Bonded together in better joint quest

Insulated rail joints are a critical signaling system and safety component, providing electrical isolation and stability between two rail sections. Railroads long have used bolted joints on low-tonnage, slow-speed rail, such as secondary and yard tracks, and bonded joints on high-tonnage, high-speed mainlines.

Freight railroads predominantly install bonded insulated joints to provide track circuits, detect rail breaks and control signal traffic blocks on heavy axle-load lines. But designs for widely used, conventional glued bonded joints haven’t change much in more than a century while axle loads have steadily increased.

Today, many bonded joints are breaking down under heavier tonnages because of electrical or mechanical failure. So, during the past few years, railroads, researchers and suppliers have been developing and testing new designs and components, and exploring different manufacturing techniques to extend glued bonded joints’ service life. Their goal: ensure bonded joints last as long as the rail they’re attached to.

“We’ve been working with railroads for the past five to six years, developing improved and stronger joint geometries, and investigating better steel chemistries, rail end grinding practices and longer-lasting, tougher adhesives,” says Tom Urmson, vice president of engineering for Portec Rail Products Inc., which supplies various bolted and bonded insulated rail joints.

R&D focal point: Pueblo
The Transportation Technology Center Inc. (TTCI) in Pueblo, Colo., has been the epicenter of bonded joint research. As part of the Association of American Railroads’ Strategic Research Initiatives Program, the center is testing 28 prototype bonded joints with several railroads and suppliers. Twelve are conventional joints featuring improved foundations, 11 others feature new-and-improved components and five are miter-cut joints.

Undergoing tests at the Facility for Accelerated Service Testing (FAST) track, the joints as of May hadn’t yet withstood trial runs totaling 400 million gross tons, or their typical service life, according to a TTCI research report issued in spring. However, preliminary results show flexible material in and around the end-post area can reduce adhesive cracking; lower hardness rails have higher metal flow at rail ends, suggesting premium head-hardened rail be used for insulated rail joint plugs; deflections can be reduced up to 30 percent by doubling a joint bar’s modulus; and miter joints have 40 percent higher resistance to longitudinal loads than conventional insulated joints.

TTCI also is working with the Virginia Polytechnic Institute and State University to develop a stronger and more durable epoxy-insulator-steel bond for bonded joints. As of October, they found shear failure of the epoxy most often causes bonded joints to fail under heavy-axle loads. Contributing factors include the configuration of the joint, such as a structurally weak but joint, that can produce high epoxy stresses, environmental degradation of the epoxy and high dynamic load impacts.

The university’s and TTCI’s initial findings show steel surface preparation processes, such as amino-propyl silane treatment, help reduce the effects of weathering on the epoxy bond, and an insulator cloth used between the rail and joint bars lowers the joint’s strength compared with a non-insulator joint — emphasizing the need for more R&D to improve insulation methods. They also determined Kevlar^® cloth used as the rail-to-bar insulator has the potential to better withstand environmental effects than a fiberglass insulator.

In addition, TTCI is assisting BNSF Railway Co. and Union Pacific Railroad in evaluating the performance of several bonded joints in heavy-haul coal service. As of July, tests showed supported joints can significantly lower deflection and epoxy shear stress; joints with Kevlar® insulators attain longer service life than those with fiberglass insulators; and angle-cut designs help reduce deflections, insulated joint-caused dynamic loads and epoxy shear stress.

Two prototypes at TTCI
Portec Rail Products is conducting several tests at TTCI, too. The supplier is testing two prototype bonded joints with TTCI and three Class Is: a Center Liner bonded insulated joint and a LAP (long-angle projection) Design bonded insulated joint.

Undergoing tests the past two years, the Center Liner features a high-strength ComPly™ insulating material designed to create a stiffer joint through mechanical wedging action between the joint bars and rails. Field tests have shown joint deflection reductions of about 30 percent compared with Portec Rail’s current production bonded joint, and the insulator is about 15 times stronger in compression than the company’s current bonding system, the supplier says.

The Center Liner addresses the high-stress adhesive area at the rail ends, says Portec Rail’s Urmson.

The LAP Design joint is designed to be 90 percent as stiff as solid rail, which is three-and-one-half times stiffer than Portec Rail’s current production bonded joints, the company says. In testing since early 2006, the joint also offers 58 percent more bond strength than conventional bonded insulated joints.

“The LAP Design joint addresses key deterioration issues: joint stiffness and rail end batter,” says Urmson, adding that three Class Is are field testing this joint design.

Portec Rail also has assembled bonded joints featuring Kevlar^® insulators instead of fiberglass, and developed a high modulus wrap-around bonded joint that exceeds the rail stiffness and provides twice the bonding strength, the company says. Two Class Is currently are evaluating the two joint designs, which have been in track for the past two years.

The company’s rail joint line also includes a ComPly™ epoxy (dry) fiberglass insulated rail joint kit whose bars can be machined to any rail size; the Portec Poly-Insulated^® (dry) joint kit; the Thermabond™ Adhesive and Insulator System kit for in-track/field bonded joint rebuilds; and Portec-Bond™ glued joints.

About six months ago, Portec Rail subsidiary Salient Systems Inc. began commercially marketing a rail joint-related product, the SmartJoint™. In conjunction with the Salient RSM (Rail Stress Module)-StressNet™ system, the SmartJoint can help railroads measure and manage the rail neutral temperature (RNT), as well as reset the RNT to a desired high-target value after a rail break is fixed or a rail defect is removed.

A wireless device installed in the web of a rail, the RSM measures a rail’s temperature and stress every 10 minutes and relays the information to the StressNet database. StressNet then analyzes the data vs. the rail’s neutral temperature and can notify appropriate personnel if a critical condition is reached.

The SmartJoint can determine the RNT being readjusted, monitor the plug RNT after a temporary repair and provide information on how to readjust to a desired RNT. The RSM can be mounted on any rail joint or plug to create a SmartJoint, says Salient Systems Vice President of Technology and Business Development Ryan McWilliams.

“The missing part was you’d install the rail joint and not know what the installation condition of the rail was,” he says, adding that Salient Systems recently received its first major Class I RSM order, with a number dedicated to SmartJoints and installations near critical curves, bridges and tunnels.

A non-bonded option
NedCan Products Inc. recently obtained its first Class I order for a Swiss-made Tenconi insulated rail joint NedCan began marketing and distributing in North America last year. In July, BNSF purchased four joints for field testing.

Since 1985, more than 100,000 Tenconi insulated rail joints have been installed in Europe, Asia, Australia and Africa. The mechanical or non-bonded Tenconi joint features a high-tensile steel bar and no loose insulator parts. The joint can be installed in the field in about 30 minutes without a crane or welding, says Jaap Siekman, owner and president of NedCan Products.

“It can outlast conventional glued joints,” he says. “In North America, railroads often seem to think in terms of wheel load and not so much in terms of bending stress in the joint bar. Railroads need to keep an open mind and look past glued joints.”

Tenconi recently developed specially engineered embedded magnets designed to capture metal dust produced by a rail joint, and prevent the dust from settling on the end post and causing signal faults. The embedded magnets, which are being tested in The Netherlands and United Kingdom, are applicable to North America, says Siekman.

For now, the Tenconi joint, which last year passed an AAR rolling load test at TTCI, continues to undergo testing at the center’s FAST track. The joint soon will pass 300 million gross tons (MGT) and isn’t showing any signs of fatigue, says Siekman.

About three years ago, TTCI determined a bonded rail joint’s average lifespan was about 300 MGT. But L.B. Foster Co. has bonded joints in service that are standing up to 800 MGT, says Sid Shue, the company’s general manager of rail products engineering.

L.B. Foster’s Allegheny Rail Products division supplies Toughcoat bolted joints and bonded insulated rail joints. The bonded joints feature a three-tie supported insulated joint plate designed to help reduce deflection and extend the joint’s life.

For the past two years, L.B. Foster has offered a bonded joint featuring a Kevlar^® insulator — which the company tested for four years — in place of a conventional fiberglass insulator. And last year, L.B. Foster began marketing new insulated tie plates designed to help extend a bonded joint’s life.

“We look at an insulated rail joint as a total system and not just discrete components,” says Shue.

Last year, L.B. Foster also opened a new insulated rail joint plant in Pueblo. The facility features state-of-the-art equipment and employs production processes that improve joint quality and durability, says Shue.

Raising the bar
Seneca Railroad and Mining Inc. also is searching for ways to make its insulated rail joint last longer. The company, which markets a polyurethane insulated joint, is evaluating new materials and working with end post and bushing suppliers to increase those components’ compressive strength.

The evaluation of a more fracture-resistant, rolled bar also is emerging as railroads focus on improving fatigue life, Seneca Railroad officials said in a submitted statement.

The company’s rail joint features a polyurethane insulation bonded to microalloy joint bar sections. Seneca Railroad also offers both a rubber/fiber and polyurethane insulated tie plate designed to ensure proper insulated joint performance.

To offer the best-performing bonded insulated joint possible, suppliers expect to continue pushing the R&D envelope with railroads and researchers. Adhesives will remain a key focus area, says Portec Rail’s Urmson.

“We’re looking at better adhesives that are stronger and more durable, and hold up to environmental conditions, such as harsh temperatures and moisture,” he says.