Casting Questions and Answers – Gating Design

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

1. The liquid metal that runs through the channels without friction in the mould obeys which of the following theorem?
a) Bernoulli’s theorem
b) Clausius theorem
c) Helmholtz’s theorem
d) Carnot’s theorem

Explanation: As the metal enters the pouring basin, it has the highest potential energy with no kinetic or pressure energies. But as the metal moves through the gating system, potential energy converts into kinetic energy. Thus it obeys the Bernoulli’s theorem.

2. Which of the following flows is responsible for too less pouring time of molten metal in the mould?
a) Laminar flow
b) Viscous flow
c) Turbulent flow
d) Irrotational flow

Explanation: Too less pouring time is caused by turbulent flow of nature of the molten metal. The mixing and collisions of molecules make the change in momentum and molecules get accelerated and hence high velocity, that cause the less pouring time of molten metal in the mould.

3. What will be the optimum pouring time for cast iron whose mass is 100 kg and a thickness of 25 mm? Fluidity of iron is 32 inches?
a) 24.98
b) 18.2
c) 31.32
d) 14.8

Explanation: Pouring time(t) = K[ 1.41 + T/14.59]√W sec.
where K = Fluidity of iron in inches/40
Pouring time(t) = 32/40[ 1.41 + 25/14.59]√100 = 24.988 sec.
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4. Which of the followings is the formula for calculating the choke area (A)?
a) 2W/dtC√2gh
b) W/dtC√2gh
c) W²/dtC√2gh
d) 2W³/dtC√2gh

Explanation: Choke area (A) = W/dtC√2gh, It is the main control area which meters the metal flow into the mould cavity so that the mould is completely filled within the calculated pouring time. Its unit is mm².
Where, W = Casting mass (kg), t = pouring time (second), d = mass density (kg/mm³),
h = Sprue height (mm), g = Acceleration due to gravity (mm/s²), C = Efficiency factor.

5. Which of the following methods is used for trapping the slag from entering steel casting into the mould?
a) Finn’s method
b) Down gate method
c) Whirl gate method
d) Euler’s method

Explanation: Whirl gate method utilizes the principle of centrifugal action to throw the dense metal to the periphery and retain the lighter slag at the centre. Also, the metal revolves 270 degree before reaching the exit gate so as to gain enough time for separating the impurities.
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6. Which of the following materials require a longer pouring time?
a) Non-ferrous material
b) Grey cast iron
c) Ferrous alloys
d) Brass

Explanation: For nonferrous material, a longer pouring time would be beneficial since they lose heat slowly and also tend to form dross if a metal is poured too quickly, this dross makes the quality of the material poor and further defects induced in the material.

7. Which of the following is the purpose of runner extension?
a) To make smooth surface finish
b) To make the casting of specific size and shape
c) To remove slag and dross from the metal
d) To make fast cooling of molten metal

Explanation: The metal which moves first into the gating system is likely to contain slag and dross which should not be allowed to get into the mould cavity. This could be achieved by extending the runner beyond the in-gate so the clean metal can be expected to go into the mould after completely filling the runner extension.

8. Which of the following gating systems is useful for casting drossy alloys?
a) Pressurized gating system
b) Partially pressurized gating system
c) High pressurized gating system
d) Non-pressurized gating system

Explanation: Non-pressurized gating system has choke at the bottom of the sprue base, have total runner area and in-gate areas higher than the sprue area. In this system, there is no pressure existing in the metal flow system and thus it helps to reduce turbulence. Hence this system can be used for casting drossy alloys such as aluminum and magnesium alloys.

9. Casting yield of a non-pressurized gating system is _____
a) very high
b) 80%
c) very less
d) 50%

Explanation: Tapered sprues are invariably used with an unpressurized system. Casting yield of a non-pressurized gating system gets reduced because of the large metal involved in the runner and gates. This makes the wastage of material, to avoid this, a pressurized gating system is used.

10. Smallest in-gate area in the pressurized gating system causes_____
a) turbulency
b) low velocity
c) low viscosity
d) smooth running of molten metal

Explanation: In the case of a pressurized gating system, due to the smallest in-gate area it maintains a back pressure throughout the gating system. Because of this back pressure in the gating system, the metal is more turbulent and generally flows full.

11. What is the ratio of width to the depth of in-gates in general?
a) 1:2
b) 1:1
c) 4:1
d) 2:7

Explanation: In-gates are generally made wider compared to the depth, up to a ratio of 4. This facilitates in the severing of gating from the casting after solidification. And it reduces the actual connection between the in-gate and the castings so that the removal of the gating is simplified.

12. Why large or complex castings require multiple in-gates?
a) To make smooth surface finish of the casting
b) To make uniform flow
c) To have high strength of the casting
d) To have good toughness of the casting

Explanation: Large or complex castings require multiple in-gates to completely fill all the sections of the castings effectively. Runner area is also reduced after each in-gate, such that restriction on the metal flow would be provided to make more uniformity in the metal flow.

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