Tread Braking Research Articles

Rail corrugation growth—Influence of powered wheelsets with wheel tread irregularities

A multibody system model for simulation of general three-dimensional train-track interaction (accounting for frequencies up to several kHz) is used to investigate the hypothesis that rail corrugation is generated by powered wheelsets on the Swedish high-speed train X2. Part of the braking effort on the powered wheelsets is accomplished by tread braking with cast iron brake blocks. In particular, the influence of wheel corrugation, which is present because of such braking, on rail corrugation growth is studied. The numerical model uses an iteration scheme including simulation of dynamic train-track interaction in the time domain coupled with a long-term wear model. Measured wheel–rail contact forces and measured rail roughness are compared to the simulated results. Wheel–rail contact forces are considerably higher when wheel irregularities are present. However, the averaging effect from several passing wheelsets with different sets of wheel irregularities is found to give a rate of rail corrugation growth similar to the one obtained if the wheels had been completely round. The rail corrugation wavelengths are found to be explained by irregular wear due to high wheel–rail contact forces and slip caused by local rail bending modes between the two wheelsets in a bogie.

Review of research into wheel/rail rolling noise reduction

Rolling noise is the main source of noise from railway operations at conventional speeds, and even at 300 km/h, it is at least as important as aerodynamic noise. In the last decade, several large research projects have been carried out across Europe with the aim of reducing wheel/rail rolling noise at source. Much of the research has concentrated on freight traffic as this has been perceived as the major source of nuisance because of its relatively high noise levels and the operational necessity of running at night. The solutions considered have included means of reducing wheel and rafl surface roughness, improved wheel and track designs for low noise generation, and local shielding applied to the vehicle and track. These have demonstrated a number of successful concepts, including wheel shape optimization, wheel damping, rail damping, bogie shrouds, low barriers, and modified tread braking. This article summarizes the main results obtained and discusses the prospects for implementation of the technology in practice.

Train-Track Interaction and Mechanisms of Irregular Wear on Wheel and Rail Surfaces

Summary High-frequency train-track interaction and mechanisms of wheel/rail wear that is non-uniform in magnitude around/along the running surface are surveyed. Causes, consequences and suggested remedies to relieve the problems are discussed for three types of irregular wheel/rail wear: (1) short-pitch rail corrugation on tangent tracks and large radius curves, (2) wheel corrugation as caused by tread braking, and (3) wheel polygonalisation. The state-of-the-art in modelling of dynamic train-track interaction in conjunction with prediction of irregular wear is reviewed.

Freight car curving performance in braked conditions

Railway freight vehicles that are run with full payload on long downhill slopes with many tight curves must be braked more or less continuously. The influence of braking on the curving performance of iron ore freight cars equipped with different types of three-piece bogie designs and pneumatically actuated single-block tread brakes run on curved track in a downhill slope is investigated. The focus is put on the change in performance in terms of self-steering ability, track forces and expected wear in contacts between wheels and rails. Modelling and simulation of the strongly non-linear dynamic interaction between vehicle and track in braked conditions are performed. The large influence of wheel/rail profile matching and the quite different responses to braking for the studied vehicles are shown.

Noise-related roughness of railway wheel treads-full-scale testing of brake blocks

Results from full-scale tread braking experiments on an inertia dynamometer (brake testing machine) are presented. Eighteen prototypes of brake blocks are investigated. Two braking characteristics relating to the influence of the blocks on the wheel tread are studied: generation of hot spots and generation of roughness (corrugation, waviness). Wheel tread temperatures are measured during braking using an infrared (IR) technique. The wheel roughness is measured after each brake cycle when the wheel has cooled down. A roughness indicator, RλCA, relates measured roughness to expected rolling noise as generated by the wheel in operation. A correlation between the spatial distributions of temperatures and roughnesses is normally found: stronger for cast iron blocks and composition blocks and weaker for sinter blocks. The cast iron blocks are found to produce high tread roughness levels, partly owing to material transfer from brake block to wheel tread. The composition blocks are found to result in lower roughness levels than the cast iron blocks. Finally, the sinter metal blocks are found to lead to the lowest roughness levels, a fact which is probably due to the abrasive property of these blocks. Friction coefficients during braking are also measured.

Thermally induced roughness of tread-braked railway wheels: Part 1: brake rig experiments

Roughness (corrugation, waviness) on the tread of a rolling railway wheel leads to vibrations in wheels, bogies and superstructure and also in rails, sleepers and roadbed. These vibrating components radiate noise to the surroundings. A lowering of the noise levels from tread-braked freight cars is of utmost importance for the future of rail traffic. The thermomechanical interaction between brake block and wheel tread during braking has been found to cause hot spots on the wheel tread. This phenomenon is believed to be a main contributor to the development of a wavy tread surface. Due to thermal expansion of the rim material, the hot spots will protrude from the wheel tread and be more exposed to wear during the wheel/block contact than the rest of the tread surface. The non-even wear results in roughness on the tread of the wheel after cooling. In the present paper, full-scale tread braking experiments on an inertia dynamometer are reported. Mainly cast iron but also composition and sinter material brake blocks are tested. A stationary pattern of temperature rises (hot spots) on the wheel tread is recorded which is found to correlate well with the measured roughness. In a companion paper results of modelling and field measurements are presented.

Roughness growth on tread-braked railway wheels: e u r o s a b o t theoretical studies

Rail and wheel surface irregularities are the main source of rolling noise. One of the main causes for wheel surface roughness is tread braking. Wheels braked by the most common tread brakes—cast iron blocks—have high roughness levels and, as usual, corrugation with wavelength of 30–100 mm. The Brite Euram research project EUROSABOT deals with new solutions for tread brakes, which would lower the roughness level, prevent the buildup of periodic roughness, and consequently reduce the rolling noise, and at the same time would follow the safety requirements of railway operation. Field measurements, discussed in detail by Stefan Buehler in a companion presentation, in parallel with laboratory studies has distinguished that the interaction of thermo-elastic and vibrational instabilities is the main reason for corrugation generation. Computer simulations describing simultaneously thermodynamical, structural, and acoustic processes of the braking operation have proved to be unpractical for parametric studies and, instead, several simplified models are used. These models have shown that the main parameters affecting roughness growth are Young’s modulus and coefficient of thermal expansion of the block material and damping of the system.