Screw blender, powder

Sohd—sohd blending can be accompHshed by a number of techniques. Some of the most common iaclude mechanical agitatioa which iacludes devices such as ribboa Headers, impellers, paddle mixers, orbiting screws, etc a rotary fixed container which iacludes twia-sheU (Vee) and double-cone blenders and fluidization, ia which air is used to Head some fine powders. 

Figure 10.15. Some mixers and blenders for powders and pastes, (a) Ribbon blender for powders, (b) Flow pattern in a double cone blender rotating on a horizontal axis, (c) Twin shell (Vee-type) agglomerate breaking and liquid injection are shown on the broken line, (d) Twin rotor available with jacket and hollow screws for heat transfer, (e) Batch muller. (f) Twin mullers operated continuously, (g) Double-arm mixer and kneader (Baker-Perkins Inc.), (h) Some types of blades for the double-arm kneader (Baker—Perkins Irtc.).

FIGURE 33 Vrieco-Nauta model 1.2 VDC-4I orbiting screw blender. Source Courtesy of Hosokawa Micron Powder Systems. 

Table 11.16 shows the composition of a PVDF blend for foam fabrication. This recipe was mixed in an intensive power blender to produce a homogeneous powder blend which was then melt blended in a high shear twin screw extruder at 200 rpm and a temperature of 200°C. Pellets were produced by extruding the melt into water and chopping the quenched extrudate. The foamable blend was extruded, through a 25 mm extruder, according to the conditions given in Table 11.17. A comparison of the properties of foamed and solid PVDF wire insulation is presented in Table 11.18.

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