A parametric study of the lubrication transport mechanism at the rail-wheel interface

Abstract

To stay competitive with other modes of transportation, today's railroads need to reduce costs and minimize capital investment. Two major ways to accomplish this are by conserving energy and reducing rail and wheel wear through more efficient lubrication of the wheel-rail interface. To accomplish this, ways to provide uniform film thickness at the wheel-rail interface and effective transport mechanisms for the grease must be better understood and managed. Locomotive on-board lubricators transfer grease indirectly from the wheel to the rail. The success of this method depends heavily on the transport mechanism, which is directly influenced by many factors including wheel and rail contour, rail geometry, dynamic characteristics of the truck, surface conditions of the wheel and rail, the viscosity and lubricity of the grease, operating temperatures of the wheel and rail, and environmental factors such as temperature and precipitation. Indirectly, the transport mechanism can be influenced by the operating characteristics of the lubricators, train action, wheel slip, environmental contamination, and human factors. The same parameters affect wayside lubrication of the rail. Lubrication can be successful only if the transport mechanism is handled in an effective manner. Lubrication of the gauge corner at the rail is a direct lubrication method. However, it is still heavily influenced by a number of parameters that can inhibit the maximum effect of lubrication, including the frequency of trains and lubrication passes and the amount of lubricant applied. This paper presents the results of an ongoing investigation on Conrail of ways to improve the transport mechanism at the wheel-rail interface and the factors that adversely affect lubrication. Some of the parameters examined are highly technical and scientific, while others are related to business and human issues that also have significant influence on successfully reducing the coefficient of friction. Data for this study were derived from full scale testing and ongoing efforts by cross-functional lubrication quality improvement teams in the field. Specifically, this research is an attempt to quantify the various issues concerning lubricant propagation that have been either qualitatively reported in the literature or hypothesized from information obtained during revenue operations. Data sources include revenue service data from testing of unit coal trains on Conrail, two separate tests conducted by Conrail at the Association of American Railroads Transportation Test Center, and data taken as a part of an ongoing process improvement project on Conrail. Issues affecting lubrication propagation that are explored include the hysteresis effects reported during start up and dry down, the relationship of surface roughness to coefficient of friction measurements, effects of rail head and wheel flange geometries, relative effectiveness of various types of on-board and wayside lubrication devices, position and number of wayside lubricant applicators, ambient temperatures, lubricant viscosities (NLGI grade), and lubricant types. Parameters measured in the various tests include locomotive energy consumed (both total electrical and traction), coefficient of friction, rail and wheel geometries, ambient and rail head temperatures, lubricant volume used, and RMS surface roughness of the rail head.