# Mechanical Metallurgy Questions and Answers – Metals – Problem and Defects in Rolled Products

This set of Mechanical Metallurgy Multiple Choice Questions & Answers (MCQs) focuses on “Metals – Problem and Defects in Rolled Products”.

1. The significant advantage of using smaller rolls in the machine is that __________
a) maximum possible reduction increases
b) power consumption reduces
c) the surface finish of the rolled product improves
d) the problem of roll flattening can be eliminated

Explanation: The maximum possible reduction in power for larger roll diameter is more. The primary use of smaller rolls is in decreasing the power consumption, but they require supporting big rolls.

2. Find the total number of rolls involved in 2 high four stand rolling mill?
a) 2
b) 4
c) 8
d) 16

Explanation: The 2 high mill indicates one roll on top and one in the bottom. Similarly 4 stand suggests that there is 4 parallel such units, so total number of the roll will be 8. Below is the diagram of the mill:

3. Which of the following mill action is like more of forging than the rolling of the metal?
a) Two high mill
b) Cluster mill
c) Planetary mill
d) Sendzimir mill

Explanation: The planetary mill consists of a primary larger roll surrounded by small backing up rolls, the sheet is pressed by small rolls as it moves and this repeats because of the size of roll; hence the action is more like forging than rolling.

4. In the given diagram, the sheet of thickness h1 is reduced to thickness h2. Find the correct relation between the velocity of the sheet? Where v1 is entering velocity and v2 is exiting velocity. Assuming the width of the sheet is constant.

a) v1=v2
b) v1>v2
c) v1<v2
d) no relation exists

Explanation: As the thickness of sheet is reducing from h1 to h2, and there is no change in width; hence the length of the sheet must have increased. The net input and output of material from roll is constant, hence the exiting velocity will be higher than entering velocity.

5. An ingot of 30mm thickness needs to reduce into sheet for further application. The best possible method to perform this task is _______
a) hot rolling
b) cold rolling
c) extrusion
d) compact extrusion

Explanation: The hot rolling is primary of most of the metalworking processes, it breaks the initial ingot into useful shapes such as slab of sheet, hot rolling is done because the power consumption is lower than cold rolling.
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6. The temper rolling or skin pass rolling is used to ___________
a) improve surface finish
b) eliminate the yield point phenomena
c) improve fatigue strength
d) refine the grain

Explanation: The yield point phenomena is associated with the formation of stretcher strain marks in deep drawn material, which causes uneven deformation of the material. Hence the skin pass rolling is to create small deformation and reach the material beyond its yield point.

7. Which of the following shape (cross-section) is not possible to make in the rolling process?
a)

b)

c)

d)

Explanation: The hollow shapes are generally made in the extrusion process, it is not possible to make in the rolling process. Hence the circular shape with hollow ring is not possible.

8. The passing of the rolled material through the square of oval-shaped cavity reduces the anisotropy of final material.
a) True
b) False

Explanation: Generally, when the metal is rolled in one direction, the grains of the metal tend to align in the same direction, so it has to be rotated by 90 degrees and then passed again. So, the alternative approach is to pass the material through a square or oval dies so that material is elongated and compressed in width at same time.

9. A sheet with an initial thickness 30 mm is rolled in two high mills with entering velocity of 5 mm/sec. If the final thickness of sheet is 15 mm find the exit velocity of rolled sheet?
a) 5mm/sec
b) 25mm/sec
c) 10mm/sec
d) 100mm/sec

Explanation: By using the consistency of volume, the total volume of the material remains same before and after rolling. So mathematically:
-> h1v1=h2v2
-> where h1, h2 is initial and final height, v1 and v2 are entering and exit velocity.
-> 30*5=15*v2
-> V2=10 mm/sec.

10. A sheet with an initial thickness 30 mm is rolled in two high mills with entering velocity of 5 mm/sec. Find the final thickness of sheet if the exit velocity of rolled sheet is 25 mm/sec?
a) 6mm
b) 5 mm
c) 1 mm
d) 2.5 mm

Explanation: By using the consistency of volume, the total volume of the material remains the same before and after rolling. So mathematically:
-> h1v1=h2v2
-> where h1, h2 is initial and final height, v1 and v2 are entering and exit velocity.
-> 30*5=h2*25
-> V2=6 mm.

11. The velocity of the sheet in the rolling machine keeps on increasing from entering to exit from the rolls.
a) True
b) False

Explanation: The total volume coming in the machine is always equal to the total volume exiting the machine; Since the thickness is less in exit, so the rate of material removal should be high. So exit velocity is always higher than entering velocity.

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