New Seal Concept for the RTM Process
During production of fiber-reinforced parts using the high-pressure RTM process, the fiber preforms are infiltrated with reactive resin in the closed mold. To prevent the resin material's escaping from the cavity during injection and curing, elastomeric profile seals are employed in the molds. However, the chemical and mechanical stresses during the process can result in changes in the sealing cord's properties. This has an adverse effect on process reliability and the molded part's quality. In addition the regular replacement of the seals causes downtime of the RTM equipment.
Researchers at the Fraunhofer Institute for Chemical Technology ICT in Pfinztal have thus been investigating an alternative approach for sealing RTM compression molds. With this approach, the sealing cord is placed directly to the edge of the fiber preform. The cord is clamped mechanically in the mold during injection and curing of the resin and in this way held in position. A PU system serves as the sealing material and is applied directly to the edge of the preform, where it cures quickly after mixing of the individual components.
According to the information provided, this alternative concept for a self-sealing preform has great potential in terms of process automation and process reproducibility. Production interruptions for manual replacement of a worn profile seal in a heated compression mold can be eliminated. The molded part's quality can be improved, since a new, unused seal is always employed at the beginning of the cycle when the compression mold is loaded.
Furthermore, the concept also increases the flexibility of process management. Thanks to the almost freely definable sealing cord geometry, process variants such as injection RTM, compression RTM, liquid resin compression molding or combinations of these variants can be performed regardless of the design of the compression mold.