Mechanical Operations

61. Ball mill is used for

1. Crushing
2. Coarse grinding
3. Fine grinding
4. Attrition

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62. Ball mills and tube mills with flint or porcelain balls are used for size reduction of

1. Asbestos
2. Rubber
3. Non-metallic ores
4. Limestone

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63. Balls for ball mills are never made of

1. Forged/cast steel
2. Lead
3. Cast iron
4. Alloy steel

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64. Basic slag is not ground in

1. Jaw crushers
2. Ball mills
3. Compartment mills
4. Tube mills

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65. Bond crushing law

1. Calls for relatively less energy for the smaller product particles, than does the Rittinger law
2. Is less realistic in estimating the power requirements of commercial crushers
3. States that the work required to form particle of any size from very large feed is proportional to the square root of the volume to surface ratio of the product
4. States that the work required for the crushing is proportional to the new surface created

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66. Bucket elevators are not suitable for the vertical lifting of _________ materials.

1. Fine (e.g. - 200 mesh size coal)
2. Sticky (e.g. clay paste)
3. Small lumpy (e.g. grains and sand)
4. Free flowing

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67. Cake resistance is

1. Important in the beginning of filtration
2. Decreased with the time of filtration
3. Independent of pressure drop
4. None of these

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68. 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).

1. 0.01 L.S
2. 0.087 L.S
3. L.S
4. L.S/0.087

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69. Capacity of flight conveyor in tons/hr is given by (where, W & D = width and depth of flight respectively in metre V = speed of the conveyor, metre/second ρ = bulk density of material, kg/m₃)

1. 3.6 W.D.V.ρ
2. 3.6 W.D.V
3. 3.6 W.V.ρ
4. 3.6 D.V.ρ

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70. Carbon black is pulverised in a

1. Hammer crusher
2. Ball mill
3. Roll crusher
4. Gyratory crusher

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