Turbomachine Diaphragm Inner Platform Interference Fit
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Solution Overview
Problem
Current steam turbine diaphragm designs require a massive inner diaphragm ring for rigidity, leading to increased material and manufacturing costs, as well as higher total pressure loads due to the need for extensive welding and complex assembly processes.
Innovation Solution
The design eliminates the inner diaphragm ring by using inner platforms with an interference fit to create a rigid band around the inner diameter, pre-stressing the aerofoils through torsional stress during assembly, which reduces material requirements and welding needs while maintaining equivalent static strength and predictable dynamic behavior.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If an inner diaphragm ring is used to provide rigidity, then the diaphragm maintains structural strength, but material requirements and manufacturing complexity increase
Solution Approach 1:
The invention merges the function of the inner diaphragm ring with the inner platforms of the stationary blades. The inner platforms are designed with an interference fit arrangement that allows them to collectively form a rigid circular structure, eliminating the need for a separate inner diaphragm ring while maintaining the required rigidity and strength.
Solution Approach 2:
The inner platforms of the stationary blades are given multiple functions: they serve as mounting surfaces for the blades, provide structural support, and through their interference fit arrangement, create the rigid circular structure previously requiring a separate inner diaphragm ring. This multi-functionality reduces overall component count and material usage.
2Strength
If an inner diaphragm ring is used for structural support, then the diaphragm maintains integrity, but the total pressure load on the diaphragm increases
Solution Approach 1:
By combining the support function into the inner platforms with interference fit, the structural integrity is maintained without the additional mass and surface area of a separate inner ring, thereby reducing the total pressure load that the diaphragm structure must withstand.
3Strength
If welding is used to attach the inner diaphragm ring to blade platforms, then structural connection is achieved, but manufacturing complexity and material requirements increase
Solution Approach 1:
The invention extracts and eliminates the inner diaphragm ring component entirely, removing the welding operations required to attach it to the blade platforms. The interference fit arrangement provides the necessary structural connection without requiring welding, thereby reducing manufacturing complexity and material requirements.
4Ease of operation
If the diaphragm ring is shrunk onto the blade platforms, then assembly is achieved, but manufacturing complexity increases
Solution Approach 1:
By eliminating the inner diaphragm ring, the complex shrink-fit assembly process is removed. The interference fit is built into the blade platform design itself, simplifying both manufacturing and assembly operations.
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 reduces material and manufacturing costs, decreases total pressure loads, and enhances the dynamic behavior of the turbine diaphragm by distributing torsional loads effectively within the blade annulus, ensuring only radial loads are applied to the diaphragm ring.
Implementation Method 1
confronting edges of the inner platforms have an interference fit with each other
Implementation Method 2
the aerofoils are in a state of torsional stress between the inner and outer platforms
Implementation Method 3
an elastic torsional stress is built into the aerofoils
Implementation Method 4
radially compressing the blade ring with the diaphragm ring to a predetermined final diameter by forcible contact between an internal surface of the diaphragm ring and external surfaces of the outer platforms
Data Source
AI summary
A turbine diaphragm includes an annulus of static blades and an outer diaphragm ring surrounding the annulus of static blades and welded to the outer platforms. Each static blade has an inner platform, an aerofoil, and an outer platform. The inner platforms serve the function of an inner diaphragm ring, thereby reducing material and manufacturing costs. Furthermore, confronting edges of the inner platforms have an interference fit with each other and the aerofoils are in a state of torsional stress between the inner and outer platforms. The latter two features improve the dynamic characteristics of the diaphragm.