Mechanical Operations Part 3 Flashcards
To get ultrafine particles, the equipment used is a
ball mil
rod mill
hammer crusher
fluid energy mill
fluid energy mill
Vacuum filter is most suitable for the
removal of fines from liquid.
liquids having high vapour pressure.
liquids of very high viscosity
none of these.
none of these.
The porosity of a compressible cake is
minimum at the filter medium.
minimum at the upstream face
maximum at the filter medium.
same throughout the thickness of cake.
minimum at the filter medium.
Which of the following conveyors cannot be recommended for transportation of abrasive materials ?
Belt conveyor
Apron conveyor
Flight conveyor
Chain conveyor
Flight conveyor
Separation of materials into products based on the difference of their sizes is called
sizing
sorting
classification
flocculation
sizing
For classification of potable (drinking) water, we use a __________ filter.
gravity sand
plate and frame
vacuum leaf
rotary vacuum
gravity sand
Hot, lumpy & abrasive materials are best transported by using a/an __________ conveyor.
apron
belt
screw
flight
apron
Additives used for promoting the floccula-tion of particles is a/an
electrolyte
surface active agent
both (a) & (b)
neither (a) nor (b)
both (a) & (b)
In case of grinding in a ball mill
wet grinding achieves a finer product size than dry grinding
its capacity decreases with increasing fineness of the products.
grinding cost and power requirement increases with increasing fineness of the products.
all (a), (b) and (c).
all (a), (b) and (c).
The capacity of a classifier in ‘tons of solid/hr’ is given by (where, A = cross-sectional area, m2 V = rising velocity of fluid, m/sec.S = percentage of solids in the suspension by volume.rho = density of solids, kg/m3)
3.6 AVS.rho
3.6 A.V.rho
3.6 A.S. rho
3.6 AVS/rho
3.6 AVS.rho
Kick’s law relates to
energy consumption
final particle size
feed size
none of these
energy consumption
__________ mill is normally used for grinding of talc.
Tube
Compartment
Ring-roll
Pebble
Ring-roll
Colloidal mills are used for __________ grinding.
coarse
intermediate
fine
ultrafine
ultrafine
Fluid medium used in the classification technique of mineral beneficiation is
air
water
either (a) or (b)
neither (a) nor (b)
either (a) or (b)
The maximum slope of a belt conveyor can be
15
30
45
60
30
The filter medium resistance is controlled by
pressure drop alone
flow rate alone
both pressure drop and flow rate
cake thickness
both pressure drop and flow rate
The unit of filter medium resistance is
cm-1
gm/cm-1
cm/gm-1
gm-1
cm-1
During size reduction by a jaw crusher, the energy consumed decreases with the
decreasing size of product at constant size of feed
decreasing machine capacity.
increasing size of feed at constant reduction ratio.
none of these.
increasing size of feed at constant reduction ratio.
Which of the following can be most effectively used for clarification of lube oil and printing ink?
Sparkler filter
Precoat filter
Disc-bowl centrifuge
Sharpies supercentrifuge
Sharpies supercentrifuge
Ultracentrifuges running at speeds upto 100000 rpm is normally used for the
separation of isotopes based on their density or molecular weights difference.
concentration of rubber latex.
separation of cream from milk.
dewaxing of lubricating oil.
separation of isotopes based on their density or molecular weights difference.
Sizing of very fine particles of the order of 5 to 10 microns is done by elutriation, which is a __________ operation.
clarification
sedimentation
flocculation
classification
classification
In the cyclone separator used for separation of dust from dust laden gas, the gas
enters the cyclone from the top.
is admitted tangentially at high velocity.
develops a helical motion inside the chamber.
both (b) and (c).
both (b) and (c).
Size reduction of fibrous materials like wood, asbestos, mica etc. is done by a disintegrator exemplified by the
Blake jaw crusher
cage mill
stamp mill
Bradford’s breaker
cage mill
The material is crushed in a gyratory crusher by the action of
impact
compression
attrition
cutting
compression
The equivalent diameter of channel of a constant non-circular cross-section of 3 cm by 6 cm will be __________ cms.
20
12
8
2
2
Which of the following may prove unsuitable for filtering volatile liquids ?
Pressure filter
Gravity filter
Centrifugal filter
Vacuum filter
Vacuum filter
__________ mean diameter of particles is given by Σ(xi/Dpi)
Mass
volume
Arithmetic
Volume surface
volume
Mass flow of granular solid (M) through a circular opening of dia, D follows
M is proportional to sqrt D
M is proportional to D2
M is proportional to D3
M is proportional to D
M is proportional to D3
Sauter mean diameter is the same as the __________ mean diameter.
mass
arithmetic
volume-surface
geometric
volume-surface
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 paint industries, blending of light paste is done by using a
masticator
charge can mixer
kneader
none of these
charge can mixer
A sand mixture was screened through a standard 10-mesh screen. The mass fraction of the oversize material in feed, overflow and underflow were found to be 0.38, 0.79 and 0.22 respectively. The screen effectiveness based on the oversize is
0.5
0.58
0.68
0.62
0.5
__________ is used for producing a thick suspension from a thin slurry.
Rotary drum vacuum filter
Rotary drum vacuum filter
Pressure filter thickener
Plate and frame filter press
Pressure filter thickener
Wet seiving is employed, when the product contains __________ materials.
abrasive
large quantity of very fine
coarse
non-sticky
large quantity of very fine
Energy requirement (per unit mass of material crushed/ground) is highest for
jaw crusher
rod mill
ball mill
fluid energy mill
fluid energy mill
The energy consumed by a ball mill depends on
its speed
its ball load.
the density of the material being ground
all (a), (b) and (c).
all (a), (b) and (c).
Energy consumption in a crusher decreases with increase in the
size of the product (at constant feed size)
capacity of the crushing machine.
size of feed (at constant reduction ratio).
all (a), (b) & (c).
all (a), (b) & (c).
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
Pclet
Brinkman
Schmidt
Pclet
The term ‘angle of nip’ is concerned with the operation of the __________ crushers.
jaw
roll
gyrator
none of these
roll
Cartridge filters are termed as ‘edge’ filters, because of the fact that the
disks have very sharp edge.
solids are not deposited at the edge of the disk.
bulk of the solids are removed at the periphery of the disks.
none of these.
bulk of the solids are removed at the periphery of the disks.
Vibrating screens have capacity in the range of __________ tons/ft2 .mm mesh size.
0.2 to 0.8
5 to 25
50 to 100
100 to 250
0.2 to 0.8
Cumulative analysis for determining surface is more precise than differential analysis, because of the
assumption that all particles in a single fraction are equal in size.
fact that screening is more effective.
assumption that all particles in a single fraction are equal in size, is not needed.
none of these.
assumption that all particles in a single fraction are equal in size, is not needed.
cumulative analysis…
…,is not needed
To remove very small amount of tiny solid impurities from liquid, we use a
pressure filter
vacuum filter
centrifugal filter
coagulant
coagulant
Screw conveyors are
run at very high rpm.
suitable for sticky materials.
suitable for highly abrasive materials.
all (a), (b) and (c)
suitable for sticky materials.
__________ mills fall in the category of tumbling mills,
Ball and pebble
Rod and tube
Compartment
all (a), (b) & (c)
all (a), (b) & (c)
Capacity of flight conveyor in tons/hr is given by (where, W & D = width and depth of flight respectively in metre V = speed of the conveyor, metre/second rho = bulk density of material, kg/m3)
3.6 W.D.V.rho
3.6 W.D.V.
3.6 W.V.rho
3.6 D.V.rho
3.6 W.D.V.rho
Which of the following is not a cutting machine?
Dicers
Knife cutters
Slitters
Tube mills
Tube mills
Weber number is significant and is concerned with the
solid-liquid mixing.
liquid-liquid mixing.
dispersion of liquid in liquid.
suspension of solid in liquid.
dispersion of liquid in liquid.
Power consumption during turbulent flow in agitation tank is proportional to the __________ of the liquid.
viscosity
thermal conductivity
surface tension
density
density
Screen efficiency is
recovery/rejection
recovery
rejection
none of these
none of these
For grinding of cereals, grains, spices, pigments, saw dust, cork etc., the most extensively used size reduction equipment is a
Buhrstone mill
ball mill
crushing rolls
hammer mill
Buhrstone mill
Handling of ashes and similar materials can be done best by a __________ conveyor.
flight
drag or slat
belt
ribbon.
drag or slat
Which of the following must be stored in silos and not in open yard ?
Coke breeze
High V.M. bituminous coal
Sand
None of these
High V.M. bituminous coal
Apron conveyors are used for
heavy loads & short runs.
small loads & long runs.
heavy loads & long runs.
none of these.
heavy loads & short runs.
AHLSR Apron Heavy Load Short Run
Sedimentation on commercial scale occurs in
classifiers
thickeners
rotary drum filters
cyclones
rotary drum filters
With increase in drum speed, in a rotary drum filter, the filtration rate
increases
increases linearly
decreases
is not affected
increases
Arrange the following size reduction equipment in the decreasing order of the average particle size produced by each of them.
Jaw crusher, Ball mill, Fluid energy mill
Ball mill, Jaw crusher, Fluid energy mill
Fluid energy mill, Jaw crusher, Ball mill
Fluid energy mill, Ball mill, Jaw crusher
Jaw crusher, Ball mill, Fluid energy mill
jaw ball fluid - decreasing order of average particle size produced
200 mesh seive size corresponds to __________ microns.
24
74
154
200
74
What is the usual value of angle of nip for crushing of ordinary rock in smooth steel crushing rolls ?
16
32
40
46
32
For a turbine agitated and baffled tank, operating at low Reynold’s number (based on impeller diameter), the power number (Np) varies with NRe as
Np is proportional to NRe
Np is proportional to N sqrt Re
Np ? constant
Np is proportional to 1/NRe
Np is proportional to 1/NRe
Which of the following is not accomplished by agitation of liquids in agitators?
Dispersing gas in liquid.
Blending of immiscible liquids.
Dispersing immiscible liquid in form of emulsion.
Suspending solid particles.
Blending of immiscible liquids.
Which of the following parts of a jaw crusher is subjected to maximum wear and tear during its operation ?
Check plates
Jaw plates
Toggles
Crush shaft
Jaw plates
Jaw plates - Maximum wear and tear
A 30% (by volume) suspension of spherical sand particles in a viscous oil has a hindered settling velocity of 4.44 um/s. If the Richardson Zaki hindered settling index is 4.5, then the terminal velocity of a sand grain is
0.90 um/s
1 um/s
22.1 um/s
0.02 um/s
1 um/s
In froth floatation, chemical agent added to cause air adherence is called
collector
frother
modifier
activator
collector
froth - air - collector
The sphericity of a solid particle of cubical shape is
π
(π/6)1/3
(π/6)1/2
π/3
(π/6)1/3
Vertical transportation of materials can be done by a/an
apron conveyor
pneumatic conveyor
bucket elevator
both(b)&(c)
both(b)&(c)
In a roll crusher, the specific power consumption and the production rate is affected by the
reduction ratio.
differential roll speed.
both (a) and (b).
neither (a) nor (b).
both (a) and (b).
A cottrel precipitator makes use of the __________ for dusty air cleaning.
electric spark
corrona discharge
alternating current
none of these.
corrona discharge
CC Cottrel Corrona
Pick out the correct statement.
Plastic chips are called non-cohesive solids.
Kick’s crushing law is, P/m = K . ln (Dsa/Dsb)
Communition is a generic term for size enlargement operation
Energy required in kwh per ton of product, such that 80% of it passes through a 200 mesh screen, is called ‘Work index’.
Kick’s crushing law is, P/m = K . ln (Dsa/Dsb)
correct Kick’s crushing law
If radius of a batch basket centrifuge is halved & the r.p.m. is doubled, then the
linear speed of the basket is doubled.
linear speed of the basket is halved.
centrifugal force is doubled.
capacity of centrifuge is increased.
centrifugal force is doubled.
The ratio of the area of openings in one screen (Taylor series) to that of the openings in the next smaller screen is
1.5
1
sqrt 2
none of these
none of these
Compressibility co-efficient for an absolutely compressible cake is
0
1
0 to 1
infinite
1
Mixing of plastic solids is generally facilitated by
dispersion
mastication
kneading
none of these
kneading
The mechanism of size reduction by a hammer mill is by impact and attrition between the
grinding element & the housing.
feed particles.
both (a) and (b).
neither (a) nor (b).
both (a) and (b).
Which of the following is not an industrial screening equipment ?
Sharpies centrifuge
Vibrating screen
Grizzly
Trommel
Sharpies centrifuge
Which of the following is not a wet classifier ?
Sharpies supercentrifuge
Hydrocyclones
Dorr Oliver rake classifier
None of these
None of these
Helical screw agitator is used for
mixing highly viscous pastes.
blending immiscible liquids.
mixing liquids at very high temperature (> 250 C).
none of these.
mixing highly viscous pastes.
HHS Helical Highly Viscous
For raschig rings, the sphericity is
0.5
1
<1
sqrt 3
<1
raschig<1
For Indian standard (IS) screens, the mesh number is equal to its aperture size expressed to the nearest deca-micron (0.01 mm). Aperture width of IS screen of mesh number 50 will be approximately __________ microns.
5
50
500
5000
500
__________ mills are termed as disintegrators.
Cage
Compartment
Pebble
All tumbling
Cage
Supporting legs of a plate and frame filter is normally made of
stainless steel
cast iron
high speed steel
wooden plank
cast iron
Plate and Frame Cast Iron Legs
Wet grinding in a revolving mill __________ as compared to dry grinding.
gives less wear on chamber walls
requires more energy
increases capacity
complicates handling of the product
increases capacity
The grinding in a hammer crusher takes place due to the
attrition
impact
both (a) & (b)
neither (a) nor (b)
both (a) & (b)
A compressible cake has the
maximum porosity at the upstream side.
maximum porosity at the filter medium.
same porosity throughout the cake thickness.
none of these.
maximum porosity at the upstream side.
Which of the following is not used as a filter medium in case of corrosive liquids ?
Nylon
Glass cloth
Metal cloth of monel or stainless steel
Cotton fabric
Cotton fabric
In ball mill operation, the feed size (Df in meters) and the ball diameter (Db in metres) are related as ( where, K = grindability constant (varying from 0.9 to 1.4 in increasing order of hard ness))
Db2 = K.Df
Db = K.Df
Db3 = K.Df
Db2 = K.Df2
Db2 = K.Df
Pine oil and cresylic acid are used as __________ in the froth floatation process.
frother
collector
depressor
conditioner
frother
Grinding characteristic of a material is given by its
HGI
angle of repose
shatter index
abrasion index.
HGI
Which of the following is not a non-metalliferous mineral?
Calcite
Fluorspar
Quartz
Cassiterrite
Cassiterrite
Filter medium resistance is important during the __________ of filtration.
early stages.
final stages.
entire process.
none of these.
early stages.
Float and sink test determines the possibility of cleaning of coal by a process based on the
gravity separation
wettability
particle shape
none of these
gravity separation
__________ baffles are provided in ball mills.
Horizontal
No
Only two
None of these
Horizontal
Mixer used for rubber compounding is
mixer-extruder
banbury internal mixer
muller mixer
pug mill
banbury internal mixer
BRC Banbury Rubber Compounding
For spheres, the specific surface shape factor is given by
AD/V
D/V
A/V
sqrt AD/V
AD/V
__________ mill is not used for grinding wheat into flour and for milling of cereals & other vegetable products.
Buhrstone
Roller
Attrition
Pebble
Pebble
In case of a hammer crusher, the final product size depends on the
feed rate.
rotor speed.
clearance between hammer & grinding plates.
all (a), (b) and (c).
all (a), (b) and (c).
Sphericity of raschig ring (whose length and diameter are equal) is
>1
<1
1
2
1
raschig L=D 1
Mixing mechanism employed in a pan mixer is by
mulling
kneading
dispersion
none of these
mulling
Chance process is used for the
cleaning of coal.
concentration of iron ore.
concentration of pyrites.
water treatment
cleaning of coal.
Which of the following screens has the maximum capacity ?
Grizzlies
Trommels
Shaking screen
Vibrating screen
Vibrating screen
Stamp mills are generally used for crushing
iron ores
gold ores
talc
diamond
gold ores
In case of a plate and frame filter press, filtrate flow through the cake follows __________ flow.
plug
turbulent
laminar
none of these
laminar
Which of the following is a batch sedimentation equipment ?
Dust catcher
Filter thickener
Dry cyclone separator
Rotary sprayer scrubber.
Filter thickener
The most suitable equipment for the transportation of 200 mesh size particles is a
bucket elevator
pneumatic conveyor
screw conveyor
belt conveyor
pneumatic conveyor
Which of the following is not used as filter aid?
Asbestos
Diatomaceous earth
Purified wood cellulose
Rice husk
Rice husk
Raw materials are charged in the iron blast furnace using
bucket elevator
skip hoist
screw conveyor
none of these
skip hoist
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 σ
μ ≥ tan σ
μ > tan 2σ
μ ≤ tan σ
μ ≥ tan σ
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
not ultrafine toothed roll
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
Turbine agitator
Perforated horizontal basket continuous
Turbine agitator
Turbine…sugar mills
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, rho= density of particles)
m/rho . Vp
m. rho/V
m . Vp/rho
Vp/m . rho
m/rho . 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
1/4 washing/final ratio
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
flint or porcelain balls - 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.
od 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.
removal of traces - 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 um 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 urn 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
SV Sulphuric 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.
JBS Jigging by 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
cm2
cm
inch
inch2
inch
__________ is the most commonly used ‘filter aid’.
Diatomaceous earth
Fuller’s earth
Vermiculite
Semi-plastic clay
Diatomaceous earth
