This set of Engineering Materials & Metallurgy Multiple Choice Questions & Answers (MCQs) focuses on “Mold Making”.
1. Which of the following is not a constituent of molding sand?
Explanation: A special type of sand is used for making molds, which is an important stage in casting. The molding sand contains refractory sand, binder, and additive. These type of sands maintain the shape at high temperatures, makes it porous and is cheap, thereby reusable.
2. What makes the molding sand refractory?
b) High-temperature treatment
Explanation: Silica sand is widely used as molding sand. It contains 80-90% of silicon dioxide. The silica gives refractoriness to the sand. The silica sand is cheap, easily available, has high thermal stability, and can be reusable.
3. How much clay does loam sand contain?
a) Up to 2%
b) Up to 10%
c) Up to 30%
d) Up to 50%
Explanation: Depending on the amount of clay content, molding sand can be classified into various types. Silica sand contains up to 2% clay, whereas weak sand contains 2-10% clay. Moderately strong sand has 10-20% clay, strong sand has up to 30% clay, and loam sand has up to 50% clay.
4. How much water does natural sand require?
Explanation: Natural sand, as the name suggests, is available as a natural deposit. These contain about 80-90% silica, 5-10% clay, and a small amount of lime and magnesia. These sand require only 5-8% water.
5. Chilled castings are made by using _________
a) Natural sand
b) Synthetic sand
c) Zircon sand
d) Chromite sand
Explanation: Chromite sand is a special kind of sand which has good refractoriness, high heat conductivity, and low expansion ratio. It is mainly used for making chilled castings. It may also be used as facing sand in steel casting.
6. Why are Kaolinite and Bentonite used as clay in molding sand?
a) High expansion ratio
b) High thermo-chemical stability
c) High coefficient of expansion
d) Non-reactive with molding sand
Explanation: Clay binders are the most common types of inorganic binder as they are natural earthy material. The most common types of clay used in molding sand are fireclay, kaolinite, and bentonite. Kaolinite and bentonite clays are useful as they have high thermo-chemical stability.
7. __________ additives improve the permeability of the molds.
d) Silica flour
Explanation: Additives are added to the molding sand to improve the properties of the mold. Seacoal is a finely powered bituminous coal used to obtain smoother and cleaner surfaces of castings. Sawdust used in dry conditions improves the permeability and deformability of the molds.
8. The molding sand in moist state is named as __________
a) Green sand
b) Loam sand
c) Backing sand
d) Parting sand
Explanation: The sand which is in moist state is known as green sand. It contains about 5-8% water and 16-30% clay. It is soft, light, and porous, and is used for simple and small-sized castings.
9. Which of the following is not a stage of mold preparation?
Explanation: Molding sand is prepared in three stages. The mixing stage involves the mixing of sand, binding, moisture, and additives. Then the sand is tempered by spraying and mixing water in the muller. Finally, the sand is conditions to remove foreign materials, aerating the sand, and other processes.
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