Rubber seal prevents leaks longer than expected

Even with more gaps than contact points, the elastic material keeps tight

Simulation of the contact points of seal and fitting, through the gaps between the two surfaces, liquid can flow out. © M. Müser / Saarland University
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When a rubber seal is leaking, can be better assessed in the future. Because a new simulation of German researchers shows that even if only 42 percent of their surface is applied to the connection piece, elastic seals still hold up completely. Contrary to previous assumptions, it therefore remains tight even with more gaps than contact points. The reason is that the contact points connect in such a way that they cut off possible leaks, the scientists around Martin Müser from the Research Center Jülich and the University of the Saarland in the journal "Physical Review Letters".

They compare the principle with that of a Swiss cheese: cheese loaf can also contain more holes than cheese. But it contains mostly individual, separate holes and no continuous, interconnected passages. Therefore, a liquid can not flow from one side of the cheese to the other. In a similar way, the elastic seal ensures that there are no gaps and that liquid can not get through.

As the researchers report, their results could help to better assess the permeability of older seals in the future. Because these become less elastic over time and then start to lick. When this point is reached, can now determine better, say the researchers. They are already working together with a medical technology company to be able to better determine the leak-tightness of syringes in the future. In these, a rubber ring ensures that the liquid drug does not run backwards out of the syringe, but is pressed into the hollow needle.

Tiny gaps open the way for the fluid

The most common form of seal is a rubber ring and two fixed connectors. The ring retains fluids because it fits snugly against the two connectors. But because all surfaces on a microscopic scale are uneven and rough, sealing ring and fitting are never completely seamless. If the tiny gaps form a continuous path, liquid can penetrate and escape to the outside. If and when this happens, researchers try to capture with simulations.

As the authors of the study report, the models have assumed that a seal with at least half of their contact surface must rest firmly on the pipe or other fitting to be still tight. However, these calculations did not take into account how the elastic sealing material behaves microscopically, say the researchers. They have now included this elasticity in their simulations for the first time. display

In their model, M ser and his colleagues assumed that the surface of the fixed connection piece contained bumps of different sizes but of similar shape. When the rubber seal and this rough surface are pressed against each other, the larger protrusions deform the elastic surface of the seal and thereby also influence how well the smaller protrusions and depressions are covered. To what extent this happens and where gaps and gaps then open up, the researchers simulated their simulation. (Doi: 10.1103 / PhysRevLett.108.244301)

(Physical Review Letters, 19.06.2012 - NPO)