FEATURE for short duration or requires special materials. However, this is not stated on the data sheets. Only one company mentions the problems of flexibility at low temperature and describes how the low temperature rating is decided. And then there is the pressure effect. Does this matter? Well I am aware of some very recent, even current problems that have occurred causing very expensive seal changes and shut downs leading to severe loss of revenue that can be directly attributed to what can best be described as over enthusiastic specification of elastomers. One involved low temperatures and the other high, interestingly in the 200 to 230ºC region. Whether the fault in these cases was an OEM ordering on the basis of a data sheet or a recommendation by the seal supplier I cannot be sure, but it is not necessarily central to the argument. The data sheets are published without any qualifications about the actual duty or the inherent properties of the material and users are accepting the numbers without question.
What should we do? Elastomer used for seal manufacture is not black magic. It is an engineering material, even though it is little understood by most of us. Metals are specified to be used well within their known working limits. We do not take the same care with elastomers, and then wonder why they fail.
It seems to me that there should be some cooperative action by the major manufacturers to devise a common standard for the presentation of material performance limits, together with the constraints necessary to work successfully at the figures quoted. This may include limits on extrusion, interference, and other factors such as metal work movement at low temperature. I know that this is complicated, but we need to start somewhere. The alternative is that major sectors of industry loose confidence in elastomer seals and start to write them out of company or industry specifications, and hence there will be a big loss of business, particularly for the premium materials. My information is that this is already happening. Who is going to do this? It is perhaps not a total coincidence that some members of the new Elastomeric and Polymeric Seals Division of the European Sealing Association have recognized this as one of the important problems affecting the industry. By the time you read this they will have just held an exploratory meeting on specifications for elastomer materials. If you have any views or input to this work I am sure that they will be interested to hear from you, and for additional seal companies to join the group. Alternatively for OEM’s and users I am happy to collect and collate any views that you may have on this subject. All replies will be treated as confidential, unless you specifically wish them to be
published. And, if there is a clear consensus it can be passed on to the ESA for input to their work.
References 1. Editor’s comment, Sealing Technology, February 2004, p 16. 2. Robert Flitney, Seals and Sealing Handbook, Elsevier, 2007. 3. Robert Fuller, Advanced polymer architecture sealing solutions for oil and gas applications’ Sealing Technology, September 2006. 4. BS EN 1759-1:2004 ‘Flanges and their joints. Circular flanges for pipes, valves, fittings and accessories, class-designated. Steel flanges, NPS 1/2 to 24’ 5. ‘High performance elastomers’ James Walker &Co. 6. H-P Weise, H. Kowalewsky and R. Wenz, ‘Behaviour of elastomer seals at low temperature’ Vacuum, 1992. Contacts: European Sealing Association, Tegfryn, Tregarth, Gwynedd LL57 4PL, UK. Tel/Fax: +44 1246 600250, Email: [email protected]
, Web: www.europeansealing.com. R.K.Flitney, Editor, Sealing Technology, 66 De Vigier Avenue, Saffron Walden, CB10 2BN, UK, Tel: +44 1799 501659, Email: [email protected]
Conference Report Conferences and Publications
International Conference on Fluid Sealing
Three days of sealing presentations provide plenty to discuss
he 19th International Conference on Fluid Sealing and the 6th EDFLMS Poitiers Workshop collaborated to hold the events at a single venue on 25-27 September 2007 and benefited from improved attendance at both meetings. Approximately thirty delegates attended both meetings, a substantial improvement on the four who patronized both when they were held a week apart two years ago.
his event was compressed from what had become a traditional two and a half days into a very full two days and benefited from a programme that aligned very well with the workshop meeting that followed. The first day comprised two sessions on seals particularly applicable to fluid power, one on rotary shaft lip seals and one on static seals and valves. This was followed by a day more focused on process and similar applications with elastomer seal performance, mechanical seals and turbomachinery seals. The fluid power sessions were an interesting combination of analytical work and test results. The elastohydrodynamic model of a reciprocating seals with a double lip by Richard Salant from Georgia Institute of Technology continues to provide results that meet with the approval
of experienced observers, which is much more than can be said for any previous attempts at predicting the performance of reciprocating seals. The work from M Kozma of Budapest University suggests taking almost the opposite approach by assuming that the elastomer is smooth. The effects of seal counter surfaces were covered in some detail with Frank Steep from Merkel Freudenberg providing an update on the work to provide improved definition of rod surfaces. A very sensible suggestion during the discussion on this paper was that seal suppliers should collaborate to produce a standard set of recommendations of surface texture parameters and values. Several delegates were interested in this idea. A paper from Thomas Papatheodorou of Parker provided a considerable amount of data on seal tests on chrome and alternative surfaces, but unfortunately the author could not attend and this paper did not include much detail on the surface texture. Pneumatic seals were also covered in some detail with interesting results on the effect of different lubricants. Other
CONFERENCES contributions on pneumatic seals included contact pressure measurements and an investigation in the KRISTAL project to look at surface coatings on elastomers. The latter did not last too long, which was not a surprise to some of us. An interesting study of the operation and failure patterns of high pressure rotary seals for hydraulic rotary couplings was presented by M Henzler from the University of Stuttgart. Factors such as shaft start up and acceleration with different seal types was discussed followed by some typical failure modes that can affect plastic co-axial seals used in these applications. The static seals session covered both extremes with a presentation on very high temperature/ high pressure static applications, particularly for envisaged nuclear duties from Garlock, and a procedure for the qualification and certification of press-fitting connections in gas applications, using O-rings, from Gaz De France. These fittings, which use an O-ring instead of a typical brazed fitting are qualified using a five week test at a maximum of 50ºC, which a number of delegates considered to be a rather minimalist test for a component expected to be built into a domestic gas supply for perhaps 20-30 years. In the same session Latty presented a discussion of the benefits of valve and packing companies working together to provide reliable low emission valves. The session on Rotary Lip Seals contained an interesting variety of papers. Work by M Silvestri at the University of Parma demonstrated the results of calculating friction from strain measurements of a seal under dynamic conditions. NOK showed work of the study of
the lubrication of pressurized lip seals, up to 2bar, using a glass shaft. The comparative pumping effect of the seal and shaft texture has been studied by Stuttgart University and although hard turned surfaces were shown to pump along the machine lead this was found to be low compared to the pumping effect of the seal. The elastomer materials session was very well supported by presentations from Parker. The life prediction by numerical simulation developed by the company takes a rather more fundamental approach than previous work in this area, but while effective still requires considerable caution when used for extrapolating seal performance. Uwe Wallner presented a sound reason for the use of the Elastomer Compatibility Index, and demonstrated examples of applying it to provide very rapid answers on the potential compatibility of elastomers with an individual oil grade. Following the same theme of elastomer seal performance prediction, but in a very specific application area, BHR group presented the guidelines developed with the UK Health and Safety Executive for assessment of rapid gas decompression in high pressure gas service. The mechanical seals sessions contained a similarly varied selection of work. Professor Vizintin from the University of Ljubljana presented work studying the effect of surface texture on the lubrication performance of seal faces. His attempts to use the familiar duty parameter had met with similar results to many of us before, but he did discerned an improvement in hydrodynamic performance for very smooth surfaces.
The computer analysis of mechanical seals was covered quite comprehensively by JPSM, John Crane and also AES where CFD helped demonstrate the effectiveness of a pumping ring design. The measurement of film distribution by two-dimensional dynamic measuring system for mechanical seals using laser induced fluorescence was discussed by Eagle Industry. This requires the use of a glass seal face which could be a negative factor compared with the recently introduced capacitance methods used to measure seal face conditions with actual materials. The paper on ethylene oxide sealing with mechanical seals by Craig Watkinson, of Greene Tweed was concerned with the elastomer seals that can see unpredictable failures in this application. The serious effects of air contamination in EO systems were demonstrated using case studies. Design rules and operational procedures to avoid potentially serious failures were provided. In the turbo machinery session Gordon Kirk from Virginia Polytechnic discussed the use of CFD to investigate the complex flow in labyrinth seals and compared the results with established bulk flow models. This demonstrated some interesting flow results. Helm, Spliethoff and Neef described a test method for qualifying brush seals which used an optical measurement to obtain the gap between the shaft and bristles and hence the blow down, or leakage through the seal. The technical sessions were complemented by the traditional BHR Group hospitality. The evening before the conference delegates were invited to the town hall for a reception with the Mayor and the conference dinner was held in the local Chateau Ribaudière which provided an excellent meal in very convivial surroundings.
Papers presented Fluid Power
The Mayor of Poitiers welcomes the 19th International Conference on Fluid Sealing to the city. The conference organizer, in kilt, may be a Scotsman but he lives in Northampton which is twinned with Poitiers. Photo by permission of Centre Presse, Poitiers.
‘Elastohydrodynamic model of a reciprocating hydraulic rod seal with a double lip’, B Yang, R Salant, Georgia Institute of Technology, USA. ‘Hydrodynamic and boundary lubrication of elastomer seals’ M Kozma, Budapest University of Technology and Economics, Hungary. ‘Counter surfaces of hydraulic sealing system for heavy-duty applications’ F Steep, G Wüstenhagen, Merkel Freudenberg Fluidtechnic GmbH, Germany. ‘Problems and failure patterns of high pressure rotary seals and pertinent solutions for