Interface - The Journal of Wheel/Rail Interaction

RAIL GRINDING

Specialized Rail Profile Grinding on MBTA
by Bob Tuzik • April 10, 2005

Rail Grinding has been used to solve a host of problems on transit systems. It recently was used in Boston to remove a new wrinkle. A specialized grinding program was initiated in 2002 on the heels of a series of light-rail derailments on the Massachusetts Bay Transportation Authority (MBTA) Green Line that occurred in the summer of 2000.

An initial study indicated that the 63-degree wheel flange angle on the cars was not sufficient to prevent derailments. As a result, the MBTA adopted a new Interim Wheel Profile (IWP) with a 75-degree flange with a 1:20 taper to replace the 63-degree wheel flange with a 1:40 taper that had been used.

Introducing the new flange angle was only the first step in the MBTA's plan to reduce derailment potential, extend wheel and rail wear life and improve wheel/rail interaction on the system. The new 75-degree flange angle raised Nadal's (L/V) limit by 50%, which permitted higher lateral forces, but the flange angle deteriorated rapidly and was difficult and costly to maintain.

While most transit properties establish their re-truing cycles based on mileage and flange thickness, MBTA's cycles were based on a more elusive change in the flange angle. A 72-degree maintenance limit (later relaxed to 68 degrees for the wheels with solid axles and 72 degrees for the center, low-floor independently rotating wheels) was established for the cars. Based on these limits, wheels required re-profiling every 3,000 miles and were condemned for diameter by 20,000 miles.

"We weren't wearing the flanges thin," says Joseph Oriolo, MBTA's Senior Project Manager - Maintenance-of-Way. "We were cutting the wheels because of the change in flange angle."

In addition to the issues relating to flange angle, wheels on the MBTA have a shallow, 3/4-inch flange length. As the wheel flanges contacted the gauge face of the rail, they wore the upper portion of the rail and created a shelf beneath the tip of the flange (see Figure 1). The shelf became an area of concern. Depending on the diameter of the wheel relative to the length of the flange, flange bearing could occur.

"We had to find a way to remove that shelf or replace the rail," Oriolo said.

Rail replacement was considered but was rejected as too costly. MBTA concluded that it had to find a cost-effective way to grind away the shelf that had been carved into the rail, then grind a 10- to 20-degree angle on the gauge-face that would be compatible with the 75-degree IWP. The problem was, grinding at those angles had never been done in North America.

High-Angle Grinding
In order to remove the shelf that the wheel flanges had cut and to grind the appropriate angle on the gauge face of the rail, the rail grinder would have to be able to position grinding motors to grind at 75 degrees or greater. Up to that point, production grinders were capable of grinding at a maximum 45 - 50 degrees. While switch grinders were capable of grinding at steeper angles, none were capable of operating within MBTA's clearance envelope or on the system's tight-radius curves.

"Not only did we have to grind at an impossible angle, but we had to figure out how to do it productively," Oriolo said.

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