OTEN Notes on Engineered Products

Engineering Studies

Preliminary Course

Stage 6

Household appliances

ES/S6 – Prelim 41080 P0020451

Acknowledgments

This publication is copyright Learning Materials Production, Open Training and Education Network – Distance Education, NSW Department of Education and Training, however it may contain material from other sources which is not owned by Learning Materials Production. Learning Materials Production would like to acknowledge the following people and organisations whose material has been used.

Board of Studies, NSW

All reasonable efforts have been made to obtain copyright permissions. All claims will be settled in good faith.

Matrials development: John Burns

Revised version: Brian Jobson, Jeff Appleby, Joesphine Wilms and Stephen Russell Coordination: Jeff Appleby and Nicola Pegum

Illustrations: Tom Brown and David Evans

DTP: Nick Loutkovsky and Carolina Barbieri

Copyright in this material is reserved to the Crown in the right of the State of New South Wales. Reproduction or transmittal in whole, or in part, other than in accordance with provisions of the Copyright Act, is prohibited without the written authority of Learning Materials Production.

Revised 2001

Module contents

Subject overview ................................................................................iii Module overview................................................................................ vii Module components ................................................................ viii Module outcomes......................................................................ix Indicative time............................................................................x Resource requirements...............................................................x

Icons.....................................................................................................xi Glossary............................................................................................. xiii Directive terms.................................................................................. xix Part 1: Household appliances – development.........................1–33 Part 2: Household appliances – materials ..............................1–41 Part 3: Household appliances – mechanics ............................1–41

Part 4: Household appliances – electricity and

communication ................................................................1–63 Part 5: Household appliances – Engineering report...............1–20 Bibliography........................................................................................21 Module evaluation.............................................................................23

Subject overview

Stage 6 Engineering Studies Preliminary Course and HSC Course each have five modules.

Engineering Studies Preliminary Course

Household appliances examines common appliances

found in the home. Simple appliances are analysed

to identify materials and their applications.

Electrical principles, researching methods and

techniques to communicate technical information are

introduced. The first student engineering report is

completed undertaking an investigation of materials

used in a household appliance.

Landscape products investigates engineering

principles by focusing on common products, such as

lawnmowers and clothes hoists. The historical

development of these types of products demonstrates

the effect materials development and technological

advancements have on the design of products.

Engineering techniques of force analysis are

described. Orthogonal drawing methods are

explained. An engineering report is completed that

analyses lawnmower components.

Braking systems uses braking components and

systems to describe engineering principles. The

historical changes in materials and design are

investigated. The relationship between internal

structure of iron and steel and the resulting

engineering properties of those materials is detailed.

Hydraulic principles are described and examples

provided in braking systems. Orthogonal drawing

techniques are further developed. An engineering

report is completed that requires an analysis of a

braking system component.

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Bio-engineering examines both engineering principles and also the scope of the bio-engineering profession. Careers and current issues in this field are explored. Engineers as managers and ethical issues confronted by the bio engineer are considered. An engineering report is completed that investigates a current bio- engineered product and describes the related issues that the bio-engineer would need to consider before, during and after this product development.

Irrigation systems is the elective topic for the preliminary modules. The historical development of irrigation systems is described and the impact of these systems on society discussed. Hydraulic analysis of irrigation systems is explained. The effect on irrigation product range that has occurred with the introduction of is detailed. An engineering report on an irrigation system is completed.

HSC Engineering Studies modules

Civil structures examines engineering principles as

they relate to civil structures, such as bridges and

buildings. The historical influences of engineering,

the impact of engineering innovation, and

environmental implications are discussed with

reference to bridges. Mechanical analysis of bridges

is used to introduce concepts of truss analysis and

stress/strain. Material properties and application are

explained with reference to a variety of civil

structures. Technical communication skills

described in this module include assembly drawing.

The engineering report requires a comparison of two

engineering solutions to solve the same engineering

situation.

Personal and public transport uses bicycles, motor

vehicles and trains as examples to explain

engineering concepts. The historical development of

cars is used to demonstrate the developing material

list available for the engineer. The impact on

society of these developments is discussed. The

mechanical analysis of mechanisms involves the

effect of friction. Energy and power relationships are

explained. Methods of testing materials, and

modifying material properties are examined. A

series of industrial manufacturing processes is

described. Electrical concepts, such as power

distribution, are detailed are introduced. The use of

freehand technical sketches.

Lifting devices investigates the social impact that

devices raging from complex cranes to simple car

jacks, have had on our society. The mechanical

concepts are explained, including the hydraulic

concepts often used in lifting apparatus. The

industrial processes used to form metals and the

methods used to control physical properties are

explained. Electrical requirements for many devices

are detailed. The technical rules for sectioned

orthogonal drawings are demonstrated. The

engineering report is based on a comparison of two

lifting devices.

Aeronautical engineering explores the scope of the

aeronautical engineering profession. Career

opportunities are considered, as well as ethical

issues related to the profession. Technologies unique

to this engineering field are described. Mechanical

analysis includes aeronautical flight principles and

fluid mechanics. Materials and material processes

concentrate on their application to aeronautics.

The corrosion process is explained and preventative

techniques listed. Communicating technical

information using both freehand and computer-aided

drawing is required. The engineering report is based

on the aeronautical profession, current projects and

issues.

Telecommunications engineering examines the

history and impact on society of this field. Ethical

issues and current technologies are described.

The materials section concentrates on specialised

testing, copper and its alloys, semiconductors and

fibre optics. Electronic systems such as analogue

and digital are explained and an overview of a

variety of other technologies in this field is

presented. Analysis, related to telecommunication

products, is used to reinforce mechanical concepts.

Communicating technical information using both

freehand and computer-aided drawing is required.

The engineering report is based on the

telecommunication profession, current projects and

issues.

Figure 0.1 Modules

Module overview

In Part 1 you will begin to investigate the historical developments of household appliances. Some useful terms will be introduced. You will explore the development of floor cleaners, electric irons and

refrigerators.

To help you understand the importance of material selection for household appliances you will learn about the methods of classifying materials. The atomic structure and bonding of materials will be analysed. Lastly you will learn about research methods to prepare you for writing an engineering report at the end of the module.

You will build on your knowledge of materials and components by studying about the use of metals. Types of metals, such as ferrous and non-ferrous, will be explained.

You will then learn about cutting and joining currently used in household appliances. Polymer materials and ceramic materials and their uses are explored. Additional researching techniques are introduced, which you will need to help you eventually complete your Engineering Report.

In part 3 you will develop a basic understanding of engineering mechanical principles.

Concepts such as mass and force are defined. Next scalar and vector quantities are classified and a method of determining components of a force is explained.

In Part 4 of this module you will study basic forms of

electricity/electronics for household appliances. Principles such as potential difference, current, and components are described.

You will learn how to identify principles of electrical safety and learn about induction. Freehand orthogonal drawing concepts are detailed.

By part 5 you have practiced and completed your research methods and will know most of the steps for writing your engineering report.

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It will be time to pull all those skills together and collate your information into one report. You will need to research and study one household appliance. You will develop your report using your writing skills to communicate information and drawing skills to illustrate your work.

Module components

Each module contains three components, the preliminary pages, the teaching/learning section and additional resources.

• The preliminary pages include:

– module contents

– subject overview

– module overview

– icons

– glossary

– directive terms.

Figure 0.2 Preliminary pages

• The teaching/learning parts may

include:

– part contents

– introduction

– teaching/learning text and tasks

– exercises

– check list.

Figure 0.3 Teaching/learning section

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• The additional information may include:

– module appendix

– bibliography

– module evaluation.

Additional resources

Figure 0.4 Additional materials

Support materials such as audiotapes, video cassettes and computer disks will sometimes accompany a module.

Module outcomes

At the end of this module, you should be working towards being able to:

• describe the types of materials, components and processes used to make household appliances and explain any implications for engineering development (P1.2)

• explain the relationship between properties, uses and applications of materials in engineering (P2.1)

• develop written, oral and presentation skills and apply these to engineering reports (P3.2)

• applied graphics as a communication tool (P3.3)

• describe the developments in technology and their impact on engineering products (P4.1)

• describe the influence of technological change on engineering and its effect on people (P4.2)

• identify the social, environmental and cultural implications of technological change in engineering (P4.3).

Extract from Stage 6 Engineering Studies Syllabus, © Board of Studies, NSW, 1999. Refer to <http://www.boardofstudies.nsw.edu.au> for original and current documents.

Indicative time

The Preliminary course is 120 hours (indicative time) and the HSC course is 120 hours (indicative time).

The following table shows the approximate amount of time you should spend on this module.

Preliminary modules Percentage of time Number of hours Household appliances 20% 24 hr Landscape products 20% 24 hr Braking systems 20% 24 hr Bio-engineering 20% 24 hr Elective: Irrigation systems 20% 24 hr

HSC modules Percentage of time Number of hours Civil structures 20% 24 hr Personal and public transport 20% 24 hr Lifting devices 20% 24 hr Aeronautical engineering 20% 24 hr Telecommunications engineering 20% 24 hr

There are five parts in Household appliances. Each part will require about four to five hours of work. You should aim to complete the module within 20 to 25 hours.

Resource requirements

During this module you will need to access a range of resources including: • access to an early and late model household appliance • technical drawing equipment such as

− rule, pencils, eraser and compasses

− protractor and set squares.

For research you are encouraged to use the Internet, CD Roms and books through your local, school or TAFE library.

Icons

As you work through this module you will see symbols known as icons.

The purpose of these icons is to gain your attention and to indicate particular types of tasks you need to complete in this module.

The list below shows the icons and outlines the types of tasks for Stage 6 Engineering studies.

Computer

This icon indicates tasks such as researching using an

electronic database or calculating using a spreadsheet.

Danger

This icon indicates tasks which may present a danger and

to proceed with care.

Discuss

This icon indicates tasks such as discussing a point or

debating an issue.

Examine

This icon indicates tasks such as reading an article or

watching a video.

Hands on

This icon indicates tasks such as collecting data or

conducting experiments.

Respond

This icon indicates the need to write a response or draw

an object.

Think

This icon indicates tasks such as reflecting on your

experience or picturing yourself in a situation.

Return

This icon indicates exercises for you to return to your teacher when you have completed the part. (OTEN OLP students will need to refer to their Learner's Guide for instructions on which exercises to return).

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Glossary

As you work through the module you will encounter a range of terms that have specific meanings.

The list below explains the terms you will encounter in this module. These terms are bolded the first time they occur in the text.

alternating current when electrons flow (electric current) first in one direction and then flows back again and continue

this back and forth motion

atom a component of all matter

body-centred cubic A type of crystal structure

abbreviated to BCC

box up divide a shape into sections/areas/cubes so that it is broken down into easier to draw segments

brush A connector used to maintain electric contact between stationary and moving parts in a motor.

ceramics materials are versatile engineering materials, including such common items as brick, porcelain, glass,

and cement

commutator a device for reversing the direction of an electric current in a motor

dichlorodifluoromethane a ‘non toxic’ substitute for ammonium as a coolant, now banned, abbreviated to CFC-12

coefficient of expansion a measurement that describes the change in size of material relative to the temperature

compressive force describes a force applied to an object that attempts to compress the object

conventions agreed upon rules or practices

crystalline material the atoms form into definite repeating patterns or ‘lattice’ structures

density a measurement of a materials mass per unit volume

xiii

direct current when electrons flow (electric current) in one direction along the conductor

direction a measurement of the angle (normally measured off the horizontal) measured in degrees

drawing into wire pulling metal through a die to form a wire ductile able to be stretched without failure

elasticity the property of a material to return its original shape after a distorting force has been removed

electrical current the movements of electrons along the conductor in a particular direction which produces an

electric current

electrical conductivity the ability of a material to conduct electricity

electrons orbit the nucleus in layers (shells) and are negative in charge

electro-chemical bonds hold the atoms more rigidly together

electromagnet a magnet made by passing electrical current through a coiled conductor wrapped around a

ferrous core

element passing an electric current through a wire, thereby creating heat

elements materials composed of only one type of atom

equilibrant an equal force acting as a balance to maintain, or bring about, a state of equilibrium

ergonomics designing for bodily needs of a given working environment

face-centred cubic A tpe of crystal structure

abbreviated to FCC

ferrous metals metals which contain primarily iron with small proportions of other materials

force the interaction between bodies

force component a component of a vector is the effect of that vector in a specific direction. The components

of a vector add to equal the original vector

formability a material’s ability to be deformed or shaped by bending, stretching, compressing

freon a coolant used in the refrigeration process – is damaging to the ozone layer

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frictional properties the property of a material that describes the amount of grip a material has when sliding in

contact with another surface

fusible able to be joined together

hardness the property of a material to resist penetration or scratching when brought into contact with

another material

hexagonal close packed A type of crystal structure

abbreviated to HCP

lattice created when the atoms form into definite repeating patterns

magnetic flux density magnetic field strength; a magnetic field is represented by lines of ‘flux’ – the denser the

field or lines of flux, or the closer the lines are,

the stronger the magnetic filed

magnetic properties the ability of a material to become magnetic

magnetic induction a process enabling the spin axes of electrons to be aligned thus creating a magnet

magnitude the size or how much of something

mass the amount of matter that is contained within that object

melting point the temperature at which the material begins to become a liquid

neutrons are located in the nucleus, have no electrical charge and are a similar size to the protons

newton is a unit of force represented by the symbol N nichrome a metal alloy of nickel and chromium non ferrous metals metals which contain little or no iron non-oxidising does not form an oxide, chemically stable

nucleus lies at the centre of the atom, consisting of protons and neutrons

opacity the property of a material that stops the passage of light, that is, you cannot see through it

orthogonal drawing where an object is fully described by projecting a series of related views from various

viewing positions (above, front on, side on)

porcelain a ceramic product that is stable, smooth and is an insulator

primary bonds the main bonds holding material together

protons are located in the nucleus, are positive in charge and are equal in number to the electrons orbiting

the nucleus

prototype an initial version of an item, often produced at the development stage of a product

radiated heat heat that is transmitted through the air

relative density a measurement for material describing how compact the mass of the object is relative to

other materials

resistance to corrosion describes the property of a material that allows it to not corrode quickly in a service application

resistance to creep the property of a material to maintain its original length for a long period of time when a small

load is applied

resultant force describes effects when a system of two or more forces is analysed

rotor Rotating coil used in simple electric motors

scalar quantity is a quantity that requires only magnitude (size) for its complete understanding

secondary bonds weak bonds normally caused by attraction between positive and negative parts of molecules

that are close to one another

stability describes how a material reacts to external changes

stator Are the stationary magnets used in an electric motor

Steel an alloy of iron and carbon

stiffness the property of a material to maintain shape

strength the property of a material to withstand forces. Normally strength is specified as yield strength,

tensile strength, compressive strength, shear

strength

tensile force describes a force applied to an object that attempts to stretch the object

xvi

thermal conductivity the property of a material to conduct heat

thermopolymer polymers which, once set, can be melted and re-formed

thermosetting polymers which, once set, cannot be remelted or reshaped

tonne a tonne, represented by the symbol T, is equal to 1000 kg

tough able to have force applied without failure

toxicity describes how harmful a material is to the environment

_Locateraddress of an Internet site abbreviated to URL Uniform Resource

vector quantity that has magnitude and direction/sense

vector quantity a quantity that requires direction as well as magnitude for its complete understanding

xvii

xviii

Directive terms

The list below explains key words you will encounter in assessment tasks and examination questions.

account account for: state reasons for, report on;

give an account of: narrate a series of events or

transactions

analyse identify components and the relationship between them, draw out and relate implications

apply use, utilise, employ in a particular situation appreciate make a judgement about the value of

assess make a judgement of value, quality, outcomes, results or size

calculate ascertain/determine from given facts, figures or information

clarify make clear or plain

classify arrange or include in classes/categories

compare show how things are similar or different

construct make, build, put together items or arguments contrast show how things are different or opposite

critically

(analyse/evaluate)

add a degree or level of accuracy depth, knowledge and understanding, logic, questioning, reflection and quality to (analysis/evaluation)

deduce draw conclusions

define state meaning and identify essential qualities demonstrate show by example

xix

describe provide characteristics and features discuss identify issues and provide points for and/or against

distinguish recognise or note/indicate as being distinct or different from; to note differences between

evaluate make a judgement based on criteria; determine the value of

examine inquire into

explain relate cause and effect; make the relationships between things evident; provide why and/or how

extract choose relevant and/or appropriate details extrapolate infer from what is known

identify recognise and name

interpret draw meaning from

investigate plan, inquire into and draw conclusions about justify support an argument or conclusion

outline sketch in general terms; indicate the main features of

predict suggest what may happen based on available information

propose put forward (for example a point of view, idea, argument, suggestion) for consideration or action

recall present remembered ideas, facts or experiences recommend provide reasons in favour

recount retell a series of events

summarise express, concisely, the relevant details synthesise putting together various elements to make a whole

Extract from The New Higher School Certificate Assessment Support Document, © Board of Studies, NSW, 1999.

Refer to <http://www.boardofstudies.nsw.edu.au> for original and current documents.

Household appliances

Part 1: Household appliances – development

Part 1 contents

Introduction............................................................................................2 What will you learn?....................................................................2 Overview of early technology............................................................3 Household appliances ........................................................................6 Common household appliances .................................................7 Developing your research skills........................................................25 Exercises............................................................................................27 Progress check...................................................................................31 Exercise cover sheet.........................................................................33

Part 1: Development of household appliances 1

Introduction

In this part of the module you will examine the development of different household appliances through case studies.

Looking at developments in household appliances allows you to gain an appreciation for engineering innovation through past achievements and focus on the connection between the needs of society and the engineering field which drives the development of new and better products.

When researching developments you will need to find out about early forms of technology, the societal effects of the scientific and industrial revolution and the effect on engineering development.

As you are reading keep in mind how developments in household appliances affect different groups of people in society. For example, ask yourself would a 19th century copper kettle be safe for people to use, such as an older person with arthritis, a child under twelve, a slightly built person, easy to produce, affordable to buy and economical to repair?

Keep these issues in mind in your study of the developments of household appliances.

You will need to write an engineering report in the last part of this module. This will require research into the material used in a household appliance.

What will you learn?

You will learn about:

• the historical and societal influences by studying;

– the historical developments of household appliances

– the effects of engineering innovation on people’s lives.

You will learn to:

• outline the historical development of household appliances

• describe the effect of engineering innovation on people’s lives.

Extract from Stage 6 Engineering Studies Syllabus, © Board of Studies, NSW, 1999. Refer to <http//www.boardofstudies.nsw.edu.au> for original and current documents.

2 Household appliances

Overview of early technology

The development of engineering principles and techniques can be closely linked to the general development of societies. Engineering has been a central force in all economic and social growth. In this part of the module you will examine several engineering developments and consider some effects they had on society.

Before you begin …

What would you consider is the most important mechanical invention of all time?

Our choice will be revealed later!

It is not necessary to study ancient civilisations in order to gain some understanding of the effect of engineering. However, you could research the effect the development of tools had on ‘stone age’ society. You could research the developments of agricultural implements and the agrarian revolution. You could research the earliest use of metals (and their smelting) and the dramatic effect they had on societies during the bronze and iron ages.

There is also a history of engineering and science principles. These are revealed in the groundbreaking books and manuscripts of Aristotle (Greek civilisation) Michelangelo, Leonardo da Vinci and Machiavelli

(renaissance period in Italy). This list could continue to fill a book!

Technological advancement has tended to ebb and flow over the many centuries. There have been periods of development followed by periods of little change. This pattern ended by about 1750, the start of the ‘Industrial Revolution’. The period from 1750 to the 1900s saw change like the world had never seen previously. This revolution in technology has only been surpassed by the technology revolution you are living with today.

The following list provides a few examples of the many thousands of engineering developments during this period.

Part 1: Development of household appliances 3

Try to think of one additional invention or development for each of the following areas:

• materials

– developments in the iron making industry

– automation of textile manufacture

– development of coal as an industrial energy source

– development of building materials such as bricks and reinforced concrete

– mass production of glass

• transport

– invention of the steam engine

– development of a railway system

– expansion of the canal systems

– development of the steam turbine (ship propulsion) – development of the internal combustion engine

– development of the automobile

– development of the air ship

• tool making

– development of accurate clocks for navigation

– development of accurate distance/size measuring devices

– development of accurate cutting devices for machine manufacture

• chemical knowledge

– artificial fertiliser

– explosives

– dyes and inks

– medicines (iodine, anaesthetics, carbolic acid)

– voltaic battery

• communication knowledge

– printing press

– telegraph

– telephone

– typewriter

– photography/video

4 Household appliances

– computer

– satellite

• electricity

– electric lighting

– electric motor

– electric generator

• food and agriculture

– mechanised farm machinery

– food processing plants

– food preservation, packaging and refrigeration.

Back to the original question, which would you consider the most important mechanical invention of all time? If you answered the ‘wheel’ then you agree with most people.

The invention of the wheel

The wheel appeared as early as 3 500 BC in Mesopotamia where the first application was the potters’ wheel. This technology was quickly adopted for transportation in the four-wheeled carts and chariots.

You have now had a brief overview of some technology developments. You will build on this information in the later modules. You will now read about developments in household appliances.

Part 1: Development of household appliances 5

Household appliances

When you look at household appliances and how they have developed over the last century you will find it is an interesting way of identifying technological and engineering change. Many current models only look vaguely similar to the products first developed. When you consider the models of today, you can see that many changes to the design have taken place.

Some of the reasons for new developments include:

• the development of new materials such as polymers

• the invention of new power sources, for example, electricity and solar power.

List two other factors that may have brought about new developments in household appliances.

1 _______________________________________________________ 2 _______________________________________________________

Did you answer?

The development of control devices and the new applications of existing materials

Engineers, over time, have modified the household appliances to suit today’s environment, modifying the external appearance, changing the materials used, and addressing safety issues.

There are also less obvious changes and modifications to appliances to make the product more attractive and profitable in the market place.

6 Household appliances

Common household appliances

A tour of the average home will reveal many household appliances.

The kitchen probably has more household appliances than any other room in the home, you are likely to find a fridge, freezer, juicer, toaster, non-stick pan, microwave oven, wall oven, cook top, coffee percolator, even an electric knife.

1 Spend five minutes in the kitchen and list all the household appliances specifically designed for food preparation.

_______________________________________________________ _______________________________________________________ _______________________________________________________

Did you answer?

Some of the kitchen appliances you may have found in the kitchen include fridge, freezer, blender, juicer, toaster, electric fry pan, electric wok, microwave oven, wall oven, cook top, coffee percolator, food processor, electric knife, electric can opener, popcorn maker …

Many kitchen appliances were invented as labour saving items. They use electric motors instead of manual labour to get jobs done. For example, there are electric food processors for chopping, electric blenders to puree, electric beaters to mix and electric brooms to sweep up the mess when you are finished cooking.

In another part of a typical house you will find the entertainment area complete with television, radio, cassette recorder, compact disc player, some of which today are controlled remotely.

These labour saving devices were only possible after the discovery of electricity and the invention of small electric motors. Most of them weren't invented until after homes in North America and Europe were ‘electrified’, that is connected to a source of electricity, in the 20th century.

Common household appliances include:

• food mixer

• floor cleaners

• clothes iron

• bread toaster

• kettle

• refrigerator.

Part 1: Development of household appliances 7

Before the introduction of electricity, many household appliances were manually operated.

You will examine the developments of common household appliances over time and the impact of engineering innovations on individuals.

Complete the following table:

a describe the functional features of the early model household appliances

b identify a significant change in design to this product in the late model equivalent.

Appliance Early model Late model

kettle In the 1800s a kettle was commonly made from iron.

The water was heated by a

wood fire. The product was

heavy and hot to touch

clothes iron __________________________ __________________________

__________________________

stove __________________________ __________________________

__________________________

Did you answer?

In the 1990s a kettle was commonly made from

polymer. The water was heated by an electric

element. The product is light weight and cool to touch.

_________________________ _________________________ _________________________ _________________________ _________________________ _________________________

clothes iron • made of cast iron • made from aluminium and polymers

stove • made from cast iron • source of heat wood

• steel powered by gas and/or electricity

8 Household appliances

How did you go?

You would have found that today people use household appliances to save time and energy.

You may also have noticed `these appliances have changed many times in the last 50 years.

The food mixer

Many household appliances only vaguely resemble the products first developed.

Examine figure 1.1 which shows an early model food mixer.

Figure 1.1 The early 1920s food mixer

Compare this early model food mixer to a late model food mixer by listing three design differences.

1 _______________________________________________________ 2 _______________________________________________________ 3 _______________________________________________________

Did you answer?

• exposed motor housing and gearing

• revolving base plate/mixing bowl

• metal frame (insulated).

Part 1: Development of household appliances 9

When you consider the models of today, you can see that many changes to the design have taken place.

Over time engineers have modified the food mixer by:

• changing the external appearance to make it more appealing

• using the latest materials

• taking safety issues into account for example, reduced the noise level

• using the latest manufacturing techniques to increase efficiency, productivity and most importantly profitability.

Floor cleaners

This case study looks at the historical development of floor cleaning appliances.

In this section you will examine the:

• 1858 carpet sweeper

• 1920s pump vacuum

• 1930s electric vacuum

• 2000 electric upright vacuum.

The floor sweeper

In 1858 H.H. Herrick designed the Brush sweeper.

Figure 1.2 Brush sweeper Figure 1.3 Sectioned view of the brush sweeper

10 Household appliances

The functional features of this appliance included:

• ability to clean carpets and smooth floor surfaces such as timber • the mechanism was contained within the strong, lightweight case • the brush consisted of helical rows of tufts

• every second row of tufts were to suit flat timber floors whilst the other rows of tufts were designed for carpeted surfaces.

• the brush height was adjustable

• the sweeper was pushed back and forth to turn the brushes. The dust was collected in pans that could be opened and emptied

• furniture was protected by a rubber guard that went round the outer case.

The advantage of this type of floor cleaner was that it used no electricity, which many households did not have at that stage.

The electric vacuum cleaner

Hubert Cecil Booth, an Englishman, designed and patented the first practicable vacuum cleaner, but a number of patents for machines like this had already been granted to other inventors.

Figure 1.4 Early electric vacuum cleaner

The problem for the early electric vacuum-cleaners was the motor.

Early electric motors were both large and heavy. This led to the development of ducted vacuum cleaning systems that catered for many

Part 1: Development of household appliances 11

rooms, but only had one motor. Public buildings and blocks of flats were suited to this ducted vacuum system which had the motor located in a plant room or basement. This is similar to the ducted systems that some homes have today.

Early in the twentieth century, Axel Wenner-Gren, was determined to develop a vacuum cleaner that was low priced and light in weight for easy handling. He developed a design that had a ‘closed fan’.

The fan is housed, and air is forced through a confined intake. This development gave powerful suction from a small cleaner and is still a component in current vacuum cleaner designs.

The upright vacuum cleaner

The electric upright type of vacuum cleaner was developed from the earlier carpet sweeper.

The tuft brushes are now motor-driven and beater bars have been developed and incorporated to move dust and dirt up enabling the brushes to be more effective. A powerful fan forces the dust and dirt into a disposable bag and the exhaust air is cleaned leaving the vacuum cleaner by passing through a disposable filter.

Figure 1.5 Electric upright vacuum cleaner

The cylinder style vacuum

The cylinder style vacuum cleaner is designed with most components such as the inlet tube, motor, fans and dust bag to be in-line. This style of vacuum cleaner relies on suction alone and thus has neither revolving brushes nor beater bars.

12 Household appliances

Figure 1.6 Sectioned view of a cylinder style vacuum cleaner

Recent developments

The vacuum cleaner shown below is the latest design. It has developed into a light but powerful machine, and is also stylish and suitable for mass production.

stick design

optional cord

^{see-through canister}specialist

attachments

power head

Figure 1.7 Late model vacuum cleaner

It is an important task to analyse the effect of any product and the effect that product has on people’s lives. While the latest machine improves the cleaning of the floors, and greatly decreases the time required to clean the floors, there are other social and environmental effects.

The machine requires an initial outlay of household funds. It will require maintenance. Use of the machine will add slightly to the electricity bill. It will take up storage space. At the same time, the machine will allow a carpet floor covering to be kept low in dust, and therefore much healthier for the occupants of the house.

Part 1: Development of household appliances 13

The domestic clothes iron

Stones heated in the fire or in boiling water were the first tools used for smoothing out wrinkles in clothes.

The flat iron

By 1850 there were two iron options available:

• the flat iron – was made of iron and heated on a fire. Manufactured in the eighteenth and nineteenth centuries.

• the box iron – where a piece of preheated iron or a lump of coal was placed in the box to keep the iron hot.

Flat irons, sometimes known as ‘sad irons’, were made from cast iron. This made them very heavy and ironing became a time consuming chore that required considerable muscular effort, both in the home and industrial situation.

Figure 1.8 Early flat iron

Weight, cleanliness and the hot handle were the major concerns for the user. The handle problem was partly overcome when a detachable wooden handle was patented in 1865.

The weight of the hot iron was important as this helped with the flattening of fabric. The iron was made in different shapes and sizes for different purposes, such as pressing sleeves and hats.

Box irons provided an option to the flat iron where a hollow section was incorporated into the design to receive either:

• a piece of preheated iron

• a lump of coal to keep the box iron hot.

This type of iron was an improvement on the flat iron heated in the fireplace as it collected soot and had to be cleaned before use.

14 Household appliances

Bellows were used to blast air into the box and keep the coals hot. An outlet was included to allow the smoke from the coals to escape from the box.

Figure 1.9 Box iron and bellows

What effect do you think the escaping smoke could have on the ironing environment?

__________________________________________________________ __________________________________________________________

Did you answer?

• the coal smoke would make the clothes smell after ironing

The self-heating irons

The next development in iron technology were self-heating irons. They were fuelled with natural gas, gasoline, or alcohol that often exploded. The electric iron was patented in 1882 but it didn't become popular until electricity became available in homes.

Figure 1.10 Sectioned-view of a self heating iron

Part 1: Development of household appliances 15

The diagram above shows a very early electric iron that has been sectioned to allow you to see the heating lamp. Heating elements were developed later. Also note that timber was still used for the handle.

The electric irons

Early electric irons were similar to ‘sad irons’. As time went by polymers were developed and instead of the wooden handles a material called Bakelite was used.

Ironing was now starting to become faster and easier due to weight reduction and manufacturers paying more attention to the style of the products.

Westinghouse, a major manufacturer, designed a streamlined iron that started a trend. The Bakelite handle was designed to fit a woman's hand. Different temperature settings were available for various fabrics.

The steam iron

Sunbeam produced a steam iron called the Steam-0-Matic. The use of steam, rather than the weight of the iron was the major factor in removing wrinkles from the clothes.

Figure 1.11 Steam iron

With emphasis on steam rather than weight, alterative materials were used in the manufacture of irons. Aluminium rather than iron meant that irons were becoming much lighter.

Recent developments

Today irons have been designed by engineers using the latest materials and manufacturing processes, incorporate a range of features to ensure:

• comfort

• appearance

• safety and ergonomics

16 Household appliances

Figure 1.12 A late model iron

1 From the previous diagram, list two the functional features of the latest model iron.

i ___________________________________________________ ii ___________________________________________________

2 Explain the benefits of one of these functional features. _______________________________________________________ _______________________________________________________ _______________________________________________________

3 List new materials and explain the advantages of the use of these materials.

_______________________________________________________ _______________________________________________________ _______________________________________________________

4 List two safety features that are in the latest model of the iron. i ___________________________________________________ ii ___________________________________________________

Part 1: Development of household appliances 17

Did you answer?

1 i temperature control

ii steam spray function

2 The temperature – can be change so as to not damage the materials to be ironed.

3 Plastics have decreased the weight of the iron and because they do not conduct heat well they are safe to use

4 i auto turn off – if the iron is accidentally left on it will turn itself off ii plastic body ensures the operator is safe from electric shock

The refrigerator

Refrigeration is the process of lowering the temperature of a substance. It is a common method of food preservation.

The time-line below gives you an overview of the main historical developments of the refrigerator.

Notice how the materials and shape has changed through the years.

Figure 1.13 Evolution of the refrigerator

Early ice boxes

The icebox was the first household appliance used for refrigeration. The ice manufacturing factory produced the ice and it was delivered to businesses and houses by cart.

Early ice boxes used wood for the cabinet, sawdust for insulation and tin or zinc as lining.

18 Household appliances

Figure 1.14 Early ice boxes

Early model refrigerators

The first refrigerated storage machines were developed during the early 1900s. The machines were very large, steam driven, manually operated and sometimes leaked ammonia.

The first refrigerators and freezers driven by electricity were developed in the 1920s and the 1930s. It was not until the late 1940s that the first researchers successfully scaled down the machines to a size suitable for shops.

Figure 1.15 Early 1920s model refrigerator

In the 1950s and 1960s a further development took place. Frost-free refrigerators became available. These were more efficient and further reduced the time required in household maintenance of the machine.

Part 1: Development of household appliances 19

Over time, research and development vastly improved the machines, but by the 1960s it was evident that the Chloro Fluoro Carbons (CFCs) had a harmful effect on the earth’s ozone layer and, therefore, the environment.

By the 1970s new refrigerants had been developed which were very energy efficient. All CFCs were eliminated from the machines.

In 1992, researchers developed ‘Green freeze’, a hydrocarbon refrigerant. This material is now becoming the coolant most commonly used.

Late model refrigerators

Late model refrigerators can come equipped with a computer within the door. This computer has a large screen and key pad situated on the door front that allows Internet ordering of food and other functions.

Figure 1.16 Computer refrigerator

The bread toaster

In the eighteenth-century English people made toast in their fireplaces with a rack called the hanging griller. Another tool was the salamander, a metal disk with a long handle or simply used long handled forks to toast their bread.

Since the time of Thomas Edison, engineers have been using wire as an element. When used for lighting, the wire is sealed in a vacuum or surrounded by an inert gas. This prevents the element from oxidising or burning. The toaster element had to perform the heating task in open air.

20 Household appliances

The basic principle for most toasters is cooking the bread by radiant heat. The heat is created by passing an electric current through a wire, known as an element.

In 1905 an engineer called Albert Marsh applied for a patent on an alloy of Nickel and Chromium, which came to be known as Nichrome. The alloy can be described as being:

• very low in electrical conductivity

• very fusible

• non-oxidising to a very high degree

• tough and sufficiently ductile to permit drawing into wire.

Consider that at this time electricity was not commonly wired into houses. The common wall power outlet was still only a dream for the future.

The electric flip sided toaster

General Electric, in 1909, made the first successful electric toaster called ‘D-12’. It was made from a wire rack and heating element attached to a porcelain base that toasted one side of bread at a time.

There were variations of the early toasters, some were made with two doors while others had slots or perforated, decorative designs.

Figure 1.17 Flip sided toaster

One model from Universal had porcelain knobs that were cool to the touch. Westinghouse developed the ‘Turnover Toaster’ which turned the toast when you opened its doors.

Part 1: Development of household appliances 21

Some manufacturers produced a ‘Combo Toaster’ that cooked toast on the table instead of on the stove. This could make coffee and toast at the same time. Hotpoint developed the ‘El Grillo Perc-O-Toaster’ oven which could cook eggs and fry bacon.

Regulating time for cooking was a problem. People did not enjoy eating burnt toast or burning their fingers. This problem lead to an automatic one-slice pop-up toaster being invented in 1919.

The automatic pop up toaster

The first automatic pop up toaster for the home came in 1926. It was called the ‘Toastmaster’. The Toastmaster is considered to be the most popular appliance ever produced.

Figure 1.18 Automatic up toaster

Functional features of the automatic toaster included:

• The motif design on each side of the toaster served a purpose. It took attention away from any scratches or dents on the chrome surface.

• A manual temperature control to make toast light, medium or dark and automatic pop up mechanism.

• It was sleek, a simple shape, shiny chrome, rounded corners, and had horizontal lines.

22 Household appliances

Identify possible safety problems in the automatic Pop up toaster. __________________________________________________________ __________________________________________________________

Did you answer?

Some of the safety issues you may have identified include:

• potential burns risk resulting from the metal housing which conducts heat

• potential fire risk resulting from an inaccurately adjusted manual temperature or malfunctioning automatic pop up.

Today’s toasters are designed for many consumer benefits

Feature Benefit

spring-loaded tray pops toast up

polymer parts safe to touch, convenient to use nichrome wire wrap good conductor heats to red hot hinged/removable crumb tray easy clean, hygienic electric-cord storage tidy, safe storage

wide double/single slot accommodate variable sized slices time release lever select degrees of browning temperature sensor consistent browning electronic safety cut-out switch safe to operate

automatic switch off mechanism prevent overheating

Part 1: Development of household appliances 23

A late model toaster

Figure 1.19 Late model toaster

Improvements on today's toasters include: four or six slots, warming racks for heating croissants and slide-out trays for cleaning.

The materials used in the appliance include:

• polypropylene for top and side housing

• chrome-plated steel for the top plate

• polyvinyl chloride (PVC) for the cord set

• polycarbonate for the crumb tray.

24 Household appliances

Developing your research skills

Research is a critical function for professional engineers. You will be refining your research skills by researching the history of household appliances in preparation for your engineering report.

If an engineer is going to produce a new household appliance, most certainly a research process will be implemented.

Research

To do research involves a process or a series of linked activities moving from beginning to end. The research process is not absolutely rigid. However, there is a sense in which the research process will be weakened or made more difficult if the first steps are not executed carefully.

Process

1 Clarifying the issue

During Phase 1 the researcher clarifies the issue to be researched and selects a research method(s). This may require selecting sample materials, experimentation, working collaboratively with others.

2 Collecting data

During phase 2 the researcher collects evidence about the research question. Sources such as the Internet, CD-ROM, encyclopaedia, specialist text, journals are all locations where information can be gathered.

NOTE:

Care must be taken when gathering information from the Internet. Check for authenticity by checking whether the source is qualified, it cannot be assumed that the person(s) who placed the information on the Internet are authorities on the subject. Check the site is fully maintained by a reliable source such as a University or large organisation.

Part 1: Development of household appliances 25

3 Analysing and interpreting information

During phase 3 the researcher relates the evidence collected to the research question asked, draws conclusions about the question and acknowledges the limitations of the research.

Reminder

In ‘Developing your research skills’ you have learnt the basic skills for researching. You should now select a household appliance and begin to investigate the development of the product from the earliest to the latest model. This will help you prepare for the first section of the engineering report - the background information on your chosen appliance.

Turn to the exercise sheet and complete exercise 1.1 to 1.6.

26 Household appliances

Exercises

Exercise 1.1

a List an invention or innovation that occurred in the period 1750 to 1900 in the following areas:

• materials ____________________________________________ • transport ___________________________________________ • tool making __________________________________________ • chemical knowledge ___________________________________ • communications ______________________________________ • power sources _______________________________________ • food and agriculture ___________________________________

b List an invention or development in the following areas that has occurred since the 1900s:

• material _____________________________________________ • transport ___________________________________________ • communication _______________________________________ • power sources _______________________________________

Exercise 1.2

Choose three of the inventions or innovations listed in Exercise 1.1 and describe the effects that these inventions have had on people’s lives.

a _______________________________________________________ _______________________________________________________ _______________________________________________________ _______________________________________________________ _______________________________________________________

Part 1: Development of household appliances 27

b _______________________________________________________ _______________________________________________________ _______________________________________________________ _______________________________________________________ _______________________________________________________ _______________________________________________________

c _______________________________________________________ _______________________________________________________ _______________________________________________________ _______________________________________________________ _______________________________________________________ _______________________________________________________

Exercise 1.3

Compare an early food mixer, to a modern mixer. The one you have at home will be fine for a comparison, even if it is 15 years old. In your comparison, comment on the following aspects:

a materials

_______________________________________________________ _______________________________________________________ _______________________________________________________ b safety

_______________________________________________________ _______________________________________________________ _______________________________________________________ c easy of use

_______________________________________________________ _______________________________________________________ _______________________________________________________

28 Household appliances

Exercise 1.4

Explain some of the disadvantages of the early ice box.

In your answer examine four of the following areas:

• ease of use

• running costs

• safety

• operating systems

• the storage capacity

• the environmental and social effects.

a _______________________________________________________ _______________________________________________________ _______________________________________________________

b _______________________________________________________ _______________________________________________________ _______________________________________________________

c _______________________________________________________ _______________________________________________________ _______________________________________________________

d _______________________________________________________ _______________________________________________________ _______________________________________________________

Exercise 1.5

a What recent technology has been incorporated into the latest model refrigerator to reduce the environmental effects of CFCs?

_______________________________________________________ _______________________________________________________ _______________________________________________________

b Identify four safety features on the latest model fridge. You may need to research this information at an electrical store or on the Internet by typing in some of the well known brand names of refrigerators.

i ___________________________________________________ ii ___________________________________________________ iii ___________________________________________________ iv ___________________________________________________

Part 1: Development of household appliances 29

Exercise 1.6

List three features of a late model electric toaster and outline the benefits of each.

Feature Benefit

30 Household appliances

Progress check

During this part you examined the development of a range of household appliances, such as the food mixer, floor cleaner, clothes iron, refrigerator and toaster.

Take a few moments to reflect on your learning then tick the box that best represents your level of achievement.

_❏✓ _{Agree – well done}

_Uncertain

_Disagree

_❏✓ _{Disagree – revise your work}

_Agree

_❏✓ _{Uncertain – contact your teacher}

I have learnt about

• historical and societal influences by studying;

– the historical developments of household

appliances

– the effects of engineering innovation on people’s

lives.

I have learnt to

• outline the historical development of household

appliances

• describe the effect of engineering innovation on

people’s lives.

Extract from Stage 6 Engineering Studies Syllabus, © Board of Studies, NSW, 1999. Refer to <http://www.boardofstudies.nsw.edu.au> for original and current documents.

During the next part you will investigate a range of engineering materials commonly used in household appliances.

Part 1: Development of household appliances 31

32 Household appliances

Exercise cover sheet

Exercises 1.1 to 1.6 Name: _______________________________

Check!

Have you have completed the following exercises?

❐ Exercise 1.1

❐ Exercise 1.2

❐ Exercise 1.3

❐ Exercise 1.4

❐ Exercise 1.5

❐ Exercise 1.6

If you study Stage 6 Engineering Studies through a Distance Education Centre/School (DEC) you will need to return the exercise pages with your responses.

Return the exercise pages with the Title Page cover attached. Do not return all the notes, they should be filed for future reference.

If you study Stage 6 Engineering Studies through the OTEN Open Learning Program (OLP) refer to the Learner’s Guide to determine which exercises you need to return to your teacher along with the Mark Record Slip.

Part 1: Development of household appliances 33

Household appliances

Part 2: Household appliances – materials

Part 2 contents

Introduction ..........................................................................................2 What will you learn? ...................................................................2 Appropriate selection of materials....................................................3 Material descriptions ..................................................................4 Material comparisons .................................................................5 Properties of materials................................................................7 The atomic structure of material ................................................10 Bonding of material ..................................................................11 Metals .....................................................................................16 Polymers .................................................................................24 Ceramics.................................................................................27

Developing your research skills......................................................31 Exercises............................................................................................33 Progress check..................................................................................39 Exercise cover sheet........................................................................41

Part 2: Materials and household appliances 1

Introduction

Of particular interest to the engineer is the development of materials and how this has affected the appliance design. In this part you will be examining material classification, properties and the structure to gain a good understanding about the appropriate selection of materials.

What will you learn?

You will learn about:

• classification of materials

• properties of materials – physical and mechanical

• the structure and bonding of materials

• the types of metals suitable for cutting and joining methods • the types of polymers including thermopolymers and thermosets • ceramics and the types used in household appliances.

You will learn to:

• distinguish between and explain reasons for the use of ferrous and non-ferrous metals as components of household appliances

• compare the suitability of joining and cutting methods used on metals

• distinguish between thermopolymers and thermosets

• identify the types of ceramics used in household appliances. Extract from Stage 6 Engineering Studies Syllabus, © Board of Studies, NSW, 1999. Refer to <http://www.boardofstudies.nsw.edu.au> for original and current documents.

2 Household appliances

Appropriate selection of materials

Material selection is critical in household appliances.

The design engineer, when selecting a material for a particular purpose, must consider many things. Some of these considerations are summarised in figure 2.1.

safety durability

ergonomics performance

^{Functionality}ease of manufacture

Workability

ease of repair

Availability

short term long term

feel

Selecting

material

Aesthetics

initial cost

Cost

look

Environmental

manufacture cost

Special

energy efficiency radioactivity

pollution

impact

properties

thermal

disposability

sustainability

Figure 2.1 Materials selection chart

electrical

chemical

When designing, the engineer will find it convenient to have engineering materials classified into groupings for quick reference.

Part 2: Materials and household appliances 3

Material descriptions

There are a number of classification methods for identifying and grouping materials. Some methods are shown below.

Material Description

_MetalsNormally exhibit properties such as: good conductors of heat and electricity; high density; display some

formability (ductile or malleable); normally solid at room

temperature, for example, iron, copper, gold.

_CeramicsInorganic, non-metallic solids processed or used at high temperature. As well as the common pottery,

sanitary white ware, tiles and the like, there are ‘high

tech’ applications which are used extensively in

industrial applications.

_PolymersGenerally known as plastics. They are based on the chemistry of carbon and are generally excellent

insulators and easily moulded into complex shapes.

_NaturalMaterials that are found naturally in the environment. They require little modification before use, for example,

stone, gold.

_BiologicalA sub-set of natural materials that only includes materials that are produced from living things, for

example, wood, leather.

_ConductorsMaterials that allow relatively easy transmission of heat and/or electrical current.

_{Semi-conductors}Materials that form a special category of inorganic, non-metallic solids processed at high temperature.

They are insulators, but, with minute amounts of

additional elements, can be made to conduct electrons

in specific circumstances. They are the building blocks

of transistors, solid state electronics and computers.

_InsulatorMaterials that resist the transmission of heat and/or electrical current.

4 Household appliances

Material comparisons

The following tables compare the use of material in older appliances with recent appliances. This should be a useful guide for when you investigate your own appliance later in this module.

Materials used to manufacture vacuum cleaners

Outlined below is a comparison of the materials used in an early model vacuum cleaner with a late model vacuum cleaner.

Early model vacuum cleaner Late model vacuum cleaner

Steel –

handles, frame members, nuts bolts, fan blades, wheels and motor parts.

Polymer –

limited use – electrical insulation and some body parts.

Copper –

specifically for electrical

conductivity for wires and motor parts.

Other materials –

cloth dust collection bag, brass zipper, chrome coated badges, rubber belts, cloth packing in electrical cord.

Steel –

nuts and bolts, motor parts. Huge reduction from 1950 model.

Polymer –

extensively used for:

• electrical insulation

• integrated body parts

• nuts and bolts

• wheels and tyres

• brushes and hoses.

Copper –

specifically for electrical

conductivity for wires and motor parts.

Other materials –

disposable paper dust bags,

semi-conductor materials in

electronic components.

Part 2: Materials and household appliances 5

Materials used to manufacture clothes irons

The following table provides a comparison of the materials used in an early electric clothes iron and a later model electric clothes iron.

Early model clothes Iron Late model clothes Iron

• Steel – fittings

• Cast iron – base

• Polymer – Bakelite electrical fittings • Copper – electrical wire

• Cloth – electrical insulation

• Stainless steel – base

• Polymer – PVC electrical insulation • Copper – electrical wire

• Ceramic – electronic components

Materials used to manufacture refrigerators

The following table provides a comparison of the materials used in an early model refrigerator with a late model refrigerator.

Common materials

Early model pressed metal fridge

Common materials

Late model computer fridge

Steel – most panels/shelving Steel – most panels

Polymer –

rare – electrical components (bakelite) /door seals

Copper –

all electrical components including the cooling coils and the motor components

Other material –

CFC’s/ freon

Polymer –

common – handles/door seals/drawers/shelving

electrical components

Insulation for heat transfer Copper –

all electrical components including the cooling coils and the motor components

Other material –

blended refrigerant called R406

6 Household appliances

Materials used to manufacture toasters

The following table provide a comparison of the materials used in an early toaster and a late model toaster.

Early model toaster Late model toaster

Steel –

most of the toaster body and frame

Polymer –

rare – in early models the thermosetting polymer ‘Bakelite’ was used in electrical plugs and electrical insulation situations.

Copper –

used for all electrical connection from the wall to the element

Other material –

porcelain, bakelite

Steel –

many of the body parts and attachments

Polymer –

common – mainly in the electrical components, handles and as a base for the enamel paint

Copper –

no change as all electrical components and wiring

Other material –

semi-conductor, found in electronic components

Properties of materials

The ability of an engineer to select appropriate material is critical. Selection needs to be based on the engineering properties of the material.

The service requirements of a material may involve properties which fall in one or all of the following three categories.

Mechanical Properties Physical properties Chemical properties

• strength

• elasticity

• toughness

• resistance to creep • resistance to fatigue • frictional properties • hardness

• electrical conductivity • thermal conductivity • relative density

• melting point

• coefficient of expansion • magnetic properties

• resistance to corrosion

• stability

• toxicity

Part 2: Materials and household appliances 7

Common engineering materials

In order to select the most appropriate material you must be familiar with the properties of that material.

You should be able to nominate its properties, including its strengths and weakness in certain situations.

Examples of common engineering materials that you will need to become knowledgeable about include:

• steel

• ceramic

• thermosoftening polymer

• thermosetting polymer

• cast iron

• aluminium

• brass

• copper

• glass.

Characteristics of materials

The material properties that describe characteristics of interest to the engineer when selecting materials include:

Density: a measurement of a materials mass per unit volume. Metals are usually dense. Non-metals are usually less dense.

Formability: a description of a materials’ ability to be deformed or shaped by bending, stretching, compressing.

Compressive force: describes a force applied to an object that attempts to compress the object.

Tensile force: describes a force applied to an object that attempts to stretch the object.

Opacity: the property of a material that stops the passage of light that is, you cannot see through it.

Strength: the property of a material to withstand forces. Normally strength is specified as yield strength, tensile strength, compressive strength, shear strength and so on.

8 Household appliances

Elasticity: the property of a material to return its original shape after a distorting force has been removed.

Toughness: the property of a material to withstand application of impact force without failure.

Stiffness: the property of a material to maintains shape.

Resistance to creep: the property of a material to maintain its original length for a long period of small load application.

Frictional properties: the property of a material that describes the amount of grip a material has when sliding in contact with another surface.

Hardness: the property of a material to resist indentation or scratching when brought into contact with another material.

Electrical conductivity: the property of a material to conduct electricity. Thermal conductivity: the property of a material to conduct heat.

Relative density: a measurement for material describing how compact the mass of the object is relative to other materials.

Melting point: the temperature at which the material begins to become a liquid.

Coefficient of expansion: a measurement that describes the change in size of material relative to the temperature.

Magnetic properties: the property of a material to become magnetic.

Resistance to corrosion: describes the property of a material that allows it to not corrode quickly in a service application.

Toxicity: describes how harmful a material is to the environment, due to the effect on things in that environment.

Stability: describes how a material reacts to external changes. Turn to the exercise sheet and complete exercise 2.1.and 2.2

Part 2: Materials and household appliances 9

Atomic structure

The properties if materials are determined by their atomic structure.

An element is a pure substance and is made up of one type of particle. A list of all known elements can be found in the Periodic Table. In this table all of the elements are represented by letters, for example H for hydrogen and O for oxygen.

Hydrogen 3

Lithium

Beryllium 12

Hydrogen

Atomic number Symbol

Name

Boron 13

Carbon 14

Nitrogen ¹⁵P

Oxygen 16

Fluorine 17

Helium 10

Neon 18

Sodium

Potassium 37

Rubidium 55

Caesium 87

Francium

Magnesium 20

Calcium

Strontium 56

Barium

Radium

Scandium

Yttrium

57-71

LANTHANIDES 89-103 ACTINIDES

Lanthanum

Actinium

Titanium

Zirconium

Hafnium

104

Rutherfordium

Cerium

Thorium

Vanadium

Niobium

Tantalum

105

Dubnium

Praseodymium 91

Protactinium

Chromium 42

Molybdenum 74

Tungsten

106

Seaborgium

Neodymium 92

Uranium

Manganese 43

Technetium 75

Rhenium

107

Bohrium

Promethium 93

Neptunium

Iron

Ruthenium 76

Osmium 108

Hassium

Samarium 94

Plutonium

Cobalt

Rhodium 77

Iridium

109

Meitnerium

Europium 95

Americium

Nickel

Palladium 78

Platinum 110

Uun Ununnilium

Gadolinium 96

Curium

Copper

Silver

Gold

111

Uuu

Unununium

Terbium

Berkelium

Zinc

Cadmium 80

Mercury

112

Uub

Ununbium

Dysprosium 98

Californium

Aluminium 31

Gallium

Indium

Thallium

113

Holmium 99

Einsteinium

Silicon

Germanium 50

Tin

Lead

114

Uuq

Ununquadium

Erbium

100

Fermium

Phosphorus 33

Arsenic

Antimony

Bismuth

115

Thulium

101

Mendelevium

Sulfur

Selenium

Tellurium

Polonium

116

Uuh

Ununhexium

Ytterbium 102

Nobelium

Chlorine

Bromine

Iodine

Astatine

117

Lutetium

103

Lawrencium

Argon

Krypton

Xenon

Radon

118

Uuo

Ununoctium

Figure 2.2 Periodic Table

The particles that make up an element are called atoms and each atom will contain a number of subatomic particles. Protons, electrons and neutrons are the main subatomic particles. The protons are positively

charged and the neutrons, no electrical charge, are found in the nucleus, or the centre of the atom. The electrons, negatively charged, orbit the nucleus in an outer layers called a shells. There are an equal number of protons and electrons in an atom so that it is electrically neutral.

10 Household appliances

nucleus

Figure 2.3 Structure of an atom Bonding of materials

electron neutron proton

Atoms rarely exist by themselves; it is uncommon to come by a single atom of an element. Single atoms are usually unstable and need to combine with others to form a stable substance or molecule, similar atoms form an element or when different atoms combine they form compounds.

The joining together of atoms is known as bonding. There are two main categories of bond types:

• strong bonds that are a result of the transfer of valence electrons. Such bonds are referred to as intramolecular bonds or primary bonds. Examples include ionic, covalent and metallic bonding

• weak intermolecular bonds are caused by the attraction between positive and negative parts of molecules that are close to one another. Such bonds are sometimes referred to as secondary bonds and can include hydrogen bonding and van der Waals forces.

Part 2: Materials and household appliances 11

Table of Comparative Bond strengths

Intramolecular bonds Bond Type Typical bond strength (KJ/mol)

Ionic 1000

covalent 300

Metallic 300

Intermolecular bonds

hydrogen bonding 30

Van der Waals 10

Intramolecular bonds or primary bonds

Ionic bonding is the electro-static attraction between oppositely charged ions.

For example a sodium atom (Na) has 11 electrons orbiting the nucleus in three shells. The inner most shell can only contain 2 electrons and is said to be full. The next shell contains 8 electrons and is also full. This leaves one electron in the outer most electron shell. The Na has a desire to have a completed outer shell therefore it loses the outer valence election and

becomes positively charged. When an atom becomes charged it is known as an ion.

Na Na

+ e^–

Sodium (Na) Sodium ion (Na⁺) Electron

Figure 2.4 Formation of a sodium ion

Chlorine (Cl) has 17 electrons, 2 in the innermost shell, 8 in the next shell and 7 in the outermost shell. The Cl finds it easier to complete the outer shell by gaining an electron rather than casting away the 7 electrons. The Na atom can supply this electron. By adding an extra electron the Cl becomes a negatively charged ion.

12 Household appliances

–

+ e Cl ^–

Chlorine (Cl) Electron

Figure 2.5 Formation of a chloride ion

Chloride ion (Cl^–)

With the formation of these ions there develops an electrostatic attraction between the ions.

–

Figure 2.6 Attraction between 2 oppositely charged ions

In reality this process occurs many times, and many Na⁺ and Cl^–ions are formed so the electro-static attraction is shared between all of the ions. This arrangement forces the ions into a particular ordered pattern, such that there are 6 positive ions surrounding each negative ion. This is known as a crystal.

_Cl^–_Na⁺_Cl^–_Na+

Figure 2.7 Sodium Chloride crystal

Do you think that the ions can move about freely?

No – the ions are firmly held in place.

Ionically bonded materials are typically salts in the solid state and have high melting points.

Covalent bonding – involves the sharing of the outer valence electrons. Classical examples of covalently bonded atoms are with hydrogen, oxygen and carbon.

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The hydrogen atom has only 1 electron in its outer shell but has a desire to have this shell filled. Remember that this shell only requires 2 electrons to be filled. The Oxygen atom (O) on the other hand has 9 electrons, 2 in the inner shell and 6 in the outer shell.

H O

Figure 2.8 Hydrogen and Oxygen atoms

To satisfy their requirements of full outer shells the O and H share their electrons. Actually the oxygen needs 2 hydrogen atoms.

O H

Figure 2.9 Molecule of H₂O

Covalently bonded materials therefore share their outer valence electrons.

Polymers are typically covalently bonded materials and are excellent thermal and electrical insulators as there are no free electrons to conduct current.

Make a sketch showing how carbon and hydrogen could be covalently bonded?

Metallic bonding as the name suggests is typically found in metals and in many ways is the simplest to understand. The metallic atoms simply discard their outer valence electrons, those electrons in the outermost shell. These then form a cloud of electrons that are shared with all of the positively charged metallic ions.

metallic ion

sea of

delocalised

electrons

two-dimensional

representation

Figure 2.10 Metallic Bonded materials

three-dimensional representation

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The electrons are free to move about this matrix and are not held in fixed positions. These electrons are called delocalised.

Metals are conductors of heat and electricity as the electron cloud is not fixed and is free to move.

Intermolecular bonds or secondary bonds

These are weak bonds normally caused by attraction between positive and negative parts of molecules that are close to one another.

Look closely at the H₂O molecule that is described in the covalent bonding section above, the O atom attracts the shared electrons more strongly than the H atom. This will mean that a slight negative charge will develop on the O atom and a positive charge on the H. This will mean that the water molecule will be polar, it has a slightly negative O end and a slightly positive H end.

δ^–

δ⁺

Figure 2.11 Water molecule showing polarity

The importance of this polar nature becomes apparent when the water molecule changes state from liquid to solid. With the reduction in thermal energy the polarity of the molecule forces it to arrange itself in an ordered (crystal) manner.

δ⁺δ^–δ⁺δ^–

δ⁺δ^–

Figure 2.12 Ice – showing secondary bonds

This is a dramatic and common example of secondary bonding. Because of the special characteristics of hydrogen this type of bonding is known as hydrogen bonding. This is the strongest example of secondary bonding, other types of bonds are known as van der Waals forces and are generally very weak.

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Particle theory

When considering the structure of matter it is sometimes easier to think of it as consisting of a series of particles. These particles are usually found in one of three states of matter – gas, liquid or solid. As a solid, the particles can arrange themselves randomly or in definite repeating patterns. Materials that form repeating patterns are known as crystalline and those that do not are non-crystalline or amorphous.

Metals are crystalline, as the atoms form into one of three repeating patterns, hexagonal close packed (HCP), face centred cubic (FCC) or body centred cubic (BCC).

_{close packed}Face centred cubic Body centred cubic Hexagonal

Figure 2.13 Metallic crystalline structures

Metals

Are you familiar with the term ferrous and non-ferrous metals? Write down an example of a ferrous and a non-ferrous metal.

__________________________________________________________ __________________________________________________________

Did you answer?

Ferrous non ferrous

• steel • copper

• cast iron • aluminium

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Ferrous metals

Ferrous metals are metals that are primarily iron, with small proportions of other materials.

The words iron and steel are commonly used in everyday language but their links to each other are not always understood.

Iron (Fe) by itself is an element, but when it is mixed with a small amount of carbon it becomes an iron alloy known as steel.

It is not known when or where people first made iron from iron ore, but it is believed that crude weapons and ornaments were made from the iron found in meteorites about 4000 BC. The process of making iron from iron ore developed in different parts of the world and by about 1000 BC, advanced civilisations were making iron.

The production of steel started in the early 1800s but it was not until the late 1800s that steel could be manufactured in large, inexpensive quantities. Steel making technology developed rapidly during the 1900s.

Types of steels

All steels are composed of iron (Fe) and small amounts of carbon (C) – less than 2%. If carbon is present in greater quantities the material is called cast iron.

Only those steels that have another element added, to give the steel special qualities, are called alloy steels for example stainless steel.

Stainless steels are special steels containing elements that promote a resistance to corrosion. For example, household appliances such as kettles, toasters and pans are made with alloy steel.

Figure 2.14 Stainless steel household appliances

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There are a number of methods for classifying steels. They can be by the way they are used or by composition.

Classification of steels by use:

• Dead mild steel – 0.07%C to 0.15%C, soft steel that can be severely cold worked

• Mild steel – 0.15%C to 0.25%C, relatively soft, can be welded, difficult to heat treat

• Medium Carbon Steel – 0.25%C to 0.55%C, these steels can have their properties altered by various heat treatment procedures.

• High Carbon steels – 0.55%C to 0.9%C, used when high strengths or good wear resistance are required.

• Carbon tool steels – 0.9%C to 1.6%C, used for cutting tools Classification of steels by composition:

Hypo-eutectoid steels – 0.0008%C to < 0.83%C, these steels exhibit the phases ferrite and pearlite. Ferrite is a soft material but as the quantity of carbon increases so does the amount of pearlite.

• Eutectoid steels – these steels are very strong and contain 100% pearlite

• Hyper-eutectoid steels – > 0.83%C but usually less than 1.6%C; the pearlite phase is present however the development of a cementite phase is becoming evident.

Non-ferrous metals

Non-ferrous metals are metals that contain no iron or only very small quantities

Examples of non-ferrous metals include:

• Copper

Copper (Cu) is refined from copper sulphides (Cu₂S or CuFeS₂). It is a reddish brown metal, which is malleable, ductile with high electrical and heat conductivity and is highly corrosion-resistant and takes a high polish

Copper is used in the form of wire and strip for electrical appliances and conductors and in the form of sheet and tube for heating appliances.

Common alloys of copper include the brasses (Cu –Zn) and bronzes (Cu – Sn).

Brasses can be used for tube and wire, condenser tubes, marine propellers, switch gear and brazing materials, to improve the machinability of the brasses it is usual to include a small quantity of

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lead (Pb). Bronzes are commonly used for coinage, water fittings and bearings.

• Aluminium

Aluminium is refined from bauxite (Al₂O₃.nH₂O). It is a very light metal, low specific gravity but has very good conductive capacity. It is an extremely good conductor of electricity and is used extensively for power cables. The low strength aluminium needs to be reinforced with a steel core for this purpose.

Aluminium has excellent corrosive properties as well, as it readily forms an inert oxide when exposed to the atmosphere.

Alloys of aluminium are often used in the aircraft industry and the automotive industry.

Lead, zinc and tin are other examples non-ferrous metals that are commonly used in industry.

Joining metals

There are many joining techniques. During this part of the module, several traditional joining methods are described.

Bolts, rivets and screws cause little disturbance to the metallurgy of the base metal whereas soldering, brazing and welding are methods of permanently joining metals together and can have a profound effect on the metallurgy of the materials that are being joined.

Nuts and bolts

Bolts can be secured by the addition of a nut or they can be screwed directly into a material. They are often used as a non-permanent method of fixing two or more surfaces or parts together and can be made from a range of materials depending on their application.

Solid rivets

A solid rivet is a very old fashioned method of joining metal. You would find it difficult to locate one on a modern appliance. For this method you need to:

• drill a hole in both pieces of metal to be joined

• insert the rivet into the hole

• burr the rivet

• set the rivet.

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Figure 2.15 A solid rivet

This method was replaced in most situations by the use of a Pop Rivet. For this technique you need to:

• drill a hole

• insert the pop rivet through the hole

• set the rivet using special pliers.

Figure 2.16 A pop rivet

It is difficult to find a pop rivet in many modern appliances.

Self-tapping screw

Self-tapping screws are designed to be inserted into a drilled hole that is smaller than the screw or these screws may have a drill end that self drills the hole. As the screw enters the hole it cuts its own thread (cutting a thread in a hole is termed ‘tapping’). The thread enables the screw to be removed and reinserted. The screws are generally made from hardened steel.

drill tap

Figure 2.17 self-tapping screw

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Welding

Welding is described as the bonding of metals by the application of heat. Arc welding and gas welding result in the localized melting of the base metal while forge and resistance welding are a product of the localised application of pressure. This can cause significant changes to the structure of the base metal.

Two methods that do not appreciably alter the structure of the base metal are soldering and brazing.

Soft Soldering

Soft soldering is a quick method of joining metals at relatively low temperatures (250 – 350°C). Solder is an alloy of tin and lead.

The parts to be joined are firstly chemically cleaned with a flux. The components are heated, solder is introduced to the joint and is then allowed to cool and harden.

The common use for solder in household appliances is for electrical joints, such as an electronic components joined to circuit boards.

Brazing

Brazing is known as hard soldering. It is performed at higher temperatures and produces a stronger joint. Brazing alloys commonly contain 50% to 60% copper – zinc alloys and melt in the 850 to 900^oC range.

Alloys of silver, copper and zinc are known as silver solder and melt in the 600–800^oC range.

The higher melting temperature requires the use of an oxy-propane or oxy-acetylene heat source.

Other welding processes are carried out at significantly higher temperatures than brazing. These welding operations can be classified as either pressure welding or fusion welding.

Pressure or Resistance welding

In pressure (resistance) welding, the metals are heated but are not melted and pressure is applied to effect the weld. No additional filler metal is required.

Resistance welding is a process of applying an electric current to materials that are held under spot pressure. Spot welding is an example of this technique. It is extremely quick and very suitable for sheet metal

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products. Electrodes clamp the two sheets and a short charge of electricity is applied. The resistance to the flow of this charge, caused by the sheet metals between the clamping electrodes, produces heat. The heat and pressure at this instant causes the materials to join. You may have seen robotic arms operating in automobile factories. They resistance weld car body parts together. In a variation to this process, the electrodes can also be in the form of rollers and a continuous seam can be made.

Electric arc welding

Fusion welding involves the localised melting of the base metal and the application of a filler metal, a wire or a flux-coated electrode.

An electric arc is struck to generate the heat required to melt the base metal and a filler material is used to complete the weld.

This type of welding forms an extremely strong bond between the metals that have to be joined but usually forms a scale on the outer surface of the weld, this scale has to be removed prior to a visual inspection of the welded zone.

The formation of the scale can be minimized by the introduction of an inert gas shield at the weld point thus eliminating atmospheric oxidation at the weld surface. This method is known as metal inert gas (MIG) welding. If a tungsten electrode is used as the electrode tip with the inert gas then this is known as tungsten inert gas (TIG) welding.

Can you think of any other metal joining techniques used on a household appliance?

Cutting metals

You may be aware of several ‘high-tech’ methods of cutting. Examples would be laser cutting and high-pressure water-jet cutting. At this stage it is important to consider the basics of cutting.

Shearing

Shearing cuts material, but achieves the cut without removing a waste strip. Snips are an example of a shear cut, often used to cut thin sheet metal. Thick sheet metal can be cut by machine operated blades. Normally only one blade moves. Industrial punches use the shear method of cutting. It has the advantage of a smoother cut edge, a quick cutting action and can be very efficient with less waste created.

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Sawing

Sawing removes a waste section of the material. Hacksaws are an example. In this process, the edge being cut is not bent or distorted. Hacksaws are mainly used for cutting rods, bars and angles to required lengths and thick sheet metals to shape. Hacksaws can be hand held tools or machine operated. Blades are made from tungsten steel for the cutting the hardest material or from high-speed steel for general work. The sawing process is generally slow however, and is uncommon in the industrial situation.

Flame cutting

Using a gas-flame torch to cut ferrous metals is common. Oxyacetylene flames are the mostly used. Steel needs temperatures in the range of 2000°C for this process, and therefore you will not find this technique used to produce fine work in household appliances. The process is more suited to preparation of larger section objects.

Drilling

Drilling is the cutting of round holes in metal. This is done by rotating and feeding the required drill into the work. Drilling machines can be bench mounted (usually driven by a motor and belts) or hand held electric drilling machines. The bench drill capacity is normally limited to 13 mm diameter while the hand held drills usually have a capacity ranging from 1 mm to 13 mm.

Turning

The lathe is used mainly for machining circular surfaces, that is cylindrical or conical but can be used for producing flat surfaces, drill holes, machine slots, and for many more functions.

Milling

Milling machines have a rotating cutting wheel that spins. The work to be shaped is secured to a sliding table. The work is introduced to the cutting wheel, rather than the cutting wheel moving to the work. This system is very efficient when producing machined slots or flat surfaces.

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