PTFE Shaft Seal Coining for Static and Dynamic Sealing
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Solution Overview
Problem
Existing PTFE shaft seals face challenges in achieving a balance between dynamic and static sealing performance, with shaped features for dynamic sealing often compromising static sealing and vice versa, leading to fluid leakage under static conditions.
Innovation Solution
A PTFE shaft seal design featuring coined fluid pumping impressions on one side and a coined static band on the opposite side, with the static band being thinner and groove-free to enhance both dynamic and static sealing capabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the wafer material is removed by cutting to create grooves, then dynamic pumping capability is improved, but manufacturing complexity and material loss increase
Solution Approach 1:
The traditional cutting process is replaced with a coining process that uses compressive mechanical force to permanently deform the PTFE material into the desired groove shapes. This substitution eliminates material removal, reduces manufacturing steps, and leverages the viscoelastic properties of PTFE to achieve the same functional result through deformation rather than subtraction
Solution Approach 2:
The manufacturing approach changes from removing material (cutting) to deforming material (coining). By changing the fundamental manufacturing parameter from material removal rate to applied compressive stress, the process becomes more efficient and better suited to PTFE's material properties, reducing both complexity and waste
2Productivity
If coining is used to create permanent deformations for groove features, then manufacturing efficiency is improved, but precise control of groove geometry becomes more difficult
Solution Approach 1:
The coining process parameters (compressive force magnitude, application rate, and duration) are optimized to match PTFE's viscoelastic response characteristics. By controlling these parameters, the process achieves consistent groove geometries through material deformation rather than cutting, maintaining precision while improving manufacturing efficiency
Solution Approach 2:
The PTFE wafer's inherent flexibility and viscoelasticity are exploited during coining, allowing the material to deform smoothly into the desired groove shapes under compressive load. This flexibility enables the coining process to achieve precise geometries through controlled deformation rather than rigid cutting operations
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 ensures effective fluid retention under static conditions while allowing dynamic fluid return, improving sealing performance in both modes without compromising the other.
Implementation Method 1
Coining is also a known process in which the portion of the wafer to be coined is subjected to heavy and localized compressive loads which causes permanent deformation of the affected regions
Implementation Method 2
The running surface of the PTFE wafer is sometimes shaped by cutting or coining to impart a groove pattern that operates in a dynamic mode to pump fluid from inner running surface back toward the housing
Implementation Method 3
the coined static band provides improved static sealing about a shaft extending through a shaft opening in a case
Data Source
AI summary
A method of manufacturing a PTFE rotary shaft seal assembly is provided. The assembly includes an annular seal case mountable within a bore of a housing and a wafer fabricated of PTFE. An outer region of the wafer is captured by the seal case and in inner region extends to a central opening of the wafer. The method includes coining the wafer to form coined fluid pumping impressions on a first side of the wafer and coined flexing impressions on an opposite second side of the wafer. The method also includes forming a coined static band portion encircling the central opening and being free of fluid pumping impressions.