Automotive industry bumpers

The most successful application of the RIM-process is in the production of polyurethane-based materials. Other systems, such as composites based on polycaproamide, epoxy resins, and unsaturated polyesters can also be processed by reactive injection molding. New reactive systems have also been specially created for the RIM-process260 because of the exceptional opportunities it offers for manufacture of finished articles from engineering plastics with a high modulus of elasticity and impact strength. The automotive industry, which is the main customer for RIM-articles, can utilize this technology to manufacture of massive parts such as body panels, covers, wings, bumpers and other made of newly developed plastics. 

Applications for BMs are used to contain many different products that include foodstuffs, beverages, household products (appliances, air conditioners, furniture at home/office/hospital/sports arenas, etc.), personal care products, medicine/pharmaceutical products, automotive parts [bumpers, spoilers, air ducts, seat backs, etc.], construction panels, tote boxes, trays, leisure items (toys, floatation, marine buoys, canoes, sailboards, sports goods, etc.), industrial parts (business machines, tool boxes, trash containers, hot water tanks, etc.), and so on.215-217... 

The automotive industry started to use plastics in 1946. Since then, its content steadily increases (see Figure 16.4). Today, the plastics for automotive apphcations are dominated by polymer alloys, blends, and composites. The reason for it is the need for automotive parts to show a wide range of performance characteristics that are virtually impossible to meet using a single-component polymer. Thus, for example, in Saturn, front fenders and rear quarter panels are from PA/PPE, door outer skins are from PC/ABS, the bumper fascias are TPO, etc. 

Though originally developed for the automotive industry for the production of car bumpers, the RIM process has found its greatest success in the shoe industry, where semiflexible polyurethane foams have proved to be good soling materials. 

Because of the low pressure (0.3 MPa) in the mold as compared to those encountered in thermoplastic injection molding (150 MPa) this process is suitable for the production of thin part with large surface areas. A significant application for this is in panel formation in the automotive industry, including fascias, door panels, spoilers, grills, and bumpers. While a rigid foam part with a flexural strength of 700 MPa would require a thickness of 7 mm, a RRIM part, because of the reinforcement, would allow a much smaller thickness (< 3 mm) by virtue of the increase in flexural modulus. 

Extensive use is made of ethylene-propylene rubber in the automotive industry. Because of its paintability, this elastomer is used as the gap-filling panel between the grills and bumper, that provides a durable and elastic... 

Polyolefins are used in automotive industry due to their low cost, good weather resistance, and excellent properties. They can be used in many parts to reduce the vehicle weight, save fuel, increase comfort, and reduce CO2 emission. Polyethylene (UHMWPE or HDPE), for example, is used to absorb vibration and noise and for impact protection. Polypropylene is one of the lightest polyolefins, and with a proper design, an improvement in the passenger safety can be achieved. Polypropylene can also be used in bumper systems to absorb the kinetic energy. 

New trend is the use of polyolefin nanocomposites for the automotive industry in different parts such as in coatings, tires, electric and electronic equipment, breaking systems, frames, body parts, and bumper systems. 

Polypropylene nanocomposites are remarkable for their better mechanical properties, such as high tensile strength and modulus, and for their dimensional stability. They have a wide range of applications in the automotive sector [7-11]. The PP composites are used in automotive industry as battery supports, instmment panel carriers, body panel reinforcements, front-end modulus, underbody aerodynamic covers, electronic boxes, pedals and their supports, door panels and door modules, bumper beams, fender extensions, wheel covers, hub caps, and trim rings for wheels (Fig. 11.4). 

Vibration welding is nsed extensively by the automotive industry in the manufacture of components snch as car bumpers, air intake manifolds, fuel pumps, instrument panels, parcel shelves, inner door panels and for the hermetic sealing of air ducting to the internal surface of the dashboard. Other applications include spectacle frames, typewriter covers, filter housings, motor saw housings and heating valves. 

PU elastomers processed by RIM are widely used in automotive industries. Examples are bumper covers, external body panels, modular windows and exterior and interior trims. Such elastomers are also used in eqnipment housing, sports equipment and furniture. Castable PU elastomer sheets are used as vibration damping materials and acoustic window materials for various naval and civil applications. Because of higher water resistance, PU elastomers are preferable as encapsulant materials for underwater electronics. 

The automotive industry uses foam in air conditioning units and seats, and is increasingly attracted to the weight saving and energy absorbing properties of foam in bumpers and interior fascias. Foamed wood filled plastics composites will become popular if quality and homogeneity can be assured. 

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