This set of Casting, Forming and Welding Multiple Choice Questions & Answers (MCQs) focuses on “Permanent Mould Casting”.
1. Which of the following is the main purpose of using permanent mould casting?
a) Variety in production
b) Production of castings with complexities
c) Large scale production
d) Production of highly expensive castings
View Answer
Explanation: Making a mould for every casting to be produced may be difficult and expensive for the large scale production. Therefore, a permanent mould, called die may be made from which a large number of castings, anywhere between 100 to 250,000 can be produced easily, depending on the complexity and alloy used for the casting.
2. In permanent mould casting, only the metallic type of cores can be used, as the mould material used is also metallic.
a) True
b) False
View Answer
Explanation: Cores are used in permanent mould casting for making any hollow portions in the casting. The cores can be made out of metal or sand also when sand cores are used in the casting, the process is called semi-permanent moulding. The sand core of complex shapes can be used with undercuts easily in the casting.
3. For complicated shapes, it is better to use collapsible metal cores rather than a single metal core in the casting.
a) True
b) False
View Answer
Explanation: It is difficult to securely position the metallic core as a single piece due to the dimensional variations that are likely to occur. So the collapsible metal cores (multiple piece cores) are sometimes used in permanent moulds, but the designer has to provide coarse tolerance on the dimensions.
4. Metallic core is more preferable than the sand core in the permanent mould casting.
a) True
b) False
View Answer
Explanation: Metallic core is not preferable that the sand core, because the metallic core cannot be complex with undercuts and the like. Also, the metallic core is to be withdrawn immediately after solidification; otherwise, its extraction becomes very difficult because of its shrinkage.
5. Experiment with gating systems in sand casting is performed before the construction of gating systems for the metallic mould.
a) True
b) False
View Answer
Explanation: The gating and risering systems used in the permanent mould casting are very similar to that of the sand casting. In fact, to get the proper gating arrangement, it is desirable first to experiment with various gating systems in sand casting and then finally arrive at the correct gating system for the metallic mould.
6. It is desirable to have drafts or undercuts as much as possible in the mould cavity, to have greater strength of the castings.
a) True
b) False
View Answer
Explanation: The mould cavity should be simple without any undesirable drafts or undercuts because these interfere with the ejection of the solidified castings and makes the casting weak and less durable. And care should be taken to see that progressive solidification occurs toward the riser, in the designing of permanent moulds.
7. Which of the following is not the function of coating of refractory materials on the mould?
a) Prevent the soldering of metal to the mould
b) Minimize thermal shock to the mould
c) Control the rate of casting solidification
d) Increase the heat transfer rate
View Answer
Explanation: The moulds are coated with a refractory material to increase the mould life by preventing the soldering of metal to the mould, by controlling the direction and rate of the casting solidification and also by minimizing the thermal shock to the moulding material. Coatings can be a mixture of sodium silicate, clay, soap, stone, talc etc.
8. What should be the maximum desirable thickness of the coatings applied to the mould?
a) 0.8 mm
b) 2 mm
c) 5 mm
d) 10 mm
View Answer
Explanation: The main requirement of a coating is that it should be inert to the casting alloy. The coating can be applied by brushing or spraying. It should be thick enough to fill up any surface imperfections. Generally, the maximum desirable thickness of a coating of refractory material is about 0.8 mm.
9. The coating is applied thicker at surfaces, where the faster cooling rate is required.
a) True
b) False
View Answer
Explanation: The coatings can be both of insulating type and lubricating type. The coatings can be applied thicker at surfaces, which need to be cooled slowly, for example, sprues, risers, thin sections and runners. More the thickness of the coatings less will be the heat transfer rate from the castings.
10. In permanent mould casting, the temperature at which the mould is used does not depend on _____
a) casting weight
b) casting wall thickness
c) pressure in casting
d) pouring temperature
View Answer
Explanation: Under the regular casting cycle, the temperature at which the mould is used depends on the casting weight, casting shape, casting cycle frequency, pouring temperature, wall thickness of the castings, wall thickness of the mould and the thickness of the mould coating.
11. In permanent mould casting, the mould is pre-heated to its operating temperature before the actual use of mould.
a) True
b) False
View Answer
Explanation: When the casting is done with the cold die, the first few castings are likely to have misruns (Misrun is caused when the metal is unable to fill the mould cavity completely) till the die reaches its operating temperature. To avoid this, the mould must be pre-heated to its operating temperature, preferably in an oven.
12. Permanent mould casting is suited to low volume production of moderate or complex shapes of casting.
a) True
b) False
View Answer
Explanation: To economize the use of metallic mould, the permanent mould casting is particularly suited to high volume production of simple, small castings with uniform wall thickness and no intricate details. The materials which are cast in permanent moulds are zinc alloys, copper alloys, magnesium alloys, grey cast iron etc.
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