Design and Technology - Core Technical Principles
Industry
Automation - use of control systems e.g. CNC (Computer Numerically Controlled) equipment for design and manufacture.
Reduced labour costs, improved productivity.
Greater precision, control, consistency and quality.
Flexible production due to CNC being reprogrammable.
Greater job opportunities for engineers.
High cost of buying, installing and repairing systems.
Risk of power failure and system errors
Robotics - use of machines to carry out complex tasks such as locating parts on an assembly line.
Ideal for repetitive or dangerous tasks.
Can carry extremely heavy loads.
Can be programmed to do different tasks.
Cannot replace human judgement when making complex decisions.
May lead to fewer jobs for people.
As new technologies emerge, companies need to adapt the place of work:
More flexible building design for improved performance and speed of product to market.
Automation and remote working, such as driverless vehicles.
Smaller factory units as automated ordering of materials (JIT) reduces storage space.
Automated Storage and Retrieval Systems (ASRS) may eliminate the use of manual handling.
Tools and Equipment
Multi-purpose equipment increases operational flexibility.
Equipment organised into flexible manufacturing cells to respond to changes in demand.
Tools more automated to improve safety and speed of manufacture.
Enterprise
Crowdfunding
Donation - money is given but not returned
Debt - Investors hope to receive their money back, sometimes with interest.
Equity - Investors have the opportunity for a share in the business.
An individual or business that shows initiative and takes a risk in setting up and running new ventures.
Virtual marketing
Online presence pros and cons
Increased sales
Relatively cheap to set up and run
Sometimes complicated/difficult to navigate
Spam e-mails to advertise products are frowned upon.
Fairtrade
Protects the rights of farmers in developing countries.
Guarantees fair prices for those workers.
Co-operatives
An enterprise that is jointly owned and democratically controlled by its members.
Pros and cons
Can increase purchasing and marketing power
Are easy to form with limited liability.
Often have limited resources or funding
Can be hard to manage efficiently.
Sustainability
Meeting the needs of the present without compromising the needs of future generations.
Finite resources
Non-renewable
Examples
Fossil fuels
Metal ores and minerals
Non-finite resources
Can be replenished through natural methods and can sustain the level of demand.
Examples
Plants or algae produced to manufacture fuels such as biodiesel
Oils from plants used to produce environmentally-friendly plastics.
Managed timber is used for building and furniture construction
Disposal of waste
Life Cycle Assessment
Reduce
Reuse
Recycle
Recover
Reduce the amount of waste produced (e.g. reducing packaging and size of products, improving quality control and sending emails instead of letters)
Reuse products or materials that would otherwise become waste. E.g. using re-fillable ink cartridges.
Recycle materials to reduce the amount of new raw materials required, e.g. recycling plastic and glass bottles.
Recover waste generated in factories, e.g. using waste heat energy to heat the factory.
People
Technology Push
Research and development departments use new technologies to manufacture products where there was no existing consumer demand.
New materials with improved properties
New and improved manufacturing processes making products more affordable
Advanced technology.
E.g. development of Apple products, such as the iPad - new products developed regularly to make people want to buy them.
Market pull
Consumers desire new and improved products.
Manufactures want to secure a larger part of the market.
Manufacturers must respond to market trends.
Competitors introduce improved or new products.
Changing job roles
It is predicted that two-thirds of children who are about to begin their education will have jobs that do not yet exist.
Job roles changing due to an increase in computer technology and artificial intelligence.
Some offices are now connected through virtual connections (conferencing) allowing for home working.
Companies will need people with technological skills who can respond quickly to change.
People will need to become skilled in new technology.
Culture
Fashion
The dominant style in a given time period.
Affects areas of society including clothing, makeup or furniture.
Fashions come and go relatively quickly.
Social media means latest fashions are found more easily.
Product Data Management (PDM) helps manufacturers analyse what is in or out of fashion in real time.
Trends
Reflect the general direction or development towards something new or different.
Technology helps companies to predict trends.
Trends may have different lead times so companies must have flexible manufacturing systems.
Lead time - the amount of time it takes for a company to deliver a product to market from the start of the design process.
Faiths and beliefs
Manufactures must be careful to research their market to ensure:
Their products do not give offensive images or messages.
Their products do not use materials which are against the market's beliefs.
They are aware of their workers' needs such as breaks for worship or particular clothing requirement.
Culture
The shared general beliefs or customs of a specific group of people.
Society
Design for the disabled
Assistive technology
Covers small devices such as pencil grips and text-to-speech readers to larger things such as wheelchairs.
Prosthetic limb technology.
Design for elderly
communication/monitoring devices
mobility
independence with mechanical/electronic aids.
Religious groups
Some manufacturers have a range of designs that addresses the needs of each group
Technology can aid religious groups, e.g. prayer schedules
Environment
Continuous improvement of products
Improved products have reduced carbon footprint
Early replacement of existing products leading to increased use of transport, finite resources and landfill.
Efficient Working
How it is acheived
Lean manufacturing
Just in time (JIT) production
Improved transport infrastructure
Redesigned factory layout
Better quality assurance and control systems
Results
Fewer mistakes, lower costs, less stock and storage, products made to order.
Relies on efficient supply chains, as breaks in supply chain affect production.
Production Techniques and Systems
Pollution
Life cycle assessments:
Using renewable energy sources to reduce CO2 emissions
Ensuring waste can be reduced, reused and disposed of easily.
Making production energy efficient.
Governments can help with regulations such as tax.
Global Warming
Caused by increase in carbon emissions from burning fossil fuels.
Effects
Rising sea levels
Unpredictable weather
Extinction of species
Crop failure
Renewable energy sources designed to combat global warming.
Computer Aided Design (CAD)
Designs can be shared electronically
Ideas tested, evaluated and modified on screen
Parts can be expanded for detail
Processes simulated
Workers need retraining
There is a risk that electronic files can be lost or sent to the wrong place
Computer Aided Manufacture (CAM)
Lean Manufacturing
Uses computer software and hardware to translate CAD models into manufacturing instructions for CNC machine tools
Greater reliability and quality, flexible and improved productivity
Machine tools are faster and more accurate and can be reprogrammed.
Reduced costs
Less human involvement (reduced morale)
High set up costs.
Workers safe from potentially dangerous processes
Method to eliminate waste in a manufacturing system
Minimal storage - stock materials delivered just when needed and products made only to order.
Production carefully set up to eliminate delays and reduce material movement.
Rigorous quality assurance systems
Labour used efficiently
Flexible Manufacturing Systems (FMS)
Deliver high value products quickly.
Can respond quickly to changes in demand or supply.
Machinery grouped together to be more efficient and may be handled by computer systems
Close relationships with manufacturers, suppliers and retailers.
Just in Time (JIT)
Materials/components in right place at right time.
New stock only ordered when needed.
Storage costs reduced
Small batches of products can be produced cost effectively.
A break in the supply chain can cause delays.
Critical evaluation
Planned obsolescence
Some companies plan for their products to become obsolete in a certain timeframe by:
Choosing appropriate parts to suit predicted life span
Deciding on frequency of upgrading elements of the design or full relaunch
Launching new products by using new technologies or to meet new trends
Obsolescence increases demand by encouraging purchasers to buy again sooner.
Companies use cheaper components which only last as long as the planned life.
Consumers may complain about having to buy more regularly.
Design for maintenance
Ethics
Designers have to decide whether their products can be repaired by users at a much lower cost than it could be replaced.
Product has extended life spam which is perceived to save customers money.
Idea of saving money improves reputation of business.
Technical support is expensive
Company has to use storage space for stock for repairs.
Consumers will not want to buy new products.
Home repair may lead to safety issues.
Companies must not:
Exploit host countries, workers or suppliers
Damage the envionment
Forget the needs of the end user and the impact of the products.
The environment
Companies must balance the demand for new products against the needs of the environment using Life Cycle Assessment (LCA)
- materials processing, separation and use
- energy consumption and emissions
- wastes and by products of manufacturing
- transport for production distribution and use.
- packaging, construction and disposal
Fossil fuels
Coal:
Natural Gas:
Oil:
- Large amount of electrical energy can be created from coal. Reliable and stable
- Power stations efficient at converting energy and cost effective once set up
- Extraction of coal has environmental impacts on the landscape.
- Large amount of pollution is produced.
- Large amounts of electrical energy can be created. Reliable and stable
- Cost effective to extract as it is a ready made fuel, and needs less processing and is cleaner than coal and oil.
- Pollution produced
- Extraction can damage environment through emissions or damage caused from fracking.
Processed to provide different energy sources, e.g. petrol, diesel and paraffin
- Power stations efficient at converting energy from oil and are cost effective once set up
- Convenient source of power as the energy supply. More portable in vehicles
- Large amount of pollutants produced.
- Impact of environmental disasters is high.
Nuclear Power
Producing nuclear energy:
- Heat energy from nuclear fission produces steam to drive a turbine
- Turbine drives a generator, producing electricity.
One kilogram of uranium contains two to three million times the energy equivalent of oil or coal
Wind farms require up to 360 times as much land area.
Advantages
No need for large amount of space
Does not produce carbon emissions
Reliable and not dependent on weather.
Low volume of waste produced = less pollution from the transport
Reduces demand for finite resources such as oil.
Disadvantages
Risk of nuclear accidents
Disposal of nuclear waste is expensive and takes a long time to decay
High levels of security required
Decommissioning nuclear plants safely is costly - high risk of contamination
Construction, operation and decommissioning of the reactor may harm the environment
Renewable Energy
Wind
Solar
Tidal
Large amounts of power available but barrages across estuaries cause ecological damage.
Hydro-electrical
Expensive setup and construction of dams may harm the environment.
Biomass
Large amounts of water required to grow biomass.
Energy and Storage Systems
Kinetic pumped storage
During the day, water held in dam flows down slope, creating kinetic energy to spin a turbine.
When demand is low, excess electricity used to pump water from lower dam back to main reservoir to top up water available to generate power.
Batteries and Cells.
Use chemical energy
Chemical reaction produces electrons that collect at negative terminal and flow to positive terminal when connected in a circuit.
Alkaline (Primary) Batteries
Higher energy, longer shelf life and more environmentally friendly when disposed of compared to rechargeable batteries.
Only used until the charge has been drained.
Rechargeable Batteries
Cost more but can be used many times. Cheaper in the long run and produce less waste.
Initial cost is higher than primary batteries.
Modern Materials
Graphene
Lightest know compound
Stiff and strong (200 times stronger than steel)
Thin (1 atom thick)
Conducts electricity and heat.
Uses: Aircraft parts, artificial joints, sports equipment.
Liquid Crystal Displays (LCDs)
Respond to electrical input from an electrode to block or allow a back light to shine through and generate various colours to form images on the screen.
Compact, low energy use, sharp and bright image.
Restricted viewing angle
Nano materials
Less than 1 to 100 nanometers thick.
Used as thin films or surface coatings, e.g. self-cleaning glass or insulation.
Improve properties of materials (e.g. strength, conductivity, hardness, waterproofing, fire retardancy)
Metal Foams
Made of a base metal (e.g. Aluminium) with gas-filled pores added to increase the volume of the metal.
Have high porosity and strength.
Have good thermal conductivity.
Are light, with good energy absorption.
Uses: impact absorbing features in vehicles.
Titanium
Lightweight metal with low density.
Corrosion resistant
Good strength to weight ratio
Stiff and tough.
Uses: Aircraft parts and artificial joints.
Coated Metals
Metals can be coated with other materials to protect them, improve performance or aesthetics.
Zinc (galvanising) protects steel from rusting.
Teflon (PTFE) provides non-stick coating for kitchen pans.
Smart Materials
Shape memory alloys
e.g. Nitinol - programmed (heated at high temp) and when deformed will reform at certain temperature. Different alloys have different trigger temperatures.
Save space and require fewer parts.
Are expensive
Wear out after time.
Thermochromic Pigments.
Change colour due to temperature changes. Change can be reversible or permanent.
Improve safety.
Detect and indicate change.
Decay over time.
Photochromic pigments
Change colour due to exposure to UV rays. Change in colour reversed when stimulus is removed.
Can help create multi-use products.
Can be slow to react and expensive.
Composite Materials
Produced by combining two or more different materials to create a material with enhanced properties.
Glass Reinforced Plastic (GRP)
Plastic reinforced with strands/woven fibres of glass and is built up in layers.
Good strength to weight ratio
Cheaper than carbon fibres.
Can be coloured with resins.
Carbon Fibre Reinforced Plastic
Plywood
Plastic reinforced with stands/woven fibres of carbon and built up in layers.
Excellent strength to weight ratio.
Very rigid, with greater rigidity than glass fibres.
Manufactured wood formed from layers of veneers bonded together by glue.
Stable in all directions.
Available in large sheets.
Technical Textiles
Conductive fabrics
Include conductive materials (e.g. carbon, titanium, nickel, copper) strands woven, knitted, sewn, cut or braided into fabric.
They can conduct electricity and connect electronic components, which can be used in clothing for lighting or controls, or in athletic garments with heart rate monitors.
Fire Resistant Fabrics
Based on aramid fibres, which are heat resistant.
Used when there is a need for a higher level of insulation and for fire resistance for a set period of time.
e.g. home furnishings and specialist clothing, such as welding overalls.
Microfibres incorporating micro encapsulation
Microfibres: synthetic fibres less than one denier thick.
Micro encapsulation: solid substances such as cosmetics or medicines are encapsulated in tiny thin-walled bubbles of natural or synthetic materials.
The textiles may contain small soluble particles. May be used for adding therapeutic fragrance or medication into clothing.
Kevlar
Very high strength to weight ratio.
Very flexible and not affected by moisture.
can be used as a replacement for steel and spun into ropes for mooring boats.
Systems approach to designing
A method to break down the stages of a process into a series of steps.
Three sections
Input
Output
Process
Flow charts
Open loop
Output not measured.
Closed loop
Output is measured.
Electronic Systems - Inputs
Light Sensor
High resistance when dark, low resistance when light.
Temperature Sensor (thermistor)
High resistance when cold, low resistance when hot.
Pressure sensor
Can be switches that are on or off or gauges that have a change in resistance when there is an applied pressure or force.
Switches
Toggle switch (single throw)
Push to make (PTM) (normally open (NO))
Push to break (PTB) (normally closed (NC)) used on fire alarms or control systems.
Electronic systems - Processes
Microcontrollers
Make decisions and determine an output
Can be programmed using machine code.
Programmable interface controllers (PICs)
microcontrollers that can be programmed and used as counters, tiemrs or for making decisions.
Inexpensive and are used in a wide range of commercial products such as cars, remote controls, etc.
Timers
e.g. 555 timer, produces single (monostable) or multiple (astable) pulses.
Electronic systems - outputs
Speakers
change electrical pulses into recognised audible sound
Current flows into coil and creates an electromagnet, which creates movement. Movement transferred to a cone which creates sound waves.
Buzzers
Convert electric current into an audible buzz, normally used as an alarm.
Lamp
Light emitting diode (LED)
Component that gives off light.
Replacing bulbs as they are long lasting and low power consumption.
Normally grouped in a cluster to provide good levels of light and can still work when one of the LED fails.
electromagnets switched on and off repeatedly to vibrate a metal disk between two magnetic poles.
Types of movement
Linear
Motion in a straight line
Reciprocating
Back and forth movement in a straight line.
Rotary
Motion that goes around a central point.
Oscillating
Motion that swings backwards and forwards in an arc from a central point.
Levers
First order
Used to lift greater loads but effort has to move greater distance than the load.
Second order
Also used to lift greater loads with the effort moving a greater distance than the load.
Third order
Effort in this lever is more than is applied to the load. Used for precision work (tweezers)
Mechanical Advantage
MA = load/effort
First and second order levers always provide an MA of greater than 1. The MA of third order levers is always less than 1.
Simple gear trains
Velocity Ratio
VR = distance moved by effort/distance moved by load
Linkages
Reverse motion
Converts movement in one direction to movement in the opposite direction
Used in a gear lever mechanism in a car.
Push/pull
Two levers used to convert movement in one direction to movement in the same direction
Used in car windscreen wipers.
Bell crank
Fixed angle lever that converts motion through that angle to allow an input force to be transmitted around a corner.
Used on a brake mechanism on a bike.
Simple gear train - when two spur gears are meshed and fixed on parallel shafts.
Idler gear
To make the driven gear rotate in the same direction, and idler gear is used.
The idler gear does not change the output speed.
Compound gear train
Speed change in simple gear trains is limited to the number of teeth on the two gears, and space available for the gear system.
Combining a number of simple gear trains can achieve higher speed changes. This is called a compound gear train.
Velocity Ratio
VR = number of teeth on driven / number of teeth on driver (EXPRESS AS A RATIO)
Output speed
For compound gear trains the overall velocity ratio is calculated by multiplying the individual velocity ratios for each simple gear train.
Output speed = input speed / velocity ratio
speed of rotation expressed in RPM (revolution per minute)
Specialist gears
Bevel gears
Transmit rotary motion through 90 degrees
When bevel gears have the same number of teeth they are called mitre gears.
Worm and worm wheel
Used to make large reductions in speed
Gear meshes with the worm, which is the driver.
The worm has only 1 tooth. Remember this when calculating velocity ratio.
Rack and pinion
Gear wheel and rack change rotary motion to linear motion and vice versa. Examples found in pillar drills and car steering system.
Distance moved by rack = teeth on pinion gear / teeth per metre on rack
Cams and followers
Types of cam
Pear shaped
Follower remains stable for about half the cycle.
Rises and falls in the second half.
E.g. camshaft in a car to open and close valves.
Eccentric
Follower gradually rises and falls in a smooth and continuous movement.
E.g. steam engines.
Drop (snail) cam
Follower gradually rises and falls in sudden movement.
e.g. shaping machine (hammer)
Movement from cam and follower
Rise
Fall
Dwell - follower remains stationary.
Stroke - range of movement from the follower.
Rotation - movement of cam.
Types of follower
Flat
Greater load carrying capabilites
Increased friction
Less accurate.
Knife edge
Greater accuracy
Wears quickly
Large side thrust
Roller
Reduced friction
Runs at high speed
More complex
Higher cost
Pulleys and belts
Pulleys
Pulley - a wheel with a shaped groove. The belt fits in the groove connecting two pulleys and motion is transferred by friction.
Pulley system - Two pulley wheels on separate shafts are connected by a belt. Motion and force transmitted from driver pulley to driven pulley. Speed, direction and force of rotation can be changed.
Belts
Round - efficient, can be crossed to change direction.
V-belt - Reduces slippage by wedging into the pulley wheel.
Flat - good grip at speed due to large surface area. Can be crossed to change direction.
Toothed - no slippage as belt fits into teeth and pulley. Could pose as a safety risk if something gets trapped.
Velocity ratio
VR = driven diameter / driver diameter
Output speed
Input speed / velocity ratio
Papers and Boards
How it's made
Chips of wood processed using chemicals to make pulp.
Filtered and moved through rollers to remove the water and flatten the paper.
Most papers can be recycled.
Paper thickness measured in grams per square metre (gsm)
Paper
Bleed proof (120-150 gsm)
Takes colour well, thin grades, similar to cartridge paper but with a smooth surface.
Low cost.
Used for presentation work.
Cartridge (120-150 gsm)
Slight texture on surface, creamy white colour.
Used for drawing as it takes paint well.
Medium cost.
Grid (80-100 gsm)
Grid printed on surface.
Low cost.
Used for working drawings.
Layout (50 gsm)
Thin, translucent with smooth surface, can be used to trace.
Low cost.
Used for preparing ideas or tracing.
Tracing (60-90 gsm)
Transparent, smooth surface, hard, ink absorption is slow, strength allows for erasing mistakes.
Good quality can be expensive.
Boards
Generally thicker and heavier or made from more layers, than paper.
Can be laminated to other materials to create different properties for specific purposes.
Types
Corrugated card (fairly cheap)
Corrugated paper sandwiched between two outer layers. Excellent impact resistance, absorbs shock, strength for weight. Used for packaging as it provides protection.
Duplex board (medium cost)
Made up of two layers. Tough and thin, and often water resistant. White so can be printed on. Used for pharmaceutical packaging and paper plates.
Foil-lined board (higher cost)
Has foil coating laminated onto on surface. Gives board resistance to moisture. Used for food packaging and cartons.
Foam core board (medium cost)
Rigid polystyrene foam sandwiched between two outer layers. White, very light, flat and rigid. Used for models and mounting work.
Inkjet card (medium cost)
Treated to absorb inkjet and can move through the printer. Used for high quality printing.
Solid white board (higher board)
Entirely made from wood pulp and bleached white. Strong and rigid and makes an excellent printing surface. Used for display packaging, cosmetics, etc.
Natural timbers
Hardwoods
These trees
Have broad leaves and its seeds are found in a fruit.
Usually deciduous.
Grow slowly, often taking over 100 years to be big enough for timber.
Were common in Britain
Mahogany
Strong and durable.
Very rare tropical wood
Good for quality furniture.
Beech
Strong and tough, close grained, does not splinter easily.
Expensive
Good for kitchen implements, toys, chair legs.
Ash
Strong, durable, flexible, attractive grain, light in colour and fairly straight.
Expensive
Good for furniture, baseball bats.
Oak
Strong, durable and heavy.
Expensive, corrodes iron.
Good for furniture and barrels. Previously used for building houses.
Balsa
Lightweight, soft and easy to cut.
Too weak for construction work.
Good for model construction or floats in old boats.
Softwoods
These trees
Have needle-like leaves
Are usually evergreen
Planted for timber, grow quickly, and a lot cheaper than hardwood timber.
Pine
Strong and easy to work.
Lightweight and generally cheaper. Attractive grain.
Can warp and split.
Good for interior construction.
Larch
Harder and tougher than most conifers, heartwood resins act as preservatives.
May twist in humidity.
Good for outdoor use, e.g. cladding.
Spruce
Straight, even grain, small knots, quite strong.
Little resistance to damp and rot.
good for indoor use, furniture, joists with preservatives.
Manufactured boards
Features
Made into large sheets with uniform thickness and strength, dimensionally stable.
Available in thin sections that would be stronger than natural timber of the same dimensions.
Exposed edges will need treatment and flat surfaces usually need covering with veneer or laminate.
Manufacturing process
- Wood processed into chips
- Particles mixed with an adhesive
- The mixture is compressed into shape with rollers and heated to cure adhesive
- Boards are trimmed to standard sizes
Types
Medium Density Fibreboard (MDF)
Wood fibres mixed with adhesive and then formed together under heat and pressure.
Dense, very smooth flat surface that can be easily machined and painted.
Cheap as it is made from waste wood.
Heavy fine dust produced when cut and sanded, which requires extraction/ventilation.
Chipboard
Flakes, chips or strands of timber are coated in adhesive resin and pressed into shape.
Flat and stiff
Cheap as it is made from waste wood
Poor resistance to moisture.
Does not have good aesthetic qualities.
Plywood
Manufactured board formed from layers of veneers bonded by glue to form a flat sheet
Cross layered structure gives excellent strength and better impact resistance.
Poor resistance to moisture as the veneers are porous.
Metals and Alloys
Ferrous metals (contain iron) so most are magnetic and may rust.
Mild steel
Cast iron
High carbon / tool steel
Non-ferrous metals do not contain iron, and therefore will not rust.
Aluminium
Copper
Tin
Zinc
Alloys are a mixture of two or more metals or elements, which has improved properties and characteristics
Brass - plumbing, door fittings, musical instruments.
Stainless steel
High speed steel - used for drill bits, lathe tools and milling cutters.
Polymers
Thermoforming polymers
Recycled and reformed with heat
Lightweight
Low cost
Come in wide range of colours.
All thermoforming polymers are tough.
Thermosetting polymers
Cross linked chains mean that once the polymer has set into shape it cannot be reformed using heat.
Hard, rigid and brittle, resistant to electricity, heat and chemicals
Cannot be recycled.
Textiles
Natural fibres
Wool
Sourced from animal hair such as sheep and goats
Good insulator, breathable, absorbs dyes and is lightweight. Creases drop out.
Prone to shrinking, dries slowly.
Uses: Pullovers, shirts, trousers.
Cotton
Fibrous material encasing seeds of the cotton plant.
Soft, breathable, cool, strong, insulating, good abrasion resistance.
Shrinkage, wrinkles, attacked by mildew.
Uses: Shirts, sheets, swimwear, blouses.
Silk
Fibres taken from silkworm cocoons
Soft, lustrous, dyes well, very strong, lightweight, comfortable, absorbent.
Expensive, needs special care cleaning.
Uses: Luxury wear, shirts, ties, pyjamas.
Synthetic Fibres
Polyester
Strong, durable, quick drying, dyes well, resists shrinkage/chemicals
Low absorbency, static electricity problems.
Uses: Dresses, curtains, sails.
Polyamide
Durable, lightweight, chemical/wrinkle resistant, easy to wash
Stains easily, low moisture absorbency
Uses: Parachutes, sportswear
Elastene
Lightweight, abrasion/chemical resistant, stretches, strong.
Colours with age, low moisture absorbency.
Uses: active sportswear, swimwear
Combining Fabrics
Knitted
Knitted fabrics made by looping warp (down) and weft (across) yarns together making a flexible fabric.
Woven
Plain weave woven fabrics are strong and hard wearing. Fibres interlaced in a criss-cross pattern, weft and warp aligned at right angles to each other.
Selvedge - edge of fabric where wefts double back forming an edge that does not need to be hemmed to prevent fraying.
Non-woven fabrics
Made by tangling fibres together to make sheet materials.
Bonded fabrics
Use webs of synthetic fibres that are bonded together with heat or chemicals (adhesives). They don't fray and are cheap to produce but not as strong as woven fabrics.
Used for interlining in curtains and clothing.
Felted fabrics
Use wool fibres that are bonded using heat, moisture and pressure. Felted fabric is a good insulator and does not fray.
Little strength or elasticity, and difficult to wash and susceptible to moths.
Materials and properties
Physical properties - can be observed or measured without changing the composition of a material.
Mechanical properties - its ability to resist certain external forces.
Absorbency - the ability of a material to soak up a liquid.
Density - mass per unit volume
Fusibility - the ability of a material to melt into a liquid or molten state when heated.
Electrical conductivity
Thermal conductivity
Strength - Ability to withstand force
Hardness - ability to resist abrasive wear
Toughness - ability to withstand sudden stress or shocks
Malleability - ability to permanently deform when worked without breaking.
Ductility - the ability to be drawn out or stretched without breaking.
Elasticity - ability to bend and return to shape.