topic 4 - raw material Flashcards
what are mechanical properties?
when you apply an external force on a material and how it reacts.
what are physical properties?
they can be determined without damage or destruction and relate to the interaction of the material with energy and matter in its various forms.
what are aesthetic properties?
Properties that have an appeal to the human senses of beauty and pleasure.
Aesthetics are subjective and qualitative. Whereas physical and mechanical properties are objective and quantitative.
what are smart properties?
Are designed materials that have one or more properties that can be significantly changed in a controlled fashion by external stimuli, such as stress, temperature, moisture, pH, electric or magnetic fields.
what are the physical properties?
density
hardness - ability of the material to resist scratching or indentation.
electrical resisitivity - ability of a material to resist electricity.
thermal conductivity - ability of a material to let heat through it with minimal resistance.
thermal expansion
what are the mechanical properties?
Tensile strength - ability of a material to resist stretching forces.
Elasticity - ability of a material to be deformed and then return to its original form when the external force is removed.
Stiffness - ability of a material to resist/withstand bending forces.
Compressive strength – ability of a material to resist compression/squashing forces.
Toughness – the ability to withstand fracturing under sudden impact.
Plasticity – the ability of a material to be permanently deformed.
Ductility – ability of a material to be drawn out (stretched without snapping).
what are growth characteristics of trees?
the innermost ring is the oldest and tends to be much harder. trees grow from the inside outwards. growth rings happen once a year.
what is plywood?
an odd number of veneers are glued and compressed at 90 degrees to eachother.
what is MDF?
tiny softwood fibres are glued together and compressed under heat.
it is resistant to warping, machines well, and has a smooth surface.
what is chipboard?
particle boards made from softwood particles that are glued together and compressed under heat.
textured surface, commonly laminated, porous, cheap, structurally weak, unifrom thickness.
what is blockboard?
softwood stripes are glued and compressed between two double layers of veneers.
excellent structural strength, very stable, resistant to water, heat, chemical, and insects, available in interior and exterior grade.
why are manufactured boards better than wood?
- available in different range of thicknesses, minimises waste.
- large sheet sizes, cover large surface area.
- uniform thickness.
- can be engineered to enhance properties.
- no warping or shrinking.
- easy to obtain.
what are the benefits of applying finish?
- changes its appearance
- protection from moisture
- protection from insects and fungal attacks
- increases its hardness
- increases its stability
- makes it food safe
what is the composition of glass?
starts as silicate (commonly known as sand). because glass is made of sand, it makes it cheap, as it is an abundant raw material.
types of glass (will come up in mock)
what are the benefits of laminated glass?
- good uv protection
- good sound insulation
- high resistance to impact
- can be laminated with different materials for different applications.
how would you answer a 9 marker? e.g. 3 what are three ways laminated glass can improve the safety of car users when used for the windscreens?
- give the definition of laminated glass
- describe how you would change the polymer
- what properties does the polymer give the glass now and how does it influence it
- link it to safety of a car
what are the benefits of tempered glass?
- excellent tensile strength (scratch and impact resistant)
- shatters into small rounded fragments
e.g. shower screen door
what is tempered glass?
tempered (or toughened glass) is a type of safety glass processed by thermal or chemical treatments to increase its strength compared with normal glass.
what is laminated glass?
laminated glass is a type of safety glass consisting of two or more layers of glass (with one or more thin polymer interlayers between them) which prevent the glass from breaking into large sharp pieces.
what are thermo-setting plastics?
strong secondary bonds meaning once heated and formed, a chemical change takes place, and they cannot be reformed.
e.g. think of an egg
what are thermoplastics?
strong primary bonds along polymer chains but weak secondary bonds linking them. allowing them to be reformed when reheated.
e.g. think of ice
what is PETE and what number?
1.
PETE can be recycled into fibres to make fleeces.
Formed through blow moulding. Main cost is machinery and tooling (moulds, jigs, templates etc).
what is HDPE and what number?
2.
HDPE is high density polyethylene – commonly used in water bottles, carrier bags, and wheely bins. Rotational moulding, mainly used for plastic balls etc. 3m^3 capacity.
what is V and what number?
3.
V is pvc vinyl –
used to make cling film, windowsills, gutters. Can sometimes get UPVC (ultraviolet grade pvc) which makes it more brittle. Made using extrusion (gets pushed through a die/opening).
what is LDPE and what number?
- LDPE is low density polyethylene – similar to HDPE but just has a lower density and is therefore less rigid.
what is PP and what number?
- PP is polypropylene –
used in furniture, Tupperware.
Most commonly used polymer on the planet. Injection moulded (same process as extrusion but uses an enclosed mould). Injection moulding is also the most commonly used process. Gives you different thicknesses.
what is PS and what number?
- PS is polystyrene –
low density makes the coffee cups, takeaway boxes.
which metals are ferrous (magnetic)?
Cast iron - brittle, high density, good compressive strength e.g. vice
Mild steel – malleable, ductile, good tensile strength e.g. stool.
Tool steel – hard, brittle
High-speed steel – high friction resistance e.g. drill bit
Stainless steel – corrosion resistance, hard, difficult to work e.g. sink
which metals are non-ferrous?
Aluminium – low density (lightweight), corrosion resistant, ductile
Copper – low thermal resistance, low electrical resistance, ductile, oxidises.
Lead – high density (heavy), highly malleable, poisonous/carcinogenic.
Zinc – high resistant to corrosion.
Brass – highly decorative, polishes well, ductile.
why are metals alloyed and what does it do?
most metals are not useful in their pure form. Therefore, they are mixed with other metals (alloyed). The crystal structures combine and put strain on the base material, this makes it harder for them to disform and improves the yield strength and tensile strength
what two ways can you change the working properties of metals?
tempering:
A heat-treating process designed to increase the toughness of an iron-based metal by heating it and allowing it to cool in air. Tempering decreases the hardness of the material, which usually increases the ductility and decreases the brittleness. The temperature you heat it to will affect the level of ductility.
work hardening:
aka strain hardening or cold working. Toughening a metal through plastic deformation. Makes the metal more brittle but harder.
what are super alloys (will be in mock)?
an alloy that exhibits excellent mechanical strength, resistance to thermal creep deformation, good surface stability, and resistance to corrosion.
