ADVANCED MATERIALS - HIGH-PERFORMANCE COMPOSITE SOLUTIONS FOR RAIL

Determining Enduring Comfort in ARailcar Seat Cushion: Is A FirstImpression Reliable?Ken Kozicki, Rogers Corporation

As you stroll from Messe hall toMesse hall at Innotrans, or wanderoutside to queues of rail

enthusiasts and business professionalsalike, waiting their turn to step into anyone of a sea of updated, new andfuturistic passenger coaches, the mostprevalent and obvious fixture within anyinterior, rendering, brochure, or maze ofbooth exhibits is the seat or array ofseats. The type of seat will vary from themost outrageously luxurious - slated fora VIP very high speed Oriental Expresspod - to the simplest and ergonomic thatallows for rows and rows of passengersin a configuration that would be suitablefor the rush hour of London, Shanghai orSao Paulo.

In addition, there will be a multitude ofstyles, reflecting the most recent trends,fashions and local preferences. It is onlyhuman that you will take a try and sit onone, two, or as many as possible of theseseats. And in a matter of a few seconds,you will determine if that seat iscomfortable or not! What has takenteams of engineers and designersmonths, if not years, to conceptualise,design, prototype, test (and re-test), willbe given a judgment in less than tenseconds. So from that, one could wonderjust how important is the first impressionof a railcar seat? Of course, there is aplay on this statement, which will beaddressed in a bit.

Final designs, needless to say, are notonly a function of style and comfort. Othervariables and requirements must beconsidered if a seat is to be selected forservice. Those that are most critical resultfrom specifications such as the number

of seating positions per coach (asrequired by the transit authority),materials’ standards for flame, smoke,and toxicity (FST), type of train service(urban metro system versus suburbancommuter), and severity of usage. Thereare also new concerns of sustainabilityand end-of-life. This is being driven byquestions related to the disposal of theseat: “What will become of a worn,damaged, or obsolete seat?” Will it bethrown into a land-fill? What are thedecomposition ramifications of that seatin a land-fill? Transit authorities arebecoming even more proactive withinitiatives to reuse or recycle thecomponents of the seat at end-of-life.Lastly, as with any publicly-fundedprogramme, the overall cost of the seat

must be in agreement with the budgetslated for the project at hand.

Regardless of the final product,however, and after all of theserequirements have been factored in, thecommon feature among most all seats isthe cushion. And while it is obvious thatcushions have differences in profile,appearance and texture, it is not obviousthat there are different types of materialsused to fabricate the cushions. Thesematerials are usually in the form of foam,such as a filled-polyurethane, silicone,and melamine. The foam which isspecified for the fabrication of the cushionwill have been tested to the various FSTstandards, ensuring the safety of thepassengers. In addition, some of thefoam materials may have been cycle

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Rider comfort has a lot to do with a seat cushion’s ability to “pushback” over thecourse of its service life

tested to simulate wear and usage, whichbrings us back to our earlier statement offirst impressions. Often, seat cushionfoam materials are tested and certified toa characteristic known as indention forcedeflection (IFD).

A typical IFD test method will becomprised of a disk of a determineddiameter that compresses the foammaterial a certain percentage of itsthickness, and then measures theamount of “pushback” force the foam has.This is its indention force deflection, andis directly related to the comfort of theseat. In production, the foam will becertified according to this test. If it is

within the IFD tolerance range, the foamwill be qualified for seat cushionfabrication. The cushion eventually findsits way to an Innotrans exhibit or (ideally)put into service. The foam and seat areready to be scrutinised by you, the user,and a determination is made - in just amatter of seconds - if it is comfortable. Atthat point, the first impression or first IFDis made, and objectively, the cushion, asevaluated by true data, should becomfortable. This is independent of thetype of foam material, whether it is filled-polyurethane or silicone foam. However,subjectively, one may be consideredmore comfortable than another, but this

would be dependent on the overall seatdesign.

The real test is months later; after thecushion has been in service and cycledthrough thousands of IFDs. Is the seatcushion still reporting the same pushbackforce as it did on day one? The answer isdifferent for each type of foam material.Silicone foam will only lose about five percent of its original pushback force in aslong as ten years. Filled polyurethanefoam will take on a compression set overa relatively short period of time.Compression set is defined as thepermanent loss of (push back) force overtime. This can be easily observed. Theupholstery of the seat will be loose; nolonger tightly stretched over the foam.The cushion will seem flattened, and willnot distribute the weight of the passengerevenly or in the same pattern, as it did onday one, or with its first IFD. The changein weight distribution is ultimately thecause to what is, both objectively andsubjectively, defined as uncomfortable.On balance, an open cell silicone foamprovides the best long-life solution for railseating in all categories: compliance toFST standards, almost identical comfortperformance throughout its entireservice, and an overall savings inmaintenance cost.

So we end as we started: Does it makesense to judge comfort with the firstimpression? A seating showroom in avenue like Innotrans would offer a moreconvincing story if it was not displayingand demonstrating brand new foamcushions, but rather cushions that havebeen in the field for years - because that’sthe real test for comfort after many, manyimpressions! ■

ABOUT AUTHORAuthor Ken Kozicki is Market

Development Manager for Rogers HighPerformance Foams Division, located inCarol Stream, Illinois, USA. Heconcentrates on advanced materials foruse in the rail industry including floatingfloors and seating. An engineering andbusiness development veteran of theautomotive and electronics industries, heholds a Masters degree in Engineeringfrom the University of Illinois at Chicagoand an MBA from the University ofDetroit. He can be reached atKen.Kozicki@rogerscorp.com.

2-D & 3-D view of thin profile seat with loaded urethane

2-D & 3-D view of thin profile seat with silicone foam

ADVANCED MATERIALS - HIGH-PERFORMANCE COMPOSITE SOLUTIONS FOR RAIL

59Railway Technology International