ISSUE 011 Autumn 2021 Candela C-7 hydrofoil speedboat dossier l In conversation: Robert Hoevers l Battery recycling focus l Vehicle dynamics insight l ZeroAvia hydrogen-electric aircraft digest l Motor materials

thermoplastic elastomer alternatives because of this application’s high requirements for tolerance compensation. For seals that come into contact with high-voltage cables, the materials of choice are silicone rubbers, owing to their high electrical breakthrough strength. EV manufacturers are adopting technologies that are new or come from other industries. Examples include immersion cooling systems that use dielectric coolants that are still under development for automotive applications, and heat-shielding practices and materials transferred from aerospace. In general, EVs are developing in a fast and agile manner, and materials development has to keep up. While the core function of a sealant is to keep vital fluids in and contaminants out – and its resistance to assaults from heat, pressure, vibration and aggressive chemicals is essential to that – they also have other characteristics that can make them multifunctional. In EV batteries, for example, many of the sealants and adhesives contribute in more than one way to their overall performance. Thermal and electrical conductivity/insulation properties can be very important, as can the flexibility to allow for differences in the CTE among the materials that make up the battery system. Noise reduction and vibration damping properties can also be very important. If the inherent properties of the material don’t meet the full multifunction requirements of a particular part, one solution can be to bond or mould the sealant to another material. For example, a soft rubber lip can be moulded into the rim of a stiff plastic connector or sensor housing to produce a component with two, three or four functions. In coolant systems, for example, a temperature sensor receptacle can be moulded into a short connecting piece of pipework that acts as a carrier, along with a damping element and a sealing bead. Such components can be made of materials that stand up to almost all media, can compensate for dynamic misalignment in the application and can accept low-friction coatings for reducing the force required for assembly. Weight reduction This kind of approach can also reduce the number of parts and the weight of the vehicle. However, the large weight savings associated with the use of adhesives and sealants results from the flexibility it allows manufacturers in using advanced materials with high strength- and stiffness-to-weight ratios, while forming bonds that are more resistant to fatigue, contaminants and corrosion than conventional fasteners. As well as established materials such as aluminium alloys, plastics and composites, these include exotics such as materials incorporating foams or micro-balloons. New lightweight materials including plastics, composites and a variety of metals are also finding their way into battery structures. This mix of dissimilar materials in close contact can promote corrosion, which adhesives and sealants can help prevent by creating an insulating barrier between them. Some applications on lightweight designs can be a severe test for sealing technologies, owing to a combination of the small cross-sections of the flanges to be joined and micro- movements. Anticipated requirements for foam gasketing to enable further weight reduction also promise to be challenging. While weight reduction is high on the agenda for EVs, the use of regenerative braking makes additional weight less critical than it is for pure IC-engined vehicles, because the kinetic energy can be re-used. In this respect, the seals themselves contribute very little to the overall weight of the car, so weight reductions in the seals themselves probably have more marketing than technical value. The exception here are thermal interface materials in batteries, which are used in large amounts – sometimes 10 kg per car – and are expensive. In energy-saving terms, however, it is more important to reduce friction (in dynamic seals used in rotating components) than it is to reduce weight in the seals themselves. Simulating seals As in many industries, simulation is of growing importance in the design and manufacture of sealing components such as O-rings and gaskets. In design, simulation is used to identify the temperature and pressure ranges in which the seal would be vulnerable to failure in a particular application. For example, with too little pressure between a gasket and the counter- surface against which it must seal, Conductive seals earth static charges that build up in electrical machines, preventing damage to bearings by providing an alternative current path (Courtesy of Freudenberg Sealing Technologies) 68 Summer 2021 | E-Mobility Engineering Focus | Sealing