Liquid flow in molds with prelocated fiber mats

Abstract

The mechanism associated with mold filling in the manufacture of structural RIM (SRIM) and resin transfer molding (RTM) composites is studied by means of flow visualization and pressure drop measurements. To facilitate this study, an acrylic mold with a variable cavity was constructed and the flow patterns of nonreactive fluid flowing through various layers, types, and combinations of preplaced glass fiber reinforcement mats were photographed for both evacuated and nonevacuated molds. The pressure drops in the flow through a single type of reinforcement (e.g., a continuous strand random fiber mat) and also a combination of reinforcement types (e.g., a stitched bidirectional mat in combination with a random fiber mat) were recorded at various flow rates to simulate high‐speed feeding processes (e.g., SRIM) and low‐speed feeding processes (e.g., RTM). By changing the amount of reinforcement placed into the mold, the permeabilities of the different types and combinations of glass fiber mats were obtained as a function of porosity. It is shown that partially evacuating the mold cavity decreases the size of bubbles or voids in the liquid, but ultimately increases the maximum pressure during filling. The results also show that glass fiber mats exhibit anisotropic permeabilities with the thickness permeability, Kz, being extremely important and often the determining factor in the pressure generated in the mold during filling.

Wetting of fiber mats for composites manufacturing: I. Visualization experiments

“…These bubbles eventually accumulate at the end of the fiber mold. This dynamic void trapping and mobilization is similar to what has been observed by most researchers (Molnar et al, 1989) and industrial practitioners.…”

“…Their study implies that voids can be ignored at high flow rates or short mold filling time. This is obviously contradictory to the conventional experimental observations in resin transfer molding (Molnar et al, 1989). It seemed that Mahale et al considered the air bubbles outside fiber bundles only.…”

“…Incomplete wetting or impregnation often results in the formation of voids or air entrapment. Although the occurrence of voids has been frequently documented and is recognized as a major problem in composites (Bascom and Romans, 1968;Kohn et al, 1968;Williams et al, 1974;Judd and Wright, 1978;Gonzalez, 1983;Behrens, 1983;Macosko, 1989;Kardos et al, 1986;Kamal et al, 1986;Gutowski et al, 1987;Molnar et al, 1989;Elmendorp and During, 1990;Hayward and Harris, 1990;Parnas and Phelan, 1991;McGeehan, 1991;Mahale et al, 1992;Lundstrom et al, 1992;Stabler et al, 19921, the exact mechanism of void formation is not clear due to its complexity. Generally, the void or air bubble formation can include mechanical entrapment as well as growth of bubbles existing in the resin phase.…”

Characterization and Processing of Nanocellulose Thermosetting Composites

“…Many factors affect the filling of a mold, including the permeability of the fiber mats, the presence of gaps in the mold, the positions of inlet and outlet gates, and the rates of resin injection from different inlet ports. Often, it is not possible for the mold designer to visualize and design an adequate system for resin infusion by intuition alone; as a result, mold-filling simulations are used to optimize mold performance [96][97][98][99][100][101][102][103][104][105][106][107]. Numerical simulations allow designers to optimize mold design in virtual space quickly and economically.…”

Recent Advances on Fractal Modeling of Permeability for Fibrous Porous Media

“…A comparison on the dimensionless permeability of porous fibrous porous media among XFP model proposed based on fractal by Xiao et al41 (denoted by real line), available models not based fractal technology64,65 (denoted by broken line) and existing experimental data[65][66][67][68][69] (denoted by symbols).…”