What Are The Swelling Performances Of Cylinder Seals?
Jul 21, 2021
The swelling properties of cylinder seals are mainly manifested in the following two types:
(1) Infinite swelling: The linear polymer is dissolved in a benign solvent and can absorb the solvent without restriction until it dissolves into a homogeneous solution. So dissolution can also be seen as the result of unlimited swelling of the polymer. For example, NR rubber swells in gasoline.
(2) For cross-linked polymers and linear polymers in poor solvents, swelling can only be carried out to a certain extent. No matter how long the contact with the solvent is, the amount of inhaled solvent will no longer increase and reach equilibrium, and the system will always Maintain a two-phase state. For example, the nitrile rubber seal material (a kind of synthetic rubber) can swell in the organic solution of liquefied dimethyl ether.
The swelling mechanism of nitrile rubber in the organic solution of liquefied dimethyl ether can be roughly understood as: when the valve of the cylinder is opened, the liquefied dimethyl ether in the bottle contacts the nitrile rubber seal in the valve, and the nitrile rubber will swell; When the cylinder valve is closed, the inside of the valve is gradually "dried", the swelling property of nitrile butadiene rubber gradually declines, and the volume of the rubber shrinks. As the number of valve openings increases and the content of dimethyl ether blended in the liquefied petroleum gas increases After many times of stress cycles of "swelling and shrinking", the rubber stress decreases and the aging speeds up. In the end, the rubber elasticity fails and the performance of the seal decreases, which causes the valve to leak.
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