Welded Rotor Shaft Rings for Corrosion-Stressed Blade Slots
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Solution Overview
Problem
Current rotor shafts for steam turbines face challenges with high tensile and corrosion stresses, particularly in low-pressure regions, where material selection is costly and production methods limit achievable strengths and homogeneity, making it difficult to maintain static and oscillation strength, and corrosion resistance, especially when repairing cracked or corroded components.
Innovation Solution
A rotor shaft design featuring a shaft base member made from a cost-effective material with rings of higher strength and corrosion resistance, applied via narrow-gap welding, allowing for optimized material properties in high-stress areas like blade grooves, enabling better mechanical and corrosive performance without the need for expensive, high-grade materials across the entire shaft.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If high-grade materials are used throughout the entire rotor shaft, then strength and corrosion resistance are improved, but manufacturing cost increases significantly
Solution Approach 1:
The patent applies different material grades to different regions of the rotor shaft based on their specific functional requirements. High-grade materials with superior strength and corrosion resistance are used only in critical areas such as blade groove regions subjected to high tensile and corrosion stresses, while cost-effective materials are used in less critical regions. This local differentiation resolves the contradiction by achieving necessary performance only where required, thereby reducing overall manufacturing cost while maintaining strength and corrosion resistance in critical zones.
Solution Approach 2:
The rotor shaft is constructed as a composite structure comprising multiple material regions. The shaft includes a base material and overlay materials with different properties, where the overlay material in critical regions provides enhanced strength and corrosion resistance. This composite approach allows the shaft to achieve the performance of high-grade materials in critical areas while using cost-effective materials elsewhere, thus resolving the contradiction between strength/corrosion resistance and manufacturing cost.
2Ease of manufacture
If monolithic rotor shafts are produced using conventional forging and heat treatment, then production is simplified, but achievable strength and homogeneity are limited by material mass and diameter
Solution Approach 1:
The rotor shaft is segmented into multiple material regions with different properties rather than being produced as a homogeneous monolithic structure. The shaft comprises a base material and overlay materials applied to specific regions, allowing each segment to be optimized for its functional requirements. This segmentation enables the use of high-performance materials in critical areas without the need to upgrade the entire shaft, thereby achieving superior strength and homogeneity in critical zones while maintaining production simplicity through modular manufacturing approaches.
Solution Approach 2:
The patent changes the material parameters (composition, microstructure, properties) in different regions of the rotor shaft to optimize performance. By applying overlay materials with specific compositional and microstructural characteristics to critical regions, the shaft achieves enhanced strength and homogeneity in those areas. This parameter differentiation allows the shaft to overcome the limitations of conventional monolithic production while maintaining manufacturing simplicity through controlled material application processes.
3Ease of repair
If build-up welding is used to repair cracked rotor shafts, then component replacement is avoided, but welding defects and loss of forged material properties occur
Solution Approach 1:
The patent enables the recovery and restoration of rotor shaft components through controlled material application rather than complete replacement. By applying overlay materials to repaired regions with precise control over the material properties and bonding process, the shaft restores its structural integrity and performance. This approach avoids the defects associated with conventional build-up welding while maintaining the benefits of component repairability, as the controlled material application process preserves forged material properties and eliminates welding defects.
4Strength
If Superclean variant of 3.5NiCrMoV steel is used, then strength and purity are improved, but production complexity and cost increase by 10-20%
Solution Approach 1:
The patent applies the high-purity Superclean material only to critical regions of the rotor shaft where superior strength and corrosion resistance are required, rather than using it throughout the entire shaft. This local application resolves the contradiction by achieving the benefits of high purity and strength only where necessary, thereby reducing production complexity and cost while maintaining the enhanced properties in critical zones.
Solution Approach 2:
The rotor shaft is constructed as a composite with different material grades in different regions. The Superclean variant is used as an overlay material in critical areas, while cost-effective materials are used in non-critical regions. This composite structure achieves the strength and purity benefits of the Superclean material without requiring the entire shaft to be produced with this complex and expensive material, thereby reducing overall production complexity and cost.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This design allows for cost-effective adaptation of material properties to specific load requirements, enhancing static strength, low-cycle fatigue resistance, and corrosion resistance, while enabling more homogeneous production and repair of damaged areas, reducing the need for costly material and minimizing welding defects.
Implementation Method 1
the ring is connected to the shaft base member by means of narrow-gap welding in a materially integral manner
Data Source
AI summary
A rotor shaft for a turbine rotor of a turbine, in particular a steam turbine, having a shaft main body made of a first material and at least one ring which is made of a second material and is attached to the shaft main body, wherein the second material has equal or greater strength and/or greater corrosion resistance than the first material, wherein at least one blade slot is formed on the ring, and wherein the ring is materially bonded to the shaft main body by narrow-gap welding.