Rotor Disc Balancing with Sacrificial Protrusions

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Solution Overview

Problem

Existing rotor disc balancing techniques for turbomachines, particularly those using high strength alloys, face challenges in minimizing internal stresses and preventing crack propagation when adding or removing material, such as through machining holes for balancing weights.

Innovation Solution

The implementation of a gas turbine rotor disc design featuring circumferentially disposed sacrificial protrusions delimited by stress-relieving slots, allowing for selective material removal from the free end of these protrusions to balance the rotor disc, thereby reducing internal stresses and mitigating crack propagation risks.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If material is added or removed from rotor disc for balancing, then weight distribution is adjusted, but internal stresses increase and crack propagation risk increases

Engineering Contradiction:

Improvebalancing precisionVSAvoidstructural integrity

Core Design Contradiction:

Manufacturing precisionVSStrength

Solution Approach 1:

The rotor disc is segmented into multiple balancing regions with discrete sacrificial protrusions that can be independently removed. This segmentation allows precise control over material removal locations and amounts, enabling accurate balancing while distributing stress concentrations across multiple controlled locations rather than creating large stress concentrations from single modification sites.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different regions of the rotor disc are given different properties - sacrificial protrusions are provided in specific locations where material removal is needed for balancing, while stress-relieving slots are strategically positioned in areas prone to stress concentration. This local differentiation allows balancing operations to be performed with minimal impact on overall structural integrity.

Inventive Principle:

Principle #3Local quality

2Manufacturing precision

If balancing weights are added to rotor disc, then weight distribution is adjusted, but stress concentrations increase around attachment holes

Engineering Contradiction:

Improvebalancing precisionVSAvoidstress concentration

Core Design Contradiction:

Manufacturing precisionVSObject-affected harmful factors

Solution Approach 1:

Instead of adding material (balancing weights) to achieve proper weight distribution, the invention uses the inverse approach by selectively removing material (sacrificial protrusions). This inversion eliminates the need for attachment holes and associated stress concentrations while still achieving the desired balancing effect.

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The harmful element (excess material causing imbalance) is extracted through selective removal of sacrificial protrusions. This extraction approach avoids the harmful effects of adding material, such as stress concentrations around attachment holes, while achieving the same balancing objective.

Inventive Principle:

Principle #2Taking out (Extraction)

3Manufacturing precision

If material is removed from rotor disc for balancing, then weight distribution is adjusted, but damage tolerance decreases

Engineering Contradiction:

Improvebalancing precisionVSAvoiddamage tolerance

Core Design Contradiction:

Manufacturing precisionVSReliability

Solution Approach 1:

Sacrificial protrusions are pre-formed during manufacturing before the rotor disc enters service. This preliminary action ensures that material removal locations are precisely controlled and structurally optimized, maintaining damage tolerance while enabling future balancing operations. The protrusions are designed with specific geometries that minimize stress concentrations during both manufacturing and operation.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The sacrificial protrusions act as intermediaries - they are temporary features added during manufacturing that facilitate future balancing operations. These protrusions mediate between the conflicting requirements of maintaining structural integrity and enabling precise balancing, as they can be cleanly removed without compromising the underlying rotor disc structure.

Inventive Principle:

Principle #24Intermediary (Mediator)

Data Source

PatentUS9127556B2Rotor disc and method of balancing

Publication Date: 2015.09.08 PRATT & WHITNEY CANADA CORP

AI summary

A rotor disc, such as one made of a damage intolerant material or other material sensitive to stress concentrations, has at least one balancing assembly which includes a plurality of circumferentially spaced-apart sacrificial protrusions projecting between adjacent stress-relieving slots. Selective material removal is permitted from the rotor disc, while managing stress concentrations in the rotor disc created by such material removal, such that the rotor disc may be balanced without detrimentally affecting its service life.