Direct extrusion molding machine

Figure 5.38 Direct extrusion-molding machine (Reifenhoiser).

The third and most successful approach was accomplished on a wheel-type blow molding machine. Unlike the shuttle machine where only gravity acts on a downward extruded parison, a wheel machine draws or pulls the parison from the die. This allows extension in the extrusion direction and the opportunity to thin down the barrier layer and reorient the mica platelets. 

Molecular weight can be controlled by addition of a small amount of monobasic acid. This polyamide melts at 265°C and is highly czystaUine. The polymer can be run directly to spinning machines to produce fiber, or it can be extruded as a heavy ribbon which is chilled and chipped. The pol3uner may be remelted to spin into fiber, or it may be used for extrusion of molded objects, or it can be made into molding powders. 

In the injection molding machine shown in Figure 13, the clamp unit is on the left and the injection unit on the right. A mold is shown in position between the platens of the clamp unit with one half of the mold fastened to the fixed platen and the other to the movable platen. When the mold is opened, the movable platen moves away from the fixed platen and the molded part can be removed. After part ejection, the mold is closed in preparation for the next injection cycle. In contrast to extrusion, the screw in the injection imit rotates only during part of molding cycle. When the screw turns, it pumps melt forward. The rearward movement of the screw is controlled by the placement of a limit switch, which stops the hydraulic motor. The maximum length of reciprocation is approximately three screw diameters. The shot size is directly proportional to the amoimt of screw... 

Another factor that dictates the mechanical performance of polymers is the appearance of chain orientation. In the case of fibers, it is customary to pre-stretch in order to achieve a high degree of orientation in the axial direction. In films or other profiles made by extrusion or injection molding, chain orientation is usually obtained in the flow (machine) direction. This is manifested by an increase in tensile strength and a decrease in elongation in the machine direction, while the opposite is trae in the transverse direction. This calls for measurements in both directions. In two-dimensional objects this phenomenon is undesirable, as it leads to asymmetric properties (anisotropy). Similar behavior may be found in reinforced materials (with long fibers), in... 

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