Chapter 1 - Materials and their Properties
1. Types of Materials:
Materials are what objects are made of.
They can be classified into several categories.
Leaving Cert Engineering focuses on metals, plastics, and some composite materials.
Hard, strong, shiny materials, extracted from rocks and minerals.
Includes alloys, which are solid solutions of metals and other elements.
Good conductors of heat and electricity.
Can be shaped by heat and force.
Wood:
Natural material from tree trunks and branches.
Can be cheap, easy to work with, and aesthetically pleasing.
Composed of long chains of molecules.
Natural polymers include silk, wool, natural rubber, cellulose, DNA, proteins.
Synthetic polymers include plastics, made from oil, coal, and gas by-product chemicals.
Plastics can be easily molded into different shapes at low temperatures.
Mixtures of substances (traditionally containing clay).
Usually baked in an oven until very hard.
Brittle and good electrical insulators.
Mixtures or layers of different materials bonded together.
Can be extremely strong (e.g., concrete) or light and strong (e.g., fiberglass and carbon fiber).
Fiberglass is plastic reinforced with glass fibers.
Carbon fiber is made from carbon fibers bonded in plastic resin.
Flexible material made by weaving fibers together.
Fibers can be natural (e.g., cotton, wool) or synthetic (e.g., nylon, polyester).
2. Material Properties - Why They Are Important
Materials are useful due to their properties, such as strength, softness, ease of cutting or molding, weather resistance, cost, etc..
Understanding material properties is essential to use them effectively.
Properties help determine if a material is suitable for a specific job.
3. Forces and Material Deformation
Understanding material properties requires knowledge of forces and their direction.
Types of Forces:
Compression: A material being squashed is under compression, with compressive forces acting on it.
Tension: A material being stretched is under tension, with tensile forces acting on it.Shear: Shear forces act inward but are not in line with each other, potentially causing the material to break by shearing (sliding against itself).
How Materials Deform and Break
Elastic Deformation: When a small force is applied, the material undergoes elastic deformation, returning to its original shape if the force is removed.Plastic Deformation: With more force, the material can undergo plastic deformation, becoming permanently deformed and not returning to its original shape if the force is removed.
Fracture: With further force, the material will eventually break or fracture.
Deformation and property measurement are detailed further in Chapter 15.
4. Properties of Materials
A strong material requires a large force to deform plastically or fracture.
It can support a large load without permanent deformation.
Strength depends on the direction of applied force.
Compressive Strength: Materials strong under compression can support large compressive loads without plastic deformation or breaking (e.g., concrete).
Tensile Strength: Materials with high tensile strength can withstand large pulling forces without plastic deformation or breaking (e.g., steel cables).
Shear Strength: Materials with high shear strength will withstand high shear forces before deforming or breaking (e.g., adhesives).
An elastic material can deform significantly from its original shape and still return to it.
Highly useful in steel springs and rubber seals (e.g., rubber, spring steel).
Plasticity: How much a material can be permanently deformed before breaking.
Ductility: A ductile material stretches a lot (deforms plastically) under a tensile (pulling) force (e.g., copper, aluminum).
Malleability: A malleable material flattens easily (deforms plastically) under a compressive force (e.g., gold, silver, pewter).
A brittle material breaks easily when impacted.
When hit, it doesn't deform elastically or plastically, going straight to the fracture stage (e.g., glass, ceramics, concrete, cast iron).
Note: Strong materials can be brittle (e.g., construction bricks are strong in compression but shatter easily).
A tough material is difficult to break by impacting it; it is impact-resistant.
It absorbs impact energy by deforming and only fractures under very high energy impacts.
A tough material is strong and not brittle (e.g., mild (low-carbon) steel).
A hard material is difficult to scratch or indent, resisting plastic deformation of its surface (e.g., diamond, tungsten carbide).
A stiff material is rigid, requiring a lot of force to deform it elastically.
Measured by Young's Modulus of Elasticity (see Chapter 15 Mechanical Testing) (e.g., glass).
The weakening of a material due to repeated alternating forces.
Repeated movement spreads cracks throughout the material (e.g., all metals and plastics).
The slow plastic deformation of a material under a constant force.
The force required for creep is less than the material's normal strength support.
Usually occurs only at high temperatures (e.g., all metals and plastics).
How easily electricity flows through the material.
Metals are good conductors.
Materials that do not conduct electricity well are insulators (e.g., plastics, ceramics are good insulators).
Thermal Conductivity:
How easily heat flows through the material.
Metals are good thermal conductors.
Plastics and ceramics are good thermal insulators.
Melting Point
The temperature at which a material changes from a solid to a liquid (e.g., Iron: 1500∘C).
Expansion:
The amount a material increases in size when heated.
Corrosion Resistance:
How well a material can withstand damage from oxidizing (rusting) or other chemical reactions of the surface with the environment.
Corrosion-resistant examples: stainless steel.
Damaged by corrosion examples: iron, steel.
Chapter 2 - Introduction to Metals and Alloys
1. Definition of Metals and Alloys
Metals:
Generally strong, shiny solid materials.
Malleable (can be shaped by force).
Made from ore extracted from the earth.
Good conductors of heat and electricity.
Can be combined with other metals or elements (like carbon) to form alloys.
Recyclable and reusable by melting down.
The largest subgroup of all elements.
Common pure metals include iron, copper, silver, gold, tin, lead, and aluminum.
Atoms:
Tiny building blocks of all matter.
Consist of a nucleus surrounded by orbiting electrons.
Different atoms have a different number of electrons and particles in the nucleus.
Elements
A material made up of only one type of atom.
A pure substance with no other elements in it.
There are 94 naturally occurring elements on Earth.
Alloys:
A combination of metals, or a metal with other elements, where components are mixed at the atomic level.
Examples: steel (iron & carbon) and brass (copper & zinc).
Made by melting a metal and mixing in other metals or elements.
Metals in alloys are bonded together in a metallic bond.
Have better properties (e.g., harder, stronger, more corrosion-resistant) than constituent metals or elements alone.
Composites:
Two or more materials bonded together where each material is still recognizable (not fully mixed at the atomic level).
Examples of metal composites: galvanized steel and plastic-coated steel.
Atomic Structure:
How atoms are arranged and bind to each other.
Determines many material properties (solid, liquid, gas, conductivity, strength).
"Metal" in general usage
Often refers to any material containing metal, including pure metals, alloys, or metal composites.
2. Classification of Metals and Alloys
Ferrous Metals and Alloys
Contain iron.
Strong, usually magnetic.
Corrode (rust) easily.
Examples: cast iron and steel.
Iron itself is not used as a pure metal but becomes useful when alloyed with carbon to create steel.
Non-Ferrous Metals and Alloys
Do not contain iron.
Do not corrode (or corrode very slowly).
Non-magnetic
Examples: aluminum, copper, gold, silver, lead, zinc, tin, brass, bronze.
Have low melting points.
More expensive than ferrous metals.
Many are used alone for properties like corrosion resistance.
Also used as major alloying elements with steel.
3. Properties and Applications of Non-Ferrous Metals
Aluminum:
Properties: Light, non-toxic, resistant to corrosion, good conductor of heat, most used metal after steel.
Applications: Aircraft bodies, food and drink cans, cooking (foil, pots), window and door frames.
Copper:
Properties: Good conductor of electricity and heat, ductile, non-corrosive in water.
Applications: Electrical wires, water pipes/plumbing, cookware.
Zinc:
Properties: Resistant to corrosion.
Applications: Coating steel to prevent corrosion (galvanizing, e.g., outdoor roofs).
Lead:
Properties: Soft, easily malleable, dense and heavy, low melting point, resistant to corrosion, toxic.
Applications: Flashings for roofs, shielding against X-rays, car batteries, weight for ship keels.
Tin:
Properties: Soft, low melting point, non-corroding, non-toxic.
Applications: Alloyed with lead to form soft solder, coats steel to make tinplate for food and drink cans.
Tungsten:
Properties: Very high melting point, hard, dense.
Applications: Alloys for cutting tools (tungsten carbide, high-speed steel), light bulb filaments.
Titanium:
Properties: Extremely light, strong, very corrosion resistant, bio-compatible, expensive.
Applications: Aircraft parts, jet engines, medical implants (replacement bones, staples, stents), prosthetic limbs.
Chromium:
Properties: Very shiny, does not corrode.
Applications: Alloys with steel to form stainless steel, coats/plates steel to form 'chrome'.
Manganese:
Properties: Hard, brittle, makes very strong steel alloys.
Applications: Alloying component in stainless steel, alloyed with steel to make military helmets, used to increase hardenability of steels.
Silver, Gold:
Properties: Do not corrode, shiny, good conductors of electricity.
Applications: Jewellery, ornaments, high-quality electrical connections.
4. Iron-Carbon Alloys
Irons and steels are iron-carbon alloys.
Carbon comes from the iron and steel-making process.
Classified by percentage of carbon.
Higher carbon percentage leads to harder and more brittle material.
Irons (high carbon)
Pig Iron: % Carbon: > 4%.
Description: Pinkish, very brittle metal, created from iron ore using a blast furnace.
Applications: Too brittle to use directly, used to make cast iron and steel.
Cast Iron: % Carbon: 2.1%-4%.
Description: Made from pig iron using a cupola furnace, easily cast into shapes, high compressive strength, resistant to wear, more brittle than steel, rusts easily.
Applications: Engine blocks, crankshafts, machine tools, cookware.
Grey Cast Iron (HL): % Carbon: 2.1%-4%.
Description: High impact-resistance, tougher, less brittle than white cast iron, made by adding silicon and slow cooling.
White Cast Iron (HL): % Carbon: 2.1%-4%.
Description: Harder, more brittle than grey cast iron, made by fast cooling.
Applications: Bearings, brake pads.
Carbon Steels (low to high carbon):
Steel is an iron-carbon alloy where the carbon percentage is less than 2.1%.
Made from pig iron and/or scrap metal in a basic oxygen furnace or electric arc furnace.
Carbon steels are those where carbon is the primary alloying element (small amounts of silicon and manganese allowed).
Common and inexpensive.
Low-Carbon Steel (Mild Steel): % Carbon: 0.03%-0.25%.
Description: Ductile, malleable, tough, easily forged, machined, welded, rusts easily, cannot be heat-treated.
Applications: Sheet metal, cans, car bodies, structural frames, nuts, bolts, nails, machinery parts.
Medium Carbon Steel % Carbon: 0.25%-0.6%.
Description: Stronger and harder than mild steel, good mix of strength and toughness, can be heat-treated, machinable.
Applications: Crankshafts, gears, railway tracks, structural beams, hand tools.
High-Carbon Steel (Carbon Tool Steel): % Carbon: 0.6%-1.5%.
Description: Strongest and hardest, most brittle, difficult to machine and weld, can be heat-treated to harden surface further.
Applications: Cutting tools, hammers, chisels, springs, ball bearings.
5. Alloy Steels:
Have more alloying elements added than carbon steel (e.g., chromium, tungsten, manganese).
Carbon content can be low, medium, or high.
Stainless Steel:
Composition: Low carbon, high (>11%) chromium, also nickel and manganese.
Description: Corrosion-resistant, shiny surface.
Applications: Cutlery, medical & dental instruments, cooking utensils.
High-Speed Steel (HSS) / Tool Steel:
Composition: High carbon, plus tungsten (18%), plus cobalt.
Description: Retains hardness and cutting edge at high-speed cutting.
Applications: Drill bits, lathe cutting tools, milling tools.
Spring Steel:
Composition: Medium-to-high carbon, plus manganese.
Description: High-elasticity steel, hard.
Applications: Springs, clips, music wire/strings.
6. Coated/Plated Steels
Galvanized Steel:
Plating Metal: Mild steel plated with zinc.
Description: Resistant to corrosion.
Applications: Outdoor furniture, roof panels, ladders.
Tinplate
Plating Metal: Mild steel plated with tin.
Description: Resistant to corrosion, safe for food.
Applications: Food and drink cans.
7. Copper-Based Alloys
Brass:
Composition: Copper (65%), Zinc (35%).
Description: Resistant to corrosion, ductile and easy to work, decorative.
Applications: Electrical fittings, plumbing fittings, hinges, screws, musical instruments.
Bronze:
Composition: Copper, Tin.
Description: Stronger and harder than brass, resistant to corrosion.
Applications: Statues, propellers, valves.
8. Other Non-Ferrous Alloys
Soft Solder:
Composition: Tin (60%), Lead (40%).
Description: Low melting point, good electrical conductivity.
Applications: Making electrical connections.
Lead-Free Solder:
Composition: Tin (95%), Silver (4%), Copper (1%).
Description: Low melting point, good electrical conductivity, no toxic lead.
Applications: Wave soldering in electronics factories.
Titanium Alloys:
Composition: Titanium (90%), Aluminum (6%), Vanadium (4%).
Description: Very light and strong, very corrosion-resistant, very heat-resistant, bio-compatible.
Applications: Medical implants, aircraft and spacecraft parts, high-performance sports equipment.
Magnesium Alloys:
Composition: Magnesium (90%), Aluminum (10%).
Description: Lightest of all, easy to cast and machine.
Applications: Spacecraft parts, camera parts, alloy wheels.
9. Introduction to Corrosion of Metals
Corrosion is damage to materials caused by reaction with their environment.
Causes of Corrosion:
Oxidation (rusting): Metals react with oxygen (or nitrogen) in the air to form metal oxide.
Bad for cast iron and steel: iron oxide (rust) is weak and allows further air penetration, leading to complete failure.
Good for copper, zinc, aluminum: oxide forms a protective layer, preventing further oxidation.
Gold and silver do not corrode, they tarnish (become dull/stained) and need cleaning.
Galvanic: Two dissimilar metals in contact can cause an electrochemical reaction, leading to corrosion of one of them.
Stress: High stress points (sharp edges, bends) can cause stress corrosion.
10. Protection against Corrosion Design
Choose corrosion-resistant materials (plastics, non-ferrous metals, alloys).
Do not expose corrosion-prone metals to outside weather.
Avoid designs where water can pool, no sharp edges/stress points.
Alloying: Combine steel with chromium to form stainless steel.
Coatings: Coat metal with paint, lacquer, or plastic.
Plate steel with a non-ferrous metal (e.g., zinc, called galvanizing).
Sacrificial Protection (HL): Place a more reactive metal (e.g., zinc) in electrical contact with the metal to be protected (e.g., steel). The more reactive metal will corrode first.
11. Recycling of Metals and Alloys
Metals can be recycled and reused by melting them down.
A large proportion of all steel is made from scrap metal using electric arc furnaces.
Aluminum is well-suited to recycling; it only takes 5% of the energy to produce recycled aluminum compared to primary aluminum from ore (bauxite). This is why drink cans are recycled.
Gold, silver, copper, brass, zinc, and lead are expensive and always recycled.
Chapter 3 - Introduction to Plastics
1. Introduction to Plastics
Plastics are synthetic (man-made) materials.
They are derived from chemicals produced by the oil and gas industry.
There are thousands of plastic types with millions of uses in products and engineering.
2. Advantages of Plastics
Light and easily mouldable into any shape.
Suitable for mass-production.
Cheap, costing much less energy to produce than metals.
Insulators of electricity and heat.
Waterproof.
Do not corrode.
Smooth, can be colored, and do not require surface finishing.
Most plastics are non-toxic for food and drink use.
Most plastics are recyclable.
3. Disadvantages of Plastics
Damage the environment if not recycled.
Not biodegradable.
Clog landfills, seas, and rivers.
Can kill animals, fish, and birds if eaten.
Can enter the human food chain.
Release toxic gases if incinerated.
4. Polymers
Plastics are synthetic polymers.
Polymers are extremely long molecules, which are groups of atoms bonded together.
The properties of a polymer material depend on how these long molecules are arranged and bonded.
Thousands of source molecules (monomers) bond together to form one long polymer molecule.
Synthetic polymers are called "plastics" because they possess the property of being very plastic (meaning capable of permanent deformation).
Most polymers (thermoplastics) are easily reshaped by applying low heat.
Natural polymers exist in nature, including silk, wool, cellulose, proteins, and natural rubber.
5. Types of Plastics
Thermoplastics:
Can be melted and reshaped.
Have low tensile strength.
Are soft and flexible.
Have a low melting point.
Are recyclable.
Suffer from creep (slow plastic deformation under constant force).
Examples include Polythene (PE), Polypropylene (PP), Polystyrene (PS), Acrylic (PMMA), Nylon (polyamides), PVC (polyvinyl chloride), and ABS (acrylonitrile butadiene styrene).
Have linear or branched chains with weak secondary bonds between polymer chains. These weak bonds can be broken by heat, allowing the plastic to soften and chains to slip, becoming soft. When cooled, weak forces hold the chains together again.
Thermosetting Plastics:
Cannot be melted and reshaped.
Can only be molded once during creation.
Have higher tensile strength.
Are stiffer.
Are good insulators of electricity and heat.
Are non-recyclable.
Examples include Phenol Formaldehyde (PF) (Bakelite), Urea Formaldehyde (UF), Melamine Formaldehyde, Polyurethanes, and Epoxy resins.
Have cross-linked chains with strong primary bonds between the chains and cross-links. This lattice of strong chemical bonds makes them stiffer, stronger, and more resistant to heat. These strong chemical bonds cannot be broken by heat, so thermosets do not soften and reshape; they just burn.
Elastomers (HL):
Are elastic, rubber-like.
Return to original shape when stretched.
Are soft and flexible.
Can seal against gas & liquid.
Have low tensile strength.
Can be thermoset or thermoplastic.
Thermoset elastomers have cross-links between polymer chains, making them stiffer, stronger, and unable to be heated and reshaped. Examples include Vulcanized natural rubber, Polybutadiene (synthetic rubber), Neoprene, and Silicone Rubbers.
Thermoplastic elastomers (TPEs): can be heat-softened and reshaped. Examples include EVA and Spandex (Lycra).
Have coiled chains that can stretch out and return to their original shape.
Some polymers have shape memory, returning to their original shape when heated.
6. Common Thermoplastics and Their Applications
Polyethylene (PE): (Variants: LDPE, HDPE, PET)
Properties: Can be clear and thin, not strong, hygienic, non-toxic, biocompatible, low melting point, does not vacuum form well.
Applications: Bottles, food packaging, lunchboxes, shopping bags, clingfilm.
Polypropylene (PP):
Properties: Light, tough, stiffer than polythene, resistant to wear, cheap, biocompatible, hard to glue.
Applications: Chairs, bottle tops, food boxes, clothes hangers.
Acrylic (PMMA):
Properties: Very transparent, smooth, high-quality finish, hard (can crack), low cost, shapes in a vacuum former, bends on a strip heater.
Applications: Glass substitute, car lights, safety glasses, shop signs, fridge trays.
Nylon (polyamides):
Properties: Strong, hard to break, hard-wearing, slippy, low-friction, can be machined.
Applications: Gears, bearings, ropes, fishing lines, tent frames, fabric for clothes.
ABS and HIPS (high-impact polystyrene):
Properties: Impact-resistant, tough, non-toxic, safe, high gloss finish, easy to vacuum-form.
Applications: Toys, electronic casings.
PVC (Polyvinyl Chloride) / UPVC (Unplasticised PVC):
Properties: Strong, dense, heavier, resistant to chemicals, can be made rigid (uPVC) or flexible (PVC), cheap, low melting point.
Applications: Drain pipes, bank cards, wire insulation, window frames, vinyl records.
Expanded Polystyrene (EPS) (styrofoam, aeroboard):
Properties: Very light (90% air bubbles), absorbs impacts, heat insulation, shapes with a wire cutter, doesn't degrade or recycle.
Applications: Packaging, cavity wall insulation (beads), inside cycling helmets.
7. Common Thermosetting Plastics and Their Applications
Phenol Formaldehyde (PF) (Bakelite):
Properties: Hard, stiff, hard-wearing, heat and flame resistant, electrical insulator, absorbs impacts without chipping or cracking, chemical resistant.
Applications: Handles for cooking pots, electrical plugs, sockets, switches, snooker balls, printed circuit boards.
Urea Formaldehyde (UF)
Applications: Kitchen worktops.
Melamine Formaldehyde
Applications: Snooker.
Polyurethane Foam:
Properties: Expanded with bubbles, can be stiff or flexible, good thermal insulation.
Applications: Furniture stuffing, spray-on attic insulation.
8. Common Elastomers (HL) and Their Applications
Thermoplastic Elastomers:
EVA (Ethylene-Vinyl-Acetate)
Properties: Flexible, resists impacts, clear, glossy, non-toxic, biocompatible.
Applications: Mouth guards, flip flops, crocs, hot glue sticks.
Thermoset Elastomers:
Natural Rubber / Vulcanized Rubber
Properties: Natural rubber is cross-linked using sulfur and heat to create a stiffer and more durable material; elastic.
Applications: Tyres, gloves, seals.
Synthetic Rubbers (Polybutadiene, Neoprene, Silicone Rubber):
Properties: Wetsuits (Neoprene), waterproof, durable.
Applications: Wetsuits (Neoprene), seals, medical implants (Silicone Rubber).
9. Plastic Composites and Laminates
Plastics are strengthened by bonding with another material to form a composite.
This is commonly achieved by bonding glass or carbon fibers in a thermoset resin, using lamination or pultrusion processes, to form a very strong and light material.
GRP (Glass-Reinforced Plastic) (Fiberglass):
Construction: Glass fibers are set in a thermoset resin.
Properties: Light, strong, mouldable.
Applications: Boat hulls, storage tanks, fishing rods.
Carbon Fibre:
Construction: Carbon fibers set in a thermoset/thermoplastic.
Properties: Very light and strong.
Applications: Aircraft, spacecraft, supercars, race bikes, golf clubs.
10. Plastics End-of-Life and Disposal Issues
When plastic products reach the end of their life, the options in order of favorability are: (1) Reuse, (2) Recycle, (3) Incineration, (4) Landfill.
Issues with Disposing and Recycling of Plastics
Long Life: Plastics do not biodegrade and can take hundreds of years to break down. However, bacteria are being discovered and cultivated that can break down plastic.
Thermosets: Thermoset plastics cannot be melted down and recycled, unlike thermoplastics.
Landfill: Plastics in landfill can pollute groundwater and harm wildlife.
Incineration (burning): Incineration greatly reduces waste in landfills, and energy can be recovered from the heat generated. However, toxic gases are released, although some can be treated.
11. Biodegradable Plastics
Biodegradable plastics are becoming more available, often using plant starches (e.g., corn starch).
Challenges include: they are relatively expensive, and using corn for plastics reduces corn availability for food production.
Chapter 4 - Choosing Materials
1. Introduction to Choosing Materials
This chapter provides examples and practice for selecting suitable materials.
It's recommended to read Chapters 1, 2, and 3 first.
This chapter focuses on material selection, while Chapter 35 covers the broader design process and considerations.
2. Choose Materials - A Process
A general process for choosing suitable materials involves:
Understanding the required product features (e.g., shapes, functionality, aesthetics, safety).
Understanding the necessary material properties (e.g., strength, weight, heat/electrical conductivity).
Knowing and researching a wide selection of materials and their properties.
Choosing the material whose properties best match the required properties.
This process involves comparing the desired features and properties with the properties of available materials to choose the best match.
3. Choosing Materials - Initial Decisions & Tips
Heat or Electrical Conductors: If a product needs to conduct heat or electricity, the only choice is metal.
Heat or Electrical Insulators: For heat or electrical insulation, polymers or ceramics are suitable choices.
Heavy Loads: For products bearing heavy loads, steels or steel-reinforced concrete are the main options.
Strong and Very Light: If a product needs to be strong but also very light, consider:
Alloys of aluminium, titanium, or magnesium;
Polymer composites like carbon fiber or GRP (glass-reinforced plastic/fiberglass).Hard Cutting Edge: For a hard cutting edge, choices include hardened high-carbon steel, high-speed steel (tungsten steel alloy), or ceramics like tungsten carbide.Strong but Soft to Touch: Plastic-coated steel can be considered.Recyclable: Metals and most thermoplastics (or glass, paper) are recyclable choices.Biocompatible: For compatibility with the human body, choose titanium, polythene, or PVC.
4. Further Tips when Choosing Metals
Good Conductors of Heat: Copper, aluminium, cast iron.
Good Conductors of Electricity: Copper, silver.
Easily Drawn into Wires: Copper.
Corrosion-Resistant: Galvanized steel, stainless steel, tinplate, zinc, aluminium, copper, bronze.
Shiny, Stain-Resistant Surfaces: Stainless steel, anodised aluminium.
Structural Supports: Mild or medium-carbon steel, low-alloy steels, aluminium tubing.
Sheet Metal: Mild (low-carbon) steel, aluminium.
Stable, Impact, and Vibration-Resistant: Cast iron (e.g., engine blocks, machine tool bases).
Malleability: Copper, lead, tin, gold, silver.
Decorative: Gold, silver, brass, bronze.
Cutting Edges/Tool Ends: Hardened and tempered steel.
Hard Surface yet Tough and Impact-Resistant: Surface-hardened mild steel or cast iron.
5. Further Tips when Choosing Polymers
Thin Flexible Sheets (bags, bottles, containers): Polythene.
More Rigid Stronger Casings, Seats: Polypropylene.
Good Heat Insulators: Expanded polystyrene, polyurethane foam.
Pipes, Flexible Electrical Wire Insulation: PVC.
Hard-Wearing, Strong, Slippy (e.g., gears): Nylon.
Transparent Glass Substitute, Gloss-Finish: Acrylic.
Tough, Wear-Resistant, Non-Toxic (e.g., toys): ABS.
Hard, Scratch-Resistant, Heat & Electrical Insulators: Thermosets (e.g., phenol formaldehyde).
Soft, Flexible, Rubber-Like, Good Air and Gas Seals: Elastomers like synthetic rubber, silicones.
6. Examples of Suitable Material Choices with Reasons
The document provides a table of objects, their suitable materials, and the reasons for their selection. Here are some examples:
Pizza Oven, Stove, Fuel Burner: Cast Iron - Dense, heavy, stable, doesn't distort, holds heat/remains hot, helps to keep a steady temperature.
Scriber, File, Centre Punch, Hammer, Tap: High-Carbon Steel - Strong, hard, and hard-wearing. The surface/ends/edges can be further hardened using heat treatment.
Bicycle Frame:
Mild Steel - Strong, tough, cheap (but requires paint).
Aluminium - Light, corrosion-resistant.
Titanium alloy - Very light, strong, corrosion resistant, expensive.
Carbon Fibre - Very light, strong, non-corrosive, expensive.
Car Bodies:
Sheet mild steel - Cheap, easily pressed into shapes, spot welded etc.
Sheet aluminium - Lighter, corrosion-free.
Fiberglass - Corrosion-free, suitable for molding.
Car Wheels: Aluminium Alloy - Light, strong, shiny, corrosion-resistant, dearer than steel.
Car Door Trims: Silicone Rubbers - Flexible, form air and gas seals.
Cutlery, Kitchen Sink: Stainless Steel - Non-toxic, doesn't rust or stain, looks well, cheap.
Hot-Water Cylinder: Copper - Corrosion-resistant, long lifespan, non-toxic, malleable.
Bolts, Screws: Steel (strong, cheap) or Brass (looks well).
Electrical Wire: Copper - Good conductor of electricity, ductile, corrosion-resistant, malleable.
Jewellery: Gold, Silver, Brass - Do not corrode, shiny, good conductors of electricity.