PLASTICS

PLASTICS

1. WORKING WITH PLASTICS

   • Marking
     • You must protect the plastic if it's not already protected.
   • Joining by cohesion
     • Two pieces of plastic can be fused together by heating them or using solvents
   • Joining by adhesion
     • You can use special types of adhesives to join the plastic.
   • Cutting
     • if the sheets are thin, they can be cut bya cutter or pressing in one side and doing a pry on the other side.
   • Drilling
     • When the diammeter of a hole is done, you should do it by drilling, however, if the diammeter ys bigger than 6mm, it must first done with the drill untill the hole has 4mm and then, you must make it bigger with a file.
   • Mechanical joining
     • You can use rivets,screws,nuts and bolts to join plastic.
   • Sawing
     • with thicker sheets, cuts must be done with a saw, like with wood or metal.

2. PROPERTIES OF PLASTICS

   • Low melting point
   • Acustic insulator
   • Maleable
   • Thermal insulator
   • Low density
   • Resistant to breakage
   • Electrical insulator
   • Resistant to oxidation
   • Resistant to moisture
   • Very inexpensive
   • Easy to create and transform
   • Easy mouldable
   • Flexible

3. POLYMERS AND PLASTICS

   • Polymers are materials made of very large molecules, which are in turn made up of smaller molecules called monomers
   • Natural
     • They come from plant-based materials such as latex or cotton or they can also come from products of animal origin such as silk or casein.
   • Synthetic
     • Yhey are made up of mineral-based materials like petroleum or natural gas, we refer to this group as plastics.

4. TYPES OF PLASTICS

   • Thermostables
     • This type of plastics can only be heated and moulded once, as when they are reheated, they burn.
     • UF (urea formaldehyde)
     • UP (polyester resins)
     • PF (polyphenols)
     • Melamine
     • Bakelite
   • Thermoplastics
     • Plastics that when they are heated toa certain temperature, they can be moulded. An important characteristic is that even after cooling, they can be reheated to repeat the process as many times as desired
     • PP (polypropylene)
     • PS (polystyrene)
     • PET (polyethylene terephthalate)
     • PVC (polyvinyl chloride)
     • PE (polyethylene)
     • PC (polycarbonate)
     • TEFLON
   • Elastometers
     • Very flexible and they recover their shape and dimensions. They degrade easily with and cannot be re-melted.
     • Rubber
     • Neoprene

5. IDENTIFYING PLASTICS

   • Deppending on the type of plastic, they can have different properties and we can identify the type of plastic by testing the plastic

6. PLASTICS AND THE ENVIRONMENT

   • there are being some serius problems about pollution and non-biodegradable plasics whichpollute more and more the environment. To solve all this problems, we can use the law of the three R's.
   • Reduce
     • Only buy the things you need
   • Reuse
     • Reuse to generate less rubbish
   • Recycle
     • Recycle to make new objects.

7. FORMING PLASTICS

   • Blow moulding
     • It is done by blowing into a tube previously made by extrusion. As the tube is placed into a mould, the air cause it to adopt the shape of the mould.
   • Injection moulding
     • The melted plastic is injected into a chamber and pushed with a piston to a mould. It's used to make casings for kitchen appliances.
   • Extrusion
     • It's used with thermoplastics to obtain large objects. The plastic is introduced through a hopper into a worm and to a hot tube, then, it goes into a refigeration chamber.
   • Compression moulding
     • It's used with thermoset plastics. The plastic is placed into a mould and a counter mould. Using pressure and heat the plastic is melted and adopts the desired shape.
   • Vacuum forming
     • It's used with thermoplastic sheets that are heated and placed into a mould . When the vacuum is turned on, it forces the sheet to adapt to the shape of the mould.

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