The Technological World. Chapter 12

Transcription

1 The Technological World Chapter 12

2 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 ST

3 ST 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)

4 ST P 387

5 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)

6 Main Other ST 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)

7 Checkup Observatory: The Environment Page 418, Questions 1 and 2 ST

8 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 ST

9 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

10 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. ST

11 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 ST

12 Solid Oak Furniture

13 Oak Flooring

14 Maple Baseball bats

15 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

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17 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. ST

18 Particle Board

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20 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. ST

21 Degradation and Protection of Wood 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)

22 Treated wood

23 Cedar Docks and Decks

24 Ceramics

25 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. ST

26 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. ST

27 ST 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 Fragility - very fragile

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29 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 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.

30 Ceramics can be fragile

31 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 ST

32 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. ST

33 Metals and Alloys

34 Alloy Bike Frames

35 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 ST

36 ST

37 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 Please write into notes ST

38 Oxidation of Metals

39 Rustproofing

40 Techniques to enhance the properties of Metals & Alloys ST 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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42 Plastics

43 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. ST

44 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 ST

45 The Degradation and Protection of Plastics Plastics tend to degrade over time. Slow Cracks form Change in colour Causes & Prevention Write into notes please Penetration of a liquid Waterproof coating Oxidation Add an antioxidant UV Add a pigment that absorbs UV ST

46 Mythbusters What is bulletproof

47 Composites

48 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. ST

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50 Kevlar is a composite

51 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. ST

52 Checkup Observatory: The Environment Page 418, Questions 3 to 6 ST

53 Review Observatory: The Environment Page 421, Review Questions A to D Credits All images are from: Observatory: The Environment Editions du Renouveau Pedagogique Inc