The volume expansion rate of fluorosilicate rubber compound in different materials is affected by multiple factors such as medium type, temperature conditions, formula design and process parameters. Its variation law can be analyzed through the following key scenarios：


1. The volume expansion rate in the fuel medium
In the fuel environment, the volume expansion rate of fluorosilicate rubber compound is usually controlled at a low level. 


This difference stems from formula optimization: by adding inorganic fillers such as silica, the volume expansion rate can be reduced by about 20%, but part of the elasticity will be sacrificed; the use of segmented vulcanization process (first low temperature pre-vulcanization and then high temperature secondary vulcanization) can form a more stable three-dimensional network structure, reducing the volume change during temperature fluctuations.


2. Volume expansion rate in solvents and chemical media
The tolerance of fluorosilicate rubber to non-polar solvents (such as aromatics) is better than that of ordinary silicone rubber.


Experimental data show that in a mixed system of methanol and gasoline (85vol% gasoline + 15vol% methanol), the volume swelling of fluorine silicone rubber is about 10%; however, when the fluorine content is reduced to 66%, the volume swelling at low temperatures will increase significantly.This shows that the strong electronegativeness of fluorine atoms effectively inhibits the penetration of solvent molecules by enhancing the interaction between molecular chains.


In addition, fluorosilicate rubber compound can still maintain a low volume expansion rate in polar solvents such as ketones, and its range of good solvents is narrow, which further highlights its solvent resistance characteristics.


3. Volume expansion rate under extreme temperature conditions
The coefficient of thermal expansion of fluorosilicate rubber compounds is usually on the order of 10-1/℃, and the specific value is affected by the formula.


For example, an aviation hydraulic seal adopts a customized formula of fluorine silicone, and the coefficient of thermal expansion is controlled at 3.2×10-1/℃±5% in the working range of -55℃ to 175℃.However, in an ultra-low temperature environment (below -40℃), the increase in material brittleness will lead to nonlinear mutations in the expansion coefficient, and special attention needs to be paid to the design margin.


After long-term high-temperature aging (such as continuous operation at 150℃ for 1000 hours), the coefficient of thermal expansion does not exceed 15% of the initial value, showing excellent thermal stability.


4. Volume expansion rate control in practical applications
In the design of seals, the matching of volume expansion rate and sealing stress needs to be considered comprehensively.
For example, after 50 start-stop cycles of flange gaskets in a chemical plant, the bolt preload decreased by about 18%. Through the formulation of a regular re-tightening system (maintenance when the preload attenuates to 70% of the design value), leakage accidents have been successfully avoided.


In addition, there may be a 5%-8% expansion difference between the flow direction and the vertical direction of the molded fluorosilicate rubber products, and the deformation margin needs to be reserved in the design.


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