Screw-helical mechanism

Screen extruders utilize a screw-feed mechanism consisting of single or twin helical screws rotating in... 

Plasticator A very important component in a melting process is the plasticator with its usual specialty designed screw and barrel used that is used in different machines (extruders, injection molding, blow molding, etc.). If the proper screw design is not used products may not meet or maximize their performance and meet their cost requirements. The hard steel shaft screws have helical flights, which rotates within a barrel to mechanically process and advance (pump) the plastic. There are general purposes and dedicated screws used. The type of screw used is dependent on the plastic material to be processed. 

In this part, two series of 44 copolymers with coiled main-chain structures and 45 copolymers with stiff main-chain conformations were described. It was concluded that both optically inactive 42 and 43 adopt helical conformations with an equal proportion of P and M screw senses by means of UV and CD spectra as well as molecular mechanics calculations. A marked positive cooperative induction effect of the preferential screw sense in 44 and 45 copolymers was found. However, there is a marked difference in the helical cooperativity between 44 and 45, probably because of the differences in their global and local conformations. This difference can be related to the persistence of the helical conformation against defects allowing change of... 

The climb of mixed dislocations possessing some screw character can proceed by basically the same jog-diffusion mechanism as that for the pure edge dislocation.10 On the other hand, a pure screw dislocation can climb if the excess vacancies convert it into a helix, as in Fig. 11.10. Here the turns of the helical dislocation possess... 

An excellent historical review and applications of this type of extruder were produced by White (53), and the flow was modeled by Janssen et al. (62) and Wyman (63), whose derivation we follow. The easiest way to visualize the conveying mechanism of a counterrotating intermeshing TSE is to place a robot viewer into the screw channel at point 0 in Fig. 6.37(d) and let it report its observations. We first stop the rotation of the screws and tell our viewer to explore the space around it. It will report that the space is entirely confined by steel walls the barrel surface from above, the flights of screw A at either side, and the intermeshing flight of screw B both up-channel and down-channel. The space is a helically distorted C-shaped channel that can be shown schematically, as in Fig. 6.46, or by molding silicone rubber into the space in Fig. 6.47. Clearly, by fully... 

Apart from the a-helix in proteins (Fig. 3, Table 2), a helical structure is also found for the conformation of the structural subunits of collagen and tropocollagen three screw-shaped polypeptide chains, constructed alternately mainly from glycine, proline and hydroxyproline, are wound around each other and form a rigid cable. The single strands of this helix form a structure by far wider open than those known in the polypeptide helix series. Other molecules which are structurally similar to collagen are found in other areas where mechanical endurance is important. Myosin... 

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