Key Concepts: Plastics and textiles.

1. Plastic Materials.

• Plastics consist of long chains of atons which are mostly composed of carbon.

• Plasticscan be classifield into natural and synthetic plastics

• Plastic materials are resistant, insulation (against electricity, heat and sound) ductile, malleable, impermeable and ligth.

• There are three types of plastics recycling processes: chemical and mechanical recycling and energy recovery.

2. The Clasification of Plastics.

• Thermoplastics are usually made from petroleum products. The most common theroplastics are:

- Polyethylene terephalate (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

- Melanine

- Polyester resins

• Typical elastomers include rubber and neoprene

3. Plastics Forming Techniques.

• Various industrial techniques can be used to manufacture plastics products, such as: Extrusion, calendaring, vacuum forming and moulding.

• The main techniques for using moulds are as follows: blow, moulding and compresion moulding.

4. 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 and lines, cutting, drilling, filing and sanding joining.

• You must always pay special attention to health and safety rules.

5. Textiles

• Both natural and syntheetic fibres can be woven to make a variety of textiles

• Natural fibres may come from animal sources (wool, silk), plant sources (cotton, line, esparto, bamboo) and mineral sources (gold, silver, and copper fibre)

8 ELECTRONICS

8.1 Electronic components

• Fixed resistance or resistor:

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

• Variable resistance or potentiometer

The value of a variable resistance or potentiometer can be adjusted between zero and the maximum value specified by the manufactured.

• Resistance that dependes on a physical factor

The physical factors that affect resistance may be temperature or the amount of ligtht, for example.

Resistance that depends on temperature is called a thermistor.

• Negative temperature coefficient (NTC): The resistance decreases as the temperate rises.
• Positive temperature coefficient (PTC): The resistance increases as the temperaature rises.

LDR: resistance thatvaries according to the amount of ligth received. The resistance decreases as the amount of ligth increases.

• Capacitors

Capacitors are componets that can store an electrical charge. The value of a capacitors indicates the charge in volts that it can store. This is measured in farads (F)

• Diodes

A diode is an electronic component made from semiconductor materials. A diode has two electrodes: an anode (A) and a cathode (K)

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

7.ELECTROMAGNETIC CONTROL SYSTEMS

An electromagnetic control systems activates the various parts of a machine, at the rightmoment and for the rigth amount of time, ensuring that the machine funtions properly.

7.1 Cam switch controller

The device on the side of the pulley in the picture above is called a cam. The shape of this deviceallows us to control the moment and duration of an activity, such as the running or the motor or the illumination of a ligth bulb.

7.2 Limit switches

The picture below shows an electrical control system for a water tank. The battery provides power for the pump, which moves water from the lower tank to the upper tank. When the upper tank is full, a limit switch turns off the pump.

6.0 (2)ELECTROMAGNETIC MECHANISMS

6.2 Electric Motor
An electric motor is a device that can transform electrical energy into movement. It uses the forces of atracction and repulsion between a magnet and an electricallycharged wire.

6.3 Relays
A relay is an electromagnetic component that works as a switch. When electricity passes through the coil, it acts like a magent. The coil attracts a moveable metal contact towards another fixed contact. When yhe electricity shops flowing, the moveable contact goes back to its original position.

6.ELECTROMAGNETIC MECHANISM

6.1 Electromagnetic Generators

Transform mechanical energy into electricity. There are two types of generators, depending on the type of current that is produce. Direct current called dynamos, and produce alternating current are called alternators.

Dynamos:

Consists of a magnet and rotary coil. the coil is located between the two poles of the magnet.
The ends of the coil have two semi.circular conductor, wich form communator.

Alternators:

Is almost identical to a dynamo, exept for the commutator, which consists of two metallic rings connected to carbon brushes. Produce alternating current.

5.1 EFFECTS OF ELECTRIC CURRENT

5.3 Electromagnetic effects.

The scientis Michael Faraday discouvert the opposite effect. He noticed that electricity could be generated by using a magnet and an electrictical conductor this principle allows us to build dynamos and alternators.

5.4 Sound
we can transform the electric current into suond(bells, buzzers). This is based on the piezoelectric effect.

5.EFFECTS OF ELECTRIC CURRENT

5.1 Heat

The energy that an electric current produces as heat is called the Joule Effect. It is expressed by the following formula:  E= I2 x R v t

5.1 Light

There are various ways that electricity can be used to produce ligth.

Incandescent bulbs: When an electric current passes through the metalic filament of a ligth bulb, it produces ligth.

Fluorescent tubes. Inside fluorescent tubes, there is a metallic, normaly made of tungsten.
There is also an inert gas, such as argon, and a small amount of mercury. When an electric current passes through the filament, electrons are emited into inert gas.
Unfortunated, flourescent tubes contain a numbers of toxic substances, such as phosphor and mercury.