HAL m/w demands: grinding and lubrication: NRC of Canada and TTCI have been testing and monitoring track to find new ways to make track last longer under heavy tonnage - heavy-haul maintenance

Railway Track and Structures, July, 2002 by Mischa Wanek

Track in a high-tonnage area presents particular maintenance worries and challenges. Here is a look at what National Research Council of Canada and Transportation Technology Center, Inc., have been testing, finding out and implementing to meet the challenges.

NRC Canada

NRC of Canada believes that maintaining the wheel/rail interface in a healthy condition is one of the key features of a successful track maintenance program for heavy-haul operations.

The wheel/rail philosophy used in heavy haul differs substantially from that used in commuter rail and transit, which have lower axle loads--typically between 16 and 20 tons. For passenger systems the primary concerns are controlling corrugation, noise and vibration, reducing wheel wear, preventing wheel climb and improving ride quality. In heavy haul, the major issues are rail wear and contact fatigue, as well as reducing fuel consumption and damaging lateral track forces.

Fred Prahl, of NRC's Rail Division, said, "The rail grinding program is a critical part of any heavy-haul maintenance program.

"For some, it is used only in a corrective way, to remove rail-surface defects such as checking, corrugation, spalls and plastic flow," he noted. "To be of real value, however, a grinding program should prevent the formation of surface defects due to rolling contact fatigue and establish and maintain correct rail profiles."

Prahl continued: "Therefore, the wheel/rail interface maintenance challenges for heavy haul include a regular grinding program that is designed to remove just enough metal to prevent the initiation of rolling contact fatigue defects on the rail surface without wasting serviceable rail steel. This is sometimes called the Magic Wear Rate because one uses grinding to create the effect of just enough natural wear to suppress the development of surface defects. Hand-in-hand with this goes the grinding in of rail profiles designed to improve steering, reduce lateral forces in curves, reduce wheel-flange and high-rail gauge-face wear, reduce the chance of derailments, reduce hunting and slow the development of corrugations.

"The importance of correct rail profiles cannot be over-emphasized," Prahl said. "Rail-grinding equipment can consistently profile rail to a few thousandths of an inch. Most of us would question whether such accuracy has any meaning in a railroad environment. In fact, because of the nature of the contact between wheel and rail (the contact patch is only about the size of a dime), very small changes in both wheel and rail profiles have a significant influence on the distribution and magnitude of wear and surface fatigue across the railhead and wheel tread."

Both Burlington Northern and Santa Fe and Canadian Pacific Railway have made preventive grinding an integral part of their track maintenance programs.

For BNSF, NRC developed the "preventive-gradual" strategy, which allows the immediate adoption of preventive grinding intervals without first restoring the rail to a clean surface condition.

"The rail is transitioned to the desired profile and to a crack-free state on a gradual basis," Prahl said. "Test programs on both railroads have verified that preventive grinding reduces rail wear and grinding costs compared to corrective strategies."

NRC also firmly believes that to attain maximum benefit from a wheel/rail optimization program, a railroad should also include a friction-management program m its maintenance plans. Friction management includes gauge-face lubrication as well as control of friction at the top of the rail.

"For many years, heavy-haul railroads have applied lubrication to the rail's gauge face to help control wheel and rail wear and produce substantial savings in train fuel consumption," Prahl pointed out. "Taking advantage of Portec Rail Products, Inc.'s new technology in wayside lubricators, CPR recently established a '100-percent-effective lubrication program' on their Thompson Subdivision. The effort concentrated on the gauge face and, in the first year, produced rail savings of $943,000. This number is projected to grow to $2.4 million over a four-year period. Curve resistance was reduced by 44 percent and the overall fuel savings was 5.7 percent."

Prahl noted that using specially-designed top-of-rail friction modifiers (such as Kelsan's KELTRACK [TM]) to control the friction coefficient to about 0.35 offers heavy-haul railroads the following additional benefits:

* Reduced lateral loads in curves

* Additional fuel savings

The NRC notes that the use of top-of-rail friction modifiers can also mitigate wheel and rail surface damage caused by rolling contact fatigue. While both lubricants and friction modifiers are effective at inhibiting crack initiation due to contact fatigue, friction modifiers provide the added ability to minimize crack growth.

TTCI: Grinding, friction control

TTCI has been monitoring grinding test sites on Canadian National and Norfolk Southern since the mid-1990s. According to Kevin Sawley, engineer at TTCI, the sites are still monitored, but have been placed on the back burner due to the length of time they have been in effect. Sawley noted that they had run their course and served their purpose.