Cooling the extrudate

Several unique products are made by extrusion and the dies needed to make these products are classified as 1) sheet dies 2) flat-film and blown-film dies 3) pipe and tubing dies 4) profile extrusion dies and 5) co-extrusion dies. Furthermore, each product type has unique hardware downstream of the die to shape and cool the extruded melt. To aid the reader, detailed illustrations of the various die designs and the complementary downstream cooling and shaping hardware are shown. 

There are two patented techniques for sizing and cooling the extrudate. In the Gatto process, the part is extruded from an undersized die and allowed to foam outside the die as it enters the water-cooled vacuum calibrator, which determines the final shape... 

PP and PB were dry-blended, and the mixture was fed into a 5.1-cm (2 inch) Rheotec extruder. For some of the samples a Berlyn extruder was used. The extruder was operated at a flow rate of 9 kg/h with a screw speed of 20 rpm and staged temperature zones to ensure a melt temperature of 244°C. The blends were extmded into 4 mil (0.102 mm) films on a chrome-plated casting roll in which the quench temperature was controlled at 12.2°C, so that the structure of PP is mesomorphous. The materials used for the various samples, and the processing conditions used, are given in Table 11.44. It is important to cool the extruded form of the blends rapidly so that mesomorphous PP is obtained. 

Multilayered laminates with an ABS outer layer can be produced by coextrusion. In this process two or three different polymers may be combined into a multilayered film or sheet. Adhesion is enhanced by cooling the extruded laminate directly from the melt rather than in a separate operation after the components of the sheet have been formed and cooled separately. In one process flows from individual extruders are combined in a flow block and then conveyed to a single manifold die. All the polymer streams should have approximately the same viscosity so that laminar flow can be maintained. 

It has been foundl l that by adjusting the PVDF extrusion conditions, light transmission in the 280 to 330 nm (Domo rays) can be maximized. The percent transmission of light showed little dependence on the film/sheet thickness in the range of 0.02-2 pm, which could not be explained by the conventional Beer s Law. More than 40% transmission was obtained when the spherulite size of the polymer was less than 10 pm in the film thickness range of 0.02 to 2 mm. One procedure to obtain such a film was to extrude polyvinylidene fluoride into a film at 270°C followed by cooling the extrudate on a chill roll maintained at 120°C. The film was next oriented, in two steps, in longitudinal and transverse directions by stretch ratios of 2.8 and 3, respectively. 

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