The static seal for systems and their actual age
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An static seal for large plants in industry or Energy Technology often have to last a good twenty years. Previously used calculation tools meant that the components were often larger than was necessary. Freudenberg Sealing Technologies has now developed a method that takes material changes into account at the molecular level. This increases reliability with less material.
Static seals must have a very long service life in plant engineering. Should an anchorage of the tower be sealed Wind Turbine If this is to be protected against the ingress of salt water on the high seas, the seal must function properly for more than twenty years. The service life of a seal is limited by setting or stretching, i.e. physical relaxation. On the other hand, the material loses its elasticity over time due to chemical changes.
Under the influence of atmospheric oxygen or ozone, the Aging of seals two effects. The polymer chains and polymer networks break up under mechanical stress and oxidation processes create additional oxygen bridges in the network. Both effects influence sealing-related properties such as contact pressures of the sealing surfaces, rigidity or the ability to regain the original contour after deformation (deformation rest).
Storage tests with the Arrhenius method
As a rule, engineers determine whether a material meets the requirements for a specific application using so-called storage tests. A test specimen is exposed to temperatures of significantly more than 1000 ° C over a longer period of time, usually 100 h.
To predict temperature-dependent aging, engineers have so far extrapolated the measured values using a method that is based on Svante August Arrhenius, a Swedish chemist and Nobel Prize winner. The rule of thumb for these is: An increase in temperature by 10 ° C leads to a doubling of the reaction speed. This enables accelerated aging tests to be carried out at elevated temperatures.
This method works reliably if the correct test parameters are assumed. If this is not the case, the lifetime prognosis can be very wrong. The prognosis can only be checked through measurements. Not a satisfactory procedure - especially when talking about very long test times. It was therefore imperative to improve the methodology.
Improve the lifespan model
The FST experts pursued two main starting points: First, they significantly improved the service life model by using the Oxygen attack related the elastomer to the structural mechanical behavior of the material and set up a chemical oxidation equation. The model was implemented numerically efficiently and implemented in a commercial finite element program (FEM) in order to be able to calculate any geometry. The FEM can now calculate local oxidation processes and their effect on the mechanical material behavior.
Central Freudenberg research on board
At the same time, the engineers wanted to further develop the measurement methods with which the parameters for the material model are determined. This is intended, for example, to reduce the amount of static seals used up during the aging process Amount of oxygen let determine. The extent of the chemical attack can be estimated based on the amount of oxygen. "Thanks to the improvement of the measurement methods, the material model and the applicability to three-dimensional components, a precise procedure for the service life forecast results," explains Dr. Boris Traber, responsible for global advance material development at FST.
The process, which was developed together with the central research department Freudenberg Technology Innovation, was first verified on material samples with different diameters. It is now used in initial applications in the construction of offshore wind turbines.
Traber only sees this as Beginning of a new simulation era for sealing technology: "In future, we will be able to give our customers in plant engineering a reliable best-before date, even over very long periods of time." A library with models for various component geometries and Materials is currently under construction. At the same time, the simulation is expanded so that application-specific cycles with changing temperatures and mechanical loads can also be calculated.
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