high-speed test at boundary conditions
TRANSCRIPT
The starting point for the work was a perceivedrequirement for a mild lubricated wear test.Environmental concerns are forcing large andvery rapid changes to engine oil formulations.As new anti-wear components of engine oils aredeveloped a reliable way of assessing the anti-wear and anti-scuff effectiveness of new addi-tives and formulations quickly and cheaply isrequired. Current lubricated, mild wear, tests arenot up to the job. It would also be helpful tohave a more ‘scientific’ mild wear test to help inresearch on lubricated wear.
Most current mild wear tests are based onpure sliding, non-conforming contact with highsliding speeds. Because of the high sliding speed,the test often operates in mixed-lubrication andis then sensitive to viscosity. The pressure is usu-ally unrealistically high particularly at the startof the test.
One potential solution is to rotate both sur-faces, to give a mixed sliding and rolling wearinterface. This distributes wear around contactand so there is much less change in local geome-try and thus contact pressure. However it does
introduce a problem of accurate wear measure-ment.
Wear depends on sliding distance, so toobtain sufficient wear in a reasonable time ahigh sliding speed is required. But a high slidingspeed normally means a high entrainment speedand thus a high EHL film thickness, and so lesswear.
By moving the surfaces in opposite direction,contra-rotation, can produce a high slidingspeed with a low entrainment speed. If two testmaterials are rubbed together at different speedsin opposite directions it is possible to obtainhigh sliding, and thus plenty of wear, in bound-ary lubrication conditions. The current testshave involved a ball on disk mini tractionmachine, as shown in Figure 1.
The problem then becomes measuring thewear, which is distributed along a wear track on
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12Sealing Technology June 2006
Adhesive/coating and gel types can be handledin the same manner as standard silicone typematerials.
Regardless of the type used, the base poly-mer structure based on the perfluoropolyetherbackbone provides:
• Low-temperature flexibility as low as–50°C.
• High-temperature stability as high as200°C.
• Excellent resistance to a variety of fuels,additives, solvents, acids and alkalis.
The introduction of perfluoroether elastomerprovides engineers with a wide range of oppor-tunities to improve the processing and perfor-mance of sealing, coating and bonding opera-tions in various applications exposed to severeconditions.
Contact:Shin-Etsu Chemical Co. Ltd. 1-10 Hitomi,Matsuida-machi, Annaka-shi, Gunma,Japan, Tel: +81 27 384 5380, Fax: +81 27384 5308, Email: [email protected],Web: www.shinetsu.jp
This feature is based on a paper presented at the5th International MERL Conference, ‘OilfieldEngineering with Polymers 2006’ organized byMERL and Rapra Technology. For copies of theProceedings contact: MERL Wilbury Way,Hitchin, Hertfordshire SG4 0TW, UK. Tel: +441462 427850, Fax: +44 1462 427851, Web:www.merl-ltd.co.uk. Or contact: RAPRATechnology, Shawbury, Shrewsbury, ShropshireSY4 4NR, UK. Tel: +44 1939 250383, Fax:+44 1939 251118, Email: [email protected], Web: www.polymercon-ferences.com
Figure 12. The hardness change caused by chemicals on SIFEL3702 compared with FKMand FVMQ.
Figure 13. The hardness change caused by chemicals on adhesive grades of material.
Figure 14. The hardness change caused by acidson a potting gel grade of perfluoropolyether.
High-speed test atboundary conditionsBy Bob Flitney
Professor Hugh Spikes from Imperial College in London has developed a testthat is designed to be applicable to the testing of lubricants with metal-to-metalbearing combinations, but the basic idea of providing boundary lubrication at ahigh sliding speed has some potential interest for seal material testing.
Patents
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13Sealing Technology June 2006
both surfaces, in a metal-to-metal combination.The current work, which is studying metal-to-metal lubricated contacts, has developed a tech-nique using atomic emission spectroscopy withinductively coupled plasma (ICP-AES). Thispermits very accurate assessment of the wear par-ticles in the oil. The results so far have demon-strated good repeatability and have been com-pared with alternative measurement methods.More details of the test method and resultsobtained can be found in Reference 1.
The method of wear measurement discussedin this work is very specific to the sliding paircombination being tested. However, the basictest method provides an interesting approach asseal testing presents the same problem. It is usu-ally very difficult to accelerate material testingwithout creating unrealistic loads. Increasing thespeed increases the lubrication often to the bene-fit of the mating pair and not the test period.This paper may provide the source of ideas forsome new approaches to this ever-present prob-lem.
Reference1. J. Fan and H. Spikes: New test for mild lubri-cated wear in rolling-sliding contacts. STLE
Annual Meeting, Las Vegas, Nevada, USA, May2005.
Contact:Professor Hugh Spikes, Head of TribologySection, Department of MechanicalEngineering, Imperial College London, SouthKensington Campus, London SW7 2AZ, UK.
Tel: +44 20 7594 7063, Email:[email protected], Web: www.imperi-al.ac.uk/me
This article is based on a presentation made byProfessor Spikes to the British Fluid PowerAssociation (BFPA) Technical Committee TC 16:Fluids on 26 January 2006.
Figure 1. Diagrammatic view of the ball on disk tester used for the contra-rotating tests.
Piston seal
Applicant/Inventor: G. Liepold(USA)This patent relates to piston sealsthat may be used for the transferof sterile fluids. A plastic pistonhas circumferential channels thatcontain a ribbed plastic wiper that
seals against the cylinder bore. Anumber of geometries are shown.There is additionally a design thatis cantilevered from the pistonskirt.Patent number: WO 2006/015324Publication date: 9 February 2006
Examples of the piston and seal arrangement for a sterile fluid transfer device, from WO 2006/015324.
Valve gasket with retainer
Applicant: Waters Investments Ltd,USAThis patent is concerned with theseals for valve components on equip-ment such as high pressure liquidchromatography instruments. Once agasket has aged and creep hasoccurred it is susceptible to being dis-placed when the pressure fluctuates.Analytical instruments, in particular,
are sensitive to the rebound and pres-sure ripple effect, and pressure can befrom 350 bar up to 1400 bar. One ofthe valve components will have areceiving groove to retain the gasketin position during pressure fluctua-tions.Patent number: WO 2006/02400Inventors: J.A. Janiuk et al.Publication date: 2 March 2006
Seal with leakage vent
Applicant: Waters Investments Ltd,USAThis invention discusses methodsof providing a defined path tovent fluid in the event of seal fail-ure. It is concerned with preserv-ing the integrity of surfaces withclosely controlled tolerances toprevent damage in the event of aleak. This patent is concerned
particularly with high pressure gaschromatography up to 1400 bar,but the designs shown appear tobe similar to those which are stan-dard practice on other high pres-sure fittings.Patent number: WO 2006/023653Inventors: J. Angelosanto, J.A.Luongo and F.A. RubinoPublication date: 2 March 2006