Split Stern Tube Seal with Tungsten Carbide and Polyamide-Imide
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Solution Overview
Problem
Existing stern tube seal systems fail due to the brittle nature of silicon carbide materials and lack a backup seal subsystem, making them difficult to install and maintain, with single inflatable seals requiring costly and time-consuming underwater procedures for maintenance.
Innovation Solution
A split-design stem tube seal system featuring a metal stator ring with a polyamide-imide sealing face and a tungsten carbide-coated rotor ring, along with a fluid-activated backup seal and dual inflatable seals for emergency protection, utilizing a spring assembly to maintain constant face pressure and accommodate shaft deflections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If silicon carbide materials are used for stator and rotor sealing faces, then sealing performance is improved, but reliability deteriorates due to brittle nature
Solution Approach 1:
The patent applies composite materials by combining a metal substrate (providing toughness and strength) with a ceramic coating layer (providing hardness and wear resistance). Specifically, the rotor ring uses a metal substrate with a ceramic coating on the sealing face, while the stator ring uses a metal substrate with a polymer coating. This composite structure resolves the contradiction by providing both the reliability of strong, non-brittle materials and the sealing performance of hard, wear-resistant surfaces.
2Reliability
If a single seal system is used, then device complexity is reduced, but reliability deteriorates due to lack of backup seal
Solution Approach 1:
The patent implements beforehand cushioning by incorporating a backup seal system that activates when the primary seal fails. The backup seal includes a resilient lip seal and an inflatable seal positioned outboard of the primary face seal. This preventive measure ensures continuous protection against water ingress even after primary seal failure, resolving the contradiction between reliability and complexity by adding redundancy that activates only when needed.
3Ease of operation
If a non-split seal design is used, then structural integrity is improved, but ease of operation deteriorates due to difficult installation and maintenance
Solution Approach 1:
The patent applies segmentation by dividing the seal system into separable components: a stator ring that remains stationary in the stern tube and a rotor ring that rotates with the shaft. The rotor ring is further divided into a clamp ring portion and a sealing portion. This segmented design allows the rotor ring to be installed and removed independently while the stator ring remains in place, resolving the contradiction between ease of operation and structural integrity by enabling modular maintenance without compromising the overall seal system integrity.
4Duration of action of moving object
If uniform sealing face width is used, then manufacturing simplicity is improved, but durability deteriorates due to uneven wear distribution
Solution Approach 1:
The patent applies asymmetry by designing the stator ring sealing face with a tapered width rather than uniform width. The sealing face is wider at the forward end and narrower at the rearward end. This asymmetric geometry ensures more uniform wear distribution across the sealing face by redistributing contact pressure, resolving the contradiction between durability and manufacturing simplicity. While the tapered geometry requires slightly more complex manufacturing, it significantly extends seal lifespan by preventing localized wear concentration.
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 system provides a durable, low-friction, long-lasting seal with reduced maintenance costs, meeting leak rate requirements and enabling continued operation with emergency backup seals, while the split design facilitates easier installation and maintenance.
Implementation Method 1
a foam body including a gel material configured to expand in the presence of fluid and disposed to urge the lip seal into engagement with the rotor to seal the rotor in the presence of fluid
Implementation Method 2
a spring assembly about the shaft biasing the confronting sealing faces into engagement with each other
Implementation Method 3
The rotor ring wider sealing face may include a second material. For example, the wide sealing face may include a tungsten carbide coating on the metal rotor ring
Data Source
AI summary
A seal system includes a face seal rotor ring including a wide sealing face preferably made of tungsten carbide. The stator ring includes a narrower sealing face confronting the rotor ring wide sealing face. The stator ring sealing face is preferably made of polyamide-imide and tapers to narrower widths rearwardly.