Phased Array UT of Shrunk-On Disks
Reinhart & Associates, Inc. performs phased array ultrasonic testing (PAUT) of shrunk-on disks utilizing the scanning system shown in Figure 1 and either a Harfang X-32 or Sonatest VEO PAUT instrument. The scanning system is composed of an arm manipulator that holds the ultrasonic search unit at a location predetermined by the dimensions determined by using a drawing of each disk and/or estimated dimensions. The motion control part of the system allows the transducer to be manipulated in and out in the radial direction and to be skewed angularly. The skewing of the transducer points the sound beam in the direction where it is maximized (i.e., maintained perpendicular to the disk bore or tangent to the disk bore). The system also uses a pump to deliver of ultrasonic couplant to the search unit head during scanning. Prior to ultrasonic examination, the system is calibrated using a calibration block containing artificially cut notches simulating expected defects in the keyway and disk bore areas. The scanning is performed by rotating the rotor at a controlled speed of less than 1 rpm using power rollers or a lathe.
The ultrasonic scanning of the shrunk-on disks is performed by first calculating the ultrasonic refracted shear wave beam angle needed to examine the bore and keyway configurations of each disk. To perform these calculations, a cross section drawing of each disk or an original drawing, if available from the OEM, is used. However, if the physical shrunk-on disk geometries are not available, then an ultrasonic thickness survey is done from the hub and web faces to generate a drawing using the estimated dimensions. These dimensions combined with actual physically peripheral dimensions are used to estimate expected ultrasonic refracted angles, sound path, and transducer position with respect to the disk web and hub areas of each disk. Indications can be then identified by location in the disk bore and keyway regions. The range of refracted angles commonly used for the examination will cover from 0 to 90 degrees. Using these parameters, the scans are performed from the inlet and exhaust faces of each disk. Single crystal conventional ultrasonic transducers are also used to verify and assist in detection and sizing of indications
Figure 2 shows a sketch and nomenclature used to identify a specific scan of the disk bore and/or keyway; in this case, it is for a web scan in the 0-deg, CW, and CCW from the inlet and exhaust sides of a disk. Figure 3 shows a typical sectorial and B-scans of a disk bore surface scanning from the web inlet face to the exhaust face at 0-deg skew. Figure 4 shows generic nomenclature used for shrunk-on disks. Figure 5 shows a 3D solid model of a disk bore with a PAUT sector scan overlay.
