Casting, Forming and Welding Multiple Choice Questions & Answers (MCQs) on “Shell Moulding”.
1. Which of the following synthetic resins are used for mixing with sand in shell moulding?
a) Thermosetting resins
b) Epoxy resins
c) Fiber glass resins
d) Kevlar
Answer: a
Clarification: The synthetic resins used in shell moulding are essentially thermosetting resins, which get hardened by heat. Phenol formaldehyde resins are mostly used, which combines with sand to form a proper mixture for shell moulding. The mixture formed has high strength and resistance to heat.
2. Grain size of the sand particles has no affects on the surface finish of the casting.
a) True
b) False
Answer: b
Clarification: Generally, for the preparation of shell moulding sand, dry and fine sand that is completely free of the clay is used. The grain size to be chosen depends on the surface finish required on the casting. Too much fine a grain size requires a large amount of resin, which makes the mould expensive.
3. In shell moulding sand preparation, the resin is combined with a catalyst (hexa) to develop the_____
a) thermoplastic characteristics
b) toughness of the resin
c) thermosetting characteristics
d) viscosity of the resin
Answer: c
Clarification: The phenolic resins used in shell moulding have excess of phenol and acts like a thermoplastic material. During coating with sand the resin is mixed with a catalyst such as hexa methylene tetramine (hexa) in a proportion of 14 to 16 % so as to develop the thermosetting characteristics.
4. Which of the following compositions of the shell sand is used for avoiding of thermal crack during pouring?
a) Silica sand
b) Zircon sand
c) Resin
d) Additives
Answer: d
Clarification: Generally, additives are added to the sand mixture to improve the surface finish and also for the avoiding of any thermal crack during pouring. Some of the additives used are coal dust, manganese dioxide, calcium carbonate, pulverized slag and ammonium boroflouride.
5. Which of the following lubricants is added to the resin sand mixture for better flowability of the sand?
a) Lead stearate
b) Magnesium stearate
c) Sulphur stearate
d) Zinc stearate
Answer: d
Clarification: Some lubricants such as zinc stearate and calcium stearate are added to the resin sand mixture to improve the flowability of the sand, which helps in covering of maximum part of the metallic pattern efficiently and also permit easy release of the shell from the pattern.
6. Which of the following devices is used for the mixing or complete formation of the shell sand mixture?
a) Chucker
b) Mueller
c) Semi circular roller
d) Semi cylindrical roller
Answer: b
Clarification: Sand, hexa and additives, which are all dry, are mixed inside a Mueller for a period of 1 minute, then the liquid resin is added and mixing is done for another 3 minutes. Then by introducing cold or warm air into the Mueller, mixing is continued till all the liquid is removed from the mixture and coating of the grains is achieved to the desired degree.
7. Which of the following metals is used for the preparation of patterns in shell moulding?
a) Aluminium
b) Copper
c) Grey cast iron
d) Brass