Please enable JavaScript.

Coggle requires JavaScript to display documents.

PLASTICS (1.3. Ecological properties (Chemical recycling. We apply…

- - - - Separation and crushing.
      - Floating
      - Agglutination
      - Extrusion
      - Pelletising
- - - - This technique has four stages;
        
        We put thermoplastic, in granular form, into a previously heated cylinder.
        
        We apply pressure by means of a large, rotating screw, which forces the melted material out, through a nozzle.
        
        We cool the shaped material slowly in a refrigerated water bath until lt's solid.
        
        Finally, we collect the pieces of plastic through a feeder system.
    - - Thermoplastic produced by the extrusion method is passed through a series of hot cylinders to produce sheets of varying thickness. With this technique, we can produce different finishes, for example, glossy, matt or textured. This depends on the outer coating applied by the final cylinder.
    - - We use plastic sheets with a large surface for this technique
        1. We put thermoplastic into a mould.
        
        We then use a heater to heat the mould and soften the plastic.
        3.We extract the air below the sheet so that the plastic is pulled against the inside walls of the shaped mould, and the desired form is created .
        
        We leave the mould to cool, then remove the object.
    - - There are three principal techniques:
        
        Injection moulding
        
        We inject melted thermoplastic into a mould
        2.When the material has cooled and solidified, we extract it from the mould.
        
        Blow moulding
        
        1.We put a tubular-shaped piece of plastic into a hollow mould which has the same shape as the object that we want to make
        
        We close the mould and blow pressurised air into it, so that the plastic adheres to the sides of the mould and takes its shape
        
        When the object is cold, we remove it from the mould.
        
        Compression
        
        We put thermostable plastic, which can be in granular form, into the base of a cavity mould.
        
        The outer part of the cavity mould, shaped the same, is closed to compress the material inside. We then heat it and it becomes soft and malleable.
        
        The plastic adapts to the shape of the cavity between the two parts of the mould.
        
        We extract the object when the plastic has cooled and solidified.
    - - We can use different tools and machines to finish the plastic objects that we have made.
        
        Principal techniques are cutting, perforating, trimming and filing.
        
        Cutting
        
        Cutter : To cut sheets of different thickness, depending on their hardness.
        
        Scissors: To cut soft, thin flexible sheets.
        
        Steel bit: To cut sheets less than 1 mm in thickness.
        
        Fretsaw: To cut soft, low density plastics. Can make straight, slanting and curved cuts.
        
        Jig saw: To cut very large sheets of plastic, and rigid plastics in general. Can make straight, slanting and curved cuts.
        
        Power press: To cut flat sheets of low density plastic. Makes simple objects by applying pressure.
        
        Hot metal thread trimmer: To cut sheets of soft thermoplastic.
        
        Perforating
        
        Drill bit: Tool that makes holes in plastics. Consists of inserting a long, thin, round and threaded piece of metal into the head of the machine that revolves at high speed for cutting holes.
        
        Trimming and filing
        
        A file has a rough surface. Used to finish the surfaces and edges of hard materials. A rasp has an even rougher surface, covered with "teeth". Used to finish the surfaces and edges of soft materials.
- - - - We can join and then separate objects with mechanical fasteners.
        
        Nut and bolt : Used to fasten two objects together. Nut used to tighten the bolt.
        
        Standard screw: Used to fasten two objects. Holes must be drilled first before the screw is inserted.
        
        Double ended screw : Each end of the screw can be inserted into one of a pair of objects.
    - - We use this type of joint when we don't want to separate or dismantle the pieces. We can use adhesives or soldering.
        
        Adhesives
        
        Main types:
        
        Resins with two components : liquid, high water resistance.
        
        Acrylic cement : liquid, used mainly with PVC and polystyrene.
        
        Contact adhesives : liquid, work instantly after applying to both surfaces , used with all types of plastics.
        
        Soldering
        
        Joining thermoplastics using heat and pressure.