Effectiveness and efficiency are two key aspects in rail grinding. Effectiveness measures how well the grinding objectives are reached--low-contact stress, good curving performance, high-speed lateral stability and successful surface defect removal. Efficiency is influenced by how the grinding interval and pattern choices affect the cost of grinding.

Rail grinding is commonly used by North American railroads as a maintenance procedure for removing rail corrugations, for surface defect removal and for restoring the shape of the rail to improve wheel and rail interaction.

The total cost of rail life and rail grinding is related to wheel/rail interaction. Reduced surface rolling contact fatigue and wheel/rail wear resulting from favorable wheel/rail contact could extend grinding intervals and reduce metal removal rate, thereby prolonging rail life and reducing maintenance cost.

Establishing an adequate grinding program includes properly designed ground profiles, grinding procedures and wheel/rail interaction monitoring procedures.

Two rail grinding trials conducted by Transportation Technology Center, Inc., on curves of two freight service lines discussed here demonstrate the need to further improve current grinding practices.

Properly-designed ground rail profiles

Rail profiles are generally not ground back to the new rail shapes. The ground rail shapes are important for wheel/rail contact conditions after grinding.

On curves, conformal or close conformal contact is advisable for the high rail. High rails in curves generally become worn to a conformal stage with contacting wheels. This stage is considered as a desirable condition of contact for producing lower contact stress and lower wear. Grinding may only be needed to remove a layer of metal for reducing or eliminating surface defects.

Aggressive removal of metal from the gauge corner of the high rail during grinding is not recommended. Figure 1 shows an example of high-rail profile measured before and after the first pass of grinding on a six-degree curve. The wheel in Figure 1 was measured on a car operating on one of the service lines. The wheel produced desirable conformal contact with the worn high-rail profile. A gap of about 0.8 mm at the wheel flange root/rail gauge corner resulted from the first pass of grinding, which gave a rolling radius difference of eight mm at two-contact points on the same wheel. A considerable amount of metal removal (either by grinding or wear) is required to return the wheel and rail profiles to conformal contact conditions.