Mechanical Operations Flashcards
Short distance transportation of grain, gravel, sand, ash, asphalt etc. is done by using a __________ conveyor.
- flight
- slat or drag
- ribbon
- screw
screw
Equivalent diameter of a particle is the diameter of the sphere having the same
- ratio of surface to volume as the actual volume.
- ratio of volume to surface as the particle.
- volume as the particle.
- none of these.
ratio of surface to volume as the actual volume.
If dp is the equivalent diameter of a non-spherical particle, Vp its volume and sp its surface area, then its sphericity is Φs is defined by
- Φs = 6 Vp/dp sp
- Φs = Vp/dp sp
- Φs = 6 dp Sp/Vp
- Φs = dp Sp/Vp
Φs = 6 Vp/dp sp
Power required to drive a ball mill with a particular ball load is proportional to (where, D = diameter of ball mill )
- D
- 1/D
- D^2.5
- 1/D^2.5
D^2.5
Pick out the wrong statement.
- Recycled coarse material to the grinder by a classifier is termed as circulating load.
- Wear and tear in wet crushing is more than that in dry crushing of materials.
- Size enlargement (opposite of size reduction) is not a mechanical operation.
- A ‘dust catcher’ is simply an enlargement in a pipeline which permits the solids to settle down due to reduction in velocity of the dust laden gas.
Size enlargement (opposite of size reduction) is not a mechanical operation.
In continuous filtration (at a constant pressure drop), filtrate flow rate varies inversely as the
- square root of the velocity.
- square of the viscosity.
- filtration time only.
- washing time only.
square root of the velocity.
For sizing of fine materials, the most suitable equipment is a
- trommel
- grizzly
- shaking screen
- vibrating screen
vibrating screen
Which of the following is not categorised as a “mechanical operation” ?
- Agitation
- Filtration
- Size enlargement
- Humidification
Humidification
Which of the following is a pressure filter ?
- Leaf filter (Moore filter).
- Plate and flame filter.
- Rotary drum filter.
- Sand filter.
Plate and flame filter.
Tabular bowl centrifuges as compared to disk bowl centrifuges
- operate at higher speed.
- employ bowl of larger diameter.
- can not be operated under pressure/vacuum.
- can’t be used for separation of fine suspended solids from a liquid.
operate at higher speed.
Pebble mills are tumbling mills widely used for grinding in the manufacture of paints & pigments and cosmetic industries, where iron contamination in the product is highly objectionable. Pebbles used in pebble mill are made of
- bronze
- stainless steel
- flint or porcelain
- concrete
flint or porcelain
Filter aids like asbestos, kieselguhr, diatomaceous earth etc. are used to increase the porosity of the final filter cake & reducing the cake resistance during filtration. Filter aid is
- added to the feed slurry.
- precoated on the filter medium prior to filtration.
- separated from the cake by dissolving solids or by burning it off.
- all ‘a’, ‘b’&’c’.
all ‘a’, ‘b’&’c’.
Which of the following relationships between co-efficinet of friction (μ) between rock & roll and a (half of the angle of nip) of the particle to be crushed is correct ?
- μ > tan α
- μ ≥ tan α
- μ > tan 2α
- μ ≤ tan α
μ ≥ tan α
Pick out the wrong statement pertaining to the roll crushers.
- Maximum feed size determines the required roll diameter.
- For hard material’s crushing, the reduction ratio should not exceed 4.
- Both the rolls run necessarily at the same speed.
- Reduction ratio and differential roll speed affect production rate & energy consumed per unit of surface produced.
Both the rolls run necessarily at the same speed.
Which of the following is not an ultrafine grinder (colloid mill)?
- Micronizers
- Agitated mills and fluid energy mills
- Toothed roll crusher
- Hammer mills with internal classification
Toothed roll crusher
Two particles are called to be equal settling, if they are having the same.
- size.
- specific gravity.
- terminal velocities in the same fluid & in the same field of force.
- none of these.
terminal velocities in the same fluid & in the same field of force.
Which of the following is the most suitable for handling fibrous and dense slurries ?
- Propeller agitator
- Cone type agitator
- Turbine agitator
- Radial propeller agitator
Cone type agitator
__________ centrifuge is normally used in sugar mills.
- Tubular bowl
- Disc-bowl
- Suspended batch basket
- Perforated horizontal basket continuous
Suspended batch basket
Solid particles separation based on the difference in their flow velocities through fluids is termed as the
- clarification
- classification
- elutriation
- sedimentation
classification
Diatomaceous earth is a/an
- explosive
- filter aid
- filter medium
- catalyst
filter aid
The distribution given by microscopic analysis of powder is
- number
- length
- area
- volume
number
Number of particles in a crushed solid sample is given by (where, m = mass of particles in a sample, Vp = volume of one particle, ρ= density of particles)
- m/ρ . Vp
- m. ρ/Vp
- m . Vp/ρ
- Vp/m . ρ
m/ρ . Vp
For a non-spherical particle, the sphericity
- is defined as the ratio of surface area of a sphere having the same volume as the particle to the actual surface area of the particle.
- has the dimension of length.
- is always less than 1.
- is the ratio of volume of a sphere having the same surface area as the particle to the actual volume of the particle.
is defined as the ratio of surface area of a sphere having the same volume as the particle to the actual surface area of the particle.
In washing type plate and frame filter press, the ratio of washing rate to the final filtrate rate is
- 4
- 1/4
- 1
- 1/2
1/4
Ball mills and tube mills with flint or porcelain balls are used for size reduction of
- asbestos
- rubber
- non-metallic ores
- limestone
non-metallic ores
Size reduction of __________ is accomplished in steam heated rollers and roll crushers.
- resins
- gums
- hard rubber
- waxes
hard rubber
The capacity of a belt conveyor depends upon two factors. If one is the cross-section of the load, the other is the __________ of the belt.
- speed
- thickness
- length
- none of these
speed
Which of the following is not a part of the Blake jaw crusher?
- Hanger
- Check plates
- Toggles
- Pitman
Hanger
If a force greater than that of gravity is used to separate solids & fluids of different densities, the process is termed as the
- sedimentation
- flocculation
- dispersion
- centrifugation
centrifugation
Filter aid is used to
- increase the rate of filtration.
- decrease the pressure drop.
- increase the porosity of the cake.
- act as a support base for the septum.
increase the porosity of the cake.
Which of the following mineral dressing operations is termed as ‘comminution’?
- Panning
- Spiralling
- Tabling
- None of these
None of these
The capacity of a pneumatic conveying system depends upon the
- bulk density of materials.
- pressure of the conveying air.
- diameter of the conveying line.
- all (a), (b) and (c).
all (a), (b) and (c).
Pick out the wrong statement.
- Close circuit grinding is more economical than open circuit grinding.
- Cod oil, beef tallow or aluminium stearates are used as grinding aids in cement ‘industries’.
- The equipment used for the removal of traces of solids from a liquid is called a classifier.
- Size enlargement is a mechanical operation exemplified by medicinal tablet making.
The equipment used for the removal of traces of solids from a liquid is called a classifier.
Gravity settling process is not involved in the working of a
- hydrocyclone
- classifier
- dorr-thickener
- sedimentation tank
hydrocyclone
Froth floatation is the most suitable for treating
- iron ores
- sulphide ores
- quartzite
- none of these
sulphide ores
The energy required per unit mass to grind limestone particles of very large size to 100 μm is 12.7 kWh/ton. An estimate (using Bond’s law) of the energy to grind the particles from a very large size to 50 μm is
- 6.35 kWh/ton
- 9.0 kWh/ton
- 18 kWh/ton
- 25.4 kWh/ton
18 kWh/ton
Which of the following is the most suitable for cleaning of fine coal dust (<0.5 mm) ?
- Trough washer
- Baum jig washer
- Spiral separator
- Froth floatation
Froth floatation
Pick out the correct statement:
- Removal of iron from ceramic material is necessitated (by magnetic separation method) so as to avoid discolouration of ceramic products.
- The operating cost of shaking screen is more than that of a vibrating screen.
- Screen capacity does not depend upon the specific gravity of the minerals.
- Asphalt is best crushed using toothed roll crusher.
Removal of iron from ceramic material is necessitated (by magnetic separation method) so as to avoid discolouration of ceramic products.
Range of compressibility co-efficient of the commercial compressible cake obtained in filtration operation is
- 0.01 to 0.1
- 0.1 to 0.3
- 0.2 to 0.8
- 0.2 to 0.4
0.2 to 0.8
Highly viscous liquids & pastes are agitated by
- propellers
- turbine agitators
- multiple blade paddles
- none of these
multiple blade paddles
The value of ‘angle of nip’ is generally about
- 16°
- 32°
- 52°
- 64°
32°
Size reduction of the __________ can be suitably done by ball mills, crushing rolls and rod mills.
- metalliferrous ores
- non-metallic ores
- basic slags
- asbestos & mica
metalliferrous ores
Sulphuric acid mist is arrested by using a __________ scrubber.
- packed wet
- hollow wet
- venturi
- co-current
venturi
The main size reduction operation in ultrafine grinders is
- cutting
- attrition
- compression
- impact
attrition
In case of a hammer crusher,
- crushing takes place by impact breaking.
- maximum acceptable feed size is 30 cms.
- reduction ratio can be varied by adjusting the distance from cage to hammers.
- all (a), (b) and (c).
all (a), (b) and (c).
Jigging is a technique by which different particles can be
- separated by particle size.
- separated by particle density.
- separated by particle shape.
- mixed.
separated by particle size.
Crushing of mineral particles is accomplished in a ‘cage mill’, when one or more alloy steel bars are revolved in opposite directions. It is a type of __________ mill.
- impact
- roll
- vibratory
- none of these
impact
Balls for ball mills are never made of
- forged/cast steel
- lead
- cast iron
- alloy steel
lead
200 mesh screen means 200 openings per
- cm^2
- cm
- inch
- inch^2
inch
__________ is the most commonly used ‘filter aid’.
- Diatomaceous earth
- Fuller’s earth
- Vermiculite
- Semi-plastic clay
Diatomaceous earth
Energy consumed for crushing one ton of material ranges from __________ kWh.
- 0.01 to 0.1
- 0.5 to 1.5
- 2 to 3.5
- 4 to 5.
0.5 to 1.5
For transporting pasty material, one will use a/an
- apron conveyor
- belt conveyor
- screw conveyor
- bucket elevator
screw conveyor
Where the density difference of the two liquid phase to be separated is very small (as in milk cream separator), the most suitable separator is a
- disc bowl centrifuge.
- sharpies supercentrifuge.
- batch basket centrifuge.
- sparkler filter.
disc bowl centrifuge.
A tube mill compared to a ball mill
- has a higher length/diameter ratio.
- produces a coarser product.
- has a higher diameter/length ratio.
- uses much larger balls.
has a higher length/diameter ratio.
Trommels separate a mixture of particles depending on their
- size
- density
- wettability
- electrical & magnetic properties
size
Basic slag is not ground in
- jaw crushers
- ball mills
- compartment mills
- tube mills
jaw crushers
Grindability of a material does not depend upon its
- elasticity
- hardness
- toughness
- size
size
Shape factor for a cylinder whose length equals its diameter is
- 1.5
- 0.5
- 1.0
- 2.0
1.5
In case of a hammer crusher, the
- feed may be highly abrasive (Moh’s scale >5).
- minimum product size is 3 mm.
- maximum feed size may be 50 mm.
- rotor shaft carrying hammers can be vertical or horizontal.
rotor shaft carrying hammers can be vertical or horizontal.
Dust laden air can be purified using a
- cyclone separator
- bag filter
- gravity settler
- tubular centrifuge
cyclone separator
Rittinger’s number designates the new surface created per unit mechanical energy absorbed by the material being crushed. Larger value of Rittinger’s number of a material indicates its
- easier grindability
- poor grindability
- high power consumption in grinding
- none of these
easier grindability
Capacity (in tons/hr) of jaw/gyratory crusher is equal to (where, L = length of the receiving opening, cm S = greater width of the discharge opening, cm)
- 0.01 L.S
- 0.087 L.S
- L.S
- L.S/0.087
0.087 L.S
Vacuum is applied in __________ zone, in case of a general type continuous rotary drum vacuum filter.
- filtering
- washing
- drying
- all (a), (b) & (c)
all (a), (b) & (c)
General crushing equation is given by d(P/m)= - K (dDₛ/Dₛⁿ). Bond’s crushing law is obtained by solving this equation for n = __________ and feed of infinite size.
- 1
- 1.5
- 2
- 2.5
1.5
Which of the follwoing mechanical conveyors does not come under the division ‘scrapers’ ?
- Ribbon conveyor
- Flight conveyor
- Bucket elevators
- Drag conveyor.
Bucket elevators
__________ mixer is used for devulcanisation of rubber scrap & making water dispersion & rubber solution.
- Tumbler
- Banbery
- Muller
- Rubbon blender
Banbery
Which of the following mechanical conveyors does not come under the division ‘carriers’ ?
- Belt conveyor
- Bucket elevator
- Screw conveyor
- Apron conveyor.
Screw conveyor
Screen capacity is not a function of
- its openings size.
- screening mechanism.
- screening surface.
- atmospheric humidity.
atmospheric humidity.
Which of the following is a vacuum filter ?
- Filter press
- Rotary disc filter
- Batch basket centrifuge
- Tank filter (Nutsch filter)
Rotary disc filter
Pine oil used in froth floatation technique acts as a/an
- collector
- modifier
- frother
- activator
frother
Length/diameter ratio of a ball mill is
- 1.5
- 1
- < 1
- > 1
< 1
Feed size of ≥ 25 cms can be accepted by
- ball mill
- rod mill
- fluid energy mill
- jaw crusher
jaw crusher
Which is the most suitable conveyor for transportation of sticky material ?
- Apron conveyor
- Belt conveyor
- Screw conveyor
- Pneumatic conveyor
Screw conveyor
The most suitable equipment for removing the fine dust particle (< 1 micron dia.) from air below its dew point will be a/an
- bag filter
- electrostatic precipitator
- cyclone separator
- wet scrubber
electrostatic precipitator
Laminar flow region is said to exist during agitation of a liquid in an agitator, when the value of Reynolds number is
- > 10
- <10
- > 100
- <100
<10
Filtration of water in a paper mill is done by a/an __________ filter.
- open sand
- plate and frame
- vacuum leaf
- sparkler
open sand
Moore filter is a __________ filter.
- leaf
- press
- rotary
- sand
leaf
Sphericity of a cubical particle, when its equivalent diameter is taken as the height of the cube, is
- 0.5
- 1
- √2
- √3
1
Ball mill is used for
- crushing
- coarse grinding
- fine grinding
- attrition
fine grinding
In case of a ball mill,
- coarse feed requires a larger ball.
- fine feed requires a larger ball.
- operating speed should be more than the critical speed.
- none of these
coarse feed requires a larger ball.
Maximum size reduction in a ball mill is done by the, __________ action.
- attrition
- compression
- impact
- cutting
impact
increasing the capacity of a screen __________ the screen effectiveness.
- decreases.
- increases
- does not effect
- none of these
decreases.
The power number for a stirred tank becomes constant at high Reynolds number. In this limit, the variation of power input with impeller rotational speed (N) is proportional to
- N°
- N^1
- N^2
- N^3
N^2
Bond crushing law
- calls for relatively less energy for the smaller product particles, than does the Rittinger law.
- is less realistic in estimating the power requirements of commercial crushers.
- states that the work required to form particle of any size from very large feed is proportional to the square root of the volume to surface ratio of the product.
- states that the work required for the crushing is proportional to the new surface created.
calls for relatively less energy for the smaller product particles, than does the Rittinger law.
Flow of filtrate through the cake in a plate and frame filter press is best described by the __________ equation.
- Kozney-Karman
- Hagen-Poiseulle’s
- Fanning’s
- Kremser
Kozney-Karman
The controlling resistance in a rotary drum vacuum filter is the __________ resistance.
- piping
- cake
- filter medium
- none of these
cake
Which of the following is used for primary crushing of very hard lumpy materials ?
- Toothed roll crusher
- Gyratory crusher
- Ball mill
- Tube mill
Gyratory crusher
Coal is finally pulverised to 200 mesh size for burning in boilers by a
- hammer crusher
- ball mill
- roll crusher
- gyratory crusher
ball mill
Crushing efficiency is the ratio of the
- surface energy created by crushing to the energy absorbed by the solid.
- energy absorbed by the solid to that fed to the machine.
- energy fed to the machine to the surface energy created by crushing.
- energy absorbed by the solid to the surface energy created by crushing.
surface energy created by crushing to the energy absorbed by the solid.
The resistance offered by the filter used in a bag filter is proportional to (where, c = dust concentration, and s = particle size )
- c/s
- s/c
- s . c
- 1/s . c
c/s
Cement clinker is reduced to fine size by a
- roll crusher
- ball mill
- tube mill
- hammer mill
tube mill
The crushed material received for separation is called feed or
- tailing
- heading
- concentrate
- middling
heading
For spheres, volume shape factor is given by
- π(=A/D²)
- 2π(=2A/D²)
- π/6(=V/D³)
- AD/V
π/6(=V/D³)
Which of the following agitators having a large blade area, rotating at slow speed is used for mixing high viscosity liquids ( > 50000 centipoise) ?
- Propeller
- Helical screw
- Flat blade turbine
- Curved blade turbine
Helical screw
__________ is defined as the geometric mean of the relative rejections and the relative recoveries of two minerals.
- Separation efficiency
- Selectivity index
- Concentration ratio
- none of these
Selectivity index
The operating speed of a ball mill should be __________ the critical speed.
- less than
- much more than
- at least equal to
- slightly more than
less than
__________ are used for the separation of coarse particles from a slurry of fine particles.
- Thickeners
- Classifiers
- Hydrocyclones
- Decanters
Classifiers
Fibrous material is broken by a
- rollcrusher
- squirrel-cage disintegrator
- ball mill
- tube mill
squirrel-cage disintegrator
__________ is the most suitable for compounding rubber and plastic solids.
- Banbery mixer
- Pan mixer
- Pug mill
- Charge can mixer
Banbery mixer
Out of the following size reduction equipments, the maximum feed size can be accepted by the
- tube mill
- ball mill
- jaw crusher
- jet pulveriser
jaw crusher
Bucket elevators are not suitable for the vertical lifting of __________ materials.
- fine (e.g. - 200 mesh size coal)
- sticky (e.g. clay paste)
- small lumpy (e.g. grains and sand)
- free flowing
sticky (e.g. clay paste)
The most common filter aid is
- diatomaceous earth
- calcium silicate
- sodium carbonate
- silica gel
diatomaceous earth
For removal of very small amounts of precipitate from large volume of water, the most suitable filter is the __________ filter.
- plate & frame
- shell & leaf
- sand
- rotary vacuum
sand
For separation of sugar solution from settled out mud, we use a __________ filter.
- sparkler
- plate and frame
- centrifugal
- rotary drum vaccum
centrifugal
The sphericity of a cylinder of 1 mm diameter and length 3 mm is
- 0.9
- 0.78
- 0.6
- 0.5
0.9
Pulverised coal passing through 200 mesh screen has a diameter of 0.074 mm (74 micron). The same passing through 50 mesh screen will have a dia of __________ mm.
- 0.007
- 0.30
- 50
- 0.014
0.30
What is the selectivity index, if the grade of tailings & concentrate is the same ?
- 0
- ∞
- 1
- 0.5
1
The most suitable equipment used to devulcanise rubber scrap and to make water dispersion & rubber solution is a
- boundary mixer.
- propeller agitator.
- sharpies centrifuge.
- none of these.
boundary mixer.
Traces of solids are removed from, liquid in a
- classifier
- clarifier
- sparkler filter
- rotary vacuum filter
clarifier
__________ balls capable of grinding the feed in a ball mill gives the maximum efficiency.
- Cast iron
- Minimum size
- Maximum size
- Elliptical
Minimum size
The speed of a rotary drum vacuum filter may be about __________ rpm.
- 1
- 50
- 100
- 500
1
Colloid mills achieve size reduction mainly by
- impact
- attrition
- cutting
- compression
attrition
Mesh indicates the number of holes per
- square inch
- linear inch
- square foot
- linear foot
linear inch
For achieving maximum capacity of the ball mill, the ball charge should be equal to about __________ percent of the ball mill volume.
- 10
- 25
- 50
- 75
50
According to Bond crushing law, the work required to form particle of size ‘D’ from very large feed is (where (S/V)p and (S/V)f are surface to volume ratio of the product and feed respectively).
- (S/V)p
- √(S/V)p
- (S/V)²p
- (S/V)f
√(S/V)p
Which of the following gives the work required for size reduction of coal to -200 mesh in a ball mill most accurately ?
- Rittinger’s law
- Kick’s law
- Bond’s law
- none of these
Rittinger’s law
Electrical energy consumed by a jaw crusher is not a function of the
- average feed size
- average product size
- machine capacity
- none of these
none of these
Size reduction mechanism used in Jaw crushers is
- attrition
- compression
- cutting
- impact
compression
Trommels employ __________ for screening of materials.
- fibrous cloth
- woven wire screen
- punched plate
- none of these
punched plate
A widely used size reduction equipment for __________ is Bradford breaker.
- talc
- coal
- iron core
- wheat
coal
Ultra centrifuges are used for the separation of __________ solid particles.
- coarse
- fine
- colloidal
- dissolved
colloidal
Specific surface area is the surface area of a unit __________ of materials.
- weight
- volume
- either (a) or (b)
- neither (a) nor (b)
either (a) or (b)
A __________ mill is a revolving mill divided into two or more sections by perforated partitions in which preliminary grinding takes place at one end and the finishing grinding at the discharge end.
- compartment
- tube
- rod
- pebble.
compartment
Size reduction does not occur due to compression in case of
- rod mills
- gyratory crushers
- jaw crushers
- smooth roll crushers
rod mills
According to Taggart’s rule for selecting between a gyratory crusher and a jaw crusher; the later should be used, if the hourly tonnage to be crushed divided by the square of the gape expressed in cm is less than
- 0.00184
- 0.0184
- 0.184
- 1.84
0.0184
Which of the following represents the plot of filtrate volume versus time for constant pressure filtration ?
- Parabola
- Straight line
- Hyperbola
- Exponential curve
Parabola
Driving force in case of filtration by a centrifuge is the
- speed of the centrifuge.
- centrifugal pressure exerted by the liquid.
- narrow diameter of the vessel.
- formation of highly porous cake.
centrifugal pressure exerted by the liquid.
Rod mills employed for grinding
- employ a steel shell having L/D ratio of 1.5 to 3.0.
- is useful for handling sticky materials.
- employ steel rods of 2-12 cms diameter extending over full length of the mill.
- all ‘a’, ‘b’ & ‘c’.
all ‘a’, ‘b’ & ‘c’.
Production rate __________ with increased fineness, with a given energy input to the size reduction machine.
- decreases
- increases
- remains unchanged
- may increase or decrease; depends on the machine
decreases
Gold ore concentration is mostly done using
- jigging
- tabling
- froth floatation
- elutriation
tabling
Mixing of light fine powder such as insecticides is done by
- banbery mixer
- pug mill
- impact wheels
- kneader
impact wheels
Run of mine (ROM) coal is crushed by a __________ for use in domestic ovens.
- jaw crusher
- hammer crusher
- ball mill
- tube mill
hammer crusher
Sphericity is the ratio of the surface area of a spherical particle having the same volume as the particle to the surface area of the particle. Which of the following has the maximum value of sphericity ?
- Sphere
- Cube
- Cylinder (L/D = 1)
- Raschig rings
Sphere
The unit of specific cake resistance is
- gm/cm^2
- cm/gm
- cm/gm^2
- gm/gm
gm/cm^2
Size reduction of asbestos and mica is done by
- hammer mills
- rod mills
- gyratory crushers
- crushing rolls
hammer mills
The study on washability of coal is done by using the __________ technique.
- tabling
- elutriation
- heavy media separation
- none of these
heavy media separation
A suspension of glass beads in ethylene glycol has a hindered settling velocity of 1.7 mm/s, while the terminal settling velocity of a single glass bead in ethylene glycol is 17 mm/s. If the Richardson-Zaki hindered settling index is 4.5, the volume fraction of solids in the suspension is
- 0.1
- 0.4
- 0.6
- none of these
0.6
__________ conveyor is the most suitable for long distance transportation of cold, non-abrasive granular/irregular shape/fine materials.
- Bucket
- Belt
- Screw
- Apron
Belt
The specific cake resistance for compressible sludges is a function of the pressure drop
- over cake
- over medium
- overall
- none of these
over cake
Moisture can be removed from lubricating oil using
- tubular centrifuge
- clarifier
- sparkler filter
- vacuum leaf filter
tubular centrifuge
Tabling process used for separating two materials of different densities by passing the dilute pulp over a table/deck, which is inclined from the horizontal surface at an angle of about
- 1 to 2°
- 2 to 5°
- 5 to 10°
- 10 to 15°
2 to 5°
Pick out the wrong statement.
- Gape is the greatest distance between the crushing surfaces or the jaws.
- The angle of nip (2α) is the angle between roll faces at the level where they will j ust take hold of a particle and draw it in the crushing zone.
- Crushing efficiency is the ratio of the energy absorbed by the solid to the surfaces energy created by crushing.
- Reduction ratio is the ratio of the maximum size of the particles in the feed to that in the product.
Crushing efficiency is the ratio of the energy absorbed by the solid to the surfaces energy created by crushing.
Addition of filter aid to the slurry before filtration is done to _____ of the cake.
- increase the porosity
- increase the compressibility co-efficient
- decrease the porosity
- decrease the compressibility co-efficient
increase the porosity
Which of the following terminology is not used for size reduction of materials to fine sizes or powders?
- Comminution
- Dispersion
- Pulverisation
- Compression
Compression
A tube mill as compared to a ball mill
- employs smaller balls.
- gives finer size reduction but consumes more power.
- has larger length/diameter ratio (>2 as compared to 1 for ball mill).
- all (a), (b) and (c).
all (a), (b) and (c).
Kick’s law assumes that the energy required for size reduction is proportional to the logarithm of the ratio between the initial and the final diameters. The unit of Kick’s constant is
- kW. sec/kg
- kWh/kg
- kWh/sec. kg
- kg/sec.
kW. sec/kg
Which of the following gives the crushing energy required to create new surface ?
- Taggarts rule
- Fick’s law
- Rittinger’s law
- none of these
Rittinger’s law
In filtration, the use of ‘filter aid’ helps in
- reducing the filtration pressure.
- accelerating the rate of filtration.
- deplugging the filter medium.
- enhancing the cake porosity in case of a dense impermeable cake.
deplugging the filter medium.
Critical Speed (Nc) of a ball mill is given by(where R1 andR2 are radii of ball mill and the ball respectively).
- Nc = (1/4n) √[g/(R1-R2)]
- Nc = (1/2n) √[g/(R1-R2)}
- Nc = (1/n) √[g/(R1-R2)}
- Nc = (1/2n) √[(R1-R2)/g]
Nc = (1/2n) √[g/(R1-R2)}
Gizzlies are used for separating __________ solids.
- coarse
- fine
- any size
- none of these
fine
Which of the following clay mixing devices is vacuum operated for deairation of clay?
- Banbery mixer
- Pug mill
- Muller-mixer
- None of these
Pug mill
Pick out the material having minimum Rittinger’s number.
- Calcite
- Pyrite
- Quartz
- Galena
Quartz
__________ mills are termed as impactors.
- Hammer
- Cage
- Rolling-compression
- none of these
Hammer
In case of a revolving mill, wet grinding compared to dry grinding
- requires more energy.
- has less capacity.
- complicates handling & classification of the product.
- none of these.
none of these.
To get a fine talc powder from its granules, the equipment used is
- roller crusher
- ball mill
- jaw crusher
- gyratory crusher
ball mill
For a cyclone of diameter 0.2 m with a tangential velocity of 15 m/s at the wall, the separation factor is
- 2250
- 1125
- 460
- 230
230
Higher is the mesh number, smaller will be the aperture size of the screen. It means that the aperture size of a 200 mesh screen will be smaller than that of 20 mesh screen. This is valid for
- British standard screens.
- German standard screens (DIN 1171) etc.
- American standard screens (ASTM and Tyler standard screens).
- all (a), (b) and (c).
all (a), (b) and (c).
Pick out the wrong statement.
- Cummulative analysis for determining surface area is preferred over differential analysis, because of the assumption that “all particles in a simple fraction equal in size” is not needed for cummulative anslysis unlike differential anlaysis.
- A gate diagram is a plot of cummulative percent by weight undersize vs. the reciprocal of diameter, in which the area beneath the curve represents the surface.
- Capacity of crusher in choke feeding is increased.
- Rolling of pebbles/balls from top to bottom of the heap in tumbling mills is called ‘cascading and throwing of the balls through the air to the toe of the heap is called ‘cataracting’.
Capacity of crusher in choke feeding is increased.
Which of the following size reduction equipments employs mainly attrition for ultrafine grinding ?
- Jet mills
- Fluid energy mill
- Micronizer
- all (a), (b) and (c)
all (a), (b) and (c)
Tank filter (e.g., Nutsch filter) is
- a high pressure filter.
- a continuous filter.
- used for small scale filtration work.
- a leaf filter.
used for small scale filtration work.
In bag filters, filter fabrics are never made of
- metallic wire woven mesh
- polyester fibres
- cotton fibres
- nylon fibres
metallic wire woven mesh
Use of ‘grinding aids’ is done in __________ grinding.
- dry
- wet
- ultrafine
- intermediate
dry
Height of liquid in agitation tank is normally maintained equal to the tank diameter. However, if the tank is too tall and a large liquid hold up is desired, then two or more impellers mounted on the same shaft may be used. The clearance between the tank bottom and the bottom most impeller should be about (where, D = impeller diameter)
- 0.5 D
- D
- 1.5 D
- 2 D
D
Which of the following is the most suitable filter for separation of abrasive solids suspended in a corrosive liquid ?
- Sand bed filter
- Plate and frame filter press
- Vacuum filter
- Batch basket centrifuge.
Vacuum filter
All resistances during washing of cake
- increases
- decreases
- remain constant
- none of these
remain constant
A __________ mixer resembles a ball mill without balls.
- banbery
- pug mill
- tumbling
- pan
tumbling
__________ conveyor is the most suitable for short distance transportation of non-abrasive loose materials like garbage, grain, food wastes etc.
- Flight
- Screw
- Drag
- Belt
Flight
As the product becomes finer, the energy required for grinding
- decreases
- increases
- is same as for coarser grinding
- is 1.5 times that for coarser grinding
increases
Gyratory crushers compared to the reciprocating jaw crushers
- have greater capacity per unit of discharge area.
- crush intermittantly.
- are less suitable for coarse materials.
- have less steady power consumption.
have greater capacity per unit of discharge area.
At low Reynold’s number, the power (P) required for agitating a fluid in a stirred tank becomes independent of inertial forces. In this limit, indicate which of the following relations is satisfied:
Po = ρ/ρN^3 D^5 : Power number
Re = ρ N D^2/μ: Reynold’s number
N is the impeller rotational speed, and D is the impeller diameter.
- Po ∝ Re^-1.0
- Po ∝ Re^0.0
- Po ∝ Re^0.5
- Po ∝ Re^1.0
Po ∝ Re^-1.0
Which of the following grinding mills has the horizontally arranged rods as the grinding elements thereby delivering more uniform granular products with minimum fines ?
- Compartment mill
- Rod mill
- Pebble mill
- Tube mill.
Rod mill
Rittinger’s crushing law states that
- work required to form a particle of any size is proportional to the square of the surface to volume ratio of the product.
- work required to form a particle of a particular size is proportional to the square root of the surface to volume ratio of the product.
- work required in crushing is proportional to the new surface created.
- for a given machine and feed, crushing efficiency is dependent on the size of the feed & product.
work required in crushing is proportional to the new surface created.
Sphericity of pulverised coal is
- 1
- <1
- > 1
- ∞
<1
Which is a secondary crusher for a hard & tough stone ?
- Jaw crusher
- Cone crusher
- Impact crusher
- Toothed roll crusher
Cone crusher
Pick out the wrong statement pertaining to the turbine agitator.
- Recommended peripheral speed for the turbine agitator is 200-250 metres/minute.
- Pitched blade turbine agitator gives only radial flow with complete absence of the axial flow.
- Generally, the diameter of the agitator is kept between l/3rd to l/6th of the tank diameter while the blade length is l/4th of agitator diameter (with central disc, it is l/8th of the agitator diameter).
- Turbine agitator should be located at a height not less than one agitator diameter length from the bottom. If the depth of liquid in the tank is more than twice the agitator diameter, two agitators should be used.
Pitched blade turbine agitator gives only radial flow with complete absence of the axial flow.
Which of the following is the softest material ?
- Talc
- Feldspar
- Corundum
- Calcite
Talc
Which of the following is a continuous filter?
- Plate and frame filter
- Cartridge filter
- Shell and leaf filter
- None of these
None of these
rpm of a trommel at critical speed is given by (where, D = Diameter of trommel in ft)
- 76.65/D
- 76.75/√D
- 76.65/D^2
- 76.75√D
76.75/√D
Optimum ratio of operating speed to critical speed of a trommel is
- 0.33-0.45
- 1.33-1.45
- 0.5-2
- 1.5-2.5
0.33-0.45
Grinding efficiency of a ball mill is of the order of __________ percent.
- 1-5
- 40-50
- 75-80
- 90-95
1-5
Trommels are revolving screens which normally operate in the range of __________ rpm.
- 1 - 2
- 15 - 20
- 40 - 50
- 60 - 75
15 - 20
A centrifugal filtration unit operating at a rotational speed of w has inner surface of the liquid (density ρL) located at a radial distance R from the axis of rotation. The thickness of the liquid film is δ and no cake is formed. The initial pressure drop during filtration is
- (1/2) w² . R² . ρL
- (1/2) w² . δ² . ρL
- (1/2) w² . δρL (2R + δ)
- (1/2) w² . R . ρL(R + 2δ)
(1/2) w² . δρL (2R + δ)
Separation of solid suspended in liquid into a supernatant clear liquid and a denser slurry employs a process termed as the
- coagulation
- flocculation
- sedimentation
- clarification
sedimentation
Half the angle of nip, (α), for a roll crusher is given by (where, dr, dp and df are diameters of crushing rolls, feed particles and rolls gap respectively).
- cos α = dr+ dp / dr + df
- cos α = dr+ df / dr + dp
- tan α = dr+ dp / dr + df
- cos α = dr+ dp / dr + df
cos α = dr+ df / dr + dp
Pick out the wrong statement.
- For the compressible cake, voidage & the specific resistance of the cake can be assumed to be constant.
- Cake resistance is independent of the pressure drop.
- Crushing of explosive materials are done by employing drygrinding.
- Gyratory crusher is a coarse crusher.
Cake resistance is independent of the pressure drop.
Pick out the correct statement.
- Angle of repose is always greater than the angle of slide.
- A hopper is a small bin with a sloping bottom.
- A silo is a short height vessel of very large diameter used for the storage of high volatile matter coal.
- Pine oil is used as a ‘modifying agent’ (for activating or depressing the adsorption of filming agents) in froth floatation process.
A hopper is a small bin with a sloping bottom.
Activators are those chemicals which help buoying up one mineral in preference to the other in the froth floatation process. Which of the following is an activator?
- Cresylic acid
- Copper sulphate
- Calcium carbonate
- Sodium carbonate
Copper sulphate
In a size reduction crushing operation, feed size is 300 to 1500 mm while the product size is 100 to 300 mm. This is a case of the __________ crushing.
- secondary
- fine
- primary
- ultrafine
primary
As per Taggart’s formula, the capacity (kg/hr) of Jaw & Gyratory crushers (for gapes of 10 to 60 cms) is equal to (where, L = Length of feed opening, cms S = Maximum width of discharge opening, cms )
- LS
- 93 LS
- 250 LS
- √LS
93 LS
Pick out the wrong statement.
- More commonly used jaw crusher between Dodge jaw crusher and Blake jaw crusher is the later one.
- There are only four methods namely compression, impact, attrition and cutting, which the size reduction equipments employ.
- Cutting machines mainly employ ‘attrition’ for size reduction of solids.
- Operating principles of Dodge and Blake jaw crushers are combined in the working of universal jaw crushers.
Cutting machines mainly employ ‘attrition’ for size reduction of solids.
Which of the following minerals is not subjected to magnetic separation method?
- Rutile
- Galena
- Chromite
- Siderite
Galena
Cake resistance is
- important in the beginning of filtration.
- decreased with the time of filtration.
- independent of pressure drop.
- none of these.
none of these.
In a mixer, the quantity, (v. L/D) is termed as __________ number(where, v = longitudinal velocity of material, L = length of the mixer, D = diffusivity in axial mixing).
- Weber
- Peclet
- Brinkman
- Schmidt
Peclet
