Steinbeis experts help develop a new method for cross-linking liquid silicone rubber in the injection molding process
First developed in the 1970s, liquid silicone rubber (LSR) has become increasingly important as a material in recent years. There are number of reasons for this growing interest. Not only does it offer uniform mechanical and electrical properties spanning a range of temperatures, but it is also highly durable over time, it is resistant to UV influences, ozone, and chemicals, and it is biocompatible. A team of experts at Esslingen University of Applied Sciences has joined forces with Plastics Center, a Steinbeis Transfer Center, and developed an innovative method that makes it possible to determine how to cross-link LSR in real time during injection molding processes – with unprecedented accuracy. Not only does their innovative invention significantly shorten production cycles, but it also ensures that manufactured components are cross-linked as best possible in keeping with the strictest quality standards.
With two injection molding machines for processing liquid silicone rubber (LSR) and two-material composite components, the Plastics Center is in an ideal position to conduct LSR research.
The material properties offered by LSR can be applied to areas such as seals used in the automotive and aviation industries, cable insulation in the electrical industry, baking tins in the food industry, medical implants, and medical devices. It also possesses outstanding optical properties that enable it to be used in LED systems and matrix headlights. In addition to these remarkable application properties, LSR offers processing advantages. It can be processed accurately in short cycles during the injection molding process (sometimes without post-curing) and still retains a long pot life at room temperature of over three days.
Cutting costs and improving quality
The Plastics Center is working intensively on LSR, its properties, and processing in the injection molding process and has developed a new method for accurately determining the cross-linking of liquid silicone rubber during the injection molding process. The scientific basis for this development stems from analytical investigations into cavity pressure curves during injection molding processes. This investigative work was conducted by experts at Esslingen University of Applied Sciences and funded by Baden-Württemberg Stiftung as part of a research program looking into biofunctional materials and surfaces. The researchers were able to identify the point on the internal pressure curve of molds that is crucial for cross-linking. This is the point at which, driven by cross-linking, the rise in the density of the liquid silicone overlaps with its thermal expansion. Accurately ascertaining this inflection point on the internal pressure curve of molds makes it possible to assess the exact moment material in a mold is fully cross-linked. By comparing measurements using dynamic differential calorimetry, the Steinbeis experts were able to confirm consistent correlations between the inflection points on pressure curves and cross-linking processes.
This innovation offers groundbreaking advantages. First, cycle times are significantly reduced, since the injection molding process can now be controlled more efficiently. Knowing the ideal time to cure LSR makes it possible to steer clear of safety margins previously applied to curing times. Not only does this help cut costs, but it also enables components to be made available more quickly.
The new technology also offers unprecedented levels of quality assurance. Because the degree of LSR cross-linking is monitored continuously during processes, potential defects or quality inconsistencies can be detected and corrected early – in situ, if required, for individual components. This reduces reject rates and significantly increases the overall reliability of the manufacturing process.
Application of the method to detect the cross-linking of a component within the process monitoring system: This allows cycle times to be shortened significantly.
Steinbeis Entrepreneur Professor Dr.-Ing. Matthias Deckert emphasizes the wide range of applications for this technology: “Our invention has every potential to revolutionize the production of LSR components, across numerous industries. The combination of shorter production cycles, enhanced quality, and reliable quality controls makes this technology an invaluable mold for industrial companies in every corner of the globe.”
From research into practical application
While the university specialists continue to carry out the scientific groundwork for the project, the experts at Steinbeis are currently working on transferring the technology to other hot cross-linking materials. Their next objective is to identify companies interested in further development of the method – for which a patent application has already been filed by Baden-Württemberg Stiftung – until it is ready to be commercialized.
Contact
Prof. Dr. Matthias Deckert (author)
Steinbeis Entrepreneur
Steinbeis Transfer Center Plastics Center (Neckarsulm)
Dennis Weißer (author)
Research assistant
Faculty of Mechanical and Systems Engineering | Esslingen University of Applied Sciences (Esslingen)
Dennis Mayer (Autor)
Research assistant
Faculty of Mechanical and Systems Engineering | Esslingen University of Applied Sciences (Esslingen)
227254-41