This set of Casting, Forming and Welding Multiple Choice Questions & Answers (MCQs) focuses on “Cast Irons – 2”.
1. What should be the range of percentage of carbon (C) in iron (Fe) to be called as cast iron?
Explanation: Cast iron is the oldest ferrous material that is used for commercial purposes. It is mainly a mixture of iron (Fe) and carbon (C). It can also include materials like sulfur (S), silicon (Si), and manganese (Mn). Generally, for the cast iron, the percentage of carbon in iron is 2 to 5 percent.
2. The shaking out of cast iron casting from mould cavity is known as fettling process.
Explanation: The cast iron is first melted in furnace and then poured into the mould cavity. After cooling of cast iron in the mould it is broken out. All the excess of metal from the process, gates, runners etc are removed in a process called as fettling, which also have operations like grinding and shot blasting to produce the good surface finish of the castings.
3. Cast iron generally has low tensile strength but excellent compressive strength.
Explanation: Cast iron is normally of nonmalleable and brittle nature which defines that, it is not easy to bend or stretched the casting into any shape due to low tensile strength. Cast iron parts tend to fracture by little of deformation, but cast iron has excellent compressive strength which highly required in making of structures of buildings and bridges.
4. Which of the following types of iron represents purest form of iron in the manufacturing process?
a) Pig iron
b) White cast iron
c) Wrought iron
d) Grey cast iron
Explanation: The purest form of iron is wrought iron which has negligible amount of carbon in it. It is highly malleable and tough material which can be used for making products by rolling or forging operation instead of casting process. It is basically obtained by melting pig iron which is also called crude iron.
5. Which of the following types of cast iron includes black flakes of graphite in it?
a) White cast iron
b) Grey cast iron
c) Ductile cast iron
d) Malleable cast iron
Explanation: Grey cast iron generally includes thin and little black flakes of graphite. These black flakes cause cast iron to appear in grey color, so it is called as grey cast iron. Presence of graphite can make it use as a lubricant in some manufacturing processes. But it has less tensile strength and toughness than the other cast irons.
6. The cast irons are highly corrosive resistant material due to presence of high silicon content in it.
Explanation: The composition of cast iron generally varies depending on the grade of pig iron used in its manufacturing process. High silicon content in cast iron makes it resistance to oxidation and corrosion by creating a tight adhering oxide layer to minimize other further attacks. Iron castings are used in applications where this type of resistance gives relatively good service.
7. High manganese content in cast iron provides excellent weld-ability of the material.
Explanation: Cast iron mostly contains 2 to 5% carbon, 1 to 3% silicon and approx 1% manganese. The presence of such contents makes their weld-ability poor. Cast irons are relatively cheap and can be easily casted into any complex shapes and machined, but most of the grades of cast iron are not weld-able.
8. Cast iron is widely used in industries because of its high ratio of performance to cost involved in manufacturing.
Explanation: Cast iron is widely used because of its high ratio of performance to the cost that they offer. This high value of ratio is also achieved by easy controlling of microstructure and properties in the casting condition, this enables its various applications without giving any heat treatment to the casted parts or components.
9. Grey cast iron generally has poor machinability due to the presence of graphite flakes in it.
Explanation: When the fracture of grey cast iron occurs, the crack path follows the graphite flakes and the fracture surface appears grey in color due to the presence of graphite. The graphite flakes have good damping features and high machinability because the graphite flakes work as a chip breaker and also lubricates the tools or machines.
10. Which of the following parts are mostly manufactured by using grey cast iron?
b) Surgical equipment’s
c) Thin sheets
d) Engine blocks
Explanation: The fluidity and expandability of molten grey cast iron at the time of solidification, due to the formation of graphite flakes, this iron becomes ideal for the manufacturing of shrinkage free and intricate castings components like engine blocks. The graphite presence greatly enhances mechanical properties in grey cast iron.
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