Gap impregnation is a fairly new process for the production of high-performance parts of fiber-reinforced plastics (FRP) in only a few minutes. In this process, which is similar to RTM, a temporary flow gap is created. This temporary flow gap and the inclined position of the mold result in rapid, reproducible injection of the resin system with low resistance. The exceptionally fast impregnation of the preform in the space of only a few seconds allows the use of the highly reactive resin systems that are needed for part production on an industrial scale.
At the Institute of Plastics Processing (IKV) in Industry and the Skilled Crafts at RWTH Aachen University, an automated gap impregnation unit was developed back in 2009 and installed in the IKV pilot plant. Recent tests with the unit have been aimed at using not only epoxy resin systems but also alternative resin systems such as polyurethanes (PU) for the series production of fiber-reinforced plastics parts (FRP). In cooperation with IKV, BASF Polyurethanes GmbH, Lemförde, has developed, a new, highly reactive and compact crosslinking PU system for FRP.
In this project, attention is focused on the verification and optimization of a long open processing time of the PU system during injection and impregnation of the FRP parts in combination with fast, latent crosslinkage with isothermal mold temperature control. Furthermore, the demolding behavior is analysed with the use of internal release agents. For the tests, both flat parts and curved parts with varying thicknesses and a projected surface area of 500 x 500 mm2 are used. The parts are made of glass- and carbon fiber reinforced plastics. Irrespective of the reinforcing fiber, the fiber volume content of the continuous fiber-reinforced parts is between 45 and 50 percent. Process times of less than six minutes - from mold closure to removal of the crosslinked part - were achieved.
Depending on the volume of the part, the injection, impregnation and consolidation account for a maximum of 23 seconds, while crosslinkage of the parts in the mold, heated isothermally to 80 °C, takes around four minutes. It was thus possible to successfully demonstrate a sufficiently long processing time of the latent reacting PU systems in the impregnation and consolidation process. Furthermore, a new modification of the PU systems with internal release agents allows reliable demolding. The impregnation quality of the parts is very good and comparable with that of highly reactive epoxy resin systems. This means that the PU systems developed by BASF are an attractive alternative to epoxy resin systems.
About IKV
IKV, the Institute of Plastics Processing at RWTH Aachen University, is Europe-wide the biggest research and education institute engaged in the field of plastics processing enjoying outstanding reputation. More than 300 staff are employed in finding solutions to problems connected with processing, materials technology and part design in the plastics and rubber industries. IKV's close contacts with industry and science, together with its outstanding facilities, enable cutting-edge research in plastics technology and ensure that students benefit from a comprehensive, practically oriented course of study. Plastics engineering graduates from IKV are thus soughtafter experts in industry. In organizational terms, IKV is divided up into the four specialist departments of Injection molding and PU Technology, Extrusion and Further Processing, Part Design and Materials Technology, and Composites. The Institute also takes in the Centre for Analysis and Testing of Plastics, and the Training and Further Education department. IKV is run by an Association of Sponsors, which currently has a membership of more than 230 plastics companies from all over the world. Univ.-Prof. Dr.-Ing. Christian Hopmann is Head of the Institute and Managing Director of the Association of Sponsors. He also holds the Chair of Plastics Processing at the Faculty of Mechanical Engineering at RWTH Aachen University.