Torsional Rheometer Cavity Pressure Stabilization
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Solution Overview
Problem
Existing torsional rheometers experience inaccurate and non-repeatable test results due to pressure loss in the die cavity caused by polymer sample shrinkage during temperature changes, leading to slippage and a shift in the signal phase.
Innovation Solution
Incorporation of compliant members, such as Belleville washers or coiled compression springs, in series with load-bearing components to deflect and maintain cavity pressure by allowing the die cavity to close more tightly as the sample shrinks, combined with a feedback loop to adjust air pressure based on pressure transducer readings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a fixed rigid structure is used for the die cavity, then the structure is simple and stable, but the cavity pressure varies due to sample shrinkage during temperature changes
Solution Approach 1:
The patent transforms the rigid fixed structure into a dynamic system by introducing compliant members (springs or Belleville washers) that allow the die cavity to dynamically adjust its volume in response to sample shrinkage. This enables the system to maintain stable cavity pressure through automatic mechanical compensation rather than requiring complex active control systems.
Solution Approach 2:
The patent changes the physical state of the die cavity structure from rigid to compliant by incorporating elastic elements. These compliant members change their mechanical properties (deflection, compression) in response to pressure changes, allowing the cavity volume to automatically adjust and maintain uniform pressure despite temperature-induced sample shrinkage.
2Reliability
If the die cavity pressure is allowed to drop due to sample shrinkage, then the structure remains simple, but the sample slips on the die face and test results become inaccurate
Solution Approach 1:
The compliant members create a self-regulating system where the die cavity automatically compensates for sample shrinkage without external intervention. As the sample shrinks and pressure drops, the compliant members deflect, causing the die cavity to close more tightly and automatically restore pressure, ensuring continuous reliable contact between sample and die face.
Solution Approach 2:
The system incorporates inherent mechanical feedback through the compliant members that sense pressure changes and automatically adjust cavity volume in response. This passive feedback mechanism ensures that any pressure drop due to shrinkage is immediately compensated, maintaining the friction necessary for accurate test results.
3Stress or pressure
If the die cavity closes tightly to maintain pressure, then pressure stability is improved, but the structure becomes more complex requiring compliant members
Solution Approach 1:
The patent introduces flexible compliant members (springs or Belleville washers) into the load-bearing structure of the die cavity. These flexible elements allow the cavity to dynamically adjust its tightness, closing more tightly when pressure drops to maintain uniform pressure while keeping the overall structure relatively simple.
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
Maintains consistent cavity pressure despite sample shrinkage, ensuring accurate and repeatable test results by preventing slippage and maintaining strain on the material.
Implementation Method 1
a compliant member disposed in series with a load-bearing component in which the compliant member is configured to deflect
Implementation Method 2
combined with a feedback loop to adjust air pressure based on pressure transducer readings
Data Source
Figure 1
Figure 2~2A
Figure 3
AI summary
A method and apparatus is disclosed for compensating for a reduction of die cavity pressure in a torsional rheometer caused by shrinkage of the test sample. In one embodiment, a compliant member is placed in series with load-bearing components of the rheometer. This compliant member deflects when pressure in the die cavity is reduced resulting in the die cavity becoming smaller to increase the pressure within the die cavity.