Resin flow gradient

Consider a cake of moulding resin between the compression platens as shown in Fig. 4.63. When a constant force, F, is applied to the upper platen the resin flows as a result of a pressure gradient. If the flow is assumed Newtonian then the pressure flow equation derived in Section 4.2.3 may be used... 

For thick epoxy laminates processed in the autoclave, voids once formed and stabilized can only be removed by dissolution or by resin flow. Furthermore, resin gradients are deleterious to structural laminates. These two key phenomena make an understanding of resin transport vital to the development of any processing model. 

In the past, various resin flow models have been proposed [2,15-19], Two main approaches to predicting resin flow behavior in laminates have been suggested in the literature thus far. In the first case, Kardos et al. [2], Loos and Springer [15], Williams et al. [16], and Gutowski [17] assume that a pressure gradient develops in the laminate both in the vertical and horizontal directions. These approaches describe the resin flow in the laminate in terms of Darcy s Law for flow in porous media, which requires knowledge of the fiber network permeability and resin viscosity. Fiber network permeability is a function of fiber diameter, the porosity or void ratio of the porous medium, and the shape factor of the fibers. Viscosity of the resin is essentially a function of the extent of reaction and temperature. The second major approach is that of Lindt et al. [18] who use lubrication theory approximations to calculate the components of squeezing flow created by compaction of the plies. The first approach predicts consolidation of the plies from the top (bleeder surface) down, but the second assumes a plane of symmetry at the horizontal midplane of the laminate. Experimental evidence thus far [19] seems to support the Darcy s Law approach. 

This model can also provide resin pressure gradients, resin flow rates, consolidation profiles, and, when combined with the void model, void profiles at any point in the laminate. 

The numerical solutions necessary to solve the practical three-dimensional problems agree well with the closed-form analytical solutions for simpler one- and two-dimensional cases with constant material properties. The resin pressure gradient in the thickness (vertical) direction for a well-dammed laminate (no horizontal flow) is nonlinear. 

The fabrication of composite laminates having a thermosetting resin matrix is a complex process. It involves simultaneous heal, mass, and momentum transfer along with chemical reaction in a multiphase system with time-dependent material properties and boundary conditions. Two critical problems, which arise during production of thick structural laminates, are the occurrence of severely detrimental voids and gradients in resin concentration. In order to efficiently manufacture quality parts, on-line control and process optimization are necessary, which in turn require a realistic model of the entire process. In this article we review current progress toward developing accurate void and resin flow portions of this overall process model. 

In the past, various resin flow models have been proposed (2, 15-19). Two main approaches to predicting resin flow behavior in laminates have been suggested in the literature thus far. In the first case, Kardos et al.2), Loos and Springer15), Williams et al.16) and Gutowski17) assume that a pressure gradient develops in the laminate both in the vertical and horizontal directions. These approaches describe the resin flow in the laminate in terms of Darcy s Law for flow in porous media, which requires knowledge of the fiber network permeability and resin viscosity. Fiber... 

To maintain the resin content gradient through the laminate thickness and to avoid unwanted resin flow between the layers, the corrosion barrier is allowed to gel before the structural laminate is applied. After the gelling of the corrosion barrier another CSM is applied before either filament winding commences or WR is applied. The resin in the corrosion barrier is allowed to gel but not to cure completely. If it is completely cured it will be difficult to obtain good adhesion between the two layers and grinding of the outer surface of the corrosion barrier will be required prior to commencing the buildup of the structural layer. 

Darcy s law describes the overall relationship between the velocity and the pressure gradient, and not the details of the velocity and pressure at each point inside the microscale fiber structure. Usually, this is sufficient to model the resin flow in RTM while designing the mold as we are interested in macroscopic variables such as mold fiU time, maximum value of the injection pressure required and locations of gates/vents to ensure complete mold filling. 

The void can only be driven by the flow, if the air pressure gradient inside it is equal or lower (it is negative) than the one corresponding to the resin flow. At the interfacial points 1 and 2, the capillary pressure is present and acts on both sides inside the void. Thus the pressure gradient is only caused by the... 

Figure 3 Gradient separation of anions using suppressed conductivity detection. Column 0.4 x 15 cm AS5A, 5 p latex-coated resin (Dionex). Eluent 750 pM NaOH, 0-5 min., then to 85 mM NaOH in 30 min. Flow 1 ml/min. 1 fluoride, 2 a-hydrox-ybutyrate, 3 acetate, 4 glycolate, 5 butyrate, 6 gluconate, 7 a-hydroxyvalerate, 8 formate, 9 valerate, 10 pyruvate, 11 monochloroacetate, 12 bromate, 13 chloride, 14 galacturonate, 15 nitrite, 16 glucuronate, 17 dichloroacetate, 18 trifluoroacetate, 19 phosphite, 20 selenite, 21 bromide, 22 nitrate, 23 sulfate, 24 oxalate, 25 selenate, 26 a-ketoglutarate, 27 fumarate, 28 phthalate, 29 oxalacetate, 30 phosphate, 31 arsenate, 32 chromate, 33 citrate, 34 isocitrate, 35 ds-aconitate, 36 trans-aconitate. (Reproduced with permission of Elsevier Science from Rocklin, R. D., Pohl, C. A., and Schibler, J. A., /. Chromatogr., 411, 107, 1987.)...

The sample is loaded at a flow-rate of 1 ml/min onto the FPLC column equilibrated with the same MOPS buffer used to resuspend the RNA pellets. The free nucleotides are completely removed with a 5-ml wash with 350 mM NaCl and the RNA is eluted with a 20-ml (350—750 mM NaCl) linear gradient and analyzed by PAGE/urea gel electrophoresis (see later). Up to 2 mg of RNA can be loaded onto and eluted from a 1-ml (of resin) mono Q column without loss of resolution. The homogeneity of RNA in the fractions collected, as seen by gel electrophoresis, should be >90%. The appropriate fractions are pooled and the RNA collected by ethanol precipitation. The RNA pellet is washed twice with 70% ethanol, air-dried, and finally redissolved in DEPC-treated H20. The total recovery after the entire procedure of purification is = 90%. This protocol yields = 800 pmoles of purified 002 mRNA/pmole template DNA. 

The target discharge temperature for the extrusion is 240 °C, and the maximum screw speed is 130 rpm (N = 2.167 rev/s). What will be the expected production rates for both resins at 130 rpm At 240 °C the melt density of the resins is 735 kg/mT As presented in Sections 1.4 and 7.4, the net flow in the extruder is the difference between the rotational flow and the flow induced by the pressure gradient Qp. The data in Table 7.2 was calculated from the example in Section 1.5.1 and Table 7.1 ... 

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