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pps proceeding
Symposium: Injection Molding & Molds
Oral Presentation
 
 

Visualization of Flow Patterns and Dead Volume by Means of Various Die Geometries Based on Different Rubber Compounds

Kerschbaumer Roman Christopher (1)*, Lechner Bernhard (2), Perko Leonhard (3), Friesenbichler Walter (2)

(1) Polymer Competence Center Leoben GmbH - Leoben - Austria, (2) Montanuniversitaet Leoben, Chair of Injection Molding of Polymers - Leoben - Austria, (3) Woco Industrietechnik GmbH - Bad Soden-Salmuenster - Germany

Avoiding dead volumes in rubber injection molding as well as in rubber extrusion is necessary to obtain rubber parts or semi-finished products with a high quality. Thus, it is substantial to know the complex flow behavior of the rubber compound at the entrance of various die geometries. In an extended study these aspects have been investigated for different rubber compounds. The apparatus used in this work to visualize the complex flow patterns and dead volume was a Capillary Rheometer (CR) manufactured by GOETTFERT GmbH in combination with a number of dies, characterized with a half inlet angel of 30 or 90 degrees and various lengths. The cylinder of the Capillary Rheometer, alternatingly filled with several colored rubber compounds of the same height (e.g. black and white discs), was heated up to testing temperature. During the tests the piston movement was stopped at a pre-defined position and the sample was cured in the cylindrical canal of the CR. After that, the sample was removed and cut in half along its long axis to visualize the flow patterns. Subsequently, the tests were repeated with the speed of the piston varying between 0.1 and 17.5 mm/s to evaluate the influence of volume rate on flow pattern formation. Moreover, the influence of different die geometries (in terms of the inlet angle) and different die lengths was also determined. Firstly, it could be shown that the inlet flow behavior and the resulting dead volumes are independent of the piston speed and the die-length. Thereby, no significant differences in the flow patterns were observed between the tested rubber compounds. Secondly, significant elongational flow could be detected in the area of the die- entrance and the centerline region.