Multi-Piece Locking Blade for Steam Turbine Rotor Stress Reduction
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Solution Overview
Problem
Steam turbine rotor and blade assemblies experience high stress concentrations due to centrifugal and thermal loads, particularly at the points where blade retention screws are tapped into the rotor, which can adversely impact rotor fatigue life.
Innovation Solution
A multi-piece locking blade assembly with a base and side hooks is used, featuring pilot holes and screws that secure the locking blade within a dovetail slot, eliminating the need for screws to be tapped into the rotor and reducing stress concentrations by utilizing hooks within a locking blade groove.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If blade retention screws are tapped directly into the rotor, then the locking blade can be securely attached, but stress concentrations are created in the rotor
Solution Approach 1:
The locking blade is divided into multiple segments: a base portion, first and second side hooks, and intermediate hooks. This segmentation allows the locking blade to be assembled from separate components that can be independently positioned and secured, distributing stresses rather than concentrating them at single tap holes in the rotor.
Solution Approach 2:
The locking blade groove acts as an intermediary feature in the rotor that receives and secures the locking blade without requiring direct tapping into the rotor body. The groove provides a dedicated space for the locking blade's base and hooks, eliminating the need for stress-intensive tap holes while maintaining secure attachment.
2Strength
If traditional dovetail attachment is used for buckets, then secure mounting is achieved, but the last bucket cannot be properly closed without additional retention features
Solution Approach 1:
The locking blade combines multiple functions into a single component: it provides closure for the bucket assembly, attaches to the rotor via the groove mechanism, and secures the last bucket in position. This merging of closure and attachment functions eliminates the need for separate retention features and simplifies the overall assembly.
3Reliability
If multiple retention features are added to secure the locking blade, then attachment reliability improves, but manufacturing complexity increases
Solution Approach 1:
The locking blade groove is pre-formed in the rotor during rotor manufacturing, and the locking blade is designed with pre-positioned hooks and base features. This preliminary preparation allows for simple assembly where the locking blade is inserted into the groove and secured with standard fasteners, avoiding complex manufacturing steps while ensuring reliable attachment.
Data Source
AI summary
The present application provides a turbine rotor and blade assembly for a steam turbine. The turbine rotor and blade assembly may include a rotor, a number of buckets positioned about the rotor and a locking blade positioned about the rotor. The locking blade may include a base, a first side hook, and a second side hook. The locking blade may include a first side pilot hole defined between the base and the first side hook and a second side pilot hole defined between the base and the second side hook.