Food Packaging Technology Questions and Answers for Campus interviews on “Manufacture of Tinplate – 4”.
1. Softer strength steels are used for drawn.
a) True
b) False
Answer: a
Clarification: The given statement is true. Higher strength steels are suitable for welded food cans, while softer, more formable grades are better for drawn cans and components such as aerosol tops and bottoms, fish or beverage cans.
2. Tinplating is the method of depositing tin on steel.
a) True
b) False
Answer: a
Clarification: The given statement is true. Tinplating is the method of depositing tin on steel. The quality or type of steel used depends on the purpose for which tinplate will be used.
3. The method of making tinplate by electroplating is also known as ________
a) selective tinplating
b) uniform tinplating
c) bilayer tinplating
d) differential tinplating
Answer: d
Clarification: The method of making tinplate by electroplating is also known as differential tinplating. The introduction of the electroplating process enabled a different thickness of tin to be applied to the two surfaces of the steel. Differential tinplating is the most cost-effective method and is efficient in covering interior and exterior of the container in a single step.
4. Ferrostan process is halogen process in differential tinplating.
a) True
b) False
Answer: b
Clarification: The given statement is false. Acid stannous sulfate process is generally known as the Ferrostan process. It is preceded by cleaning in a pickling and degreasing unit, followed by thorough washing to prepare the surface. Following which the coating is passivated and is flow melted.
5. Halogen process is a method of differential tinplating.
a) True
b) False
Answer: a
Clarification: The given statement is true. In this method, plating is done via electroplating using halogen gas. Using halogen in tinplating has additional benefits as it increases the stability. Also, halogen in the process can be recycled and reused.
6. The melting point of tin is around ________
a) 190°C–200°C
b) 260°C–270°C
c) 350°C–360°C
d) 200°C–210°C
Answer: b
Clarification: The melting point of tin is around 260°C–270°C. It has the lowest melting point in group 14 elements. It can undergo harsh treatments. This therefore makes it a preferable choice in manufacture of metal cans.
7. Flow melting is a method of melting the tin for tinplating.
a) True
b) False
Answer: a
Clarification: The given statement is true. Flow melting consists of heating the strip to a temperature above the melting point of tin (typically, 260°C–270°C), followed by rapid quenching in water.
8. During tinplating _______ is formed.
a) FeCl2
b) SnCl2
c) FeSn2
d) SnO2
Answer: b
Clarification: During tinplating, a small quantity of the tin–iron compound FeSn2 is formed; the weight and structure depend on the time and temperature, as well as other factors such as the surface condition of the steel. The structure and weight of this alloy layer plays an important role in several forms of corrosion behavior.
9. Film formed from electrolytic treatment is usually <1 μm thick.
a) True
b) False
Answer: a
Clarification: The given statement is true. An electrolytic treatment in a sodium dichromate electrolyte is the most widespread. It results in the formation of a film (usually <1 μm thick), consisting of chromium, chromium oxides and tin oxides, the quantity and form of these basic constituents determining the varying properties of the film.
10. _______ is the final step in tinplating.
a) De-oiling
b) Activating
c) Passivating
d) Oiling
Answer: d
Clarification: After tinplating, the plate is given a light oiling. It is obviously essential that the oil used is approved for use in food packaging; cotton seed oil was used for many years but this has now been largely superseded by dioctyl sebacate (DOS).
11. The oil is applied by electrostatic precipitation or direct plate immersion.
a) True
b) False
Answer: a
Clarification: The given statement is true. The oil is applied by electrostatic precipitation or direct plate immersion. The quantity of oil (applied uniformly to both sides) is carefully controlled because an excessive oil film can cause de-wetting of enamels and printing inks, which are applied during subsequent container manufacture.
12. The oil film weights are generally in the range of_______
a) 5–10 mg m-2
b) 1–5 mg m-2
c) 10–15 mg m-2
d) 1–5 mg m-2
Answer: a
Clarification: The oil film weights are generally in the range of 5–10 mg m-2 to help preserve it from attack, and to assist the passage of sheets through container forming machines without damaging the soft tin layer.
Food Packaging Technology for Campus Interviews,