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The Technological
World
Chapter 12
Chapter 12
Manufacturing Technical Objects
There have been many inventions that have improved the quality of our lives. We will refer to these inventions as technical objects.
In this chapter we will look at what must be considered when designing and manufacturing an object:
1. Materials and their properties
2. Technical Drawings
3. Manufacturing of the objects
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12.1 Constraints & Deformations
Stress caused by normal use.
Constraints are the different types of stresses.
1. Compression (crush)
2. Tension (stretch)
3. Torsion (twist)
4. Deflection (bend)
5. Shearing (cut)
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Deformation is the change in shape
caused by a constraint.
1. Elastic (go back to original shape)
2. Plastic (changed into new shape)
3. Fracture (break)
12.2 Mechanical Properties Mechanical properties of a material determine
how it will react when subjected to one or more
constraints.
1. Hardness (resist dents without breaking)
2. Elasticity (return to it’s original shape)
3. Resilience (resist shocks)
4. Ductility (stretches)
5. Malleability (flattened/bent without breaking)
6. Stiffness (keep it’s shape)
7. Resist Corrosion
8. Electrical conductivity (carry current)
9. Thermal conductivity (transmit heat)
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Main
Other
Checkup
Observatory: The Environment
Page 418, Questions 1 and 2
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12.3 Categories of Materials and
their Properties
Let’s have a closer look at the following
materials and their properties:
1. Wood and Modified Wood
2. Ceramics
3. Metals and Alloys
4. Plastics
5. Composites
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Please paste table into notes!
You need to be able
to explain using
these properties
why a certain
material is or is not
a good choice
Degradation and Protection
The degradation of a material is the
decline in some of its properties due to the
effects of the surrounding environment.
The protection of a material is the
application of procedures that prevent or
delay its degradation.
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Wood and Modified Wood
Wood comes from harvesting trees &
processing wood chips.
Hardwood comes from deciduous trees
maple, oak, & birch
Softwood comes from coniferous trees
spruce, pine & fir
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Solid Oak Furniture
Oak Flooring
Maple Baseball bats
Other considerations include:
1. Aesthetic appeal
2. Hardness, elasticity, resilience, and toughness
3. Low thermal and electrical conductivity
4. Ease with which it can be worked
5. Colour
6. Its lightness relative to its strength
Modified Wood
Modified wood
treated wood
wood mixed with other substances
Eg. plywood, particle board & fibreboard
These are sheets, chips, or fibres of wood
that are glued together in sheets.
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Particle Board
Degradation and Protection of Wood
Unprotected wood can degrade swiftly.
Since wood is an organic substance, many fungi, microorganisms, and insects can infest the wood, feed off it and cause it to rot.
Wood can be painted, stained, varnished or treated with other protective coatings to help prevent its deterioration.
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Treated wood is made resistant to rot by:
Dipping it in an alkaline solution containing copper. This wood usually has a greenish colour.
Heating it to a high temperature.
Some woods, such as cedar, have a natural resistance to rot.
Coatings (paint, stain, varnish)
Degradation and Protection of Wood
Treated wood
Cedar Docks and Decks
Ceramics
Ceramics
A ceramic is a solid material obtained by
heating inorganic matter containing
various compounds, usually oxides.
When the raw material is heated, the
water evaporates, and the bonds between
the constituent compounds are
rearranged.
A ceramic is always solid at room
temperature.
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Traditionally, most ceramic objects were
made out of clay and sand. Sand is used
for making glass.
Although other materials are now used,
clay and sand are still widely used as they
are both plentiful and inexpensive.
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Properties of Ceramics Their properties depend on the raw material and
the method of baking.
Ceramics can be a good choice for many objects because:
Low electrical conductivity used as insulators
High degree of hardness building materials & cutting tools
Heat resistance and low thermal conductivity dishes, cookware & thermal insulators
Resistance to corrosion used in ducts for fumes or water
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Terracotta Army Sculptures depicting the armies of Qin Shi Huang,
the first Emperor of China.
It is a form of funerary art buried with the emperor
in 210–209 BC and whose purpose was to protect
the emperor in his afterlife.
discovered in 1974 by some local farmers in
Lintong District, Xi'an, Shaanxi province.
The figures include warriors, chariots and horses.
over 8,000 soldiers, 130 chariots with 520 horses
and 150 cavalry horses, the majority of which are
still buried.
Ceramics can be fragile
The Degradation and Protection of Ceramics
Can be degraded by some acids & bases
A thermal shock (a sudden change in temperature)
can cause damage to a ceramic object.
Glazes can be used to protect the ceramics
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Metals and Alloys A metal is a material extracted from a
mineral ore. Metals are usually shiny in appearance and are good conductors of heat and electricity.
The pure metal is rarely used.
An alloy is a mixture of a metal with one or more other substances, which may be metallic or nonmetallic. The mixture of materials results in more desirable properties.
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Metals and Alloys
Alloy Bike Frames
There are two main types of alloys:
Ferrous alloys whose main component is
iron.
Nonferrous alloys whose main component is
a metal other than iron
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The Degradation and Protection
of Metals & Alloys The main cause for metal and alloy degradation
is oxidation, where the material reacts with
oxygen. This is commonly referred to as rusting.
Metals & Alloys can be protected by coating it
with a substance that isolates it from the oxygen
in the air:
Metallic coatings: zinc, chrome, gold, silver, nickel,
aluminum, lead
Other coatings: paint, enamel, grease, resin
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Please write into notes
Oxidation of Metals
Rustproofing
Techniques to enhance the properties of Metals & Alloys
Steel heat treatments
These methods include: Quench hardening
Atoms are rearranged at high temperatures and then set by
dropping into a cool liquid (water, oil, …)
Hardens the steel but is brittle!
Tempering Atoms are rearranged at lower temperatures than quenching
Hardens the steel (less brittle than above & softer)
Annealing Very slow process!
Restores the properties of steel once they have been modified by welding.
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Plastics
Plastics made from fossil fuels
petroleum and natural gas
Monomers are extracted from the fossil fuels and are arranged into long chains called polymers.
Plastic is a material made of polymers, to which other substances may be added to obtain certain desirable properties.
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Types of Plastics A thermoplastic is a plastic that becomes soft
enough when heated to be molded or remolded and that hardens enough when cooled to hold its shape. Most plastic objects are made of this type.
Most thermoplastics can be recycled
A thermosetting plastic is a plastic that remains permanently hard, even when heated. Often harder and more resilient than thermoplastics
Include melamine and polyesters
Cannot be recycled in Quebec
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The Degradation and Protection of Plastics
Plastics tend to degrade over time.
Slow
Cracks form
Change in colour
Causes & Prevention
Penetration of a liquid
Oxidation
UV
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Write into notes please
Waterproof coating
Add an antioxidant
Add a pigment that absorbs UV
Composites
Composites A composite is formed by combining materials
from different categories to obtain a material with
enhanced properties.
A composite has two main parts: the matrix and
the reinforcement.
The matrix is the body of the material. It
surrounds and supports the reinforcement and
gives the object its shape.
The reinforcement is inserted into the matrix to
strengthen the object.
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The Degradation and Protection of
Composites
The degradation of composites usually
takes one of two forms: 1. The deformation or fracture of the matrix (body)
or the reinforcement (skeleton).
2. The loss of adherence between the matrix and
the reinforcement.
The speed of degradation depends on
the type of matrix and reinforcement and
the conditions of use.
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Checkup
Observatory: The Environment
Page 418, Questions 3 to 6
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Review
Observatory: The Environment
Page 421, Review Questions A to D
Credits All images are from:
Observatory: The Environment
Editions du Renouveau Pedagogique Inc
