Same structure, improved make up: while the basic design of crossing diamonds has been the same for years, researchers are investigating different materials that are both cost effective and easily maintained - Brief Article

Railway Track and Structures, July, 2002 by Mischa Wanek

Railroads know how to make two tracks cross seamlessly. However, the problem lies in the deformation of those tracks. Diamond crossings continue to be one of the most-costly areas of track maintenance, While certain advancements, such as ramped frogs or Meridian Rail's straight rail reversible crossings, have provided new standards, railroads continue the search for a more-cost-effective and lower-maintanence material.

Testing at TTCI

Transportation Technology Center, Inc., has made progress in its testing of crossing diamonds. It currently has a number of tests under way related to crossing diamonds, including tests on bainitic steel, fasteners and frogs. One of the test programs on bainitic steel three-rail crossing diamonds has gone through many design changes, including a different corner design and ramping in the running surfaces.

"We know from testing that the running surface ramps work well," said David Davis, principal engineer at TTCI. "What was needed was a more durable, stronger steel that would hold its shape. Bainitic microstructure steel was a good candidate.

"The herringbone corner is our attempt to make the application of three-rail diamonds wider," said Davis. "Three rails turned crosswise create a series of dips and humps. The herringbone eliminates one rail from the branchline running surface and the ramps help smooth out the rest."

The research portion of the three-rail program is complete and testing will continue through 2003 to develop life-cycle- performance data. Implementation of this technology has been released to suppliers; however, issues concerning the welding of bainitic to pearlitic rail steel has impeded its use.

TTCI also has four test frogs out on CN/IC and UP lines. The CN/IC crossing diamond at Oilman, Ill., has been in service for two years, while the diamonds on the UP at Zeigler, Ill., and Hoxie, Ark., have been in service for less time, but are producing similar results to the diamond in Oilman.

"We take measurements on them periodically and they are all performing very well," said Davis. "The amount of wear and deformation on those is much less than what we see on typical crossings at the same tonnage."

TTCI's future will include revenue service testing a flange-bearing concept. Preliminary tests on three existing prototypes at FAST have produced promising results.

"The AAR, on behalf of its member railroads, has obtained a waiver of the Federal Railroad Administration's Track Safety Standards, part 213.137, regarding allowable flangeway depth in frogs," said Davis. "This waiver will allow a limited number of revenue service tests in the next three years. Part 213.137, written to prevent tread-bearing frogs from inadvertently becoming flange-bearing frogs, would otherwise prevent implementation of flange-bearing frogs in most track."

NS: Coming ever closer

Norfolk Southern has been on its own quest to find and produce a better crossing diamond. Although still in the experimental stage, NS has made progress finding new materials and designs through its own tests.

"We designed our own test a couple of years ago and dropped a 27,500-pound impact hammer on one-inch-diameter coupons to determine which materials deformed the least under heavy impact," said Hayden Newell, Norfolk Southern's manager of innovative research. "The diamonds are being beaten down just from wheel impact, so we thought if we could quantify some materials just by looking at that, it might get us in the right ball park."

NS compared heat-treated rail, a bainitic sample and a tool steel, made by Carpenter Technology Corp., called AerMet 100TM, to austenitic manganese steel and found that the material from Carpenter, the AerMet 100, looked the most promising.

The railroad then designed and built two fixtures, one made out of the AerMet 100, while the other was made of explosion-hardened manganese steel. The fixtures, which consisted of a small section of material with a flangeway cut out to simulate a crossing diamond, were placed in a high-tonnage, low-speed yard track in Roanoke, Va.

"We've been monitoring that for two years," said Barry Gillespie, Norfolk Southern's manager process improvement-six sigma. "The AerMet is holding up really well. The amount of deformation is significantly less than the manganese steel and, based on the results of those tests, we're getting ready to take the next step."

That next step requires putting a replaceable insert casting or machined part in a crossing. The railroad is trying to get Carpenter to produce the test pieces.

"It's a replaceable insert, but that type of part is typically made by casting, where the product Capenter makes is a rolled product," said Newell. "We're trying to get them [Carpenter] to figure out how big of a rolled product they can make because it wouldn't be cost effective to do a casting design at this point."

NS doesn't plan on keeping any future findings about its crossing diamonds locked safely away nor will its hunt for a better crossing diamond ever be finished.