Mechanical Operations

371. Wet grinding in a revolving mill _________ as compared to dry grinding.

1. Gives less wear on chamber walls
2. Requires more energy
3. Increases capacity
4. Complicates handling of the product

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372. Wet sieving is employed, when the product contains _________ materials.

1. Abrasive
2. Large quantity of very fine
3. Coarse
4. Non-sticky

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373. 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?

1. 0.5
2. 1
3. 2.76
4. 0.66

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374. What is the selectivity index, if the grade of tailings & concentrate is the same?

1. 0
2. ∞
3. 1
4. 0.5

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375. What is the usual value of angle of nip for crushing of ordinary rock in smooth steel crushing rolls?

1. 16°
2. 32°
3. 40°
4. 46°

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376. Wheat is ground into flour in a

1. Hammer crusher
2. Roller crusher
3. Impact mill
4. Fluid energy mill

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377. Where the density difference of the two liquid phase to be separated is very small (as in milk cream separator), the most suitable separator is a

1. Disc bowl centrifuge
2. Sharpies super-centrifuge
3. Batch basket centrifuge
4. Sparkler filter

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378. Which is a secondary crusher for a hard & tough stone?

1. Jaw crusher
2. Cone crusher
3. Impact crusher
4. Toothed roll crusher

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379. Which is the most suitable conveyor for transportation of sticky material?

1. Apron conveyor
2. Belt conveyor
3. Screw conveyor
4. Pneumatic conveyor

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380. Which of the following achieves the least reduction ratio for a given feed size?

1. Jaw crusher
2. Roll crusher
3. Cone crusher
4. Gyratory crusher

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