Importance of lubrication position on squeal noise mitigation

The tram of Bilbao managed by Eusko Trenbideak had high squealing noise levels when negotiating some curves on its trajectory. In order to minimise those levels a lubrication system was tried. The lubricator is the same grease commonly applied in the wheel flange to avoid wearing, so it is not specific for acoustic use. It is applied on the rolling band of the wheel and by means of contact it is spread on the top of rail. In order to quantify the effect of the lubrication on squeal noise, a measurement campaign was carried out where noise levels with and without lubrication were measured. The results showed that there were three different squealing frequencies. The lubrication on the rolling band was very effective in one squealing frequency. Nevertheless it did not have effects and, in some cases, it even increased noise levels in other frequencies. Taking into account the results, the effect of the flange lubrication was analysed. As conclusion it was found out that the effect of lubrication on squeal noise has dependence on the lubrication position.