Screw configuration

The screw configuration is normally either a ribbon-type helical screw or a series of paddles mounted on a common shaft. Materials of construction are selected based on the specific application and materials to be mixed. Typically, the screws are either steel or stainless steel, but other materials are available. 

FIGURE 35.26 Typical screw configurations for corotating twin-screw extmders (TSEs). 

The main problem with nanofillers is the need for complete exfoliation. Some special compounding techniques have been developed such as, for example, the ZSK MEGA compounder by Coperion Werner Pfleiderer with a special screw configuration. 

All of the data in Fig 7.5 were analyzed using linear regression. The summation of the helix and core-regressed flow rates are plotted in Fig. 7.5 as the red dotted line. The experimental superposition for the flows induced by the screw elements essentially overlaid the regression line for the screw configuration rate. Thus, it was concluded that the helix is the pump in the single-screw extruder, and core rotation reduces the flow by dragging the fluid back toward the extruder inlet. 

Campbell, G.A., Cheng, H., Wang, C., Bullwinkel, M., and te-Riele, M.A., An Experimental Investigation of Screw Configuration on Temperature Rise in Single Screw-Pump Extruders, SPE ANTEC Tech. Papers, 48, 189 (2002)... 

Melt-rich Solids-rich Melt-bound Very deformed Slightly deformed Undefonned suspension suspension solid particulates solid particles solid particles solid particles States of the stream Schematic representation Co-TSE screw configuration... 

Fig. 10.17 The counter- and co-rotating thin-flight, open C-shaped channels used in the three-dimensional FEM study of Katziguara et al. (32). The two-screw configurations are identical except for the sense of rotation. [Reprinted by permission from T. Katziguara, Y. Nagashima, Y. Nakano, and K. Funatsu, A Numerical Study of TSEs by 3-D Flow Analysis - Development of Analysis Technique and Evaluation of Mixing Performance for Full Flight Screws, Polym. Eng. Sci., 36, 2142 (1996).]...

Along with the screw configuration, the residence time distribution in twin screw extruders is also influenced by the process parameters. As shown in Fig. 4.24, throughput has a greater influence on the average residence time than screw speed and pitch [7]. 

Figure 4.23 Residence time distribution for different screw configurations in a co-rotating twin screw extruder (constant screw speed and throughput)...

Effects of changing screw configuration (or geometry), process values and also materials can be quickly determined... 

If, in addition, the barrel of the trial machine is manufactured from a transparent material (Fig. 9.20), the mixing behavior in the machine can be observed first-hand. This provides valuable information about the mixing performance of a screw configuration. 

With the aid of the experimental techniques that have been briefly described here, the mixing performance of screws can be investigated with relatively little effort. Such investigations are useful, for instance, when developing new screw elements and optimizing screw configurations. With the proper equipment, it is also possible to investigate dispersion processes. 

Suitable screw configuration and screw speed ensure compensation of heat loss, particularly after flash and also after the initial forward venting. The vacuums in the individual degassing zones are designed to avoid excessive foaming of the polymer solution or even crumbs in the degassing opening. 

Neutral mixing elements can be fitted at any point in the screw configuration. They are always completely filled and must be overrun by upstream elements. 

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