Single Crystal Seed Tapered Core Gap Prevention

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Solution Overview

Problem

In the manufacturing of nickel-based superalloy disks for gas turbine engines, traditional single crystal casting techniques face issues with thermal expansion mismatch between the seed and ceramic mold, leading to gap formation and defects due to the lack of contact between the seed and internal core during heating, which affects the quality of the cast product.

Innovation Solution

The process involves using an axisymmetric single crystal ring seed with a tapered configuration that matches the internal core's taper, allowing the core to translate vertically and maintain contact, thereby eliminating the gap and ensuring continuous contact during thermal expansion, and using an axisymmetric investment casting mold assembly to cast a single crystal thick-walled tube.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Temperature

If the seed is inserted into the ceramic mold at room temperature and heated to casting temperatures, then the seed and mold reach operating temperature, but thermal expansion mismatch causes a gap to form between the seed and internal core

Engineering Contradiction:

Improvecasting temperatureVSAvoidgap between seed and core

Core Design Contradiction:

TemperatureVSManufacturing precision

Solution Approach 1:

The seed is pre-heated to casting temperature before being inserted into the ceramic mold. This preliminary heating action prevents thermal expansion mismatch and gap formation that would occur if the seed were inserted at room temperature and then heated, thereby maintaining manufacturing precision while achieving the required operating temperature

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

A refractory material is placed in the gap between the seed and the internal core to compensate for potential gap formation. This cushioning material prevents direct contact between the molten metal and the core, eliminating defects while allowing the seed and core to expand at different rates during heating

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

2Reliability

If the seed and ceramic mold are heated to casting temperatures, then the casting process can proceed, but the gap allows molten metal infiltration causing extraneous grains and defects

Engineering Contradiction:

Improvecast qualityVSAvoidextraneous grains and defects

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The seed is pre-heated to casting temperature before insertion into the mold, preventing gap formation that would allow harmful molten metal infiltration. This preliminary action ensures reliable casting quality by eliminating the source of extraneous grains and defects before the casting process begins

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

A refractory material is introduced as an intermediary substance between the seed and the internal core. This mediator prevents direct contact between molten metal and the core through potential gaps, thereby preventing extraneous grain formation and casting defects while allowing the thermal expansion process to proceed

Inventive Principle:

Principle #24Intermediary (Mediator)

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 prevents the formation of extraneous grains and defects, enhancing the creep resistance and thermal mechanical fatigue capability of the cast material by maintaining consistent contact between the seed and core during the casting process, resulting in improved temperature and mechanical performance.

Implementation Method 1

A thermal expansion mismatch between the seed and ceramic mold causes a gap to form between the seed and the internal core

Methodology Applied

Scientific EffectThermal expansion: Thermal Expansion

Implementation Method 2

The axisymmetric single crystal ring seed is inserted into the ceramic mold at room temperature. The assembly is heated up to casting temperatures.

Methodology Applied

Scientific EffectFriction: Friction

Data Source

PatentEP3549694B1Method and apparatus to prevent gap in cylindral seeds around an internal ceramic core

Publication Date: 2022.01.26 RTX CORP

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AI summary

A process for casting a single crystal axisymmetric thick walled tube comprising forming a axisymmetric single crystal ring seed (86) around a circular internal core (84), wherein the ring seed (86) has an inner diameter (94) and a taper (96) on the inner diameter (94), and the internal core (84) has an outer diameter (100) and a matching taper (96) on the outer diameter (94), the matching taper (96) matching the taper (96) of the inner diameter (94) of the ring seed (86), and the internal core (84) being free to translate in a vertical direction relative to the ring seed (86); and heating the ring seed (86) so as to expand the ring seed (86) relative to the internal core (84), and allowing the circular internal core (84) to translate relative to the ring seed (86) in a direction of the force of gravity, thereby maintaining contact between the circular internal core (84) and the ring seed (86).