511. The thickness of a plate is reduced from 30 mm to 10 mm by successive cold rolling passes using identical rolls of diameter 600 mm. Assume that there is no change in width. If the coefficient of friction between the rolls and the workpiece is 0.1, the minimum number of passes required is

1. 1. 3

   
   
   

   2. 4

   
   
   

   3. 6

   
   
   

   4. 7

   
   
   

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1. View Hint View Answer Discuss in Forum

   h_i = 30 mm     µ = 0.1 D = 60 mm
   h_f = 10 mm     R = 300 mm
   Δh = 20 mm
   Draft of single pass
   (Δh)₁ = µ² = (0.11)² × 300
   

   No = passes =	20	= 6.67 ≃ 7 passes.
   	3

   Correct Option: D

   h_i = 30 mm     µ = 0.1 D = 60 mm
   h_f = 10 mm     R = 300 mm
   Δh = 20 mm
   Draft of single pass
   (Δh)₁ = µ² = (0.11)² × 300
   

   No = passes =	20	= 6.67 ≃ 7 passes.
   	3

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512. In a rolling process, the roll separating force can be decreased by

1. 1. Reducing the roller diameter

   
   
   

   2. Increasing friction between the rolls and the metal

   
   
   

   3. Reducing front tension to rolled material

   
   
   

   4. Providing back up rollers

   
   
   

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1. View Hint View Answer Discuss in Forum

   As roll diameter decreases for the same reduction the contact length decreases. So less force will be required.

   Correct Option: A

   As roll diameter decreases for the same reduction the contact length decreases. So less force will be required.

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513. Anisotropy in rolled components is caused by

1. 1. Change in dimensions

   
   
   

   2. Scale formation

   
   
   

   3. Closure of defects

   
   
   

   4. Grain orientation

   
   
   

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1. View Hint View Answer Discuss in Forum

   When a material having different value of property in different Direction, called as anisotropic material

   Correct Option: D

   When a material having different value of property in different Direction, called as anisotropic material

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514. In a rolling process, thickness of a strip is reduced from 4 mm to 3 mm using 300 mm diameter rolls rotating at 100 rpm. The velocity of the strip (in m/sec) at the neutral point is

1. 1. 1.57

   
   
   

   2. 3.14

   
   
   

   3. 47.10

   
   
   

   4. 94.20

   
   
   

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1. View Hint View Answer Discuss in Forum

   V =	πDN
   	60

   
   At Neutral Point, Roll velocity and plate velocity are equal.

   Correct Option: A

   V =	πDN
   	60

   
   At Neutral Point, Roll velocity and plate velocity are equal.

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515. The maximum possible percentage reduction in area per pass during wire drawing of an ideal plastic material without friction is of the order of

1. 1. 37

   
   
   

   2. 50

   
   
   

   3. 63

   
   
   

   4. 75

   
   
   

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1. View Hint View Answer Discuss in Forum

   σd = σ0		Ai
   		Af

   
   

   Ai	= R → Extrusion Ratio
   Af

   
   If σ_d = σ₀ {Maximum possible Reduction}
   

   1 = ln		Ai
   		Af

   
   

   e =	Ai
   	Af

   
   

   % Reduction =	Ai − Af	× 100 =		1 −	1		× 100
   	Ai				e

   
   % Reduction = 63%

   Correct Option: C

   σd = σ0		Ai
   		Af

   
   

   Ai	= R → Extrusion Ratio
   Af

   
   If σ_d = σ₀ {Maximum possible Reduction}
   

   1 = ln		Ai
   		Af

   
   

   e =	Ai
   	Af

   
   

   % Reduction =	Ai − Af	× 100 =		1 −	1		× 100
   	Ai				e

   
   % Reduction = 63%

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