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An anti-wear ceramic coating originally developed for Formula One racing cars could offer cyclists an effective braking solution for lightweight carbon composite wheels. The ultra-thin, lightweight ceramic coating* can be applied to the rims of carbon composite wheels to provide a tough, long-lasting and durable braking surface that is capable of delivering high levels of modulation-even in wet conditions.
The coating offers improved stopping distance and wet weather performance, and it enables the use of standard hard-rubber brake materials in place of the specialist blocks that are normally used for carbon rims. In addition, the black color of the coating complements the standard black composite rims. Testing by a professional cyclist during a pre-season training camp in Majorca demonstrated consistent performance during 3400 km of riding in all-weather conditions.
Multiple BenefitsThe increased availability of lower priced carbon wheels has led to a marked increase in their usage. Until now, the use of the carbon rim as the braking surface required compromises in brake performance, notably in wet weather conditions or where high temperatures are experienced (such as steep descents).
Cork-based pads reduce the risk of damage to the rim surface, but are ineffective and can disintegrate in wet conditions. Other methods, such as aluminium braking rings or more complex disc setups, negate the weight benefits of a carbon wheel. By providing a better braking surface, the ceramic coating allows cyclists to retain light hubs and rims, as well as more slender and aero-efficient forks.
"Testing with standard rubber blocks suggests that our coating offers a significant improvement in stopping distances and no wear to the coating or wheel rim," says Peter Whyman, Sales director for Zircotec, the coating's manufacturer. "Dexter Gradias, the cyclist who undertook the trials in Majorca, believed that in slippery conditions, control under braking was 'excellent' and pad wear was reduced. The rubber blocks lasted for over 2500 km of varied riding."
The testing also highlighted the coating's ability to protect the wheel from heat and abrasion; these attributes are derived from the unique application process. Molten ceramic is sprayed at a very high temperature in a carefully controlled process that ensures the underlying carbon composite is protected.
The composite coating process enables composites to function in temperatures above their melting point. Testing for a typical application resulted in a composite surface temperature reduction of more than 125°C. The coatings can also be engineered to suit specific requirements by adjusting the coating properties (both through-thickness and across the surface of a component) to cope with "hot spots" and different forms of heat transfer, such as radiant, conductive, or convective heating.
"Zircotec developed the ability to safely coat composites for motorsport," explains Whyman. "We currently coat composite parts for more than 70% of the F1 grid and have developed bespoke protection methods for the substrate."
The result is a coating that features excellent bond strength and minimal wear. "The ceramic protects the carbon surface from damage inflicted by road grit that becomes trapped between the rim and pad material, which is currently an issue with existing setups," says Whyman.
Future ApplicationsThe new ceramic coating for carbon composites is the subject of a recent patent filing, and the use of the technology for bike wheels is just one of the potential applications. Other applications could include aerospace and defense projects, where interest in the use of composites continues to rise.
In addition, a new ceramic thermal barrier technology will allow high-strength, lightweight materials to be used in high-wear environments for which they have previously been unsuitable. A range of plasma-sprayed coatings has already been successfully applied to metallic components and enabled the reduction of surface temperatures by over 170°C in some automotive applications.
For wear resistance, the solutions are either metal-based or-in the case of the cycle application-ceramic (primarily zirconia). The composite materials that can be coated include carbon fiber, sintered nylon and fiberglass.
"We are investigating using our coatings to allow composites to be adopted in other new areas," adds Whyman. For example, one specialized applications involves electrical insulation of 10,000 V at cryogenic temperatures and under vacuum using alumina coatings.
For additional information, contact Zircotec at 22 Nuffield Way, Abingdon, Oxfordshire OX14 1RL, UK; (44) 01235-546050; fax (44) 01235-546059; or e-mail firstname.lastname@example.org.
*Developed by Zircotec, Oxfordshire, UK.