Every second year the EDF-PPRIME Workshop is dedicated to sealing technology. This week the 17th edition of this event was held at the EDF Lab Paris-Saclay focusing on minimizing both leakage and friction of rotary seals.
The event started on Tuesday with an introductory tutorial on the lubrication of dynamic shaft seals organized by the University of Poitiers.
The introduction and the face seals part was carried out by Noël Brunetière (Institut PPrime). Aurelian Fatu (Institut PPrime) explained the working principle and the modelling techniques of elatomeric radial lip seals. Finally Mihai Arghir (Institut PPrime) and Amine Hassini (EDF R&D) focused on the non-contacting seals and the relevant role of the sealing components to the dynamics of rotor-machinery. The day finished with a traditional French cuisine dinner at the restaurant La Grange.
On Wednesday the conference was hold at the IFMI amphitheater of the EDF facilities. There were no parallel sessions which allowed the author to summarize the contribution of all the speakers.
After a brief opening speech, the first presentation was done by Lang Klaus (Eagle Burgman) who went through the different legislations regarding allowable leakage rates and the upcoming EU Ecodesign Directive. This last one directly affects the sealing components requiring to increase their efficiency. In other words, to lower the friction.
Lang Klaus (Eagle Burgman) keynote speech.
He emphasized on the impossibility of achieving zero leakage and zero friction and closed his speech with a joke: “Nature, in million years, could not develop any animal with wheels; that is because nature was not able to prevent the leakage on its bearings”.
The next presentation by Yuichiro Tokunaga (Eagle Industry) showed the impact of surface texturing to mechanical shaft seals friction. He introduced a new mechanical seal concept, at least for the author, where gas and liquid are combined. This hybrid mechanical shaft seal allows to work with lower frictions for a wide range of speed. For low speeds liquid lubrication is used to obtain face separation while at higher speeds, when there is not a demand for such the higher liquid viscosity, gas overtakes the load carrying function. Mohand Adjemout (Latty International) presented a complex test rig allowing him to research on the thermal shocks on seals, i.e. fracture due to a sudden change of temperature. To do that hot water is rapidly pumped to his test bench leading to a sudden temperature variation. Stefan Lamapert (Delft University) followed with an interesting presentation on ferrofluid seals. He showed his research on the sealing capabilities of ferromagnetic fluids and discussed on the feasibility of using such almost frictionless seals for low pressure applications. Dale Rice (VSP Technlogies) presented the tools nowadays available for predicting leakage rates in gaskets. He stated that both the EN 135555 and PVRC ROTT test are reasonably correlated and they can be used together. He emphasized on the importance on the dimensional accuracy of the gaskets to obtain effective sealing.
Christoph Burkhart (MEGT) on elastomeric seals modeling.
Mohamed Jarray (Institut PPrime) presented an isothermal model of a viscous seal. He showed good agreement between Reynolds Equation solution, Navier-Stokes solution and the experimental testing. Auger Greg (Thordon Bearings) showed impressive cases of refurbishing sealing components of hydraulic turbines in New Zeland, Brasil and Italy. The cases presented allowed to decreases the leakage on such components while extending their lifespan. Later Samia Dahite (Institut PPrime) carried out a great introduction to radial segmented seals and the computational methods used to model them. An interesting comparison between running with perpendicular and inclined grooves was presented. Cori Watson (University of Virginia) showed a multi-phase model of viscous seal. The model proved to be especially useful for optimizing the maximum pressure difference that a viscous seal can bear before leakage occurs. She also showed that that by using a single phase model, instead of a multi-phase one, the results were still fairly accurate.
Christoph Burkhart (MEGT) presented the work of his colleague Stefan Thielen who could not attend to the workshop. He stated that 30% of the elastomeric rotary lip seal failures come from shaft failures. A time-dependent lip seal model including the shaft roughness was presented. The impact of artificially made dimples on the shaft and their orientation was studied by the use of flow factors. Youssef Bahi (ENSAM/UMI) reasoned over the complexity of decreasing both leakage and friction of seals at the same time. The first one demands for a lower gap height while the second requires a thicker lubricant film and a greater hydrodynamic pressure build-up. He presented a complete quasi-static model of a reciprocating U-cup seal. Gerrit Weiser (TUHH) closed the presentations with an extensive study on friction between several fluoroelastomer-lubricant combinations. The different pairs of materials were tested at different speeds and temperatures for several days. The load is kept constant. The test rig she used replicates the working conditions of an elastomeric radial lip seal including both leading and trailing edges. She showed that the friction coefficient is anything but constant in speed, temperature and time. The impact of certain lubricant additives on the friction coefficient was also shown.
Gerrit Weiser (TUHH) closing the workshop.
The 17th EDF – PPRIME Workshop ended with a visit to the EDF testing facilities located in a building nearby. Although highly intestesting, the testing facilities did not include any seals testing test rig. The EDF seals tests are currently carried out in a different location in France.
F. Xavier Borras on 5th of October 2018
Surface Technology and Tribology
University of Twente