Free-rise process

FIGURE 2.71 Schematic of a free-rise process for manufacture of glass-reinforced foam laminates. 

Several manufacturiag processes can be used to produce phenohc foams (59,79) continuous production of free-rising foam for slabs and slab stock similar to that for polyurethane foam (61,80) foam-ia-place batch process (61,81) sandwich paneling (63,82,83) and sprayiag (70,84). 

Here, the case of free rise in an open mold is analyzed. Because of the very low thermal conductivity of a plastic foam, an adiabatic process will be considered. The nonadiabatic case in a closed mold leads to integral-skin foams. These foams exhibit a mass density gradient, with unfoamed skins in contact with the mold walls (Marciano et al., 1986). 

A variety of formulations and their modifications are used for producing slabstock urethane foams. The formulation variations are based on available raw materials, foam properties required, product costs and production processes. Examples of formulations for producing free-rise slabstock foam are shown in Tables 16 and 17. A comprehensive list of slabstock formulations has been prepared by Iwata and his co-workers (191). The list is shown in Table 18. 

Figure 35. Free rise, continuous lamination process (72).

Foods of animal origin are suspected to contain some amount of COP formed by autoxidation. Cholesterol autoxidation is a well-established free radical process that involves the same chemistry that occurs for the oxidation of unsaturated lipids. Cholesterol contains one double bond at the carbon-5 position therefore, the weakest points in its structure are at the carbon-7 and carbon-4 positions. However, due to the possible influence of the hydroxyl group at carbon-3 and the tertiary carbon atom at carbon-5, the carbon-1 position is rarely attacked by molecular oxygen, and therefore the abstraction of an allylic hydrogen predominantly occurs at carbon-7 and gives rise to a series of A and B ring oxidation products. In the chain reaction,... 

Implementing lead-free assembly processes in the automotive industry gives rise to unique requirements that must be met for successful product introduction. The most challenging... 

Drying agents may be divided broadly into (a) those which combine with water reversibly and (6) tho.se which react chemically with water by a non-revcrsible process giving rise to a new water-free compound. Sodium, calcium carbide and phosphorus peiitoxide belong to the latter class and wih be discussed in Section 11,39. 

Both the cone-shaped and the wedge-like pore give rise to simple, hysteresis-free behaviour. The meniscus is nucleated at the apex of the cone (Fig. 3.14(a)) or at the intersection of the two planes of the wedge (Fig. 3.14(b)), giving a spherical meniscus in the first case and a cylindrical one in the second. In both systems the process of evaporation is the exact reverse of that of condensation, and hysteresis is therefore absent. 

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