Melt distribution

The silica carrier of a sulphuric acid catalyst, which has a relatively low surface area, serves as an inert support for the melt. It must be chemically resistant to the very corrosive pyrosulphate melt and the pore structure of the carrier should be designed for optimum melt distribution and minimum pore diffusion restriction. Diatomaceous earth or synthetic silica may be used as the silica raw material for carrier production. The diatomaceous earth, which is also referred to as diatomite or kieselguhr, is a siliceous, sedimentary rock consisting principally of the fossilised skeletal remains of the diatom, which is a unicellular aquatic plant related to the algae. The supports made from diatomaceous earth, which may be pretreated by calcination or flux-calcination, exhibit bimodal pore size distributions due to the microstructure of the skeletons, cf. Fig. 5. 

Zou, H.B., 2000. Modeling of trace element fractionation during non-modal dynamic melting with linear variations in mineral/melt distribution coefficients. Geochim. Cosmochim. Acta, 64 1095-1102. 

If 0 = 0 and a =0 for all i, which is the case for perfect fractional melting with constant mineral/melt distribution coefficients, Eq. (3.26) reduces to the following equation of Shaw (1970) ... 

McKenzie, D. and O Nions, R.K., 1991. Partial melt distributions from inversion of rare earth element concentrations. J. Petrol., 32 1021-1091. 

The flat dies, or slot dies as they are sometimes called, are used to produce webs in a variety of processes. They all have an interior manifold for distributing the plastic and lips for adjusting the final profile of the web (extrudate). Some dies have movable restrictor bars for changing the manifold for proper melt distribution (Figure 17.10). All flat dies have flexible lips that can be adjusted by bolts to remove humps or bumps in the web s profile. Die lips can have their adjustment bolts push only, where internal plastic melt pressures are adequate to keep the lips positioned against the bolts, or can be push/pull for low pressure applications. Direct acting or differential thread designs (for minute adjustments) are available. Profile variations of at least 3% or less can be achieved with flat dies. 

Peach C. L. and Mathez E. A. (1993) Sulfide melt-silicate melt distribution coefficients for nickel and iron and imphcations for the distribution of other chalcophile elements. Geochim. Cosmochim. Acta 57, 3013—3021. 

Kent R. W., Saunders A. D., Kempton P. D., and Ghose N. C. (1997) Rajmahal basalts, eastern India mantle sources and melt distribution at a volcanic rifted margin. In Large... 

Preparation by Direct Addition of Pure O2F2 to Pure CIF. In a typical example 1.130 grams of O2F2 were vacuum-distilled into a borosilicate glass reaction vessel (Kel-F test tubes may also be used) of about 100-oc. volume, melted, distributed evenly on the walls of the lower half of the reaction vessel by rotation, and frozen at 90° K. The stoichiometric amount (1 1 mole) or 0.880 gram of GIF (measured as a gas) was added in portions of 100 mg. After each addition the reaction vessel was warmed up to 119° K. (melting point of GIF) and then slowly to 140° K. The violet compound, O2GIF3, is rapidly formed, by direct addition ... 

Fig. 3 Schematic of spiral mandrel blown film die operation (1) ring-shaped melt distribution (2) die body (3) spiral flow mandrel (4) sizing ring (5) spreader (6) film bubble (7) frost line (8) solidified film (9) bubble collapsing rollers (10) nip rollers (11) external bubble cooling air (12) internal bubble cooling air inlet (13) internal bubble cooling pipe and (14) heated internal bubble air return.

Three different approaches have been used. Firstly, the distribution of the major elements between mineral phases and a coexisting silicate melt may be calculated from experimental phase equilibrium data using regression techniques. Secondly, mineral-melt equilibria can be determined from mineral-melt distribution coefficients. A third, less empirical and more complex, approach is to use equilibrium thermodynamic models for magmatic systems. These require a thermodynamically valid mixing model for the liquid and an internally consistent set of solid-liquid thermodiemical data. 

The back line of the coat-hanger manifold is further from the exit of the die at the center than it is on the ends. This could result in a die that will deflect its opening more at the center, causing uneven melt distribution. See die, multiflow die, T-slot. 

Newest "super-concentrates" provide highest level of melt distribution, greatest letdown ratio, supplier press release. Teknor Apex Company 2008. 

Thin film is inflated from extruded tube consequently to the die exit. The blown film dies could be in general divided to spider and spiral types, as presented in Fig. 4.3. Since spiral dies provide more uniform melt distribution and eliminate weld or knit lines caused by the spider holding the mandrel, they almost replaced... 

Fig. 21. Lanthanide mineral/melt distribution coefficient values for plagioclase from volcanic rocks, also showing wide variations related to the composition of the bulk rock. (Data by courtesy of Dr. A. Ewart, University of Queensland, Australia.)...

Fig. 22. The regular variation of mineral/melt distribution coefficients for plagioclase with ionic radius, showing the effect of lattice size and valency. Eu enters the Ca " (r = 1.12 A) site more readily than the trivalent lanthanides, the largest (La) of which have preference over the smaller (Yb).

Coathanger die n. A sheet-, or film-extrusion die whose melt-distribution manifold has the obtuse-isoceles outline of a coathanger. This popular die design is said to yield uniform distribution of material across the full width of the extruded web, thus producing sheet of laterally more uniform thickness. Side-fed blow-molding dies and spiral-type dies for blown film may also be spoken as a coathanger dies. 

Spider runners (spider gating) n. A design for melt distribution to multiple cavities in an injection mold in, which the cavities are arranged in a circle and fed by runners radiating from a central sprue. 

The fishtail die is shown in Fig. 9.13(b). This die results in a more uniform melt distribution than the T-die however, a completely uniform distribution is still difficult to obtain with this geometry. Analyses of the flow in fishtail dies have been made by Ito [7] and Chejfec [8]. 

The most common die used in blown film extrusion is the spiral mandrel die. In this die, the polymer is divided into a number of spiraling channels with the depth of the channels reducing in the direction of flow. The popularity of the spiral mandrel die is due to its relatively low pressure requirement and its excellent melt distribution characteristics. Spiral mandrel dies can be used with a wide range of materials over a wide range of operating conditions. 

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