MODIFICATION TECHNIQUES

• Modifications techniques use tools and machines to make changes to prefabricated materials, such as sheets, bars or mouldings.
• Examples of these techniques include: measuring→marking→cutting→drilling→filing and sanding→joining
• You must always pay special attention to health and safety rules

PLASTING FORMING TECHNIQUES

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

THE CLASSIFICATION OF PLASTICS

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

1. Polyethylene terephthalate (PET)
2. High-density polyethylene
3. Polyvinyl chloride (PVC)
4. Low-density polyethylene
5. Polypropylene
6. Moulced polystyrene
7. Expanded polystyrene or Styrofoam

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

1. Polyurethane
2. Bakelite
3. Melamine
4. Polyester reisns

• Typical elastomers includ rubber and neoprene

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 mechanical recycling and energy recovery.

ELECTROMAGNETIC CONTROL SYSTEM
An electromagnetic control system activates the various parts of a machine, at the right moment and for the right amount of time, ensuring that the machine functions properly.
Electromagnetic control systems often use cams and limit switches.

CAM SWITCH CONTROLLER
A camshaft is a cylindrical device with protrusions that make contact with other devices in order to activate or desactivate them.
The shape of a cam allows us to  control the moment and duration of an activity, such us the running of a motor or the illumination of a light bulb.

LIMIT SWITCHES
A limit switch detects when preassure is being applied to it. There are two types of limit switch: NORMALLY CLOSED (N/C) and NORMALLY OPENED (N/O)

EFFECTS OF ELECTRIC CURRENT

Heat

The energy that an electric current produces in the form of heat is called the Joule Effect. It is expressed by the following formula:

                                     E=I2xRxt

Light
There are varioues 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 phenomenon is called a light-emitting diode (LED)

Fluorescent tubes
Inside a fluorescent tube, there is a metallic filament. There is also an inert gas, and a small amount of mercury. When an electric current passes trough the filament , electrons are emitted into the inert gas. This react with the mercury, creating ultraviolet light. Then the phosphor coating insisde the tube transforms the ultraviolet light into visible light.

Light emitting diodes (LED)
A LED has layers of of semiconductor materials. When electricity is applied to the LED, the electrons and holes cross over into the active layer, where they combine and produce photos, or particles of lights.

Electromagnetic effect
The scientist Michael Faraday discovered the opposite effect . He noticed that electricity could be generated by using a magnet and an electrical conductor. This principle allows us to build dynamos and alternators. Electromagnets use electric current to create magnetic fields.

Sound
We can transform electric current into sound by using electromechanical devices, such as bells and buzzers. The piezoelectric effect lets us use electricicty to produce sounds.