Mechanical Operation

1. Which of the following is a coarse crusher?

a) Dire crusher b) Conical crusher

c) Single roll crusher d) Jaw crusher

2. Which of the following is a fine crusher ?

a) Hammer mill b) Edge runner mill

c) Pin mill d) Tube mill

3. Which of the following is

**coarse crusher ?**__not a__
a) Blake jaw crusher b) Disc crusher

c) Dodge jaw crusher d) Gyratory crusher

4. The size of feed to a fine crusher is

a) 60 to 1 ½ inch b) 2 to ¼ inch

c) ¼ to 1/8 inch d) less than 1/8 inch

5. Force responsible for size reduction in a hammer mill is predominantly

a) Impact b) Shear

c) Compressive d) none of the above

6. Names of a variety of size reduction equipment are given below. Classify them as coarse crushers, intermediate crushers and fine crushers.

Crushing rolls Dodge jaw crusher

Disc crusher Griffin mill

Ball mill Raymond mill

Tube mill Ring roller mill

Blake jaw crusher Conical crusher

Pin mill Edge runner mill

Hammer mill Buhrstone mill

Roller mill Gyratory crusher

Centrifugal ball mill

7. A broad classification of the size reduction equipment and a test of sizes of the materials fed into different equipment are given below. Selected the proper equipment – feed size combination.

__Equipment__

__Feed size__

Coarse crushers 0.2 mm

Intermediate crushers 5 to 2 mm

Fine crushers 50 to 5 mm

Colloid mills 1500 to 40 mm

8. In Blake jaw crusher, the angle between the jaws is usually

a) 5

^{0}b) 15^{0 }c) 30^{0 }e) 90^{0}
10. Length to diameter ratio of a ball mill is usually around

a) 0.25 b) 1 – 1.5

b) 10 d) 100

11.Length to diameter ratio of a tube mill is usually around

a) 1 or 2 : 10 b) 3 or 4 : 1

c) 400 or 500 : 1 d) 1000 or 2000 : 1

12. The characteristics of a ball mill and a tube mill are similar. Now, under otherwise uniform conditions (identical feed size, feed flow rate, etc.) a tube mill will produce

a) a finer product

b) a coarser product

c) a product of the same size as that produced by a ball mill

d) a product the size of which can not be even roughly predicted.

13. The Hardinge mill is basically a

a) Jaw crusher b) Roll crusher

c) Ball mill d) Colloid mill

14. Let R : Radius of ball mill; r : radius of particle. The critical speed of a ball mill is given by the expression

_{}

_{}

_{}

_{}

15. When a ball mill rotates at a speed higher than the critical speed, its efficiency is

a) maximum b) minimum

c) optimum d) none of these

16. Ball mills take feed upto about

a) 1 mm in size b) 50 mm in size

c) 500 mm in size d) 1400 mm in size

17. Conventional ball mills are now being replaced by a new type of ball mill which is vibrated instead of being rotated and the rate of passage of material is controlled by the slope of the mill. Now, increase in the slope of the mill.

a) Decreases the capacity of the plant and Decreases the product size

b) Increases the capacity of the plant but decreases the product size but

c) Increases the capacity of the plant and Increases the product size

e) Increases the capacity of the plant and decreases the product size

18. As the product size from a ball mill decreases,

a) the capacity and power requirement of the mill increase

b) the capacity increases, but the power requirement decreases

c) the capacity and power requirement of the mill decrease

d) the capacity decreases, but the power requirement increases

19. Force responsible for size reduction in a smooth roll crusher is predominantly

a) compressive b) impact

c) shear d) none of these

20. Force/Forces responsible for size reduction in a toothed-roll crusher is/are

a) impact b) shear

c) compressive d) a combination of all (a), (b), (c)

21. Select the correct “size reduction equipment predominant force responsible for size reduction” combination from the following lists :

Equipment Force (s) responsible for size reduction

Gyratory crusher Impact

Edge runner mill Shear

Fluid energy mill Tensile

Pin disc mill Compression

22. A bread classification of the different size reduction equipment and a list of product sizes obtained from the different equipment are given below. Select the proper equipment product size combination.

a) coarse crushers 0.01 cm

b) intermediate crushers 5 to 0.5 cm

c) fine crushers 0.01 microns

d) colloid mills 0.5 to 0.01 cm

23. The energy consumed by a crusher under conditions of “choke feeding” is

a) more than that in “free crushing”

b) less than that in “free crushing”

c) equal to that in “free crushing”

24. If size reduction is to be accomplished by passing the material only once through the crusher,

a) “free crushing” is a better choice

b) “choke feeding” is a better choice

c) both “free crushing” and “choke feeding” are equally useful

d) none of these

25. Under otherwise uniform conditions, size reduction ratio obtained in a ball mill

a) is greater than that obtained in a jaw crusher

b) is smaller than that obtained in a jaw crusher

c) is equal to that obtained in a jaw crusher

d) cannot be predicted, more information required

26. Grinding can be carried out either wet or dry. Now, power consumption in wet grinding is

a) more than that in dry grinding and plant capacity is increased

b) less than that in dry grinding and plant capacity is reduced

c) equal to that in dry grinding and plant capacity remains almost unchanged

d) less than that in dry grinding and plant capacity is increased

27. Which of the following statements about the advantages of wet grinding over dry grinding is/are incorrect ?

a) amounts of fines produced by wet grinding is less than that produced by dry grinding

b) removal of product is easier

c) dust formation is eliminated

d) plant capacity is reduced

28. In a ball mill, the optimum diameter of the balls used for grinding is approximately proportional to

a) the feed size b) the square of the feed size

c) the square root of the feed size d) none of the above

29. Optimum grinding conditions in a ball mill usually occur when the bulk volume of the balls is around

a) 10% of the volume of the mill b) 50% of the volume of the mill

c) 90% of the volume of the mill d) none of the above

30. Which of the following statements about the superiority of a Hardinge mill to a ball mill of similar size is/are incorrect ?

a) Hardinge mill consumes less power

b) It produces a finer product

c) its capacity is larger

d) Optimum speed of the mill can easily be fixed up

31. Standard screens always have

a) rectangular apertures b) triangular apertures

c) square apertures d) circular apertures

32. A “100 – mesh” screen means

a) there are 100 apertures per inch

b) each aperture of the screen has a diameter of 1/100 inch

c) each aperture has a diameter of 1/100 cm

d) none of the above

33. In the context of separation of particles by screening two terms are important : screen effectiveness and screen capacity. An increase in screen capacity

a) results in an increase in screen effectiveness

b) results in a reduction in screen effectiveness

c) does not alter the screen effectiveness at all

d) may alter the screen effectiveness marginally

34. For size reduction of a large plastic sheet into small units of fixed dimensions, which equipment is the most useful ?

a) jaw crusher b) roll crusher

c) rod mill d) rotary knife cutter

35. For a particle (coefficient of friction = μ ) to be crushed by a smooth roll crusher (angle of nip = L), which of the following relationships has to be satisfied ?

a) α ³ 2 tan

^{-1}μ b) μ ³ ½ tan^{-1}α
c) α £ 2 tan

^{-1}μ d) μ £ 2 tan^{-1}α
36. Crushing efficiency is the ratio of –

a) surface energy created by crushing to energy absorbed by the solid

b) energy absorbed by the solid to that fed to the machine

c) energy fed to the machine to surface energy created by the machine

d) energy absorbed by the solid to surface energy created by machine

37. Which of the following is a possible value of the angle of nip of a roll crusher ?

a) 5

^{0}b) 20^{0}c) 50^{0}d) 75^{0}
38. Crushing efficiencies are usually around

a) 0.1 to 2% b) 10 to 20%

c) 50 to 60% d) 80 to 90%

39. Bond crushing law states that the work required to produce particles of diameter Dp from very large fed is

a) proportional to the surface – to – volume ratio of the feed

b) proportional to the surface – to – volume ratio of the product

c) proportional to the square-root of the surface–to–volume ratio of the feed

d) proportional to the square-root of the surface–to–volume ratio of the product

40. Size reduction in a gyratory crusher is effected primarily by

a) impact b) shear

c) compression d) attrition

41. Work index is defined as

(a) The gross energy in kWh per ton of feed needed to reduce a very large feed to such a size that 80% of the product passes a 100 – Mm screen.

(b) The gross energy in kWh per kg of feed needed to reduce a particle of 0.5 m dia to such a size that 80% of the product passes a 100 – Mm screen.

(c) The gross energy in kWh per ton of product needed to reduce a very large feed to a product size of 0.01 m.

(d) None of the above.

42. According to Rittinger’s law, crushing efficiency

a) depends on the feed size b) depends on the product size

c) depends on both feed and product sizes

d) is constant and for a particular machine and feed material, is independent of the feed and product sizes.

43. The sphericity, Φ

_{s}, is defined by the relation_{}

_{}

_{}

_{}

44. For spheres and cubes, sphericity is equal to one. For a cylinder whose length is equal to diameter, sphericity is equal to –

a) 0.28 b) 0.65 c) 0.73 d) 1.0

45. There is a sample of spheres of a material; the diameter of each sphere is 1 mm. For this sample,

a) sauter mean diameter > arithmetic mean diameter

b) sauter mean diameter < mass mean diameter

c) arithmetic mean diameter > mass mean diameter

d) none of the above, All dia are equal

46. In constant – pressure filtration,

a) the filtrate flow rate is maximum at the start and decreases continuously to the end

b) the filtrate flow rate is minimum at the start and increases continuously to the end

c) the filtrate flow rate is constant throughout,

d) increases slowly to a constant value

47. At the beginning of filtration, the cake resistance is

a) maximum, b) optimum

c) minimum and greater than zero d) zero

48. A rotary drum filter is –

a) a continuous vacuum filter b) a discontinuous pressure filter

c) a continuous pressure filter d) none of the above

49. The thickness of cakes formed on industrial rotary vacuum filters is usually between

a) 0.5 and 2 mm b) 3.2 and 38 mm

c) 80 and 100 mm d) 200 and 400 mm

50. Filter aids are added to the slurry prior to filtration in order to form

a) compact cakes of low porosity b) cakes of increased porosity

c) crystalline cakes d) none of the above ;

51. Which of the following is a coarse crusher?

a) Dire crusher b) Conical crusher

c) Single roll crusher d) Jaw crusher

52. Which of the following is a fine crusher ?

a) Hammer mill b) Edge runner mill

c) Pin mill d) Tube mill

53. Which of the following is

**coarse crusher ?**__not a__
a) Blake jaw crusher b) Disc crusher

c) Dodge jaw crusher d) Gyratory crusher

54. The size of feed to a fine crusher is

a) 60 to 1 ½ inch b) 2 to ¼ inch

c) ¼ to 1/8 inch d) less than 1/8 inch

56. Force responsible for size reduction in a hammer mill is predominantly

a) Impact b) Shear

c) Compressive d) none of the above

57. Names of a variety of size reduction equipment are given below. Classify them as coarse crushers, intermediate crushers and fine crushers.

Crushing rolls Dodge jaw crusher

Disc crusher Griffin mill

Ball mill Raymond mill

Tube mill Ring roller mill

Blake jaw crusher Conical crusher

Pin mill Edge runner mill

Hammer mill Buhrstone mill

Roller mill Gyratory crusher

Centrifugal ball mill

58. A broad classification of the size reduction equipment and a test of sizes of the materials fed into different equipment are given below. Selected the proper equipment – feed size combination.

__Equipment__

__Feed size__

Coarse crushers 0.2 mm

Intermediate crushers 5 to 2 mm

Fine crushers 50 to 5 mm

Colloid mills 1500 to 40 mm

59. In Blake jaw crusher, the angle between the jaws is usually

a) 5

^{0}b) 15^{0 }c) 30^{0 }e) 90^{0}
60. Length to diameter ratio of a ball mill is usually around

a) 0.25 b) 1 – 1.5

b) 10 d) 100

61.Length to diameter ratio of a tube mill is usually around

a) 1 or 2 : 10 b) 3 or 4 : 1

c) 400 or 500 : 1 d) 1000 or 2000 : 1

62. The characteristics of a ball mill and a tube mill are similar. Now, under otherwise uniform conditions (identical feed size, feed flow rate, etc.) a tube mill will produce

a) a finer product

b) a coarser product

c) a product of the same size as that produced by a ball mill

d) a product the size of which can not be even roughly predicted.

63. The Hardinge mill is basically a

a) Jaw crusher b) Roll crusher

c) Ball mill d) Colloid mill

64. Let R : Radius of ball mill; r : radius of particle. The critical speed of a ball mill is given by the expression

_{}

_{}

_{}

_{}

65. When a ball mill rotates at a speed higher than the critical speed, its efficiency is

a) maximum b) minimum

c) optimum d) none of these

66. Ball mills take feed upto about

a) 1 mm in size b) 50 mm in size

c) 500 mm in size d) 1400 mm in size

67. Conventional ball mills are now being replaced by a new type of ball mill which is vibrated instead of being rotated and the rate of passage of material is controlled by the slope of the mill. Now, increase in the slope of the mill.

a) Decreases the capacity of the plant and Decreases the product size

b) Increases the capacity of the plant but decreases the product size but

c) Increases the capacity of the plant and Increases the product size

e) Increases the capacity of the plant and decreases the product size

68. As the product size from a ball mill decreases,

a) the capacity and power requirement of the mill increase

b) the capacity increases, but the power requirement decreases

c) the capacity and power requirement of the mill decrease

d) the capacity decreases, but the power requirement increases

69. Force responsible for size reduction in a smooth roll crusher is predominantly

a) compressive b) impact

c) shear d) none of these

70. Force/Forces responsible for size reduction in a toothed-roll crusher is/are

a) impact b) shear

c) compressive d) a combination of all (a), (b), (c)

71. Select the correct “size reduction equipment predominant force responsible for size reduction” combination from the following lists :

Equipment Force (s) responsible for size reduction

Gyratory crusher Impact

Edge runner mill Shear

Fluid energy mill Tensile

Pin disc mill Compression

72. A bread classification of the different size reduction equipment and a list of product sizes obtained from the different equipment are given below. Select the proper equipment product size combination.

a) coarse crushers 0.01 cm

b) intermediate crushers 5 to 0.5 cm

c) fine crushers 0.01 microns

d) colloid mills 0.5 to 0.01 cm

73. The energy consumed by a crusher under conditions of “choke feeding” is

a) more than that in “free crushing”

b) less than that in “free crushing”

c) equal to that in “free crushing”

74. If size reduction is to be accomplished by passing the material only once through the crusher,

a) “free crushing” is a better choice

b) “choke feeding” is a better choice

c) both “free crushing” and “choke feeding” are equally useful

d) none of these

75. Under otherwise uniform conditions, size reduction ratio obtained in a ball mill

a) is greater than that obtained in a jaw crusher

b) is smaller than that obtained in a jaw crusher

c) is equal to that obtained in a jaw crusher

d) cannot be predicted, more information required

76. Grinding can be carried out either wet or dry. Now, power consumption in wet grinding is

a) more than that in dry grinding and plant capacity is increased

b) less than that in dry grinding and plant capacity is reduced

c) equal to that in dry grinding and plant capacity remains almost unchanged

d) less than that in dry grinding and plant capacity is increased

77. Which of the following statements about the advantages of wet grinding over dry grinding is/are incorrect ?

a) amounts of fines produced by wet grinding is less than that produced by dry grinding

b) removal of product is easier

c) dust formation is eliminated

d) plant capacity is reduced

78. In a ball mill, the optimum diameter of the balls used for grinding is approximately proportional to

a) the feed size b) the square of the feed size

c) the square root of the feed size d) none of the above

79. Optimum grinding conditions in a ball mill usually occur when the bulk volume of the balls is around

a) 10% of the volume of the mill b) 50% of the volume of the mill

c) 90% of the volume of the mill d) none of the above

80. Which of the following statements about the superiority of a Hardinge mill to a ball mill of similar size is/are incorrect ?

a) Hardinge mill consumes less power

b) It produces a finer product

c) its capacity is larger

d) Optimum speed of the mill can easily be fixed up

81. Standard screens always have

a) rectangular apertures b) triangular apertures

c) square apertures d) circular apertures

82. A “100 – mesh” screen means

a) there are 100 apertures per inch

b) each aperture of the screen has a diameter of 1/100 inch

c) each aperture has a diameter of 1/100 cm

d) none of the above

83. In the context of separation of particles by screening two terms are important : screen effectiveness and screen capacity. An increase in screen capacity

a) results in an increase in screen effectiveness

b) results in a reduction in screen effectiveness

c) does not alter the screen effectiveness at all

d) may alter the screen effectiveness marginally

84. For size reduction of a large plastic sheet into small units of fixed dimensions, which equipment is the most useful ?

a) jaw crusher b) roll crusher

c) rod mill d) rotary knife cutter

85. For a particle (coefficient of friction = μ ) to be crushed by a smooth roll crusher (angle of nip = L), which of the following relationships has to be satisfied ?

a) α ³ 2 tan

^{-1}μ b) μ ³ ½ tan^{-1}α
c) α £ 2 tan

^{-1}μ d) μ £ 2 tan^{-1}α
86. Crushing efficiency is the ratio of –

a) surface energy created by crushing to energy absorbed by the solid

b) energy absorbed by the solid to that fed to the machine

c) energy fed to the machine to surface energy created by the machine

d) energy absorbed by the solid to surface energy created by machine

87. Which of the following is a possible value of the angle of nip of a roll crusher ?

a) 5

^{0}b) 20^{0}c) 50^{0}d) 75^{0}
88. Crushing efficiencies are usually around

a) 0.1 to 2% b) 10 to 20%

c) 50 to 60% d) 80 to 90%

89. Bond crushing law states that the work required to produce particles of diameter Dp from very large fed is

a) proportional to the surface – to – volume ratio of the feed

b) proportional to the surface – to – volume ratio of the product

c) proportional to the square-root of the surface–to–volume ratio of the feed

d) proportional to the square-root of the surface–to–volume ratio of the product

90. Size reduction in a gyratory crusher is effected primarily by

a) impact b) shear

c) compression d) attrition

91. Work index is defined as

(a) The gross energy in kWh per ton of feed needed to reduce a very large feed to such a size that 80% of the product passes a 100 – Mm screen.

(b) The gross energy in kWh per kg of feed needed to reduce a particle of 0.5 m dia to such a size that 80% of the product passes a 100 – Mm screen.

(c) The gross energy in kWh per ton of product needed to reduce a very large feed to a product size of 0.01 m.

(d) None of the above.

92. According to Rittinger’s law, crushing efficiency

a) depends on the feed size b) depends on the product size

c) depends on both feed and product sizes

d) is constant and for a particular machine and feed material, is independent of the feed and product sizes.

93. The sphericity, Φ

_{s}, is defined by the relation_{}

_{}

_{}

_{}

94. For spheres and cubes, sphericity is equal to one. For a cylinder whose length is equal to diameter, sphericity is equal to –

a) 0.28 b) 0.65 c) 0.73 d) 1.0

95. There is a sample of spheres of a material; the diameter of each sphere is 1 mm. For this sample,

a) sauter mean diameter > arithmetic mean diameter

b) sauter mean diameter < mass mean diameter

c) arithmetic mean diameter > mass mean diameter

d) none of the above, All dia are equal

96. In constant – pressure filtration,

a) the filtrate flow rate is maximum at the start and decreases continuously to the end

b) the filtrate flow rate is minimum at the start and increases continuously to the end

c) the filtrate flow rate is constant throughout,

d) increases slowly to a constant value

97. At the beginning of filtration, the cake resistance is

a) maximum, b) optimum

c) minimum and greater than zero d) zero

98. A rotary drum filter is –

a) a continuous vacuum filter b) a discontinuous pressure filter

c) a continuous pressure filter d) none of the above

99. The thickness of cakes formed on industrial rotary vacuum filters is usually between

a) 0.5 and 2 mm b) 3.2 and 38 mm

c) 80 and 100 mm d) 200 and 400 mm

100. Filter aids are added to the slurry prior to filtration in order to form

a) compact cakes of low porosity b) cakes of increased porosity

c) crystalline cakes d) none of the above ;

101. Hydrogenation of vegetable oils is conducted in “slurry reactors” which are basically agitated tanks. The purpose(s) of agitation is / are

a) to disperse hydrogen gas through the oil

b) to suspend catalyst uniformly throughout the entire volume of oil

c) to remove heat of reaction effectively so that oil is maintained at a constant temperature

d) all of the foregoing.

102. It can be shown by dimensional analysis that the power dissipated by an agitator can be correlated with two dimensionless numbers (characteristic of the system considered). The dimensionless numbers are

a) Reynolds number and Weber number

b) Weber number and Froude number

c) Reynolds number and Schmidt number

d) Reynolds number and Froude number

103. Below are given a list of agitators employed for liquid agitation in industry and a list of the different flow patterns achieved due to agitation. Select the right agitator-flow pattern combination.

**Agitator Flow pattern**

1. Propeller A. Axial flow with peripheral recirculation

2. Turbine B. Peripheral flow

3. Anchor C. Axial flow

4. Archimedes screw with guide cylinder D. Radial flow

104. Power number is proportional to the ratio of

a) drag force acting on a unit area of impeller to the inertial stress

b) gravity force acting on a unit area of impeller to the inertial stress

c) the inertial stress to the gravitational force per unit area acting on the fluid

d) none of the above

105. Below are given a number of cases, Identify the one for which Froude number is important,

a) Baffled tanks b) Side-entering propellers

c) Reynolds number less than 300 (unbaffled tank)

d) Reynolds number greater than 300 (unbaffled tank)

106. For a baffled vessel fitted with a six-blade turbine agitator being employed for liquid agitation,

a) the influence of Reynolds number on Power number becomes negligible at low Reynolds number values

b) the influence of both Reynolds number and Froude number on Power number becomes negligible at high Reynolds number values (greater than 10000)

c) the influence of both Reynolds number and Froude number on Power number becomes extremely important at high Reynolds number values (greater than 10000)

d) none of the above

107. At low Reynolds number the lines of power number vs. Reynolds number for both baffled and unbaffled tanks

a) coincide and the slope of the line on logarithmic coordinates is – 1

b) coincide and the slope of the line on semi-logarithmic coordinates is – 1

c) do not coincide, but they are parallel and have slope equal to – 2 on logarithmic co-ordinates

d) do not coincide, they are not parallel either; the sloped on logarithmic coordinates are – 1 and – 2 for baffled and unbaffled tanks

108. Consider agitation of a liquid in a baffled vessel by a turbine agitators having six flat blades. The power number for this case is practically constant for Reynolds number greater than

a) 1 b) 100 c) 1000 d) 10 000

109. Under otherwise uniform conditions two closely spaced turbines on the same shaft draw

a) the same power as that by a single turbine

b) approximately 2.4 times the power drawn by a single turbine

c) approximately 5 times the power drawn by a single turbine

d) approximately 9.6 times the power drawn by a single turbine

110. Under otherwise uniform conditions the shape of a tank (baffled as well as unbaffled) has

a) a very great effect on power number

b) relatively little effect on power number

c) on effect at all on power number