Melting elementary step

Subsequent to polymer manufacture, it is often necessary to remove dissolved volatiles, such as solvents, untreated monomer, moisture, and impurities from the product. Moreover, volatiles, water, and other components often need to be removed prior to the shaping step. For the dissolved volatiles to be removed, they must diffuse to some melt-vapor interface. This mass-transport operation, called devolatilization, constitutes an important elementary step in polymer processing, and is discussed in Chapter 8. For a detailed discussion of diffusion, the reader is referred to the many texts available on the subject here we will only present the equation of continuity for a binary system of constant density, where a low concentration of a minor component A diffuses through the major component ... 

Fig. 5.4 Summary of the main mechanisms of the elementary step of melting. (I) Reprinted from Z. Tadmor and C. G. Gogos, Principles of Polymer Processing, Wiley, New York, 1979. (II) Reprinted by permission from C. G. Gogos, Z. Tadmor and M. H. Kim, Melting Phenomena and Mechanisms in Polymer Processing Equipment, Adv. Polym. Technology, 17, 285-305 (1998).

The lumped-parameter model approach becomes particularly useful when dealing with the plasticating extrusion process discussed in the next subsection, where, in addition to melt flow, we are faced with the elementary steps of solids handling and melting. 

A more common situation, however, is that before there is any significant frictional heating, an axial position is reached where the barrel is heated to well above the melting point, forcing the creation of a him of melt. In either case, this marks the end of that portion of the process in the extruder called the solids conveying zone, where only solids are present and the only elementary step that occurs is handling of solids. 

Fig. 10.6 The single-stage FCM. (a) Size 15 FCM with chamber opened and rotated hydraulically (b) top view of staged apex twin rotors and the axial zones for carrying out the solids feed handling and the melting and mixing elementary steps (c) cross-sectional view of two rotor orientations, tip-to-tip (cx) and tip-to-flat (c2). [Reprinted by permission from E. L. Canedo and L. N. Valsamis, Farrel Continuous Mixer Systems for Plastics Compounding, in Plastics Compounding—Equipment and Processing, D. B. Todd, Ed., Hanser, Munich, 1998.]...

We now discuss the elementary steps of processing as they occur in the twin screw segment of the CRNI tangential extruders melt pumping in the single screw segment was covered in Chapter 9. 

Injection molding involves two distinct processes. The first comprises the elementary steps of solids transport, melt generation, mixing, and pressurization and flow, which are carried... 

Each of the reactions is supposed to occur in several elementary steps. The state of oxygen in the melt is not specified. Supposedly, tetravalent vanadium is oxidized to pentavalent vanadium in reaction (V.62) and pentavalent vanadium is reduced to tetravalent vanadium in reaction (V.63). 

Disk extruders. There are several types of screwless extruders. These machines employ a disk or a drum to plasticate, mix, and extrude. Most designs are based on viscous drag flow. They include Maxwell s elastic melt extruder, Westover s stepped disk and drum extruders, and Diskpack [39]. The Diskpack extruder has the capability of performing all the elementary steps of plastics processing by combination of differently shaped rotating... 

Elementary steps and their dynamic behavior have been observed on surfaces of a wide variety of crystals. However, no one has so far succeeded in directly visualizing growing elementary steps of ice crystals, besides our recent works [16, 19]. The difficulty in visualization is mainly due to (i) the small height of elementary steps of ice crystals, (ii) high equilibrium vapor pressure of ice, and (iii) QLLs that appear on ice crystal surfaces at temperatures near the melting point... 

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