During production, waviness of the running area is mainly caused by the necessary setting process. In later operation, this will lead, for example, to amplified running noise and will require additional re-grinding of the rail. Apart from high costs this grinding process will also cause abrasion of the hardened sections in the rail head. According to the norm, the waviness is determined by placing a metal ruler of fixed length (e.g. 3 mtr.) and measuring of the minimal and maximal deviation by means of a thickness gauge. Apart from the long test periods, this measuring method is not absolutely independent of the tester and allows only limited possibilities of documentation in the form of a test protocol.
Therefore, a non-contact measuring device is in operation at a major rail manufacturer's for several years. By means of 4 laser sensors the running area is scanned on-line, in a non-contact method during production. The software of a high-performance computer is capable of determining the amplitude and wavelength of the surface waviness by Fourier Transformation. By means of a ruler created by the software, the min. and max. values are being determined analogue to measuring by hand.
Comparative measurements over a longer period have shown that deviations of max. 0.05 mm between both measuring methods occur. Just recently, also the rail evenness at a 90° angle to the running surface is being registered. The measuring system has been examined and approved by leading railway companies. This year, a further rail manufacturer has incorporated this measuring system into his production.