Mechanical Operations

151. Grinding efficiency of a ball mill is of the order of _________ percent.

  1. 43952
  2. 40-50
  3. 75-80
  4. 90-95

Correct answer: (A)
43952

152. Grizzlies are used for separating _________ solids.

  1. Coarse
  2. Fine
  3. Any size
  4. None of these

Correct answer: (B)
Fine

153. Gummy & sticky materials like molasses, sugar etc. are best transported/handled by using a _________ conveyor.

  1. Drag
  2. Ribbon
  3. Screw
  4. Slat

Correct answer: (B)
Ribbon

154. Gyratory crushers compared to the reciprocating jaw crushers

  1. Have greater capacity per unit of discharge area
  2. Crush intermittently
  3. Are less suitable for coarse materials
  4. Have less steady power consumption

Correct answer: (A)
Have greater capacity per unit of discharge area

155. Half the angle of nip, (α), for a roll crusher is given by (where, dr, dp and df are diameters of crushing rolls, feed particles and rolls gap respectively).

  1. cos α = (dr + dp)/(dr + df)
  2. cos α = (dr + df)/(dr + dp)
  3. tan α = (dr + dp)/(dr + df)
  4. sin α = (dr + dp)/(dr + df)

Correct answer: (A)
cos α = (dr + dp)/(dr + df)

156. Handling of ashes and similar materials can be done best by a _________ conveyor.

  1. Flight
  2. Drag or slat
  3. Belt
  4. Ribbon

Correct answer: (B)
Drag or slat

157. Height of liquid in agitation tank is normally maintained equal to the tank diameter. However, if the tank is too tall and a large liquid hold up is desired, then two or more impellers mounted on the same shaft may be used. The clearance between the tank bottom and the bottom most impeller should be about (where, D = impeller diameter)

  1. 0.5 D
  2. D
  3. 1.5 D
  4. 2 D

Correct answer: (B)
D

158. Helical screw agitator is used for

  1. Mixing highly viscous pastes
  2. Blending immiscible liquids
  3. Mixing liquids at very high temperature (> 250 °C)
  4. None of these

Correct answer: (A)
Mixing highly viscous pastes

159. Higher is the mesh number, smaller will be the aperture size of the screen. It means that the aperture size of a 200 mesh screen will be smaller than that of 20 mesh screen. This is valid for

  1. British standard screens
  2. German standard screens (DIN 1171) etc
  3. American standard screens (ASTM and Tyler standard screens)
  4. All (A), (B) and (C)

Correct answer: (D)
All (A), (B) and (C)

160. Highly viscous liquids & pastes are agitated by

  1. Propellers
  2. Turbine agitators
  3. Multiple blade paD5les
  4. None of these

Correct answer: (C)
Multiple blade paD5les

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