Foundry Model for Turbine Blade Casting
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Solution Overview
Problem
The complex geometry of turbomachine blades in investment casting often leads to the formation of parasitic grains at intersections, particularly at the trailing edge and expansion bar, which can weaken the part and complicate directed solidification.
Innovation Solution
Incorporating a thin veil with a free edge between the platform and expansion bar, and a progressive transition to avoid sharp angles, along with a selector channel for controlled solidification, to facilitate a more gradual transition and reduce grain formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a refractory core is used to form cooling slots at the trailing edge, then cooling efficiency is improved, but the core becomes fragile and positioning control becomes difficult
Solution Approach 1:
The patent applies local quality by varying the thickness of the refractory core along its length. The core has reduced thickness at the trailing edge to form effective cooling slots, while maintaining greater thickness at other locations to ensure structural robustness and ease of positioning during casting and cooling.
2Temperature
If the core thickness is reduced at the trailing edge to improve cooling, then cooling efficiency is improved, but the core becomes more fragile
Solution Approach 1:
The core is designed with non-uniform thickness, being thinner at the trailing edge for effective cooling slot formation and thicker at other portions to maintain structural integrity and positioning stability during the casting process.
3Shape
If complex mold cavity geometry is created at intersections, then the blade shape is achieved, but the risk of grain generation increases significantly
Solution Approach 1:
The patent applies curvature by replacing sharp angles at critical intersections (such as where the expansion bar meets the platform) with rounded transitions. This eliminates abrupt geometric changes that would otherwise act as nucleation sites for parasitic grain formation during solidification, while still achieving the required blade shape.
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 minimizes the formation of parasitic grains, ensuring better thermomechanical properties and allowing for easier machining of the expansion bar, while maintaining directed solidification for improved part quality.
Implementation Method 1
to ensure that its thermal expansion is controlled. To achieve this, the model can include a guide bar adjacent to the trailing edge, with a varnished surface of the refractory core flush on each side of the model between the trailing edge and the expansion bar. The varnish on these surfaces, which can be removed from the shell mold along with the model material, ensures a small gap (on the order of a few hundredths of a millimeter) between the refractory core and the shell mold, so as to guide the core's expansion at this point perpendicular to its thickness.
Implementation Method 2
These are formed by dipping the pattern or cluster of patterns in slip, followed by sprinkling the slip-coated pattern or cluster with refractory sand to form a shell around it. This shell is then fired to solidify the slip and consolidate the entire structure.
Data Source
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AI summary
The invention pertains to the field of foundry, and more particularly relates to a model (12) for lost-model foundry, in the shape of a turbine engine blade having a base (15) and a body (14) separated by a platform (20) substantially perpendicular to a main axis of the blade. The blade body (14) has a lower surface (17), an upper surface (16), a leading edge (18), and a trailing edge (19). The model (12) further includes a heat expansion rod (21) adjacent to the trailing edge (19), and a refractory core (23) imbedded in the model (12) but having, both on the lower surface (17) side and on the upper surface (16) side, a lacquered surface (31) flush between the trailing edge (19) and the heat expansion rod (21). A web (24) extends between the platform (20) and said heat expansion rod (21), and has a free edge (25) therebetween. The invention also relates to a method for making a shell mold from said model (12), and to a foundry method using said shell mold.