This set of Casting, Forming and Welding Multiple Choice Questions & Answers (MCQs) focuses on “Cold Rolling”.
1. In metal forming, cold rolling process is completely different from the work hardening process.
a) True
b) False
View Answer
Explanation: In metal forming, cold working or rolling process is also known as work hardening process, which basically defined as the process of strengthening a material by plastic or permanent deformation. Plastic deformation occurs when a material is altered after its elastic region, this process makes the material hard and strong.
2. Cold rolling process only affects the tensile strength of the material which being rolled.
a) True
b) False
View Answer
Explanation: Cold rolling process is a very important process because it allows altering of desired mechanical properties of the material. Cold rolling not only affects the tensile strength, but it also affects the hardness, yield strength, tensile strength and ductility of the material. This process is very economical as the heating cost is excluded from the process.
3. The dislocation density of the material increases during the process of cold rolling or work hardening.
a) True
b) False
View Answer
Explanation: In cold rolling or work hardening process, dislocations contact with each other and accept configurations which prevent the movement of other dislocations in the material. During the process, the dislocation density increases, this also makes increase in the flow stress of the material. Flow stress is defined as the instantaneous value of stress required to continue the plastic or permanent deformation.
4. The dislocations in the material only act as strong obstacles to the movement of other dislocations.
a) True
b) False
View Answer
Explanation: In general, the dislocations in the material can be acts as either strong or weak obstacles to the movement of other dislocations of the material, which basically depends on the type of interaction that occurs between the movements of dislocations. This process is mainly considered for strengthening the material which being rolled during the process.
5. The dislocation density of the material is defined as the ratio of total dislocation length per unit volume of the material.
a) True
b) False
View Answer
Explanation: In general, the dislocation density of a material is defined as the ratio of total dislocation length per unit volume of the material. It is also defined as the number of dislocations that intersect a unit area of a random part of the material. The dislocation density mainly determines the strength of the material.
6. Cold rolling is a process of permanent deformation of material below its re-crystallization temperature.
a) True
b) False
View Answer
Explanation: Cold rolling or working is a process of permanent or plastic deformation of materials below the re-crystallization temperature, and this process is generally performed at the room temperature. This process is widely used for producing products of better surface finish with superior dimensional control.
7. In cold rolling process, no any residual stresses are induced in the material during the operation.
a) True
b) False
View Answer
Explanation: In cold rolling process, strain hardening occurs during the expansion or compression of metal plate, which increases the value of flow stress, so that the required rolling force increases, which further lead to inducing of residual stresses in the material. This residual stresses then can be removed from the material by the annealing process.
8. Which of the following methods of heat treatment is best suitable for treating the output of cold rolling?
a) Quenching
b) Case hardening
c) Annealing
d) Cyanide hardening
View Answer
Explanation: The plastic deformation of metal plate in cold rolling includes changing of grain shape, increase in dislocation density and strain hardening of the material. These changes make the metal plate hard and ductile less. So, annealing is a process of heat treatment in which material regains its softness and relieves all its residual stresses.
9. The cold rolling process requires very heavy forces for the accomplishment of rolling operation.
a) True
b) False
View Answer
Explanation: In the cold rolling process, the metal plate is compressed between the gaps of two large heavy rollers. This process does not require much of heating the metal plate, so it becomes very difficult to alter the shape of material as the temperature of a material is less than its re-crystallization temperature, and strain hardening also occurs which further makes the metal hard. Hence, this process requires very heavier forces for the accomplishment of rolling operation.
10. Over work hardening of material can induce high brittleness in the material.
a) True
b) False
View Answer
Explanation: When the material is processed by cold rolling then it loses its ductility by increasing its strength. The process includes strain hardening of the material which induces stresses in the material and when the process is continued and crosses the limit, then the material becomes very hard and brittle, which can only be overcome by annealing process.
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