Axial-Entry Rotor Blade Assembly With Gradual Shroud Interference
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Solution Overview
Problem
Current methods for assembling rotor blades in steam turbines face challenges such as complex machining requirements, operational drawbacks, and difficulties in maintaining shroud interference at high rotational speeds, leading to inefficiencies and increased manufacturing costs.
Innovation Solution
The method involves inserting male dovetails into female dovetail slots with a convergent and skewed insertion direction, allowing for gradual shroud interference and reduced pitch, which simplifies the assembly process and maintains blade connection without additional components or complex geometries.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If airfoil shrouds include extra material to maintain contact at high speed, then shroud interference is improved, but device complexity and manufacturing difficulty increase
Solution Approach 1:
The patent changes the pitch parameter of the rotor blades to create interference-fit shrouds. By adjusting the pitch to be slightly larger than the nominal value, the shrouds are designed to interfere with adjacent shrouds when the rotor operates at high speed, maintaining blade connection without requiring complex additional structures. This parameter modification directly resolves the contradiction by achieving reliable shroud interference through a simple dimensional change rather than complex construction.
2Reliability
If complex coupling systems are used to assemble blades, then shroud interference is maintained, but ease of manufacture and assembly deteriorate
Solution Approach 1:
The patent extracts and eliminates complex coupling systems from the blade assembly process. Instead of using additional coupling components or complex assembly procedures, the solution relies solely on the interference-fit design of the shrouds themselves, which naturally maintain blade connection during operation. This extraction of unnecessary complexity directly improves ease of manufacture while maintaining shroud interference reliability.
3Ease of manufacture
If rotor blades are designed for axial entry, then assembly simplicity is improved, but manufacturing precision requirements worsen
Solution Approach 1:
The patent introduces asymmetry in the pitch parameter to create intentional interference between shrouds. This asymmetric design, where the pitch is deliberately made slightly larger than nominal, provides self-aligning characteristics during axial insertion. The interference-fit geometry guides the blades into proper alignment as they are inserted axially, reducing the actual precision requirements despite the complex interference geometry. The asymmetric pitch design transforms a potential precision problem into a self-correcting assembly feature.
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 approach enables efficient shroud interference and robust assembly of rotor blades, capable of withstanding high centrifugal loads and severe steam conditions, while reducing assembly complexity and costs.
Implementation Method 1
the blades of the rotor tend to elongate. This is known as the centrifugal elongation of the rotor blades. This phenomenon causes that the airfoil shroud moves to a larger diametral position
Data Source
AI summary
A rotary machine assembly for a turbomachine, such as a rotor, having a rotor wheel where a plurality of circumferentially spaced female dovetail slots are obtained. The rotary machine assembly also comprises a plurality of blades. Between each blade and the adjacent one there is an interface angle. Each blade comprises a male dovetail, configured to fit with a corresponding female dovetail slot of the rotor wheel along an insertion direction. The female dovetail slots are shaped so that the insertion direction of each male dovetail is convergent with the rotation axis of the rotor wheel, so as to form with it an insertion angle, so as to insert gradually all the male dovetails into the female dovetail slots and packing them also gradually. A method for assembling a rotary machine assembly, which does not require any specific tool, is also disclosed.