Automotive

Affordable, lightweight ceramic/aluminum brake rotors developed

Affordable, lightweight cerami...
Empa ceramics specialist Jakob Kübler, with some of the materials used in the brake rotor coating
Empa ceramics specialist Jakob Kübler, with some of the materials used in the brake rotor coating
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Empa ceramics specialist Jakob Kübler, with some of the materials used in the brake rotor coating
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Empa ceramics specialist Jakob Kübler, with some of the materials used in the brake rotor coating

When it comes to making cars more energy-efficient – whether they're battery- or gas-powered – getting their weight down is one of the best things you can do. Unfortunately, the cast iron brake rotors currently used in most vehicles are quite heavy. Lighter ceramic rotors certainly do exist, although their high price mostly limits their application to expensive sports cars. Soon, however, ceramic-coated aluminum rotors may be a cost-effective lightweight alternative for economy cars.

The rotors are being developed in a collaboration between Switzerland's Empa research institute, Italy's Politecnico di Torino, Spanish brake manufacturer Fagor Ederlan, Liechtenstein soldering company Listemann AG and the Fiat's CRF research center.

While straight-up aluminum rotors would certainly be lighter than iron, they would also be too soft. The ceramic coating provides a durable source of friction, plus it also serves to disperse the heat, which could melt unprotected aluminum.

That coating, although only about 2 mm thick, is made up of 15 layers of material. The main ingredient is aluminum oxide, which is relatively strong, abundant and inexpensive. It's mixed with layers of silicon carbide to increase thermal conductivity, along with a wear-resistant top layer and an adherent bottom layer.

Each of the materials is first combined with water to form a sludge, which is then applied to a piece of synthetic film. Those coated films are then compressed together, and subjected to high heat. As the carrier films are subsequently burned away, the bonded layers of material are left behind to constitute the finished coating.

Because aluminum expands three to four times more than ceramics when exposed to the heat caused by braking, the coating can't be applied to the rotors all in one continuous piece. If it was, it would crack as the aluminum beneath it expanded. Instead, it's soldered onto the aluminum in the form of individual tiles laid side-by-side. That way, as the metal expands, the tiny gaps between the tiles can take up the strain by temporarily widening.

Unfortunately, due to aluminum's low melting point, soldering has to be performed on it at relatively low temperatures. If those temperatures are too low, however, then the solders will fail when temperatures rise while braking. As a result, the project partners are still exploring better methods of affixing the tiles to the rotors. They're hoping to have a working prototype ready by next April, with a commercial product following sometime over the next few years.

Michigan-based materials company REL is also working on low-cost lightweight brake rotors, made from a ceramic fiber-reinforced metal matrix composite.

Source: Empa

6 comments
Mike Malsed
the problem with ceramic brakes is that they are completely ineffective until they heat up, and you need to drive at speed with them in order to get them up to temp - add water and you cool off the ceramic and it becomes cool and slick again. Friend has a car dealership and the cars that have ceramic brakes routinely come back to the dealership until people figure out how to "pre-brake" enough to keep them up to temp. Basically, they have to ride the brake pedal, especially in the rain, in order to keep them warm enough to actually work.
MarylandUSA
As a former science-and-technology writer, I'm impressed byhow clearly author Ben Coxworth has explained the challenges and the approach used to solve them. Nice work--especially the paragraph explaining why the coating had to be applied in tiles.
Jim Sadler
Has anyone tried titanium with a ceramic coating? Might be pricey but should be strong enough to do the job.
Robert Flieger
I love decreasing unsprung weight. Hopefully they can figure out how to give them good feel and work over the normal heat ranges while still keeping costs low.
DaveWesely
Robert Flieger hit the nail on the head. It's about unsprung weight, not the total weight of the vehicle that matters here. Unsprung weight is the weight of the wheel components attached to the springs and shock absorbers. The more unsprung weight, the slower the tire response to road irregularities. This affects handling and safety at high speeds. Fuel economy - not so much.
Don Duncan
I wonder what the weight savings will be compared to the extra cost? I assume they do a "payback" calculation but based on what price for fuel? This technology has another important fuel saving possibility. Pots and pans would cook faster and use less energy. I would NOT use pure AL but I would use it with a protective coating if tests showed no bleed through. I noticed the cooperation of 5 companies on this invention. This is more important that the particular problem they are trying to solve.