PLASTICS AND TEXTILES

KEY CONCEPTS:

PLASTIC MATERIALS

+Plastics consist of long chains of atoms wich are mostly composed of carbon.

+Plastics can be classified into natural and synthetic plastics.

+The process of manufacturing plastic is called polymerisation.

+Plastic material are resistant, insulating ( against electricity, heat and sound), ductile,malleable, impermeable and light.

+There are three types of plastic recycling processes: chemical and mechanicalrecycling and energy recovery.

THE CLASSIFICATION OF PLASTICS

+Thermoplastics are usually 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: estrusion, calendaring, 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 tools and machines to make changes to prefabricated materials, such as sheets, bars or mouldings.

+Examples of these techniques include: measuring  drawing marks ad lines  cutting  drilling  filing 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 copper fibres).

+Synthetic fibres, such as nylon, poliester, rayon and Lycra, are plastic materials.

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



electronic components
 in the section, we will analyse the most common electronic components.

fixed resistance or resistor
 opposes the flow of electric currents. its value which we measure in ohms, is indicated by a code of colours and numbers.

variable resistance or potentiometer
what the difference between a potentiometer and a variable resistor
A variable resistor is made up of a potentiometer wired with the center leg tied to one or the other end of the pot. This permits it to act like a variable resistor.

resistance that depends os a physical factor
There are four factors that influence the resistance in a conductor. Thickness, length, and temperature. The fourth factor is the conductivity of the material that is used. Some metals (copper, silver) are just more electrically conductive than others (iron, aluminum)

capacitors
are components that can store an electrical charge (the value of capacitor indicates the charge in volts that it can store -- farads)

diodes
diode is a two-terminal electronic component that conducts primarily in one direction; it has low (ideally zero) resistance to the current in one direction, and high (ideally infinite) resistance in the other.


transistors
A transistor is a semiconductor device used
to amplify or switch electronic signals and electrical power
(they are made from the base, the collector and the emitter)

ELECTROMAGNETIC CONTROL SYSTEM
An electromagnetic control system activates the various parts of a machined, at the right moment and for the right amount of time, ensuring that the machine functions properly.


CAM SWITCH CONTROLLER
Cam limit switches are used to convert a mechanical motion into an electrical control signal for automatic controls for positioning and for end of limit travel switching onto mechanical side as actuators.


LIMIT SWITCHES
Limit switch is a switch operated by the motion of a machine part or presence of an object. A limit switch is an electromechanical device that consists of an actuator mechanically linked to a set of contacts.

SOUND
we can transform electric current into sound by using electromechanical devices, such as bells and buzzers.


ELECTROMAGNETIC MECHANISMS
Are devices that can convert movement into electricity or vice versa.

ELECTROMAGNETIC GENERATORS 
Transform mechanical energy into electricity:

Dynamos
A dynamos consist of a magnet and a rotary coil. The coil is located between the two poles of the magnet. The ends of the coil have tow semi-circulaar conductors, which form the commutator. These conductors are attached to carbon brushes, which in turn are conected to electrical wires. When electricty is applied to the coil, it rotaters and begins to generate direct current in the coil.



Alternators
A simple alternator is almost identical to a dynamo, except for the commutator, which consist of two metallic rings connected to carbon brushes, Instead of direct current, this produces altenating current.


ELECTRIC MOTORS
An electric motor is a device that can transform electrical energy into movement. It uses the forces of attraction and repulsion between a magnet and an electrically-charged wire.


RELAYS
A relay is an elctromagnetic component that works as a switch. When electricity passes through the coil, it acts like a magnet. The coil attracts a moveable metal contact towards another fixed contact. When the electricity stops flowing, the moveable contact goes back to its original position.

ELECTROMAGNETIC EFFECTS
The magnetic field is a effect can be used to produce movement, for example in electric motors, relays and other devices. 
The scientist Michael Faraday discovered the opposite effect. The most common are dynamos and alternators.

Types of current
Direct current
Between the terminals of a battery, there is a continuos, stable flow of energy. If we use a voltmeter to measure the current in a car battery, the result will always be 12 volt. This is called direct current.--

Alterneting current
 Alternating current occurs when charge carriers in a conductor or semiconductor periodically reverse their direction of movement.
The variation of any electrical parameter over a period of time (in this case the electric current) is an electric signal.
The tension or voltage of domestic electricity is analternating signal because it alternates between positive and negative values. Its waveform is alsosinusoidal, with a smooth, regular shape.--


The efficiency of alterning current
The average power of alternating current is equal to the direct current that is needed to produce the same effect. In the case of an alternating sinusoidal current, the average power would be as follow: Vef = Vmax /√2 
 

Transformers
Transformers consist of two windings made of copper wire.
If we apply an alternating current to one of them (V1), it will
produce a certain voltage in the other (V2) The value will 
depend on the number of times that the copper  wire has 
been wrapped around each winding, represented as n1 and 
n2:  V1/V2 = n1/n2

EFFECTS OF ELECTRIC CURRENT

The movements of electrons though conductive
materials produces effects that have useful
application.

HEAT:The energy that an electric current 
produces as heat is called the Joule Effect.
Formula: E=|x|xRxt


LIGH:
There are various ways that electricity
can be used to produce ligh.


Incandescent bulbs: When an electric current
passes through the metallic filament of a 
light bulbs, it produces light.


Fluorescent tubes: There is a metallic 
filament, normally made of tungsten.
An electric current in the gas excites mercury vapor which produces short-wave ultraviolet light that then causes a phosphor coating on the inside of the lamp to glow.


Light-emitting diode(LED):is a semiconductor device that emits visible light when an electric current passes through it. The light is not particularly bright, but in most LEDs it is monochromatic, occurring at a single wavelength.