Irregular shapes

Extruded blow molded 3-D products are produced. This approach provides the designer with a relatively very important approach in the art of hollow formed products. It is an ideal approach that has many cost-to-performance advantages. Complex, irregular 

All bottle weights are finish weights (flash being considered 100 percent reusable). 

Examples of different blow molded shapes are shown in Figs. 8-45 to 8-48. 

This technique is also called nonaxisym-metric blow molding. In conventional EBM the parison enters the mold rather in a straight tube. In 3-D BM the parison is laid or oriented in the mold prior to closing. It is manipulated in the tool cavity providing complex geometric products that can have 

---

In practice, it may be possible with care to float somewhat larger particles than those corresponding to the theoretical maximum. As illustrated in Fig. XIII-7, if the particle has an irregular shape, it will tend to float such that the three-phase contact occurs at an asperity since the particle would have to be depressed considerably for the line of contact to advance further. The resistance to rounding a sharp edge has been investigated by Mason and co-workers [62]. 

The technique just described requires the porous medium to be sealed in a cell, so It cannot be used with pellets of irregular shape or granular material. For such materials an alternative technique Introduced by Eberly [64] is attractive. In Eberly s method the porous pellets or granules are packed into a tube through which the carrier gas flows steadily. A sharp pulse of tracer gas is then injected at the entry to the tube, and Its transit time through the tube and spreading at the exit are observed. A "chromatographic" system of this sort is very attractive to the experimenter,... 

Fig. 1.15 A log-normal plot. Note the irregular shape, arising from the smallness of the sample. (Courtesy, DallaValle )...

This effect of concentration is particularly pronounced with irregularly shaped particles. A possible explanation of the variation in the specific resistance is in terms of the time available for the particles to orient themselves in the growing cake. At higher concentrations, but with the same approach velocities, less time, referred to as particle relaxation time, is available for a stable cake to form and a low resistance results. 

This empirical equation attempts to account for complex bubble coalescence, spHtting, irregular shapes, etc. Apparent bubble rise velocity in vigorously bubbling beds of Group A particles is lower than equation 16 predicts. 

Eor reverberation room tests of some irregularly shaped items, such as items of furniture, the number of sabins of absorption per item is commonly reported, rather than the absorption coefficient. It is important that the number and arrangement of the items also be reported because both of these factors can affect the results of the test. 

The characteristics of a powder that determine its apparent density are rather complex, but some general statements with respect to powder variables and their effect on the density of the loose powder can be made. (/) The smaller the particles, the greater the specific surface area of the powder. This increases the friction between the particles and lowers the apparent density but enhances the rate of sintering. (2) Powders having very irregular-shaped particles are usually characterized by a lower apparent density than more regular or spherical ones. This is shown in Table 4 for three different types of copper powders having identical particle size distribution but different particle shape. These data illustrate the decisive influence of particle shape on apparent density. (J) In any mixture of coarse and fine powder particles, an optimum mixture results in maximum apparent density. This optimum mixture is reached when the fine particles fill the voids between the coarse particles. 

Inasmuch as friction conditions determine the flow characteristics of a powder, coarser powder particles of spherical shape flow fastest and powder particles of identical diameter but irregular shape flow more slowly. Finer particles may start to flow, but stop after a short time. Tapping is needed in order to start the flow again. Very fine powders (fine powder particles to coarser ones may increase the apparent density, but usually decreases the flow quality. Metal powders having a thin oxide film may flow well. When the oxide film is removed and the friction between the particles therefore increases, these powders may flow poorly. 

The particle size deterrnined by sedimentation techniques is an equivalent spherical diameter, also known as the equivalent settling diameter, defined as the diameter of a sphere of the same density as the irregularly shaped particle that exhibits an identical free-fall velocity. Thus it is an appropriate diameter upon which to base particle behavior in other fluid-flow situations. Variations in the particle size distribution can occur for nonspherical particles (43,44). The upper size limit for sedimentation methods is estabHshed by the value of the particle Reynolds number, given by equation 11 ... 

Vibratory Compaction. Vibratory compaction (38,53) provides a means of forming irregular shape compacts from ungranulated powders. Under agitation, a powder bed tends to rearrange to a configuration of closest packiag. The ampHtude and frequency of vibration required for compaction are dependent on the size and size distribution of the particles present, and the size of the compact, and are determined experimentally. 

Particle shape also affects the sintering of a powder compact. Jagged or irregular shaped particles, which have a high surface area to volume ratio, have a higher driving force for densification and sinter faster than equiaxed particles. High aspect ratio platey particles, whiskers, and fibers, which pack poorly, sinter poorly. 

Dip coating is very commonly used for coating continuous objects that are not flat, such as fibers, and for irregularly shaped discrete objects. Tears or drops of coating at the bottom of dip coated articles may be removed by electrostatic attraction as the article is moved along a conveyor. 

Impression Plasters. Impression plasters are prepared by mixing with water. Types I and II plasters are weaker than dental stone (types III and IV) because of particle morphology and void content. There are two factors that contribute to the weakness of plaster compared to that of dental stone. First, the porosity of the particles makes it necessary to use more water for a mix, and second, the irregular shapes of the particles prevent them from fitting together tightly. Thus, for equally pourable consistencies, less gypsum per unit volume is present in plaster than in dental stone, and the plaster is considerably weaker. 

Irregular-shaped particles exhibit greater surface area than regular-shapea cubes and spheres, the amount of this increase being possibly 25 percent. The effect of particle size and size distribution on effective surface, in a shaft employed for calcination of limestone, is shown in... 

Fig. 12-88. Curve A shows the calculated surface based on an assumed 50 percent void volume and cubical-shaped particles. The B set of cui ves applies to such unscreened irregularly shaped particles as are usually encountered in practice.

Paiiicle. shape. Some types are pellets, egg shapes, blocks, spheres, flakes, chips, rods, filaments, ciystals, or irregular shapes. 

TABLE 20-18 Media for Stirred and Vibratory Mills ( S = spheres/ C = cylinders/ I = irregular shapes)... 

Some debris may enter the tube and then become lodged. Turbulence created at the site of the debris often produces crescent or irregularly shaped erosion-corrosion patterns (Figs. 11.11 through 11.13). 

Figure 14.10 shows the end profile of a sectioned stack plate with deep, irregularly shaped casting voids at the intersection of walls. Sectioning through these void zones revealed deep internal tunnel porosity (Fig. 14.11). When viewed under a low-power microscope, the contours of porous areas showed distinct solidification features (dendrites).

One important class of integral equation theories is based on the reference interaction site model (RISM) proposed by Chandler [77]. These RISM theories have been used to smdy the confonnation of small peptides in liquid water [78-80]. However, the approach is not appropriate for large molecular solutes such as proteins and nucleic acids. Because RISM is based on a reduction to site-site, solute-solvent radially symmetrical distribution functions, there is a loss of infonnation about the tliree-dimensional spatial organization of the solvent density around a macromolecular solute of irregular shape. To circumvent this limitation, extensions of RISM-like theories for tliree-dimensional space (3d-RISM) have been proposed [81,82],... 

---