Comminution-Grinding (PPT) Flashcards
THE OPERATION OF APPLYING
A FORCE ON THE PARTICLE TO
BREAK IT IS CALLED ____
SIZE REDUCTION
____ IS A GENERAL TERM FOR SIZE REDUCTION THAT MAY BE APPLIED WITHOUT REGARD TO THE ACTUAL BREAKAGE
MECHANISM INVOLVED.
COMMINUTION
FRACTURE IN THE PARTICLE
OCCURS AS A RESULT OF
____.
APPLICATION OF A FORCE
WHEN A FORCE IS APPLIED
ON A PARTICLE, ____
WILL DEVELOP WITHIN THE
PARTICLE. WHEN THIS
STRESS EXCEEDS ULTIMATE
STRESS, THE PARTICLE WILL ____
___
STRESS
BREAK
occurs when a force (shear force) acts parallel to
the surface of the particle.
ATTRITION OR ABRASION
causes immediate fracture with no residual stresses.
IMPACT
can be applied at either a fast or a slow rate. Under the conditions of slow compression, energy applied is just sufficient to load comparatively few regions of the particle to the fracture point and only a few particles result. Their size is
comparatively close to the original particle size. Under the conditions of rapid loading such as in high velocity impact, applied energy is well in excess of that required for fracture.
COMPRESSIVE FORCE
the edges or corners of a particle will break due to the application of oblique forces, generally impact forces, on the particle.
CHIPPING
“𝑒𝑛𝑒𝑟𝑔𝑦 𝑜𝑓 𝑏𝑟𝑒𝑎𝑘𝑎𝑔𝑒 𝑖𝑠 𝑑𝑖𝑟𝑒𝑐𝑡𝑙𝑦 𝑝𝑟𝑜𝑝𝑜𝑟𝑡𝑖𝑜𝑛𝑎𝑙
𝑡𝑜 𝑡ℎ𝑒 𝑎𝑚𝑜𝑢𝑛𝑡 𝑜𝑓 𝑛𝑒𝑤 𝑠𝑢𝑟𝑓𝑎𝑐𝑒𝑠𝑝𝑟𝑜𝑑𝑢𝑐𝑒𝑑”
RITINGGER’S LAW
“the work input is proportional to the new
crack tip length produced in particle breakage”
BOND’S LAW
IS THE REPRESENTATION OF THE
HARDNESS OF THE MATERIAL OR THE
RESISTANCE OF THE MATERIAL TO
BREAKING OR CRUSHING. IT ALSO
REPRESENTS THE AMOUNT OF ENERGY
THAT IS NECESSARY TO REDUCE THE
MATERIAL INTO A SPECIFIED SIZE FROM A
SPECIFIED INITIAL SIZE ALSO.
WORK INDEX
EASE WITH WHICH
MATERIALS CAN BE COMMINUTED
ORE GRINDABILITY
TYPES OF COMMINUTION OPERATION
CRUSHING
GRINDING
is that operation or group of
operations in a Mineral Beneficiation
plant whose object is to reduce large
lumps to fragments, the coarsest
particles in the crushed product being
1/20 inch or more in size. The size of
coarsest particles is 1/2 inch in many
cases.
CRUSHING
The ratio of the maximum size of the particle in the feed to the maximum size of the particle in the product.
REDUCTION RATIO
CLASSIFICATIONS OF CRUSHER
Primary crushers
JAW CRUSHER
GYRATORY CRUSHER
CLASSIFICATIONS OF CRUSHER
SECONDARY CRUSHER
Reduction gyratory, Cone crusher, Rolls crusher
CLASSIFICATIONS OF CRUSHER
TERTIARY CRUSHER
SHORT-HEAD CONE CRUSHER
CLASSIFICATIONS OF CRUSHER
FINE CRUSHER
IMPACT CRUSHER
CLASSIFICATIONS OF CRUSHER
SPECIAL CRUSHER
Bradford Breaker, Toothed Roll crusher
Consist of two jaw plates set at an acute angle, to
each other which forms crushing chamber.
One jaw is fixed and kept vertical, the other jaw is
a movable or swing jaw and is moved to approach
and recede alternately from the fixed jaw.
JAW CRUSHER
has 1 toggle plate.
It has less weight and thus cheap
SINGLE-TOGGLE TYPE
has 2 toggle
plates and can crush materials that are
brittle, tough, and abrasive
DOUBLE TOGGLE TYPE
If the swing jaw is pivoted at
the top, it has a fixed
receiving area and variable
discharge area.
BLAKE CRUSHER
If the swing jaw is pivoted at the
bottom, it has a fixed discharge
area and variable receiving area
DODGE CRUSHER
If the swing jaw is pivoted at an
intermediate position, it has both variable
receiving and discharge areas
UNIVERSAL CRUSHER
distance between the 2 jaw
plates at the feed opening
GAPE
distance between the 2 jaw
plates at the discharge opening
SET
MINIMUM DISTANCE
SA BLAKE CRUSHER NI
CLOSED SET
MAXIMUM DISTANCE
SA BLAKE JAPON NI
OPEN SET
MAXIMUM AMPLITUDE
SA BLAKE
THROW
They consist of two vertical truncated conical
shells of which the outer hallow conical shell is
stationary and the inner solid conical shell is
made to gyrate. In a ____ the inner conical shell is pointing up and outer conical shell is pointing
down
GYRATORY CRUSHER
FIXED CRUSHING SURFACE IN GYRATORY CRUSHER
CONCAVE
MOVEABLE CRUSHING SURFACE IN GYRATORY CRUSHER
MANTLE
____ is the modification of
gyratory which has straight or curved heads and
concaves and used for secondary crushing.
REDUCTION GYRATORY CRUSHER
The ____ is a modified gyratory.
Both the outer and inner
conical shells are pointing
up
CONE CRUSHER
The most widely used type of cone
crusher.
SIMONS CONE CRUSHER
The ____ is another type
having a spherical steel head and used
for tertiary crushing.
TELSMITH GYRASPHERE
❖Used for tertiary crushing.
❖Short, Flat-angle liners.
GYRADISC
Can handle clay/plastic feed material
Can easily be installed in underground mines
Requires less floor area
Maintenance required
JAW CRUSHER
greater capacity than jaw crusher
cannot handle clayey materials
its large sections makes it difficult to install underground
requires large floor area
lesser maintenance required
GYRATORY CRUSHER
short spindle
spindle is not suspended
downward flare bowl
spring-protected bowl
CONE CRUSHER
longer spindle
suspended spindle
upward flare concave
no spring for concave
GYRATORY CRUSHER
____ consists of two smooth heavy
horizontal cylinders revolving towards
each other and the feed material is nipped
between the rolls and pulled downward
through the rolls by friction.
ROLL CRUSHER
____ reduce the particles by impact
forces applied through sharp blows of fixed or
free-swinging hammers revolving about central
rotor at high speed to the free-falling particles
against stationary surfaces.
IMPACT CRUSHER
HAMMER MILL (PIVOTED)
❖Hammers can weigh up to
____ kg
❖Feed size up to ____ cm
❖Rotor speeds between ____ RPM
100KG
20CM
500-3000 RPM
HAMMER MILL (FIXED)
❖Used for coarser crushing
~____𝑚𝑒𝑡𝑒𝑟𝑠
❖ Rotor speed is ____ RPM
❖Feed rate ____ MT/h
1.5 METERS
250-500 RPM
1500-3000 MT/h
It consists of a slightly inclined cylindrical
chamber with a perforated wall and rotates
about its axis at a low rpm
BRADFORD CRUSHER
In a roll crusher, the force of compression
and friction makes the particles to crush.
Rolls are subjected to high pressure so that
comminution takes place by compressive
forces as well as by inter-particle breakage.
The force applied to the crushing zone is
controlled by a hydro-pneumatic springs
HIGH PRESSURE GRINDING ROLLS
Impact crushing + High-intensity grinding + multi-particle pulverizing
TIDCO BARMAC CRUSHERS
WHEN THE MATERIAL FED TO THE CRUSHER IS AT A SLOW RATE, THE INDIVIDUAL PARTICLES ARE CRUSHED FREELY
FREE CRUSHING
WHEN THE MATERIAL FED TO THE CRUSHER IS AT A HIGH RATE, THE CRUSHER IS CHOKED, AND IT PREVENTS THE COMPLETE DISCHARGE OF CRUSHED PRODUCT
CHOKED FEEDING
THE FEED MATERIAL IS REDUCED BY ONE CRUSHER.
THE PRODUCT OF THIS CRUSHER IS SCREENED, AND ONLY OVERSIZE MATERIAL IS CRUSHED
BY ANOTHER CRUSHER OF SMALL SIZE AS THE THROUGHPUT IS LESS
OPEN CIRCUIT CRUSHING OPERATION
THE
OVERSIZE
MATERIAL FROM THE SCREEN IS
FED
BACK TO THE SAME
CRUSHER AS THE CIRCULATING
LOAD
CLOSED CIRCUIT CRUSHING OPERATION
AN OPERATION USED FOR THE
SEPARATION OF PARTICLES ACCORDING
TO THEIR SIZES.
SCREENING
WHY USE INDUSTRIAL SCREENING?
❖Sizing and classifying materials.
❖To grade materials.
❖To prepare a closely sized feed.
❖Trash removal and media recovery.
❖Dewatering.
❖Desliming.
MATERIAL FACTORS SA SCREENING
❖BULK DENSITY OF THE MATERIAL.
❖SIZE AND SIZE DISTRIBUTION OF THE PARTICLES.
❖SIZE OF THE PARTICLE RELATIVE TO THE APERTURE.
❖SHAPE OF THE PARTICLE.
❖MOISTURE CONTENT OF THE MATERIAL.
MACHINE FACTORS SA SCREENING
❖ SIZE OF THE APERTURE.
❖ SHAPE OF THE APERTURE.
❖ SIZE OF THE SCREEN SURFACE.
❖ PERCENT OPENING AREA.
❖ ANGLE OF INCIDENCE OF THE PARTICLE ON THE SCREEN SURFACE.
❖ SPEED AT WHICH THE PARTICLE STRIKES THE SCREEN SURFACE.
❖ THICKNESS OF THE MATERIAL ON THE SCREEN SURFACE.
❖ BLINDING OF THE SCREEN SURFACE.
❖ TYPE OF SCREENING.
❖ TYPE OF MOTION GIVEN TO THE SCREEN SURFACE.
❖ SLOPE OF THE SCREEN DECK.
❖ MECHANICAL DESIGN FOR SUPPORTING AND TIGHTENING THE SCREEN DECK.
Detachment or freeing of dissimilar particles from each other (valuable mineral particles and
gangue mineral particles)
LIBERATION
Contains both valuable and
gangue minerals
MIDDLING PARTICLES
TYPES OF MIDDLING
FURTHER SIZE REDUCTION INCREASE LIBERATION
RECTILINEAR
TYPES OF MIDDLING
DIFFICULT TO LIBERATE
VEIN
TYPES OF MIDDLING
FURTHER REDUCTION WILL INCREASE LIBERATION BUT A SIGNIFICANT PART ARE STILL VERY HARD TO LIBERATE
SHELL
TYPES OF MIDDLING
VERY FINE REDUCTION TREATMENT
OCCLUSIONS
When the run-of-mine ore is reduced in size to grain size of
valuable mineral, all the valuable mineral particles exist as free particles, no matter
whether remaining particles are free or locked particles of gangue minerals.
INTERGRANULAR LIBERATION
If the physical properties of the adjacent minerals are not so dissimilar, comminution to grain size does not result in rupturing the bond between adjacent dissimilar minerals. Fracture occurs across the grains producing locked particles. Hence to detach valuable mineral, the ore is further reduced in size.
TRANSGRANULAR LIBERATION
The percent of that mineral
liberated and occurring as free
particles in relation to the total
amount of the same mineral
present intheore.
DEGREE OF LIBERATION
Localized stresses at the
surface, occurs when insufficient energy is
applied to cause significant fracture of the
particles
ABRASION
Occurs when energy applied is
just sufficient to load comparatively few
regions of the particles to the fracture
25 point
CLEAVAGE
The applied energy is
well in excess of which is required for
fracture
SHATTER
CONSISTS
OF A HORIZONTAL ROTATING
STEEL SHELL SUPPORTED
BY END BEARINGS ON
WHICH HALLOW TRUNNIONS
REVOLVE
GRINDING MILL
is the last stage of the
comminution process. The particles are
reduced from a maximum upper feed
size of 3/8 inch, to some upper limiting
product size ranging between 35 mesh
and 200 mesh (420 microns and 74
microns).
GRINDING
used in Dry Grinding.
VIBRATORY FEEDER
the material is fed by gravity
SPOUT FEEDER
the entire mill feed enters the drum, and an
internal spiral carries it and fed to the mill.
DRUM FEEDER
the material is fed to the drum and
the scoop picks it up and fed to the mill. ____ are
sometimes used in place
SCOOP FEEDER
❖ lined by replaceable liners usually made of alloy steel but sometimes of rubber.
❖ Some types of liners are smooth, shiplap, wave, wedge bar, rib, stepped, osborn, lorain, etc.
INTERIOR OF GRINDING MILL
❑Loose crushing bodies
❑Either steel balls, rods, pebbles
❑Attrition or shearing forces
GRINDING MEDIA
THE INTERNAL WORKING FACES
OF MILLS CONSIST OF RENEWABLE LINERS, WHICH MUST WITHSTAND IMPACT, BE WEAR RESISTANT, AND PROMOTE THE MOST FAVORABLE MOTION OF THE CHARGE
MILL SHELL LINERS
the mill shell is rotated, and motion is imparted to the charge
via the mill shell. The grinding medium may be steel rods, balls, or rock itself.
TUMBLING MILLS
the mill shell with either a horizontal or a vertical orientation is stationery and motion is imparted to the charge by the movement of an internal stirrer.
STIRRED MILLS
TYPES OF DISCHARGE
OVERFLOW
GRATE DISCHARGE
CRUSHED ORE + WATER + GRINDING MEDIUM
Mill Charge
uses steel or iron balls as
grinding medium. ____ usually
have a length to diameter ratio of
1.5 to 1.0
BALL MILL
According to the shape of the mill,
the ball mills are classified as ____
and cylindrical mills
CYLINDROCONICAL
An ____ where no balls occupy this zone
during operation.
EMPTY ZONE
A ____ where no grinding takes place.
DEAD ZONE
A ____ where balls roll on each
other and grinding takes place by slippage
between ball layers before they are lifted.
ZONE OF CIRCULAR PATH
A ____ where the balls spread
out and falldown.
ZONE OF PARABOLIC PATH
simple rolling of one
ball over the other
CASCADING
FREE FALL OF BALLS
Cataracting
As the speed of the mill increases, the balls are lifted higher and a stage is reached where the balls are carried around the shell and never allowed to fall.
CENTRIFUGING
- the material is fed at both ends of the mill.
- The product is discharged through a
70 circumferential port at the centre of the shell.
CENTER PERIPHERAL DISCHARGE MILL
- the material is fed at one end of the mill.
- the ground product is discharged from the
other end.
END PERIPHERAL DISCHARGE MILL
discharge grates are fitted through which
pulp flows freely and lifted-up to the level of
the discharge trunnion
GRATE DISCHARGE MILL
The material is fed at one end and the
product is discharged through the other
end by overflow
OVERFLOW DISCHARGE MILL
❖A ____ is a grinding mill where length to
diameter ratio is 3 to 5.
❖It is also known as a pebble mill as it uses ceramic
pebbles made of flint or porcelain as the grinding
media.
TUBE MILL
are used when iron contamination in
the product is highly objectionable such as in the
manufacture of paints, pigments, cosmetics, etc.
PEBBLE MILL
❖____use coarse ore particles as grinding medium.
❖Grinding is achieved by the action of ore
particles on each other when particles of
ore of different sizes are rotated together
in a tumbling mill.
AUTOGENOUS MILL
❖Autogenous grinding differs from
grinding with metal balls or rods in
that the breakage is much more
confined to zones of weakness in the
rock, such as ____ and ____.
CRYSTAL SURFACES AND FINE CRACKS
uses a combination of the ore and a
reduced charge of balls or rods as a grinding
medium to overcome the difficulties
encountered in autogenous grinding.
SEMI AUTOGENOUS MILL
IS USUALLY CARRIED OUT WITH 20–35%
WATER BY WEIGHT. THE CHIEF ADVANTAGES OF ____ ARE INCREASED CAPACITY (AS MUCH AS 15%)
FOR A GIVEN SIZE OF EQUIPMENT AND LESS POWER
CONSUMPTION PER TON OF THE PRODUCT.
WET GRINDING
____ IS USED WHENEVER PHYSICAL OR
CHEMICAL CHANGES IN THE MATERIAL OCCUR IF WATER IS
ADDED. IT CAUSES LESS WEAR ON THE LINERS AND
GRINDING MEDIA
DRY GRINDING
IS THE TERM USED TO DESIGNATE THE
SIZE OF THE GROUNDED PRODUCT IN TERMS OF THE
PERCENTAGE OF THE MATERIAL PASSING THROUGH A
GIVEN MESH
MESH OF GRIND
WHEN A GRINDING MILL IS FED
WITH A MATERIAL, IT SHOULD BE AT A RATE CALCULATED
TO PRODUCE THE CORRECT PRODUCT IN ONE PASS
OPEN CIRCUIT GRINDING
WHEN THE MATERIAL OF THE
REQUIRED SIZE IS REMOVED BY A CLASSIFIER FROM THE
GROUND PRODUCT TO SEND TO THE SUBSEQUENT
OPERATION AND OVERSIZE IS RETURNED TO THE SAME
GRINDING MILL
CLOSED CIRCUIT GRINDING
THE AMOUNT OF SOLIDS BY WEIGHT
FED BACK TO THE GRINDING MILL
CIRCULATING LOAD
