The generation of wave-like flow marks on an injection molded polymer strip was experimentally studied using laser interferometry with a He-Ne laser during the filling process. A microscope camera system was used to observe the interference fringe patterns through a calcium fluoride observation window of an experimental mold. A geometric analysis of the flow marks was calculated with a simple optical theory that gave the surface shape change as a function of optical path difference. The variation of local flow mark depths was obtained as a function of the distance from the melt flow front, and the time after the passage of the flow front. It was found that the polymer started to shrink when it contacted the mold wall surface, and this deformation caused a warp on the molded surface that was the origin of flow marks. It was also shown that the hill and valley shape of the flow marks grew with time. In a previous paper, one of the authors reported a model that described the wave-like flow mark generation from a thermal engineering point of view. The results obtained in this study correspond to the surface deformation that was discussed in the previous paper. Therefore the present authors believe that the flow mark generation model proposed in the previous paper is proper.

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The reciprocating plastication process in injection molding is performed intermittently and the relative positions of the screw and heating cylinder always changes. In order to visualize the process, we developed a glass-inserted heating cylinder and screw displacement tracing unit which fixes the view to one position of the screw and captures video images at that position. In this study, we analyzed the reciprocating plastication process of polypropylene. The results can be summarized as below:
(1) The resin melting process can be shown clearly by an extended lamination image of the screw surface, which is created from the obtained video images. The solid bed ratio, which is the ratio of the solid bed width to the channel width, was calculated from the extended image. The variation of this solid-bed ratio reflects the change in the melting pattern. The results confirm that a quantitative analysis of the reciprocating plastication process is feasible.
(2) Two types of solid-bed break-up phenomena occurred in the second half of the screw compression zone in each molding condition. It is thought that the solid-bed is partially low density at the start of the charge process at the entrance of the screw compression zone and the second half of the feed zone, and that the break-up occurs as the plastication process progresses.

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In this paper, the measurement of melt temperature profiles inside a nozzle was carried out using several types of screws, and the influence of screw configurations on the plastication process, especially on the temperature characteristics of the injection melt were investigated. The results can be summarized as below:
(1) Two common trends were seen in the temperature profiles using each screw: the generation of concentric temperature profiles at the cross section of the nozzle channel and the temperature drop towards the latter stage in the injection process.
(2) The increase of the screw compression ratio and feed zone length causes a drop in the average melt temperature. But, in the high compression ratio screw, the melt temperature in the latter stages of the injection process rose due to the recovery of the shearing operation in an early stage of the charging process, and temperature uniformity was observed.
(3) It was confirmed that barrier flight screws are very effective for obtaining melt temperature uniformity, and the barrier flight must be located in front of the compression zone to avoid overheating and time loss.
(4) A maximum value in the temperature variation between injection shots was seen in the case of high compression ratio and long feed screw.

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An experimental visual observation and theoretical study were carried out to investigate the dynamic behavior of bubble nucleation and growth in a foam extrusion die. In this study, a mixture of polypropylene and isobutane was extruded through a slit die with glass windows, and gas bubbles in the flow channel were observed using a CCD camera and a high-speed video with a long-distance microscope.
Some new facts were found about the macroscopic foaming behavior and the microscopic bubble nucleation behavior. Macroscopically, the foaming position, where bubbles started to grow, moved downstream towards the die exit with increasing extrusion pressure, and the foaming pressure was lower than the polymer/gas equilibrium pressure. Microscopically, bubbles started to grow at several points in the die, and there seemed two typical styles of gas bubble nucleation; formation of bubbles accompanied with a wedge shaped gas film and formation of single bullet shaped bubbles.
We also constructed a new model to simulate the bubble nucleation and growth simultaneously in a shear flow field. A threshold value in nucleation rate was introduced to explain bubble nucleation under supersaturation conditions. Numerical results showed good agreement with experiments.

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