PARALLEL SCREW

The third type of compounding device is the extruder. Next to its use for fabrication (which will be dealt with in 11.4.2), it is applied as a mixer. In essence, it is a screw pump, in which the mass to be mixed is transported in a heated cylinder by a screw, or, with twin-screw extruders, by two parallel screws. During this transport melting and intensive mixing take place. At the end of the screw the blend is pressed through a number of openings and cooled down in most cases the strands thus obtained are on-line cut into granules. 

Counter-rotating twin screw extruders are used almost exclusively for the production of uPVC pipes, profiles and sheet because they treat material more gently than single screws. Parallel screw and conical twin screw extruders are compared. Cincinnati Milacron Austria introduced its Argos parallel twin screw extruders last year. These machines are intended to complement the company s Titan conical screw range. Coextrusion of foamed core pipes is also described. 

Extruders Extruders can also be used to blend powders, but usually only in conjunction with a subsequent melting operation. They consist of parallel screws that are constructed of individual sections that are specifically designed to move or mix the material as it passes through the extruder. The configuration of the screws affects the residence time of the material in the extruder, which can affect the degree of blending achieved. 

ICRR - parallel screws high speed and long L/D... 

Besides the single-screw extruder (SSE), there is the twin-screw extruder (TSE), that is, two parallel screws rotating within the same cylindrical housing [8]. 

The following example shows the possibilities of material flow simulation. In the model of an assembly system which is designed to produce 140 pieces/hr, the number of the workpiece carriers is increased. The result is a higher production level at some of the examined stations, but at some locations the higher number of workpiece carriers cause a blockage of stations that have successor stations with a higher cycle time. Thus, the increase of workpiece carriers has to be done in small steps with a separate simulation after each step to find the optimum. In this example, a 10% increase in the number of workpiece carriers and the installation of a second, parallel screwing station lead to a production increase from 120 to 150 pieces/hr. 

ICRR — parallel screws high speed and Iraig L/D Amut SpA, Bandera, Battenfeld, Bausano, Clextral, Ermefa, Ikegai, JSW, KraussMaffei, Leistritz, Maplan, Mapre, Reinhauser, Toshiba, Weber... 

Parallel screws are used in high speed extruders, conical screws are not used... 

Due to the stress field around dislocations, there is an interaction between dislocations. Dislocations of like sign attract and dislocations of opposite sign repel. The force between two parallel screw dislocations and the force between two parallel edge dislocations are given, respectively, by ... 

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