Axial-Entry Rotor Blade Assembly for 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 difficulty in maintaining shroud interference at high rotational speeds, leading to inefficiencies and increased manufacturing costs.
Innovation Solution
A method involving axial-entry rotor blades with convergent and skewed insertion angles, allowing for gradual insertion of male dovetails into female dovetail slots, which increases shroud interference and reduces pitch, enabling uniform packing and contact between airfoil shrouds without additional components or complex tooling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If airfoil shrouds include extra material to maintain contact at high speed, then shroud interference is maintained, but device complexity and manufacturing difficulty increase
Solution Approach 1:
The patent changes the geometric parameters of the dovetail slot, specifically introducing a convergence angle relative to the radial direction. This parameter change allows the shroud interference to be maintained through the insertion geometry itself rather than requiring excessive shroud material, thereby reducing blade construction complexity while preserving reliability
Solution Approach 2:
The patent employs asymmetric dovetail slot geometry where the slot is not symmetric with respect to the radial direction but has a specific convergence angle. This asymmetry enables the shrouds to interfere properly during insertion without requiring equal material distribution, simplifying the overall blade construction while maintaining contact at operational speeds
2Reliability
If complex coupling systems are used to assemble blades with shroud interference, then shroud contact is ensured, but ease of manufacture decreases
Solution Approach 1:
The dovetail slot geometry is designed to automatically generate the required shroud interference through its convergence angle during the insertion process. The system is self-configuring, eliminating the need for complex external coupling mechanisms or specialized assembly tooling, thereby improving ease of manufacture while ensuring reliable shroud contact
3Ease of operation
If axial-entry blades are used for rotor assembly, then ease of operation improves, but maintaining shroud interference at high speed becomes difficult
Solution Approach 1:
The patent introduces a convergence angle parameter for the dovetail slot that transforms the simple axial insertion motion into an effective interference-generating mechanism. This parameter change allows axial-entry blades to maintain shroud interference at high speeds by converting the straightforward axial motion into proper shroud contact through the angled geometry
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 simplifies the assembly process, maintains shroud interference under centrifugal loads, and supports high steam conditions, enhancing the efficiency and robustness of rotor assemblies while reducing manufacturing complexity and costs.
Implementation Method 1
The insertion direction is convergent with the rotation axis of the rotor wheel, forming with it an insertion angle
Implementation Method 2
at operational speed, the blades of the rotor tend to elongate. This is known as the centrifugal elongation of the rotor blades
Data Source
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AI summary
A rotary machine assembly (1) for a turbomachine, such as a rotor, is disclosed. The rotary machine assembly (1) comprises a rotor wheel (2) where a plurality of circumferentially spaced female dovetail slots (21) are obtained. The rotary machine assembly also comprises a plurality of blades (3). Between each blade and the adjacent one there is an interface angle. Each blade comprises a male dovetail (32), configured to fit with a corresponding female dovetail slot of the rotor wheel along an insertion direction (I). The female dovetail slots are shaped so that the insertion direction of each male dovetail is convergent with the rotation axis (R) of the rotor wheel, so as to form with it an insertion angle (a), so as to insert gradually all the male dovetails into the female dovetail slots and packing them also gradually. Also disclosed is a method for assembling a rotary machine assembly, which does not require any specific tool.