Centering Pin Fixation via Axial Constriction Expansion
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Solution Overview
Problem
Existing methods for connecting centering pins to core lattices in pressurized water reactors are complex, costly to produce, require high force for assembly, and are difficult to remove, especially when different plate thicknesses are involved, leading to potential mandrel jamming or breakage and challenging disassembly.
Innovation Solution
A method where the fixing section of the centering pin is initially a hollow cylinder with a uniform outer diameter, allowing for easy expansion using a widening tool to form an axial form fit, reducing production complexity and enabling easy removal by reversing the expansion process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If material weakenings (grooves) are provided in the fixing section to enable radial deformation with a mandrel, then the fixing section can be widened to create form fit, but the centering pin becomes very complex in shape and requires high manufacturing costs
Solution Approach 1:
The invention changes the geometric parameters of the fixing section by providing an axial constriction instead of circumferential grooves. This single parameter change (adding a narrowing in the axial direction) enables the fixing section to be divided into two portions (first and second portions) with different diameters, allowing radial deformation to engage behind the plate edge while maintaining a simpler overall structure compared to multiple grooves
Solution Approach 2:
The fixing section is segmented into a first portion (before constriction) and a second portion (after constriction) by the axial narrowing. This segmentation allows the second portion to be radially deformed and engaged behind the plate edge while the first portion remains larger and can be accessed by the mandrel, achieving fixation without requiring complex multi-groove structures
2Reliability
If a mandrel is pushed with great force into the constriction to widen the fixing section, then the form fit is achieved, but the mandrel often jams in the centering pin or breaks off
Solution Approach 1:
The constriction is pre-formed in the fixing section during manufacturing, creating a ready-made deformation zone. The mandrel simply needs to pass through this pre-prepared constriction and apply radial force to expand the second portion, rather than forcing deformation through material yield. This preliminary preparation of the constriction geometry makes the assembly process much easier and more reliable
3Reliability
If the fixing section engages behind the plate edge in a hook-like manner, then axial fixation is achieved, but the centering pins can only be removed with difficulty
Solution Approach 1:
The fixing mechanism is made dynamic through the radially deformable second portion. During assembly, the mandrel expands this portion to engage behind the plate edge for secure fixation. During removal, the process is reversed by applying radial force to collapse the expanded portion back into the constriction, allowing easy withdrawal. This dynamic deformability provides both secure installation and easy removal
4Manufacturing precision
If the groove wall position is matched to plate thickness for proper engagement, then fixation works for that thickness, but different centering pins must be produced for plates with different thicknesses
Solution Approach 1:
The centering pin design with an axial constriction and radially deformable second portion is universal and can be used with plates of different thicknesses. The deformation amount and engagement depth automatically adapt to the specific plate thickness during assembly, eliminating the need to produce different centering pin variants for different plate specifications
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 production and assembly of centering pins, allows for reliable fixation with minimal force, and facilitates easy removal by reversing the expansion process, accommodating various plate thicknesses without the need for complex shapes or high manufacturing costs.
Implementation Method 1
A second axial section of the centering pin is used to fix it to the plate and is inserted into a receiving hole in the plate for this purpose. At its free end, the second axial section transitions into a radially outwardly deformable fixing section which, in the final assembly state, engages behind the outside of the plate facing away from the inside with a flared projection protruding from the bore, forming a form fit in an axial direction pointing towards the center of the reactor pressure vessel.
Data Source
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AI summary
The invention relates to a connecting assembly of a centering pin (10) on a core grate (3) of the reactor pressure vessel (1) of a pressurized-water reactor, which centering pin is used to center a fuel element (2), wherein the centering pin (10) is retained in an accommodating bore (16) of a plate (4) present on the core grate (3), with an expanded projection (19) protruding from the accommodating bore (16), in such a way that a form closure is formed. In a pre-assembly state, in which said form closure does not yet exist, the fixing segment (18) is a hollow cylinder, which has, over the entire length of the hollow cylinder, an outer circumferential surface (27) that extends on the lateral surface of a circular cylinder having uniform outside diameter (26). In a final assembly state, the projection (19) is expanded as a consequence of an expansion by means of an expanding tool in such a way that said form closure is formed.