Carbon Face Seal Geometry to Prevent Axial Separation
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Solution Overview
Problem
Carbon face seals in gas turbine engines experience dynamic instability, leading to coupled radial and axial displacements that can result in premature failure due to excessive wear and stress, particularly in extreme situations where the axial gap opens, causing leaks and rapid wear beyond the capability of the spring element.
Innovation Solution
A dry face seal system with a seat section having a varying outer diameter surface and a chamfer surface, along with an axial undercut, is designed to limit relative radial freedom of movement, preventing axial separation between the seal and seat, and incorporating a bellows spring for axial biasing, which is captured between a spring carrier and a seal carrier, to maintain engagement and reduce dynamic excursions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the seal and seat are allowed to have relative radial movement during operation, then the seal can accommodate dynamic conditions, but coupled axial displacements occur leading to seal separation and premature failure
Solution Approach 1:
The seal system is divided into functional segments: a sealing assembly with seal and seat, a bellows spring for axial biasing, a spring carrier, and a seal carrier. This segmentation allows each component to perform its specific function while working together to prevent dynamic instability.
Solution Approach 2:
The bellows spring acts as an intermediary element between the sealing assembly and the carriers, providing axial biasing force to maintain engagement between the seal and seat while accommodating dynamic movements without causing separation.
2Stability of the object's composition
If the spring element is designed to handle extreme axial separation, then it can accommodate large dynamic excursions, but the spring element becomes overly complex and less effective
Solution Approach 1:
The bellows spring is pre-biased to provide continuous axial force that cushions against dynamic excursions before they can cause separation. This preemptive cushioning maintains engagement without requiring the spring to be overly complex or capable of handling extreme separations.
Solution Approach 2:
The bellows spring changes its compression parameter dynamically to maintain constant axial biasing force throughout operation, adapting to varying dynamic conditions while maintaining simple, effective design.
3Ease of manufacture
If the seal system uses a simple structure without additional constraint features, then it is easier to manufacture, but it cannot effectively limit radial excursions and prevent axial separation
Solution Approach 1:
The solution adds axial dimension control through the bellows spring and carrier assembly, which constrains radial excursions by converting them into axial compression of the spring, thereby preventing seal separation without complicating the basic seal structure.
Solution Approach 2:
The bellows spring and carrier assembly serve multiple functions: providing axial biasing force, limiting radial excursions, and preventing axial separation, all within a relatively simple structural addition that does not significantly complicate manufacturing.
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
The design effectively limits dynamic radial excursions, preventing axial separation and reducing wear, thereby enhancing the structural integrity and operational reliability of the seal system by constraining relative radial displacement and distributing contact forces effectively.
Implementation Method 1
a bellows spring axially biases the seal into engagement with the seat
Implementation Method 2
The sliding engagement causes frictional heating
Data Source
AI summary
An apparatus has a first member, a shaft rotatable relative to the first member about an axis, and a seal system. The seal system has: a seal carried by the first member and having a seal face; and a seat carried by the shaft and having a seat face in sliding sealing engagement with the seal face. The seal system is a dry face seal system. The seat further includes a section having: an outer diameter surface encircled by the seal; and a rim.