Casting, Forming and Welding Questions and Answers Part-7

1. Which of the following properties must a material possess to be used in mold making?
a) High refractoriness
b) Chemical and thermal stability
c) High permeability
d) All of the mentioned

Answer: d
Explanation: A material must have all of the above properties so as to be a good mold making material.

2. Which of the following group of material type is used in mold making
a) Metallic only
b) Non-Metallic only
c) Both metallic as well as non-metallic
d) Neither metallic nor non-metallic

Answer: c
Explanation: Both metallic as well as non-metallic materials are used for making molds.

3. Which of the following non-metallic material is not used in the synthesis of molds?
a) Magnesite
b) Silimanite
c) Zircon
d) Valcanised rubber

Answer: d
Explanation: Valcanised rubber has a very low refractoriness, hence, using valcanised rubber for making molds can cause damage to the mold cavity or metallic structure so formed.

4. High refractoriness of a material refers to its __________
a) Slipperyness of the material
b) Chemical strength towards other material
c) Strength to withstand at high temperature
d) Ability to get dissolved in molten metal

Answer: c
Explanation: Refractoriness is the resistance to self deformation at high working temperatures. A material must possess such property in order to withstand the temperature of molten metal during casting.

5. Which of the following is a perfect composition of clay (Bentonite) used in moulding sand?
a) Al2O3
b) Al2O3.2SiO2
c) Al2O3.2H2O
d) Al2O3.2SiO2.2H2O

Answer: d
Explanation: entonite is one type of clay used in moulding sand as a binder. Its chemical formula is represented as Al2O3.2SiO2.2H2O.

6. Which of the following material is not used for mold making?
a) Iron
b) Zinc
c) Mild steel
d) Alloy steel

Answer: b
Explanation: Zinc (Zn) has a very low melting point, making it non-dependable material to be used as the material for mold making.

7. Phosphorus is added to steel mold for which of the following reason?
a) It increases strength and hardness of steel
b) It increases refractoriness of steel
c) It increases porosity of steel
d) It increases finishing of steel

Answer: a
Explanation: Phosphorus has the ability to increase strength and hardness of steel material when added to it in the right compostion (2-4%).

8. Which of the following is a perfect composition for medium carbon steel?
a) Upto 0.3%
b) 0.3-0.6%
c) 0.6-1.7%
d) 1.7-3%

Answer: b
Explanation: The sequence of composition is in order from low carbon steel to high carbon steel till 1.7% carbon. Medium carbon steel belongs to a region of 0.3-0.6% carbon.

9. A form of cast iron in which free carbon is present in the form of nodules in the matrix of cementite and ferrite. This form of cast iron is ____________
a) Malleable iron
b) Pig iron
c) Wrought iron
d) None of these

Answer: a
Explanation: Malleable iron is one type of cast iron in which free carbon is present in the form of nodules in the matrix of cementite and ferrite.

10. Which of the following percent of carbon is correct for Eutectoid steel (at 723oC in Fe3-C diag)?
a) 0.05%
b) 0.5%
c) 0.6%
d) 0.8%

Answer: d
Explanation: At 723oC in Fe3C diagram the transformation change takes place. The carbon content at this point is 0.8% and is called as eutectoid steel.