MECHANICAL OPERATION Flashcards
Short distance transportation of grain, gravel, sand, ash, asphalt etc. is done by using a __________ conveyor.
Screw
Equivalent diameter of a particle is the diameter of the sphere having the same
ratio of surface to volume as the actual volume.
If Dp is the equivalent diameter of a non-spherical particle, Vp its volume and SAp its surface area, then its sphericity is Φs is defined by
Φs = 6 Vp/(Dp ⋅ SAp)
Power required to drive a ball mill with a particular ball load is proportional to (where, D = diameter of ball mill )
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.
C. 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.
For sizing of fine materials, the most suitable equipment is a
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 Frame Filter
Tabular bowl centrifuges as compared to disk bowl centrifuges
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
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 of these)
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
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)?
Toothed roll crusher
Two particles are called to be equal settling, if they are having the same.
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 ?
Cone type agitator
__________ centrifuge is normally used in sugar mills.
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
filter aid
The distribution given by microscopic analysis of powder is
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)
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.
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
non-metallic ores
Size reduction of __________ is accomplished in steam heated rollers and roll crushers.
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
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 of these
all 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.
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
sulphide ores
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
0.2 to 0.8
Highly viscous liquids & pastes are agitated by
multiple blade paddles
The value of ‘angle of nip’ is generally about
32°
Size reduction of the __________ can be suitably done by ball mills, crushing rolls and rod mills.
metalliferrous ores
Sulphuric acid mist is arrested by using a __________ scrubber.
venturi
The main size reduction operation in ultrafine grinders is
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 of the above
all of the above
Jigging is a technique by which different particles can be
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
Balls for ball mills are never made of
Lead
__________ is the most commonly used ‘filter aid’.
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
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
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
Bond’s crushing law isobtained 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’ ?
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
Feed size of ≥ 25 cms can be accepted by
jaw crusher
Which is the most suitable conveyor for transportation of sticky material ?
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
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
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
Sphericity of a cubical particle, when its equivalent diameter is taken as the height of the cube, is
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
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.
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 ?
Gyratory crusher
Coal is finally pulverised to 200 mesh size for burning in boilers by a
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
tube mill
The crushed material received for separation is called feed or
heading
For spheres, volume shape factor is given by
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
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)
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
squirrel-cage disintegrator
_________ is the most suitable for compounding rubber and plastic solids.
Banbery mixer
