Ceramic Core Rod Coating for Firing Crack Prevention
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Solution Overview
Problem
The manufacturing of ceramic cores for aircraft engine blades faces challenges during the firing process due to the expansion of rods, which can cause cracking and render the cores unusable, as existing solutions require manual removal of extra thicknesses that may lead to re-cracking.
Innovation Solution
A method involving coating the rods with a material having a flash point below a temperature threshold, such as varnish, to prevent cracking by creating space around the rods during firing, allowing the material to ignite and expand before the ceramic does, thus avoiding mechanical stress on the core.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If rods are used to secure the upper and lower portions of the ceramic core, then the structural integrity and assembly of the core is improved, but cracking occurs during firing due to thermal expansion of the rods
Solution Approach 1:
A coating layer is applied to the surface of the rods as an intermediary substance. This coating has a higher thermal expansion coefficient than the ceramic and decomposes at a specific temperature during firing, creating expansion space that accommodates the rod's thermal expansion and prevents cracking of the ceramic core
Solution Approach 2:
The physical and chemical parameters of the rod surface are changed by applying a coating layer with different thermal properties. The coating's decomposition temperature and expansion characteristics are specifically selected to match the firing process requirements, transforming the rod's thermal behavior from harmful to beneficial
2Reliability
If extra thickness is added to the core to prevent cracking during firing, then the reliability during firing is improved, but manual removal of the extra thickness is required and cracks may reappear, reducing productivity
Solution Approach 1:
The coating layer is applied to the rods before the firing process begins. This preliminary action creates the necessary expansion space in advance, eliminating the need for post-firing corrective actions such as adding and removing extra thickness, thereby improving productivity
Solution Approach 2:
The harmful effect of thermal expansion is extracted and isolated to the coating layer, which is designed to decompose and be removed during firing. This separates the expansion accommodation function from the final core structure, eliminating the need for subsequent material removal 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 method effectively prevents cracking during the firing process, making the ceramic cores more reliable and reducing the risk of them becoming unusable, as the expansion of the rods is accommodated without applying additional thicknesses that might re-crack the core.
Implementation Method 1
The ignition temperature of the glaze, or an equivalent material coating the stems, allows for the creation of a space around the stem, which then expands at a temperature higher than that of the glaze's ignition
Implementation Method 2
During the heating process, the rods expand
Data Source
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AI summary
The method of manufacturing a ceramic core for a blade comprising a lower part forming a core body, an upper part forming a squealer tip recess and a set of rods for holding the upper part and the lower part together, comprises: · a step of coating the rods with a material that has a flash point below 1000°C; · a step of positioning the rods in a mould; · a step of moulding the upper and lower parts by injecting ceramic; · a step of firing the ceramic core.