This set of Mechanical Metallurgy Multiple Choice Questions & Answers (MCQs) focuses on “Metals – Classification of Rolling Process”.
1. The earing defect in the rolling of the work piece is not caused by _________
a) too high speed
b) low clearance between the roll and workpiece
c) blank holding
d) material dependent
View Answer
Explanation: The non-uniform clearance between the workpiece and roll does not have a direct impact on causing hearing of the workpiece, while the material property, too high speed can cause earing defect.
2. The roll separating force between the rolling rolls will increase if _____________
a) roll diameter increases
b) roll diameter decreases
c) number of rolls increases
d) number of rolls decreases
View Answer
Explanation: The roll separating force between the roll increases with an increase in the roll diameter. This is because of the contact area between the rolls also increases.
3. The roll separating force between the rolls can be decreased by lowering the friction between the workpiece and the rolls.
a) True
b) False
View Answer
Explanation: Reducing the friction between the workpiece and the roll will decrease the separating force because the normal component of friction force will decrease as the friction decreases.
4. Appling the back tension on workpiece will shift the neutral point towards ____________
a) exit of roll
b) entrance of roll
c) does not shift
d) depends upon the magnitude of the force
View Answer
Explanation: Appling the back tension in rolling, shifts the neutral point towards the exit point of the rolls. The vice versa of this statement is also true.
5. Which of the following statement is correct about the coefficient of friction between the roll and workpiece?
a) The coefficient of friction is constant throughout the arc of contact
b) The coefficient of friction always acts in a single direction throughout the arc of contact
c) The friction force act opposite to roll direction in the entrance and along the roll direction in exit
d) The friction force act in the roll direction in entrance and opposite to the roll direction in exit
View Answer
Explanation: The roll friction always opposes the entry of incoming workpiece in the entrance. But at the exit, it resists and try to draw the material inside the roll, so friction acts in the opposite direction.
6. The arc of contact between the roll and the workpiece is circular in geometry, and its radius is smaller than the roll radius.
a) True
b) False
View Answer
Explanation: The arc of contact between the roll and the workpiece is circular in geometry and its radius is greater than roll radius. This is because of the elastic deformation of roll which increases the contact area.
7. The sheet has an initial thickness of 30 mm with roll diameter of 300 mm and coefficient of friction equal to 0.2. Find the final thickness of the sample in case maximum reduction is carried out in a single pass?
a) 12 mm
b) 18 mm
c) 24 mm
d) 30 mm
View Answer
Explanation: The maximum possible reduction in a single pass is equal to:
-> Δh=u2 R; where u is coefficient of friction, and R is roll diameter.
-> Δh=0.22 300=12 mm
-> So, maximum possible reduction after a single pass will be equal to 12 mm
-> So, final thickness will 30-12=18 mm.
8. Find the coefficient of friction of the roll having diameter 100 mm and the maximum possible reduction is 1 mm?
a) 0.01
b) 0.1
c) 0.5
d) 1
View Answer
Explanation: The maximum possible reduction in a single pass is equal to:
-> Δh=u2 R; where u is coefficient of friction, and R is roll diameter.
-> 1=u2 100
-> u = √1/100 =0.1
-> coefficient of friction is equal to 0.1.
9. The position of the neutral point in rolling does not depend upon __________
a) diameter of roll
b) percentage of reduction
c) coefficient of friction
d) composition of material
View Answer
Explanation: The diameter of the roll, percentage of reduction and coefficient plays a crucial role in deciding the position of neutral point along the arc of roll, but composition of material does not significantly affect the position of neutral point.
10. Find the angle of contact for an arc on a roll having the maximum reduction equal to 2 mm and roll diameter 800 mm?
a) 2.86 degrees
b) 4.28 degrees
c) 82.2 degrees
d) 54 degrees
View Answer
Explanation: The relationship between the maximum reduction in thickness and the roll diameter is:
-> Δh = 2R(1-cosα)
-> 2 = 2*800(1-cosα)
-> Cosα=0.99875
-> α=2.86 degrees.
11. If the coefficient of friction of material with the roll is 0.2, find the angle of a bite?
a) 11.3 degree
b) 16.25 degrees
c) 21.02 degrees
d) 71.29 degrees
View Answer
Explanation: Let’s suppose the angle of the bite is equal to θ.
If the coefficient of friction is u, the relationship between the angle of bite and coefficient of friction is:
-> u=tan(θ)
-> 0.2=tan(θ)
-> θ = 11.3 degree.
Sanfoundry Global Education & Learning Series – Mechanical Metallurgy.
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