This set of Manufacturing Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Casting Defects”.
1. Which of the following defect is not a gas defect?
a) Blow holes
b) Air inclusions
c) Run out
d) Pin hole porosity
View Answer
Explanation: Blow holes, air inclusions and pin hole porosity are known as “gas defects” in casting. Blow holes and open blows are spherical, flattened or elongated cavities present inside the casting or on the surface of the casting. These are caused b moisture left in the mold and core. Air inclusions are due to absorption of gases by the molten metal in the furnace, they cannot escape and weaken the mold during casting. These are due to high pouring temperatures. Pinhole defects are a form of gas porosity. They are usually small, elongated holes at or immediately below the casting surface with the long axis of the pinhole perpendicular to the casting surface.
2. Which gas defect is caused by hydrogen in molten metal?
a) Blow holes
b) Air inclusions
c) Open blows
d) Pin hole porosity
View Answer
Explanation: As hydrogen is such a small atom, it can diffuse rapidly once it is absorbed, creating pinholes. Hydrogen being absorbed by the molten metal inside the furnace and inside the cavity. This is the main reason for the evolution of pinhole porosity.
3. Cuts, washes, swell, drop etc. are the examples of which of the following casting defects?
a) Gas defect
b) Pouring material defect
c) Moulding material defect
d) Metallurgical defect
View Answer
Explanation: Moulding material defects are caused by the characteristics of molding materials. Cuts, washes, swell, drop etc. are some known examples of this type. These are caused by poor strength of moulding sand or molten metal flowing at high velocity.
4. When the molten metal leaks out of mould which defect occurs?
a) Run out
b) Misrun
c) Fusion
d) Drop
View Answer
Explanation: A run out occurs when molten metal leaks out of the mould during pouring. This is caused by defecting moulding boxes, faulty clamping and weighing and by casting too near the edge of the box. This defect is avoided by modifying the moulding system, providing proper line and providing proper gating system.
5. Which of the following defects is not an example of type “pouring material defects”?
a) Misrun
b) Cold shut
c) Slag inclusion
d) Hot tear
View Answer
Explanation: Misruns, cold shut, shrinkage cavity, micro porosity, mismatch and metal penetration are the pouring metal defects. Among these, misrun is caused when the metal is unable to fill the mould cavity completely. Cold shut is caused when two metal streams while meeting in the mould cavity do not fuse together properly.
6. The lower fluidity of molten material causes _________
a) Misrun
b) Cold shut
c) Misrun & Cold shut
d) Fusion
View Answer
Explanation: Fluidity is a very important consideration in metal casting. Cold shuts and misruns can be caused by a lack of fluidity in the metal.
7. Defects caused by the chilling of the casting are known as?
a) Hot spots
b) Hot tears
c) Shrinkage cavity
d) Swell
View Answer
Explanation: Hot spots are the thick sections, those cool slower than other sections causing abnormal shrinkage. Defects such as voids cracks and porosity are created at these hot spots.
8. During melting process flux is added to react with impurities to form?
a) Cavity
b) Slag
c) Cold shut
d) Blow holes
View Answer
Explanation: Slag is said to be refuse produced as a result of melting nonferrous material which have a high melting point, it is thus formed when added flux to interact with impurities. If slag is not completely removed it may cause slag inclusions.
9. Which defect is caused due to the conversion of moisture to steam because of the heat of molten metal?
a) Blow holes
b) Open blows
c) Air inclusions
d) Cold shut
View Answer
Explanation: Blow holes are entrapped gases, which are formed as a result of gases from mould, molten metal and stream sand. Further these are caused due to the conversion of moisture to steam because of the heat of molten metal.
10. Defect which occurs due to the solidification of casting is known as?
a) Swell
b) Misrun
c) Metal penetration
d) Shrinkage cavity
View Answer
Explanation: Shrinkage cavity is a void on the surface of the casting caused mainly due to uncontrolled and haphazard solidification of the metal. These can be of two types,
i. External shrinkage defects and
ii. Closed shrinkage defects.
The main causes are inadequate and improper gating and risering system, too much high pouring temperature, and improper chilling.
Sanfoundry Global Education & Learning Series – Manufacturing Engineering.
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