Graphite Fiber Seal Assembly for Harsh Environments
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Solution Overview
Problem
Existing seals and sealing materials fail to effectively seal in harsh environments due to high friction requirements, which render them unusable in applications like nuclear power plants where high radiation and extreme temperatures degrade materials, and excessive compressive forces reduce output force or torque in actuators.
Innovation Solution
A seal made from substantially incompressible and inelastic materials, such as graphite or carbon fibers, is formed by wrapping strands to create a seal that can be compressed into contact without excessive force, using techniques like Bellville springs and form bodies to achieve sealing contact between moving parts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If graphite or carbon fiber seals are used in harsh environments, then sealing capability in extreme temperatures and radiation is improved, but friction and required compressive force increase excessively
Solution Approach 1:
The patent changes the fundamental material parameters from elastomeric or conventional compressed foil to incompressible and inelastic materials like graphite or carbon fiber. This parameter change allows the seal to maintain sealing capability without requiring excessive compressive forces, as the inelastic material deforms plastically to conform to sealing surfaces rather than elastically rebounding
Solution Approach 2:
The patent employs composite construction by braiding or weaving carbon fibers or graphite strands to create a structured seal assembly. This composite approach combines the incompressibility and inelasticity of carbon/graphite materials with a braided configuration that distributes compressive forces evenly, reducing the overall force required while maintaining sealing effectiveness in harsh environments
2Reliability
If coarse surface braided rings are used for dynamic sealing, then sealing capability is improved, but friction increases considerably
Solution Approach 1:
The patent applies local quality by creating a dual-texture seal structure where the outer surface maintains a relatively smooth finish for low-friction contact with the stem, while the inner braided structure provides the necessary compliance and sealing capability. This local differentiation allows the seal to achieve dynamic sealing without excessive friction
Solution Approach 2:
The patent changes the surface parameter of the braided ring from coarse to fine by using very fine carbon fibers or graphite strands in the braid construction. This parameter change reduces the surface roughness and corresponding friction while maintaining the inelastic deformation capability needed for effective sealing in dynamic applications
3Force
If fine braided packing is used to reduce compressive force, then required compressive force is reduced, but such materials are not currently available
Solution Approach 1:
The patent segments the seal assembly into multiple fine braided or woven layers of carbon fiber or graphite strands. By dividing the sealing function across multiple fine layers rather than relying on a single coarse element, the assembly achieves effective sealing with reduced compressive force requirements while using commercially available fine fiber materials
Solution Approach 2:
The patent creates a composite structure by braiding or weaving fine carbon fibers or graphite strands into a packed ring configuration. This composite construction transforms available fine fiber materials into a functional sealing assembly that reduces compressive force requirements while maintaining sealing effectiveness, thereby making fine-braid functionality achievable with current material capabilities
Data Source
AI summary
A sealing assembly, for example a piston ring, for use in harsh environments, e.g., high radiation levels. The piston ring has an annular sealing surface which together with a member forming a radially outer annular cylinder surface, e.g., a cylinder, forms a seal pocket. Received in the seal pocket is an annular seal comprised of a plurality of wraps of at least one strand of a substantially incompressible and inelastic material such as graphite fiber. The assembly further includes a compression ring and compression assembly which compresses the seal body between the support surface and the compression ring to displace the seal body into sealing engagement with the radially inner and outer sealing surfaces.