Reinforced Fluoroelastomeric Bladder for Dimensional Stability
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Solution Overview
Problem
Existing mandrels, such as those using reinforced silicon rubber bladders, face issues with dimensional stability and structural strength, leading to non-uniform pressure and shrinkage during composite part layup and curing, especially in long tubular parts with strict dimensional requirements.
Innovation Solution
A collapsible mandrel employing a reinforced fluoroelastomeric rubber bladder with a low coefficient of thermal expansion and fiberglass reinforcement, which maintains dimensional stability and structural rigidity, allowing for multiple use cycles with minimal thermal expansion and shrinkage, and can be easily extracted by collapsing under vacuum.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If reinforced silicon rubber bladder is used for mandrel, then the mandrel can be collapsed for extraction, but the bladder shrinks rapidly over time and provides non-uniform pressure
Solution Approach 1:
The patent changes the material parameter from silicon rubber to fluoroelastomeric rubber, which has superior dimensional stability and resistance to shrinkage. This material substitution maintains the collapsibility feature while eliminating the rapid shrinking problem that occurred with silicon rubber bladders during repeated use and autoclave cycles.
Solution Approach 2:
The patent employs a composite structure combining fluoroelastomeric rubber with fiberglass reinforcement. This composite material provides both the flexibility needed for collapsibility and extraction, and the structural integrity to maintain dimensional stability and provide uniform pressure during curing, resolving the contradiction between ease of operation and reliability.
2Ease of manufacture
If reinforced silicon rubber bladder is used, then the mandrel can be used for layup, but thermal growth and post-cure shrinkage prevent use in parts with strict dimensional requirements
Solution Approach 1:
The patent substitutes silicon rubber with fluoroelastomeric rubber, which has a lower coefficient of thermal expansion and superior resistance to post-cure shrinkage. This parameter change in material properties enables the mandrel to maintain precise dimensions during thermal cycling and curing, allowing its use in parts with strict dimensional requirements while still providing adequate layup support.
Solution Approach 2:
The fiberglass reinforcement embedded in the fluoroelastomeric rubber creates a composite structure that provides both the structural strength needed for layup support and the dimensional stability required for precision parts. The composite material resists thermal growth and post-cure shrinkage, ensuring manufacturing precision is maintained.
3Temperature
If nylon tubular bagging film is used for autoclave pressure, then the part can be cured, but the film lacks structural strength to support layup
Solution Approach 1:
The patent creates a composite material system combining fluoroelastomeric rubber with fiberglass reinforcement. This composite provides both the structural strength and rigidity needed to support the layup process and the thermal stability required for autoclave curing. The fiberglass provides tensile strength while the fluoroelastomeric rubber provides flexibility and thermal resistance, resolving the contradiction between curing capability and structural strength.
Solution Approach 2:
The patent changes from using nylon bagging film to using fluoroelastomeric rubber as the bladder material. This parameter change in material selection provides both adequate structural strength for layup support and the thermal properties necessary for autoclave curing, eliminating the need to separate the support function from the curing function.
4Shape
If standard rubber bladder is used, then the mandrel can be inflated for shaping, but gas permeability at elevated temperature causes porosity in the part
Solution Approach 1:
The patent changes the material parameter from standard rubber to fluoroelastomeric rubber, which has significantly lower gas permeability, especially at elevated temperatures. This material substitution maintains the inflatability and shaping capability of the mandrel while eliminating the harmful effect of gas permeation that causes porosity in the cured part.
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 mandrel provides improved dimensional control and part quality by reducing porosity and enabling complex profiles, while lowering tooling costs and recurring tooling costs through reduced shrinkage and improved structural support during layup and curing.
Implementation Method 1
The bladder includes inner and outer layers of fluoroelastomeric rubber having a reinforcement sandwiched therebetween... exhibits minimal shrinkage over repeated uses and which can be employed for use in multiple cure cycles... minimal thermal expansion and virtually no post-cure shrinkage... lower coefficient of thermal expansion (CTE) of the fluoroelastomeric rubber
Implementation Method 2
The mandrel is capable of collapsing under applied vacuum for ease of extraction from an enclosed part
Implementation Method 3
The lower gas permeability rate of fluoroelastomeric rubber at elevated temperature may also contribute to improved part quality by reducing the possibility of porosities in the part
Data Source
Figure 1~4
Figure 5~8
Figure 9~12
AI summary
A collapsible mandrel (30) comprises an inflatable bladder (35). The bladder (35) includes a reinforcement (46) sandwiched between inner and outer layers (42,44) of a fluoroelastomeric rubber.