Mechanical Operations

A. Magnetic separation method can be employed to treat both dry & wet ores
B. Reduction ratio in crushing operation is defined as the ratio of minimum feed size to the
maximum product size
C. Gyratory crusher is used for coarse crushing
D. Screens are of stationary, moving and vibratory types

A. Cumulative analysis for determining surface area is preferred over differential analysis,
because of the assumption that “all particles in a simple fraction equal in size” is not needed
for cumulative analysis unlike differential analysis
B. A gate diagram is a plot of cumulative percent by weight undersize vs. the reciprocal of
diameter, in which the area beneath the curve represents the surface
C. Capacity of crusher in choke feeding is increased
D. Rolling of pebbles/balls from top to bottom of the heap in tumbling mills is called ‘cascading
and throwing of the balls through the air to the toe of the heap is called ‘cataracting’

A. For the compressible cake, voidage & the specific resistance of the cake can be assumed to be
constant
B. Cake resistance is independent of the pressure drop
C. Crushing of explosive materials are done by employing dry-grinding
D. Gyratory crusher is a coarse crusher

A. Recommended peripheral speed for the turbine agitator is 200-250 metres/minute
B. Pitched blade turbine agitator gives only radial flow with complete absence of the axial flow
C. Generally, the diameter of the agitator is kept between l/3rd to l/6th of the tank diameter while
the blade length is l/4th of agitator diameter (with central disc, it is l/8th of the agitator
diameter)
D. Turbine agitator should be located at a height not less than one agitator diameter length from
the bottom. If the depth of liquid in the tank is more than twice the agitator diameter, two
agitators should be used

A. Angle of repose is always greater than the angle of slide
B. A hopper is a small bin with a sloping bottom
C. A silo is a short height vessel of very large diameter used for the storage of high volatile
matter coal
D. Pine oil is used as a ‘modifying agent’ (for activating or depressing the adsorption of filming
agents) in froth floatation process

A. Plastic chips are called non-cohesive solids
B. Kick’s crushing law is, P/m = K . ln (D̅ sa/D̅ sb)
C. Communition is a generic term for size enlargement operation
D. Energy required in kwh per ton of product, such that 80% of it passes through a 200 mesh
screen, is called ‘Work index’

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

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

A. Close circuit grinding is more economical than open circuit grinding
B. Cod oil, beef tallow or aluminium stearates are used as grinding aids in cement ‘industries’
C. The equipment used for the removal of traces of solids from a liquid is called a classifier
D. Size enlargement is a mechanical operation exemplified by medicinal tablet making

A. Removal of iron from ceramic material is necessitated (by magnetic separation method) so as
to avoid discolouration of ceramic products
B. The operating cost of shaking screen is more than that of a vibrating screen
C. Screen capacity does not depend upon the specific gravity of the minerals
D. Asphalt is best crushed using toothed roll crusher