Mechanical Operations

171. 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.

  1. Primary
  2. Secondary
  3. Fine
  4. Ultrafine

Correct answer: (B)
Secondary

172. 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.

  1. Secondary
  2. Fine
  3. Primary
  4. Ultrafine

Correct answer: (C)
Primary

173. In a size reduction crushing operation, the feed size is 10 to 50 mm, while the product size is 2 to 10 mm. This is a case of _________ crushing.

  1. Primary
  2. Secondary
  3. Fine
  4. Ultrafine

Correct answer: (C)
Fine

174. In bag filters, filter fabrics are never made of

  1. Metallic wire woven mesh
  2. Polyester fibres
  3. Cotton fibres
  4. Nylon fibres

Correct answer: (A)
Metallic wire woven mesh

175. 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 hardness))

  1. Db2 = K.Df
  2. Db = K.Df
  3. Db3 = K.Df
  4. Db2 = K.Df2

Correct answer: (A)
Db2 = K.Df

176. In case of a ball mill,

  1. Coarse feed requires a larger ball
  2. Fine feed requires a larger ball
  3. Operating speed should be more than the critical speed
  4. None of these

Correct answer: (A)
Coarse feed requires a larger ball

177. In case of a hammer crusher,

  1. Crushing takes place by impact breaking
  2. Maximum acceptable feed size is 30 cms
  3. Reduction ratio can be varied by adjusting the distance from cage to hammers
  4. All (A), (B) and (C)

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

178. In case of a hammer crusher, the final product size depends on the

  1. Feed rate
  2. Rotor speed
  3. Clearance between hammer & grinding plates
  4. All (A), (B) and (C)

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

179. In case of a plate and frame filter press, filtrate flow through the cake follows _________ flow.

  1. Plug
  2. Turbulent
  3. Laminar
  4. None of these

Correct answer: (C)
Laminar

180. In case of a revolving mill, wet grinding compared to dry grinding

  1. Requires more energy
  2. Has less capacity
  3. Complicates handling & classification of the product
  4. None of these

Correct answer: (D)
None of these

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