Turbine Diaphragm Mechanical Interference Fit Assembly
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Solution Overview
Problem
The construction of steam turbine diaphragms using traditional welding methods is costly and prone to metallurgical defects, with deep penetration welds requiring specialized equipment and causing stress that necessitates heat treatment.
Innovation Solution
A novel diaphragm structure where static blade units are retained by mechanical means, eliminating the need for welding, with radially inner and outer platform portions interlocking with corresponding features on the diaphragm rings to form port walls, allowing assembly without fusion techniques.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If traditional welding methods are used to join diaphragm components, then structural strength is achieved, but manufacturing cost increases and metallurgical defects occur
Solution Approach 1:
The diaphragm is divided into separate components (inner ring, outer ring, blade units with platforms) that are manufactured independently and then assembled through mechanical interference fits rather than welding. The inner ring has an interference fit with the inner platforms, while the outer ring has an interference fit with the outer platforms, eliminating the need for costly welding operations.
Solution Approach 2:
The patent replaces the welding process (thermal/chemical joining method) with a mechanical interference fit system. The dimensional interference between ring bore/platform outer diameters and ring outer diameters/platform inner diameters creates a press-fit mechanical connection that substitutes for welding, thereby eliminating metallurgical defects and reducing manufacturing costs.
2Strength
If deep penetration welds are used to join diaphragm components, then structural integrity is achieved, but specialized welding equipment is required
Solution Approach 1:
The diaphragm assembly is segmented into discrete components (inner ring, outer ring, blade units) that are joined through mechanical interference fits rather than requiring deep penetration welds. This segmentation allows for simpler manufacturing equipment and eliminates the need for specialized welding apparatus.
Solution Approach 2:
The patent substitutes the welding process (which requires specialized equipment) with a mechanical interference fit system. The dimensional interference creates a press-fit connection that achieves structural integrity without requiring advanced welding equipment, thereby reducing device complexity.
3Strength
If welding is used to assemble diaphragm components, then components are joined, but stress relief heat treatment is required
Solution Approach 1:
The patent replaces the welding process with a mechanical interference fit system. The dimensional interference between components creates a press-fit connection that joins components without introducing thermal stress, thereby eliminating the need for stress relief heat treatment and reducing overall assembly process time.
Solution Approach 2:
The patent changes the joining parameter from thermal (welding) to mechanical (interference fit). By using dimensional interference to create a press-fit connection, the process avoids thermal cycling and stress introduction, eliminating the requirement for subsequent heat treatment operations.
4Strength
If platform type construction with solid rings is used, then structural rigidity is achieved, but manufacturing cost increases
Solution Approach 1:
The solid ring structure is segmented into separate components (inner ring, outer ring, blade units with platforms) that are assembled through mechanical interference fits. This segmentation maintains structural rigidity through proper dimensional design while reducing manufacturing cost by eliminating welding operations.
Solution Approach 2:
The patent substitutes welding (which increases manufacturing cost) with a mechanical interference fit system that maintains structural rigidity. The dimensional interference creates a rigid press-fit connection without the need for costly welding operations, thereby reducing manufacturing cost while preserving structural integrity.
Data Source
AI summary
An axial flow turbine diaphragm is constructed without welding or other metal fusion or melting techniques. Static blade units are attached to inner and outer diaphragm rings by radially inner platform portions that engage the radially inner ring, and radially outer platform portions that engage the radially outer ring, the inner platform portions being elongate in the circumferential direction of the turbine diaphragm and the outer platform portions being elongate in a direction compatible with the stagger angle of the aerofoils. The outer circumference of the radially inner ring has a blade unit retaining feature of complementary shape and orientation to the inner platform portions of the static blade units, and the inner circumference of the radially outer ring is provided with a plurality of blade unit retaining features of complementary shape and orientation to corresponding outer platform portions of the static blade units.