Mechanical Operations 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.
Power required to drive a ball mill with a particular ball load is proportional to (where, D = diameter of ball mill )
D2.5
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
Pick out the wrong statement.
Size enlargement (opposite of size reduction) is not a mechanical operation.
For sizing of fine materials, the most suitable equipment is a
vibrating screen
In continuous filtration (at a constant pressure drop), filtrate flow rate varies inversely as the
square root of the velocity.
Which of the following is not categorised as a “mechanical operation” ?
Humidification
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
Tabular bowl centrifuges as compared to disk bowl centrifuges
operate at higher speed.
Which of the following is a pressure filter ?
Plate and flame filter
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
all ‘a’, ‘b’&’c’
Pick out the wrong statement pertaining to the roll crushers.
Both the rolls run necessarily at the same speed.
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
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
The distribution given by microscopic analysis of powder is
number
Diatomaceous earth is a/an
filter aid
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
Which of the following mineral dressing operations is termed as ‘comminution’?
None of these
Filter aid is used to
increase the porosity of the cake
The capacity of a pneumatic conveying system depends upon the
all (a), (b) and (c).
Pick out the wrong statement.
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
Pick out the correct statement:
Removal of iron from ceramic material is necessitated (by magnetic separation method) so as to avoid discoloration of ceramic products.
Which of the following is the most suitable for cleaning of fine coal dust (<0.5 mm) ?
Froth floatation
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
Range of compressibility co-efficient of the commercial compressible cake obtained in filtration operation is
0.2 to 0.8
The value of ‘angle of nip’ is generally about
32°
Highly viscous liquids & pastes are agitated by
multiple blade paddles
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,
all (a), (b) and (c).
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
200 mesh screen means 200 openings per
inch
Energy consumed for crushing one ton of material ranges from __________ kWh.
0.5 to 1.5
For transporting pasty material, one will use a/an
screw colaveyor
__________ is the most commonly used ‘filter aid’.
Diatomaceous earth
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
A tube mill compared to a ball mill
has a higher length/diameter ratio.
Trommels separate a mixture of particles depending on their
size
Basic slag is not ground in
jaw crushers
Grindability of a material does not depend upon its
size
Shape factor for a cylinder whose length equals its diameter is
1.5
In case of a hammer crusher, the
rotor shaft carrying hammers can be vertical or horizontal.
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)
0.087 L.S
Dust laden air can be purified using a
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
__________ mixer is used for de-vulcanisation of rubber scrap & making water dispersion & rubber solution.
Banbery
Which of the follwoing mechanical conveyors does not come under the division ‘scrapers’ ?
Bucket elevators
Which of the following mechanical conveyors does not come under the division ‘carriers’ ?
Screw conveyor
Screen capacity is not a function of
atmospheric humidity.
Vacuum is applied in __________ zone, in case of a general type continuous rotary drum vacuum filter.
all (a), (b) & (c)
Which of the following is a vacuum filter ?
Rotary disc filter
Pine oil used in froth floatation technique acts as a/an
frother
Length/diameter ratio of a ball mill is
< 1
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
Filtration of water in a paper mill is done by a/an __________ filter.
open sand
Sphericity of a cubical particle, when its equivalent diameter is taken as the height of the cube, is
1
Laminar flow region is said to exist during agitation of a liquid in an agitator, when the value of Reynolds number is
<10
Moore filter is a __________ filter.
leaf
Maximum size reduction in a ball mill is done by the, __________ action.
impact
Ball mill is used for
fine grinding
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
N2
In case of a ball mill,
coarse feed requires a larger ball
Flow of filtrate through the cake in a plate and frame filter press is best described by the __________ equation.
Kozney-Karman
increasing the capacity of a screen __________ the screen effectiveness.
decreases.
Bond crushing law
calls for relatively less energy for the smaller product particles, than does the Rittinger law.
The controlling resistance in a rotary drum vacuum filter is the __________ resistance.
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.
The resistance offered by the filter used in a bag filter is proportional to (where, c = dust concentration, and s = particle size )
c/s
The crushed material received for separation is called feed or
heading
For spheres, volume shape factor is given by
π/6(=V/D3)
__________ is defined as the geometric mean of the relative rejections and the relative recoveries of two minerals.
Selectivity index
Cement clinker is reduced to fine size by a
tube mill
Which of the following agitators having a large blade area, rotating at slow speed is used for mixing high viscosity liquids ( > 50000 centipoise) ?
Helical screw
The operating speed of a ball mill should be __________ the critical speed.
less than
Use of baffles in agitators help in minimiZing the __________ tendency.
both (a) & (b)
Fibrous material is broken by a
squirrel-cage disintegrator
__________ are used for the separation of coarse particles from a slurry of fine particles.
Classifiers
Out of the following size reduction equipment, the maximum feed size can be accepted by the
jaw crusher
__________ is the most suitable for compounding rubber and plastic solids.
Banbery mixer
Bucket elevators are not suitable for the vertical lifting of __________ materials.
sticky
The most common filter aid is
diatomaceous earth
For removal of very small amounts of precipitate from large volume of water, the most suitable filter is the __________ filter.
sand
For separation of sugar solution from settled out mud, we use a __________ filter.
centrifugal
The sphericity of a cylinder of 1 mm diameter and length 3 mm is
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.
0.30
What is the selectivity index, if the grade of tailings & concentrate is the same ?
1
The most suitable equipment used to devulcanise rubber scrap and to make water dispersion & rubber solution is a
boundary mixer.
Traces of solids are removed from, liquid in a
clarifier
__________ balls capable of grinding the feed in a ball mill gives the maximum efficiency.
Minimum size
The speed of a rotary drum vacuum filter may be about __________ rpm.
1
For achieving maximum capacity of the ball mill, the ball charge should be equal to about __________ percent of the ball mill volume.
50
Electrical energy consumed by a jaw crusher is not a function of the
none of these
Mesh indicates the number of holes per
linear inch
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)^1/2
Colloid mills achieve size reduction mainly by
attrition
Trommels employ __________ for screening of materials.
punched plate
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
Size reduction mechanism used in Jaw crushers is
compression
A widely used size reduction equipment for __________ is Bradford breaker.
coal
