Die Dichtungsextrusion ist ein Hauptanliegen für hydraulische Anwendungen, insbesondere dort, wo hoher Druck herrscht oder die Extrusionsspalten größer sind als normal. Früher haben sich die Ingenieure bei der Abschätzung des Extrusionspotenzials auf Tabellen oder Näherungsformeln gestützt. Als Ergebnis von Forschung, Experimenten und FEA-Simulationen hat System Seals jedoch ein Extrusionsberechnungswerkzeug entwickelt, mit dem Ingenieure vorhersagen können, wann Thermoplasten durch Extrusion versagen. System Seals nutzt solche Werkzeuge, um neue Dichtungstechnologien zu entwickeln.
Figure1. Cross section of extruded seal
EXPERIMENTAL PROCEDURE AND FEA MODEL DEVELOPMENT
To investigate the relationships between e-gap, material, and extrusion, PTFE seals in a basic square profile were installed into a pressure intensifier as well as seals with a POM backup. All profiles were tested at 21, 34, 48 MPa under 3 radial e-gaps (.5, 1, 1.5mm). After testing concluded, the seals were immediately removed, visually inspected, and measured for extrusion. After, seals were sectioned and imaged for visual confirmation. Simultaneously, FEA models were constructed to duplicate the seal size, pressures, materials, and e-gaps. After a relationship was extracted between the FEA and experimental results, additional FEA models were constructed for the current and new seal designs under various operating conditions.
The FEA models confirmed the experimental results, which indicated the relationships between pressure, e-gap, and extrusion potential. And by running simulations on various seal designs, we were able to develop a new seal design with an active back-up ring that is extrusion resistant.
Typical FEA model and probes
Because the initial experimentation and FEA simulations were so successful, we conducted nearly 300 additional FEA simulations which lead to the development of mathematical models that we use to predict extrusion for a wide variety of materials.
Figure 19. Design Tree for FEA Backup Ring Simulations
CONCLUSIONS
Older seal designs cannot effectively resist extrusion onset, due to larger e-gaps, higher pressures, and larger loads and deflections. As a result, new designs are required. To reduce the time and costs required to go to market with a new design capable of functioning in the more extreme operating conditions, a combination of both FEA and empirical experimentation were used for this investigation. As a result, a next generation rod seal was developed which can withstand the higher pressures and e-gaps without extruding. In conjunction, consideration was given to increases in e-gaps due to guidance system deflections and rod-to-cylinder eccentricity. Furthermore, our design and simulation procedure included the impact of temperature on extrusion resistance of materials, as determined by DMA testing data. Therefore, cylinder manufactures and engineers can design for larger e-gaps and clearances without the concern over seal extrusion and the associated system failures.
