# Casting Questions and Answers – Centrifugal Casting

This set of Casting, Forming and Welding Multiple Choice Questions & Answers (MCQs) focuses on “Centrifugal Casting”.

1. Which of the following forces provides continuous pressure on the metal in centrifugal casting?
a) Spring force
b) Centrifugal force
c) Gravitational force
d) Frictional force

Explanation: In centrifugal casting, mould is rotated rapidly about its central axis as the metal is poured into it. Because of the centrifugal force, continuous pressure is applied to the metal as it solidifies. The slag and the other inclusions being lighter gets separated from the metal and segregates toward the centre.

2. Which of the following methods of casting is best suited for casting of hollow pipes and tubes?
a) Investment casting
b) Permanent mould casting
c) Die casting
d) Centrifugal casting

Explanation: Specifically, true centrifugal casting is generally used for the making of hollow pipes and tubes, which are axi-symmetric with a concentric hole. Molten metal is accumulated at the inward surface of the mould by the rotation of the mould and then the solidification of a melt is taking place.

3. Special type of sand cores is mainly used for the making of hollow part in the centrifugal casting.
a) True
b) False

Explanation: In centrifugal casting, there is no requirement of any core for the making of the concentric hole. As the metal is always pushed outward because of the centrifugal force, application of core is eliminated. Only the oxides and slag part separate from the metal and segregate at the centre.

4. The axis of rotation of the mould should be horizontal for the casting of long pipes in centrifugal casting.
a) True
b) False

Explanation: In centrifugal casting, the axis of rotation of the mould can be horizontal, vertical or any angle in between. Generally, very long pipes are cast with a horizontal axis, whereas short pieces are more conveniently cast with a vertical axis, as it requires less area for the casting operation.

5. Dry sand cores may be required for the provision of spigot at the end section of the casting.
a) True
b) False

Explanation: When after the proper ramming of sand to confirm to the outer contour of the pipe to be made, dry sand cores may be introduced for the provision of end details such as spigot ends, or flanged ends to the casting. Meanwhile there is no requirement of any cores for the making of the hollow section of the castings.
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6. Which of the following parts is provided in between the mould and casing to reduce the vibrations?
a) Steel balls
b) Metallic roller
c) Viscous fluid
d) Grease

Explanation: After the completion of the mould, the flask is balanced dynamically so as to reduce the occurrence of undesirable vibrations during the casting process. And the metallic rollers are used in between the rotating mould and the stationary casing to avoid the jerks and for the damping of vibrations.

7. In centrifugal casting, only sand moulds can be used due to the problem of sticking of metal.
a) True
b) False

Explanation: Not only sand moulds, the metallic moulds can also be used in the centrifugal casting process for large scale production. As inducing of high temperature of metallic mould can be avoided by water circulation through it and sticking problem can also be solved by casting of non-sticking materials.

8. In centrifugal casting, the casting yield is approximately equaled to 100%.
a) True
b) False

Explanation: There is no need for the gates and runners in the centrifugal casting process, which saves a lot of molten metal. This makes the increase in casting yield, reaching almost 100%. And no any application of cores makes the castings very economical for the large scale production.

9. It is also possible to make un-symmetric shape of casting in true centrifugal casting by introducing some variations to the mould.
a) True
b) False

Explanation: It is not possible to make un-symmetric shape of casting in centrifugal casting, only certain shapes which are axi-symmetric and having concentric holes are suitable to make in the centrifugal casting. And equipment are also expensive, so this method is suitable only for large scale production.

10. Castings made by the centrifugal casting process have negligible porosity.
a) True
b) False

Explanation: In centrifugal casting, the inclusions such as slag and oxides get segregated towards the centre and can be easily removed by a machining process. And also the application of pressure on the metal throughout the solidification causes the porosity to be eliminated and gives rise to dense metal.

11. In centrifugal casting, a movable pouring basin is employed for the pouring of molten metal.
a) True
b) False

Explanation: The molten metal is poured into the mould in requisite quantity through a movable pouring basin. The thickness of the pipe determined by the amount of metal poured into the mould. Then after the completion of pouring, mould is rotated at its operational speed till it solidifies to form the requisite tubing.

12. The speed of rotation is almost double in semi centrifugal casting as compared to the true centrifugal casting.
a) True
b) False

Explanation: In semi-centrifugal casting method, complicated but axi-symmetric shapes of casting can be possible to make and this is accomplished by pouring of molten metal into the mould, which is rotated about a vertical axis. And the rotating speeds used in this process are not as high as in the case of true centrifugal casting.

13. Which of the following types of centrifugal casting process is used for the casting, whose shape of casting is not axi-symmetric?
a) True centrifugal casting
b) Semi centrifugal casting
c) Centrifuging
d) Full centrifugal casting

Explanation: Centrifuging is a process which is used in order to obtain higher metal pressures during solidification when the shapes of the casting are not axi-symmetrical. This process is mainly suitable for small jobs of any shape. In this method, a number of small jobs are joined together in a radial manner and then the further process of casting is done.

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