Automotive seals: Proliferation and electrification

Development work at two leading companies show how seals suppliers are adapting both to established and emerging automotive industry trends. Patrick Raleigh reports in the Jan/Feb edition of European Rubber Journal magazine

London -  While embracing opportunities presented by electric vehicles (EVs), makers of automotive sealing products must continue to adapt to more established market shifts around parts-proliferation and materials selection.

The latter trends are perhaps most obvious in body sealing parts, which, notes Wolfgang Engel of Hutchinson Body Sealing Systems, have become highly specific to individual car models.

As a consequence, there are few common parts for different vehicles and hardly any carry-over parts from previous car models, said Engel, who is based in Montargis, France.

In a presentation at the DKT18 conference, Engel said that the number of car models in Europe had increased by 74% over the last 20 years, while average product lifecycle had dropped from 9.7 years to 5.6 years.

As well as requiring more and different original and spare parts to be produced and more product design work, the trend has also meant more product launches with less time to recover ramp-up costs.

To cope with such demands, elastomer sealing manufacturers need to standardise design software and process simulation software across all plants, according to Engel.

Tool designs, he added, should also be standardised to reduce development cost and time and equipment geared to produce a wide range parts in both high and low quantities.

Hutchinson’s approach is, therefore, to have a standard global approach to its extrusion processes, in which up to six different materials can be incorporated in a single profile.

For instance, said Engel, software is standardised for die design and flow simulation in every extrusion plant and each extrusion line employs identical rubber-shaping and vulcanisation modules.

Rubber versus TPEs

Another issue concerns materials selection, due particularly to the increasing opportunities to use thermoplastic elastomers (TPEs) in automotive sealing applications.

As Engel explained, only 20 years ago EPDM was the polymer of choice for all body sealing parts, which were basically designed to prevent ingress of water, dust and noise into the vehicle interior.

However, TPE-based alternatives have made in-roads into the market. This, said Engel, is partly due to their better ageing properties, which mean surfaces are less affected by UV, cleaning agents and other substances.

Environmental regulations, he noted, are another factor: the EPDM rubber vulcanisation process generates fumes, CO2 and VOC emissions – as does demand for odour-free parts.

“Rubber replacement by TPEs is ongoing and will continue into the future,” said Engel. “Body sealing system suppliers must, therefore, develop competence in TPE design and processing.”

“In-house TPE recipe development and production will be fundamental to staying competitive,” the Hutchinson expert emphasised.

Battery pack

When it comes to vehicle electrification, Freudenberg Sealing Technologies (FST) has been to the fore in recognising the need to adapt to e-mobility trends in the automotive industry.

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.

Mounting pressure

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.”