Mechanical Operation Flashcards
Which of the following is the most suitable for handling fibrous and dense slurries ?
Cone type agitator
Cone type agitator
__________ centrifuge is normally used in sugar mills.
Suspended batch basket
Suspended batch basket
Solid particles separation based on the difference in their flow velocities through fluids is termed as the
Separation of particles of various sizes, shapes and densities by allowing them to settle in a fluid is called
classification
classification
In washing type plate and frame filter press, the ratio of washing rate to the final filtrate rate is
1/4
1/4
If a force greater than that of gravity is used to separate solids & fluids of different densities, the process is termed as the
centrifugation
centrifugation
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
18 kWh/ton
Which of the following is the most suitable for cleaning of fine coal dust (<0.5 mm) ?
Froth floatation
Froth floatation
Highly viscous liquids & pastes are agitated by
multiple blade paddles
multiple blade paddles
The value of ‘angle of nip’ is generally about
32°
32°
Shape factor for a cylinder whose length equals its diameter is
1.5
1.5
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
easier grindability
__________ mixer is used for devulcanisation of rubber scrap & making water dispersion & rubber solution.
Banbery
Banbery
Which of the following is a vacuum filter ?
Rotary disc filter
Rotary disc filter
Pine oil used in froth floatation technique acts as a/an
frother
frother
Length/diameter ratio of a ball mill is
< 1
< 1
Feed size of ≥ 25 cms can be accepted by
jaw crusher
jaw crusher
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
electrostatic precipitator
Coal is finally pulverised to 200 mesh size for burning in boilers by a
To get a fine talc powder from its granules, the equipment used is
Carbon black is pulverised in a
ball mill
ball mill
Cement clinker is reduced to fine size by a
tube mill
tube mill
The operating speed of a ball mill should be __________ the critical speed.
less than
less than
__________ are used for the separation of coarse particles from a slurry of fine particles.
Classifiers
Classifiers
Which of the follwoing mechanical conveyors does not come under the division ‘scrapers’ ?
Bucket elevators
Bucket elevators
Which of the following mechanical conveyors does not come under the division ‘carriers’ ?
Dry powdery solid materials are transported by a __________ conveyor.
Screw conveyor
Screw conveyor
For separation of sugar solution from settled out mud, we use a __________ filter.
centrifugal
centrifugal
The sphericity of a cylinder of 1 mm diameter and length 3 mm is
0.9
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
0.30
What is the selectivity index, if the grade of tailings & concentrate is the same ?
1
1
The most suitable equipment used to devulcanise rubber scrap and to make water dispersion & rubber solution is a
boundary mixer.
boundary mixer.
Traces of solids are removed from, liquid in a
clarifier
clarifier
__________ balls capable of grinding the feed in a ball mill gives the maximum efficiency.
Minimum size
Minimum size
The speed of a rotary drum vacuum filter may be about __________ rpm.
1
1
Colloid mills achieve size reduction mainly by
attrition
attrition
For achieving maximum capacity of the ball mill, the ball charge should be equal to about __________ percent of the ball mill volume.
50
50
Which of the following gives the work required for size reduction of coal to -200 mesh in a ball mill most accurately ?
Which of the following gives the crushing energy required to create new surface ?
Rittinger’s law
Rittinger’s law
Size reduction mechanism used in Jaw crushers is
compression
compression
A widely used size reduction equipment for __________ is Bradford breaker.
coal
coal
Ultra centrifuges are used for the separation of __________ solid particles.
colloidal
colloidal
Size reduction does not occur due to compression in case of
Which of the following grinding mills has the horizontally arranged rods as the grinding elements thereby delivering more uniform granular products with minimum fines ?
rod mills
rod mills
According to Taggart’s rule for selecting between a gyratory crusher and a jaw crusher; the later should be used, if the hourly tonnage to be crushed divided by the square of the gape expressed in cm is less than
0.0184
0.0184
Gold ore concentration is mostly done using
For benefication of iron ore, the most commonly used method is
tabling
tabling
Mixing of light fine powder such as insecticides is done by
impact wheels
impact wheels
Run of mine (ROM) coal is crushed by a __________ for use in domestic ovens.
hammer crusher
hammer crusher
Size reduction of asbestos and mica is done by
hammer mills
hammer mills
A suspension of glass beads in ethylene glycol has a hindered settling velocity of 1.7 mm/s, while the terminal settling velocity of a single glass bead in ethylene glycol is 17 mm/s. If the Richardson-Zaki hindered settling index is 4.5, the volume fraction of solids in the suspension is
0.6
0.6
__________ conveyor is the most suitable for long distance transportation of cold, non-abrasive granular/irregular shape/fine materials.
Belt
The specific cake resistance for compressible sludges is a function of the pressure drop
over cake
over cake
Moisture can be removed from lubricating oil using
tubular centrifuge
tubular centrifuge
Tabling process used for separating two materials of different densities by passing the dilute pulp over a table/deck, which is inclined from the horizontal surface at an angle of about
2 to 5°
2 to 5°
Gizzlies are used for separating __________ solids.
fine
fine
Which of the following clay mixing devices is vacuum operated for deairation of clay?
Molten ammonium nitrate is mixed with ground limestone in fertilizer plant in a
Pug mill
Pug mill
Pick out the material having minimum Rittinger’s number.
Quartz
Quartz
__________ mills are termed as impactors.
Hammer
Hammer
For a cyclone of diameter 0.2 m with a tangential velocity of 15 m/s at the wall, the separation factor is
230
230
Use of ‘grinding aids’ is done in __________ grinding.
dry
dry
Which of the following is the most suitable filter for separation of abrasive solids suspended in a corrosive liquid ?
Vacuum filter
Vacuum filter
All resistances during washing of cake
remain constant
remain constant
A __________ mixer resembles a ball mill without balls.
tumbling
tumbling
__________ conveyor is the most suitable for short distance transportation of non-abrasive loose materials like garbage, grain, food wastes etc.
Which of the following conveyors cannot be recommended for transportation of abrasive materials ?
Flight
Gyratory crushers compared to the reciprocating jaw crushers
have greater capacity per unit of discharge area.
have greater capacity per unit of discharge area.
Sphericity of pulverised coal is
<1
<1
General mechanism of size reduction in intermediate and fine grinder is by
impact and attrition.
impact and attrition.
Reduction ratio of crushers is the
ratio of feed opening to discharge opening.
ratio of feed opening to discharge opening.
Which is a secondary crusher for a hard & tough stone ?
Cone crusher
Cone crusher
There is practically no alternative/competitor to __________ in the beneficiation treatment of sulphide ores.
froth floatation
froth floatation
Separation of isotopes is generally done using a/an __________ centrifuge.
ultra
ultra
Temperature of the product during ultrafine grinding
increases
increases
Reciprocating screens are normally inclined at an angle of 5° with the horizontal and employ gyratory motion at feed end & reciprocating motion at the discharge end. They are not suitable for the screening of the
heavy tonnages of rocks or gravel.
heavy tonnages of rocks or gravel.
Separation of materials of the same density based on their sizes by using then-different rates of flow is called
sizing
sizing
For a sphere falling in the constant drag co-efficient regime, its terminal velocity depends on its diameter (d) as
d^2
d^2
During washing of filter at the end of constant pressure filtration, the rate of washing equals the rate of filtration
at the end of filtration.
at the end of filtration.
In screen analysis, the notation +5 mm/-10 mm means particles passing through
10 mm screen and retained on 5 mm screen.
10 mm screen and retained on 5 mm screen.
Optimum ratio of operating speed to critical speed of a trommel is
0.33-0.45
0.33-0.45
Grinding efficiency of a ball mill is of the order of __________ percent.
1-5
1-5
The value of work index does not change materially from one equipment to another. If the value of work index determined for close circuit grinding is Wi, then the same for open circuit grinding will be
1.34 Wi
1.34 Wi
Maximum size reduction in a fluid energy mill is achieved by
interparticle attrition
interparticle attrition
Trommels are revolving screens which normally operate in the range of __________ rpm.
15 - 20
15 - 20
Which of the following comes in the category of primary crusher for hard and tough stone ?
Jaw crusher
Jaw crusher
Which of the following crushers can be considered as a combination of a jaw crusher and a roller crusher ?
For the preliminary breaking of hard rock, we use a
Which of the following is a coarse crusher?
Gyratory crusher
Gyratory crusher
Ultrafine grinders operate principally by
attrition
attrition
What is the critical rotation speed in revolutions per second, for a ball mill of 1.2 m diameter charged with 70 mm dia balls ?
0.66
0.66
Crushing efficiency of a machine ranges between __________ percent.
0.1 to 2
0.1 to 2
Percentage of drum submerged in the slurry in case of rotary drum filter is
30
30
Ribbon blenders are exclusively meant for
non-flowing powder and thin pastes.
non-flowing powder and thin pastes.
Gelatinous solid (which plug the septum) can be filtered by a __________ filter.
precoat
precoat
The opening of a 200 mesh screen (Taylor series) is
0.0074 cm
0.0074 cm
Separation of solid particles based on their densities is called
sorting
__________ are mixed using ribbon blenders.
Dry powders
Dry powders
For crushing of solids, the Rittinger’s law states that the work required for crushing is proportional to
the new surface created.
the new surface created.
In a size reduction crushing operation, feed size is 300 to 1500 mm while the product size is 100 to 300 mm. This is a case of the __________ crushing.
primary
primary
The process by which fine solids is removed from liquids is termed as
Separation of a suspension or slurry into a supernatant clear liquid (free from particles) and a thick sludge containing a high concentration of solid is called
sedimentation
sedimentation
Which of the following crushing laws is most accurately applicable to the fine grinding of materials ?
Rittinger’s law
Rittinger’s law
Gummy & sticky materials like molasses, sugar etc. are best transported/handled by using a __________ conveyor.
ribbon
ribbon
Sorting classifiers employing differential settling methods for separation of particles make use of the differences in their
terminal velocities
terminal velocities
In constant pressure filtration,
rate of filtration decreases with time
rate of filtration decreases with time
The critical speed of a trommel (N) is related to its dia (D) as
N ∝ 1/sqrtD
N ∝ 1/sqrtD
Which of the following minerals is not subjected to magnetic separation method?
Galena
Galena
Which of the following is not a revolving/tumbling mill used for size reduction?
__________ mills are termed as disintegrators.
Size reduction of fibrous materials like wood, asbestos, mica etc. is done by a disintegrator exemplified by the
__________ mill is not a revolving mill.
Cage mill
Cage mill
Which of the following achieves the least reduction ratio for a given feed size?
Roll crusher
Roll crusher
In a size reduction crushing operation, feed size is 100 to 300 mm. while the product size is 10 to 50 mm. This is a case of the __________ crushing.
secondary
secondary
Work index is the gross energy (kWh/tonne of feed) necessary to reduce a very large feed to such a size that 80% of product particles will pass through a 0.1 mm screen. The value of work index determined for wet grinding should be multiplied with __________ to get the same for dry grinding.
1.34
1.34
Choke crushing (in case of a Jaw crusher) compared to free crushing
consumes more power.
consumes more power.
The specific surface of sherical particles is proportional to (where, Dp = diameter of particle).
1/Dp
1/Dp
Gravity stamp mill is meant for the __________ crushing.
fine
fine
Washability curve based on float and sink test enables an assessment to be made of the possibility of cleaning a coal fraction based on the
density separation.
density separation.
Hot, lumpy & abrasive materials are best transported by using a/an __________ conveyor.
apron
apron
The maximum slope of a belt conveyor can be
30°
30°
The equivalent diameter of channel of a constant non-circular cross-section of 3 cm by 6 cm will be __________ cms.
2
2
The unit of filter medium resistance is
cm-1
cm-1
Mass flow of granular solid (M) through a circular opening of dia, D follows
M ∝ D^3
M ∝ D^3
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
0.50
0.50
Vibrating screens have capacity in the range of __________ tons/ft2 .mm mesh size.
0.2 to 0.8
0.2 to 0.8
To remove very small amount of tiny solid impurities from liquid, we use a
coagulant
coagulant
Weber number is significant and is concerned with the
dispersion of liquid in liquid.
dispersion of liquid in liquid.
For grinding of cereals, grains, spices, pigments, saw dust, cork etc., the most extensively used size reduction equipment is a
Buhrstone mill
Buhrstone mill
Handling of ashes and similar materials can be done best by a __________ conveyor.
drag or slat
drag or slat
Apron conveyors are used for
heavy loads & short runs.
heavy loads & short runs.
200 mesh seive size corresponds to __________ microns.
74
74
A 30% (by volume) suspension of spherical sand particles in a viscous oil has a hindered settling velocity of 4.44 μm/s. If the Richardson Zaki hindered settling index is 4.5, then the terminal velocity of a sand grain is
1 μm/s
1 μm/s
If radius of a batch basket centrifuge is halved & the r.p.m. is doubled, then the
centrifugal force is doubled.
centrifugal force is doubled.
Compressibility co-efficient for an absolutely compressible cake is
1
1
Mixing of plastic solids is generally facilitated by
kneading
kneading
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
Db2 = K.Df
Pine oil and cresylic acid are used as __________ in the froth floatation process.
frother
frother
Grinding characteristic of a material is given by its
HGI
HGI
Mixing mechanism employed in a pan mixer is by
mulling
mulling
Which of the following screens has the maximum capacity ?
Vibrating screen
Vibrating screen
Stamp mills are generally used for crushing
gold ores
gold ores
Which of the following is a batch sedimentation equipment ?
Filter thickener
Filter thickener
The most suitable equipment for the transportation of 200 mesh size particles is a
For the transportation of ultrafine particles, the equipment used is a
pneumatic conveyor
pneumatic conveyor
Particle size range in which dust catcher (gravity settling chamber) works most effectively and efficiently is __________ microns.
< 74
< 74
__________ centrifuge is the most suitable for separation of non-friable crystals.
Perforated horizontal basket continuous
Perforated horizontal basket continuous
A propeller agitator
produces mainly axial flow.
produces mainly axial flow.
Reciprocal of sphericity is termed as the
shape factor
With increase in the pressure drop across the cake, the specific cake resistance for the compressible sludge
increases
increases
Size reduction of ice and gypsum can be accomplished suitably by a __________ crusher.
toothed roll
toothed roll
The ratio of the actual mesh dimension of Taylor series to that of the next smaller screen is
sqrt2
sqrt2
Which of the following is not used as a surface active agent in a flocculation operation?
Quartz
Quartz
Which of the following is a fine crusher?
Toothed roll crusher
Toothed roll crusher
The optimum moisture content in solids to be crushed/ground ranges from __________ percent.
3 to 4
3 to 4
The capacity of a gyratory crusher is __________ that of a jaw crusher with the same gape, handling the same feed & for the same product size range.
2.5 times
2.5 times
Dispersion of a gas through liquid is done by using a
sparger
sparger
