Mechanical Operations Flashcards by Baj Balmes

Short distance transportation of grain, gravel, sand, ash, asphalt etc. is done by using a __________ conveyor.

flight
slat or drag
ribbon
screw

screw

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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.

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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

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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

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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.

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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.

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For sizing of fine materials, the most suitable equipment is a

trommel
grizzly
shaking screen
vibrating screen

vibrating screen

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Which of the following is not categorised as a “mechanical operation” ?

Agitation
Filtration
Size enlargement
Humidification

Humidification

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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.

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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.

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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

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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

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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.

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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

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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.

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18.
__________ centrifuge is normally used in sugar mills.

Tubular bowl
Disc-bowl
Suspended batch basket
Perforated horizontal basket continuous

Suspended batch basket

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Solid particles separation based on the difference in their flow velocities through fluids is termed as the

classification

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Diatomaceous earth is a/an

explosive
filter aid
filter medium
catalyst

filter aid

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The distribution given by microscopic analysis of powder is

number
length
area
volume

number

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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

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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.

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In washing type plate and frame filter press, the ratio of washing rate to the final filtrate rate is

1/4

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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

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Size reduction of __________ is accomplished in steam heated rollers and roll crushers.

resins
gums
hard rubber
waxes

hard rubber

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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)

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

50. __________ is the most suitable for compounding rubber and plastic solids. Banbery mixer Pan mixer Pug mill Charge can mixer

Banbery mixer

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Mechanical Operations Flashcards

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