Method for producing a base body of a turbine blade
A way of producing turbine rotor blades or the bottom bodies includes a) supplying the bottom body, which has, after one another along a longitudinal axis, a blade origin, a blade platform along with a blade airfoil( b) sensing a value of at least one parameter of the body, at least among those parameters representing a vibrational land of the body( c) comparing the sensed value with a predetermined target span, d) when the sensed value is located away from the target interval, reducing the mass of the body, whereas the reduction of the mass occurs at the blade root and/or on the blade platform by introducing at least one recess or by lowering a dimension beneath the corresponding target value.
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It’s known to give turbine rotor blades using a protective layer, in order for them to have an increased lifetime during operation in a gas turbine. Often employed as a protective layer to the turbine rotor blade made in a casting processis a corrosion protection layer of the type MCrAlY. The application of the protective layer occurs in the region of the surface that’s exposed to the hot gas of the gas turbine during operation. This region comprises both the blade airfoil andthe platform of the turbine rotor blade, where the blade airfoil is integrally formed. Aside from the rust protection layer, a thermal barrier coating may be implemented from the aforementioned region, so as to minimize as much as possible theamount of heat introduced to the base substance of the turbine rotor blade out of the gas. The application of the layers thereby alters the vibrational behavior of the turbine rotor blade.
It is also known that turbine rotor blades are excited to vibrate throughout the functioning of the gas turbine. The vibrational excitation is due to the rotation of the rotor on which the turbine rotor blades are procured. Additionally contributing tothe vibrational excitation of the blade airfoils of the turbine rotor blades is the hot gas impinging on them. Considering that the blade airfoils of the turbine rotor blades rotate downstream of a ring of tanks guide vanes–seen at the path of flow of thehot gas–they’re excited to vibrate by hot gas pulsating on them. It is therefore required that every turbine rotor blade has a high resonant frequency, so that the various excitation frequencies of both the vibrational excitationoriginating from the rotational rate of the rotor and the vibrational excitation originating from the hot gas do not lead to an unacceptably great vibration of the blade airfoil. Accordingly, in the prior art the turbine rotor blades were created insuch a manner that their resonant frequency deviates from the excitation frequencies of the stationary gas turbine. At the development of the turbine rotor blade, it’s also guaranteed that, overall, the finished turbine rotor blade pleases the requirementswith respect to normal resonance, including with regard to the rotor rates to be expected.
It is thus envisaged from the production process of the turbine rotor blade to test each individual turbine rotor blade because of its vibrational properties. In this test, the turbine blade is clamped in the origin and made to vibrate by amechanical impulse. Afterward the vibrational response of the turbine blade, and in particular its blade airfoil, is felt. If the vibrational response of the turbine rotor blade doesn’t comply with the specified frequency values for your resonantfrequency, it has to be discarded or manipulated by way of appropriate measures in such a way that it matches the prerequisites for the resonant frequency, and is thus appropriate for operation. In order turbine rotor blades that are not intended tobe used from the gas turbine just due to their vibrational property are passed for use, it is known for example from EP 1 985 803 A1 to present a recess from the tip of the blade airfoil, whereby the mass of the turbine rotor blade canbe reduced during its free, vibratory end. By cutting the mass of the turbine rotor blade, the vibrational property is positively influenced. Its resonant frequency can be shifted to higher values by removing the mass.
In addition, it is known by EP 0 537 922 A1 to insert a tubular damper in the blade platform of a turbine rotor blade. This damper may be pushed out slightly under rotational force, and thus come in contact with a platform of a neighboringblade to soften blade-to-blade vibrations during operation.
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