Sheet Molding Compound SMC

5 POLYMER CURING AND THICKENING 11.5.1 Sheet Molding Compound (SMC) 

Magnesium oxide and hydroxide are incorporated into polyester resins for the purpose of modifying the viscoelastic response of the compound. The 

The introduction of MgO or Mg(OH)2 into the resin [typically at about 2-4 parts per hundred (pphr) of polymer] induces an increase in viscosity, which helps reduce separation of glass fiber from the resin and also converts the resin into a semisolid nontacky sheet. This sheet is then subjected to heat and pressure during the molding process to affect a cure. 

The mechanism of the thickening reaction is believed to be due to Mg2+ ion complexing with dicarboxylic acid species of the resin see reaction (11.3), resulting in formation of a higher molecular weight species (Gruskiewicz and Collister, 1982)  

It has been demonstrated that the Brunaver, Emmett and Teller (BET) specific surface area of magnesium oxide correlates well with its thickening activity, while for magnesium hydroxide particle size correlates with thickening activity (Casey et al., 1989). 

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Composites. The history of phenoHc resin composites goes back to the early development of phenoHc materials, when wood flour, minerals, and colorants were combined with phenoHc resins to produce mol ding compounds. In later appHcations, resin varnishes were developed for kraft paper and textile fabrics to make decorative and industrial laminates. Although phenoHcs have been well characterized in glass-reinforced composites, new developments continue in this area, such as new systems for Hquid-injection molding (LIM) and sheet-molding compounds (SMC). More compHcated composite systems are based on aramid and graphite fibers. 

Two-component urethane adhesives are used to bond sheet molding compound (SMC) panels for automotive OEM and aftermarket applications. Two-part urethanes are used as laminating adhesives in the RV industry. 

Sheet molding compound (SMC) consists of randomly oriented chopped fibers in a matrix of resin and filler. SMC is produced in the continuous manner shown in Figure 1-16. Note that the polyethylene film protects the roller system from getting gummed up with the resin-filler paste. The rug-like rolls of SMC are then used in compression molding machines to create large parts such as the sides of cars and trucks. 

Shear modulus, polyamide, 138 Sheet molding compounds (SMCs), 30 Shoe sole products, 205 Shore hardness gauge, 243 Side-chain liquid crystalline polymers, 49 Side reactions, in transition metal coupling, 477... 

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. 

The technique for monitoring the dielectric loss factor is relatively simple. Two metal electrodes are placed opposite each other at critical locations on opposite sides of the mold. When the sheet molding compound (SMC), is placed between the electrodes, a capacitor is formed. The dielectric power loss is monitored continually throughout the molding cycle, as outlined in Section 6.1.2.2. 

Sheet molding compound (SMC) is a composite material that has been used as an alternative to steel for more than 30 years. SMC consists of a glass-fiber-filled unsaturated polyester and vinyl ester resin that has been compacted into a sheet. These sheets are then placed into compression molds and formed into body panels, and these panels are then coated mainly by dual-cure coatings. ... 

Special grades of styrenic block copolymers are useful modifiers for sheet molding compounds (SMC) based on thermoset polyesters. They improve surface appearance, impact resistance, and hot strength. 

Recently Sands et al.97) and Methven et al. 98) developed sheet molding compounds (SMC) and sandwich structures based on polyester syntactic foams. 

A typical UP formulation for sheet molding compounds (SMC) is shown in Table 2.18. 

The matrix can be either a thermoset or thermoplastic. The oldest and still widest used material for compression molded products is phenolic. The thermoset materials used to manufacture fiber reinforced compression molded articles is unsaturated polyester sheet or bulk, reinforced with glass fibers, known as sheet molding compound (SMC) or bulk molding compound (BMC). In SMC, the 25 mm long reinforcing fibers are randomly oriented in the plane of the sheet and make up for 20-30% of the molding compound s volume fraction. 

With these properties and values the finite difference technique was used to model the curing process in sheet molding compound (SMC) plates using a heat balance with an exothermic reaction as... 

In Europe, car manufacturers first used a half product, a sheet molding compound (SMC) made of sheets of fibers pre-impreg-nated with resin. In the USA they used a different process named RIM (Reaction Injection Molding) which allowed the bumper to be painted the same color as the rest of the structure. 

The resin matrix can be either thermosetting or thermoplastic. Thermosetting resins such as epoxy, polyimide, polyester, and phenolic are used in applications where physical properties are important. Polyester and epoxy composites make up the bulk of the thermoset composite market. Of these two, polyesters dominate by far. Reinforced with glass fiber, these are known as fiberglass-reinforced plastics (FRPs). FRPs are molded by layup and spray-up methods or by compression molding either a preform or sheet molding compound (SMC). 

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