- 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, insultating, ductile, malleable, impermeable and light.
- There are three types of plastic recycling processes: chemical and mechanical recycling and energy recovery.
- 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
· Polyester resins
- Typical elastomers include rubber and neoprene
- Various industrial techniques can be manufacture plastic products, such as: extrusion, calendering, vacuum forming and moulding.
- The main techniques for using moulds are as follows: blow moulding, injection moulding and compression moulding.
- Modification techniques use tools and machines to make changes to prefabricated materials, such as sheets, bars or muldings.
- Examples of these techniques include: measuring, drawing marks and lines, cutting, drilling, filing and sanding and joining.
- You must always pay special attention to health and safety rules.
- 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, polyester, rayon and Lycra, are plastic materials.
Saturday, 27 May 2017
Thursday, 27 April 2017
ELECTRONIC COMPONENTS
- Resistor.
Opposes the flow of electric currents, which we measure in ohms, is indicated by a code of colours and numbers.
Opposes the flow of electric currents, which we measure in ohms, is indicated by a code of colours and numbers.
- Variable resistance.
The value of a variable resistance can be adjusted between zero and the maximum value specified by the manufacturer.
- Resistance that depends on a physical factor.
· Depends on temperature is called a thermistor:
Negative temperature coefficient (NTC): the resistance decreases.
Positive temperature coefficient (PTC): the resistance increases.
· LDR: the resistance varies according to the amount light received. Decreases as the amount of light increases.
- Capacitors.
Are components that can store an electrical change. The value of a capacitor indicates the change volts that it can store. This is measured in farads (F).
- Diodes.
It allows electric current flow in one direction. A diode has two electrodes: an anode (A) and a cathode (K).
A LED only gives off light when an electric current flows through it. Diode symbol:
ELECTROMAGNETIC CONTROL SYSTEMS
An electromagnetic control system activates parts of a machine, at the right moment and for the right amount of time, ensuringthat the machine functions properly.
- Cam swith controller.
The shape of a cam control the moment and duration of an activity, for example, the light of a bulb.
- Limit switches.
The battery provides power for the pump, which moves water from the lower tank to the upper tank. The limit switch is activated when the upper tank is full and the float rises to a certain level.
- Cam swith controller.
The shape of a cam control the moment and duration of an activity, for example, the light of a bulb.
- Limit switches.
The battery provides power for the pump, which moves water from the lower tank to the upper tank. The limit switch is activated when the upper tank is full and the float rises to a certain level.
Wednesday, 12 April 2017
ELECTROMAGNETIC MECHANISMS
Electromagnetic mechanisms convert movement into electricity or vice versa.
- Electromagnetic generators.
Transform mechacical energy into electricity. There are two types of generators, depending on the type of current that is produced:
· Dynamos: consists of a magnet and a rotary coil. The coil is located between the poles of the magnet. The coil have two semi-circular conductors, which form th conmutator. The electricity applied generate direct current.
· Alternator: is identical to a dynamo, except for the conmutator, which consists of two metallic rings connected to carbon brushes. This produces alternating current.
- Electric motors.
Transform electrical energy into movement. Use forces of attraction and repulsion.
- Relays.
A relay is an electromagnetic component that works as a switch. When the electricity stops flowing, the moveable contact goes back to its original position.
- Electromagnetic generators.
Transform mechacical energy into electricity. There are two types of generators, depending on the type of current that is produced:
· Dynamos: consists of a magnet and a rotary coil. The coil is located between the poles of the magnet. The coil have two semi-circular conductors, which form th conmutator. The electricity applied generate direct current.
· Alternator: is identical to a dynamo, except for the conmutator, which consists of two metallic rings connected to carbon brushes. This produces alternating current.
- Electric motors.
Transform electrical energy into movement. Use forces of attraction and repulsion.
- Relays.
A relay is an electromagnetic component that works as a switch. When the electricity stops flowing, the moveable contact goes back to its original position.
Saturday, 1 April 2017
EFFECTS OF ELECTRIC CURRENT
- Heat.
The movement of electrons through an electrical cable is both slow and disorderly, the electrons often collide, increasing the temperature of the cable itself.
The energy that produces as heat is called th Joule Effect: E = I2 x R x t
- Light.
There are various ways that electricity can be used to produce light :
· Incandescent bulbs: when an electric current passes through the metallic filament of a light bulb, it produces light. This is called incandescence.
· Fluorescent tubes: the electric current passes through the filament, electrons are emitted into the inert gas, these react with the mercury, creating invisible, ultraviolet light.
· Light-emitting diodes (LED): a LED has layers of semiconductor materials. When electricity is applied to the LED, the electrons and holes cross over into the active layer, where they combine produce particles of light.
- Electromagnetic effects.
The scientist Michael Faraday noticed that electricity could be generated by using a magnet and an electrical conductor. This principle allows os to build dynamos and alternators.
- Sound.
We use bells and buzzers to transform electric current into sound.
The movement of electrons through an electrical cable is both slow and disorderly, the electrons often collide, increasing the temperature of the cable itself.
The energy that produces as heat is called th Joule Effect: E = I2 x R x t
- Light.
There are various ways that electricity can be used to produce light :
· Incandescent bulbs: when an electric current passes through the metallic filament of a light bulb, it produces light. This is called incandescence.
· Fluorescent tubes: the electric current passes through the filament, electrons are emitted into the inert gas, these react with the mercury, creating invisible, ultraviolet light.
· Light-emitting diodes (LED): a LED has layers of semiconductor materials. When electricity is applied to the LED, the electrons and holes cross over into the active layer, where they combine produce particles of light.
- Electromagnetic effects.
The scientist Michael Faraday noticed that electricity could be generated by using a magnet and an electrical conductor. This principle allows os to build dynamos and alternators.
- Sound.
We use bells and buzzers to transform electric current into sound.
Saturday, 25 March 2017
TYPES OF CURRENT
- Direct current.
Between the terminals of a battery, there is a continuous, stable flow of energy. This is called direct current.
- Alternating current.
The variation of any electrical parameter over a period of time is an electric signal. The tension or voltage of domestic electricity is an alternating signal because it alternates between positive and negative values. Alternating current is produced by generators, such as the ones in large electrical generating stations.
- The efficiency of alternating current.
The average power of alternating current is equal to the direct current that is needed to produce the same effect.
- Transformers.
Transformers consist of two windings made a cooper wire. If we apply an alternating current to one of them, it will produce a certain voltage in the other. The value will depend on the number of times that the cooper wire has been wrapped around each winding.
Between the terminals of a battery, there is a continuous, stable flow of energy. This is called direct current.
- Alternating current.
The variation of any electrical parameter over a period of time is an electric signal. The tension or voltage of domestic electricity is an alternating signal because it alternates between positive and negative values. Alternating current is produced by generators, such as the ones in large electrical generating stations.
- The efficiency of alternating current.
The average power of alternating current is equal to the direct current that is needed to produce the same effect.
- Transformers.
Transformers consist of two windings made a cooper wire. If we apply an alternating current to one of them, it will produce a certain voltage in the other. The value will depend on the number of times that the cooper wire has been wrapped around each winding.
TYPES OF CIRCUITS
- Series circuit.
In a series circuit the current flows through all the elements. The total voltage is the sum of the tensions at the end of each element.
To calculate the total resistance of a circuit, we add the resistance values.
- Parallel circuit.
In a parallel circuit, the various components share the same input and output. If identical batteries are connected in parallel, the voltage of the circuit will not increase.
- Combination circuit.
A combination circuit has some elements connected in series and other elements connected in parallel.
The current remains constant between elements that are connected in series, at the same time, the voltage remains constant between elements that are connected in parallel.
In a series circuit the current flows through all the elements. The total voltage is the sum of the tensions at the end of each element.
To calculate the total resistance of a circuit, we add the resistance values.
- Parallel circuit.
In a parallel circuit, the various components share the same input and output. If identical batteries are connected in parallel, the voltage of the circuit will not increase.
- Combination circuit.
A combination circuit has some elements connected in series and other elements connected in parallel.
The current remains constant between elements that are connected in series, at the same time, the voltage remains constant between elements that are connected in parallel.
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