Weld lines markedly reduce the strength of FRTP injection moldings, which are often used for structural parts. The effects of weld lines on strength are closely related to molding conditions such as resin temperature, injection rate, injection pressure, etc. They are also related to fiber orientation in FRTP, which results in difficulties in the proper design of moldings. This study aims to clarify the effects of weld lines on the strength of short fiber reinforced Polyamide. Dumbbell type tensile specimens with a weld line were molded under several molding conditions. Furthermore, SEM observations of the fracture surface were carried out and the distributions of fiber orientation were measured. The results were obtained as follows. (1) A “back flow” occurred in the weld region when using the multi-cavity mold and led to the re-orientation of fibers in the flow direction. (2) The specimens did not break at the weld lines on the surface because of the back flow. (3) The distribution of fiber orientation on the fracture surface were influenced by molding conditions. The number of fibers oriented in the flow direction increased and the distribution became more uniform by increasing holding pressure. (4) The weld strength was improved by the back flow up to a maximum of about 140% with efficient holding times.

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In this report, the melting behavior of thermoplastic materials has been investigated, which is important in the analysis of the plasticating performance of single screw extruder with forced feeding section. Screw removal experiments were carried out to observe the melting process of polypropylene and polyethylene. Based on these experimental results, an improved melting mechanism was utilized to accelerate the melting rate in the screw channel. The rapid melting of the solid bed is accomplished by conduction heat, viscous dissipation in the melt film and solid circulations caused by drag force and high pressure gradients. This improved melting mechanism was observed experimentally in the newly developed screw channel, which was different from Tadmor's melting model.

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The rheological properties of composites filled with 10∼50 wt% of fibers were studied. The flow activation energy was not affected by the addition of fibers. The plots of swell ratio against shear stress were independent of melt temperature.
The orientation factors of extrudates and of the samples removed from the capillary after terminating extrusion were examined at various shear rates by WAXD. A skin-core structure was found in the extrudates but not in the sample removed from the capillary. The fibers in the skin were highly oriented along the flow, whereas the fibers in the core were oriented in a zig-zag manner.
Goettler's theory for estimating the effect of extensional flow in a reservoir on the distribution of orientation angle could well describe the distributions obtained here. However, the orientation factors estimated from the theory are always smaller than the experimental valves. One possible reason can be ascribed to the neglect of shear effects.

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Although screw extruders have been used for the production of films, pipes, sheets and many other kinds of plastic products, there is still room for improvement. The melting process has an important role in extruders. According to the results of computer simulations on the melting process in a single screw extruder, the melting rate of a polymer solid bed will increase strongly if the heat transfer surface can be enlarged. For ordinary screw extruders, it is very difficult to increase the heat transfer surface using the conventional screw geometry. Therefore, a disk type extruder was assembled as a modification to a single screw extruder. A trial apparatus was examined from various aspects. In this disk type extruder polymeric materials flow by relative motion between a fixed spiral plate where a rectangular channel was cut spirally from the center to the circumference and a moving flat plate. Usage of two surfaces of these plates for heating was very effective in increasing the melting rates. The extruder could extrude materials at rates less than 95g·min^-1 and under pressures less than 9.5MPa. At higher pressures, the extruder developed leaks through the circumference. The leakage could probably be prevented by cooling the first turn of the channel sufficiently to keep the materials from melting. From the residence time distribution measured under steady extrusion, it was clear that there is circulation flow over flights. Mixing may thus be enhanced by longer shear loading by circulatory flow in the extruder.

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This paper describes a new method of manufacturing plastic lenses. Injection molding is the process usually employed to produce plastic lenses. In spite of its popularity, this method presents some problems such as long molding times, adverse optical influence due to molecular orientation near the gate zone and the high cost of the mold. In order to solve these problems, we have developed a new technique to manufacture plastic lenses-called Vibro-Thermoforming-which is a derivation of Vibro-Punching. This is based on a reciprocating half-blanking process with a concentration of thermal energy produced by local deformation. Lenses are then formed from the thermo-softened material. This process can be used for manufacturing lenses from PMMA sheets in 31.5 seconds. The interference fringe number is about 0.3, the resulting surface roughness in R_max is 0.04μm and the birefringence index is approximately the same as for injection molding.

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