This set of Foundry Multiple Choice Questions & Answers (MCQs) focuses on “Types of Sand Moulds”.
1. In the molding sands, which of the following are the major properties?
b) Sand Grains
c) Size of the grains
d) Permeability, sand grains and size of the grains
Explanation: The shape and size of the sand grain would greatly affect the various molding sand properties. The sand grain size and the sand grain could be coarse or fine and the grain shape should be round or angular. The sand permeability should depend on the type of casting to be manufactures. All these properties make a sand quality optimum.
2. The rate at which the casting is removed from the green sand mould is __________
b) Min 2-3 hours later
c) More than 6 hours
d) Around 2 days
Explanation: In a green sand mould, metal is poured immediately and the casting taken out. These are most commonly used and are adapted for rapid production, where the molding flasks are released quickly.
3. Green sand mould acquires the highest floor space.
Explanation: The green sand mould is used for the rapid production of the castings. It can be used to produce a wide range of castings. As the mould is produced, the casting is prepared. Hence, it requires less floor space as no storage is involved.
4. Hot tearing of the casting is least observed in _______________
a) Green sand moulds
b) Dry sand moulds
c) Skin dried sand moulds
d) Size of the grain
Explanation: The hot tearing of the casting refers to the one of the types of casting defect that weakens the strength of the casting defects. As the moisture is present in the green sand mould, the hot tearing is considerably reduced in the green sand mould.
5. All the sand moulds should have a great venting capacity.
Explanation: The venting is done in the sand moulds so that the gases are let out after the metal is poured in it. If these gases are not let out, they tend to form casting defects on the surface of the castings. Hence all the sand moulds should have great venting capacity.
6. The permeability _________ with the grain size.
a) Remains same
d) Depends on the sand
Explanation: The grain size increases with the coarse grains. The coarse grains would have more void space between the grains which increases with permeability. Similarly, the finer grains would have lower permeability.
7. Uncontrolled permeability in the green sand mould leads to ___________
a) Blow Holes
Explanation: The rate of flow of air passing through a standard specimen under a standard pressure is termed as a permeability number. The permeability of these holes should be properly controlled, otherwise blow holes and gas inclusions are likely to form.
8. The strength of the dry sand mould depends on ________
a) Sand Quality
b) Sand grain
Explanation: The dry sand mould is prepared using the heating method. Dry sand moulds are the green sand moulds which are completely dried by keeping in an oven in 150 to 350 C for 8 to 48 hours. Due to the great interference of heat, the strength is dependent on the binders in the molding sand.
9. Dry sand moulds have high strength than the green sand moulds to form large castings.
Explanation: Dry sand moulds gave higher strengths than the green sand mould and are preferred because they are less likely to be damaged during handling. Hence they are generally used for medium and large castings.
10. Skin dried mould is preferable for large moulds over the dray sand moulds.
Explanation: Though the dry sand mould is preferable for large moulds because of the expense involved, the compromise is achieved by drying only the skin of the mould cavity with which the molten metal comes into contact, instead if the full mould.
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