used when
material is delivered with initial velocity in the direction of slope
• Size of grizzly;- depends upon
1. the size of feed
2. Percentage of under size
3. Slope
4. Aperture
Width is governed by the thumb rule that minimum width should beat least' three time- the size of the
largest lumps in the fed if the feed is fair1y uniform in size or twice as wide if large lumps are rare
The width is usually determined, however by other factors such as chute width ,width of car or skip , dumper
supplying the feed or receiving width of crusher
Length is determined by the amount of screening to be done, i.e., if the aperture 'is small and the percentage
of undersize large,' more length must be .provided than under reverse conditions: Steep grizzlies should
be longer-than flat-ones. No quantitative rules can be set down length is frequently made twice the width
but for no logical reason.
Advantages;- simplicity in construction and operation, ruggedness
Dis advantages;- inefficiency, loss of head room. Blinding, breakage of over size

10. Cantilever grizzly
• Cantilever grizzly improves the screening capacity of the older type of fixed bar
screens by (a) use of bars tapering lengthwise as well as vertically (b) omitting all
cross bars except two at the top essential for support .The lower two-thirds or more
of each bar is thus free to vibrate under impact from dumping of the load this
together with diverging space between bars multiplies the capacity of a rigid and
equally spaced grizzly by four or five times

11. Self-cleaning grizzly
• The revolving arms prevent material from sticking between the bars .ore containing
10 to 12% moisture which could not be handled by other types of grizzlies and
previously had been dried and re handled at considerable expense

12. Moving bar Grizzly-
• Moving bar Grizzly- Alternate bars rise and subside . Helps in the forward
movement of the material with TURNING OVER
• Moving grizzlies of various types are used for the purpose of bettering screening,
lessen-ing breakae of material and saving headroom The first two purposes hate
determined then use in coal breakeis the second in many ore treatment plants
• Moving-bar grizzly Bars are mounted at one end on an eccentric, adjacent bars
180 degree apart, and are so driven that they move forward at the high position
Speed is about 150 r.p.m. power, 5 to 7.5 hp,, The forward movement together
with a forward inclination of about 10degree , moves lump material gently along
the grizzly and at the same time turns it over well and allows fines to drop
through. Usual range of spacing, 3/4 to 3 in. capacity, 4 tons per hr. per sq. ft. at 1
in, spacing.

13. TRAVELING GRIZZLY
• Traveling grizzly consists of short lengths of rail running across between two
sprocket chains the latter operating over head and tail sprockets gear—driven
this grizzly is placed directly under i feed chute and is normlly of adjustable
speed to regulate feed to a crushing machine.
• Undersize passes through the upper run and is delivered both sides by chutes.
Oversize is discharged over the head sprocket
• Any material that tends to wedge between the bars is readily freed at the head
sprocket because of spreading of the bars in passing around
• Speeds range usually between 10 and 20 ft permin.

14. ROLL SCREENS. A bank of rolls are arranged in the form of a cascade. They provide square apertures between adjacent rolls. Used to
screen finer sizes ( 10-100 mm) of HARDER ORES. Costly, Less efficient.

15. REVOLVING SCREEN OR TROMMEL
• Trommels One of the oldest screening devices is the trommel or revolving screen,
which is a rotating cylindrical shells of screen material ( punched sheet ). rotating
at between 35 and 45% critical speed.
• It essentially consist of through shaft consisting two or more 4 to 6 arms spider, on
the outer end of which circular bands are mounted on which screen cloth is
stretched. The main shaft is supported in bearing at the two ends.
• Several drive methods are employed , the commonest is the so called right angle
drive, consisting of a bevel gear mounted the end of the trommel shaft and driven
by a bevel pinion on the counter shaft , the letter being driven by pulley and belt for
dry screen
• They are 3-4 ft in dia and 5-10 ft long.
• The material to be screened flows into the shell. The shell rotates. The shell is kept
in an inclined position. The particles move towards the discharge ( lower ) end. The
undersize particles are collected at the bottom.

17. • Application
1. Trommels can handle material from 55 mm down to 6 mm, and even smaller
2. sizes can be handled under wet screening conditions.
3. Trommels remain widely used in some screening duties including aggregate screening plants
and the screening of mill discharge streams
4. On gold and tin dredges
5. For sizing of construction gravel and crushed stone
6. Scrubbing and washing wet sticky material
7. Rough size separation
• Advantages
1. Simplicity in construction and operation
2. Low cost and low operating cost
3. Freedom from vibration
4. Small loss of head room
5. General ruggedness
• Disadvantages
1. Blinding
2. Difficult to repair
3. Low capacity since only part of the screen surface is in use at any one time
4. Low efficiency

18. • Types/ classification of trommel
1. Series trommel
2. Compound or concentric trommel
3. Stationary trommel
4. Moving trommel
• Series trommel
• Trommel may be arranged in series with discharging its undersize consecutively
finer trommel. Trommels can be made to deliver several sized products by using
trommel screens in series from finest to coarsest
• The first cylinder is fed with the crushed ore. Very fine particles are separated. The
coarse oversize is fed to the next screen and the process continues.
• This method however required great deal of floor space

19. Compound or concentric trommel
• Trommels can be made to deliver several sized products by using trommel screens
using concentric trommels with the coarsest mesh being innermost.
• Compound trommel has a series of concentric screen cylinders , with the coarsest at
the centre and finest at outer. Screens are made to rotate on a single shaft. The
coarsest screen is the innermost and the finest screen is the outermost
• Coarse fraction is removed first
• They are used when several short range products are desire from one long range
feed and head room is at premium
• It suffer from disadvantage that failure of inner screen is difficult to observe and
they are difficult to replace when worn.

21. Gyratory screen
• This type of screen which impart a combined gyratory and vertical motion throught
the whole screen surface. They are widely used for fine screening applications, wet
or dry, down to 40 µm.
• The basic components consist of a nest of sieves up to around 2.7 m in diameter
supported on a table which is mounted on springs on a base, suspended from
beneath the table is a motor with double shaft extensions, which drives eccentric
weights and in doing so effects horizontal gyratory motion.
• Vertical motion is imparted by the bottom weights, which swing the mobile mass
about its centre of gravity, producing a circular tipping motion to the screen, the top
weights producing the horizontal gyratory motion.
• Ball trays and ultrasonic devices may be fitted below the screen surfaces to reduce
• blinding. Circular screens are often configured to produce multiple size fractions

22. SHAKING SCREENS.
• Shaking screen consist essentially a shallow rectangular box two to four or more times as long as width,
open at one end, fitted with a screen bottom and shaken by means of suitable mechanism which alone on
in conjunction with slope of the screen surface
• The methods of support of the frame and means of shaping varies considerably may be by rod, chan
• A screen with substantially linear motion in the plane on the main frame
• Shaking screen have a reciprocating movement mechanically induced in the horizontal direction and are
mounted horizontally or at gentle slope.
• They operate in the range of 60- 800 strokes per minutes and with speed from 30- 200rpm.
• The screen may be suspended from rod or chains.
• Shaking is done sidewise or endwise .The material gets lifted and thrown forward when the screen moves
to the front. When it moves back, the material is tossed in air. This causes largest particles on top and
allows smaller ones to pass through the mesh..
• Low capacity and high maintenance are disadvantages
• Use
1. May be used for both conveying and size separation
2. find greatest use as grading screen for relatively large sized feeds, down to about 12 mm
3. They are widely used for coal preparation
4. Use in abrasive metalliferous ores

23. Reciprocating screen
• Reciprocating screen employ a horizontal gyratory motion to the feed end of a
rectangular screen by means of an unbalanced rotating shaft rotating at about
1000rpm
• The horizontal circular motion at the feed end gradually diminishes through the
length of the machine to an elliptical movement and finally to an approximate
straight line reciprocating motion at the discharge end
• The circular motion at the fed end immediately spread the material across the full
width of the screen surface, even though it is fed from a single point. this horizontal
circular motion also stratifies the material causing fine material to sink down against
the mesh
• As the material travel down the screen surface it enters the area of gradually
diminishing screening motion at the discharge end . The reduced action aids the
screening out near mesh particles
• The screen is slightly inclined and in some commercial screens have ball tray below
the screen, resilient ball confines in this tray are deflected against bevel strip by the
machine motion and bounce continuously against undersize of the screen mesh thus
reducing blinding
• These screens are used for separating mainly dry of light material in the range of
10mm to 250 micro meter and some times down to 40 micro meter

25. Classification
• Classification;- is a operation in which a mass of grain of mixed sized and specific gravity is allowed or
caused to settle through a fluid medium which may be either in motion or stationary state
• Classification is separation of particles according to their settling rate in a fluid
• Classification - used to classify particles of 2-3 mm sizes to 0.02-0.03 mm. Normally used to size finer
than 35 mesh screens.
• Applications
1. Separation into relatively coarse and relatively fine size fraction , typically for separation too fines to be
economically screened
2. To effect concentration of smaller heavier particle from large lighter particles
3. To split in long range size distribution in to fraction
4. To restrict the property distribution of particles entering in concentration process
5. To control close circuit grinding
Hydro cyclone application
1. Coal fine recovery
2. Chemical beneficiation
3. Gypsum recovery
4. Sand de sliming and sizing
5. cleaning cooling and processing water
Spiral classifier
1. Classification in small to medium tonnage circuits
2. Primary classification in two stages circuits with cyclone as secondary
3. De sliming and dewatering
4. Sand recovery

26. Principles of classification
• When a solid particle falls freely in a vacuum, it is subject to constant acceleration and its
velocity increases indefinitely, being independent of size and density. Thus a lump of lead
and a feather fall at exactly the same rate.
• In a viscous medium, such as air or water, there is resistance to this movement and the value
increases with velocity. When equilibrium is attained between the gravitational and fluid
resistances forces, the body reaches its terminal velocity and thereafter falls at a uniform rate.
• Effectively all resistance to motion is due to the shear forces or viscosity of the fluid and is
hence called viscous resistance.
• At high velocities the main resistance is due to the displacement of fluid by the body, and
viscous resistance is relatively small; this is known as turbulent resistance.
• Classifiers consist essentially of a sorting column in which a fluid is rising at a uniform rate .
Particles introduced into the sorting column either sink or rise according to whether their
terminal velocities are greater or lesser than the upward velocity of the fluid. The sorting
column therefore separates the feed into two products an overflow consisting of particles with
terminal velocities lesser than the velocity of the fluid and an underflow or spigot product of
particles with terminal velocities greater than the rising velocity.

27. • Free settling Free settling refers to the sinking of particles in a volume of fluid which is large with respect to the total
volume of particles, hence particle crowding is negligible. For well-dispersed ore pulps, free settling predominates
when the percentage of solids by weight is less than about 15.
• Consider a spherical particle of diameter d and density D~ falling under gravity in a viscous fluid of density Df under
free-settling conditions, i.e. ideally in a fluid of infinite extent. The particle is acted upon by three forces: a
gravitational force acting downwards, an upward buoyant force due to the displaced fluid, and a drag force D acting
upwards.
• Terminal velocity by Stokes' law for a particular fluid
• and Newton's law can be
• where k and k 2 are constants, and (D s -Df) is known as the effective density of a particle of density D s in a fluid of
density Df
• Stokes' law is valid for particles below about 50 µm in diameter. The upper size limit is determined by the
dimensionless Reynolds number
• Newton's law holds for particles larger than about 0.5cm in diameter. There is, therefore, an intermediate range of
particle size, which corresponds to the range in which most wet classification is performed, in which neither law fits
experimental data.
• Free settling ratio;-Consider two mineral particles of densities D a and D b and diameters d a and d b respectively,
falling in a fluid of density Df at exactly the same settling rate. Their terminal velocities must be the same,and hence
from Stokes' law
• This expression is known as the free-settling ratio of the two minerals, i.e. the ratio of particle size required for the two
minerals to fall at equal rates.
• Similarly from Newton's law
• The general expression for free-settling ratio can be deduced
• where n = 0.5 for small particles obeying Stokes‘ law and n = 1 for large particles obeying Newton' s law.The value of n
lies in the range 0.5-1 for particles in the intermediate size range of 50 p~m-0.5 cm.

28. • Hindered settling
• As the proportion of solids in the pulp increases, the effect of particle crowding
becomes more apparent and the falling rate of the particles begins to decrease.
• The system begins to behave as a heavy liquid whose density is that of the pulp
rather than that of the carrier liquid; hindered-settling conditions now prevail.
Because of the high density and viscosity of the slurry through which a particle
must fall in a separation by hindered settling, the resistance to fall is mainly due to
the turbulence created and a modified form of Newton's
• Law can be used to determine the approximate falling rate of the particles
• where Op is the pulp density.
• The lower the density of the particle, the more marked is the effect of reduction of
the effective density, D s - Dp, and the greater is the reduction in falling velocity.
Similarly, the larger the particle, the greater is the reduction in falling rate as the
pulp density increases.
• This is important in classifier design; in effect, hindered-settling reduces the effect
of size, while increasing the effect of density on classification.
• The hindered-settling ratio can be

29. Methods of classification
• Many different types of classifier have been designed and built. They may be grouped,
however, into two broad classes depending on the direction of flow of the carrying current.
1. Horizontal current classifiers such as mechanical classifiers use some mechanism for
removing the sand products from the device generally this mechanism operate against gravity
and are essentially of the free-settling type and accentuate the sizing function;
2. vertical current or hydraulic classifiers rely for sands discharge on flow properties of the
sands stream aided by gravitational and centrifugal forces and are usually hindered-settling
types and so increase the effect of density on the separation
The principal horizontal-current-apparatus (mechanical classifiers) have mechanical devices
to agitate the pulp and to transport the settled grains away from the separating zone; the
others, variously called sand tanks, sand cones,, de sliming cones, and the like, are
characterized by a tank converging downwardly to a spigot discharge for the settled grains.
Horizontal-current classifiers normally, although not necessarily make two products only.
Hydraulic classifiers are characterized by the utilization of a rising current of extraneous -water
(hydraulic water) to effect sorting. The principal type, because it does the best work is the
hindered-settling classifier, having a constriction in the sorting column; the free settling type,
without constriction, is rarely used except for the roughest type of work. The hydraulic
classifiers are used primarily, to separate long-range feeds 10-m or less in the limiting size,
into a number of grades, usually for subsequent gravity concentration.
on the basis of media
1. Dry classification
2. Wet classification

30. Hydraulic classifier/ vertical current classifier
• These are characterised by the use of water additional to that of the feed pulp,
introduced so that its direction of flow opposes that of the settling particles.
• They normally consist of a series of sorting columns through each of which a
vertical current of water is rising and particles are settling out .
• The rising currents are graded from a relatively high velocity in the first sorting
column, to a relatively low velocity in the last, so that a series of spigot products
can be obtained, with the coarser denser particles in the first spigot and the fines
in the latter spigots.
• Very fine slimes overflow the final sorting column of the classifier. The size of
each successive vessel is increased, partly because the amount of liquid to be
handled includes all the water used for classifying in the previous vessels and
partly because it is desired to reduce, in stages, the surface velocity of the fluid
flowing from one vessel to the next.
• Hydraulic classifiers may be free- or hindered settling types. The former are
rarely used; they are simple and have high capacities, but are inefficient in sizing
and sorting. They are characterised by the fact that each sorting column is of the
same cross-sectional area throughout its length. The greatest use for hydraulic
classifiers in the mineral industry is for sorting the feed to certain gravity
concentration processes so that the size effect can be suppressed and the density
effect

32. Settling cone
• The pulp is fed into the tank as a distributed stream at F, with the spigot discharge S
initially closed. When the tank is full, overflow of water and slimes commences,
and a bed of settled sand builds up until it reaches the level shown.
• If the spigot valve is now opened and sand discharge maintained at a rate equal to
that of the input, classification by horizontal current action takes place radially
across zone D from the feed cylinder B to the overflow lip.
• The main difficulty in operation of such a device is the balancing of the sand
discharge and deposition; it is virtually impossible to maintain a regular discharge
of sand through an open pipe under the influence of gravity. Many different designs
of cone have been introduced to overcome this problem
• These are the simplest form of classifier, in which there is
little attempt to do more than separate the solids from the liquid,
i.e. they are sometimes used as dewatering units in small-scale
operations. They are often used in the aggregate industry to
de-slime coarse sands products.

33. MECHANICAL CLASSIFIERS
• A mechanical classifier is essentially a settling tank with parallel sides, a vertical or
nearly vertical wall at one end, a sloping bottom which extends to a height above
the top of the end wall, and a mechanism in the tank which serves both to agitate the
pulp therein and to remove the settled solid.
• The conveying-agitating mechanism may be a reciprocating rake, a spiral, or a flight
conveyor
• The principal use of the mechanical classifier is in closed-circuit wet grinding
Machines are available to rake as much as 1,000 t.p.d. of sand per ft. of tank width,
which satisfies the circulation demand of any present-day grinding mill. Other
milling uses are for de sliming, dewatering granular material, and washing when
scrubbing is unnecessary.
1. Rake classifier
2. Spiral classifier
3. Log washer

34. Rake classifier
• The apparatus comprises a tank, one or more rakes, and a mechanism for actuating
the rakes.
• The tank has parallel vertical side walls a, a substantially vertical wall b at one end,
and a sloping bottom c of such length that its upper earl rises above the level of the
top of end wall b. The tank is thus capable of holding liquid up to the level of the
top of the end wall b. The rakes consist of a plurality of parallel blades e,
• set perpendicular to tank bottom c and to the longitudinal axial plane of the tank.
They are carried on a frame consisting of two parallel longitudinal members d,
suitably cross-braced, and hung by plates f, two each side, from the actuating
mechanism.
• The mecha-nism consists of a system of cranks, eccentrics, and links designed to
propel the rakes in a path so shaped that each point in each blade describes a rough
rectangle with long sides parallel to the bottom and the ends in the planes of the
blades. Gear-driven shaft g revolves counterclockwise

35. • causing crank ii to revolve. Pin j in the end of h it causes the left end of connecting
rod k to follow. The other end of k is pinned to, sup-ported, and constrained by the
upper end of link l, the lower. end of which is pinned to a bearing on the tank.
Members f are hung by pin non link m, which, in turn, is hung on pin o on the
connecting rod k. The lower end of link m bears adjustably against angle p, which is
welded between members f. The effect Of p is to prevent m from swinging down-
ward on o but to leave m free to move upward around o under the influence of an
upward force on p. Eccentric i actuates bell crank q, which rocks on fulcrum r that
forms one end of another angle lever s pivoted on t and actuated by adjusting screw
u, The lower end of bell crank q is pinned to the lower end of link v the upper end
of which is pinned to a link w is, similar in-its action to link ,m. The motion paths of
upper and lower members f are readily traced; and from them the paths of any part
of the rake frame. Lift of the rakes is • usually about 90 to 95% of the-height of the
rake blades
• Feed is introduced and flows thence over a distributing apron toward the high end
of the tank. The heavier sands settle into the zone of the rakes and are raked up the
s1ope. and out of the tank slime and the finer sands are carried over the rear wall in
suspension

36. Log washer
• A log washer has two functions
1. To disintegrate clay and clay bounded sand matrices
2. To separate disintegrated fines from lumps
• Log washer comprises essentially one or two heavy inclined members or logmembers or logs (1)
mounted rotatably on a slope of 0 -2.5 to 3 inch per feet in a rectangular or round-bottomed trough. (2),
with bottom on the same slope fitted with blades which agitate and turn over the feed in water in a box
and the same time push the settled material up an inclithe settled lump material up an inclined bottom by
reason of the spiral positioning of the blades. Discharge of fines is effected by overflow, in suspension in
water- at the lower end of the box.
• Logs were made originally',12 to 18inch stick, shod full length with iron straps, and fitted with chilled-
iron gudgeons ,the lower, gudgeon or both gudgeons passing through a stuff ing-box and carried in a‑
thrust bearing. end of the shaft passes through a water-sealed stuffing box.
•

37. • In the modern figured, the logs are made-of angles welded to form an box girder.
Base plates (3) for holding reversible Alloy-steel- blades (4) are for wooden log,
welded to the logs in such spacing (about 4 per ft.) and position that the blades.from
an interrupted spiral with a pitch angle of' 65 to 70°'and a diameter of 20 to 40 in
• Logs are made in 20 to 35 ft lengths an 2 log machines rotation is in opposite
directions, rising in the center.
• Boxes are normally of steel, hut often of wood, with adjustable overflow (6) and
sand-discharge spout (6). Clearance between blade-tip circle and 'box bottom should
he greater than the largest lump of feed
• The upper. 8 to 10 ft of the box is usually sprayed Normal speed range is 140 to 190
f.p.m on peripheral, the higher figure corresponding to the greater-blade-tip circle;,
speeds up to 240 f.p.m.

38. TUMBLING SCRUBBERS
• Drum scrubber in its simplest form is a cylindrical welded-steel shell, 5 to 7 ft. r by
8 to 25 ft. long, with plane or conical ends.
• It is mounted, with axis horizontal on tires and rollers, and revolved 10 or 12 rpm
by spur gear. It is lined with chilled or manganese-steel blocks, usually in alternate
course of smooth and lifter types , the lifters being set at an angle so as to both
elevated and convey settled material from feed to discharge end.
• Water and suspended fines flow through either concurrent or countercurrent by
reason of difference in diameter of feed and discharge opening
• Lifter of spiral or radial types on the discharge head a may be used to lift the
scrrubed rock to the discharge opening
• Feed size for standard construction is usually .4 -in.
• limiting Larger to 10-in. require larger-feed and
discharge openings and redesigned discharge-head
lifters.

39. Spiral clssifier
Spiral Classifier comprises an inclined tank a, of the same general nature as that of the rake type , and one
or two spirals b mounted on through-shaft c substantially parallel to the tank bottom. The spiral structure
effects the necessary agitation in the pool and conveys settled sand up the bottom to the sand-discharge lip
d. Feed is introduced substantially at pool level, through one or both side wall, at a distance from the
overflow weir e equal to about one half pool length. Pool level is main tamed as desired by adjusting the
height of e. Overflow drops into box f. piped away through g. .
Tank bottom Is rounded .Tank is usually made of steel but it may be of wood concrete, or special corrosion
resistant material The bottom is protected from wear by a sand layer below the reach of the spiral
spiral consists of sections of heavy steel ribbon of proper form and width fastened to the outer ends of arms
clamped to the large hollow shaft c .The ribbon forms a double-pitch screw White iron replaceable shoes
protect the ribbon

42. THANK YOU
VIJAY KUMAR
LECTURER IN MINING ENGG
GOVT. POLYTECHNIC ,BICHOLIM-GOA-INDIA