Engineers at FST have developed several sealing systems for EV batteries – an application that is becoming more critical as these units increase both in terms of physical size and energy-density.
Every battery housing has a cover, so the entire battery need not be discarded if fairly small defects appear. No road-spray can be allowed through the gap between the cover and the housing.
Ingress is, therefore, blocked by a perimeter seal that ranges from two-and-a-half to five metres in length, according to a statement from the German company.
Fire-safety is another vital consideration, FST pointed out: the seal must resist flames over a relatively long period, and help ensure that any fire that those occur does not spread.
Battery seals for EVs undergo flame-spread tests similar to those in use in the aviation industry, the company said. These are harmonised with the US, standard UL 94, in which materials are given a classification based on flame speed.
Helped by aviation experts, at the Tillsonburg facility in Canada FST said it achieved the highest ‘V0’ classification, for one of its compounds. In the testing, the flame completely died out in ten seconds.
The ability of a seal to resist a fire over the desired timeframe not only depends on the material chosen for the component – it is also related to whether the seal is properly mounted.
FST said it has, therefore, developed sealing solutions that completely preclude improper mounting, including by robots on high-volume production lines.
These include a ‘foldable seal’ design – fixed aluminium elements with a sealing profile on the outer edge to provide stability and integrated mounting points for the clips used to attach the seal at the housing cover.
The elements are connected to one another using the continuous sealing profile, which exhibits high flexibility and can compensate for small dimensional deviations in the housing.
As the foldable seal is a complete component and does not need to be assembled from separate elements, the reliability of the installation “rises dramatically”, according to the company.
FST has also developed its own endurance tests so it can evaluate housing seals for traction batteries and verify that their operation is problem-free.
The tests avoid the need to use real housings, as the size of these units makes them hard to handle. Instead, they use an hydraulic ram with a frequency of up to 50 hertz to act on a sealed test housing comprising two halves.
According to FST, the set-up simulates the aerodynamic torsion that occurs in actual driving, with slight overpressure continually maintained inside the housing to ensure detection of any leaks.
“The entire test setup is in a climate chamber so the impact of the temperature can be recorded, the company also pointed out.”
“The electric car will prevail,” said Paul Hailey, vice president of the FST gasket division. “But manufacturing large batteries in high volumes is a major challenge for our customers. With our sealing solutions, we are going to help them master this.”