56. In a rolling process, sheet of 25 mm thickness is rolled to 20 mm thickness. Roll is of diameter 600 mm and it rotates at 100 rpm. The roll strip contact length will be

1. 1. 5 mm
      

   
   
   

   2. 39 mm
      

   
   
   

   3. 78 mm
      

   
   
   

   4. 120 mm

   
   
   

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1. View Hint View Answer Discuss in Forum

   Given : t₁ = 25 mm, t_f = 20 mm , R = 300 mm, N = 100 r.p.m
   
   Angle subtended by the deformed zone at the roll center,
   

   Qi = √	(ti - tR)
   	R

   
   Q_i = √(25 - 20) /300 = 0.129 rad.
   ∴ Roll strip contact length = θ . R = 0.129 × 300 = 38.72 mm
   

   Correct Option: B

   Given : t₁ = 25 mm, t_f = 20 mm , R = 300 mm, N = 100 r.p.m
   
   Angle subtended by the deformed zone at the roll center,
   

   Qi = √	(ti - tR)
   	R

   
   Q_i = √(25 - 20) /300 = 0.129 rad.
   ∴ Roll strip contact length = θ . R = 0.129 × 300 = 38.72 mm
   

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57. Hot rolling of mild steel is carried out

1. 1. at recrystallization temperature
      

   
   
   

   2. between 100°C to 150°C
      

   
   
   

   3. below recrystallization temperature
      

   
   
   

   4. above recrystallization temperature

   
   
   

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1. View Hint View Answer Discuss in Forum

   Hot working is carried out at above Recrystallization temperature.
   Hot working > 0.6 T_m
   and Recrystallization Temp = 0.5 T_m
   T_m = melting point.

   Correct Option: D

   Hot working is carried out at above Recrystallization temperature.
   Hot working > 0.6 T_m
   and Recrystallization Temp = 0.5 T_m
   T_m = melting point.

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58. The atomic packing factor for a material with body centered cubic structure is _______ .

1. 1. APF = 0.68

   
   
   

   2. APF = 1.68

   
   
   

   3. APF = 0.78

   
   
   

   4. APF = - 1.68

   
   
   

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1. View Hint View Answer Discuss in Forum

   4r = a√3
   
   

   a =	4r
   	√3

   
   APF = 0.68

   Correct Option: A

   4r = a√3
   
   

   a =	4r
   	√3

   
   APF = 0.68

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59. In a green sand moulding process, uniform ramming leads to

1. 1. less chance of gas porosity

   
   
   

   2. uniform flow of molten into the mould cavity

   
   
   

   3. greater dimensional stability of the casting

   
   
   

   4. less sane expansion type of casting defect

   
   
   

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1. View Hint View Answer Discuss in Forum

   Sand will go to last corners of casting

   Correct Option: B

   Sand will go to last corners of casting

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60. Casting process
    A. Slush casting
    B. Shell moulding
    C. Dry sand moulding
    D. Centrifugal casting
    Product
    1. Turbine blade
    2. Machine tool bed
    3. Cylindrical block
    4. Hollow castings like lamp shades
    5. Rain water pipes
    6. Cast iron shoe brake

1. 1. A – 5, B – 3, C –2, D – 4

   
   
   

   2. A – 4, B –5, C –2, D – 3

   
   
   

   3. A – 4, B – 3, C –2, D – 5

   
   
   

   4. A – 2, B – 5, C –4, D – 3

   
   
   

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1. View Hint View Answer Discuss in Forum

   A – 4, B – 3, C –2, D – 5

   Correct Option: C

   A – 4, B – 3, C –2, D – 5

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