Rotor Balance Tabs and Scallops for Low-Stress Turbine Balancing
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional methods for balancing gas turbine engine rotors through material removal create high stress areas and surface defects, such as undulations and undercut notches, which can lead to further stress concentration zones and require additional polishing to control surface finish, potentially removing beneficial compressive stresses.
Innovation Solution
A method involving the machining of a circumferential array of stress shielding scallops and balance tabs on the rotor, allowing for controlled material removal from these tabs to correct imbalances without introducing high stress concentrations, thus avoiding the need for polishing and minimizing residual unbalance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If material removal is performed by milling grooves or notches into the rotor surface for balancing, then the rotor imbalance can be corrected, but high stress areas and surface defects are created
Solution Approach 1:
The rotor surface is segmented into multiple discrete balance tabs arranged circumferentially around the rotor. Each tab can be independently machined to remove material, allowing precise control of material removal while maintaining structural integrity. The tabs are separated by stress shielding scallops that prevent stress concentration from propagating between tabs.
Solution Approach 2:
The balance tabs are designed with specific geometric features including rounded leading edges and controlled root radii to optimize stress distribution locally. The tabs have varying heights and positions tailored to the specific balancing requirements, allowing localized material removal without affecting the entire rotor structure.
2Measurement precision
If manual material removal is performed to perfect the balance, then balancing precision can be improved, but uncontrolled surface defects and stress concentration zones are created
Solution Approach 1:
Manual hand-held machining tools are replaced with automated CNC machining systems that precisely control the material removal process. The automated systems maintain consistent cutting parameters, speeds, and feeds to produce uniform surface finishes without the variability and defects associated with manual operations.
3Manufacturing precision
If polishing is performed to control surface finish and correct surface defects, then surface quality is improved, but beneficial compressive stresses are removed
Solution Approach 1:
The rotor surface undergoes preliminary machining operations including milling and turning that inherently produce acceptable surface finishes without requiring subsequent polishing. The balance tabs are machined with controlled surface finishes from the outset, eliminating the need for polishing operations that would remove beneficial compressive stresses.
4Measurement precision
If multiple balancing operations including polishing are conducted, then balancing precision is improved, but process complexity and time increase
Solution Approach 1:
The balancing operation is merged with the initial rotor manufacturing process. The balance tabs are machined during the same manufacturing run as the rotor itself, and the surface finish requirements are built into the machining parameters. This integration eliminates separate polishing and multiple balancing operations, reducing overall process complexity while maintaining precision.
Data Source
AI summary
A method of balancing a gas turbine engine rotor comprises the step of obtaining a rotor disc with a circumferential array of balance tabs projecting from a peripheral rim of the disc. Stress shielding scallops are defined in the rotor disc between the tabs. The balancing is achieved by removing material from at least one of the tabs.