This set of Foundry online test focuses on “Moulding Sand Binders and Additives”.
1. _____________ is the mixture offering a very high stability to the mould.
Explanation: High quality bentonite bonded molding sands are able to offer the optimum solution for mold stability, providing not only the requisite mechanical properties but the necessary flexibility for the production of castings that comply with the ever stringent demands for quality and productivity.
2. Which of the following is the most basic binder used in the molding sand?
d) Manganese oxide
Explanation: Even though the major portion of the molding sand in silica (96%), clay and water form the binder component of this sand. It is used to provide these sand grains adhesive property so that the grains stick to the pattern to form a casting of appropriate and required shape.
3. Oxides of alumina are always treated as impurities in the molding sand.
Explanation: The oxides of alumina, sodium and magnesium have excellent binding properties. They are added to the molding sand to enhance its mold ability and dimensional properties. However, their constituency should be limited to 2% or less as its excess quantity can cause defects in the castings and effect the fusion point of silica sand.
4. ____________ sand is highly used for investment casting process.
a) Silica Sand
c) Loam sand
d) Chromite sand
Explanation: The Zircon sand has high thermal conductivity, high chilling power and high density. It requires a very small amount of binder. It is used to manufacture precision steel castings requiring better surface finish which is the main objective of the investment casting process.
5. Chromite sand requires the least amount of binders.
Explanation: Chromite sand is crushed from the chrome ore. As the fusion point of this sand is high as 1800 C, it requires a small amount of binder (3%). It is also used to manufacture heavy steel castings requiring a better surface finish.
6. The ____________ sand is the most versatile sand.
a) Loam sand
b) Chromite sand
d) Olivine sand
Explanation: The olivine sand contains all the minerals such as Fosterite (Mg2SiO4) and Fayalite (Fe2SiO4) which is suitable for almost all the type of casting manufacturing processes. The same mixtures can be used for a range of steels but it is very expensive.
7. The ________ is used to activate the clay binders to perform its functions.
b) Helium gas
c) Nitrogen gas
d) Alkali metals
Explanation: In a foundry, clay is used in the form of bentonite which requires water to activate itself. Bentonite can absorb more water which increases its bonding power. The clay also activates the other basic constituents like mixtures of lime and alkalis to reduce refractoriness.
8. Which of the following binder immediately increases the binding properties?
a) Cereal binder
Explanation: The Cereal binder when added to the molding sand increases the binding properties by 2% as soon as it is added. It has excellent mixing properties and the wide availability increases its probability of being used.
9. The sodium bentonite binder imparts swelling properties to the molding sand.
Explanation: Sodium Bentonite provides better swelling properties- volume increases some 10 to 20 times, high dry strength which lowers the risk of erosion, better tolerance of variations in water content, low green strength and high resistance to burnout, which reduces clay consumption.
10. Sodium bentonite and Calcium bentonite has the same binding properties.
Explanation: Sodium and Calcium bentonite has contras properties. Sodium Bentonite provides better swelling properties volume increases some 10 to 20 times, high dry strength which lowers the risk of erosion whereas the Calcium Bentonite has the low dry strength but higher green strength.
Sanfoundry Global Education & Learning Series – Foundry and Forging.
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