Flake thickness

In practice, platelet crystals are synthesized with a layer thickness d calculated to produce the desired interference colors (iridescence) [5.206], [5.207], Most nacreous pigments now consist of at least three layers of two materials with different refractive indices (Fig. 73). Thin flakes (thickness ca. 500 nm) of a material with a low refractive index (mica) are coated with a highly refractive metal oxide (e.g., Ti02, layer thickness ca. 50-150 nm). This results in particles with four interfaces that constitute a more complicated but still predictable thin film system. The behavior of more... 

The burning characteristics of propint s are classified as "degressive", "neutral" and "progressive". The degressive type for use in firearms is usually in the form of grains, thick flakes, thick strips or nonper-forated cylinders (such as cords of Cordite). 

Capacity Flake thickness Flake size Flake temperature... 

Flake thickness four controllable variables help determine flake thickness (1) oil temperature to the roll, (2) chill roll temperature, (3) speed of the chill roll, and (4) the feed mechanism. 

Adequate extractor drain time is the most economic manner in which to minimize weak miscella retention. Maintaining the desired miscella flux rate is also important. Thus, once again, there is a need to maintain proper flake thickness, minimize surface moisture, and minimize fine material particles in the material bed to minimize weak miscella retention. 

A typical five-high roll assembly consists of four upper rolls, each 35.6 cm (14 in) in diameter by 121.9 cm (48 in) in width, and a bottom roll, 40.6 cm (16 in) by 121.9 cm (48 in), operating at a peripheral speed of about 192m/min (630ft/min). This unit can process 72.6 Mg (80 short tons) of cottonseed or 10,571 dm (300 bushels) of flaxseed in 24 h. However, the actual capacity depends on flake thickness. Detailed data on the capacity and efficiency of cottonseed flaking rolls have been reported by Wamble (34). 

Cottonseed meats are usually rolled to a thickness of 0.127-0.254 mm (0.005-0.010 in) for mechanical pressing. For solvent extraction, flake thickness is seldom less than 0.2-0.25 mm (0.008-0.010 in). The repeated passage of the material through the rolls results in considerable breaking of the individual flakes, but this is not disadvantageous for seeds that are to be mechanically pressed. Many oilseeds, especially small seeds such as flaxseed and sesame, are usually flaked in preparation for pressing. 

Accepting that the last traces of oil are more difficult to dissolve does not nullify the basic conclusions to be derived from the preceding theories based on simple diffusion with free miscibility of solvent and oil. If free miscibility does not exist in the latter stages of extraction, this means simply that the effective concentration of solute is not the concentration of oil in the solid seed material but a lower concentration that is limited by the solubility of the oil in the solvent. The rate of diffusion will be less than observed in the earlier stages, not because the diffusion coefficient has decreased, but because the oil content of the solid material is no longer a proper measure of its instantaneous content of diffusible material. The diffusion or extraction rate will, for example, still be inversely proportional to the square of the flake thickness. 

Note that K in the equation T = KIT is a measure of the ease of extraction of flakes 0.01 in. thick, whereas is a measure of the influence of flake thickness on the extraction rate. Thus, soybean flakes extract more readily than cottonseed flakes of equivalent thickness. Cottonseed flakes, in turn, extract more readily than flaxseed flakes (Figure 20). The extraction rate of flaxseed is highly sensitive to flake or particle thickness, whereas that of soybean is less so. And cottonseed is less sensitive to flake thickness than either. The value of n for soybean flakes was substantially... 

Dehont et al. developed Eq. (1) for the linear variation of flake thickness at a specific roll diameter ... 

Dehont et al. assumed that the material in the compaction area remains horizontal and moves at the peripheral speed of the rollers. They also considered that the angle a is independent of the roller diameter size and noted that the flake thickness ei depends on the roller speed, the roller surface, and the compaction pressure. All these parameters influence the density of the flake, d. Dehont et al. concluded that if the same flake thickness was obtained with different roller diameters, the flake density would be greater with larger diameter rollers. This is due to the greater nip angle formed, with the larger rolls allowing more material to be compacted. 

Parrott evaluated compaction of several pharmaceutical powders into compact sheets that were sized by an oscillating granulator into granules. He studied flake thickness, bulk and tap densities, angle of repose, and flow rate after sizing. His work demonstrated that one could improve most granule densities but not necessarily improve granule flow properties. ... 

Roll gap is defined the narrowest distance between the two rolls. At any given compaction pressure, a specific roller gap will yield a corresponding fixed flake thickness (allowing for some product expansion). A fixed feed rate for a fixed roller speed and compaction pressure maintains the flake thickness. Rollers get too close if the material feed is too low and vice versa. Therefore, in principle, acceleration or deceleration of product delivery system can cause variations in the ribbon thickness and density. By monitoring the roll gap in a feedback loop, a constant material feed can be achieved. 

Figure 12.6. The generation of flakes, (a) Cutting action of a knife-ring flaker (Fisher, 1974). (h) Typical distribution of flake thickness (Jager, 1975) (c) Cutting action of a large drum flaker (courtesy Pallmann, Zweibmcken, Germany), (d) Ring refiner (Fisher, 1972).

Solids feed preparation usually plays a crucial role in leaching processes. The use of line particles usually win spied up diffusive transfer of solutes from the solid to the extract. However, if too fine a size is used, extract may not be able to flow Ibrongh solid beds as rapidly as desired, flow pressure drop may be excessive and cause undesirable bed compaction, displacement instability will he enhanced, extract cling will increase, solid-liquid separation difficulty may increase, and excessive amocrats of intracellular colloidal material may be released. Therefore, the use of a compromise particle size is almost invariably desirable. Except for flaked oilseeds, where flake thicknesses of the order of 0.2 mat are necassery to obtain adequate oil release, particle diameters or thicknesses in the 2-5 mm range usually represent a good choioe for industrial scale extractions. 

Botanical Structure Figure 5 illustrates the effect of flaking thickness on oil yield and rate of recovery from soybean feedstock. Rate of extraction increases and yield improves as flake thickness decreases. An oil yield of 97.4% was achieved from 0.10mm flakes however, yield decreased to 87% and 67% for flake thicknesses of 0.38mm and 0.81mm respectively. (O... 

Size reduction or flaking is carried out on decorticated seed to produce a flake thickness of 0.3-0.4 mm. The cooking operation has a residence time of about 40 min with a final temperature of 95-105 C. About 5-7% moisture in the cooked meats is generally sufficient for good pre-press operation. 

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