Spectral Measurements:

The measurements were carried out using an AGILENT brand spectrometer (Figure 1). The spectral band is from 2µm to 15µm. The detector is a DTGS
Figure 1: Measurements with the FTIR-4300 infrared spectrometer

Measurements of emissivity:

Measurements of total directional emissivity are carried out using the emissometer EM2 and EM3. The EM2 emissometer is used to measure emissivity in the wide band (1 to 50 µm) and EM3 in the 8-12 µm band. Figure 2 shows the two emissometers used.

Figure 2: EM2 emissometer on the left and EM3 on the right

Results
The spectral measurements were carried out with the FTIR-4300 from AGILENT. The advantage of these measurements is to check the ratio between broadband and narrowband emissivity measurements. These measurements also inform us about the nature of the coating and its possible pollution by a deposit (dust, grease, …).

The measurements were made on several identical axles. This redundancy made it possible to eliminate measurements by two screens. On the one hand by checking the standard deviation of the summations necessary for the measurement made with EM3. On the other hand by eliminating the measurements for which the ratio between the two types of emissivities calculated on the one hand with the spectral data and the measurements with EM2 and EM3 diverge strongly.

Figure 3: Spectral reflectance in% of the different surfaces measured as a function of the wavelength in µm

Conclusion:
After numerous measurements on different types of axles (type of train, paint, new and used) we can reasonably consider that the emissivity of the axle boxes can vary between 0.87 and 0.95.

Bibliographic data:

[1] Infrared Emissivity Measurements of Building and Civil Engineering Materials A new device for measuring emissivity, JP Monchau, L. Ibos, Y. Candau, V. Feuillet, M. Marchetti, J. Dumoulin, International Journal Of Thermophysics, june 2013

[ 2] Comparative study of radiometric and calorimetric methods for total hemispherical emissivity measurements, Jean-Pierre Monchau, Jacques Hameury, Patrick Ausset, Bruno Hay, Laurent Ibos & Yves Candau, Heat and Mass Transfer, Wärme- und Stoffübertragung ISSN 0947-7411, Heat Mass Transfer DOI 10.1007 / s00231-017-2238-6

[3] GUM 1995, Evaluation of measurement data – A guide to the expression of uncertainty