7Sealing Technology April 2006

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IntroductionFeedback from a number of readers suggests thatat least some of you appreciate these reviews, sothis month we have a review of the patents thathave been covered during the last 12 months.These are the World Patents published during2005.

The total number of World Patents pub-lished during 2005 was very similar to previ-ous years at approximately 120 000. Howeverthe number of patents reviewed in SealingTechnology for this period has increased from180 in 2004 to 250 for 2005, an increase ofnearly 40%. This increase has also not beenparticularly evenly spread, with an increasingnumber towards the end of the year.

To avoid the patents taking over a large pro-portion of the newsletter in the last fewmonths, we have had a slightly briefer descrip-tion and rather fewer illustrations. I hope thatyou think that this is the correct approach.This does not necessarily make life easier forthe Editor, as trying to include a brief descrip-tion that makes some sense can be rather moretime-consuming than providing a quarter of apage. And personally I find the illustrationsvery useful in understanding what is being dis-cussed, so – assuming that most readers do aswell – we try to include as many as possible. Itis usually impossible for engineers to talktogether for more than 10 minutes withoutgetting out a pencil and paper, so I assume thesame thought processes apply when trying tograsp something like patents.

I have again divided the subject categories intothe major areas of interest. Again some of these arequite specific, such as cylinder head gaskets, andothers are rather more general, such as pipe joints.Categories that I have added this year for separatemention include seals for electronics. It is alsointeresting to note that some 70% of the patentsare concerned with static seals. This presumablyreflects the fact that static seals are a very large pro-portion of the overall market, generally outnum-bering dynamic seals on most pieces of machineryand being used in many applications where thereare no dynamic seals.

An interesting aspect is the proportion ofpatents that cover manufacturing technology.Many of the developments described are con-cerned either with the manufacture of the sealitself, or with designing the seal to facilitate fit-ting of the seal during assembly of the equip-ment concerned, including the increasing trendto incorporate the seal into a component assem-bly. Manufacturing methods is not just the pre-serve of the high-volume industries, as a numberof the turbomachinery patents are concernedwith manufacturing methods for seals.

The patents this year, using my categories,were concerned with the following:

• Static seals:Gaskets, general 20Cylinder head gaskets 18Pipe joints 26Miscellaneous 34Electronics 8Fuel cells 9

Batteries 4Window and door seals 13Gasket materials 8Oil & gas, down-hole threaded pipe 6Oil & gas, general seals 8CV joint boot sealing 11

• Rotary seals:Clearance seals 13Mechanical seals 11Lip seals 11Bearing seals 10Other 8

• Reciprocating seals:Piston rings 3General 9

• Valve seals:All types 12

• Food and beverage:All types 3

• Medical:All types 7

In addition, this year I thought that it would beinteresting to look at the national distribution ofpatent applications, to see which countries aresupporting the majority of the research andpatenting effort. The distribution will not comeas a particular surprise to regular readers of thepatents section, but the actual magnitudes areboth interesting, and also rather sobering tosome of us. The nationality of the patent appli-cants is as follows:

• USA 111• Germany 42• Japan 42• France 11• UK 11• Switzerland 8• Canada 6• Finland 3• Spain 3• Australia, Austria, Korea, Italy

and Sweden 2 each• Belgium, Denmark, Liechtenstein,

New Zealand, Norway and Russia 1 each

Patent review for 2005 – even more inventionsduring the yearBy Bob Flitney

The number of patents reviewed that were published during 2005 was a signifi-cant increase over the previous two years that we have carried out this review.Comparison with 2003 and 2004 shows an increasing interest in cylinder headgaskets, bearing seals plus other lip seals applications, and also in turbomachin-ery sealing. But the biggest increase from previous years has been in the numberof patents for pipe fittings, mostly for building services and utility pipelines.The most common trend across all industries is the claims for improvements tomanufacturing and convenience of assembly.

This does not necessarily show the nationality ofthe inventors. Many global manufacturers maycommence application in either the country ofthe company headquarters, or where a compo-nent may be manufactured, which may be differ-ent to the location of the research department.In other instances the inventor names suggest tome that the work may have been carried out by aseal manufacturer, but the work is owned by amajor equipment manufacturer.

All of the patent numbers provided in the textare for 2005, so the full patent reference will beWO 2005/ followed by six digits.

Static seals and gasketsGasketsMany of the patents referred too under the head-ing of gasket involved some form of detailed gas-ket either for a particular application or to aidassembly. An example is the manhole accesscover gasket for pressure vessels that includeslocation lugs, 057056. A number of patents wereconcerned with integrated elastomer seals withina gasket structure. A number of patents coveredthe manufacture of these, such as 023452 and033559. Methods of fabricating the metal sub-strate and the molding of the elastomer are dis-cussed. Another example of purpose designedgaskets is the diesel engine cover gaskets thathave retainers to locate the push rods duringengine maintenance and assembly. The emphasisin the patents on assembly and functionality isfurther demonstrated by the number of applica-tion examples for either cure-in-place or form-in-place gaskets, one example being the use ofcure-in-place elastomer for plate heat exchangergaskets, 045346. These are extremely complexshapes, so molding the seal in place overcomesboth the complex shape and also means that theseal is retained in the groove securely duringtransport and assembly.

There have been a number of patents for theincorporation of a seal in filter bodies, such as0633361, and also a pressure cooker lid seal,057056.

A more general application oriented patent isone for low strength flanges, 001315. The gasketis replaced by a metal plate which has a grooveon each side containing a replaceable elastomerseal retained by adhesive for assembly. Thisappears to be a method of converting a low tomedium duty flange gasket to an O-ring typeflange, which would probably have made a moreeffective and economic seal for such a joint inthe first place.

Expanded PTFE tape for use as a gasket forlow load flanges has been around for many years.Two recent patents, 095828 and 103533, havecovered the inclusion of an anti-permeation layer

in the tape. The first describes the tape in gener-al, and the second the application of the tape tolarge flanges. The slightly cynical observer mightnotice with interest that the suppliers of expand-ed PTFE tapes are now suggesting that the stan-dard product is porous.

Cylinder head gasketsThese have shown a marked increase in activitywith nearly twice as many patents registeredcompared with 2004. A large majority of thesehave been from major automotive suppliers,Reinz and Federal Mogul. Almost all are con-cerned with the design and manufacture of mul-tilayer steel (MLS) gaskets. Two key areas ofinterest are to achieve a high contact stressaround the cylinder bore, without distorting theremainder of the gasket, and the effective sealingof lubricant and coolant passages by incorporat-ing elastomer seals. The design of the stopperlayer which limits the compression is covered ina number of patents, as is minimizing the num-ber of layers to reduce the cost. This also includ-ed a news story in September with theannouncement of a single layer gasket. The useof memory metal for the stopper was also includ-ed, 075857. Several very different seals includedmemory metal as a feature during the year. Thistends to attract my attention, as for a number ofyears a colleague would inevitably contribute‘memory metal’ to any brainstorming ideas ses-sion. I do not think that we ever got around toactually using it, but it is good to see that it hasfound practical applications in sealing.

The incorporation of elastomer layers to pro-vide effective sealing of coolant passages withlower bolt loading is covered in a number ofpatents. Something slightly different is an elas-tomer periphery, to prevent access of corrosiveproduct to the outside of the gasket, 080834.The layer is also electrically insulating to protect

the functional layer of the gasket. This is pre-sumably necessary where a number of dissimilarmetals are in contact and potentially exposed towater, road salt etc.

Another area of interest is the inclusion of sen-sors within the gasket. These are generally tomeasure conditions within the cylinder, such astemperature or pressure. The presence of thesesensors is presumably of interest to allow opti-mization of the engine management, to allowcontrol of fuel mixture and engine timing tooptimize power without engine knock. Anexample is shown in Figure 1. Another example,059347, emphasizes the requirement to installthe gasket and avoid distortion and damage tothe sensor when tightening the gasket in place.

Pipe jointsThe large number of patents on pipe joints coversa very wide range of applications. The mostnumerous are those concerned with plastic pipingfor building services, both small bore water supplyand large diameter waste disposal. The piping ofwater services within all types of buildings hasbecome dominated by plastic piping and the useof quick-connect fittings. As this is a very largemarket the securing of an advantageous designcan be important. This type of patent will oftencover the retention system as well as the seal. Thelarger diameters for waste disposal – and alsoextremely large diameter main service pipes – aremore concerned with aspects such as sealing onpipes of different diameters or convoluted pipesurfaces. Ground movement and misalignment ofpipes is also a concern. 047745 describes a retrofitjoint that can be used to permit relative move-ment between adjacent pipes while retaining aseal. Again we can see some concern with provid-ing reliable assembly. Patent 080854 describes afitting that is designed to provide an indicationthat it is assembled correctly and the pipe is fully

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8Sealing Technology April 2006

Figure 1. A sensor fitted to a head gasket for the measurement of cylinder conditions,from WO 2005/093297.

seated in the recess. Two patents, 008119 and008120, concerned with high pressure bite typefittings include provision to inhibit reuse of thebite fitting.

After water pipe fittings another popular subjecthas been exhaust pipe joints. These again are gen-erally aimed at effective assembly and alsoimproved gas tightness, such as 043025, as increas-ingly stringent emissions regulations mean that itis necessary to ensure that a proportion of theexhaust gas does not bypass the catalytic converter.

A further area of increasing interest covered byseveral patents is connectors and joints for vehi-cle refueling for gas powered vehicles.

Fuel cellsFuel cells are a very active area of development,and effective sealing is quite fundamental totheir operation. As some form of seal is requiredbetween each of the numerous plates and mem-branes within a fuel cell, the economic provisionof an easy to handle and reliable seal is an impor-tant aspect of the eventual commercial viability

of the devices. It is therefore not surprising that anumber of patents cover this area, such as thedesign for providing an effective seal withoutovercompressing the fuel cell stack, and withprovision for convenient connection of wiringdescribed in 045974. I would have expectedrather more than the nine patents we recorded,but this is perhaps a demonstration that they arestill very much at the development stage. That avery mature product such as automotive cylinderhead gaskets should generate twice as manypatents shows just how commercially and tech-nically competitive the automotive industry hasbecome. The overall number of patents on fuelcells is high and increasing rapidly, as can be seenin our sister publication Fuel Cells Bulletin.

Window and door sealsWindow and door seals provide an interestingvariety of designs and applications. Some ofthese are again concerned with fitting the seal,either tooling for the purpose, or a design ofseal to readily lock in position, such as 042286.

Other patents are concerned with the incorpo-ration of a magnet within the seal, presumablyfor refrigerator or freezer applications,although these are not mentioned directly.Another active area for automotive windowand door sealing is increasing the seal contactstress after closure. This has proved to beanother application area for memory metal,with two patents from General Motors,089186 and 089190, describing how the sealprofile can be changed to provide seal contact(Figure 2). These patents also include the pos-sibility of using other activation technologiessuch as electro-active polymers, and electro- ormagnetorheological fluids.

Gasket materialsThe gasket materials that were patented covereda very wide range, from a description of the steelsheet for gaskets, 007916, the composition offormed-in-place gasket material, 030866, andthe manufacture of mica-based gaskets. Alsoincluded in this section is one on a material thatwill swell when exposed to atmospheric humidi-ty or immersed in water, 079137.

Oil and gas screwed pipe jointsThere have again been a number of patents onsomething which I had always imagined was avery standard jointing system, the screwed jointsused for down-hole pipe in oil and gas wells. Aswith many other technical areas, somethingwhich has been in use for many years is nowexpected to provide a much higher standard ofservice – in this case higher temperatures andpressures, plus longer and deeper wells with con-siderable horizontal reach. And one of the laterpatents, 114029, also introduces the require-ment to pass the latest ISO testing format. Theessence of the joint designs introduced is providea screw thread form that provides the minimumresistance and then a defined contact zone whereplastic flow will occur to ensure the joint integri-ty. One joint type (in 064217) even describes asecondary operation by an axially displaceableexpansion tool to plastically deform the joint(Figure 3). This design will presumably only beused on the final production casing, as it will beextremely difficult to remove.

CV joint bootsThe number of patents that covered the sealing ofthe protective boots for constant velocity joints isalso interesting. This again must reflect the require-ment to provide increased reliability and freedomfrom visible leakage. It is claimed that 90% of CVjoint failures are caused by boot failure and loss oflubricant. Boot failure also presumably causes cont-aminant ingress to the lubricant, which would beequally deleterious. The traditional use of a hose

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9Sealing Technology April 2006

Figure 2. The use of memory metal within this window seal from WO 2005/089186 means that thesealing contact can be initiated when required.

Figure 3. A number of patents offer improved sealing of oil and gas down-hole piping. This joint fromWO 2005/064217 uses an insert tool to plastically deform the tube to complete the assembly.

clip clamping a plain section of elastomer has beenreplaced by a variety of designs that have someform of sealing beads, such as those illustrated in024260 (Figure 4). These may be integral with theboot molding or attached after the moldingprocess. An alternative idea put forward in 008090is to have a non-flexible housing connected to asliding seal on the drive shaft. I am not sure howmuch angular misalignment this design can absorbcompared with a typical boot.

Rotary sealsClearance sealsI have been reasonably liberal with my classifica-tion of clearance seals, as it also includes brush sealsand other designs concerned with turbomachinery.This section is almost entirely concerned withimprovements to seals for gas turbines and turbo-compressors. The demands for higher efficiency,

lower emissions and increased machine output arefocusing considerable attention on the sealing ofgas turbines and large rotary compressors. (This isalso discussed in one of our features this month.)

A number of patents are concerned with brushseals. The brush seal with shoes, the subject of afeature in the December issue of Sealing Technology,was covered in 001316. A number of other patentscovered the design and manufacture of brush seals,such as 091994. In this case the filaments areembedded into a bonding agent. The manufactureof honeycomb seals was also covered, 102592. Allof these seal designs appear to be relatively complexto manufacture, and as they are used as inter-stageseals there can be quite a few on a single machine.Any advances in manufacturing technology cantherefore be a considerable advantage.

A series of patents, 095829 and 103534–6,described the principle and methods of manu-facture of leaf, or lamella, seals. These have the

benefit of increased pressure resistance com-pared with brush seals, at the expense ofincreased axial envelope.

One patent, 031197, is concerned with thereplacement of segmented carbon seals on steamturbines. In order to provide the radial floatcomparable with the segmented seal, a floatingcarrier is described that will enable alternativeseal types such as brush, labyrinth or honey-comb to be used (Figure 5).

A number of the static seal patents are alsoconcerned with turbine casings. These aredesigns to operate at high temperatures withincreased amounts of relative movementbetween the sections of a casing, or between thecasing and other components such as nozzlerings etc.

Mechanical sealsThe mechanical seal patents cover a range ofdesign topics, sometimes related to a particularapplication. We again have the use of memorymetal, in this case providing drive pins, 075861.The drive pins can provide a super-elastic straincapability during start-up to enable the seal towithstand high starting torque on slurry andother arduous duties.

The use of speed sharing of multiple faceswas covered in two patents. This is a very oldidea, but the problem previously experiencedhas been ensuring that there is equal division ofthe friction so that all the dynamic faces areactually dynamic. In 071290 a seal arrangementwith multiple faces is described that is intendedfor use in very high speed applications, up to80 000 rev/min. This is a very complex sealassembly, and I would be delighted if someonewho understands how it actually works coulddescribe it for me. Slightly easier to understandis the two face seal assembly described in121615. This is aimed at reducing the peripher-al speed by half on heavy duty process pumps.This design depends on the symmetry of theseal faces to equalize the face loading for thepair of dynamic faces. It will be interesting tosee how it progresses in practice.

The duo cone seal design originally developedby Caterpillar has been in general use on earth-moving machinery for a considerable time. Theseal described in 085686 has stainless steel faceswith a wear-resistant overlay of nickel tungstencarbide. The purpose of this development is pre-sumably to provide both wear resistance andcorrosion resistance to seals of this type that havetraditionally been manufactured from tool steelsor cast iron.

A composite reinforced ceramic material isdescribed in 015063. Carbon or silicon carbidefibers are used to reinforce a silicon carbide sealface for use in jet engines. This is presumably to

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10Sealing Technology April 2006

Figure 4. A number of patents cover the design of boots for constant velocity joints that have a sealprofile where they are clamped to the joint body (WO 2005/024260).

Figure 5. This floating seal housing from WO 2005/031197 is designed to permit replacement of segment-ed carbon seals with alternatives, such as labyrinth, brush or honeycomb, without sacrificing the ability tofloat provided by the segmented seal.

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11Sealing Technology April 2006

provide a suitably fracture-resistant material toovercome the reluctance to use ceramic seal facesfor aerospace applications. Another aerospaceapplication is discussed in 040580, where thecooling of seals for engine starters and auxiliarypower units is covered. A variety of fin designsand roughened surfaces are proposed as meth-ods of increasing the heat transfer from the backface of the seal. The purpose is to reduce the sealface temperature, to avoid coking of the lubri-cating oil and reduce seal wear.

A compact mechanical seal assembly thatincludes a vibration damper in the drive assem-bly is described in 022013. Recently we havealso seen an alternative design of dry gas seal,106295. A bleed port provides aerostatic lift toreduce wear on start-up.

Lip sealsThe most numerous subject for lip seal patentshas been the design and manufacture of PTFEseals. These have varied from provision of an

elastomer outer static seal, 047740, to increasingthe flexibility of the sealing lip by use of an elas-tomer hinge, 069764.

Perhaps the most technically interestingpatent was the alternative lip geometry proposedin 085684. The purpose is to maintain the cor-rect lip geometry even if the shaft is misaligned.The seal lip has a rounded profile on the oil andair sides compared with the traditional trimmedgeometry (Figure 6).

Two patents are concerned with tandem lipseal assemblies. The configurations discussed in036033 are intended to ensure that any excesspressure between the lips is vented back to theoil side, but no application is mentioned in theEnglish abstract. The tandem seal described in116492 is specifically for automotive coolantpumps, previously the domain of mechanicalseals. The primary seal has a higher interferencethan the secondary seal. Options include a waveprofile and PTFE inserts on the lips. The use oflubricant between the lips is also covered. Are

we about to see lip seals take over from mechan-ical seals in automotive coolant pumps? Thepotential space saving is no doubt attractive,and the related cost implications could also be afactor.

Bearing sealsWhen does a lip seal become a bearing seal? Forthis review, and as a general rule for the patents,the application is directly to protect bearings. Itis probably also part of the patent title. The sub-ject and application areas is almost as wide as theapplication of bearings themselves.

The most popular subject is the incorpora-tion of sensors or electronic devices within theseal. This included IC tags, in 052397 and052398, as well as a sensor for detecting angu-lar position in 106293. As with the trend tosensors in cylinder head gaskets, the increasingdemands of modern engine management sys-tems and braking and stability control systemsrequire accurate information. But, does thismean that a problem with the sensor requirespurchase of a new bearing, and the associatedfitting costs?

The multiple deflector rings described in059412 are an interesting variation on thetheme of multiple rotating flingers in front ofa contact seal. The neck seal for rolling millbearings described in 037455 was of someinterest to me. To those who may be familiarwith the previous seals, this is a very interest-ing redesign within the overall profile of theexisting geometry to provide a much moreeffective seal. And although the applicant is aUS-based company, the names of the inven-tors suggest that a UK seal manufacturer washeavily involved.

Reciprocating sealsAll the reciprocating seals covered by newpatents were concerned with specific applica-tions. Two were for use in hydraulic braking sys-tem master cylinders with facilities provided tobleed the pressure, 032897 and 090837. Havingonly once had the experience of this facility notworking, so that the brakes stay permanentlyon, I can vouch for this being an importantaspect of the braking system. One patentseemed to patent the use of O-rings as thedynamic seals in an automotive shock absorber,which I find rather strange, but perhaps there isa good reason.

Rather more interesting was the free pistonin a cryo-cooler that is designed to reduce theclearance when there is a high pressure differ-ence across the piston, and hence avoid thepiston drift that is normally experienced(Figure 7). Something else quite different was

Figure 6. This lip seal profile, proposed in WO 2005/085684, maintains the required lip angles with the shaft during misalignment.

Figure 7. A floating piston used in cryo-coolers that is self-compensating by reducing the pistonclearance as the pressure differential increases, from WO 2005/089328.

IntroductionDuring the course of refining liquefied petroleumgas, sulfur is removed by treating the sour gasesthough a compression cycle and by reaction of areasonably strong base or amine. The specificprocess under consideration involves the use ofthree barrel compressors operating in parallel.The compressors are back-to-back designs with alow pressure and a high pressure stage.

Oilfields produce a mixture of oil, gas andwater. Oil and water are initially separated fromthe gas. Following stabilization and liquid knock-out, the gas is supplied to the low pressure stagesof the sour gas compressor. Discharge from thelow pressure stage of the compressor is passedthrough an after-cooler and another liquid

knockout drum. The gas is then fed to mediumpressure amine contactors, as shown in Figure 1,before repeating the cycle though the high pres-sure stages of the compressor. The final sweet gasstream is then processed in gas dehydration andseparation units and distributed as LPG.

Original seal designThe process seals at either end of the rotor wereoriginally designed as oil film seals. Apart fromkeeping the sour gas from leaking to the atmos-phere and contaminating the bearing lubricatingoil, these seals have the characteristic of provid-ing some level of stiffness and damping to therotordynamic behavior of the machine.

At the rotor mid-span a seal separates the lowpressure and high pressure sour gas stages. In theoriginal configuration of the machine, this inter-stage seal was a labyrinth type seal, as illustratedin Figure 2. In many cases labyrinth seals havebeen identified as being the source of rotor instability problems. Circulating flow in betweenthe labyrinth stages provides destabilizing cross-coupled forces which affect the rotor stability.The axial view in Figure 2 depicts the circulatingflow characteristics in a labyrinth type seal.

The OEM design of this particular machinewas marginally stable due to a combination ofthe positive influence from the oil film seals andthe negative influence from the labyrinth inter-stage seal. The first bending mode oscillationamplitudes are a maximum at the rotor mid-span. The conventional labyrinth seal locatedbetween the high pressure and low pressure atthe center of the span is therefore a source ofinstability.

Vibration problemsThe problem arose when the oil seals werereplaced with dry gas seals. Dry gas seals provide

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Sealing Technology April 2006

the surface tension seal for micro hydraulics,106296. The seal has been used up to 100 kPain a 2 mm diameter cylinder.

Something rather different again was theslide way seals in 119105 that included twodifferent lubricants blended into the rubber,which are designed to bleed out at differenttemperatures.

ValvesThere has been a wide selection of seals con-cerned with valves from rotary valve internalcombustion engines, 119018, a technologylooking for a sealing solution, to a numberconcerned with diesel fuel injector valve seal-ing. These again reflect the work to uprate themodern internal combustion engine. Othersincluded pressure relief valves with a built-inseal, and one as a pressure relief valve to pre-vent over-inflation of tires, 082647.

Food closuresThere have been many package sealing patents thathave not been included this year. These have pri-marily been concerned with heat sealing of plasticbags. I have included in the monthly review thosethat concern a clearly definable seal. One that par-ticularly caught my eye was the microwave storageand heating tray with pressure relief. Increasingpressure within the container will cause the seal tovent. The applicant for this patent was SteamwayFranchise Sales, which suggests to me that that theyhave experienced a number of spectacular eventsduring the microwaving of food.

MedicalThese again have been almost entirely concernedwith invasive surgery or provision of fluids duringmedical treatment. The basis of many of these isproviding a satisfactory seal to the various pipesand instruments with adequate flexibility.

ConclusionsOnce again we can see the immensely wide appli-cations of sealing technology. It is often very usefulto have an overview of activities in other areas oftechnology. Hopefully this review has helped inthis regard. Reviewing the patents each month canbe interesting to see the technical developments,but also frustrating trying to distil the informationinto a digestible form. Quite often even those writ-ten in English are difficult to edit into decipherablelanguage. With a number of others I have to workfrom the English abstract and the illustrations.Sometimes the abstracts are very helpful, on otheroccasions they are almost deliberately obstructive,providing no clue to the type of application.

The Patents section of the newsletter hasproved very useful to me, both as an indictor ofprogress in different sections of the industry andas a source of ideas for applications quite unre-lated to the patent. I trust that it serves the samepurpose for our readers.

New seals solve compressorvibration problemBy Fernando Romero – Sulzer Turbo Services, Houston, Texas, USA

Sour gas compression trains are at the heart of the sulfur removal process in asour crude refining plant. The requirements of higher emission standards andcleaner fuel are placing increased emphasis on the stability and reliability ofthese machines. This feature describes the introduction of a new labyrinth sealdesign to solve the stability problems experienced on sour gas compressors of acentral Asian oil producer.