PROCESSING OF PLASTIC COMPONENTS
- 1. UNIT-V PROCESSING OF PLASTIC COMPONENTS Types and characteristics of plastics - Moulding of thermoplastics - Principles and typical applications of : injection moulding - Plunger and screw machines - Compression moulding, Transfer Moulding - Typical industrial applications - introduction to blow moulding - Rotational moulding - Film blowing - Extrusion - Thermoforming - Bonding of Thermoplastics.
- 2. INTRODUCTION TO PLASTIC Plastic is a material consisting of any of a wide range of synthetic or semi-synthetic organic compounds that are malleable and therefore can be moulded into solid objects. Plasticity is the general property of all materials that involves permanent deformation without breaking. Polymers’ name is derived from their flexible and plastic properties.
- 3. POLYMERS & ITS CLASSIFICATION
- 4. Plastics are polymers where long chains of atoms are bonded to one another. A polymer is a substance composed of molecules with large molecular mass composed of repeating structural units, or monomers, connected by covalent chemical bonds. The word is derived from the Greek. Poly + mer = Polymer: Poly means many and Mer means units
- 5. Polymerization Process Polymerization, which means the linking of monomers to form polymers results from two kinds of chemical reaction called condensation and addition.
- 6. 1. Condensation Polymerization or Step-growth Polymerization Condensation Polymerization is a chemical reaction in which polymer is formed and a small molecule of by- product with a lower molecular weight is released. The by-product eliminated is called as condensate. The reaction can take place between two similar or different monomers. It is also called as step-growth polymerization
- 7. 2. Addition Polymerization or Chain Polymerization In addition polymerization, two or more molecules of monomers attach together to form a polymer. In this polymerization, there is no elimination of any molecule. It is a chain reaction and no by product is released.
- 8. TYPES OF PLASTICS 1. Thermoset or thermosetting plastics. They have non-linear structure of a thermoplastic polymer. Here the molecules are Cross linked together as shown in figure. Once cooled and hardened, these plastics retain their shapes and cannot return to their original form. They are hard and durable. Thermosets can be used for auto parts, aircraft parts and tires. Examples include polyurethanes, polyesters, epoxy resins and phenolic resins.
- 10. 2. Thermoplastics. They have linear structure of a thermoplastic polymer. Here the molecules are joined together in a series way as shown in figure. They are less rigid than thermosets, Thermoplastics can soften upon heating and return to their original form. They are easily moulded and extruded into films, fibers and packaging. Examples include polyethylene (PE), polypropylene (PP) and polyvinyl chloride (PVC).
- 12. Examples of Thermoset or Thermosetting Plastics 1. Polyurethane Plastics Polyurethane plastics belong to the group that can be thermosetting. Polyurethane is the only plastic which can be made in both rigid and flexible foams. The flexible polyurethane foam is used in mattresses, carpets, furniture etc. 2. Epoxy Epoxies are used in numerous ways. In combination with glass fibers it is capable of producing composites that are of high strength and that are heat resistant. This composite is typically used for filament wound rocket motor casings in missiles, in aircraft components, and in tanks, pipes, tooling jigs, 2 pressure vessels, and fixtures.
- 13. 3. Phenolic Phenolic plastics are thermosetting resins used in potting compounds, casting resins, and laminating resins. They can also be used for electrical purposes and are a popular binder for holding together plies of wood for plywood.
- 14. Thermosetting plastics Properties Uses Epoxy resin (Epoxide, ER) Good electrical insulator, hard, brittle unless reinforced, resists chemicals well. Used for casting and encapsulation, adhesives, bonding of other materials. Used for printed circuit boards (PCB’s) and surface coatings. Melamine formaldehyde (MF) Stiff, hard, strong, resists some chemicals and stains. Used for Laminating work surfaces, electrical insulation, tableware. Polyester resin (PR) Stiff, hard, brittle unless laminated, good electrical insulator resists chemicals well. Used for casting and encapsulation, bonding of other materials, car bodies, boats. Urea formaldehyde (UF) Stiff, hard, strong, brittle, good electrical insulator. Used for electrical fittings, handles and control knobs, adhesives. Phenol formaldehyde (PF, Bakelite) A colourless polymer - coloured with artificial pigments to produce a wide range of different colours. Used for dark coloured electrical fittings and parts for domestic appliances, bottle tops, kettle handles, saucepan handles.
- 15. Examples of Thermoplastics 1. Vinyl Plastics Vinyl plastics belong to the thermoplastic group. Vinyl plastics are the sub-polymers of vinyl derivatives. These are used in laminated safety glasses, flexible tubing, moulded products etc. 2. Polyacrylics Plastic Polyacrylics belong to the group of thermoplastics. Polyacrylics are transparent and decorative. Polyacrylics plastics can be shaped in any form like the windshields for airplane. 3. Polyvinyl Chloride Polyvinyl Chloride, commonly referred to as PVC or vinyl, was first invented in Germany around 1910.
- 16. 4. Polyethylene Terephthalate (PETE) PETE is one the most recycled plastic. It finds usage in various bottles like that of soda and cooking oil, etc. 5. High Density Polyethylene (HDPE) HDPE is generally used in detergent bottles and in milk jugs. 6. Polyvinyl Chloride (PVC) PVC is commonly used in plastic pipes, furniture, water bottles, liquid detergent jars etc. 7. Low Density Polyethylene (LDPE) LDPE finds its usage in dry cleaning bags, food storage containers etc. 8. Polypropylene (PP) PP is commonly used in bottle caps and drinking straws. 9. Polystyrene (PS) PS is used in cups, plastic tableware etc.
- 17. S.No Thermoplastic plastics Thermosetting plastics 1 Thermoplastic can be easily bent. Thermosetting plastics cannot be easily bent. If forced to bend, they will break. 2 Softens on heating Do not soften on heating 3 Can be moulded and reshaped Cannot be moulded and reshaped. 4 Expensive Cheaper 5 Recyclable Not recyclable 6 Soft and weak Hard and strong 7 It is used in making toys, combs and various containers. It is used in making handles of cooking utensils. 8 Example: Polythene and PVC Example: Bakelite and Melamine
- 18. Advantages of Plastics They are light in weight. They can be easily moulded and have excellent finishing. They possess very good strength, toughness and shock absorption capacity. Plastic are corrosion resistant and chemically inert. They have low thermal expansion, good thermal and electrical insulating property. Plastic is very good water resistant and possess good adhesiveness. Plastic is strong, good and cheap to produce. Plastic is a recycling process and it does not decompose.
- 19. Disadvantages of plastics: Plastic is a non-renewable resources. Plastic products take a long time to decompose. They are going to deform under load. Plastics Produces toxic fumes during burning process. The majority of the pollution found in the world’s oceans is plastic.
- 20. PLASTICS ADDITIVES AND FILLERS Additives Plastics products are made from the essential polymer mixed with a complex blend of materials known collectively as additives. Without additives, plastics would not work, but with them they can be made safer, cleaner, tougher and more colourful.
- 21. 1. Plasticizers For getting the required toughness and flexibility in plastic plasticizers are used. Example: Water, Organic solvents and resins 2. Catalyst They are used to increase the speed of polymerization process. They also called accelerators. 3. Dyes and Pigments For getting required colour in the plastics pigments are added in the process. 4. Initiators They are used to initiate the polymerization process Example: H2O is a common initiator
- 22. 5. Modifiers They are used to increase the mechanical properties of plastics such as strength, damping capacity, toughness, ductility, plasticity etc. 6. Lubricants They are used to reduce the fiction during processing. Example: Oils, Soaps and Waxes. 7. Flame Retardants They are added to increase the non-in flammability of the plastics Example: Compounds of chlorine, bromine and phosphorous.
- 23. 8. Solvents They are added to dissolving some fillers or plasticizers and helps to allow the processing in the fluid state. Example: Alcohol. 9. Elastomers It’s added to the plastics to enhance their elastic properties. 10. Stabilizers It’s assed to the plastics to retard the degradation of polymers.
- 24. Fillers It’s used to economize the quantity of polymers required and to vary the properties to some extent. The fillers are used to improve the strength and stability of the plastics. Example: Aluminum powders, carbon fiber, graphite Resin The liquid form of plastics are called resin
- 25. CHRACTERISTICS OF PLASTICS 1. Toughness or Tensile strength Plastics vary in their tensile strength from material to material. Plastics have much less toughness as compared to metals and alloys like steel. 2. Light Weight Plastics are much lighter in weight as compared to woods, metals, etc. 3. Chemical Reactivity Plastics are not affected by acids and alkaline. Natural polymers such as cotton, wool, etc are damaged by acids. 4. Appearance Transparent plastics material can be made they look like glass. Plastic can be coloured in any colour and given any shape and are used for making large variety of household products.
- 26. 5. Weather Resistance plastics are not biodegradable that is why, they do not change with weather unlike natural fibres like cotton, and wool. 6. Thermal Conductivity plastics are the bad conductors of heat. For this reason, the handles of the cooling utensils are made of plastic material. 7. Electrical Conductivity Plastics do not conduct electricity. This property of plastic is used for making electrical appliances like switches, irons, touches, bulb- holders etc. 8. Solubility in water There is no effect of water on plastics. They are insoluble in water. 9. Effect of Flame The plastics melt on bringing closer to flame.
- 27. TYPES OF PROCESSING OF PLASTICS 1. Moulding Process 2. Calendaring Process 3. Thermoforming Process 4. Casting Process 5. Fabrication Process
- 28. Moulding Processes a. Compression Moulding Process b. Transfer Moulding Process c. Injection Moulding Process d. Jet Moulding Extrusion Process
- 30. The part solidifies into a desired shape then the upper half of the die is removed to take out the part. The pressure used to compress is around 0.7-55 MPa and the temperature is somewhere around 120-200oC Application- Electrical switches fuse boxes, electrical equipment, microwave containers etc.
- 31. Advantages Low initial setup costs Fast setup time Capable of large size parts beyond the capacity of extrusion techniques Allows intricate parts Good surface finish (in general) Low rejections in products. Disadvantages Production speed is not up to injection moulding standards Limited largely to flat or moderately curved parts with no undercuts Less-than-ideal product consistency
- 33. Process in Transfer moulding The pre-heated, uncured moulding compound is placed in the transfer pot. A hydraulically powered plunger pushes the moulding compound through the sprue(s) into the preheated mould cavity. The mould remains closed until the material inside is cured (thermosets) or cooled (thermoplastics). The mould is split to free the product, with the help of the ejector pins. The flash and sprue material is trimmed off.
- 34. Advantages Product consistency better than compression moulding, allowing tighter tolerance and more intricate parts Production speed higher than compression moulding Fast setup time and lower setup costs than injection moulding Lower maintenance costs than injection moulding Ideal for plastic parts with metal inserts Disadvantages Wastes more material than compression moulding (scraps of thermosets are not re-useable). Production speed lower than injection moulding.
- 35. INJECTION MOULDING 1) RAM OR PLUNGER TYPE INJECTION MOULDING
- 36. 2) SCREW TYPE INJECTION MOULDING
- 37. Jet Moulding Extrusion Process
- 38. Working The powdered raw material, usually thermoplastic in the form of pellets, granules and powder, is fed into a hopper and carried along by a screw conveyor through the heating chamber The required shape is obtained through the die. A rotating screw carries the material forward and forces it out through the heated orifice of the die. The mould is suitably cooled by water or air blast and carried away by a running belt. The restricting effect of the die will build up a pressure until it is in a plastic state and can be extruded. The screw imparts both axial and rotary motions. Owing to continuous nature of process it is extensively used for producing long product & uniform cross-section such as rods, tubes and channels.
- 39. Calendaring Process (Plastic Sheet Making Process)
- 40. Calendaring is a continuous process involving the use of a series of heated rolls that are fed with a pre- compounded paste-like mass. As this paste-like mass passes through consecutive roll nips a continuous sheet is formed to an appropriate thickness. PVC, ABS and PS constitute the majority of calendared thermoplastics, although some grades of polyethylene and polypropylene are also used.
- 41. Thermoforming Process Thermoforming is a process of shaping flat thermoplastic sheet which includes two stages: softening the sheet by heating, followed by forming it in the mould cavity. Elastomers and Thermosets cannot be formed by the Thermoforming methods because of their cross linked structure – they do not soften when heated.
- 42. Thermoplastics which may be processed by the thermoforming method are: Polypropylene (PP) Polystyrene (PS) Polyvinyl Chloride (PVC) Low Density Polyethylene (LDPE) High Density Polyethylene (HDPE) Cellulose Acetate Polymethyl methacrylate (PMMA) Acrylonitrile-Butadiene-Styrene (ABS)
- 43. The following three methods of thermoforming are generally used Vacuum thermoforming Pressure forming Matched die forming
- 45. First stage : The plastic sheet is heated in a heater and it’s fixed in a clamp. Second stage: Now the heated sheet place on die where the air between sheet and mould is removed. Third stage : By increasing the intensity of vacuum draws the sheet against the surface of the mould where it cools and solidifies. Then the part is ejected from the mould cavity.
- 46. Advantages Good surface finishes obtained (texture, branding, in mold design) Often eliminates need for post-production painting. It can produce tighter radius formation. It can give greater undercut depth.
- 48. The high pressure air is developed between the heated plastic sheet and the pressure box. Due to high pressure, the heated plastic can be deformed into the mould cavity in a fraction of second. The formed sheet is held in the mould cavity for cooling for a few seconds. The formed part thereby solidifies and is ejected from the mould cavity.
- 49. Advantages Low initial setup costs Fast setup time Low production costs Less thermal stresses than injection moulding and compression moulding More details and better cosmetics than rotational- moulded products Disadvantages Geometries limited to thin shells or shallow shapes One side of the product can be precisely controlled by the mould dimensions while the other side can not.
- 50. Matched Die Forming Process
- 51. The thermoplastic sheet is heated with the application of heat until it softens. The preheated sheet is placed into the die surface and through punch pressure is applied on the hot sheet. The air in between die and softened sheet is evacuated by vacuum pump. Therefore, the thermoplastic sheet is formed to the mould shape. The formed sheet is cooled and ejected from the mould cavity.
- 52. BLOW MOULDING
- 54. Close the Mould: The Injected unit is removed and parison added to mould open and blowing rod with parison moved and clamped into the hollow. Now close the mould part. High Pressurized Air Applied to Mould: When the closed mould, the blowing rod opened and to allow high pressurized air into the parison. The Parison is forced by air toward the wall of below mould. So Parison come to require shape of mould cavity. Eject the mould Part: The blowing rod moved in ejection position for after cooling process completed. Now mould part is ejected.
- 58. FILM BLOWING
- 60. Stages of operation Saturation of the base with the resin solution Wet drying Size cutting Pressing
- 61. BONDING OF THERMOPLASTICS Solvent bonding Solvent bonding is a common technique used for joining injection moulded components, especially injection moulded components of amorphous thermoplastics. The components can be safely set aside to dry after 40- 60s of hold time but full bond strength will not be achieved for 24 to 48 hours.
- 62. Adhesive bonding : Adhesive bonding is one of the most convenient methods of assembling thermoplastic parts or metal parts. Advantage of adhesive bonding is the possibility of joining of similar or dissimilar materials. Adhesives distribute stresses over the entire bonded surface area and can provide hermetic seal if needed. The choice of properly type of adhesive, the cure time, cure temperature, temperature resistance, application area etc. have to be taking in account.
- 64. Ultrasonic welding incorporates the usage of very high-frequency (commonly 20 KHz), and frictional heat is generated at the interface due to the transmission of mechanical vibrations transmitted through thermoplastic adherents. It helps the thermoplastic material to melt and flow and form the interfacial bond between them. This tool holder is connected to the transducer, which generates mechanical vibration through the booster. The generated vibration is transmitted to the welding specimen by the required amplification through the booster.
- 66. Spin welding is one of the most common friction welding techniques used to weld thermoplastics and filler-reinforced thermoplastic composite components along circular mating surfaces. In this process, one of the parts is fixed while the other is rotationally rubbed against the fixed part under a specific angular velocity and axial pressure until melting occurs, followed by the cooling and solidification of the polymer.