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Conventional Processing of Polymer Matrix Composites
Published in Sanjay Mavinkere Rangappa, Jyotishkumar Parameswaranpillai, Suchart Siengchin, Lothar Kroll, Lightweight Polymer Composite Structures, 2020
M.K. Singh, N. Verma, S. Zafar
BMC materials have a dough-like structure, which is helpful to varying the chopping length and the materials getting the shape during compression. Therefore, compression molding is the primary molding technique for BMC. Thus, BMC is helpful in molding large components through automation and reduces the cycle time. It can be used to mold highly complex parts easily. In compression molding, SMCs and BMCs are the most common raw materials. This method is mostly used in automobile industries for the production of various products e.g., body panels, electrical components, grills, trim, air-conditioning ducts, and various semi-structural members. One of the inherent limitations of BMC is that the movement of materials is limited within the mold. Generally, during compression molding, the charge of BMC is placed in the center of the mold and as the closing mold presses the charge, it flows toward the edge of mold. Thus, there should be a proper selection of resin, filler, and reinforcement. As the viscosity of resin increases, the flow of material will be hindered and this could lead to separation of the components. Therefore, there is a limitation of size with BMC molding; in most cases, the maximum size of part can be 16 in. (40 cm) (Mallick, 2007).
Constituent Materials
Published in B. T. Åström, Manufacturing of Polymer Composites, 2018
Another thermoset molding compound is bulk molding compound (BMC), which differs from SMC in that the feedstock is manufactured by mixing it in bulk, i.e. in a “dough-like” process (which has given rise to the alternative name dough molding compound, DMC). BMC is in the form of a log or a rope and is sometimes called premix. The constituents are basically the same as for SMC, but the filler content is higher and the fiber content lower, see Table 2-3, so BMC is likely to flow more easily than SMC and may thus be used to manufacture components of greater geometric complexity. Fiber are generally less than 13 mm long and fiber volume fractions are in the range 0.1-0.2. Unsaturated polyester-based BMC is normally used directly after manufacture without maturing, but with other resins maturing or evaporation of solvents may be necessary. By far the most common constituents in BMC are glass and unsaturated polyester, although molding compounds based on epoxies and phenolics reinforced with glass and high-performance fibers are commercially available as well. While almost all prepregs are manufactured by someone other than the final user, SMC and BMC is commonly manufactured by the molder himself.
Compression Molding
Published in P. K. Mallick, Processing of Polymer Matrix Composites, 2017
BMC is also a ready-to-mold short fiber-reinforced thermoset used for compression molding and injection molding. It is produced in the form of a log and is supplied as a bulk material. Since it has the appearance of a dough, it is sometimes called dough molding compound. It is used in a variety of industrial applications, such as electrical fuses and switchgears, pump and motor housings, appliance parts, and under-the-hood automotive components, such as engine valve cover and timing belt pulley.
Reverse supply network design for circular economy pathways of wind turbine blades in Europe
Published in International Journal of Production Research, 2022
Athanasios Rentizelas, Nikoletta Trivyza, Sarah Oswald, Stefan Siegl
As discussed in the previous section, the customers for the recycled wind blades are the SMC/BMC manufacturers. 11 SMC/BMC manufacturers were identified in Europe with an estimated production of 287,000 t in 2018 and a 1-2% annual growth expected (Witten et al. 2018). The mechanically treated short glass fibers can substitute the filler materials that constitute around 40-50% of SMC/BMC (Witten et al. 2018). However, according to experts, only 45% of the fillers can be substituted by recycled GFRP in reality, since the rest of the SMC/BMC products should use flame retardant material such as aluminium hydroxide. According to these assumptions, the amount of SMC/BMC material demand by each of the 11 SMC/BMC manufacturers is presented in Figure 2. It is noted that the actual production output was known only for three out of eleven manufacturers; for the rest, the remaining amount from the total is evenly distributed due to the lack of more detailed data.