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Plastic can do more than just insulate – it can conduct electric current as well. What could benefit from something like this? One example is the electric car of the future. With special plastics and coatings from Freudenberg Sealing Technologies, it will be able to shed a few pounds.
Seals are undercover agents. Their mission: to keep refrigerants, fuel, coolants and oil, which are found in nearly every automobile, from “crossing the border” into the environment. These well-trained specialists also perform well in adverse conditions. But their job description will be changing over the next few years. Electric cars certainly need reliable seals to keep coolant from escaping and to extend battery life, for example.
For large-scale production, we’ve developed various alternatives that are less expensive.
Volker Schroiff, Head of Technology Management at Freudenberg
But an electric field forms wherever electric current flows – as the “right-hand rule” memorably made clear in physics class. In an electric powertrain, however, the electricity seldom flows in one direction. (The exceptions are during certain charging processes.) The car’s power electronics send alternating current at high frequencies into the veins of the electric motor, which – depending on its design – runs at rotational speeds up to 30,000 rpm. Field strengths change at a corresponding rate, producing electromagnetic waves that move through the space at the speed of light. If they are not stopped, one major result will be disruptions in the many small computers on board, and maybe even in a car stopped at the same traffic light. The only reliable measure in the battle against electromagnetic waves is to confine electric components to a housing made of an electrically conductive material or whose electrically conductive surface reflects the waves.
Plastic Replaces Aluminum
In the current generation of electric cars, the housings for batteries, motors and power electronics are made of aluminum – almost without exception. First of all, it is a good conductor of electricity. Second, it is a lightweight metal with a low specific weight. In addition, it is easily processed with pressure-casting, making it a low-cost option. To the experts at Freudenberg Sealing Technologies, all this is good – but not good enough – since every pound of excess fat has an impact on the vehicle’s range. If you could replace the aluminum components with plastics, you could reduce its weight even more. But there is an obstacle: You need an electrically conductive plastic to do this. Science has only been aware of these miracle plastics since the 1980s. They are quite expensive and are almost exclusively used in the manufacture of electronics, such as displays.
One Goal, Multiple Paths
“Intrinsically conductive plastics – that is, plastics that are conductive by their very nature – have been used at our company in isolated instances,” comments Volker Schroiff, who is in charge of Technology Management at Freudenberg Sealing Technologies. “But for large-scale production, we’ve developed various alternatives that are less expensive.” The first alternative is a plastic housing with a conductive coating, that is applied like paint. The industrial implementation is far along; Schroiff is already working with his colleagues at the Special Sealing Products business unit on a production facility concept. The second alternative is to impart plastic particles of a conductive material to the nonwoven before the injection molding stage. The advantage of this approach: No additional steps are needed in the production process. This offers cost advantages, especially for relatively small components. And in the end, there is a third approach that is well-suited to large surfaces – such as the housing cover for a traction battery. After a nonwoven’s fibers have been given an electrically conductive coating, the material is inserted into a mold where a thermoset part is produced. “We’re working closely with the nonwovens experts at Freudenberg Performance Materials on this solution,” Schroiff adds.
As soon as output reaches at least 30,000 components a year, the special plastics from Freudenberg Sealing Technologies have a cost and weight advantage over aluminum.
There were a number of findings from the first pilot projects, which involved three large, direct suppliers of electric powertrains: The ideas derived from the physics of electromagnetism perform well in practice – that is, in real-life components. And as soon as output reaches at least 30,000 components a year, the special plastics from Freudenberg Sealing Technologies have a cost advantage over aluminum, not just a weight advantage. Meanwhile, Schroiff is already moving in a new direction. In the future, the conductive layer could also consist of a razor-thin elastomer, manufactured along with the housing in a single mold, using the two-component injection molding process. The elastomer serves as a protective shield against electromagnetic waves, even as it seals against liquid and gaseous media. The process, for which a patent was filed in the summer of 2019, combines the undercover agent’s old and new missions.
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