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Kurzfassung
Es wurde eine Prüftechnologie basierend auf dem Wirbelstromverfahren entwickelt, mit der es möglich ist, oberflächennahe Fehler in Schienen zu detektieren und zu bewerten.
Die bisherigen Untersuchungen haben gezeigt, dass Fahrkantenfehler (Head Checks) mit Risstiefen bis zu 10 mm bewertet werden können. Darüber hinaus werden weitere Inhomogenitäten und Fehler wie z. B. Schleuderstellen, Belgrospi's und Squats detektiert.
Für die Anwendung der Prüftechnologie kommen 4 Anwendungsgebiete in Frage:
Ausrüstung von Schienenprüfzügen,
Manuelle Schienenprüfung,
Ausrüstung von Schienenschleifzügen,
Ausrüstung von stationären Schienenprüfständen.
Die Prüftechnik befindet sich zur Zeit in der Erprobungsphase. Der Schienenprüfzug der Deutschen Bahn AG wird in Kürze mit einem achtkanaligen Prüfsystem ausgerüstet.
Ebenfalls im Erprobungseinsatz befindet sich ein Handprüfsystem zur manuellen Schienenprüfung.
Apparently that the type testing procedure should be conducted under the conditions ensuring reproducibility of its outcomes. We investigated various factors effecting upon the reproducibility. To obtain quantitative characteristics of indications visibility the image-processing hard-and software were used. It was established that there are two main groups of these factors. The first depends on the differences between various test panels, which are used for type testing. The second one concerns the reproducibility of some stages of penetrant testing procedure (excess penetrant removing and developer application). The recommendations to increase the reproducibility of type testing are developed and illustrated experimentally.
The determination of penetrant system sensitivity as a part of type testing should be conducted ensuring reproducibility of the result. We investigated some factors effecting the reproducibility. To obtain quantitative characteristics of indications visibility, an image processing system was used [1]. We used 3 different sets of reference blocks (rb1, rb2, rb3) corresponding to type 1 of EN ISO 3452-3 [2]. Two fluorescent penetrants with different sensitivities and the same wet solvent developer were used.
It was established that the reproducibility of type testing is influenced by mainly two principal factors. First there are the differences between reference blocks. Second one concerns the reproducibility of penetrant testing procedure, especially excess penetrant removal and developer application.
According to EN ISO 3452-3 a reference block for determination of sensitivity level of fluorescent penetrants consists of a set of three nickel-chrome plated panels with 10, 20 and 30 µm plating thickness. Transverse cracks are made in each panel by stretching the panels in the longitudinal direction and width to depth ratio of the cracks should be approximately 1/20. Each panel presents a certain sensitivity level, which is characterised by the level of visibility of the indication. The highest level 3 corresponds to the panel with 10 µm thickness plating. Each panel is cut longitudinally (perpendicular to the crack) so that 2 sheets (panels A and B) with nearly the same cracks will be produced. These panels A and B of a reference block are used for relative evaluation, for example to compare sensitivities of two penetrants. It is considered that the application of the same penetrant to both panels with subsequent adequate development results in the same visibility of the indications on these panels.
Quantitative correlations between the abilities of the reference blocks used for determining of the sensitivity were obtained in our investigations. We used the relations between the measured values of light-fluxes from the indications of similar comparing areas on two panels. These indications correspond to certain cracks parts of the same total length on both comparing areas. The relations of the steps between the panel are responsible for the definition of the sensitivity groups. From our investigations it follows that the steps of the different sets are different. Besides it was established that the indications visibility for the same penetrant applied on different reference blocks might have a considerable difference depending on the penetrant sensitivity: the higher penetrant sensitivity, the smaller is such a difference between the steps 30/20 and 20/10. For example, for rb3 the relations 30/20 and 20/10 for lower sensitive penetrant (I1) reached factor 3 comparing with factor 2 for higher sensitive penetrant (I2).
Some results of the comparison between the 3 sets (rb1, rb2, rb3) investigations are summarised in Table 1 with rb1 as a reference.