Nanotechnology makes a material difference

  • 03-Dec-2009 04:22 EST
Bayer11-09Nano granules.jpg

Not a mountain range, but nanotubes produced by Bayer that are helping to take weight out of vehicle design and manufacture.

In the auto industry, saying is not necessarily meaning. It is easy for a spokesperson to say that a company is set on using advanced-technology materials to achieve weight savings in the pursuance of lower fuel consumption and emissions. But how advanced is advanced, and what does that really mean?

High-strength steel, aluminum alloys, and composites including carbon fiber are proving their effectiveness with regard to weight reduction. But where is the next step-change to help achieve the levels of vehicle efficiency in terms of fuel consumption and emissions that public, political, and legislative organizations are demanding?

Bayer MaterialScience believes the answer is the implementation of nanotechnology. “It is a way forward that is almost a new area for materials, offering very significant weight reduction without being prohibitively expensive,” said Patrick Thomas, Chairman of the Board of Management.

Already one of the world’s leading producers of carbon nanotubes, Bayer is confident that it is ideally positioned to help the auto industry meet ever more stringent environmental and energy legislation. It is soon to bring on stream a new plant at Leverkusen, Germany, that will facilitate larger industrial-scale production.

The addition of nanotubes can increase the strength and reduce the weight of existing materials, including metal, polymer plastic carbon fiber, and glass fiber.

The nanotubes produced by Bayer, called Baytubes, look similar to coffee granules. Each particle constitutes 400 trillion nanotubes. They are scrolled multiwall, rather than single-wall, and are manufactured from ethylene using a “very sophisticated” catalyst system, said Thomas.

“There are, rightly, health concerns about nanotechnology,” he said, “but we can control the physical form into a dust-free granule that does not break up, so there are no freely available inhalable small particles which might have health effects. No relevant adverse effects at realistic exposure level could be found.”

Nanotubes for engine components

Carbon nanotubes bring two salient assets to the auto industry: weight savings and increased safety. To achieve the former, Bayer has decided to focus on their incorporation into lightweight materials to make them even lighter without any loss of strength or stiffness. Initially, potential applications include engine components (notably connecting rods) and suspension parts, but a much wider automotive application is potentially likely, including spaceframes.

Nanotechnology would not be just for exotic cars, said Thomas, noting that it would be cost-effective for high-volume production within the next decade. He sees pure aluminum (not an alloy because of its propensity to suffer electrochemical corrosion) as an ideal metal for nanotube integration.

“A tensile test would show that the result would be the same properties as steel but would be about one-third lighter. And it is possible to use traditional metal manufacturing processes such as extrusion or creation of preformed, molded components using powdered metal (such as con-rods) or machined components,” Thomas explained. “Bayer has a process to achieve this. Generally light metals are ductile and nanotubes can be rolled into them using a milling process. Ceramic tooling would be required, though, because of the strength of the new material. Magnesium would also be a suitable material for nanotube linking.”

Thomas also explained that nanotechnology is suitable for incorporation within polymers. “A small amount of added nanotubes, they knit together layers of traditional carbon fiber or glass fiber matting, allowing the weight of an already light composite to be reduced by 20 to 30%.”

Enhancing safety, energy storage

Nanotechnology is already playing a part in vehicle safety, particularly in military applications. Nanotubes’ heat-transfer properties are such that a gasoline tank containing them will not catch fire when exposed to a naked flame. This is particularly significant for military vehicles; a fuel tank containing nanotubes in open sphere configuration (taking about 4% of capacity) will not explode even if a bullet passes through it.

“Nanotubes also have electric properties that make them interesting as anodes and cathodes for batteries,” explained Thomas. “Imagine a concentric single-wall nanotube system; electrons fit perfectly between the layers which provide an ideal guide plate and an almost resistance-free electron path.”

Work is now under way to incorporate nanotechnology in electrodes for fuel cells and in lithium-ion batteries. Weight could be significantly reduced for the same electrical efficiency and costs cut, making the advent of high-volume electric vehicles more feasible and practical.

Changing expectations of material makeup

Nanotechnology is only a part of Bayer’s weight-saving philosophy for the auto industry. It also includes the company’s belief that there is a need to accept that vehicles no longer have to be made mainly of metal and glass.

“People expect those materials, but if the real challenges of the industry are to be solved, we need to get used to cars being made from other materials, particularly composites and polymers,” stressed Thomas. “Manufacturing processes have to become more efficient—for example, the manufacture of glass is highly energy-intensive. And it is necessary to take costs out of the manufacturing process, even though in real terms, cars with high functionality are cheaper than they have ever been.”

Thomas said Chinese automakers are particularly forward-looking in this area: “They are willing to change the way they think about the conventional construction of vehicles. And they see no point in manufacturing hybrids, preferring to develop urban vehicles that are pure electric.”

An example of alternative construction is Bayer’s involvement in the transparent roof (manufactured by Webasto) of some versions of Daimler’s Smart city car. The glazing is polycarbonate held by a black polymer exterior frame, the whole manufactured in a single mold with multiple shots, Thomas explained.

“All screw points for the sunblind are built into the same molding process; assembly is simply a matter of screwing on the blind,” he said. “The transparent roof forms a structural component of the car. Other companies are set to use the technology, with a wide series of models to be launched during the next five years.”

The manufacturing process of the transparent roof includes firing the transparent polycarbonate component until it reaches its gel state, at which point the frame is fired, attaching to the gel as it solidifies in the mold. As the complete component cools as one, no interference patterns or optical feedback occur. It is then wet top-coated with a silicon. Cycle time takes about two and a half to three minutes.

“We believe this is a way to make cars lighter. It is production-proved,” said Thomas. “However, the car industry is intensively conservative and wary of change. We started this technology modestly with a quarter light.”

At present, the only size limit is not durability or integrity but processing capability. The Smart roof needs a 2.7-t (3-ton) press and Bayer has recently introduced a 2.3-t (2.5-ton) clamping force for premium car and SUV applications.

Polycarbonate applications

The use of polycarbonate for all vehicle glazing, including the front windshield on a production vehicle, may still be a decade away, believes Thomas—purely because the problem of abrasion, particularly from the wipers, still has to be overcome. Door glazing that raises and lowers presents similar abrasion challenges, but it can incorporate a layer of laminated glass with a film attached to the polycarbonate to form a laminated whole.

Bayer has been working on polycarbonate abrasion resistance for a decade, much of that time with former partner GE Plastics. The secret will be coating technology, explained Thomas; it has to last a car’s life, which in the future will probably be several years longer than it typically has been. To get a polycarbonate front windshield accepted would be for a wholly new model. So, adding further glazing development and proving time to model-development requirements could mean that a high-volume production example is up to 10 years away.

Bayer is also examining the increased use of roll-to-roll printing technology for easy, low-cost applications such as instrument faces and instrument panels.

“It is very difficult to print an image on a molded component, but printing is easy when the polymer is flat, with a roll of film printed roll-to-roll and just chopped off and post-formed. Ten thousand instrument panels can just fly past,” Thomas said.

They can be back-molded or back-foamed for strength. The application can also be to center consoles and integrated electronics: “It is a continuous manufacturing process rather than part assembly, simplifying final assembly,” he added.

It is possible to create, at very low cost, displays that look premium, something that is very important for showroom appeal. “And that appeal is particularly significant now, because so many cars are bought on ‘sight and feel’ by customers rather than being driven,” said Thomas.

According to Bayer’s information, more than half of new cars sold in Germany are now bought without a customer test-drive taking place. It can be regarded as axiomatic that a vehicle’s features include satisfactory ride, handling, controls’ precision, noise levels, and drive comfort.

What matters, said Thomas, is the feel of a steering wheel, the aesthetics of a dashboard, and the welcome the front seats give. Back seats are generally of less concern to both OEM and customer.

“And the time when buyers liked the smell of a new car—its paint and plastics—have gone,” he said. “Those smells are now associated with the emissions of possibly nasty substances.”

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