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.
A. Recycled coarse material to the grinder by a classifier is termed as circulating load.
B. Wear and tear in wet crushing is more than that in dry crushing of materials.
C. Size enlargement (opposite of size reduction) is not a mechanical operation.
D. 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
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.
A. Maximum feed size determines the required roll diameter.
B. For hard material’s crushing, the reduction ratio should not exceed 4.
C. Both the rolls run necessarily at the same speed.
D. 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.
18.
__________ 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
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
A. 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.
B. has the dimension of length.
C. is always less than 1.
D. 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
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
Which of the following is not a part of the Blake jaw crusher?
Hanger
If a force greater than that of gravity is used to separate solids & fluids of different densities, the process is termed as the
centrifugation
Filter aid is used to
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
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.
—A clarifier is generally used to remove solid particulates or suspended solids from liquid for clarification and/or thickening.
Gravity settling process is not involved in the working of a
hydrocyclone
Froth floatation is the most suitable for treating
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 μrn is
18 kWh/ton
Which of the following is the most suitable for cleaning of fine coal dust (<0.5 mm) ?
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 ____deg
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.
venturi
The main size reduction operation in ultrafine grinders is
attrition
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
cm2
cm
inch
inch2
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 colaveyor
bucket elevator
screw colaveyor
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
General crushing equation is given by . Bond’s crushing law isobtained by solving this equation for n = __________ and feed of infinite size.
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
sqrt(2)
sqrt(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.
impact
increasing the capacity of a screen __________ the screen effectiveness.
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^2
Bond crushing law
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
A. surface energy created by crushing to the energy absorbed by the solid.
B. energy absorbed by the solid to that fed to the machine.
C. energy fed to the machine to the surface energy created by crushing.
D. 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 [caesarian haha]
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/D^2)
2π(=2A/D^2)
π/6(=V/D^3)
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
Use of baffles in agitators help in minimising the __________ tendency.
swirling
vortexing
both (a) & (b)
neither (a) nor (b)
both (a) & (b)
__________ 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
