Taking the heat

With Red Bull Racing bringing exhaust blown diffusers back into vogue last year and now Lotus Renault’s even more radical front exit exhausts revealed in pre-season testing this year, F1 teams have been keen to develop novel ceramic coating technology to prevent damage through carbon fibre delamination. Zircotec however, has been working with most of the grid to find the solution.
The reintroduction of the exhaust blown diffuser concept to the F1 grid last year suddenly gave renewed focus to the packaging and protection of carbon composite suspension and aerodynamic components. Enabled partly by advancements in engine mapping that allow the naturally aspirated engines to release a steady, continuous output, blowing exhaust gases over (and sometimes under) the curved surface of the rear bodywork has allowed teams to drastically improve diffuser efficiency and create a low pressure area underneath the car to generate all-important downforce. For F1 designers, one of the major hurdles to incorporating blown diffusers is to protect the carbon composite components that are being directly exposed to gases at temperatures of anything between 650-1,000°C. There are several different solutions available including gold foil wrapping or thickening of carbon fibre structures, but more often now teams are turning to ceramic coatings such as those supplied by Oxfordshire-based Zircotec with its zirconia-based product, ThermoHold. Zirconia has a thermal conductivity of less than 1.7W/m K, compared with 4W/m K for alumina. Its origins are in the nuclear industry and Zircotec was previously part of the UK’s Atomic Energy Authority. Now independent, the firm’s high-temperature plasma-sprayed ceramic coatings provide lightweight, easily packaged and highly durable thermal barriers suitable for use in a range of applications. The firm uses gas plasma spraying to spray molten ceramic powder onto the composite, building up layers so that a thickness of between 250-400 microns is achieved. From protection to performance ThermoHold allows composites to function in temperatures above their melting point; with product tests giving a typical reduction in composite surface temperature of more than 125˚C. Simply put, this allows engineers to use more composites in environments where previously it would not have been possible.

From its new factory in Abingdon, the firm is experiencing a significant change in the manner its coating is being used by teams for this season. “We are now seeing engineers incorporating the coating into the design rather than merely solving heat issues after the design freeze,” says Peter Whyman, Zircotec’s sales director. “Our first coating applications provided a safe solution. With reliability proven, teams are now seeking performance gains by maintaining high gas speeds.” The 2011 version of the company’s ThermoHold for Composites coating now has a smooth surface finish option to minimise exhaust gas air flow disruption. “Our ability to finely adjust the surface finish means we can offer a smooth finish with no impact on thermal protection,” adds Whyman. Attention to detail All parts are sent to Zircotec’s factory for preparation and coating. According to managing director Terry Graham, preparation is key to durability. “The initial surface preparation techniques applied to any composite part are paramount to the reliability of the coating. This ensures that the bond coat will effectively bond onto the surface of the resin.” Zircotec is coy about how it has achieved the high levels of durability but confirms it uses a range of both physical and chemical methods. The company also claims that understanding the substrate and its curing is equally critical to achieving good adhesion and there are some cases where it is preferable to remove the top layer of resin. “Typically, glass fibre parts have very low heat treatments and may even have a range of unbound monomers in the resin,” adds Graham. “Trying to bond our coating onto this would result in the out gassing of the monomer and very poor bond strength.” 2011 will also see increased usage of the firm’s metal coatings for composites, launched in 2010. Like the ceramic coating, a proprietary bond coat is applied to the composite before applying a top layer of aluminium, molybdenum, stainless steel or tungsten. “For 2011 we are seeing opportunities to use metal coatings to improve EMC performance,” describes Graham. “Carbon is not ideal for shielding surrounding components from interference. With the reintroduction of kinetic energy systems the teams can benefit from managing this more effectively.” Forward thinking, forward exhausts 2011 has now seen the emergence of forward facing exhausts in an effort to claw back downforce from this year’s ban on double diffusers. This adds further challenges due to the extra ducting required and the fact that the exhausts will have to pass by the fuel tank, radiators and sensitive electronics. Being involved early on in development of cars, Zircotec has been able to co-design for thermal management. While specific solutions are as always a closely guarded secret, it is safe to say that ceramic coatings such as ThermoHold have already had a direct influence on packaging as crash structures and floors can be designed without requiring protective metal plates, and thickness can be carefully controlled to optimise both weight and insulation where required. Whilst most temperature control applications for composites are in motorsport, Zircotec has recently expanded into the road car arena. ThermoHold appears on the radical gas turbine/electic powered Jaguar CX-75 concept car for example, which features its own interpretation of the exhaust blown diffuser and also requires protection on ‘hot end’ inlets. The first commercial road car project is now underway with a two further examples at the feasibility stage. Two wheels too The anti-wear ceramic coating originally developed for F1 could be about to offer cyclists a highly effective braking solution for lightweight carbon composite wheels. The ultra thin, lightweight ceramic coating is applied to the rims of carbon composite wheels to provide a tough, long lasting and durable braking surface that is capable of delivering exceptional levels of modulation even in wet conditions. Essentially adding a rougher surface to the carbon rim, Zircotec’s coating offers improved stopping distances and wet weather performance, even with the use of standard hard-rubber brake materials in place of the specialist blocks normally required for carbon rims. Up until now, using the carbon rim as the braking surface has led to compromises in brake performance, especially in wet weather conditions or where high temperatures are experienced such as on steep descents, the last place anyone would want to have doubts about brake performance! Cork-based pads reduce the risk of damage to the rim surface but are ineffective and can disintegrate in the wet. Other methods, such as aluminium braking rings or switching to more complex disc setups negate the weight benefits of a carbon wheel. By providing a better braking surface, Zircotec’s ceramic coating allows cyclists to retain light hubs and rims as well as more aero-efficient forks.

www.zircotec.com