46. A strip of 120 mm width and 8 mm thickness is rolled between two 300 mm diameter rolls to get a strip of 120 mm width and 7.2 mm thickness. The speed of the strip at the exit is 30 m/min. There is no front or back tension. Assuming uniform roll pressure of 200 MPa in the roll bite and 100% mechanical efficiency, the minimum total power (in kW) required to drive the two rolls is _______.
    

1. 1. 91.34 kW

   
   
   

   2. 19.33 kW

   
   
   

   3. 3.34 kW

   
   
   

   4. 9.34 kW

   
   
   

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1. View Hint View Answer Discuss in Forum

   Velocity of Neutral plane
   By applying continuity Equation
   H_n = H₂ + 0.25∆H
   H_n = 7.2 + 0.25 × 0.8 = 7.4 mm
   V_nH_n = V₂H₂
   V2 → Exit velocity
   H2 → Final Height
   V_n = 29.19 m/min
   

   Vn =	πDN
   	60

   
   

   N =	29.19 × 60	= 30.98 rpm
   	π × 300

   
   Total power = 2Tω
   

   Total power = 2 × 1439.9 × 2π ×	30.98	= 9.34 kW
   	60

   Correct Option: D

   Velocity of Neutral plane
   By applying continuity Equation
   H_n = H₂ + 0.25∆H
   H_n = 7.2 + 0.25 × 0.8 = 7.4 mm
   V_nH_n = V₂H₂
   V2 → Exit velocity
   H2 → Final Height
   V_n = 29.19 m/min
   

   Vn =	πDN
   	60

   
   

   N =	29.19 × 60	= 30.98 rpm
   	π × 300

   
   Total power = 2Tω
   

   Total power = 2 × 1439.9 × 2π ×	30.98	= 9.34 kW
   	60

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47. In a rolling operation using rolls of diameter 500 mm if a 25 mm thick plate cannot be reduced to less than 20 mm in one pass, the coefficient of friction between the roll and the plate is _____.

1. 1. 1.1414°

   
   
   

   2. 7.1414°

   
   
   

   3. 0.1414°

   
   
   

   4. 14.1414°

   
   
   

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1. View Hint View Answer Discuss in Forum

   μ = √		(∆h)max
   		R

   
   ⇒ (∆h)_max = 25 – 20 = 5mm
   R = 250 mm
   

   ∴ μ = √		5		= 0.1414°
   		250

   Correct Option: C

   μ = √		(∆h)max
   		R

   
   ⇒ (∆h)_max = 25 – 20 = 5mm
   R = 250 mm
   

   ∴ μ = √		5		= 0.1414°
   		250

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48. In a slab rolling operation, the maximum thickness reduction (∆h_max) is given by ∆h_max = μ² . R , where R is the radius of the roll and μ is the coefficient of friction between the roll and the sheet. If μ = 0.1, the maximum angle subtended by the deformation zone at the centre of the roll (bite angle in degree) is _____.

1. 1. 5.7106°

   
   
   

   2. 32.7106°

   
   
   

   3. 51.7106°

   
   
   

   4. 0.7106°

   
   
   

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1. View Hint View Answer Discuss in Forum

   θ = tan-1μ = √		∆h
   		R

   
   ⇒ tan^-1μ = 5.7106°

   Correct Option: A

   θ = tan-1μ = √		∆h
   		R

   
   ⇒ tan^-1μ = 5.7106°

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49. With respect to metal working, match Group A with Group B:
    Group A
    P. Defect in extrusion
    Q. Defect in rolling
    R. Product of skew rolling
    S. Product of rolling through cluster mill
    Group B
    I. alligatoring
    II. scab
    III.fish tail
    IV. seamless tube
    V. thin sheet with tight tolerance
    VI. semi-finished balls of ball bearing
    

1. 1. P-II, Q-III, R-VI, S-V
      

   
   
   

   2. P-III, Q-I, R-VI, S-V
      

   
   
   

   3. P-III, Q-I, R-IV, S-VI
      

   
   
   

   4. P-I, Q-II, R-V, S-VI

   
   
   

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1. View Hint View Answer Discuss in Forum

   P – III, Q – I, R – VI, S – V

   Correct Option: B

   P – III, Q – I, R – VI, S – V

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50. In a rolling process, the state of stress of the material undergoing deformation is
    

1. 1. pure compression
      

   
   
   

   2. pure shear
      

   
   
   

   3. compression and shear
      

   
   
   

   4. tension and shear

   
   
   

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1. View Hint View Answer Discuss in Forum

   The material (metals) i s subjected to high compressive stress as a resort of friction between the roll and the metal suface.
   

   Correct Option: C

   The material (metals) i s subjected to high compressive stress as a resort of friction between the roll and the metal suface.
   

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