Mechanical OperationMCQ’S UNIT I & II 1. Pebble mills are tumbling mills widely used for grinding in the manufacture of paints & pigments and cosmetic industries, where iron contamination in the product is highly objectionable. Pebbles used in pebble mill are made of a) Stainless steel b) Bronze c) Concrete d) Flint or porcelain 2. Crushing of mineral particles is accomplished in a ‘cage mill’, when one or more alloy steel bars are revolved in opposite directions. It is a type of __________ mill. a) Vibratory b) Impact c) None of these d) Roll 3. The energy required per unit mass to grind limestone particles of very large size to 100 μm is 12.7 kWh/ton. An estimate (using Bond’s law) of the energy to grind the particles from a very large size to 50 μrn is a) 25.4 kWh/ton b) 6.35 kWh/ton c) 9.0 kWh/ton d) 18 kWh/ton 4. Size reduction of the __________ can be suitably done by ball mills, crushing rolls and rod mills. a) Non-metallic ores b) Basic slags c) Asbestos & mica d) Metalliferrous ores 5. Pick out the correct statement: a) Screen capacity does not depend upon the specific gravity of the minerals. b) Asphalt is best crushed using toothed roll crusher. c) The operating cost of shaking screen is more than that of a vibrating screen. d) Removal of iron from ceramic material is necessitated (by magnetic separation method) so as to avoid discoloration of ceramic products 6. The value of ‘angle of nip’ is generally about a) 16° b) 52° c) 64° d) 32° 7. The main size reduction operation in ultrafine grinders is a) Cutting b) Attrition c) Compression d) Impact 8. Jigging is a technique by which different particles can be a) Separated by particle size. b) Separated by particle density. c) Separated by particle shape. d) Mixed 9. A tube mill compared to a ball mill a) Uses much larger balls. b) Has a higher diameter/length ratio. c) Produces a coarser product. d) Has a higher length/diameter ratio. 10. In case of a hammer crusher, the a) Minimum product size is 3 mm. b) Feed may be highly abrasive (Moh's scale >5). c) Rotor shaft carrying hammers can be vertical or horizontal. d) Maximum feed size may be 50 mm. 11. Length/diameter ratio of a ball mill is a) >1 b) <1 c) 1 d) 1.5 12. Screen capacity is not a function of a) Atmospheric humidity. b) Screening surface. c) Screening mechanism. d) Its openings size 13. Grindability of a material does not depend upon its a) Hardness b) Elasticity c) Size d) Toughness 14. 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) a) 0.087 L.S b) L.S/0.087 c) 0.01 L.S d) L.S 15. Energy consumed for crushing one ton of material ranges from __________ kWh. a) 4 to 5. b) 0.5 to 1.5 c) 0.01 to 0.1 d) 2 to 3.5 16. Rittinger’s number designates the new surface created per unit mechanical energy absorbed by the material being crushed. Larger value of Rittinger’s number of a material indicates its a) High power consumption in grinding b) Poor grindability c) Easier grindability d) None of these 17. Trommels separate a mixture of particles depending on their a) Density b) Electrical & magnetic properties c) Size d) Wettability 18. Bond crushing law a) 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. b) Is less realistic in estimating the power requirements of commercial crushers. c) States that the work required for the crushing is proportional to the new surface created. d) Calls for relatively less energy for the smaller product particles, than does the Rittinger law. 19. Ball mill is used for a) Attrition b) Fine grinding c) Coarse grinding d) Crushing 20. In case of a ball mill, a) None of these b) Operating speed should be more than the critical speed. c) Fine feed requires a larger ball. d) Coarse feed requires a larger ball. 21. Maximum size reduction in a ball mill is done by the, __________ action. a) Impact b) Compression c) Attrition d) Cutting 22. Crushing efficiency is the ratio of the a) Energy absorbed by the solid to the surface energy created by crushing. b) Energy fed to the machine to the surface energy created by crushing. c) Surface energy created by crushing to the energy absorbed by the solid. d) Energy absorbed by the solid to that fed to the machine 23. Which of the following is used for primary crushing of very hard lumpy materials? a) Ball mill b) Gyratory crusher c) Toothed roll crusher d) Tube mill 24. Cement clinker is reduced to fine size by a a) Ball mill b) Roll crusher c) Hammer mill d) Tube mill 25. The crushed material received for separation is called feed or a) Middling b) Heading c) Tailing d) Concentrate 26. Increasing the capacity of a screen __________ the screen effectiveness. a) Does not effect b) Increases c) None of these d) Decreases 27. Feed size of ≥ 25 cms can be accepted by a) Fluid energy mill b) Rod mill c) Ball mill d) Jaw crusher 28. Which of the following relationships between co-efficient of friction (μ) between rock & roll and a (half of the angle of nip) of the particle to be crushed is correct? a) μ > tan α b) μ ≥ tan α c) μ > tan 2α d) μ ≤ tan α 29. Which of the following is not an ultrafine grinder (colloid mill)? A Micronizers . B.Agitated mills and fluid energy mills C.Toothed roll crusher D Hammer mills with internal classification . 30. Number of particles in a crushed solid sample is given by (where, m = mass of particles in a sample, Vp = volume of one particle, ρ= density of particles) A m/ρ . Vp . B.m . ρ/Vp C.m . Vp/ρ D V /m . ρ . p An estimate (using Bond's law) of the energy to grind the particles from a very large size to 50 μrn is A 6. Pick out the wrong statement. C. 31. . Size reduction of the __________ can be suitably done by ball mills. For a non-spherical particle.non-metallic ores C. B. D is the ratio of volume of a sphere having the same surface area as the particle to the actual . B.is always less than 1. crushing rolls and rod mills.9.18 kWh/ton D 25. volume of the particle. The energy required per unit mass to grind limestone particles of very large size to 100 μm is 12. D Size enlargement is a mechanical operation exemplified by medicinal tablet making.has the dimension of length.A is defined as the ratio of surface area of a sphere having the same volume as the particle to the .basic slags D asbestos & mica . actual surface area of the particle.7 kWh/ton.35 kWh/ton . C. B. A metalliferrous ores . 34.The equipment used for the removal of traces of solids from a liquid is called a classifier.Cod oil.4 kWh/ton . B. the sphericity 32. beef tallow or aluminium stearates are used as grinding aids in cement 'industries'. A Close circuit grinding is more economical than open circuit grinding. . 33. .0 kWh/ton C. A crushing takes place by impact breaking. Jigging is a technique by which different particles can be A separated by particle size. 2. It is a type of __________ mill. . B. B. .1. 35. B. . (b) and (c). C. when one or more alloy steel bars are revolved in opposite directions.inch D inch2 .cm C.reduction ratio can be varied by adjusting the distance from cage to hammers.separated by particle shape. D mixed. 200 mesh screen means 200 openings per A 2 cm . C. A Impact . In case of a hammer crusher.separated by particle density.maximum acceptable feed size is 30 cms. B. . . Crushing of mineral particles is accomplished in a 'cage mill'.vibratory D none of these . 36.Roll C. D all (a). Trommels separate a mixture of particles depending on their A Size .has a higher diameter/length ratio.01 to 0. 3. In case of a hammer crusher. 38. B.5 to 1. Energy consumed for crushing one ton of material ranges from __________ kWh. A tube mill compared to a ball mill A has a higher length/diameter ratio.toughness Size . . the A feed may be highly abrasive (Moh's scale >5).minimum product size is 3 mm. C.wettability D electrical & magnetic properties . A 0.Density C.5 C.1 . B.37.produces a coarser product. 39. .maximum feed size may be 50 mm. . C. D uses much larger balls.0.5 D 4 to 5. B. 40. . B. Grindability of a material does not depend upon its A elasticity B. D C.Hardness .2 to 3. . S C.screening mechanism.5 . General crushing equation is given by . cm S = greater width of the discharge opening.087 L.S D L. .screening surface.high power consumption in grinding D none of these . 43. Screen capacity is not a function of A its openings size. cm) A 0. C. .5 .2 2. Rittinger's number designates the new surface created per unit mechanical energy absorbed by the material being crushed.poor grindability C. 42. Capacity (in tons/hr) of jaw/gyratory crusher is equal to (where. B.D rotor shaft carrying hammers can be vertical or horizontal. Bond's crushing law isobtained by solving this equation for n = __________ and feed of infinite size. 41.1.0. B. A 1 B. Larger value of Rittinger's number of a material indicates its A easier grindability . . 44.S/0.L. B. D C.087 .01 L.S . L = length of the receiving opening. 1 C.coarse grinding C. B. .fine grinding D Attrition .1 C. Ball mill is used for A Crushing .< 1 D >1 . 46.fluid energy mill D jaw crusher . 45. 48. B.5 . Sphericity of a cubical particle. is A 0.rod mill C. . when its equivalent diameter is taken as the height of the cube. 47.5 . Feed size of ≥ 25 cms can be accepted by A ball mill . B. Length/diameter ratio of a ball mill is A 1.D atmospheric humidity. B.2 D 3 . Which of the following is used for primary crushing of very hard lumpy materials ? A Toothed roll crusher . B. A coarse feed requires a larger ball. . 50. D none of these .Gyratory crusher C. 51.is less realistic in estimating the power requirements of commercial crushers.ball mill C. 52. B. Bond crushing law A calls for relatively less energy for the smaller product particles. . D states that the work required for the crushing is proportional to the new surface created. In case of a ball mill. states that the work required to form particle of any size from very large feed is proportional C. B. to the square root of the volume to surface ratio of the product. .49.operating speed should be more than the critical speed. Coal is finally pulverised to 200 mesh size for burning in boilers by a A hammer crusher . .fine feed requires a larger ball. than does the Rittinger law. B.Ball mill D Tube mill . C.roll crusher D gyratory crusher . 0. A Cast iron . 55. __________ balls capable of grinding the feed in a ball mill gives the maximum efficiency. The sphericity of a cylinder of 1 mm diameter and length 3 mm is A 0.53.much more than C.energy fed to the machine to the surface energy created by crushing.6 0.energy absorbed by the solid to that fed to the machine. B. . C.5 . 57. 54.squirrel-cage disintegrator C.0. . Crushing efficiency is the ratio of the A surface energy created by crushing to the energy absorbed by the solid. B. D C. B. 56. The operating speed of a ball mill should be __________ the critical speed.78 . A less than .9 B. D energy absorbed by the solid to the surface energy created by crushing.ball mill D tube mill . Fibrous material is broken by a A rollcrusher .at least equal to D slightly more than . Minimum size C.50 75 . the ball charge should be equal to about __________ percent of the ball mill volume. 59. 58. B.attrition . D C.Maximum size D Elliptical . Colloid mills achieve size reduction mainly by A Impact B. For achieving maximum capacity of the ball mill.Cutting compression . A 10 B.25 .. D C. . B.machine capacity D none of these . Size reduction mechanism used in Jaw crushers is . B.(S/V)2p D (S/V)f . the work required to form particle of size 'D' from very large feed is (where (S/V)p and (S/V)f are surface to volume ratio of the product and feed respectively).average product size C. 62.Kick's law C. 63. 64. According to Bond crushing law. A (S/V)p . B.(S/V)p C. B. Which of the following gives the work required for size reduction of coal to -200 mesh in a ball mill most accurately ? A Rittinger's law .Bond's law D none of these . 61.woven wire screen C. Electrical energy consumed by a jaw crusher is not a function of the A average feed size .punched plate D none of these . A fibrous cloth . Trommels employ __________ for screening of materials.60. The constants (Kb.jaw crushers D smooth roll crushers . B. A. A Weight .Volume C. Size reduction does not occur due to compression in case of A rod mills .either (a) or (b) D neither (a) nor (b) . A compartment B. . D C.tube .both (a) & (b). B.Cutting D impact . 66.. 67. . __________ mill is a revolving mill divided into two or more sections by perforated partitions in which preliminary grinding takes place at one end and the finishing grinding at the discharge end.type of crushing machine.e. B. B. Kr and Kk) used in the laws of crushing (i.gyratory crushers C. Bond's law.compression C. Rittinger's law and Kick's law) depend upon the A feed material. Specific surface area is the surface area of a unit __________ of materials. D neither (a) nor (b). 65. .Rod pebble. 68. C.A attrition . . .hammer crusher C. . with a given energy input to the size reduction machine.remains unchanged D may increase or decrease. 71. depends on the machine . . 69. Production rate __________ with increased fineness.5 to 3. D all 'a'. A jaw crusher .employ steel rods of 2-12 cms diameter extending over full length of the mill. 'b' & 'c'.increases C. 70. A decreases . C. B. B.ball mill D tube mill . Rod mills employed for grinding A employ a steel shell having L/D ratio of 1. B.is useful for handling sticky materials.0. Run of mine (ROM) coal is crushed by a __________ for use in domestic ovens. Horsepower required for a roll crusher is directly proportional to its A reduction ratio. D both (b) and (c). Sphericity is the ratio of the surface area of a spherical particle having the same volume as the particle to the surface area of the particle. A Gape is the greatest distance between the crushing surfaces or the jaws. 73. . 75. C.gyratory crushers D crushing rolls . B. .is a tube mill lined with ceramic or other non-metallic liner. B. . C. . 74. Which of the following has the maximum value of sphericity ? A Sphere .rod mills C. . B. Size reduction of asbestos and mica is done by A hammer mills .72. B.both (a) & (b). D neither (a) nor (b). Pick out the wrong statement.employs flints or ceramic pebbles as the grinding medium.Cube C.Cylinder (L/D = 1) D Raschig rings .capacity. . A pebble mill A is a ball mill. 76. The angle of nip (2α) is the angle between roll faces at the level where they will j ust take hold of a particle and draw it in the crushing zone. B. created by crushing. . B. product. Crushing efficiency is the ratio of the energy absorbed by the solid to the surfaces energy C. 77.Pulverisation D Compression . D Reduction ratio is the ratio of the maximum size of the particles in the feed to that in the .Dispersion C. Which of the following terminology is not used for size reduction of materials to fine sizes or powders? A Comminution . . . B. kg D kg/sec. (b) and (c). 80.Fick's law C. Critical Speed (Nc) of a ball mill is given by(where R1 and R2 are radii of ball mill and the ball respectively).has larger length/diameter ratio (>2 as compared to 1 for ball mill).kWh/kg C. C. 79. C. .78. B.gives finer size reduction but consumes more power. B. A . 81. sec/kg . B. D all (a).kWh/sec.Rittinger's law D none of these . Kick's law assumes that the energy required for size reduction is proportional to the logarithm of the ratio between the initial and the final diameters. A tube mill as compared to a ball mill A employs smaller balls. . Which of the following gives the crushing energy required to create new surface ? A Taggarts rule . The unit of Kick's constant is A kW. 83. B.complicates handling & classification of the product.Pyrite . B. B. wet grinding compared to dry grinding A requires more energy.has less capacity. .D . A Hammer . A Calcite B. Pick out the material having minimum Rittinger's number. D none of these.jaw crusher .Cage C.Fine C. 85. In case of a revolving mill. 86. C. the equipment used is A roller crusher .any size D none of these . D C. B.ball mill C. A Coarse . Gizzlies are used for separating __________ solids. To get a fine talc powder from its granules.Quartz Galena . __________ mills are termed as impactors. .Rolling-compression D none of these . 84. 82. This is valid for A British standard screens. diameter.Capacity of crusher in choke feeding is increased.American standard screens (ASTM and Tyler standard screens). It means that the aperture size of a 200 mesh screen will be smaller than that of 20 mesh screen. the reciprocal of B. . in which the area beneath the curve represents the surface. D all (a). C. A gate diagram is a plot of cummulative percent by weight undersize vs. A because of the assumption that "all particles in a simple fraction equal in size" is not needed . B. smaller will be the aperture size of the screen. (b) and (c). 88.German standard screens (DIN 1171) etc. D Rolling of pebbles/balls from top to bottom of the heap in tumbling mills is called 'cascading . . Cummulative analysis for determining surface area is preferred over differential analysis. 87.D gyratory crusher . Higher is the mesh number. . Pick out the wrong statement. C. and throwing of the balls through the air to the toe of the heap is called 'cataracting'. for cummulative anslysis unlike differential anlaysis. Which of the following grinding mills has the horizontally arranged rods as the grinding elements thereby delivering more uniform granular products with minimum fines ? A Compartment mill . C.Pebble mill D Tube mill.are less suitable for coarse materials. Gyratory crushers compared to the reciprocating jaw crushers A have greater capacity per unit of discharge area. 90. . . surface to volume ratio of the product. 93.Ultrafine Intermediate . B.Fluid energy mill C. Use of 'grinding aids' is done in __________ grinding. B. B. Rittinger's crushing law states that A work required to form a particle of any size is proportional to the square of the surface to . D C. work required to form a particle of a particular size is proportional to the square root of the B. D have less steady power consumption. volume ratio of the product.Micronizer D all (a). . A Dry B. (b) and (c) .Rod mill C.89.work required in crushing is proportional to the new surface created.crush intermittantly.Wet . C. . 91. 92. Which of the following size reduction equipments employs mainly attrition for ultrafine grinding ? A Jet mills . crushing efficiency is dependent on the size of the feed & . 94. Which of the following is the hardest material ? A Calcite B.Corundum Gypsum . 96. B. C. .10-20 C.D for a given machine and feed.kW/ton D kWh. Sphericity of pulverised coal is A 1 .kWh/ton C.Quartz .>1 B.m1/2/ton . B. . D C. 97. The work index in Bond's law for crushing of solids has the following dimensions A no units (dimensionless) .compression. product. C.compression and tearing. 98. .<1 D ∞ . General mechanism of size reduction in intermediate and fine grinder is by A cutting action.20-40 D as high as 100 . B. 95. D impact and attrition. The reduction ratio for fine grinders is A 5-10 . B. P/m = K . ln C. 100.99.Impact crusher D Toothed roll crusher . . k = a constant feed & product respectively. = volume surface mean diameter of . Which is a secondary crusher for a hard & tough stone? A Jaw crusher .Cone crusher C. 102.Micron D surface area per unit mass . Size measurement of ultrafine particles can be best expressed in terms of A centimetre .determining factor for minimum dia of the feed and the product.) A P/m = K/Dp . B. B. Reduction ratio of crushers is the A ratio of feed opening to discharge opening. B. P/m = K . Which of the following equations is Rittinger's crushing law ? (where P = power required by the machine. D none of these. m = feed rate. . .ratio of discharge opening to feed opening.screen size C. D none of these. C. 101. (b) and (c). ball mills must be operated A at a speed less than the critical speed.remains constant D may increase or decrease . . C.capacity and effectiveness of the screen is increased. For efficient grinding. D powdered food & granular materials. C. Reciprocating screens are normally inclined at an angle of 5° with the horizontal and employ gyratory motion at feed end & reciprocating motion at the discharge end. 106. 107. 104. . D all (a). depends on the A state or manner of application of the crushing force.elastic constant of the material. . B.dry chemicals. depends on the material being ground . As particle size is reduced A screening becomes progressively more difficult. C. .screening becomes progressively easier. . B. .103. .decreases C. Temperature of the product during ultrafine grinding A increases . B.ultimate strength of the material.heavy tonnages of rocks or gravel. They are not suitable for the screening of the A light metal powder down upto 4 meshsize. 105. D none of these. Rittinger number which designates the new surface prduced per unit of mechanical energy absorbed by the material being crushed. B. . D C. while the product size is 2 to 10 mm. A fluid energy mill is used for A Cutting . 111.5 mm screen and retained on 10 mm screen.B. In screen analysis.Feldspar . 109.Dp/Df C. D with minimum possible small balls.at a speed equal to the critical speed.Corundum Calcite .at a speed more than the critical speed. .Grinding C.secondary . 108. This is a case of __________ crushing. the notation +5 mm/-10 mm means particles passing through A 10 mm screen and retained on 5 mm screen. A D /D .ultra grinding D Crushing . 112. . D C. B. Df and Dp are average diameters of feed and product respectively). the feed size is 10 to 50 mm. f p B. .Dp D none of these . 110. In a size reduction crushing operation. A primary B. The reduction ratio for grinders is defined as(where. B. C.fine ultrafine . Which of the following is the softest material ? A Talc B.Df . 113.5 . 117. 116.both 5 mm and 10 mm screens.45 B.45 .1. 115. then the same for open circuit grinding will be A 0. D neither 5 mm nor 10 mm screen.33-1. rpm of a trommel at critical speed is given by (where.34 Wi D 3. Maximum size reduction in a fluid energy mill is achieved by . 114. . The value of work index does not change materially from one equipment to another. C.33-0. D C. B. D C.5 Wi . Grinding efficiency of a ball mill is of the order of __________ percent.5-2 1. A 1-5 B. If the value of work index determined for close circuit grinding is Wi. A .75 D .75-80 90-95 . D 76. Optimum ratio of operating speed to critical speed of a trommel is A 0.40-50 . D = Diameter of trommel in ft) B.34 Wi .Wi C.C.5-2.1.0. A Compression . 119. dr. feed particles and rolls gap respectively). (α).Cutting D Impact .Cone crusher C. C. B.Gyratory crusher D None of these . A . . Which of the following comes in the category of primary crusher for hard and tough stone ? A Jaw crusher . Which of the following crushers can be considered as a combination of a jaw crusher and a roller crusher ? A Rod mill . dp and df are diameters of crushing rolls. B. for a roll crusher is given by (where. D . 118.Gyratory crusher D Ball mill . B. B.interparticle attrition C.Fluid energy mill C. Half the angle of nip. 120. 2 m diameter charged with 70 mm dia balls ? A 0. B. B.121. B.76 0. D all (a).2. (b) and (c). B. In a roll crusher. C.tons/ft2 C. both the rolls A have the same diameter. D all (a). .run either at the same or different speeds. . . What is the critical rotation speed in revolutions per second.66 .1. 122. 123. (b) & (c).are rotated towards each other.5 B. for a ball mill of 1.20 to 25 D 50 to 70 .0 .both (a) & (b) D tons/hr-ft2 . 124. Crushing efficiency of a machine ranges between __________ percent.5 to 10 C. A 0. Screen capacity is expressed in terms of A tons/hr . C.1 to 2 . 125.uses smaller balls. Tube mill compared to ball mill A produces finer products. . . D C.is long in comparison with its diameter. matter coal.tube mill D squirrel-cage disintegrator .rotation per second) of a trammel is equal to (where.81 m/sec2 and. r = radius of trammel. C. For the preliminary breaking of hard rock. A Angle of repose is always greater than the angle of slide. Critical speed of rotation.production rate at a given limiting size is lower. C. N (in rps . metre. .A hopper is a small bin with a sloping bottom. . B. D operation is economical. g = acceleration due to gravity = 9. . we use a A gyratory crusher . D Pine oil is used as a 'modifying agent' (for activating or depressing the adsorption of filming .product has lesser size uniformity. D . B.ball mill C. agents) in froth floatation process. In closed circuit grinding as compared to open circuit grinding. ) A . 129. B.126. 128. 127. Pick out the correct statement. B. . the A specific surface of product is more. A silo is a short height vessel of very large diameter used for the storage of high volatile C. A Secondary B. The opening of a 200 mesh screen (Taylor series) is A 0. .fine .Primary ultrafine . B. This is a case of the __________ crushing. B. .0.the size reduction ratio. feed size is 300 to 1500 mm while the product size is 100 to 300 mm. For crushing of solids. the Rittinger's law states that the work required for crushing is proportional to A the new surface created.0.130. . C. D none of these. 131. 132.0074 mm C. In a size reduction crushing operation.the change in volume due to crushing.0047 cm D 74 mili-microns . D C.0074 cm . 137.133. B.jet mill D pin mill .bag filter C.speed of the rolls .Gyratory crusher D Tube mill . To produce talcum powder. Metallic wire mesh is used as a filtering medium for the separation of dust from dust laden gas in case of a/an A air filter . 134.venturi scrubber D Hydrocyclones . 136.Toothed roll crusher C. Which of the following crushing laws is most accurately applicable to the fine grinding of materials ? A Bond's crushing law . Angle of nip of the crushing rolls does not depend upon the A diameter of the rolls . B. 135.hammer mill C.Rittinger's law D None of these. B.Kick's law C. use A ball mill . Which of the following is a coarse crusher? A Smooth roll crusher . B. B. . B. impact. reduction equipments employ. 138. There are only four methods namely compression.Compression C.Cutting machines mainly employ 'attrition' for size reduction of solids. C.Cage mill D Rod mill . universal jaw crushers.product size D feed size .N ∝ D C.C. N∝ B. Pick out the wrong statement.Pebble mill C. Soft & non-abrasive materials can be made into fines by A Attrition . A More commonly used jaw crusher between Dodge jaw crusher and Blake jaw crusher is the . N∝ 141.N ∝ D D . 140. The critical speed of a trommel (N) is related to its dia (D) as A . attrition and cutting. D Operating principles of Dodge and Blake jaw crushers are combined in the working of . Which of the following is not a revolving/tumbling mill used for size reduction? A Compartment mill . later one. B. . 139. which the size B.Cutting D none of these . .142. D C.0 B.34 4.fine ultrafine . Which of the following achieves the least reduction ratio for a given feed size? A Jaw crusher .1.34 . The value of work index determined for wet grinding should be multiplied with __________ to get the same for dry grinding.Compression Cutting .both (a) & (b). B. This is a case of the __________ crushing. C.5 . A 1. B. 143. .1 mm screen.Cone crusher D Gyratory crusher .0. D C. D neither (a) nor (b).secondary . Work index is the gross energy (kWh/tonne of feed) necessary to reduce a very large feed to such a size that 80% of product particles will pass through a 0. . feed size is 100 to 300 mm.Roll crusher C. 144. 145. Close circuit grinding by a ball mill with air sweeping employs a A classifier. use A Impact B. while the product size is 10 to 50 mm.cyclone separator between mill & classifier.Attrition . 146. For coarse reduction of hard solids. D C. In a size reduction crushing operation. A primary B. 151.rod mill C.consumes less power. A 2 Dp B. Toothed roll crushers achieve size reduction by A tearing (shear) and compression.consumes more power. 150. B.1/Dp 1/D2p .147. B.both (a) & (b). Dp = diameter of particle).roller crusher C. B. B. 148.Dp . Wheat is ground into flour in a A hammer crusher . . . The specific surface of sherical particles is proportional to (where. . C. .hammer crusher D fluid energy mill . D C. . To get ultrafine particles. D neither (a) nor (b). 149. C. the equipment used is a A ball mill .impact and attrition.impact mill D fluid energy mill . D both (a) and (c). Choke crushing (in case of a Jaw crusher) compared to free crushing A results in increased capacity. A Tube B. . B. asbestos. In case of grinding in a ball mill A wet grinding achieves a finer product size than dry grinding. D all (a).stamp mill D Bradford's breaker . D C. . mica etc. 153.Intermediate . D none of these.cage mill C.decreasing machine capacity. Size reduction of fibrous materials like wood. . the energy consumed decreases with the A decreasing size of product at constant size of feed. D C. (b) and (c). B. 154. is done by a disintegrator exemplified by the A Blake jaw crusher . C. Colloidal mills are used for __________ grinding.its capacity decreases with increasing fineness of the products. During size reduction by a jaw crusher. A coarse B.152.increasing size of feed at constant reduction ratio. . __________ mill is normally used for grinding of talc.Ring-roll Pebble . 155. B.grinding cost and power requirement increases with increasing fineness of the products. . 156. C.Compartment .fine Ultrafine . . overflow and underflow were found to be 0. 0.attrition cutting . D C. A sand mixture was screened through a standard 10-mesh screen.62 . The material is crushed in a gyratory crusher by the action of A impact B.157. The screen effectiveness based on the oversize is A 0. 159. Energy requirement (per unit mass of material crushed/ground) is highest for A jaw crusher .58 .50 B.22 respectively.compression .79 and 0.68 0.0.ball mill D fluid energy mill . B. The mass fraction of the oversize material in feed. D C.rod mill C.38.0. 158. A 0. The energy consumed by a ball mill depends on A its speed. . 164.assumption that all particles in a single fraction are equal in size. because of the A assumption that all particles in a single fraction are equal in size. B. D all (a). Vibrating screens have capacity in the range of __________ tons/ft2 . 162. 163.50 to 100 D 100 to 250 . (b) and (c). B.its ball load. 161. C. . B.the density of the material being ground.size of feed (at constant reduction ratio). (b) & (c).mm mesh size. .capacity of the crushing machine. B.Roll C. C.160. The term 'angle of nip' is concerned with the operation of the __________ crushers. A Jaw . Cumulative analysis for determining surface is more precise than differential analysis. Energy consumption in a crusher decreases with increase in the A size of the product (at constant feed size). . C. is not needed.8 . D all (a).5 to 25 C.fact that screening is more effective. B.2 to 0.Gyratory D none of these . . . 165.D none of these.Rod and tube C. . B.Compartment D all (a). . __________ mills fall in the category of tumbling mills. A Ball and pebble . (b) & (c) . 40° 46° .Ball mill.74 D 200 . 167. Fluid energy mill C. 169.ball mill C. Arrange the following size reduction equipment in the decreasing order of the average particle size produced by each of them. B. Ball mill. B. saw dust.Fluid energy mill.Slitters D Tube mills . Jaw crusher . Jaw crusher. . Which of the following is not a cutting machine? A Dicers .32° . Fluid energy mill . D C. B. B. pigments. 170. What is the usual value of angle of nip for crushing of ordinary rock in smooth steel crushing rolls ? A 16° B.. Ball mill D Fluid energy mill.154 200 mesh seive size corresponds to __________ microns.crushing rolls D hammer mill . spices. Ball mill. grains. 168. Jaw crusher. A Jaw crusher. For grinding of cereals. A 24 . cork etc. C.Knife cutters C.166. the most extensively used size reduction equipment is a A Buhrstone mill . Which of the following parts of a jaw crusher is subjected to maximum wear and tear during its operation ? A Check plates .Jaw plates C.171. . B.Toggles D Crush shaft . . the specific power consumption and the production rate is affected by the A reduction ratio. In a roll crusher.1 C. . A π . 175. . A . . D neither (a) nor (b).both (a) and (b). B.(π/6)1/2 B. 173. B. B.2 D none of these .differential roll speed. The mechanism of size reduction by a hammer mill is by impact and attrition between the A grinding element & the housing. The specific surface of spherical particles is given by (where D and ρ are diameter and density of particle). The sphericity of a solid particle of cubical shape is C. C.5 .(π/6)1/3 D π/3 . 176.172. D . C. 174. The ratio of the area of openings in one screen (Taylor series) to that of the openings in the next smaller screen is A 1. feed particles. . .Grizzly D Trommel . Which of the following is not an industrial screening equipment ? A Sharpies centrifuge .B. C.Vibrating screen C. B. D neither (a) nor (b). 177.both (a) and (b). B.increases capacity D complicates handling of the product .both (a) & (b) D neither (a) nor (b) .. .. D C.requires more energy C. 2. Wet grinding in a revolving mill __________ as compared to dry grinding.. A gives less wear on chamber walls . The cumulative mass fraction of particles smaller than size dj for a collection of Ni particles of diameter di and mass mi (i = 1. 3. . Aperture width of IS screen of mesh number 50 will be approximately __________ microns. 181. C. The grinding in a hammer crusher takes place due to the A attrition . 180.01 mm). ∞) is given by A .. B. D . For Indian standard (IS) screens. 179.500 5000 .impact C. A 5 B.50 . the mesh number is equal to its aperture size expressed to the nearest deca-micron (0..178. B. . B.182. D C. A Buhrstone B. . 183. In case of a hammer crusher.Trommels C. 186.clearance between hammer & grinding plates. Carbon black is pulverized in a A hammer crusher . __________ baffles are provided in ball mills.No C.Only two D None of these . B. D all (a).rotor speed. B.Attrition Pebble . the final product size depends on the A feed rate. (b) and (c). 184.ball mill C. A Horizontal .roll crusher D gyratory crusher . C. 185.Shaking screen D Vibrating screen . __________ mill is not used for grinding wheat into flour and for milling of cereals & other vegetable products. Which of the following screens has the maximum capacity ? A Grizzlies .Roller . B. Screen capacity is proportional to (where.1/S C. 187. Vibrating screens are used for handling large tonnages of materials. S = screen aperture) A S . Which of the following duties would require the ball mill to be operated at maximum percentage of critical speed ? . (b) or (c). Particle size range in which dust catcher (gravity settling chamber) works most effectively and efficiently is __________ microns. A smallest . In a grinding operation. B. B.unblanced fly wheels D either (a).either (a) or (b) D neither (a) nor (b) . 191. 190.S2 D -1/2 S . A <5 . B.cams or eccentric shafts C. Actual operating speed of a ball mill may vary from 65 to 80% of the critical speed. 189.. 188.largest C. The vibrating motion is imparted to the screening surface by means of A electromagnets .< 74 D > 1000 . B. . the limiting particle size is the size of the __________ particle in the sample.10 to 25 C. .Standard screens have circular opening. D 200 mesh screen has 200 openings per linear cm. Reciprocal of sphericity is termed as the A specific surface ratio . .With increase in mesh number of screens.1. .toothed roll C.sauter diameter D surface area per unit mass .shape factor C. C. A Hammer crushers operate by impact action. D Dry grindng of large particles in un-baffed mills. .2 -1/2 C. C. 195.25 cms).5 D -1/2 3 .Gyratory D none of these. Size reduction of ice and gypsum can be accomplished suitably by a __________ crusher. 193. B. . A Blake jaw .Wet grinding in high viscous suspension. B. .A Wet grinding in low viscous suspension.Dry grinding of large particles (upto 1. 194. B. The ratio of the actual mesh dimension of Taylor series to that of the next smaller screen is A 2 . Pick out the wrong statement. their diameter in microns decreases. 192. B. B. cloth supported by wire mesh. D both (b) and (c). 200. Which of the following is a fine crusher? A Blake jaw crusher .hammer crusher C. B. The screening surface of a 'reel' (a revolving screen used in flour mills) is made of silk bolting C. 197. 199.196. The optimum moisture content in solids to be crushed/ground ranges from __________ percent. . B. A 3 to 4 . B.The capacity and the effectiveness of screen are opposing factors.8 to 10 . A The capacity and the effectiveness of a screen are the same.ball mill D tube mill . . 198.Gyratory crusher C. __________ mill is not a revolving mill.Compartment . D C.Cage Tube . Pick out the correct statement. B.Toothed roll crusher D Dodge jaw crusher . Limestone is normally crushed in a A roll crusher . A Pebble B. handling the same feed & for the same product size range.C.5 times D 10 times . A same as . .2. The capacity of a gyratory crusher is __________ that of a jaw crusher with the same gape. 201. B.5 times C.10 to 15 D 15 to 20 . B. B. D energy needed to crush one ton of feed to 100 microns. What is the reduction ratio in a fine crushing operation having following feed and product sizes? A 0. .2 C. energy (kWh/ton of feed) needed to crush small feed to such a size that 80% of the product C.energy needed to crush one tonne of feed to 200 microns.202. 203.5 D 10 . . product passes through a 100 micron screen. Work index is defined as the A gross energy (kWh/ton of feed) needed to reduce very large feed to such a size that 80% of the . passes a 200 mesh screen.5 .