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1、Chapter 2 Plastics,2.1 Introduction,2.1.1 Plastics are polymers,Plastics A category of polymer They are plastic (non elastic),Properties of Plastics,Strength, Tensile strength, Tensile Modulus, Flexural Strength, Flexural Modulus,Toughness, Impact resistance, Environmental Stress Crack,Thermo Proper
2、ties, Deformation Temperature, Decomposition Temperature, Melting Point, Glass Transition Temperature,Other Properties, Electrical Properties, Chemical Resistance, Abrasion Properties,Engineering Plastics and Civil Plastics,Engineering Plastics, High Strength, Good Toughness, Good Thermo properties,
3、Examples of Engineering Plastics, PA PA6 PA66, PC, PP Modified PP, ABS, POM,Civil Plastics (Common Plastics) PP, PE, PVC, ABS, PS,2.1.2 History of Plastics Development,Parkes invents first man-made plastic,In 1862,Celluloid makes its debut,John Wesley Hyatt In 1866,Leo Baekeland in 1907 invented fir
4、st thermosetting plastics called “Bakelite”,Rayon and cellophane Louis Marie Hilaire Bernigaut 1891 in Paris and Dr Jacque Edwin Branbendenberger in 1900,The Discovery of Nylon,Wallace Hume Carothers of Dupont,PVC, Saran, and Teflon,Waldo Semon, of Goodrich discovered PVC,Ralph Wiley of Dow Chemistr
5、y discovered PVDC (Saran) in 1933,A DuPont chemist named Roy Plunkett discovered Teflon, in 1938.,Polyethylene,E.W. Fawcett and R.O. Gibson of Imperial Chemical Industries Research Lab,Plastics in modern life,“Plastics are inseparable with our modern life”“Without plastics, we cant imagine our moder
6、n life”,Plastics are used in various domains of industry and our daily lifeMachine, Auto Computer, Electric device,The applications of plastics are growing rapidly,2.1.3 Additives of plastics,The major additives include: Antioxidants, Filler, Plasticizers, Flame retardants, Colorants, Foaming agents
7、.,2.1.4 Classification of plastics,Plastics can be separated into two different groups depending on their behavior when heated. Thermoplastics and thermosetting plastics,Thermoplastics,Thermosets (Thermosetting Plastics),2.1.5 Plastics characteristics,a) Light weight in comparison to metal, glass,b)
8、 Good insulator of heat and electricity,c) Good chemical resistance,d) Multiple processing capabilities to produce complicated parts with precision,2.1.6 Plastics processing,Injection molding,Extrusion,Compression molding,Transfer molding,Blow molding,Thermoforming, rotational molding and blown film
9、, cast film, calendering,2.1.6.1 Injection molding,1) Injection unit,2) Clamp unit,3) Machine control,Figure 2-1 Diagram of injection molding,Injection Unit:,Hopper,Rotating screw or plug,Barrel with heater,Shuttle,Clamp unit:,1) Facilitate mold closure against injection pressure,2) Removal of molde
10、d parts,Two types of clamp unit are used: Hydraulic clamps, Toggle clamps.,Machine control,Injection Molding Cycle:,Starting with an empty cylinder, plastic pellets are fed from the hopper onto the rear zone of the screw. With backward movement of screw the material is plasticised with the applicati
11、on of heat from band heaters.,2. The mold closes and the injection unit moves forward until the nozzle touches the mold.,3. The screw is moved forward by the hydraulic cylinder at the rear of the machine and the injection takes place.,4. After a short while, the screw rotates to prepare the next sho
12、t of plasticized material.,5. The mold opens, the article is ejected and the mold closes for the next shot.,2.1.6.2 Extrusion,Application of extrusion, Pipe, Wire and cable, Profile, Polymer filling and blending, Polymer reinforcement,Single screw extruder Parameters: (1) Diameter of the screw (2) L
13、ength/diameter ratio (L/D) (3) Angle of the screw (4) Ratio of compression,Screw is generally divided in to three sections (1) Transportation (2) Compression or melting (3) Measuring,Transportation Characteristics: Screw deep and invariable Function: Transportation and preheat of materials Principle
14、: Fraction,(2) Compression Characteristics: Screw becoming shallow Function: Compression and melting Source of heat: Heater and shear,(3) Pumping Characteristics: Screw shallow and invariable Function: mixing and pumpingPrinciple: screw pump,Screen: Function: (1) Filtration of solid impurity (2) Cha
15、nging the flow from spiral to linear,Die Function: Shaping,Principle: High viscosity of molten materials,Multiple-screw extruder,(1) Twin-screw extruder Parallel twin-screw extruder Taper twin-screw extruder,(2) Two-screw extruder (3) Three-screw extruder,Application of Multiple-screw extruder, Fill
16、ing of the polymers, Polymer blends, Polymer reinforcement,2.1.6.3 Blow molding,Extrusion blow molding:,(1) Extrusion of the preform or parison (hollow plastic tube),(2) Closing of two mold halves on the parison, clamping the mold and cutting the parison from the top with a knife/hot wire,(3) Introduction of air to blow the parison to the shape of the mold cavity and simultaneous cooling of the mold and the blown part,(4) Opening the mold to remove the blown part,
