This week the 20th edition of the biannual International Sealing Conference (ISC) took place in Stuttgart. Around 200 assistants showed up to the 2-days sealing conference. Well-known companies such as Bosch, SKF, Trelleborg, Parker, Shell, EKK or Freudenberg showed their latest developments.
The conference was mainly hold in German and so were the most part of the presentations. Even the conference booklet is mainly written in German. Fortunately for the author, and tribonet.org readers, a simultaneous translation system was arranged so one could listen to a delayed version of the speech. Truth to be told, the translators did an outstanding job. Terms from the sealing slang such as “reverse pumping mechanism” do not look too easy to translate.
Two parallel sessions were arranged. The author mainly attended to the ones focusing on rotary elastomeric lip seals (conference room A). Due to that some relevant presentations might not be mentioned in this review.
Frank Bauer (IMA) and Ingrid Hunger (VDMA) kicked off the conference presenting the progress of the ISC in the last years and the sealing market prevision for the coming years.
Peter Waidner (Hochschule für Angewandte Wissenschaften München) keynote presentation.
The first keynote speaker was Peter Waidner (Hochschule für Angewandte Wissenschaften München) who introduced the not-so-common topic of noise in mechanical seals under stationary. The phenomena of squeaking and whistling of mechanical seals were linked to the natural resonance frequency of the seal. The viscous nature of the elastomer seal acts as a damper partially preventing the impact of the resonance phenomenon. However, when running for a long time or under too high temperatures, elastomer hardening occurs and the elastomer becomes more prone to undesired noises. He also explained the difference between stick-slip and drag-stick-slip.
The second key note speaker was Bernhard Richter (O-Ring Prüflabor Richter GmbH) who presented a several decades-long extensive study on the causes of failure of elastomeric seals. The failure mechanisms were classified within: media, temperature/aging, mechanical/physical effects and manufacturing fault. Interestingly, during the last years, the manufacturing failures considerably increased representing nowadays the 25% of the total amount of failures. This was explained to be due to the high performance materials being developed which have decreased the first two failure mechanisms.
Susanne Jaeckel (IMA) showed in her presentation the complexity of accurately measure the inner diameter of elastomeric seals. The traditional method of using metered cones was shown to be somehow dependent on the user criteria. A novel system was developed at IMA able to measure the seals inner profile using laser triangulation technique. A prototype was exhibited at the conference hall.
IMA-seals scanner exhibited at the 20th ISC.
It was stated that the measurement of the seal inner diameter before and after running is the most reliable method to measure wear. However, in case of creep, shrinkage or swelling the results might not be straight forward. It was also said that measuring the worn volume after running does not correlate well with the tribological system of the tip.
Mario Stoll (IMA) presented a comparison between the elastomeric seal lip seals, PTFE lip seals without sealing aids, PTFE lip seals with spiral groove and PTFE lip seals with sealing aids. The reverse pumping rate of seals with different laser-textured pumping aids were also presented. Still in PTFE lip seals Florian Albrecht (HAW) presented his efficient computational model including the memory effect characteristics of PTFE material. André Gütlein (Hecker Werke GmbH) introduced the hybrid seal faces produced with laser beam. Together with Timo Bernthaler (Hochschule Aalen), they exposed the advantages of additive manufacturing when producing mechanical face seals starting by the obvious one: it does not require a static sealing mechanism in its backside of the ring. Emphasis was placed on its advantages when refurbishing worn out rings.
Gert Wahl (Schunk Kohlenstofftechnik Gmbh) made an interesting presentation on the impact of plastic deformation on the ceramic rings of mechanical seals after its first run. Under such pressures the permanent deformation of the material affects the dimensional accuracy of the rings and even impact its material proprieties. He showed that the Young modulus of the sealing ring material increases with when exposed under 130 bar. This phenomenon is time-dependent until a plateau is reached after around 60 minutes. The grain size and the resin impacted this variation. Both Wataru Kimura (Eagle Industry) and Yuta Nehishi (Eagle Industry) presented their computational models of hybrid mechanical seals and the great impact of texturizing the surfaces of mechanical face seals for tidal turbines.
Veith Pelzer (IMKT) showing the reverse pumping flowrate measured for three identical seals.
Gerrit Weiser (TUH) studied the formation of blisters in fluoroelastomers using a specialized test rig resembling rotary lip seals. The test rig enables the application of a constant load on the rubber specimen. Her research attempts to determine which combination of pressure, speed and temperature triggers the appearance of blisters. Cristoph Burkhart (MEGT) compared seal tip temperature predictions of Engelke’s and Magyar’s models with experimental results. Both showed good accuracy with the measurements. Veith Pelzer (IMKT) showed the complexity of measuring the reverse pumping flowrate and its sensitivity. He showed that the measured back-pumping flow occasionally showed sudden variations which are nowadays still difficult to explain. Sumbat Bekgulyan (IMA) presented the results of a comprehensive study on reverse pumping of rotary lip seals. The following parameters were swept: seal material, nominal diameter, speed, viscosity and peak-to-valley roughness to observe its impact to reverse pumping flowrate. The results from such enormous testing matrix were fitted to a second order polynomial. The model was purposed as a tool to control the quality of elastomeric rotary seals which is, until the moment, hard to ensure. That would of course require the costumer to owe a test bench able to measure reverse pumping rates.
After such intense day of presentations dinner was served at the Maritim Hotel of Stuttgart.
Maritim Hotel of Stuttgart gala dinner.
Next morning Bas van der Vost (SKF) opened the second day of the 20th ISC presenting the SKF Samba software to predict the followability of an elastomeric lip seal under dynamic run-out. The impact of temperature and aging was included in the model. The decreases on the followability of the seal under low temperature and ageing could be predicted. He explained that the model was validated against real life experiments.
Bas van der Vost (SKF) presenting SKF Samba.
An innovative design of a radial lip seal was introduced by Holger Jordan (Trelleborg). He explained the thinking line which brought Trelleborg engineers to develop such a seal. In short, cooling down the seal tip while keeping stable reverse pumping rates. The final modular design includes pumping aids and space for two-garter springs. The revolutionary seal profile presented certainly challenges the traditional rotary lip seals working mechanism.
Holger Jordan (Trelleborg) presenting and innovative radial lip seal design.
Abdelghani Maoui (CETIM) presented a very interesting case which he faced: a large diameter polyurethane lip seal from an hydraulic dam turbine bearing showed an outstanding performance even after 7 years and a significant amount of volume do to wear. He compared such worn seal with a brand-new one in order to understand the mechanism behind such event. The worn off seal was an optimized version of the new seal: lower running temperature, lower wear rate and lower power loss while keeping the same sealing ability.
Emilia Kozuch (Loughborough University) studied the impact of the shaft axial motion to sealing failure (leakage) of rotary lip seals from gear boxes, transaxles and differentials. These shafts are usually grinded and polished however she showed that their final surface topography is detrimental to the success of the elastomeric seal. Three shafts with different topographies were tested under the same running conditions giving different results. She backed-up her findings solving the 1D Reynolds PDE (including cavitation) for the three shaft profiles. This way she shown that there is a strong correlation between the surface bearing area and the load carrying capacity of the hydrodynamic film generated.
The last block of the conference started with George Flade (Stasskol GmbH) explaining the advantages of non-contacting seals. Then Jan Totz (IMA) showed the correlation between the shaft surface imperfections with the reverse pumping mechanism of elastomeric lip seals. While grinding spots were shown to increase the reverse pumping rate, the scratches on the rod could increase or decrease it depending on the scratch orientation with respect to the direction of rotation.
Abdelghani Maoui (CETIM) showing both the worn out and brand-new seals.
Felix Schiefer (IMA) exposed his research on the twisting of the sealing mating surface. Due to torque the seals mating surface might twist leading to a certain spiral thread which heavily impacts the seals behavior. He showed that the severity of this phenomenon depends on the depth of the thread, the twist angle (thread orientation), and the frequency of the fillets. Robert Teichert (TU Bergakademie Freiburg) investigated on the contact of rotary shaft seals. He presented a specialized test rig where he compared the performance of a V-Ring with a Gamma-Ring seal.
The last session was dedicated to show industry applications of sealing components. Frank Schönberg (Freudenberg) presented the new omni-directional large diameter seal for grease lubricated bearings which counts with a two-layer lip: one metallic and the other elastomeric. Such arrangement allows running under low friction conditions while using the metal heat dissipation properties for cooling the contacting surface. Frank Sonnenschein (Garlock Gmbh) showed the challenge of dealing with abrasive media in Food&Pharma environment. Finally Johannes Kunze von Bischoffshausen (Trelleborg) presented a promising application of machine learning in the sealing industry.
Leo Dupuis (Bosch Rexroth BV) and Sravani Gullapalli (Shell) showing an example case of a reciprocating hydraulic piston.
Two closing lectures finalized the 20th ISC. First a combined presentation between Leo Dupuis (Bosch Rexroth BV) and Sravani Gullapalli (Shell) showed the importance of approaching the whole tribo-system at the same time, seal and lubricant, in order to obtain optimum results. Second Thomas Kletschowski (HAW) finalized presenting a PTFE shaft seal model considering friction, heat generation and wear.
The author got really good feedback from some presentations of the B conference room sessions he could not attend (for obvious reasons). Worth mentioning the “Unavoidable minimum leakage of PTFE-gaskets due to diffusion” from Martin Lüttecke (Faschhochschule Münster) and the “On the modeling ageing of rubber seals” presented by Manfred Achenbach (Sachverständigenbüro Achenbach).
F. Xavier Borras on 15th of October 2018
Surface Technology and Tribology
University of Twente