Engineering Metals and Alloys in Construction
Q1. Short Notes (5 Marks Each)
Copper Alloys and Their Properties
Copper alloys are formed by mixing copper with other metals to improve strength, corrosion resistance, and workability.
Brass (Cu + Zn): Good corrosion resistance and ductile. Used in fittings, sheets, and decorative items.
Bronze (Cu + Sn): Harder and stronger than brass. Used in bearings and statues.
Gunmetal (Cu + Sn + Zn): Highly resistant to corrosion and wear. Used in valves and pipes.
Cupronickel (Cu + Ni): High resistance to seawater corrosion. Used extensively in marine applications.
Conclusion: Copper alloys are widely utilized due to their durability and resistance to environmental degradation.
Comparison of Mild Steel and Cast Steel
| Aspect | Mild Steel | Cast Steel |
|---|---|---|
| Carbon Content | Low (0.15–0.3%) | Higher |
| Strength | Moderate | High |
| Ductility | High | Lower |
| Manufacturing | Rolled | Cast |
| Cost | Cheaper | More Expensive |
| Uses | Structural works | Heavy parts |
Conclusion: Mild steel is preferred for general construction, while cast steel is used where high strength is required.
Differences Between Pig Iron and Wrought Iron
| Aspect | Pig Iron | Wrought Iron |
|---|---|---|
| Carbon | High (3–4%) | Very low |
| Nature | Brittle | Ductile |
| Strength | Low | Moderate |
| Workability | Poor | Excellent |
| Use | Raw material | Gates, grills |
Conclusion: Pig iron serves as an intermediate material, whereas wrought iron is refined and highly usable.
Characteristics of Tin and Lead
Tin:
- Soft, ductile, and corrosion-resistant.
- Features a low melting point.
- Used primarily in tin plating and various alloys.
Lead:
- Heavy, soft, and highly corrosion-resistant.
- Resistant to many chemicals.
- Used in pipes and radiation shielding.
Industrial Applications of Aluminium
- Lightweight and highly corrosion-resistant.
- Used in doors, windows, and roofing sheets.
- Excellent for electrical conductors.
- Vital for aircraft and transport industries.
Common Uses of Nickel
- Essential component in stainless steel production.
- Significantly improves corrosion resistance.
- Used in plating and battery manufacturing.
Q2. Types of Iron and Ores (10 Marks)
Classification of Iron Types
Pig Iron: The first product of the blast furnace; contains high carbon (3–4%) and is very brittle.
Cast Iron: Produced by remelting pig iron; strong but brittle. Used in pipes and machine parts.
Wrought Iron: Contains very low carbon; highly ductile and malleable. Used for gates and chains.
Steel: Features controlled carbon content; strong and versatile. Used extensively in construction.
Common Iron Ores and Their Composition
- Hematite (Fe₂O₃): Considered the best ore for production.
- Magnetite (Fe₃O₄): Known for high iron content.
- Limonite: A hydrated iron ore.
- Siderite: A carbonate-based iron ore.
Engineering Applications of Iron
- Structural steel for buildings and bridges.
- Heavy machinery manufacturing.
- Railway tracks and infrastructure.
- Industrial piping systems.
Conclusion: Iron and its various forms are fundamental to modern construction and engineering.
Q3. Manufacturing of Iron (10 Marks)
Iron Production via the Blast Furnace Process
Step 1: Charging
Iron ore, coke, and limestone are added from the top of the furnace.
Step 2: Combustion
Coke burns to produce Carbon Monoxide (CO).
Step 3: Reduction
CO reduces iron oxide into molten iron.
Step 4: Slag Formation
Limestone reacts with and removes impurities to form slag.
Step 5: Collection
Molten iron is collected at the bottom of the hearth.
Chemical Reactions in Iron Manufacturing
- C + O₂ → CO₂
- CO₂ + C → 2CO
- Fe₂O₃ + CO → Fe
Primary Products of Iron Smelting
- Pig iron
- Slag
Note: Draw a sketch of the blast furnace including the throat, stack, bosh, and hearth zones.
Q4. Extraction of Aluminium (10 Marks)
Bayer Process for Alumina Purification
Bauxite is purified to produce alumina (Al₂O₃).
Hall-Héroult Process for Aluminium Electrolysis
Alumina is dissolved in molten cryolite, and electrolysis is performed.
Chemical Reactions
- Aluminium is deposited at the cathode.
- Oxygen is released at the anode.
Key Features
- Requires high electricity consumption.
- Produces high-purity aluminium.
Note: Draw a sketch of the electrolytic cell.
Q5. Types of Steel and Products (10 Marks)
Classification of Steel Varieties
- Mild steel
- High carbon steel
- Stainless steel
- Alloy steel
Common Structural Steel Products
- Structural sections (I-beams, T-sections, channels).
- Reinforcement bars (Rebar).
- Sheets and plates.
- Pipes and tubing.
Conclusion: Steel remains the most important structural material in engineering.
PAPER 2 (2023–24)
Q1. Short Notes (5 Marks Each)
Role of Metals in Building Construction
- High strength and long-term durability.
- Excellent fire resistance.
- Fully recyclable material.
- Used in structural frames and roofing.
Anodizing Process for Aluminium
An electrochemical process that forms a protective oxide layer on aluminium, improving corrosion resistance and aesthetic appearance.
Benefits of Chrome Plating
A thin chromium coating that improves surface hardness, provides a high-shine finish, and protects against corrosion.
Methods for Joining Metal Components
- Welding: Creates a permanent joint.
- Riveting: A mechanical joint method.
- Bolting: A temporary or semi-permanent joint.
- Soldering: Joining at low temperatures.
Heat Treatment Processes for Steel
- Annealing: Softens the metal for better workability.
- Hardening: Increases overall strength and hardness.
- Tempering: Reduces brittleness while maintaining strength.
Q2. Differences (10 Marks)
Ferrous and Non-Ferrous Metal Comparison
| Ferrous | Non-Ferrous |
|---|---|
| Contains iron | Does not contain iron |
| Rusts easily | Highly corrosion resistant |
| Magnetic | Non-magnetic |
| Example: Steel | Example: Aluminium |
Hot Rolled vs Cold Rolled Steel
| Hot Rolled | Cold Rolled |
|---|---|
| Processed at high temperatures | Processed at room temperature |
| Rough surface finish | Smooth, polished finish |
| Less dimensional accuracy | High precision and accuracy |
Note: Rolling reduces thickness using compressive force.
Hard Steel and Mild Steel Comparison
| Hard Steel | Mild Steel |
|---|---|
| High carbon content | Low carbon content |
| Strong but brittle | Ductile and malleable |
| Used in tools and dies | Used in general construction |
Q3. Extraction of Iron (10 Marks)
(Refer to the Blast Furnace process detailed in Paper 1, Q3. Include diagrams.)
Q4. Manufacturing of Aluminium (10 Marks)
(Refer to the Bayer and Hall-Héroult processes detailed in Paper 1, Q4.)
Q5. Procedures for Painting Metal Surfaces (10 Marks)
Reasons to Paint Metal
- To prevent oxidation and corrosion.
- To improve the aesthetic appearance.
- To protect the substrate from weather damage.
Process for Painting New Metal
- Thorough surface cleaning.
- Application of an anti-corrosive primer.
- Application of an undercoat.
- Application of the final decorative coat.
Repainting Steel Railings
- Remove existing rust using wire brushing or sanding.
- Apply a fresh layer of primer.
- Apply subsequent paint coats for protection.
Diagrams are mandatory for the examination.