PLASTICS
we also use plastics in
many economic and industnal
sectors
Origin and transformation of plastics
Depending on their origin, we can describe plastics as natural or
synthetic
Natural plastics
Synthetic plastic
are obtained directly from raw vegetable matenals
are made from compounds extracted from
petroleum, natural gas and carbon
The majority of plastics belong
to this group
The transformation of these raw materials and compounds into plastics is called polymerisation
During the manufacturing process, we can add materials such as fibreglass, textile fibres, paper, silica and sawdust to reduce production costs, and to develop certain characteristics
We can incorporate chemrcal additives to increase flexibility and to strengthen the polymers, and we can add pigments to give colour to the plastics
Properties of plastics
The properties of plastics depend on their type and on their composition
Strength, elasticity, rigidity and flexibility are characteristics of many plastics, although they vary from one type to another
There are other properties that are common to the majority of plastics
Mechanichal
Acoustic
Electrical
Thermal
Other properties
Impermeability
Low density
Ductility
Malleability
Mechanical resistance
Acoustic insulation
Electrical insulation
Thermal insulation
Ecological properties
We can recycle plastics. There are three recycling processes
Chemical recycling
We apply chemical processes to make new
materials from the original components of plasutic residues
Mechanical Recycling
We make new products from plastic
granules
Agglutination
Extursion
Floating
Pelletising
Separation and crushing
We separate the plastics according to
type and then they' re crushed
The filaments are then reduced to granules that we call pellets
We melt the material, and then it's extruded into long
filaments
The material is compacted and then incorporated
into other materials
We wash the plastics and then dry them by centrifugal
force
Energetic Recycling
We can incinerate plastics and the energy that
is produced is used tn industry, for heating or producing electricity
The majority of plastics are not yet biodegradable, but thanks to new technologies, we' re increasingly able to produce biodegradable materials
plastics that decompose on contact with certain bacteria and
biological agents
plastics that dissolve on hot or cold water
CLASSIFICATION OF PLASTICS
Thermoplastics
We manufacture thermoplastics from compounds adquired from petroleum
They' re made up of weakly formed molecular chains
When we heat them they become soft, wich allows them to be formed into different shapes
Thermostableplastics
These plastics are made from compounds derived from petroleum
They`re formed by strongly-linked chains running in different directions
When heated, they become soft and can be shaped.When cooled, they cannot be remoulded by applying heat
Elastomers
Made by vulcanisation: mixing sulphur and rubber, and heating to 160ºC
They are hard, resistant and very elastic —stretching easily under force
They' re formed by chains linked laterally and then folded over themselves, like a ball of wool or string
FORMATION TECHNIQUES
Extrusion
Lamination
Vacuum forming
1.We put thermoplastic, in granural form, into a previously heated cylinder
2.We apply pressure by means of a large, rotating screw, which forces the melted material out, through a nuzzle
3.We cool the shaped material slowly in a refrigerated water bath until it's solid
4.Finally, we collect the pieces of plastic through a feeder system
Thermoplastic produced by the extrusion method is passed through a series of hot cylinders to produce sheets of varying thtckness
With this technique, we can produce different finishes, for example, glossy, matt or textured. This depends on the outer coating applied by the final cylinder.
1.We put thermoplastic into a mould
2.We then use a heater to heat the mould and soften the plastic
3.We extract the air below the sheet so that the plastic is pulled against the inside walls of the shaped mould, and the desired form is created
4.We leave the mould to cool, then remove the object
Moulding
Injection
1.We inject melted thermoplastic into a mould
2.When the material has cooled and solidified, we extract it from the mould
Blow
1.We put a tubular-shaped piece of plastic into a hollow mould which has the same shape as the object that we want to make
2.We close the mould and blow pressurised air into it, so that the plastic adheres to the sides of the mould and takes its shape
3.When the object is cold, we remove it from the mould
Compression
1.We put the thermostable plastic, which can be in granular form, into the base of a cavity mould
- The outer part of the cavity mould, shaped the same, is closed to compress the material inside. We then heat it and it becomes soft and malleable
- The plastic adapts to the shape of the cavity between the two parts of the mould
4.We extract the object when the plastic has cooled and solidified
SHAPING AND FINISHING TECHNIQUES
We can use dtfferent tools and machines to finish the plastic objects that we have made
Cutting
Cutter
Scissors
Steel bit
Frestsaw
Jig saw
To cut sheets of different thickness, depending on their hardness
To cut soft, thin flexible sheets
To cut sheets less than 1mm in thickness
To cut soft, low density plastic
Cann make straight, slanting and curved cuts
To cut very large sheets of plastic, and rigid plastics in general
Cann make straight, slanting and
curved cuts
Power press
To cut flat sheets of low density plastic
Makes simple objects by
applying pressure
Hot metal thread thimmer
To cut sheets of soft thermoplastic
Perforating
Tool that makes holes in plastics
Consits of inserting a long, thin round and threaded piece of metal into the head of the machine thaqt revolves at high speed for cutting holes
Trimming and filing
A file has a rough surface
Used to finish the surfaces and edges of hard materials
A rasp has an even rougher surface, covered with 'teeth'
Used to finish the surfaces and edges of soft materials
Joining plastics
When plastics have been formed, shaped and finished, we can join pieces each to other
Temporary joints
Permanent joints
We can join and then separate objects with mechanical fasteners
Nut and bolt
Standard screw
Double ended screw
Used to fasten two objects together
Nut used to tighten the bolt
Used to fasten two objects
Holes must bne drilled first before the screw in inserted
Each end of the screw can be inserted into one of a pair of objects
We use this type of joint when we don't want to separate or dismantle the pieces
Adhesives
Soldering
Joining two surfaces permanently
Resins with two components: liquid, high water resistance
Acrylic cement: liquid, used mainly with PVC and polystirene
Joining thermoplastics using heat and pressure
Textiles and leather
We use textiles in the form of threads to produce cloth
Natural fibres and leather
Synthetic fibres
We get natural fibres from raw materials
Vegetable origin
Animal origin
Mineral origin
Cotton
Linen
Hemp
From the plant of the same name
Naturally white; can be dyed
Elastic and flexible
Light and absorbs moisture
Good thermal insulator
Resistant to acids
From the flax plant
Naturally white or beige
Elastic and flexible
Good thermal productor
Resistant to chlorinee and bleach
Extracted from a herbaceous plant
very strong
Used in shoemaking, crafts and decorations
Wool
Silk
From sheep
Various natural colors, but easily died
Very elastic
Excellent thermal insulator
Resistant to acids
Made from a material secreted by a worm called a silkworm, which forms extremely fine threads
Highly resistant and elastic
Good thermal and electrical insulator
Asbestos
Metals
Fibrous minerals
Fireproof
Used for fire-resistant roofs
A health risk to use aqnd inhale
Threads of gold, silver and copper
Used to make cloth
Synthetic fibres such as nylon, polyester, rayon and Lycra' are plastics
They are long-lasting, resistant and waterproof
A mixture of natural and synthetic fibres is often used to make textiles
STONE AND CERAMICS
Stone
These are materials found in nature as large blocks of rock within the Earth
Marble and granit
high density, cold to the touch, hard, high resistance to environmental conditions
widely varied natural colour
brilliant sheen when polished
used on floors and walls, in architecture and in sculpture
Slate
hard, dense and compact, making it waterproof
extracted from the Eanh in smooth, flat pieces that are cut and pressed
used mainly to cover roofs and as paving stones
Stone binders
Sand and gravel are used directly to make asphalt and also for binders, which are used to 'bind' or join other materials together
Plaster
Cement
Mortar
Concrete
processed from crushed gypsum that is dehydrated
then mixed with water to make a paste that hardens rapidly
water-soluble adhesive when first mixed that is resistant to pressure and to fire
used to make archways, partitions, and as a rovening for walls and paving, etc.
grey powder made from a mixture of crushed and heated limestone, clay and gypsum
mixed with water to make a soft paste
very strong and resistant
used to make mortar and other binders for construction materials like bricks
binder made from cement and sand, hardens when mixed with water
used to hold together construction materials like brick, cement block and
paving stone, and to make artifinal stone
mixture of gravel, sand, water and cement that dries and hardens
strong resistance to pressure
adheres to steel, used to makereinforced concrete
used to make foundations for buildings, bridges, etc.
Ceramics
Physical and chemical propertie
Clay is a fine-grained earth composed of aluminium silicates and other substances. We can mould it easily when it's wet.
It's soft, porous, resistant to high temperatures and chemically inert
It has many different. colours; it's abundant in nature and very versatile
Making ceramics
1.Preparating the clay
We clean the clay to remove traces of vegetable
matter, then apply a breakdown process using rollers
2.Mixing
We add water, anti-grease agents, fluxes and colouring
3.Modelling
We shape the clay in the form of the oblect we want to
make
4.Drying
To allow all water to evaporate
5.Baking
in an industnal oven called a kiln at temperatures between
700ºC and 1700ºC
- Glazing and enamelling
Clasification of ceramic materials
There are two large groups: structural ceramics and whiteware ceramics
Structural ceramics are permeable; whiteware ceramics are impermeable
Glass
Glass is a transparent or translucent material that can have different textures and colours
It's waterproof, smooth and hard, but fragile
It's resistant to environmental conditions and to chemical compounds
It's a good thermal, electncal and acoustic insulator
Shaping techniques
We make glass by mixing sand, soda (which acts as a flux) and limestone
We heat this mixture to 1400'C; it then melts tn form a paste
Mould blowing
We put the paste into a hollow mould which has the shape of the object we want to make
We close the mould and inject
compressed air, causing the paste to adhere
to the sides of the mould
When the mould is completely cooled, iyig
we remove the obiect
Float glass making
We float molten glass on top of a layer of molten tin
The glass spreads to form a sheet that we pass through a system of rollers
Weleave it cool
Lamination
We pass the soft material through a system of rollers The roflers can be smooth, or engraved to create a design on the glas