UNIT 3: Plastics and textiles.

PLASTIC MATERIALS.

▪ Plastics consist of long chains of atoms which are mostly composed of carbon.
▪ Plastics can be classified into natural and synthetic plastics.
▪ The process of manufacturing plastic is called polymerisation.
▪ Plastic materials are resistant, insulating (against electricity, heat and sound) , ductile, maleable, impermeable and light.
▪ There are three types of plastic recycling processes: chemical and mechanical recycling and energy recovery.

THE CLASSIFICATION OF PLASTICS.

▪ Thermoplastics are ussually made from petroleum products. The most common thermoplastics are:

∙ Polyethylene terephthalate (PET)
∙ High- density polyethylene.
∙ Polyvinyl chloride (PVC)
∙ Low density polyethylene.
∙ Polypropylene.
∙ Moulded polystyrene.
∙ Expanded polystyrene or Styrofoam.

▪ Thermosetting plastics are made from petroleum products. They include:

∙ Polyurethane.
∙ Bakelite.
∙ Melamine.
∙ Polyester resins.

▪ Typical elastomers include rubber and neoprene.

PLASTIC FORMING TECHNIQUES.

▪ Various industrial techniques can be used to manufacture plastic, products, such as: extrusión , calendering, vacuum forming and moulding.
▪ The main techniques for using moulds are as follows: blow moulding, injection moulding and compression moulding.



MODIFICATION TECHNIQUES.

▪ Modification techniques use tolos and machines to make changes to prefabricated materials, such as sheets, bars or mouldings.
▪ Examples of these techniques include: measuring➡ drawing marks and lines ➡ cutting ➡ drilling ➡ filling and sanding ➡ joining.
▪ You must always pay special attention to health and safety rules.

TEXTILES.

▪ Both natural and synthetic fibres can be woven to make a variety of textiles.
▪ Natural fibres may come from animal sources (wool, silk), plant sources (cotton, linen, esparto, bamboo) and mineral sources ( gold, silver and cooper fibres).
▪ Synthetic fibres, such as nylon, polyester, rayon and Lycra, are plastic materials.

Basic devices made with electronic components.

Electronic components are usually used to build devices:

TIMERS.

It is a device that operates for a period of time and shuts itself off automatically. A timer works in a circuit by that way:

∎At first, when we push the button, a current flows and pass through the base of the transistor, and then the LED turns on. The capacitor begins to store electric current.
∎When we reléase the button, the LED stills on for a period of time, using current from the capacitor. Finally, when there isn´t more current in the capacitor, the transistor cuts off and the LED turns off.

INTEGRATED CIRCUITS.

They consist of miniature electronic components, for example capacitors, transistors and resistors.

Transistors.

They are made from semiconductor materials and have three electrodes caled the base, the collector and the emitter. There are two types:

Each electrode is connected to a semiconductor material which releases electrons or acceps electrons.
I'm going to explain how transistors work:

⇒When there aren't electrons through the base, electrons cant pass from the collector to the emitter. This phase is called cut off.

⇒When electrons are passing through the base, electrons can pass from the collector and the emitter.
This phase is called saturation.

⇒When the flow of electrons is between cut off and saturation, the flow of electrons between the collector and the emitter is proportional. This phase is called active región.

Transistors are the basisc components of the microprocessors and memory circuits that are used in computers. This is called a transistor gain.

Electronics.

They involve the study of circuits and components that modify the intensity, direction or properties of electric currents.

ELECTRONIC COMPONENTS.

We will analyse the most usual electronic components.

Fixed resistance or resistor.

It opposes the low of an electric current and its value is indicated by a code of colours and numbers, and we measure it in ohms.
The code of colours and numbers is form by four stripes. The first two sripes are replaced by their number according to their color. The third stripe is replaced by the number of zeros that we ave to add to the previous number, according its color. The last stripe means the tolerance or the máximum deviation from the complete value.

Potentiometer.

Variable resistance or potentiometer.

Potentiometers can adjuste the value between zero and the máximum value specified by the manufacturer.

Resistance that depends on a physical factor.

There are two physical factors that can affect the resistance; temperature and the amount of light.

🔷Thermisors are the resistances that depends on the temperature. There are two types:

➖NTC (Negative temperature coefficient) : When the temperature rises, the resistance decreases.
➖PTC (Positive temperature coefficient) : When the temperature rises, the resistance increases.

🔷 LDR: These device are often used in security systems like sensors. The resistance varies according to the amount of light received. If the resistance decreases as the amount of light increases.

Thermistors.                                                                                LDR

CAPACITORS.

Capacitors are components that can store an electric charge and its value indicates the charge  in volts hat it can store. This is measured in farads.

Is necesary have precaution with this type of component.

Real capacitor.                                                                                   Capacitor symbol.

DIODES.

They are electronic components made of semiconductor materials and they can only allows eletric curent to flow in one direction. A diode is form by an anode and a cathode.

A LED only gives off light when an electric current flows through it.

Electromagnetic control systems.

At the right momento and for the right amount of time, an electromagnetic control system ensuring that the machine functions properly.

CAM SWITCH CONTROLLER.

This device allows us to control he moment and the duration of an activity such as the illumination of a light bulb.

LIMIT SWITCHES.

Limit switches are devices that detect the pressure when is being aplied to it.

Electromagnetic mechanisms.

They are devices that convert movement into electricity or vice versa using the electromagnetic phenomena.

ELECTROMAGNETIC GENERATORS.

This generators transfom mechanical energy into electricity. There are two types:

∎Dynamos, that produce direct current.
∎Alternators, that produce alternating current.

Dynamos.

 A dynamo is form by a magnet and a rotary coal located between the poles of the magnet. The commutator are two semi-circular conductors ,located in the end of the coil, attached to carbon brushes which in turn are connected to electrical wires. The coil generates direct current when electricity is applied.
The dynamos produce a pulsating direct current when they have only a coil, but if the dynamo has two or more coils it produces a constant flow of direct current.

DIAGRAM OF A DYNAMO.

Alternators.

A simple alternator is make up equal to a dynamo, except that the current is alternating and  the commutator is form by two metallic rings connected to carbon brushes.

DIAGRAM OF AN ALTERNATOR.

ELECTRIC MOTORS.

They transform electrical energy into movement using the forces of attraction and repulsion between a magnet and an electrically-charged wire.

RELAYS.

RELAY.

It is an electromagnetic component that act like a magnet attracting a moveable metal when electricity passes through the coil, and it contact towards another fixed contact . The moveable metal goes back to its original position whe electricity stops flowing.

DIAGRAM OF A RELAY.                                            RELAY.

When relays may also have two or four cicuits they are called two- or four-pole relays

Effects of electric current.

In conductive materials, the movement of electrons have useful applications.


HEAT.

When the movement of electrons is both slow and disorderly, and they often collide, the temperature increases of the cable itself.
The energy as heat produces by an electric current is called the Joule Effect, that is expressed as: E= I (square) x R x t.
The energy consumed by radiators and heaters is converted into heat.

LIGHT.

There are various forms that electricity can be used to produced light:

Incandescent bulbs.

We can produce light when in a metallic filament of a light bulb  passes an electric current. It is called incandescence.

Fluorescent tubes.

They have a metallic filament made of tungsten, and it has inside too and inert gas and a small amount of mercury. When an electric current passes through it , electrons are emitted into the inert gas. This react produces ultraviolet gas , and after phosphor coating inside the tbe transforms it into visible light.
But this type of tubes contain toxic substances, such as mercury.

Light-emitting diodes (LED)

A light-emitting diodes has layers of semiconductor materials, and it can have a n-type layer with negative charge and a p-type layer with ot enough electrons. When electricity is applied to the LED, this whole electrons cross into the active plaer, whre they produce particles of light.

INCANDESCENT BULB                FLUORESCENT  TUBE           LIGHT EMITING DIODE (LED)

ELECTROMAGNETIC EFFECTS.

The discovery maked by Michael Faraday tell us that electricity could be generated by using a magnet and an electrical conductor. It allows us to build dynamos and alternators. Magnetic fields are created thanks to the electric current produced by electromagnets.

SOUND.

Bells and buzzers help us to transform an electric current into sound. These devices are based on the piezoelectric effect that changes their shapes when we applied electricity to them.

BELL, BUZZER.

MICHAEL FARADAY