3.5.4. Calibration Measurements

In the repair shop, measurements were made to determine attenuation and propagation velocity of the acoustic signal on the decommissioned support block with the end caps removed. To simulate the sources of AE, an electronic simulator was used. The emission was produced on the shaft in the region of the fillet and at the ends of the shaft, as well as on the inner and outer rings of the bearings (Figure 18).

**Figure 18.** Scheme of the roller bearing with the protective caps removed. The points of emitting by simulator and the recommended positions for the sensors mounting.

Within the shaft, the attenuation coefficient was 5 dB/m. The presence of a high attenuation value (30–35 dB) is revealed at the boundary between bearing housings and the shaft.

The obtained results revealed that the AE testing should be performed as follows (Figure 18). For full AE testing of all 3 bearings, use the zone location with the accuracy of the element of a specific bearing. For this task, it is required to place the AE sensors at all available access points, namely 3 sensors on each of the 2 bearing housings (Figure 19a). Since the length of the shaft is small (4050 mm), it is enough to provide access to the shaft by removing the covers and to install one sensor at each of 2 ends (Figure 19b) for its full AE testing including linear location. Slow rotation of the sensor at the shaft ends does not cause significant technical difficulties with the duration of the AE testing of about 1 h.

**Figure 19.** Sensors mounted at bearing housing (**a**) and at the end of the roller bearing (**b**) with the protective caps removed.

#### 3.5.5. AE Testing

The next stage of the work is to carry out AE testing of the support without taking the object out of operation. The AE data were taken with a regular rotation of the kiln and the support for 1–2 h. Five support blocks with open caps were examined, where both the bearings and the shaft were directly accessible. Also, 10 support blocks with closed caps were tested, where access was available only to the bearings.
