Food Packaging Technology Multiple Choice Questions & Answers (MCQs) on “Manufacture of Glass – 1”.
1. Cullet is the second largest constituent in glass.
a) True
b) False
Answer: a
Clarification: The given statement is true. The largest constituent (68%–73%) is silica; the second largest constituent (15%–50%) is cullet, originating both as glass scrap from the factory and recycled glass from consumers (so-called postconsumer glass).
2. _______ glass is the most color sensitive.
a) Yellow
b) Black
c) Flint
d) Amber
Answer: c
Clarification: Flint glass is the most color sensitive with a tolerance of 1% green or 5% amber cullet in the batch mix. Amber glass can tolerate 10% green cullet, while up to a 50% mixture of amber and flint cullet can be used in the production of green glass.
3. Using cullet in glass making increases the energy requirement.
a) True
b) False
Answer: b
Clarification: The given statement is false. Cullet also reduces the amount of dust and other particulate matter that often accompanies a batch made exclusively from new raw materials. The use of cullet is economically desirable since less energy is required to melt cullet than new raw materials.
4. The temperature of glass-melting furnace is around ______
a) 800°C
b) 1000°C
c) 1100°C
d) 1500°C
Answer: d
Clarification: The raw materials are weighed, mixed and charged into a glass-melting furnace, which is maintained at a temperature of approximately 1500°C. Here, they are converted into molten glass that is chemically homogeneous and virtually free of gaseous inclusions (bubbles). The melting process consists of two phases: (i) changing the solids into a liquid and (ii) fining or “clearing up” of the liquid.
5. The process of removal of gases from glass surface is known as ___________
a) pressurization
b) refining
c) vaporisation
d) forming
Answer: b
Clarification: During the refining process, gases (principally CO2, SO2 and water vapor) produced by the chemical reaction rise to the surface of the furnace and are removed. It moves from the furnace into the working end of the furnace (mistakenly called the refiner) where thermal homogenization and cooling of the glass to the viscosity required for the particular operation begin.
6. During removal of gases, the temperature of melt increases.
a) True
b) False
Answer: b
Clarification: The given statement is false. During removal of gases, the temperature of melt decreases. The temperature of the melt is lowered from 1250°C to 1350°C to approximately 1100°C.
7. Which is the next step after refining in manufacture of glass?
a) Blowing
b) Forming
c) Annealing
d) Moulding
Answer: b
Clarification: The step after refining in manufacture of glass is forming. In this, the molten glass is molded into the desired shape. When the molten glass becomes free of gas (seed-free), it is then ready for forming into containers.
8. Gob is formed in a channel-like structure called a forehearth.
a) True
b) False
Answer: a
Clarification: The given statement is true. The glass is carried from the working end of the furnace to the forming machine in a channel-like structure called a forehearth, which is fired by a number of small burners, the aim being to ensure uniform temperature distribution throughout the depth of the glass. The glass then passes through a gob-forming mechanism which consists of a rotating sleeve and vertical plunger.
9. What is the temperature during the formation of the gob?
a) 1100°C
b) 2000°C
c) 500°C
d) 800°C
Answer: a
Clarification: Precise control of temperature and shape during the formation of the gob is required for the high speed production of accurately formed glass containers. Temperatures in the vicinity of 1100°C varying by no more than ±1°C are typical.
10. The process of converting gob of glass into a bottle or jar is called _________
a) threading
b) moulding
c) forming
d) annealing
Answer: c
Clarification: The process of converting a cylindrically shaped gob of glass into a bottle or jar is called forming, and it is essentially a controlled cooling process. While various types of forming machines are used throughout the world, the most predominant type is the IS machine. As its name implies, it consists of up to 16 sections, each one an individually functioning, hollow glass machine. It performs two basic functions: it shapes the gob into a hollow container, and simultaneously removes heat from the gob to prevent it from deforming significantly under its own weight.
11. Molten glass is also known as _________
a) body
b) gob
c) lump
d) mass
Answer: b
Clarification: The glass exits in a continuous, viscous stream which is cut by rapidly moving, horizontal steel blades to form what is known as a “gob” (i.e., a mass or lump of molten glass).
12. What is the preform before the formation of final glass jar called?
a) Mold
b) Gob
c) Tube
d) Parison
Answer: d
Clarification: The preform before the formation of final glass jar called parison or body blank. A gob of glass, accurately sheared in terms of weight and shape, is delivered into an externally air cooled, cast iron mold from above to shape a preform.
12. The pressure temperature combination in formation of glass container is around?
a) 200 kPa, 650°C
b) 100 kPa, 750°C
c) 200 kPa, 500°C
d) 500 kPa, 150°C
Answer: a
Clarification: Air at about 200 kPa is applied so that the glass is pressed against the metal surface of the blow mold, which is air-cooled to ensure rapid removal of heat. After this, the mold is opened and fully blown parison (at approximately 650°C) is removed. It is then held over a deadplate to further cool it.
13. The parison is an important factor in determining the final shape and structure of glass jar.
a) True
b) False
Answer: a
Clarification: The given statement is true. The body blank or parison is formed by pressing the gob of molten glass against the mold walls with a large plunger. The cavity is filled with molten glass, which is then pushed down into the neck ring to form the finish. A mechanical plunger in introduced into the glass which gives it a shape. Baffle or counterblow air is not used during this operation.
14. Which of the following methods is used for manufacture of lightweight bottles?
a) Screw press and blow
b) Blow and blow
c) Narrow neck press and blow
d) Neck blow and press
Answer: c
Clarification: Narrow neck press and blow (NNP&B) is a used for manufacture of lightweight bottles. It is the process in which the gob is delivered into the blank mold and pressed by a metal plunger. The plunger and gob together have the same volume as the blank mold cavity.
15. The gob is transferred to ___________ after moulding.
a) roller
b) plunger
c) former
d) annealing lehr
Answer: d
Clarification: The gob is transferred to annealing lehr after moulding. The term annealing generally refers to the removal of stress, and the annealing temperature or point is defined as the temperature at which stresses in the glass are relieved in a few minutes.