PLASTICS REPLACING METALS
SK ANSARI, SEEMA ANSARI
June 7 - 13, 2010
Over the past three decades plastics have made steady progress in automotive applications. According to an international survey, the content of plastics in automobiles has increased from 168 lb, or 4.6 per cent of the average vehicle's weight, in 1977, to 249 lb, or 7.6 per cent of vehicle weight in 2000.
Much of the success of automotive plastics thus far has been due to their ability to cut costs. Engineering plastics are the class of polymers, based on aromatic backbones, having high strength, stiffness, and toughness together with high thermal and oxidative stability, low creep, and the ability to be processed by standard techniques for thermoplastics. Engineering plastics are a group of plastic materials that exhibit superior mechanical and thermal properties in a wide range of conditions over and above more commonly used commodity plastics. Engineering resin is the term for a group of polymer plastics which exhibit a greater tendency to form crystals in their solid state than their more amorphous cousins. In general, engineering plastic resins are physically stronger and less flexible than amorphous resins and show greater resistance to fatigue, friction and wear.
There are various kinds of plastics. Acrylonitrile Butadiene Styrene plastic resin are found in toys, office equipment, cars and trucks, kitchenware and even cosmetics rely on this engineering resin. Polycarbonate is a transparent engineering plastic resin that is used in eyeglass lenses, compact discs and DVDs, and the protective coverings for vehicle headlight lamps. A thermoplastic resin with excellent mechanical, thermal and electrical properties is used as raw materials of fiber, film and engineering plastic. Polybutylene terephthalate is commonly supplied with fiber glass and/or mineral reinforcements. Polyethylene terephthalate (PET) is used in bottle manufacturing, body panels, spoilers, door handles, distributors caps, rotor, ignition components, head lamps, windshield wiper vacuum cleaner parts, fans, gears, furniture, and coffee makers. Polyphenylene oxide (PPO) resins are used for office furniture, automotive steering column covers, and appliance doors and ducts. Similarly, polycarbonate is used in microwave oven components, plated hair dryer handles, hospital equipment, electronic parts, packaging enclosures, filter cases, and laboratory supplies that require sterilization. Polyetheretherketone (PEEK) is used to fabricate items used in demanding applications, including bearings, piston parts, pumps, compressor plate valves, and cable insulation.
PLASTIC AND METAL COMBINATION
In automotive engineering and other industries, the need for lightweight construction and cost efficiency is leading to the development of hybrid components in which two or more materials can be combined. Hybrid components have properties that a single material cannot generally offer. In plastic-metal hybrid structures, the joint between plastic and metal can basically be produced in two ways: by in mould assembly (IMA) in an injection mould or by post-molding assembly (PMA). In IMA the shaped metal sheet component is inserted in the injection mould and the plastic is then molded over. At the end of the injection molding cycle, the hybrid part can be removed from the mould. In PMA technology, on the other hand, the sheet metal and plastic parts are produced separately.
PLASTIC BODY PANELS FOR CARS
Chrysler's latest concept car might look like your average urban runabout, but even just a cursory tap on the bodywork will tell you that this vehicle is something different. For although the design breaks little new ground, the Composite Concept Vehicle (CCV) is made from radically different materials to the norm, with the body being built almost entirely from plastic. The CCV outer body is constructed from four of the largest moldings ever used in an automobile. These body panels are adhesively bonded to one another and then to a steel chassis, which strengthens the entire structure and supports the power train and suspension.
Overall, instead of the 80 steel components that make up a traditional chassis, the CCV only needs six plastic parts. This design should reduce manufacturing costs by as much as 80 per cent, and plant space required for assembly could be only one sixth of that for a conventional vehicle.
The plastic body of the CCV also helps keep the vehicle light. It has a 1200lb curb weight, which is approximately 50 per cent lighter than a steel equivalent. The four body panels by themselves weigh just 2101bs in total, saving more than 400lbs compared to a metal body.
CCV MATERIAL COST
The low price of the CCV - which Chrysler intends to be an 'affordable world car - is partly thanks to the resin, which is less expensive than composites used in other car bodies. It costs just $1.50 per pound compared to carbon fibre at $10 per pound. Developments in molding technology are keys to the production of the CCV with the new resin. The molded panels, which are three times bigger than any plastic molding used in a production automobile, are produced accurately enough to meet automotive body-fit standards. Two 70lb inner shells and two 351b outer shells make up the finished car body.
VEHICLE FUEL TANK
Plastic fuel tanks can decrease vehicle weight and incidence of corrosion. Metal fuel tanks, which have historically been made of terne-coated steel (an 8 per cent tin-lead coating), are susceptible to interior corrosion from fuel and exterior corrosion from elements such as road chemicals, salt, mud, and gravel.
A defective fuel tank can pose serious risk of the vehicle burning or exploding.
High-density polyethylene (HDPE) tanks are inert to the corrosive environments inside and outside of the tank. In addition, the plastic resins that compose plastic fuel tank systems together can help dissipate electrostatic charge to prevent igniting fuel.
Plastic tanks are made of up to six layers, which work together to prevent vapor permeability and provide additional structural stability. Plastic tank systems also serve the dual purpose of decreasing the vehicle's overall weight, as an average plastic tank weighs two-thirds less than an average steel tank.
Plastic are a family of materials, not a single kind of material. Plastic have an extensive number of polymers and compounds with each kind of material having its own unique and special type of properties.
The single most important benefit in metal to plastic conversion is cost savings with improved product quality.
Thermoplastics are mostly injection molding plastics. They can be reprocessed. Thermoplastics fall into two distinctive molecular groups: amorphous and crystalline. Amorphous materials when processed act like honey; that is they never really melt, they just soften and are formed under pressure. Crystalline Materials act like solder or ice. They have a specific melt temperature and remain a solid until this temperature is reached.
Most plastic materials have greater chemical resistance than most metals. Plastics do not rust or oxidize as metals do and most are not affected, as are metals, by acids or base compounds.
Plastics reduce costs when they replace traditional materials like steel, a benefit that automakers can't ignore especially now when companies like Ford Motor Co and General Motors are under financial strains.