Gas turbines, particularly aircraft engines, have at least one rotor equipped with rotating moving blades, particularly in the region of a compressor and of a turbine, the rotating moving blades of the gas turbine being either anchored by profiled blade roots in recesses of the gas turbine rotor or being an integral part of a gas turbine rotor. If the moving blades are anchored by blade roots in corresponding recesses of the rotor, then the blade roots are profiled either according to the so-called fir tree design or according to the so-called dovetail design. The fir tree-profiled or dovetail-profiled surfaces of a root of a gas turbine blade are also called bearing flanks or bearing surfaces. During the operation of a gas turbine, the blade roots are highly stressed on their profiled bearing surfaces, particularly by fretting. The wear rate in the region of the blade roots may be reduced by hardening the blade roots on their bearing surfaces using special surface machining methods. A similar problem may arise with respect to integrally bladed gas turbine rotors, which are hardened in the region of their rotor discs so as to minimize the wear rate. The surfaces of the blades of gas turbines blades are also hardened to minimize the wear rate.
Shot blasting may be used as a surface machining method for hardening components, particularly of gas turbine components such as gas turbine blades. In conventional shot blasting, a significant surface roughening may occur on the blasted surfaces. For improving the machining quality resulting from shot blasting, it is described in U.S. Pat. No. 6,536,109 to harden blade roots of gas turbine blades, for example, in the region of their profiled bearing surfaces using ultrasonic shot blasting.
Thus, U.S. Pat. No. 6,536,109 describes such a device having an ultrasonic sonotrode, the ultrasonic sonotrode having a horizontal or level vibrating or oscillating surface, and a machining chamber extending above this oscillating surface, in which gas turbine blades with their blade roots are arranged upright for machining the blade roots in the region of their bearing surfaces. According to U.S. Pat. No. 6,536,109, for this purpose, the gas turbine blades are oriented upright such that the profiled bearing surfaces of the blade roots to be machined extend essentially perpendicular to the oscillating surface of the ultrasonic sonotrode. In this manner, it is possible to achieve only an insufficient quality in shot blasting the profiled bearing surfaces of the blade roots. Furthermore, using the device described in U.S. Pat. No. 6,536,109, it may not be possible to blast thin-walled components, since such thin-walled components may be exposed to unacceptable deformation when machined in this device.