Ceramic Core Positioning via Enlarged Head Pins
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Solution Overview
Problem
Existing methods for locating and supporting ceramic cores in shell moulds during the investment casting process face challenges with platinum pins being expensive and prone to melting, while alumina pins can exit the component under centrifugal force, leading to undesirable changes in cooling systems, especially in gas turbine components.
Innovation Solution
The method involves using pins with enlarged head portions that protrude from the ceramic core and are encased in a wax pattern, which are then surrounded by a shell mould. Upon wax removal, the enlarged head portions abut the shell mould, maintaining the core's position and ensuring the pins remain captive within the cast metal component.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If platinum pins are used to locate and support the ceramic core, then the core position is maintained during casting, but the pins melt under centrifugal force causing core movement and inconsistency
Solution Approach 1:
The patent changes the material parameter of the pins from platinum to alumina, which has a higher melting point and can withstand the centrifugal forces during casting without melting, thereby maintaining core position stability
Solution Approach 2:
The patent uses alumina pins that are cheaper than platinum and can be sacrificed during the casting process, accepting that they may exit the component under centrifugal force in exchange for cost reduction and adequate core positioning
2Loss of substance
If alumina pins are used to replace platinum pins, then material cost is reduced and pins remain within the component, but the pins exit the component under centrifugal force creating apertures
Solution Approach 1:
The patent introduces an intermediary substance (wax) that encases the alumina pins during the investment casting process. This wax coating allows the pins to be properly positioned and supported during casting while preventing them from exiting the component under centrifugal force, thus avoiding aperture creation
3Manufacturing precision
If a high number of alumina pins are used to support elongated thin ceramic cores, then core position is maintained, but pin ejection leads to changes in the cooling system
Solution Approach 1:
The wax encasement acts as an intermediary that allows multiple alumina pins to be used for precise core positioning while preventing their ejection during casting, thereby maintaining the integrity of the cooling system
Solution Approach 2:
The patent extracts the harmful effect of pin ejection by removing the pins from the component after casting through chemical dissolution of the wax encasement, leaving the core properly positioned without creating apertures that would affect the cooling system
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 effectively maintains the core's fixed position during casting and prevents pin ejection under centrifugal force, ensuring consistent wall thickness and reducing material costs by keeping the pins within the component.
Implementation Method 1
the enlarged head portions abut the shell mould, maintaining the core's position
Implementation Method 2
prevents pin ejection under centrifugal force, ensuring consistent wall thickness
Data Source
AI summary
A method locates and maintains a core in fixed space relationship within the interior of a shell mold. The method provides at least one pin extending into the core with at least one axial end of the pin protruding from the core. A wax pattern having an outer surface is formed by encasing the core and at least one protruding axial end of the pin in wax such that at least one protruding axial end of the pin terminates at the outer surface of the wax pattern. A shell mold is formed around the wax pattern such that, upon removal of the wax pattern, and in a subsequent casting process for production of hollow metal components, at least one protruding axial end of the pin abuts the shell mold, thus fixing the pin and maintaining a position of the core relative to the mold. The protruding axial end of the pin has an enlarged head.