Chancen und Möglichkeiten des Duroplast für MID-Anwendungen

Thermosets show excellent mechanical properties and chemical resistance (for most automotive fluids) even at high temperatures up to 300 °C. Furthermore they can be highly efficient processed by injection molding. So they should be particularly suited for e.g. under the bonnet applications. However, the reality shows that thermosets are, except fiber reinforced composites, heavily underrepresented in technical applications. E.g. thermosetting components only account 0,2 % to a vehicle’s weight. Therefore reasons can be found in limited knowledge, e.g. relating mold filling behavior. The objective of the study is to analyze the influence of the mold filling behavior during injection molding of highly filled phenolic compounds on mechanical properties. Injection molding filling studies, mechanical testing and optical microscopy were done while varying mold geometry (injection gate and cavity height), mold temperature and injection rate during injection molding a highly filled phenolic compound. It was found that the mold filling behavior varies with altered injection molding parameters as well as the mold geometry. In consequence of this the mechanical properties change according to the resulting reinforcement orientation. The results can help to improve part and mold design for optimal load transmission.

Chancen und Möglichkeiten des Duroplast für MID-Anwendungen

Thermosets show excellent mechanical properties and chemical resistance (for most automotive fluids) even at high temperatures up to 300 °C. Furthermore they can be highly efficient processed by injection molding. So they should be particularly suited for e.g. under the bonnet applications. However, the reality shows that thermosets are, except fiber reinforced composites, heavily underrepresented in technical applications. E.g. thermosetting components only account 0,2 % to a vehicle’s weight. Therefore reasons can be found in limited knowledge, e.g. relating mold filling behavior. The objective of the study is to analyze the influence of the mold filling behavior during injection molding of highly filled phenolic compounds on mechanical properties. Injection molding filling studies, mechanical testing and optical microscopy were done while varying mold geometry (injection gate and cavity height), mold temperature and injection rate during injection molding a highly filled phenolic compound. It was found that the mold filling behavior varies with altered injection molding parameters as well as the mold geometry. In consequence of this the mechanical properties change according to the resulting reinforcement orientation. The results can help to improve part and mold design for optimal load transmission.

Im Rahmen der vorliegenden Arbeit wurden verschiedene duroplastische Formmassen laboranalytisch hinsichtlich der rheologischen und thermischen Eigenschaften untersucht. Es wurde u.a. gezielt die absolute Materialfeuchte gesteigert, um den Einfluss dieser auf das Fließ­ Härtungsverhalten zu charakterisieren. Anschließend wurden die Materialien auf einer hochinstrumentierten Spritzgussmaschine mit einem Fließspiralenwerkzeug untersucht. Dabei konnte ein direkter Zusammenhang zwischen dem Rückfluss und dem Plastifizierdrehmoment in Abhängigkeit der Materialfeuchte und der Prozessparameter detektiert werden . Des Weiteren wurden über die Differenzdruckmessung im Fließspiralenwerkzeug die scheinbaren Viskositäten über den Fließweg ermittelt. Hierbei konnten unterschiedliche Aufschmelzeffekte über die Fließweglänge in Abhängigke it der duroplastischen Formmasse, der absoluten Materialfeuchte und der Prozessparameter detektiert werden . Durch Schererwärmung konnte die Formmassentemperatur teilweise die Werkzeugtemperatur übersteigen. Hinsichtlich der mechanischen Eigenschaften (Schlagzähigkeit, Biegefestigkeit) konnten keine signifikanten Einflussgrößen detektiert werden. Hinsichtlich des Tg konnten systematischen Unterschiede detektiert und begründet werden. Die beste Möglichkeit zur Ermittlung des Tg lieferte die TMA. Die thermischen Glasübergänge korrelieren mit den in der DSC ermittelten Aushärtegraden , wobei mit steigender Materialfeuchte ein geringer Aushärtegrad detektiert wird. / Within this paper, the rheologieal and thermie eharaeteristies of different thermosetting molding eompounds were investigated using lab analysis methods. Among others, the absolute moisture eontent was inereased purposefully to investigate its influenee on the flow-euring behavior. Subsequently, the materials were analyzed using a highly instrumented injeetion-molding maehine and a flow spiral tool. A direet link between the baekflow and the plastifieation torque dependent on the moisture eontent and proeess parameters was deteeted . Furthermore, a measurement of the differential pressure was eondueted within the flow spiral to deteet the apparent viseosity over the flow path. Within this proeess, different melting effeets over the flow eurve length depending on the molding eompound, the absolute moisture eontent and proeess parameters were deteeted. The shear heating lead to a material temperature inerease of the molding eompound, whieh was partly higher than the tool temperature . Coneerning the meehanieal eharaeteristies (impaet strength, flexural strength), no signifieant influeneing faetors eould be deteeted. In eontrast, systematie differenees of the glass transition temperature were deteeted and their eause eould be explained. The best way to determine the glass transition is the TMA. The glass transition temperatures eorrelate with the degree of eure determined with the DSC, whereas an inereasing moisture eontent is assoeiated with a lower degree of eure.