Viscosity consolidation

FIG. 20-74 Effect of binder viscosity and liquid content on final granule porosity for the drum granulation of 15 im glass baUotini. Decreasing granule porosity corresponds to increasing extent of granule consolidation. [Iveson et al., Powder Tech., 88, 15 (1996). ] With land permission from Elsevier Science SA, Lausanne, Switzerland. 

Particle size and friction strongly interact with hinder viscosity to control consolidation. Feed particle size maybe increased and fine tail of distrihiition removed. 

Curing of Polyimlde Resin. Thermoset processing involves a large number of simultaneous and interacting phenomena, notably transient and coupled heat and mass transfer. This makes an empirical approach to process optimization difficult. For instance, it is often difficult to ascertain the time at which pressure should be applied to consolidate the laminate. If the pressure is applied too early, the low resin viscosity will lead to excessive bleed and flash. But if the pressure is applied too late, the diluent vapor pressure will be too high or the resin molecular mobility too low to prevent void formation. This example will outline the utility of our finite element code in providing an analytical model for these cure processes. 

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. 

Models of the intimate contact process that have appeared in the literature are commonly composed of three parts or submodels. The first submodel is used to describe the variation in the tow heights (surface waviness or roughness) across the width of the prepreg or towpreg. The second submodel, which is used to predict the elimination of spatial gaps and the establishment of intimate contact at the ply interfaces, relates the consolidation pressure to the rate of deformation of the resin impregnated fiber tow and resin flow at ply surface. Finally, the third submodel is the constitutive relationship for the resin or resin-saturated tow, which gives the shear viscosity as a function of temperature and shear rate. 

In the in situ consolidation model of Liu [26], the Lee-Springer intimate contact model was modified to account for the effects of shear rate-dependent viscosity of the non-Newtonian matrix resin and included a contact model to estimate the size of the contact area between the roller and the composite. The authors also considered lateral expansion of the composite tow, which can lead to gaps and/or laps between adjacent tows. For constant temperature and loading conditions, their analysis can be integrated exactly to give the expression developed by Wang and Gutowski [27]. In fact, the expression for lateral expansion was used to fit tow compression data to determine the temperature dependent non-Newtonian viscosity and the power law exponent of the fiber-matrix mixture. 

Sollinger and Voges8 at Akzo Nobel (Obemburg, Germany) used off-line transmission NIR to monitor the key quality parameters in cellulose fiber (viscose) spinning solutions over time. The business value lay both in reducing the time and cost of analysis by consolidating four or... 

SiC whisker-reinforced glass matrix composites were fabricated at the same process viscosity of the matrices and were well consolidated. All the composites were 30 wt% whiskers (No. 1) composites. The properties of these composites are given in Table 3.19. A comparison of the 1723 matrix composite and the 7052 composite shows that the latter is much weaker and has a lower modulus. Comparing the 7052 and 7740 systems, the 7740 composites are weaker still. A comparison of the 0080 and 1723 systems again shows a lower performance for the 0080 composite. 

S. M. Iveson, J. D. Htster, B. J. Ennis, Fundamental studies of granule consolidation - part 1 Effects of binder content and binder viscosity, Powder Technol., 1996, 88,15-20. 

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