Body panels

A variety of thermosetting resins are used in SMC. Polyesters represent the most volume and are available in systems that provide low shrinkage and low surface profile by means of special additives. Class A automotive surface requirements have resulted in the development of sophisticated systems that commercially produce auto body panels that can be taken direcdy from the mold and processed through standard automotive painting systems, without additional surface finishing. Vinyl ester and epoxy resins (qv) are also used in SMC for more stmcturaHy demanding appHcations. 

ABS can be blended with bisphenol A polycarbonate resins to make a material having excellent low temperature toughness. The most important apphcation of this blend is for automotive body panels. 

The polyDCPD has good flexural modulus and exceUent impact resistance (61). Current uses for polyDCPD are in golf carts, snowmobiles, and automotive bumpers (62). The polymer is viewed as having a high potential, especially in automotive body panel appHcations. 

Considerable amounts of EPM and EPDM are also used in blends with thermoplastics, eg, as impact modifier in quantities up to ca 25% wt/wt for polyamides, polystyrenes, and particularly polypropylene. The latter products are used in many exterior automotive appHcations such as bumpers and body panels. In blends with polypropylene, wherein the EPDM component may be increased to become the larger portion, a thermoplastic elastomer is obtained, provided the EPDM phase is vulcanked during the mixing with polypropylene (dynamic vulcani2ation) to suppress the flow of the EPDM phase and give the end product sufficient set. 

The biggest potential weight saving, however, is in the body panels, which make up 60% of the weight of the vehicle. Here the choice is more difficult. Candidate materials are given in Table 27.3. 

If (as with body panels) elastic deflection is what counts, the logical comparison is for a panel of equal stiffness. And if, instead, it is resistance to plastic flow which counts (as with bumpers) then the proper thing to do is to compare sections with equal resistance to plastic flow. 

Table 27.5 Properties of body-panel materials toughness, fatigue and creep...

At first sight, the same is true of aluminhim alloys. But because they are heavily alloyed (to give a high yield strength) their ductility is low. If expense is unimportant, this does not matter, some early Rolls-Royce cars (Fig. 27.6) had aluminium bodies which were formed into intricate shapes by laborious hand-beating methods, with frequent annealing of the aluminium to restore its ductility. But in mass production we should like to deep draw body panels in one operation - and then low ductility is much... 

The RIM process was originally developed for the car industry for the production of bumpers, front ends, rear ends, fascia panels and instrument housings. At least one mass-produced American car has RIM body panels. For many of these products, however, a number of injection moulding products are competitive, including such diverse materials as polycarbonate/PBT blends and polypropylene/EPDM blends. In the shoe industry the RIM process has been used to make soling materials from semi-flexible polyurethane foams. 

Polycarbonate, polypropylene and modified PPO are popular materials for structural foam moulding. One of the main application areas is housings for business equipment and domestic appliances because the number of component parts can be kept to the absolute minimum due to integral moulding of wall panels, support brackets, etc. Other components include vehicle body panels and furniture. 

The development of new polymer alloys has caused a lot of excitement in recent years but in fact the concept has been around for a long time. Indeed one of the major commercial successes of today, ABS, is in fact an alloy of acrylonitrile, butadiene and styrene. The principle of alloying plastics is similar to that of alloying metals - to achieve in one material the advantages possessed by several others. The recent increased interest and activity in the field of polymer alloys has occurred as a result of several new factors. One is the development of more sophisticated techniques for combining plastics which were previously considered to be incompatible. Another is the keen competition for a share of new market areas such as automobile bumpers, body panels etc. These applications call for combinations of properties not previously available in a single plastic and it has been found that it is less expensive to combine existing plastics than to develop a new monomer on which to base the new plastic. 

Molded urethanes are used in items such as bumpers, steering wheels, instrument panels, and body panels. Elastomers from polyurethanes are characterized by toughness and resistance to oils, oxidation, and abrasion. They are produced using short-chain polyols such as polytetram-ethylene glycol from 1,4-butanediol. Polyurethanes are also used to produce fibers. Spandex (trade name) is a copolymer of polyurethane (85%) and polyesters. 

To illustrate the correct approach, consider applications in which a material is used in sheet form, as in automotive body panels, and suppose that the service requirements are for stiffness and strength in flexure. First imagine four panels with identical dimensions that were manufactured from the four materials given in Table 3-1. Their flexural stiffnesses and strengths depend directly on the respective material s modulus and strength. All the other factors are shared in common with the other materials, there being no significantly different Poisson ratios. Thus, the relative panel properties are identical with the relative material properties illustrated in Fig. 3-3. Obviously, the metal panels will be stiffer and... 

Thermoformed chassis and body panels are featured on the car. The products were made initially in the USA for assembly in China. The car will weigh less than 2000 lb (900 kg). Automotive Design Composites, Inc of San Antonio, TX, designed the vehicle to have body panels and trunk formed from coextruded sheet of ABS with an ASA cap layer that will hang on a pultruded composite frame. Ceramic tooling is used to thermoform plastic products. 

This paper summarises an initial feasibility on reeyling scrap automotive plasties and eomposites using a eatalytie conversion process. The eharaeterisationofhydroearbon products is presented for sheet moulding compound (SMC), auto shredder residue (ASR) and reinforeed polypropylene (R-PP) materials and mixtures of body panels. Gas chromatography and scanning electron microscopy is used for the material characterisation. 26 refs. 

Step growth polymerization can also yield highly crosslinked polymer systems via a prepolymer process. In this process, we create a prepolymer through a step growth reaction mechanism on two of the sites of a trifunctional monomer. The third site, which is chemically different, can then react with another monomer that is added to the liquid prepolymer to create the crosslinked species. We often use heat to initiate the second reaction. We can use this method to directly create finished items by injecting a mixture of the liquid prepolymer and additional monomer into a mold where they polymerize to create the desired, final shape. Cultured marble countertops and some automotive body panels are created in this manner. 

India s Reva EV can travel at about 35 mph. The power system is eight 6-volt EV type lead add batteries. The dent-proof body panels are made of high impad ABS (acrylonitrile butadiene styrene). It has side impact beams and electronic regenerative braking. The suspension is McPherson struts in front and coil springs in the rear. It is a two-door hatchback that... 

Low-profile additives, which control shrinkage, have emerged as a distinct science and class of additive. Unsaturated polyester resins, as do all thermosetting polymers, shrink when cured. Low-profile additives are a major class of additives used to control shrinkage, which vastly improves surface quality. This science is credited with the opening of automotive markets where surface quality is of prime importance. In exterior automotive body panels, Class A surfaces are required for market acceptance. 

Transportation Body panels, under the hood components, truck cabs, tractor components, structural elements... 

Body panels glycol/isophthalic Propylene glycol/phthalic anhydride... 

Sheet molding compounds (SMCs) and bulk molding compounds (BMCs) are the dominant materials used in automotive applications. These composites of unsaturated polyester resin, fillers and fiberglass have advantages of high stiffness, heat resistance and low coefficient of expansion. Coupled with low creep resistance, which is a distinct advantage over thermoplastic competition, and low-profile additives, which can yield Class A surfaces, these materials are well suited for applications from exterior body panels to under the hood components. 

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