Wheel squeal is a source of continuing concern for many railroads and transits, as well as for their neighbours. The underlying mechanism for squeal noise has been well understood in the literature for some time. However an integrated abatement method addressing the underlying cause of the problem has not previously been reported.
This paper describes practical experience using a water-based liquid High Positive Friction Modifier (Keltrack) applied using a Top of Rail trackside applicator (Portec Protector). This proprietary friction modifier and delivery equipment have been co-developed to provide an optimized product / delivery system that gives significant reduction of wheel squeal in curves.
Wheels experiencing lateral creep in curves are subject to roll-slip oscillations as a result of the frictional characteristics of the interface layer between the wheel and rail. These roll-slip oscillations are amplified in the wheel web leading to the familiar squeal. Providing a thin film of material between the wheel and rail with positive friction characteristics can both in theory and practice greatly reduce the magnitude of these oscillations. The friction control characteristics of Keltrack allow the material to be delivered to the top of both rails without compromising traction or braking.
Delivery of Keltrack to the contact patch is achieved with a proprietary top of rail electric trackside applicator, the Portec Protector. Key equipment features include top of rail bar design optimized for accurate and precise delivery, and control system features. The equipment is placed at the entrance to curves, and the friction modifier is carried down into the curve by the passing wheels. Application rate is optimized by control of the axle count between pump activations, and by the length of pump activation. The material is delivered to the top of both rails for optimum friction control.
The integrated product / equipment technology is now successfully controlling noise at more than twenty transit sites. Typical sound level reduction is 10–15 dB, in some cases as high as 20 dB, depending on the initial sound level. Two case studies are presented illustrating the effectiveness of this technology.